radiological impact assessment

Dr Detlof von Oertzen PO Box 8168 Swakopmund Namibia

Tel: +264 64 402 966 Mob: +264 81 314 9664 Fax: +264 88 624 989

Web: www.voconsulting.netEmail: [email protected]

RADIOLOGICAL IMPACT ASSESSMENT

on behalf of

SLR Environmental Consulting (Pty) Ltd

for the

Swakop Uranium’s Husab Mine Heap Leaching Project

Final Report: 22 June 2021

Document Number: VOC/2021/789F

Radiological Impact Assessment - Swakop Uranium’s Husab Mine Heap Leaching Project

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ABBREVIATIONS

GRN Government of Namibia

km kilometre, i.e. one thousand metres

MEFT Ministry of Environment, Forestry and Tourism

N$ Namibian dollars

SADC Southern African Development Community

ToR Terms of Reference

Client SLR Environmental Consulting (Pty) Ltd

Client contact details Sharon Meyer, [email protected]

Project Environmental Impact Assessment of the Heap Leach

Project at Husab Mine proposed by Swakop Uranium

Document title Radiological Impact Assessment

Swakop Uranium’s Husab Mine Heap Leaching Project

Document number VOC/2021/789F

Document version Final

Date of delivery 22 June 2021

Report recipient Michele Kilbourn Louw, [email protected]

SLR Environmental Consulting (Pty) Ltd

Author Detlof von Oertzen, PhD (Physics), MBA (Finance), PrNatSci,

Director, VO Consulting

Quality review Gunhild von Oertzen, PhD (Physics)

Director, VO Consulting

Declaration VO Consulting is an independent technical and

management consulting firm registered in Namibia.

The present study is based on tasks and deliverables as per

the Client’s scope of work description which is included in

the present Report.

Disclaimer Neither VO Consulting nor the author of this Report make

any warranty, express or implied, or assume any liability or

responsibility for the accuracy, complete-ness, or

usefulness of any information contained in this Report that

is implicitly or explicitly based on data and/or information

supplied by any third party.

Acknowledgements The author gratefully acknowledges the contributions by all

individuals who were consulted during the preparation of

this study.

A special word of thank you goes to Dr Hanlie Liebenberg-

Enslin of Airshed Planning Consultants (Pty) Ltd for making

available simulated dust dispersion results and associated

maps as are included in the present Report.


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Table of Contents Abbreviations ................................................................................................................... 5

Key Definitions ................................................................................................................. 6

Executive Summary .......................................................................................................... 8

1. Introduction ............................................................................................................ 10

1.1 Purpose ................................................................................................................... 10

1.2 Rationale ................................................................................................................. 10

1.3 Conceptual Approach of this Radiological Impact Assessment ................................... 10

1.4 Objectives of this Radiological Impact Assessment ................................................... 11

1.5 Methodology ........................................................................................................... 11

1.6 Assumptions and Limitations ................................................................................... 11

1.7 Structure of this Report ........................................................................................... 12

2. Legal and Regulatory Context .................................................................................. 13

2.1 Background ............................................................................................................. 13

2.2 Introduction ............................................................................................................ 13

2.3 Radiation Risks ........................................................................................................ 14

2.4 Key Legal and Regulatory Requirements ................................................................... 15

2.5 Namibian Radiological Protection ............................................................................ 16

3. Location of Swakop Uranium’s Husab Mine ............................................................. 18

4. Proposed Heap Leaching Options ............................................................................ 20

4.1 Introduction ............................................................................................................ 20

4.2 Option G ................................................................................................................. 20

4.3 Option H ................................................................................................................. 21

4.4 Option K .................................................................................................................. 21

5. Heap Leaching Process ............................................................................................ 25

5.1 Feed material characteristics ................................................................................... 25

5.2 Sourcing and storing feed material ........................................................................... 25

5.3 Processing of feed material ...................................................................................... 25

5.4 Feed material transport to the HSF .......................................................................... 25

5.5 Stacking the HSF ...................................................................................................... 25

5.6 Leaching and production of pregnant liquor at the HLF ............................................. 26

5.7 Mineral waste removal from the HLF ....................................................................... 26

5.8 Waste material transport to the heap leaching waste storage facility........................ 27


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5.9 Waste material disposal at the heap leaching waste storage facility .......................... 27

6. Radiological Impact Assessment .............................................................................. 28

6.1 Scope and Limitation ............................................................................................... 28

6.2 Introduction ............................................................................................................ 28

6.3 Approach ................................................................................................................ 28

6.4 Sources of Radiation ................................................................................................ 29

6.5 Exposure Pathways .................................................................................................. 29

6.6 Receptors ................................................................................................................ 31

6.7 Qualitative Assessment of Radiological Impacts of Heap Leaching............................. 33

6.8 Quantitative Assessment of Radiological Impacts of Heap Leaching Options ............. 35

6.9 Exposure Scenarios .................................................................................................. 48

6.10 Radiological Risk and Radiological Impact Criteria .................................................... 58

6.11 Conclusion – Radiological Impact on Select Public Receptors .................................... 59

7. Radiological Impact Ratings ..................................................................................... 60

7.1 Approach ................................................................................................................ 60

7.2 Definition of the Probability, Consequence and Overall Significance Ratings ............. 60

7.3 Impacts, Probability, Consequence and Overall Significance Ratings ......................... 61

7.4 Results of the Probability, Consequence and Overall Significance Ratings.................. 69

7.5 Fatal Flaws from the Radiological Perspective .......................................................... 69

7.6 Preferred Heap Leaching Option .............................................................................. 70

7.7 Mitigation Measures................................................................................................ 70

7.8 Concluding Remarks ................................................................................................ 70

8. Conclusions and Recommendations ........................................................................ 71

9. References .............................................................................................................. 73

Appendix A: Dust Inhalation Exposure Dose .................................................................... 75

Appendix B: Impact Classification Framework ................................................................. 76


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Abbreviations µg/m³ micrograms per cubic metre

μm micrometre, i.e. 10-6 metre

µSv/a micro-Sievert per annum (i.e. one-thousandth of a mSv/a)

ADMS Atmospheric Dispersion Modelling System

AMAD activity median aerodynamic diameter

AQSR air quality sensitive receptor

Bq Becquerel (rate of radioactive decay as disintegrations per second)

Bq/m3 Becquerel per cubic metre

DCF dose conversion factor

EIA environmental impact assessment

HL heap leaching

HLF heap leaching facility

HLWSF heap leaching waste storage facility

IAEA International Atomic Energy Agency

ICRP International Commission on Radiological Protection

km kilometre

m metre

m3 cubic metre

ml millilitre, i.e. one-thousands of a litre

mSv milli-Sievert (unit of exposure dose to ionising radiation)

mSv/a milli-Sievert per annum

Mm3 million cubic metre

MEFT Ministry of Environment, Forestry and Tourism

MME Ministry of Mines and Energy

NBR natural background radiation

NRPA National Radiation Protection Authority

PM10 particulate matter with a diameter of less than 10 micrometres

PM2.5 particulate matter with a diameter of less than 2.5 micrometres

ppm parts per million

Rn radon (including the radioactive radon isotopes Rn222 and Rn220)

ROM run-of-mine

RSO Radiation Safety Officer

SU Swakop Uranium

TLF tank leaching facility

TSF tailings storage facility

TSP total suspended particulate

UNSCEAR United Nations Scientific Committee on the Effects of Atomic Radiation

WHO World Health Organisation

WRD waste rock dump


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Key Definitions

This Report uses the following definitions:

ALARA the principle of optimisation states that radiation safety must

be optimised to ensure that the magnitude of individual

doses, the number of people exposed, and the probability of

incurring exposures are to be kept as low as reasonably

achievable (ALARA), economic and social factors taken into

account

critical group a group of persons that are expected to receive the largest

exposure dose from radiation for a specific exposure

pathway at a specific location

exposure the state or condition of being subject to irradiation. In this

context, external exposure is exposure to radiation from a

source outside the body, while internal exposure is exposure

to radiation from a source within the body

exposure dose a measure of the amount of ionising radiation that a specific

receptor was exposed to

exposure pathway a route by which radiation or radionuclides can reach humans

and cause exposure

member of the public for purposes of protection and safety, in a general sense, any

individual in the population except when subject to

occupational exposure or medical exposure. For verifying

compliance with the annual dose limit for public exposure,

this is the representative person

mitigate use of best industry practice to optimise potential exposure

optimise continuously enhancing radiation protection and radiation

safety measures to achieve exposure doses that are as low as

reasonably achievable, economic and social factors taken

into account


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potential exposure prospectively considered exposure to ionising radiation that

is not expected to be delivered with certainty but that may

result from mining and heap leaching operations

radioactive (scientific) exhibiting radioactivity; emitting or relating to the emission

of ionising radiation or particles as a result of the decay of

radionuclides, refer to [Von Oertzen, 2018]

radioactive (regulatory) designated in national law or by a regulatory body as being

subject to regulatory control because of its radioactivity,

refer to [Act, 2005] and [Regulations, 2011]

radioactive material any matter or substance containing one or more

radionuclides, but excluding any material where the activity

or activity concentration does not exceed the exemption

levels as prescribed in the [Act, 2005] and [Regulations, 2011]

radioactive source radioactive material that acts as a source of ionising radiation

radiological material mined minerals and associated mineral waste emitting

ionising radiation as a result of the radioactive decays of its

constituents.


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Executive Summary

SLR Environmental Consulting (Pty) Ltd appointed VO Consulting to undertake a radiological

impact assessment for Swakop Uranium’s proposed Husab Mine Heap Leaching Project.

This Report presents a radiological impact assessment that forms part of the Environmental

Impact Assessment for the Heap Leaching Project to be undertaken at Swakop Uranium’s

Husab Mine in the western Erongo Region of Namibia.

Swakop Uranium holds an Environmental Clearance Certificate to operate the Husab Mine

that produces uranium concentrate under the mining licence 171. In addition to the tank

leaching process that Swakop Uranium undertakes at the Husab Mine, the company wishes

to introduce a heap leaching (HL) facility (HLF) to extract uranium from low-grade uranium-

bearing run-of-mine mineral material that is often unsuitable for treatment in the company’s

existing tank leaching facility at the Husab Mine. A HLF would increase the Mine’s uranium

extraction capacity and therefore increase its total uranium concentrate output without

necessitating additional extensions and investments in its tank leaching capacities.

Three separate heap leaching options are considered in this Report:

1. Option G: comprises of a dynamic HLF including HL circuit, pad and ponds to be located

south-west of the existing on-site waste rock dumps (WRDs) and a heap leaching waste

storage facility (HLWSF) south of the existing WRDs;

2. Option H: comprises of a dynamic HLF including HL circuit, pad and ponds to be located

south of the existing processing plant and HLWSF south-west of the existing WRDs; and

3. Option K: comprises of a dynamic HLF with HL circuit south-east of the processing plant

and south-west of the existing WRDs, with the HLWSF being an extension of the WRDs.

The radiological impacts associated with the proposed heap leaching options are:

A. Generation of additional radiologically relevant dust as well as radon, which may have

adverse impacts on sensitive air quality receptors in the area around the Husab Mine;

B. Potential contamination, seepage, spills and other unintended emissions of

radiologically relevant material into the environment;

C. Generation of additional radiologically relevant mineral waste material that would have

to be disposed of in a way that minimises the emission and releases of radiologically

relevant minerals and gases into the environment;

D. Disposal of radiologically relevant mineral and non-mineral waste arising from the

proposed heap leaching process;

E. Impacts associated with the long-term management (or their absence) of the waste rock

dumps and heap leaching waste disposal facility, which may lead to unintended

emissions of radiologically relevant minerals and gases into the environment;


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F. Impacts associated with the management of mining activities that are extended by way

of the addition of a heap leach facility and would lead to unintended emissions

(including by way of the dispersion of radioactive ore dust, contamination of soil and

water resources, seepage into the soil and groundwater, spills and related unplanned

and unmitigated releases) of radiologically relevant minerals into the environment; and

G. The potential impacts associated with the failure of the heap leaching waste disposal

facility following the decommissioning of the heap leaching facility and associated

infrastructure, including waste rock dumps and tailings storage facilities, noting that

adverse impacts may arise decades after the closure of an active mining facility.

The radiological impact assessment shows that there is no material radiological difference

between the heap leaching options considered in this Report. Therefore, the ratings of

probability and consequence, as presented here, apply to all three heap leaching options.

The assessment distinguishes between “mitigated” and “unmitigated” scenarios, the former

meaning that best industry practices as applicable in hyper-arid environments are employed

to minimise undesirable impacts from releases of radionuclides into the environment.

Based on the principle of optimisation as applied in all radiological practices in Namibia, all

unmitigated heap leaching options are associated with radiological impacts that are not as

low as reasonably achievable, economic and social factors taken into account [Act, 2005].

Therefore, only mitigated heap leaching options must be considered for implementation, and

must employ best practice mitigation measures as relevant and applicable in modern open

pit mining environments in hyper-arid climates, as applicable in Namibia’s Namib desert.

The aggregate probability rating of the radiological impacts of the HL options are:

Mitigated scenarios: Medium and Unmitigated scenarios: High.

The aggregate consequence rating of the radiological impacts of the HL options are:

Mitigated scenarios: Low and Unmitigated scenarios: Medium.

The overall significance rating of the radiological impacts of the HL options are:

Mitigated scenarios: Medium and Unmitigated scenarios: Medium.

The total public exposure dose contribution associated with current mining operations at the

Husab Mine plus the proposed heap leaching operations, across all relevant exposure

pathways, was found to be below 10 μSv/a for adult and infant members of the critical groups

that are considered in this study. Such an exposure dose is less than 1/100th of the Namibian

public exposure dose limit of 1 mSv/a [Act, 2005] and is considered a trivial incremental

exposure dose as per the definitions provided by the International Commission on

Radiological Protection (refer to [ICRP, 2007a] and [ICRP, 2007b]).


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1. Introduction

In February 2021, SLR Environmental Consulting (Pty) Ltd appointed VO Consulting to

undertake a radiological impact assessment for the Heap Leach Project to be developed

at Swakop Uranium’s (SU) Husab Mine in Namibia’s Erongo Region.

1.1 Purpose

This Report presents a radiological impact assessment that forms part of the

Environmental Impact Assessment (EIA) for SU’s Heap Leach Project at Husab. The EIA

is coordinated by SLR Environmental Consulting (Pty) Ltd on behalf of SU.

This study focuses on potential radiation-related exposures associated with the

different heap leaching (HL) options considered for development at the Husab Mine.

1.2 Rationale

In Namibia, holders of mining licenses must submit an EIA in conformity with the

requirements of the Environmental Management Act of 2007 should they wish to

introduce material changes to the practices included in their existing environmental

clearance certificates. An EIA is required to apply for an Environmental Clearance

Certificate as issued by the Ministry of Environment, Forestry and Tourism (MEFT).

The rationale for undertaking a radiological impact assessment for the HL options

proposed by SU is that each of these result in the additional release of radioactive

elements into the environment, which may materially contribute to the overall impact

that the Husab Mine has on the receiving environment.

Radiological impacts associated with the HL options under consideration are quantified

to identify their radiation-related contribution and overall impacts.

1.3 Conceptual Approach of this Radiological Impact Assessment

The International Commission on Radiological Protection (ICRP) provides guidance on

how radiological impacts associated with exposures to ionising radiation from

radioactive minerals and technical devices are to be undertaken (refer to [ICRP, 2007a]

and [ICRP, 2007b]).

The radiological impact assessment presented in this Report is based on the conceptual

approach put forward by the ICRP and its applications in mineral mining and processing

as provided by the International Atomic Energy Agency (IAEA) [IAEA, 2018].


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1.4 Objectives of this Radiological Impact Assessment

This radiological impact assessment is guided by the following objectives:

a. Identify, describe and quantify the radiological impacts associated with the heap

leaching options under consideration;

b. Assess whether members of any critical group as identified in this study incur an

exposure dose exceeding the Namibian public exposure dose limit of 1 mSv/a as

a result of the current operations at the Husab Mine combined with any of the

heap leaching options under consideration; and

c. Formulate mitigation strategies to optimise public exposure doses resulting from

the proposed heap leaching operations, where relevant and applicable.

1.5 Methodology

The methodology that underpins this study is based on the following activities:

1. Provide a high-level description of the location of the Husab Mine;

2. Summarise the key legal and regulatory provisions relating to this study;

3. Describe the proposed heap leaching options proposed by SU;

4. Identify the main sources, pathways and receptors for the HL options;

5. Quantify the exposure doses incurred by select critical groups as a result of the

operation of the HL options under consideration, including by way of the

comparison of the total exposure dose with the relevant dose constraint;

6. Characterise the radiological impacts of the proposed heap leaching options in

terms of their probability of occurrence and their consequences;

7. Determine the overall significance ranking of the potential impacts associated

with the proposed heap leaching options;

8. Rank the proposed heap leaching options in terms of their overall radiation-

related impacts;

9. Identify the radiation-related fatal flaw(s) associated with the HL options; and

10. Provide conclusions and recommendations.

1.6 Assumptions and Limitations

This radiological impact assessment is based on a variety of assumptions and therefore

has certain limitations, including the following:

a. This study focuses exclusively on radiation-related impacts associated with the

proposed HL options and does not include non-radiological considerations and

their associated risks and repercussions even if these are of critical importance;


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b. The specific heap leaching option that is eventually selected by SU is assumed to

be operated in parallel with the Husab Mine’s existing tank leaching facility and

associated process infrastructure;

c. The specific heap leaching option that is eventually selected by SU is assumed to

be operated as a stand-alone facility requiring its own crusher circuit and waste

disposal facility while utilising existing on-site extraction, precipitation, final

product recovery, drum filling, drum storage, drum packing and container

storage infrastructure; and

d. The preparation of mineral feedstock that is to be processed for use on the

proposed heap leaching option necessitates that various on-site processes (such

as crushing, conveying and others) must be upscaled. This study however

assumes that the use of such existing on-site infrastructure (as was identified in

the previous bullet) will not bring about additional radiologically relevant impacts

as these are already considered and form an integral part of the Husab Mine’s

existing operations which form part and are considered in this study.

1.7 Structure of this Report

The remainder of this Report is structured as follows:

Section 2 introduces the legal and regulatory context and highlights the key

requirements relevant for this radiological impact assessment;

Section 3 introduces and describes the geographical location of SU’s Husab

Mine in Namibia’s western Erongo Region;

Section 4 summarises the heap leaching options considered by SU;

Section 5 summarises the key features of the heap leaching process to be

employed at Swakop Uranium’s Husab Mine;

Section 6 describes and quantifies the radiological impacts associated with

current mining operations at the Husab Mine plus those associated with the

proposed operations of the heap leaching facility;

Section 7 presents the radiological impact ratings associated with current

operations at the Husab Mine plus those of the proposed HL operations;

Section 8 presents the main conclusions and recommendations from the

radiological impact assessment described in this Report;

Section 9 lists the references that were used in the development of this

radiological impact assessment;

Appendix A describes how the internal exposure dose associated with the

inhalation of ambient atmospheric uranium-bearing PM2.5 dust is calculated;

Appendix B summarises how the various environmental impacts are classified.


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2. Legal and Regulatory Context

This section introduces the legal and regulatory context and highlights the key

requirements relevant for this radiological impact assessment.

2.1 Background

Humans have evolved in the presence of ionising radiation, which is emitted from

natural sources, including from cosmic radiation, radioactive terrestrial sources, food,

water, and the air we breathe. In addition, a variety of man-made sources emitting

ionising radiation make additional contributions to the perpetual sea of background

radiation in which we live [Von Oertzen, 2018].

Certain mining operations, including those undertaken by Swakop Uranium at the

Husab Mine, contribute to natural radiation to which humans are exposed. In most

cases in which radioactive mineral ores are mined, these are crushed, milled, and

concentrated, all of which adds to radiation exposures of persons at or nearby mining,

milling, and processing activities. In addition, rock stockpiles, waste rock dumps, tailings

and process facilities expose radioactive ore to the environment, which leads to an

increase of atmospheric radon and thoron exhalations as well as the concentration of

inhalable radioactive dust into the atmosphere. It may also contribute to the transport

of radionuclides into groundwater by leaching from rocks, soil and radioactively

contaminated surfaces exposed to the wind and rain.

2.2 Introduction

The International Commission on Radiological Protection (ICRP) has put forward a

conceptual model of the processes causing human exposures to ionising radiation (refer

to [ICRP, 2007a] and [ICRP, 2007b]). The model views exposure processes as a network

of events and situations with each part of the network starting from a specific source of

radiation. This radiation, or the radioactive source material giving rise to ionising

radiation, passes through environmental or other pathways, and in this way may finally

expose individuals at or close to the source of radioactive material, which in turn may

lead to an additional exposure to ionising radiation of select individuals.

In what is referred to as a source-pathway-receptor model of exposure to radiation,

radiation protection can be achieved by acting at the source of radiation, or at the

various points along the exposure pathways, and if possible, by changing the location,

behaviours and protective measures used by actually and/or potentially exposed

individuals. Radiation protection therefore includes all measures, processes and

controls applied to minimise the potential exposure to radiation. Mitigation measures


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are most effectively implemented at the source(s), in the pathway(s) and at the

receptor(s).

Although not fully supported by empirical evidence for low exposure doses, it is

assumed that there exists a proportional relationship between an increment of

exposure to ionising radiation and the resulting increment of the associated risk from

an exposure. The assumption is further that there exists no threshold for the onset of

risk. This is the essence of the so-called linear no-threshold (LNT) hypothesis, which

suggests that the health risk associated with exposure to radiation increases linearly as

the exposure dose increases.

Today, the LNT hypothesis underpins the formulation of most radiation protection

measures and processes and applies across the potential chain of exposure from the

source, via one or several pathways to the actual or potential receptor(s). Today’s

radiation protection officer identifies those parts of the chain of exposure that are most

relevant and amenable to the application of effective exposure controls by separating

the total exposure dose into its various contributing parts, which in turn allows targeted

interventions for each contributing element.

Individuals are subject to several types and categories of exposure. A mine worker who

is occupationally exposed because of the particular work that is being undertaken on a

mining site is also exposed to naturally occurring environmental ionising radiation.

Similarly, a member of the public is exposed to ionising radiation from the natural

background radiation, plus an incremental contribution due to other sources of

radiation in his/her immediate environment. These incremental contributions include

radioactive dust as well as radon and thoron progeny from nearby mining site(s), plus

radionuclides that form part of the food and water that is consumed as well as the

exposure to a variety of man-made sources of radiation that are found in the

environment.

2.3 Radiation Risks

Radiation protection practices in the mining industry focus on minimising the so-called

stochastic effects of ionising radiation. Stochastic effects are not associated with an

exposure threshold, in contrast to the so-called deterministic effects of ionising

radiation, which are certain to occur if a certain exposure threshold is exceeded.

Stochastic radiation effects are probabilistic in nature and may ensue if a cell (for

example in the body of an occupationally exposed worker) and with it the genetic make-

up of the affected cell is modified. Modified cells may, in time, develop into a cancerous

growth. In most cases where persons are exposed to low levels of radiation, the body's

repair and defence mechanisms active at the cellular level render it unlikely that


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irreparable damage occurs to the organism due to modified cells. This is indeed most

often the case in an occupational setting in which low-level radioactive ores are mined

and processed. There is no direct evidence that a threshold dose exists below which

cancerous growth will never occur. While the probability of occurrence of cancers is

higher for higher doses, the severity of any cancer resulting from irradiation is

independent of the dose that caused it. Risk minimisation implies that potential

exposures of workers or members of the public must be kept as low as reasonably

achievable, and below the dose limit as is applicable to each exposure group, as

specified by the National Radiation Protection Authority that is the national regulatory

authority tasked with radiation protection in Namibia.

In contrast, deterministic effects resulting from the exposure to radiation have a well-

defined threshold of occurrence. If an individual incurs an exposure dose above a given

threshold value, their impacts on the receptor are well known and can be predicted

with certainty. However, deterministic effects from the exposure to ionising radiation

do not occur in ordinary mining operations dealing with low-grade radioactive ores, as

typical exposure thresholds of 100 mSv or more are not readily exceeded in operations

handling naturally occurring radioactive material (NORM).

2.4 Key Legal and Regulatory Requirements

The present assessment is guided by the requirements of Namibia’s Atomic Energy and

Radiation Protection Act, Act No. 5 of 2005 [Act, 2005] and the Regulations under the

Act, i.e. the Radiation Protection and Waste Disposal Regulations, No. 221 of 2011

[Regulations, 2011].

Namibia’s legal framework as pertaining to radiation-relevant aspects is substantially

based on the following international Standards and guidance documents:

the recommendations contained in the Basic Safety Standards of the International

Atomic Energy Agency (IAEA) [IAEA, 1996], [IAEA, 2004] and [IAEA, 2014]; and

those by the International Commission on Radiological Protection (ICRP) (refer to

[ICRP, 1993], [ICRP, 1995], [ICRP, 2007a] and [ICRP, 2007b]).

The above frameworks recognise that human health and the environment must be

protected against the potentially adverse effects resulting from the exposure to ionising

radiation, as do for example arise when handling, mining, milling, and processing of

mineral ores that contain naturally occurring radioactive materials.


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2.5 Namibian Radiological Protection

In Namibia, the Atomic Energy and Radiation Protection Act, Act No. 5 of 2005 [Act,

2005], and the Radiation Protection and Waste Disposal Regulations [Regulations, 2011]

under this Act [Regulations, 2011], describe the statutory and regulatory radiation

protection and control measures applicable to individuals and entities dealing with

sources of ionising radiation.

The National Radiation Protection Authority (NRPA) was established under the Act and

is responsible for implementing all aspects relating to radiation protection in Namibia.

The heap leaching option that is ultimately selected by Swakop Uranium must comply

with the national regulatory requirements for radiological protection as expressed by

the following principles which are further expanded on in the sub-sections below:

justification of practices;

limitation (of public and occupational exposure doses); and

optimisation of (radiation-related) protection and safety.

2.5.1 Justification of practices

Regarding the justification of practices, Regulation 9 states the following (verbatim

quotes are presented in italics and are cited as such from [Regulations, 2011]):

(1) No practice or source within a practice may be licensed or registered unless

it produces sufficient benefit to the exposed persons or to society to offset the

radiation harm that it might cause, taking into account social, economic and

other relevant factors.

(2) The applicant for the licence or registration concerned must provide

sufficient information to the Director-General relating to the benefits and the

harm to support the justification of the practice.

(3) For the purposes of subregulation (1), the following practices are deemed

not to be justified whenever they would result in an increase in exposure to

ionising radiation –

(a) practices involving food, beverages, cosmetics or any other commodity or

product intended for ingestion, inhalation or percutaneous intake by, or in

relation to, a human being; or

(b) practices involving the frivolous use of radiation or radioactive substances

in commodities or products such as toys and personal jewelry or adornments.


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2.5.2 Exposure dose limitation

In regard to exposure dose limitations, Regulation 10 states [Regulations, 2011]:

(1) The normal exposure of persons must be restricted so that neither the total

effective dose nor the total equivalent dose to relevant organs or tissues,

caused by the possible combination of exposures from all practices, exceeds

any relevant dose limit specified in Schedule 2, except in the special

circumstances contemplated in regulation 11 and as contemplated in

regulation

(2) Subregulation (1) does not apply to medical exposures from licensed

practices.

The Regulations distinguish between exposure dose limits applying to members of the

public and occupationally exposed persons. For members of the public, the average

exposure dose limit of members the relevant critical group(s) may not exceed:

The estimated average doses to the relevant critical groups of members of the

public that are attributable to practices may not exceed the following limits –

(a) an effective dose of 1 mSv in a year: Provided that in special circumstances,

an effective dose of up to 5 mSv in a single year may be approved provided

further that the average dose over five consecutive years does not exceed 1

mSv per year;

(b) an equivalent dose to the lens of the eye of 15 mSv in a year; and

(c) an equivalent dose to the skin of 50 mSv in a year [Regulations, 2012].

2.5.3 Optimisation of protection and safety

Regarding the optimisation of protection and safety, Regulation 12 states:

(1) In relation to exposures from any particular source within a practice, radiation

safety must be optimised in order to ensure that the magnitude of individual

doses (except for the volume of interest in cases of therapeutic medical

exposures), the number of people exposed and the likelihood of incurring

exposures must be kept as low as reasonably achievable, economic and social

factors being taken into account: Provided that the dose to persons delivered by

the source must be subject to dose constraints specified in the license condition

imposed by the Director-General.

(2) A licensee must use, to the extent practicable, procedures and engineering

controls based upon sound radiation safety principles to achieve the objective

referred to in subregulation (1).


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3. Location of Swakop Uranium’s Husab Mine

This section introduces and describes the geographical location of Swakop Uranium’s

Husab Mine in Namibia’s western Erongo Region.

Swakop Uranium holds an Environmental Clearance Certificate to operate the Husab

Mine, producing uranium concentrate under mining licence 171.

As depicted in Figure 1, the Husab Mine’s geographical location is close to a number of

locations where members of the public live and/or work, including

the town of Arandis, which located north north-west of the Mine;

the Arandis airport, which is located north of the Mine;

Rössing Mine, which is located north of the Mine;

the Langer Heinrich Uranium Mine (which is under care and maintenance at a

time when this report was compiled) and is located south-east of the Mine;

a variety of dimension stone producers, including Stone Africa and Savanna

Marble, which are located north-west of the Mine;

Khan Mine (not operational but frequented by tourists)

a variety of tourist destinations, including

o Goanikontes;

o the Welwitschia Flats;

o the Big Welwitschia;

o the Husab campsite; and

o the Swakop River campsite, which are all in close proximity to the Mine;

a variety of uranium exploration operations, mainly taking place in a southerly

and south-easterly direction of the Mine.

various small holdings and farms in the Swakop River;

the town of Swakopmund, which is about 50 km east north-east of the Mine; and

the town of Walvis Bay, which is some 66 km south-west of the Husab.


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Figure 1: Swakop Uranium’s Husab Mine (see red arrow) in Namibia’s western Erongo Region, status June 2021

Source: [Von Oertzen, 2018] with additional annotations by VO Consulting


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4. Proposed Heap Leaching Options

This section summarises the heap leaching options considered by Swakop Uranium.

4.1 Introduction

SU considers the introduction of a heap leaching facility (HLF) to extract uranium from

low-grade uranium-bearing run-of-mine (ROM) material that is unsuitable for

treatment in the company’s existing tank leaching facility (TLF) at the Husab Mine, as

described in [SLR, 2020], [SGS, 2017], [SGS, 2021].

An HLF would increase the total leaching capacity and therefore increase the total

output of uranium concentrate without necessitating additional milling or tank leaching

capacity [SLR, 2020]. Over a 20-year period, an estimated 180 million tonnes (Mt) of

low-grade uranium-bearing feed material are available for heap leaching. This feedstock

has a uranium grade of between 100 and 400 parts per million (ppm) [SGS, 2017].

The proposed HLF would have a processing capacity of 7.5 million tonnes per year

(Mtpa) and result in the production of some 100 million pounds of uranium concentrate

(U3O8) over a 20-year life of mine assuming an average recovery of 85% [SGS, 2017].

The design of the HLF is based on a dynamic heap leaching circuit, with dedicated

leached ore residue waste storage facilities and other essential infrastructure, including

for example surface water management systems [SGS, 2021].

Husab Mine’s Environmental Management Plan requires Swakop Uranium to ensure

that the stockpiled low-grade materials are processed at the end-of-life of the Mine. An

HLF circuit would therefore create an opportunity to process such low-grade material

ahead of the Mine’s ultimate closure while generating additional revenues.

The proposed HLF circuit would be constructed in an environmentally sensitive area,

thus necessitating prudent design measures and the construction of environmental

barriers and leachate management infrastructure [SLR, 2020].

Three separate heap leaching options are considered by SU, namely Option G, Option

H and Option K, these are introduced below.

4.2 Option G

As shown in Figure 2, Option G comprises of a dynamic HLF including HL circuit, HL pad

and HL ponds located south-west of the existing waste rock dumps (WRDs). A heap

leaching waste storage facility (HLWSF) is to be located south of the existing WRDs.


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4.3 Option H

As shown in Figure 3, Option H comprises of a dynamic HLF including HL circuit, pad and

ponds to be located south of the existing plant and a HLWSF south-west of the existing

WRDs.

4.4 Option K

As shown in Figure 4, Option K comprises of a dynamic HLF including HL circuit south-

east of the on-site processing plant and south-west of the existing WRDs, with a HLWSF

as a south-easterly extension of the existing WRDs.


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Figure 2: Location of the Heap Leaching Facility under Option G

Source: Made available by SLR Environmental Consulting (Pty) Ltd, with select enhancements by VO Consulting


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Figure 3: Location of the Heap Leaching Facilities under Option H



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Figure 4: Location of the Heap Leaching Facilities under Option K



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5. Heap Leaching Process

This section summarises the key features of the heap leaching process to be employed

under Option G and Option H at Swakop Uranium’s Husab Mine.

5.1 Feed material characteristics

Feed material to be used for the proposed HLF is low-grade naturally occurring

radioactive material with a uranium grade between 100 and 400 ppm [SGS, 2017].

5.2 Sourcing and storing feed material

Some 180 Mt of low-grade uranium-bearing mineral ore is available on site and would

be the feedstock for the HLF. Feed material must be stockpiled to guarantee the

availability of feed stock for the HL process [SGS, 2021].

The stockpile is to have a capacity of some 15 Mm3 and will temporarily store ROM

material not going to the tank leaching process. This necessitates changes to the

processes used at Husab Mine as the ROM material feed profile and stockpile strategy

must satisfy the HLF’s feed requirements.

Feed material is to mainly originate at the primary crusher feeding the TLF, provided

that adequate spare capacity is available. If such spare capacity is unavailable, a

separate stand-alone primary crusher circuit is to be employed to ensure that ongoing

operational requirements of the HLF are met.

5.3 Processing of feed material

Low-grade uranium-bearing mineral feed material must be crushed in a two-stage

process involving primary and secondary crushers. Thereafter, this HLF feedstock is

screened and suitable material is stockpiled until fed into agglomeration drums, where

leaching reagents are added [SGS, 2021].

5.4 Feed material transport to the HSF

Agglomerated feed material is conveyed via overland conveyors to the HLF.

5.5 Stacking the HSF

Mobile grasshopper conveyor systems stack the agglomerated feed materials onto the

HLF. This facility is to consist of several cells to enable stacking, leaching, drain-down,

rinsing and reclamation operations, as well as a dormant cell to create additional

flexibility in operations.


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The HLF consist of the following components:

Heap leaching pad and lining system that is composed of a double-layered liner

as well as a seepage interception layer;

Storm water pond and collection channels;

Solution collection trench downhill of the HL pad and solution ponds;

Solution collection system consisting of a drainage layer and collection pipes that

are to drain the leaching solution to the ponds; and

Reclamation loading system.

5.6 Leaching and production of pregnant liquor at the HLF

The HLF is a racetrack stacking and reclamation system that is to be operated as a

dynamic HL pad with a capacity of 7.5 Mtpa. This particular leaching process is

suggested because of the particle size of the feed material that is optimised to provide

good dissolution results for the extraction of uranium.

In addition to the HL pad, the HLF consists of additional physical infrastructure including

barren solution ponds, intermediate leaching solution ponds, pregnant liquid ponds and

HL wash water ponds.

Pregnant liquor, i.e. leachate that contains uranium that has been dissolved in the HL

process, is collected by a series of solution collection pipes in the HLF’s drainage layer.

Collection pipes connect to intermediate header pipes to convey leachate to the main

outlet pipe which runs along the toe of the HLF to the solution ponds. Collection pipes

are offset and linked to a main collection pipe, which doubles halfway down the HL pad

to carry the drain down solution flow while minimising pipe sizes and drainage material

cover. Pregnant liquor is transferred to the existing tank leaching facility for further

processing.

Any potential or actual run-off, spillage or seepage of pregnant liquid produced at the

HLF into the environment must be strictly avoided. The design of the HLF envisages a

dynamic HL circuit, meaning that mineral feedstock is stacked and leached on the HL

pad and thereafter removed to a dedicated waste storage facility. The sizing of the HLF

ponds must ensure that unintended run-off is minimised even in low-probability events

such as sporadic rainstorms which occur in the Namib.

5.7 Mineral waste removal from the HLF

At the end of a leaching cycle, leached waste material is removed from the HLF circuit

and conveyed to the final disposal facility. A bucket wheel reclaimer collects residue

material from the leaching pad, and transfers it onto a conveyor system that transports

the material to a dedicated waste facility, where it will be stacked.


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Removal activities lead to radioactive contamination of equipment which must be

strictly and consistently managed to ensure that it is minimised at all times.

5.8 Waste material transport to the heap leaching waste storage facility

HLF residue material consists of leached mineral ore, noting however that this material

remains radioactive even if the recovery rate of uranium is very high. It implies that the

transport of associated waste material is to be managed to minimise the contamination

and/or cross-contamination of uncontaminated areas at all times.

5.9 Waste material disposal at the heap leaching waste storage facility

The heap leaching waste storage facilities (HLWSF) considered in this Report are

associated with the following waste disposal options:

Option G: new storage facilities south of the existing WRD, as shown in Figure 2;

Option H: new storage facilities west of the existing WRD, as shown in Figure 3;

and

Option K: the storage facilities are to be extensions in a south-easterly direction

from the existing WRDs, as shown in Figure 4.

The new HLWSF must be designed so as not to require active and ongoing management

following the deposition of mineral waste from the heap leaching process, including

those arising from the dispersion by the wind and/or seepage into the soil.

To this end, the HLWSF facilities are to be successively closed and sealed to minimise

the potential emission and/or exhalation of radionuclides into the environment, which

readily occurs as a result of several natural processes as well as by way of seepage,

overflow, the forces of the wind and/or water. The use of passive design measures to

minimise such unintended emissions and/or exhalations of radionuclides are essential.


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6. Radiological Impact Assessment

This section describes and quantifies the radiological impacts associated with current

mining operations at Husab Mine plus those associated with the proposed HL

operations.

6.1 Scope and Limitation

This section’s presentation and discussion of impacts focus strictly on the potential

radiological impacts as they relate to the receiving environment and do not consider

any non-radiological impacts that may be associated with the HL options under

consideration.

6.2 Introduction

Humans have evolved in the permanent presence of ionising radiation from natural

sources, including from radioactive terrestrial sources, cosmic radiation as well as

radionuclides in the air, water and food. In addition to the various natural sources of

ionising radiation, a variety of man-made sources have found their way into the

environment and today form part of the perpetual sea of background radiation in the

environment [Von Oertzen, 2018].

6.3 Approach

In order to identify the radiological impacts associated with the HL options identified

before, the linkages between radiological materials1 and the potential exposure to

ionising radiation emitted from these materials must be established.

This Report applies the approach to identify and quantify relevant radiological impacts

as was developed by the International Commission on Radiological Protection (ICRP).

Specifically, the ICRP uses a conceptual model for human exposure to ionising radiation

that views exposures as networks of events where each part of the network starts from

a specific source of radiation. Such radiation passes through the environment and

causes an exposure to ionising radiation that can be quantified in terms of an exposure

dose [ICRP, 2007].

The approach is underpinned by identifying the potential sources of radiation, the

exposure pathways and the ultimate receptors that incur an exposure dose and is

commonly known as the source-pathway-receptor model.

1 In the context of this study, radiological material is defined as mined minerals and associated mineral waste emitting ionising radiation as a result of the radioactive decays of its constituents.


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6.4 Sources of Radiation

The sources of radiation considered in this study comprise of unmined and mined

uranium-bearing minerals and the mineral waste that is disposed of on the on-site

mineral waste disposal facilities.

The sources of radiation are emitting ionising radiation as a result of the radioactive

decays of their constituent elements. The radioactive constituents of such mineral

materials are called radionuclides and include uranium (and thorium) and its decay

chain members, all of which emit ionising radiation when they undergo radioactive

decays [Von Oertzen, 2018].

At Swakop Uranium’s Husab Mine, the radionuclides that give rise to radiological

impacts are those from the Uranium-238 decay chain. It is noted that the concentration

of Thorium-232 and K-40 in the mined ore are comparatively low. Hence, these

elements and the relevant decay chain radionuclides are not considered in the present

analysis.

Based on the above, only those radionuclides that are members of the radioactive decay

chain of Uranium-238 and Uranium-235 are considered in the present study. It is noted

that the natural abundance of Uranium-235 is low and implies that the contribution of

this radioactive element and its decay chain members do not play a significant role in

the context of the radiological impacts assessed here.

6.5 Exposure Pathways

An exposure pathway is the route by which radionuclides or radiation can reach

receptors and potentially cause exposure to such radiation.

In the context of this study, the relevant exposure pathways are those that are

associated with naturally occurring radioactive material (NORM), including

1. external exposure to gamma radiation due to the presence of radionuclides;

2. internal radiation exposure due to the inhalation of radon and its progeny, via

the atmospheric pathway;

3. internal radiation exposure as a result of the inhalation of long-lived

radionuclides as may be contained in ambient atmospheric dust, via the

atmospheric pathway; and

4. internal radiation exposure by way of the ingestion of radionuclides, for example

from surfaces contaminated with radionuclides or the consumption of food or

water that is contaminated by radiological material, via the atmospheric as well

as the aquatic pathways [Von Oertzen, 2018].


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6.5.1 External Exposure to Gamma Radiation

Gamma radiation is highly penetrative electromagnetic radiation that is emitted

(amongst others) by radioactive materials. A variety of naturally occurring minerals exist

that contain radioactive materials including for example uranium and its decay chain

members, thorium with its associated decay chain, potassium and others [Von Oertzen,

2018].

Exposure to gamma radiation in this context is due to the presence of one or several

sources emitting ionising radiation, including for example

radioactive minerals in the natural environment;

concentrated radioactive minerals, e.g. uranium concentrate as is produced at

uranium mines;

radioactive contaminants in/on tools and equipment used in the exploration and

mining process involving naturally occurring radioactive minerals; and

sealed radioactive sources containing radionuclides, for example those used in

density/flow meters, and others.

6.5.2 Exposure to Radon and its Progeny in Air

Radon (Rn222) is a radioactive gas arising when radium (Ra226) undergoes a radioactive

decay. Radon is a decay product of the uranium decay chain.

An exposure to radiation from radon and its decay products (i.e. its progeny) occurs

when these are inhaled and undergo a radioactive decay in the receptor’s airways or

lung.

The concentration of naturally occurring radon in the air and the resulting risk of

exposure depend on many factors, including the prevailing weather conditions.

In still-air conditions, radon may build up close to the ground, in which case it is readily

inhaled. Natural thermal air movements tend to disperse radon, and mix it into the

surrounding atmosphere and/or transport it away from where it was exhaled from the

ground.

6.5.3 Exposure to Radioactive Dust in Air

Natural wind erosion and the disturbance of the soil, as is for example caused by vehicle

movements on unsealed roads, mining and mineral exploration activities generate

copious amounts of atmospheric dust. Ambient dust may contain naturally occurring


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radionuclides, which can be inhaled and/or ingested by receptors and they can

contaminate exposed surfaces.

Airborne dust is characterised by the concentration of total suspended particulates and

the concentration of the inhalable fraction of such dust. When airborne, the inhalable

fraction of dust is readily inhaled by receptors and contributes to an internal exposure

dose if such dust contains radionuclides.

6.5.4 Exposure to Radioactively Contaminated Material

There are numerous ways in which the environment can be contaminated with

radiological material. Often, contamination occurs when airborne radioactive dust

settles on exposed surfaces, which makes contaminants accessible and available to

receptors, often by way of ingestion. Ingestion can be direct, i.e. by way of the direct

intake of contaminants, or indirect, which occurs when radioactively contaminated food

or water is consumed by receptors.

Open pit uranium mining and heap leaching generate significant amounts of dust, which

can contaminate surfaces at and around such sites. A variety of agents, including the

wind, vehicles and humans readily convey non-fixed surface contaminants away from

areas where minerals are mined, processed or their waste materials are disposed of.

Conveyance of radionuclides makes them available for inhalation and/or ingestion by

receptors. Such an uptake may cause internal exposure to radiation and an associated

internal exposure dose of receptors. When food, such as livestock, fruit and vegetables,

are grown using contaminated water, radionuclides on plants or in the water are readily

transferred into such products and are ingested by humans on consumption of such

food stuff.

6.6 Receptors

In the context of the radiological impact assessment described in this Report, receptors

are those members of critical groups that are expected to receive the largest relevant

exposure dose from radiation considering a specific pathway in a specific location.

As per the ICRP, critical groups (or representative persons) are those that are most at

risk of being exposed to a specific exposure pathway. A group that is most exposed to a

specific exposure scenario is the critical group given their specific exposure situation.

A number of critical groups exist in close proximity to SU’s Husab Mine, including the

permanent and temporary settlements around the Husab Mine site where public

receptors may spend time. Figure 5 shows where the main public receptors considered

in this Report are located in the greater area around SU’s Husab Mine.


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Figure 5: Main public receptors in the greater area in which Swakop Uranium’s Husab Mine is located

Source: [Airshed, 2021]


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As depicted in Figure 5, eleven (11) locations were identified where receptors classified

as critical groups reside. Table 1 summarises these receptor locations and orders them

in terms of their location from North to South, with reference to Figure 5.

Table 1: Summary of public receptor locations used in this study

Receptor Identifier Receptor Location

1 Arandis

2 Arandis Airport

3 Rössing Mine

4 Stone Africa

5 Khan Mine (not operational but frequented by tourists)

6 Savanna Marble

7 Welwitschia Flats

8 Big Welwitschia

9 Husab campsite

10 Swakop River farm

11 Swakop River campsite

6.7 Qualitative Assessment of Radiological Impacts of Heap Leaching

Potential radiological impacts are location-dependant and the result of specific

operational practices which lead to the release of radionuclides into the environment.

Relevant operational practices include, amongst others, the

primary and secondary mineral ore crushers;

conveying crushed ore;

agglomeration;

stacking of the HLF;

removal of leached mineral waste and its disposal on on-site waste disposal

locations, including on WRDs and the TSF.


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While the location of the crusher facility remains the same for all three (3) options

considered in this Report, the locations of the HL pad and the waste disposal facilities

are specific to the options considered.

The list below provides a qualitative summary of the potential radiologically relevant

impacts associated with the HL options considered in this study:

A. Generation of radiologically relevant dust due to mining, blasting, conveying and

stockpiling of HL feed material as is of relevance for the atmospheric and aquatic

exposure pathways.

B. Crushing, screening and the associated conveyance of feed material generates

radiologically relevant dust as is of relevance for the atmospheric and aquatic

exposure pathways.

C. Conveying and stacking of agglomerated feed material onto the HSF potentially

contaminates the conveyor system as well as the area in which conveying takes

place as is of relevance for the atmospheric and aquatic exposure pathways.

D. Leaching is used to produce pregnant liquid that is radiologically relevant, while

the seepage of pregnant liquid as is of relevance for the aquatic pathway.

E. Run-off/spillage of rinse water used at the HLF and pregnant liquid may lead to

radioactive contamination of the soil as is of relevance for the atmospheric and

aquatic pathways.

F. Post-leaching handling of pregnant liquid may potentially lead to contamination

as is of relevance for the atmospheric and aquatic pathways. Handling of pregnant

liquid may lead to direct external exposure to gamma radiation.

G. The production of concentrated uranium from pregnant liquid from the HLF is

potentially associated with a multitude of new and incremental radiologically

relevant impacts. This is because the operation of the HSF increases the overall

production of uranium concentrate at the Husab Mine, which necessitates

additional handling and processing of uranium concentrate which potentially

implies additional relevant impacts on direct external exposures to gamma

radiation as well as the atmospheric and aquatic pathways.

H. Removal and handling of radioactive waste and residues from the HLF, and the

conveyance of such materials to the waste disposal facility may potentially

contaminate the soil as is of relevance to the atmospheric and aquatic pathways.

I. Disposal of waste and radioactive residues originating at the HLF may potentially

contaminate soil as is of relevance to the atmospheric and aquatic pathways.

J. Due to the climatic conditions in the hyper-arid Namib, mineral waste eventually

dries out completely. Unless covered by an inert substance, such as for example a

layer of uncontaminated soil, waste rock, clay or liner, the exposure of dry mineral


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waste residues to the forces of the wind and water as is of relevance for the

atmospheric pathway and aquatic pathways.

K. During/following high-rainfall episodes, run-off and/or spillage from the mineral

waste disposal facility may potentially lead to environmental releases in the form

of radioactive contaminants seeping into the soil as is of relevance to the

atmospheric and aquatic pathways.

6.8 Quantitative Assessment of Radiological Impacts of Heap Leaching Options

Quantitative radiological impact assessments usually consist of atmospheric, ground-

and surface-water transfer models as well as biosphere models to relate the multiple

sources of radioactivity to exposure doses incurred by members of the public. These

exposure doses are the result of potential internal and external exposure to radiation

from radioactive source material released into the environment as a result of the

operations under consideration.

The following external specialist reports are used as inputs:

a) To quantify the atmospheric dispersion of inhalable and respirable dust, the

results of the atmospheric dispersion modelling as reported by Liebenberg-Enslin

(refer to [Airshed, 2021]); and

b) To quantify the aquatic dispersion of radionuclides in ground water sources, the

results of the groundwater modelling as reported by Bittner et al. (refer to [SLR,

2021]) were used.

Based on the above inputs, the remainder of this section presents the quantitative

radiological impact assessment associated with the potential exposure of members of

the critical groups as were identified in section 6.6.

6.8.1 Atmospheric Exposure Pathway

Wind is the principal driver that causes the transport and dispersion of dust and radon

from their points of origin to sites where receptors may reside. As a result, the

atmospheric exposure pathway is critically important when quantifying the potential

radiological impacts on members of the public.

6.8.1.1 Atmospheric Dust

The atmospheric dispersion of dust was simulated in parallel with the present study

[Airshed, 2021]. Figure 6 to Figure 9 show the unmitigated and mitigated emissions from

current plus proposed HL operations, both in terms of PM2.5 emissions as well as for

total deposition due to dustfall .


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Figure 6: Simulated annual average PM2.5 dust concentrations – unmitigated emissions scenario



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Figure 7: Simulated annual average PM2.5 dust concentrations – mitigated emissions scenario



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Figure 8: Simulated average daily dustfall deposition rate – unmitigated emissions scenario



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Figure 9: Simulated average daily dustfall deposition rate – mitigated emissions scenario



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A radiological impact assessment focusing on members of the public (as opposed to

occupational impacts) must consider the contributions of radioactive particulates with

an aerodynamic diameter below 2.5 µm (PM2.5). Table 2 summarises the incremental

annual average atmospheric PM2.5 concentrations that are solely attributable to the

proposed HL projects per receptor location as identified in section 6.6,distinguishing

between unmitigated and mitigated operations, the latter meaning that dust mitigation

measures are employed, as elaborated in section 7.7.

Table 3 summarises the cumulative annual average atmospheric PM10 concentrations

that are attributable to current operations at the Husab Mine plus those due to the HL

project, again distinguishing between unmitigated and mitigated operations [Airshed,

2021].

Table 2: Incremental PM2.5 dust concentrations attributable to the HL Project only

Public Receptor Location

Annual Average Atmospheric Concentration, in µg/m3

Unmitigated Scenario Mitigated Scenario

Arandis 0.03 0.01

Arandis Airport 0.04 0.02

Rössing Mine 0.07 0.03

Stone Africa 0.05 0.02

Khan Mine 0.07 0.03

Savanna Marble 0.04 0.02

Welwitschia Flats 0.33 0.13

Big Welwitschia 0.25 0.09

Husab campsite 0.26 0.09

Swakop River farm 0.11 0.05

Swakop River campsite 0.16 0.06


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Table 3: Cumulative PM2.5 dust concentrations from the Husab Mine plus HL Project


Annual Average Atmospheric Concentration, in µg/m3


Arandis 0.23 0.11




Khan Mine 0.57 0.23







Table 4: Simulated annual average dustfall rates from the HL Project only


Daily Average Dustfall Rate, in mg/m2/day


Arandis 0.02 0.005




Khan Mine 0.17 0.051








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Table 5: Simulated annual average dustfall from the Husab Mine plus HL Project


Daily Average Dustfall Rate, in mg/m2/day


Arandis 0.32 0.10




Khan Mine 3.97 0.65







Both mitigated and unmitigated annual average PM2.5 and dustfall concentrations are

the result of an atmospheric dispersion simulation rather than being based on empirical

results [Airshed, 2021].

Based on the simulated PM2.5 concentrations in air, annual average public inhalation

doses are computed, as further described in Appendix A. Simulated dustfall results are

not considered further as these typically yield ingestion exposure doses that are at least

an order of magnitude smaller than those associated with the inhalation of PM2.5 dust.

Table 6 (Table 8) summarise the adult (infant) inhalation exposure doses (expressed in

μSv/a) at the various receptor locations considered in this Report, noting that these

results are the average incremental exposure doses due to the inhalation of PM2.5 dust

that is solely attributable to the HL project.

Table 8 (Table 9) present the total average adult (infant) exposure doses (expressed in

μSv/a) due to the inhalation of PM2.5 dust that is attributable to current operations at

the Husab Mine plus those resulting from one of the HL projects considered in this

Report.

The dust inhalation doses from current operations at Husab plus those associated with

one of the heap leaching options (refer to Table 8 and Table 9) inform the total exposure

doses determined for the exposure scenarios discussed in section 6.9 below.


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Table 6: Incremental adult dust inhalation exposure dose due to the HL project only


Annual Average Inhalation Exposure Dose, in μSv/a


Arandis 0.11 0.04




Khan Mine 0.00 0.00







Table 7: Incremental infant dust inhalation exposure dose due to the HL project only


Annual Average Inhalation Exposure Dose, in μSv/a


Arandis 0.03 0.01




Khan Mine 0.00 0.00








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Table 8: Adult dust inhalation exposure dose from Husab Mine + HL project

Public Receptor LocationAnnual Average Inhalation Exposure Dose, in μSv/a


Arandis 0.9 0.4




Khan Mine 0.0 0.0







Table 9: Infant dust inhalation exposure dose from Husab Mine + HL project

Public Receptor LocationAnnual Average Inhalation Exposure Dose, in μSv/a


Arandis 0.2 0.1




Khan Mine 0.0 0.0








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6.8.1.2 Atmospheric Radon and its Progeny

Radon is a member of the uranium decay chain and is exhaled from minerals that

contain enhanced levels of Radium-226. The mineral ores that are mined at Husab, the

mining pits, on-site ore stockpiles, waste rock dumps and post-processing mineral waste

all contain Radium-226 and therefore all exhale radon gas which is then readily mixed

into the air that is inhaled by persons both on- and off-site.

SU monitors ambient radon concentrations at various on-site locations as part of its

public exposure monitoring activities which are a regulatory requirement under

Namibia’s Atomic Energy and Radiation Protection Act [Act, 2005] and the regulations

under this Act [Regulations, 2012]. For the 2020 reporting period, atmospheric radon

concentrations were monitored at the following receptor sites [SU, 2020]:

Welwitschia campsite – to monitor exposure at nearest tourist campsite to the

mine;

Main Security Access – to monitor exposure at the mine’s perimeter;

B2 Security Checkpoint – to monitor exposure at the turn-off from the B2

highway to the mine site; and

Husab Contractors Camp – to monitor contractors residing onsite in the camp.

Monitoring was typically undertaken 2 or 3 times during the reporting period, each over

a 4-day period, as per SU’s public radiation monitoring plan. The radon-related public

exposure doses as summarised in Table 10 were reported, based on an extrapolated

exposure period of 8,760 hours per year [SU, 2020].

Table 10: Average annual public radon exposure doses at select receptor locations 2

Public Receptor Location Average Annual Public Radon Exposure Dose [μSv/a]

Welwitschia Campsite 520

Main Security Access 710

B2 Security Checkpoint 630

Husab Contractors Camp 810

2 Note: these doses include the natural background contributions, based on a full year of occupancy.


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A recent project undertaken on behalf of the Ministry of Mines and Energy assessed the

ambient radon concentrations at various receptor locations in the Erongo Region [MME,

2019]. In regard to ambient atmospheric radon concentrations, the main results were:

1. The average radon concentration at the Civic Centre in Walvis Bay, in the

monitoring period between 1 November 2016 and 15 May 2017 was 4.5 Bq/m3,

based on 10-minute averaged data in-between individual monitoring results. The

maximum radon concentration recorded was 110.5 Bq/m3.

2. The average ambient atmospheric radon concentration determined at the

Swakopmund sewer works station, in the monitoring period between 1

November 2016 and 31 December 2018, was 8.4 Bq/m3. The maximum

concentration during the monitoring period was 99.5 Bq/m3.

3. The average ambient atmospheric radon concentration determined at the

NamWater reservoir in-between Arandis and Rössing, in the monitoring period

between 1 November 2016 and 31 December 2018, was 16.7 Bq/m3. The

maximum concentration during the monitoring period was 266.0 Bq/m3 [MME,

2019].

These empirical results for the ambient atmospheric radon concentrations were used

to compute the annual average public exposure dose contributions as a result of the

inhalation of radon and its decay products. These exposure doses express the average

annual exposure dose contributions from the inhalation of radon and its progeny, and

therefore quantify the contribution of radon to total natural background radiation,

amounting to

100 μSv/a at Walvis Bay;

200 μSv/a at Swakopmund; and

400 μSv/a at the monitoring location in-between Arandis and Rössing [MME,

2019].

The various inhalation exposure doses from radon and its progeny inform the exposure

scenarios covered in section 6.8.4 below.

6.8.2 Direct External Exposure Pathway

As has been shown before and based on the results of numerous actual monitoring

campaigns, the direct external exposure pathway due to radiation sources originating

at uranium mines is important on the mining site (and therefore relevant for

occupational exposure dose management) and in situations where members of the

public are living on or very closer to areas that contain mineral waste and associated

residues that are contaminated with radionuclides [Von Oertzen, 2018].

The above is readily verified by an order-of-magnitude exposure dose calculation for a

large body of mineral ore with a specific activity due to natural uranium of 7 Bq/g, where


22 June 2021 of 77

a distance of 500 meters from such a source implies an exposure dose of

10 µSv/a, which is 1/100th of the Namibian annual public dose limit of 1 mSv/a [Act,

2005] and is considered a trivial dose under the definitions put forward by the

International Commission on Radiological Protection (refer to [ICRP, 2007]).

External exposure may also occur from soil contamination, for example as a result of

radionuclides that are deposited by way of the atmospheric and/or aquatic pathway.

However, external exposure doses from such deposition are at least an order of

magnitude smaller than those associated with the inhalation of such contaminants [Von

Oertzen, 2018]. As a result, the inhalation dose associated with radioactively

contaminated soil is a far greater contributor to the total exposure dose incurred by

members of the public, which implies that direct external exposure from such sources

is not considered in this assessment.

Based on the above reasoning, the direct external exposure pathway is not considered

relevant for any of the public receptors identified in section 6.6, as these receptor

locations are physically separated from the actual mining site and therefore the various

on-site sources of direct external gamma radiation. This implies that this pathway will

not be considered further in this radiological impact assessment as members of the

public do not readily have unfettered access to the mining site and areas where various

sources of gamma radiation are located, including the WRD, HLF and TSF.

6.8.3 Aquatic Exposure Pathway

The locations at which the receptors that have been identified in this assessment are

residing are indicated in Figure 5 (see page 32). Provided that these receptors consume

contaminated water and/or food originating at such receptor locations, an internal

exposure dose occurs. For example, members of the public could, potentially, be

exposed to radiation as a result of the ingestion of contaminated water, consuming food

that is grown on soil irrigated with contaminated water or consuming products from

livestock that has been drinking contaminated water or eating contaminated plants.

However, while the groundwater impact assessment provides evidence that

radionuclides are present in borehole waters at select receptor sites, there is no

evidence that these radionuclide concentrations are originating from the Husab Mine

[SLR, 2021]. As shown in an extensive regional assessment, most borehole waters in the

Swakop River and the Khan River are characterised by considerable radionuclide

concentrations, these are the result of in-river transfers that have been taking place for

millennia [MME, 2010]. This implies that that the ingestion dose resulting from the

direct or indirect uptake of water that may potentially be contaminated with

radionuclides from the Husab Mine is not considered in this assessment as a credible

transfer of radionuclides in groundwater is not plausible.


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6.9 Exposure Scenarios

This section elaborates specific public exposure scenarios for receptors in the locations

around the Husab Mine as identified in section 6.6, as shown in Figure 5 (see page 32).

These exposure scenarios are based on the exposure dose contributions per individual

exposure pathway as presented in section 6.8.

All exposure scenarios have in common that they are based on realistic and specific

human behaviours taking place at the receptor locations, such as time spent at the

location, purpose of stay, breathing rates and others.

6.9.1 Common Exposure Characteristics

The following characteristics apply to all exposure scenarios considered in this study:

a. all receptors are adults or infants (of less than one year of age);

b. receptors that permanently reside at a single location do so for 8 760 h/a;

c. receptors that are working at a specific receptor location are assumed to do so

for 2 000 h/a;

d. receptors that visit a specific location do so for 120 h/a (i.e. 5 days per year);

e. none of the receptors consume water extracted from a borehole at any receptor

location considered in this study; and

f. none of the receptors consume food or livestock products that relied on being

watered from borehole water at any receptor location considered in this study.

6.9.1.1 Scenario 1: Residents of Arandis

The distance between Arandis and the Husab Mine amounts to some 18.5 km. This

distance implies that radon exhalations and gamma radiation originating at the

Husab Mine do not have an impact on this location [Von Oertzen, 2018]. Residents

of Arandis consume piped water supplied by NamWater which is also (occasionally)

used to irrigate private vegetable gardens.

The consumption of such food and water will therefore not contribute to an

exposure dose that can realistically be attributed to activities at the Husab Mine. The

ingestion dose from such contaminated dust is not separately quantified as

experience shows that such a dose is at least one order of magnitude smaller than

the dose associated with the inhalation of dust.

As a result of the above considerations, this scenario only considers inhalation

exposures due to dust emissions from the fugitive sources at the Husab Mine. As

specific occupation details are unknown, the assessment assumes that the

occupancy at the town is for 8 760 h/a during which radioactively contaminated dust

attributable to mining or HL activities at the Husab Mine is inhaled.


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6.9.1.2 Scenario 2: Workers at Arandis Airport

The distance between Arandis Airport and the Husab Mine amounts to some 14 km.

This distance implies that radon exhalations and gamma radiation originating at the

Husab Mine do not have an impact on this location [Von Oertzen, 2018].

The Arandis Airport is not a residential area which implies that receptors are workers.

Water is supplied by NamWater and is not used to irrigate vegetable gardens; the

consumption of food and water will therefore not contribute to an exposure dose

that is attributable to mining or HL activities at the Husab Mine.


exposures due to dust emissions from the fugitive sources at the Husab Mine. The

assessment assumes outdoor conditions throughout the working year.

6.9.1.3 Scenario 3: Workers at Rössing Mine

The distance between Rössing Mine and the Husab Mine amounts to some 10 km.



Rössing Mine is not a residential area which implies that receptors are workers.

Water is supplied by NamWater and is not used to irrigate vegetable gardens; the

consumption of food and water does therefore not contribute to an exposure dose

that is attributable to mining or HL activities at the Husab Mine.



assessment assumes outdoor conditions throughout the working year, i.e. for 2 000

h/a.

6.9.1.4 Scenario 4: Workers at Stone Africa

The distance between Stone Africa and the Husab Mine amounts to almost 15 km.



This location is not a residential area and all receptors are workers. No borehole

water is used and the consumption of food and water does therefore not contribute

to an exposure dose that could be attributed to mining or HL activities at the Husab

Mine.



assessment assumes outdoor conditions throughout the working year, i.e. 2 000 h/a.


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6.9.1.5 Scenario 5: Tourists at the Khan Mine

The distance between the (disused) Khan Mine and the Husab Mine amounts to

some 9 km. This distance implies that radon exhalations and gamma radiation

originating at the Husab Mine do not have an impact on this location [Von Oertzen,

2018].

The Khan Mine is not a residential area and all receptors are tourists. No borehole



Mine.



assessment assumes outdoor conditions during all touristic visits, which are assumed

to be for 120 h/a.

6.9.1.6 Scenario 6: Workers at Savanna Marble

The distance between Savanna Marble and the Husab Mine amounts to some 16.5

km. This distance implies that radon exhalations and gamma radiation originating at

the Husab Mine do not have an impact on this location [Von Oertzen, 2018].

This location is not a residential area and all receptors are workers. No borehole



Mine.



assessment assumes outdoor conditions throughout the working year, i.e. 2 000 h/a.

6.9.1.7 Scenario 7: Tourists at the Welwitschia Flats

The distance between the Welwitschia Flats and the Husab Mine amounts to some

14 km. This distance implies that radon exhalations and gamma radiation originating

at the Husab Mine do not have an impact on this location [Von Oertzen, 2018].

This location is not residential and all receptors are tourists. No borehole water is

used and the consumption of food and water does therefore not contribute to an

exposure dose that could be attributed to mining or HL activities at the Husab Mine.



assessment assumes outdoor conditions during all touristic visits, i.e. 120 h/a.


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6.9.1.8 Scenario 8: Tourists at the Big Welwitschia

The distance between the Big Welwitschia and the Husab Mine amounts to some 12

km. This distance implies that radon exhalations and gamma radiation originating at

the Husab Mine do not have an impact on this location [Von Oertzen, 2018].







6.9.1.9 Scenario 9: Tourists at the Husab campsite

The distance between the Husab campsite and the Husab Mine amounts to some

11.5 km. This distance implies that radon exhalations and gamma radiation


2018].







6.9.1.10 Scenario 10: Residents at the Swakop River farms

The distance between the nearest smallholdings and farms in the Swakop River

(downstream from the confluence with the Khan River) and the Husab Mine amounts

to some 22 km. This distance implies that radon exhalations and gamma radiation

originating at the Husab Mine do not have an impact on these locations [Von

Oertzen, 2018].

The smallholdings and farms are residential in character and all receptors are

assumed to be permanently residing at these locations. Farming activities include

vegetable and small livestock production. Drinking water is mainly sourced from

NamWater supplies, including that for stock watering. Irrigation water is pumped

from the Swakop River and is used to irrigate vegetable gardens, fruit trees as well

as animal fodder such as lucerne. Livestock feeds on grass and lucerne that is sourced

on site. However, seepage waters originating from Husab Mine have not been

identified in the Swakop River [SLR, 2021]. As a result, direct or indirect ingestion


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exposure doses that can realistically be attributed to mining operations at the Husab

Mine are therefore ruled out as insignificant.


exposures due to dust emissions from the fugitive sources at the Husab Mine. As

specific occupation details are unknown, the assessment assumes that the

occupancy at the town is for 8 760 h/a during which radioactively contaminated dust

attributable to all mining operations at the Husab Mine is inhaled.

6.9.1.11 Scenario 11: Tourists at the Swakop River campsite

The distance between the Swakop River campsite and the Husab Mine amounts to

some 18.5 km. This distance implies that radon exhalations and gamma radiation


2018].

This location is not a residential area and all receptors are tourists. No borehole



Mine.




6.9.2 Public Exposure Doses

The eleven scenarios described in the previous subsections form the basis for the public

exposure dose assessment. These exposure doses express the radiological impact that

the various environmental emissions taking place at the Husab Mine have on adult or

infant members of the various critical groups.

A mathematical model was developed to translate receptor-specific exposure

conditions that characterise each exposure scenario into exposure doses for each

pathway. Specific parameters are common to all exposure scenarios and are described

in section 6.9.1, while the computation of the inhalation dose attributable to dust is

detailed in Appendix A.

The total public exposure doses for the receptors considered in this study are the sum

of the individual exposure doses across all relevant exposure pathways. As the exposure

dose attributable to the inhalation of dust depends on whether or not dust mitigation

measures are applied (as elaborated in section 7.7), the total public exposure doses for

both unmitigated and mitigated operations at the Husab Mine are presented.


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It is noted that all emissions scenarios considered in this section are for total emissions

due to current operations at the Husab plus those attributable to the proposed HL

project at the Mine.

Table 11 and Table 12 present the total incremental public exposure dose for adults as

a result of unmitigated and mitigated operations respectively, including the

contributions of the proposed heap leaching operations.

Table 13 and Table 14 present the total incremental public exposure dose for infants

as a result of unmitigated and mitigated operations respectively, including the

contributions of the proposed heap leaching operations.


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Table 11: Adult public exposure doses at select receptor locations around the Husab Mine – unmitigated scenario

Public Receptor Location Incremental Direct External Exposure

Dose [µSv/a]

Incremental PM2.5 Dust Inhalation

Dose [µSv/a]

Incremental Radon Inhalation Dose

[µSv/a]

Incremental Ingestion Dose

[µSv/a]

Total Annual Exposure Dose

[µSv/a]

Arandis n/a 0.9 n/a n/a 0.9

Arandis Airport n/a 0.3 n/a n/a 0.3

Rössing Mine n/a 0.5 n/a n/a 0.5

Stone Africa n/a 0.3 n/a n/a 0.3

Khan Mine n/a 0.0 n/a n/a 0.0

Savanna Marble n/a 0.3 n/a n/a 0.3

Welwitschia Flats n/a 0.2 n/a n/a 0.2

Big Welwitschia n/a 0.1 n/a n/a 0.1

Husab campsite n/a 0.1 n/a n/a 0.1

Swakop River farm n/a 6.1 n/a n/a 6.1

Swakop River campsite n/a 0.1 n/a n/a 0.1


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Table 12: Adult public exposure doses at select receptor locations around the Husab Mine – mitigated scenario


Dose [µSv/a]


Dose [µSv/a]


[µSv/a]


[µSv/a]


[µSv/a]













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Table 13: Infant public exposure doses at select receptor locations around the Husab Mine – unmitigated scenario


Dose [µSv/a]


Dose [µSv/a]


[µSv/a]


[µSv/a]


[µSv/a]













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Table 14: Infant public exposure doses at select receptor locations around the Husab Mine – mitigated scenario


Dose [µSv/a]


Dose [µSv/a]


[µSv/a]


[µSv/a]


[µSv/a]













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6.10 Radiological Risk and Radiological Impact Criteria

The International Commission on Radiological Protection (ICRP) has provided estimates

for the probability of harmful health effects as a result of an exposure to ionising

radiation [ICRP, 1995], [ICRP, 2007a], [ICRP, 2007b].

Specifically, the ICRP provides risk coefficients applying to a population as a whole, i.e.

independent of a particular population’s age distribution: the probability of occurrence

of a fatal cancer is given as 5.5% per Sievert. This measure of radiological risk associated

with the exposure to ionising radiation is helpful as it enables the quantification of the

overall detriment associated with such an exposure.

Table 15 presents the radiological impact criteria that will serve to interpret the total

exposure doses resulting from combination of current mining plus proposed

heap leaching operations at the Husab Mine.

Table 15: Annual public exposure doses and their associated radiological risk

Annual Public Exposure Dose Radiological Impact

Below 10 µSv/a trivial exposure dose

Below 300 µSv/a While the relevant regulatory authority has not defined a dose constraint, such exposure doses are deemed acceptable while also informing contributing entities to further optimise radiation protection measures as guided by the principle of ALARA.

Between 300 µSv/a and 1 000 µSv/a Such exposure doses remain below the public exposure dose limit as defined in Namibia [Act, 2005]. However, they indicate that contributing entities must further optimise radiation protection measures as guided by the principle of ALARA to reduce public exposures.

Above 1 000 µSv/a Exceeding the public exposure dose limit as defined in Namibia [Act, 2005]. Such public exposure doses necessitate that immediate corrective action is taken by contributing entities.


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6.11 Conclusion – Radiological Impact on Select Public Receptors

The radiological impact assessment developed in this section indicates that, for the

receptors identified as members of the critical groups and based on eleven distinct

exposure scenarios, all public radiation exposure doses from current operations at the

Husab Mine plus those that can be attributable to the proposed HL operations are

trivial as they result in total exposure doses that are less than 10 µSv/a for both adult

and infant receptors.

It must be noted that exposure doses were computed from simulated (as opposed to

actual empirical) ambient dust concentrations which are known to be associated with

considerable uncertainties.

In the absence of empirical radionuclide concentrations, inhalation dose calculations

had to assume that uranium-bearing mineral ore would be dispersed by the wind

without referring to the actual radionuclide concentration and particle size distribution

in such emissions. This approach is an approximation and is likely to overestimate the

dust inhalation dose, as fugitive dust from mining operations at the Husab Mine is

expected to consist of a mix of dust sources rather than of pure mining grade mineral

ore only.

An increase of the Husab Mine’s total production capacity implies that the risk of

adverse environmental impacts increases. The following list summarises the principal

radiological impacts of the proposed heap leaching options and associated processing

infrastructure:

A. Generation of additional radiologically relevant dust as well as radon which may

have adverse impacts on sensitive air quality receptors in the area;

B. Potential contamination, seepage and other unintended emissions of radiologically

relevant minerals and gases into the environment;

C. Generation of additional radiologically relevant mineral waste;

D. Disposal of radiologically relevant mineral and non-mineral waste;

E. Impacts associated with the possibility that the long-term management of the

waste disposal facility is suboptimal and would then result in unintended emissions

of radiologically relevant minerals and gases into the environment;

F. Impacts associated with the management of mining activities that are extended by

way of the addition of a heap leach facility and leads to unintended emissions of

radiologically relevant minerals and gases into the environment; and

G. The potential impacts associated with the ultimate failure of the waste disposal

facility following the decommissioning of the heap leaching facility and associated

infrastructure, noting that adverse impacts can potentially occur decades after the

closure of a facility.


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7. Radiological Impact Ratings

This section presents the radiological impact ratings associated with the combined

operations currently taking place at the Husab Mine plus those associated with the

proposed HL operations.

7.1 Approach

The radiological impacts associated with the combined operations currently taking

place at the Husab Mine plus those associated with the proposed HL operations are

rated in terms of a) the probability of occurrence and b) their consequences.

This rating approach uses the following methodology as elaborated in Appendix B:

a. Impacts associated with each HL option are separately rated in terms of a) their

probability and b) consequences, based on the public radiological impact

assessment presented in this Report; and

b. An overall significance rating, based on a combination of the probability of

occurrence and consequences of potential impacts, is rated on a scale of low,

medium or high for both unmitigated and mitigated scenarios.

7.2 Definition of the Probability, Consequence and Overall Significance Ratings

Appendix B defines the impact framework in terms of the probability, consequence and

overall significance ratings used in this study.

The overall significance of impacts is determined by the combination of the probability

of occurrence of an impact and the severity of its consequences, as shown in Table 16.

Table 16: Definition of the overall significance rating used in this study

CONSEQUENCE

Low Medium High

PROBABILITY

High Medium Medium High

Medium Medium Medium High

Low Low Low Medium


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7.3 Impacts, Probability, Consequence and Overall Significance Ratings

7.3.1 Impacts Associated with Heap Leaching Options per Exposure Pathway

Table 17 summarises the main impacts associated with the heap leaching options

assessed in this study per individual exposure pathway considered in this study.

7.3.2 Probability Rating of Impacts per Main Exposure Pathway

Table 18 (Table 19) presents the probability rating of impacts associated with the heap

leaching options assessed in this study for the atmospheric (aquatic and direct external)

exposure pathways.

7.3.3 Consequence Rating of Impacts per Main Exposure Pathway

Table 20 (Table 21) presents the consequence rating of impacts associated with the

heap leaching options assessed in this study for the atmospheric (aquatic and direct

external) exposure pathways.

7.3.4 Overall Significance Rating of Impacts per Main Exposure Pathway

Table 22 (Table 23) presents the overall significance rating of the impacts associated

with the heap leaching options assessed in this study for the atmospheric (aquatic and

direct external) exposure pathways.


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Table 17: Summary of main radiological impacts associated with the heap leaching options assessed in this study

Radiological Impact Relevance of Radiological Impact per Exposure Pathway

Atmospheric (dust) Atmospheric (radon) Aquatic Direct External

A. Radiologically relevant dust is released into the atmosphere

yes not applicable yes yes

B. Radon is released into the atmosphere not applicable yes not applicable not applicable

C. Radiologically relevant material is released into the environment as a result of seepage

yes not applicable yes yes

D. Radiologically relevant material is released into the environment as a result of inadequate stormwater controls and management systems

yes yes yes yes

E. Radiologically relevant mineral waste material is released into the environment

yes yes yes yes

F. The design of the waste disposal system does not cater for extreme weather events and causes radionuclide emissions into the environment

yes yes yes yes

G. Provisions on closure of the HLF do not adequately ensure the long-term containment of mineral waste, resulting in the eventual release of radiologically relevant material into the environment

yes yes yes yes


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Table 18: Probability rating of the radiological impacts assessed in this study – atmospheric pathway

Radiological Impact

Probability Rating Associated with the Radiological Impacts

Atmospheric (dust) Atmospheric (radon)

Mitigated ScenarioUnmitigated

ScenarioMitigated Scenario

Unmitigated Scenario


medium high not applicable not applicable

B. Radon is released into the atmosphere not applicable not applicable high high


medium high medium high










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Table 19: Probability rating of the radiological impacts assessed in this study – aquatic and direct external pathways

Radiological Impact

Probability Rating Associated with the Radiological Impacts

Aquatic Pathway Direct External Pathway






B. Radon is released into the atmosphere not applicable not applicable not applicable not applicable












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Table 20: Consequence rating of the radiological impacts assessed in this study – atmospheric pathway

Radiological Impact

Consequence Rating Associated with the Radiological Impacts






low low not applicable not applicable

B. Radon is released into the atmosphere not applicable not applicable low low


low medium low medium










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Table 21: Consequence rating of the radiological impacts assessed in this study – aquatic & direct external pathways

Radiological Impact







low low low low













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Table 22: Overall significance rating of the radiological impacts assessed in this study – atmospheric pathway

Radiological Impact

Overall Significance Rating Associated with the Radiological Impacts






medium medium not applicable not applicable

B. Radon is released into the atmosphere not applicable not applicable medium medium


medium medium medium medium










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Table 23: Overall significance rating of the radiological impacts assessed in this study – aquatic and direct external pathways

Radiological Impact




















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7.4 Results of the Probability, Consequence and Overall Significance Ratings

Based on the assessment of the probability of radiological impacts associated with the

heap leaching options considered in Table 17, the aggregate probability rating is:

Mitigated scenarios: MEDIUM

Unmitigated scenarios: HIGH

Based on the assessment of the consequences of radiological impacts associated with

the heap leaching options considered in Table 17, the aggregate consequence rating is:

Mitigated scenarios: LOW

Unmitigated scenarios: MEDIUM

Based on the assessment of the overall significance of radiological impacts associated

with the heap leaching options considered in Table 17, the aggregate overall

significance rating is:

Mitigated scenarios: MEDIUM

Unmitigated scenarios: MEDIUM.

7.5 Fatal Flaws from the Radiological Perspective

This radiological impact assessment defines a heap leaching option as fatally flawed if

its impacts are disruptive and/or irreversible to the continued effective functioning of

ecosystem services that are essential for life.

From a radiological perspective, there is no material difference in the overall

significance rating of the individual heap leaching options considered in this study.

In view of the principle of optimisation as applies to radiological practices in Namibia,

all unmitigated heap leaching options are excluded from further considerations and

are therefore not to be implemented as their radiological impacts are not as low as

reasonably achievable, taking economic and social factors into account.

Based on considerations presented above, this study recommends that only mitigated

heap leaching options are considered for implementation, provided that

environmental impacts are minimised by way of applying best practice mitigation

measures as applied in modern open pit mining and processing environments in

hyper-arid climates as is the case in the western Namib desert.


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7.6 Preferred Heap Leaching Option

From a radiological perspective, a specific heap leaching option that is not fatally flawed

or considered inappropriate as a result of other considerations and results in the

smallest cumulative on- and off-site footprint is the preferred option.

From a radiological perspective, there is no material difference in the overall

significance rating of the individual heap leaching options considered in this study.

Therefore, from a radiological perspective, all three heap leaching options considered

in this study can be considered for implementation, provided that best practice

mitigation measures are applied, as are described in section 7.7.

7.7 Mitigation Measures

The following measures form part of the essential mitigation approaches focusing on

reducing dust emissions from mining and milling operations, as are applicable in hyper-

arid climates, such as Namibia’s Namib desert:

a. active dust suppression measures (e.g. water sprays) at both the primary and

secondary crushers as well as in all screening operations;

b. active dust suppression in all transport, stacking and agglomeration areas;

c. passive dust control measures (e.g. by way of hooding, roofing and covering) of

crushers, screens, conveyors and grasshopper stackers; and

d. active as well as passive dust controls on all on-site service roads (e.g. dusticide

and/or water sprays).

The HLF considered in this study contribute some 5% (10%) to existing total particulate

emissions from the Husab Mine if operations are undertaken with (without) the

mitigation measures identified above [Airshed, 2021]. Similarly, this HLF adds 3% (4%)

to PM10 emissions if operations are undertaken with (without) the above mitigation

measures, and adds 1% (2%) to PM2.5 emissions if operations are undertaken with

(without) the above mitigation measures [Airshed, 2021].

7.8 Concluding Remarks

Using the above indicators for impacts, probability, consequence and overall

significance, the overall radiological significance rating is “medium”.

The total public exposure dose contribution associated with current plus proposed heap

leaching operations at the Husab Mine across all relevant exposure pathways is below

10 μSv/a for all members of the critical groups considered in this study which is a trivial

incremental dose contribution. This implies that the HL options considered do not

measurably increase the overall public risk of exposure to ionising radiation caused as

a result of the operation of any of the three HL options considered in this study.


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8. Conclusions and Recommendations

This section presents the main conclusions and recommendations based on the

radiological impact assessment described in this Report.

Swakop Uranium wishes to introduce a heap leaching facility to extract uranium from

low-grade uranium-bearing run-of-mine material that is often unsuitable for treatment

in the company’s existing tank leaching facility at the Husab Mine. A HLF increases the

Mine’s total leaching capacity and therefore increases its total product output without

necessitating additional extensions and investments in tank leaching capacities.

The following heap leaching options were considered in this Report:

1. Option G: comprises of a dynamic HLF including HL circuit, pad and ponds located

south-west of the existing waste rock dumps (WRDs) and a heap leaching waste

storage facility (HLWSF) south of the existing WRDs;

2. Option H: comprises of a dynamic HLF including HL circuit, pad and ponds located

south of the existing plant area and a HLWSF south-west of the existing WRDs and

3. Option K: comprises of a dynamic HLF with HL circuit south of the processing plant

and south-west of the existing WRDs, with the HLWSF extending the existing WRDs

in a south-easterly direction.

The principal radiological impacts of the proposed HL options are:

A. Generation of additional radiologically relevant dust as well as radon which may

have adverse impacts on sensitive air quality receptors in the area;

B. Potential contamination, seepage and other unintended emissions of

radiologically relevant minerals and gases into the environment;

C. Generation of additional radiologically relevant mineral waste;

D. Disposal of radiologically relevant mineral and non-mineral waste;

E. Impacts associated with the possibility that the long-term management of the

waste disposal facility is suboptimal and leads to unintended emissions of

radiologically relevant minerals and gases into the environment;

F. Impacts associated with the management of mining activities that are extended

by way of the addition of a heap leach facility and lead to unintended emissions of

radiologically relevant minerals and gases into the environment; and

G. The potential impacts associated with the failure of the waste disposal facility

following the decommissioning of the HLF and associated infrastructure, noting

that adverse impacts can potentially occur decades after the closure of a facility.

There is no material radiological difference between the individual heap leaching

options considered in this study. Therefore, the probability and consequence ratings


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apply to all HL options considered in this study. The assessment distinguishes between

“mitigated” and “unmitigated” scenarios, the former meaning that best industry

practices are used to prevent/minimise potential adverse environmental impacts.

Based on the principle of optimisation as applied to radiological practices in Namibia,

all unmitigated heap leaching options are associated with radiological impacts that are

not as low as reasonably achievable, taking economic and social factors into account.

Therefore, only mitigated heap leaching options must be considered for

implementation, and these are to employ best practice mitigation measures as relevant

and applicable in modern open pit mining environments in hyper-arid climates.

From a radiological perspective, the heap leaching option that results in the smallest

cumulative footprint is the preferred option. From a radiological perspective, there is

no material difference in the overall significance rating of the individual heap leaching

options considered in this study, and these options can be considered for

implementation, provided that best practice mitigation measures are applied.

The following recommendations, which are to be read with others included in the EIA

for this project, are formulated from a radiological perspective, aiming at minimising

radiation-related environmental impacts as a result of mining operations at Husab:

1. The process to dispose of the mineral waste from heap leaching is to satisfy the

Namibian regulatory requirements for the disposal of radioactive waste, as per the

Atomic Energy and Radiation Protection Act, Act No. 5 of 2005 and Regulations;

2. The operations of the HLF are to be included in the Husab Mine’s Radiation

Management Plan, which is to be submitted to the Namibian National Radiation

Protection Authority for approval prior to the commencement of HL operations;

3. Monitoring of total suspended particle concentrations in the atmosphere, total

inhalable and respirable atmospheric dust concentrations and their associated

radionuclide concentrations are to be further strengthened as part of SU’s ongoing

implementation of the Husab Mine’s Radiation Management Plan;

4. The public and occupational exposure dose monitoring programs undertaken as

part of the implementation of SU’s Radiation Management Plan are to strengthen

the monitoring of actual atmospheric and aquatic emissions into the environment;

5. All environmental releases originating from the Husab Mine’s operations are to be

regularly quantified and are to form an active part of the risk register that informs

the application of mitigation practices at the Mine; and

6. Public and occupational dose assessments are to be based on empirical data for

radionuclide concentrations and particle characteristics of dust from mining,

blasting and mineral transport, waste disposal and tailings storage facilities, and

use local weather data as part of the ongoing modelling of dispersion of dust in

the atmosphere and seepage of effluents into the groundwater.


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9. References

Act, 2005 Atomic Energy and Radiation Protection Act, Act 5 of 2005, Government of the Republic of Namibia, Windhoek, 2005.

Airshed, 2020 Air Quality Screening Assessment of the Husab Mine Heap Leach Project, Liebenberg-Enslin, H., Airshed Planning Professionals, 2020.

Airshed, 2021 Air Quality Impact Assessment of the Husab Mine Heap Leach Project, Liebenberg-Enslin, H., Airshed Planning Professionals, 2021.

IAEA, 1992 Measurement and Calculation of Radon Releases from Uranium Mill Tailings. Technical Report Series No. 333, Vienna, 1992.

IAEA, 1995 The Principles of Radioactive Waste Management. IAEA Safety Series No. 111-F, Vienna, 1995.

IAEA, 1996 International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series 115, International Atomic Energy Agency, Vienna, 1996.

IAEA, 2001 Generic Models for Use in Assessing the Impact of Discharges of Radioactive Substances to the Environment. Safety Report Series No. 19, Vienna, 2001.

IAEA, 2002 Management of Radioactive Waste from the Mining and Milling of Ores. Safety Guide No. WS-G-1.2, Vienna, 2002.

IAEA, 2004 Occupational Radiation Protection in the Mining and Processing of Raw Materials, IAEA Safety Guide No. RS-G-1.6, Vienna, 2004.

IAEA, 2018 IAEA Safety Standards, Safety Guide No. GSG 7, Occupational Radiation Protection, International Atomic Energy Agency, Vienna, 2018.

ICRP, 1993 Publication 65, Protection Against Radon-222 at Home and at Work, International Commission on Radiological Protection, Pergamon, 1993.

ICRP, 1994 Human Respiratory Tract Model for Radiation Protection, International Commission on Radiological Protection, Annals of the ICRP, 24 (1-3).

ICRP, 1995 Age-dependent Doses to Members of the Public from Intake of Radionuclides, Part 4: Inhalation Dose Coefficients, International Commission on Radiological Protection, 1995.

ICRP, 1983 Radionuclide Transformations Energy and Intensity of Emissions. ICRP Publication 38.


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ICRP, 1995 Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 4, Inhalation Dose Coefficients, ICRP Publication 71, Annals of the ICRP, Vol. 25, No. 3-4.

ICRP, 2007a The 2007 Recommendations of the International Commission on Radiological Protection, ICRP Publication 103, Annals of the ICRP, Elsevier, 2007.

ICRP, 2007b Assessing Dose of the Representative Person for the Purpose of Radiation Protection of the Public and the Optimization of Radiological Protection. ICRP Publication 101.

Kümmel, 2012 Kümmel, M., Strahlenexposition infolge bergbaubedingter Umweltradioaktivität, Bundesamt für Strahlenschutz, urn:nbn:de:0221-201204168021, April 2012.

MME, 2010 Strategic Environmental Assessment for the central Namib Uranium Rush, Ministry of Mines and Energy, Windhoek, 2010.

MME, 2019 Advanced Air Quality Management for the Strategic Environmental Management Plan for the Uranium and other Industries in the Erongo Region, Ministry of Mines and Energy, Republic of Namibia, Windhoek, 2019.

Regulations, 2011 Namibia’s Radiation Protection and Waste Disposal Regulations, No. 221 of 2011, under the Act, see [Act, 2005], Government of the Republic of Namibia, Windhoek, 2019.

SEA, 2010 Strategic Environmental Assessment for the Central Namib Uranium Rush, Geological Survey of Namibia, Ministry of Mines and Energy, Republic of Namibia, Windhoek, 2010.

SGS, 2017 SGS Time Mining (Pty) Ltd, Husab P20 Heap Leach Project Pre-feasibility Study Report, TS518-0000-T-REP-001 30, 2017.

SGS, 2021 SGS Bateman (Pty) Ltd, P20 Heap Leach Project Feasibility Study Report, M7556-0760-001REV A, 18 March 2021.

SLR, 2021 Groundwater Impact Assessment of the Husab Mine Heap Leach Project, Bittner, A. et al., 2021.

SU, 2019 Annual Report on the Implementation of the Radiation Management Plan, page 15 to 19, Swakop Uranium, 2019.

UNSCEAR, 1993 Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, 1993.

Von Oertzen, 2018 Radiation Safety Officer’s Handbook; von Oertzen, Gunhild; von Oertzen, Detlof; https://voconsulting.net/radiation, 2018.

Von Oertzen, 2020 Radiological Screening Assessment of the Husab Mine Heap Leach Project; von Oertzen, Detlof; VO Consulting, 2020.


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Appendix A: Dust Inhalation Exposure Dose

This appendix describes how the internal exposure dose associated with the inhalation

of ambient atmospheric uranium-bearing PM2.5 dust (which is the so-called thoracic

fraction of particulates that penetrate a human’s airways beyond the larynx into the

lungs) was calculated.

The exposure dose corresponding to the dust concentration in air depends on the

composition and size distribution of particulates in ambient air. In the absence of

empirical size distributions and radionuclide concentrations of dust in air, the

calculation presented in this section assumes that ambient atmospheric dust from

operations at the Husab Mine consists of uranium-bearing mineral ore in secular

equilibrium with the members of the decay chain.

The inhalation dose from such ambient dust is calculated using the following formulae

[Von Oertzen, 2018]:

��.� �� = � ∙ �� ∙ �� ∙ �� ∙ �� ∙ �� ∙ � [µ��/�]

where

� = multiplicative factor expressing the additional concentration of PM2.5

dust particles in air, assumed to be 2, [Kümmel, 2012], dimensionless;

��= simulated annual average concentration of PM2.5 dust in air, [Airshed,

2021], in [µg/m3];

��= uranium concentration in PM2.5 dust, assumed to be 650 parts per

million (ppm), in [ppm];

�� = specific alpha activity of uranium-bearing ore in secular equilibrium,

i.e. 8.3 * 12 450 Bq/g [IAEA, 2018], in [Bq/g];

�� = dose conversion factor for alpha emitters in uranium ore includes

relevant radionuclides from both the uranium and actinium decay

chains, i.e. 3.6 ∙ 10-6 Sv/Bq [IAEA, 2004], in [Sv/Bq];

�� = breathing rate of adults (infants) of 0.9 (0.2) m3/h [IAEA, 2004], in

[m3/h];

� = exposure period of 8 760 h/a for year-long inhalation by members of

the public, 2 000 h/a for members of the public working in nearby

locations and 120 h/a for tourists, in [h/a].


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Appendix B: Impact Classification Framework

This appendix summarises how the radiological impacts identified in this study are

classified.

The framework to classify radiological impacts is based on the following:

Part A defines the criteria to determine the consequence of the impact(s)

(combining intensity, spatial scale and duration) and the significance of the

impact(s), i.e. the overall rating of the impact;

Part B shows how the consequences of impacts are determined;

Part C show how the significance of impacts is determined; and

Part D describes how the overall impact significance is to be interpreted.

PART A: DEFINITION AND CRITERIA*

Definition of SIGNIFICANCE Significance = consequence x probability

Definition of CONSEQUENCE Consequence is a function of severity, spatial extent and duration

Criteria for

ranking of the

SEVERITY of

environmental

impacts

H Substantial deterioration (death, illness or injury). Recommended

level will often be violated. Vigorous community action.

M

Moderate/ measurable deterioration (discomfort).

Recommended level will occasionally be violated.

Widespread complaints.

L

Minor deterioration (nuisance or minor deterioration). Change

not measurable/ will remain in the current range. Recommended

level will never be violated. Sporadic complaints.

L+

Minor improvement. Change not measurable/ will remain in the

current range. Recommended level will never be violated.

Sporadic complaints.

M+ Moderate improvement. Will be within or better than the

recommended level. No observed reaction.

H+ Substantial improvement. Will be within or better than the

recommended level. Favourable publicity.

Criteria to rank

the DURATION

of impacts

L Quickly reversible. Less than the project life. Short term

M Reversible over time. Life of the project. Medium term

H Permanent. Beyond closure. Long term.

Criteria to rank

the SPATIAL

SCALE of impacts

L Localised - Within the site boundary.

M Fairly widespread – Beyond the site boundary. Local

H Widespread – Far beyond site boundary. Regional/ national

*H = high, M= medium and L= low and + denotes a positive impact.


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PART B: DETERMINING CONSEQUENCE

SEVERITY = L

DURATION

Long term H Medium Medium Medium

Medium term M Low Low Medium

Short term L Low Low Medium

SEVERITY = M

DURATION

Long term H Medium High High

Medium term M Medium Medium High

Short term L Low Medium Medium

SEVERITY = H

DURATION

Long term H High High High

Medium term M Medium Medium High

Short term L Medium Medium High

L M H

Localised

within site

boundary site

Fairly

widespread

beyond site

boundary

Local

Widespread

Far beyond site

boundary

Regional/

national

SPATIAL SCALE

PART C: DETERMINING SIGNIFICANCE

PROBABILITY

(of exposure to

impacts)

Definite/continuous H Medium Medium High

Possible/frequent M Medium Medium High

Unlikely/seldom L Low Low Medium

L M H

CONSEQUENCE

PART D: INTERPRETATION OF SIGNIFICANCE

Significance Decision Guide

High It would influence the decision regardless of any possible mitigation.

Medium It should have an influence on the decision unless it is mitigated.

Low It will not have an influence on the decision.

+++

radiological impact assessment

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