environmental monitoring and public dose assessment around the tokai reprocessing plant

Journal of Radioanalytical and Nuclear Chemistry, Vol. 260, No. 3 (2004) 563–577

0236–5731/2004/USD 20.00 Akadémiai Kiadó, Budapest© 2004 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht

Environmental monitoring and public dose assessmentaround the Tokai Reprocessing Plant

K. Shinohara*Tokai Works, Japan Nuclear Cycle Development Institute, 4-33 Muramatsu, Tokai-mura, Ibaraki-ken, 319-1194 Japan

(Received July 3, 2003)

Radiological effects to the regional environment around Tokai Reprocessing Plant (TRP) were assessed using both actual environmentalradiological monitoring data and doses estimated by mathematical models. The environmental monitoring showed no increase of radiological levelexcept for the influences from atmospheric explosion tests, the Chernobyl accident, and domestic accidents . Estimated annual effective dose for thepublic was only 0.1% of the annual dose limit recommended by the ICRP.

Introduction

The Tokai Reprocessing Plant (TRP) is designed foran annual reprocessing capacity of 210 tons and hasprocessed more than 1,000 tons of spent fuels used atJapanese BWR, PWR and Advanced Thermal Reactor(ATR, FUGEN) type power reactors since it beganoperation in 1977. The fuels reprocessed were bothuranium dioxide and uranium and plutonium mixedoxide (MOX). The plant site, Japan Nuclear CycleDevelopment Institute (JNC), Tokai Works, is locatedabout 100 km northeast of Tokyo. To the east is thePacific Ocean and to the west a primarily rural terrainwith a mixture of residential and agricultural areas.

The radioactive effluents are discharged from three90 m high stacks, with continuous monitoring ofradioactivity. Liquid effluents are discharged in batchmode through a pipeline stretching about 3.7 km longfrom the shoreline. Radioactivity concentrations in theliquid effluents are measured for each discharge. Themajor radionuclides are 3H, 14C, 85Kr and 129I inairborne effluents and 3H, 137Cs and plutonium in liquideffluents.

Environmental radiation monitoring has beenconducted around the site and no significant effects fromthe plant operation have been found. Because theindividual dose around the site is too small to bedetermined from the monitoring results, mathematicalmodels have been used to estimate the dose for anindividual in the hypothetical critical population groupliving near the TRP. Effective doses have beenestimated to be less than the annual effective dose limitfor the general public recommended by the InternationalCommittee on Radiological Protection (ICRP).1

* E-mail: [email protected]

Experimental

Monitoring of the effluents from the TRP

In the reprocessing plants, uranium and plutoniumare recovered from spent fuels to reuse as fuels fornuclear reactors. The spent fuel elements from thereactors are stored under water for a given period, inorder to ensure that the short-lived radionuclides decayto a very low level. The uranium oxide of spent fuel isleached in heated nitric acid. Then, uranium, plutoniumand the fission products are separated by the solventextraction process.

The TRP is designed for an annual reprocessingcapacity of 210 tons of spent fuels. The initial 235Uenrichment of fuel is 4% and the average burn-up is28,000 MWD.t–1 with a maximum of 35,000 MWD.t–1,and the cooling period is longer than 180 days. Thereprocessed amount of spent fuels since the start ofoperation in 1977 is shown in Fig. 1.

Spent fuels are transported by a ship from thereactors and stored in the water pool at the TRP to waitfor the decay of short-lived radionuclides. Fuel elementsare chopped in small, about 3 to 5 cm pieces, by ashearing machine, and then the uranium pellets areleached by nitric acid in the dissolver. The nitricsolution is fed into the solvent extraction process using30% TBP (tri-butyl phosphate) – 70% dodecane.Uranium and plutonium are separated from the fissionproducts in the first extraction step, and then uranium isseparated from plutonium in the second. Thisreprocessing process is called PUREX (PlutoniumUranium Redox EXtraction). The main radionuclidesdischarged from the reprocessing plants are long-livednuclides: 3H, 14C, 85Kr, 129I, 137Cs and transuraniumelements. Gaseous effluents, mostly 85Kr, are mainlydischarged in the shearing and dissolving processes.

K. SHINOHARA: ENVIRONMENTAL MONITORING AND PUBLIC DOSE ASSESSMENT

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Fig. 1. Amount of spent fuels reprocessed at the TRP

Other radionuclides have more complex behaviordepending on the characteristics of the treatment.Radionuclides in liquid effluents come from manyprocesses such as the low-level waste treatment,washing water for equipments and laundry water fromcleaning worker’s clothing.

Airborne effluent has been discharged from three90 m high stacks (main, sub-1 and sub-2). More than99% of 3H and 85Kr are discharged from the main stack.Part of 14C and 129I has been discharged from the stackssub-1 and sub-2.

Airborne radionuclides were continuously measuredor sampled by effluent monitors installed at the stacks.Airborne 3H was continuously sampled by effluentmonitors. Tritiated water (HTO) in the effluent wastrapped by the samplers at –20 °C by a cryostat. Otherchemical forms of 3H were oxidized with a Pt catalyst toHTO. 3H in tritiated water form was measured by aliquid scintillation spectrometer. 3H in the liquid effluentwas measured in the same way after distillation.

Airborne 14C in the effluent was continuouslysampled by effluent monitors. Carbon dioxide in theeffluent was absorbed in mono-ethanol amine (MEA).Other chemical form of carbon was oxidized with a Ptcatalyst bed to CO2 and then absorbed in MEA. MEAwas mixed with a liquid scintillator, and then 14C wasmeasured by a liquid scintillation spectrometer.

85Kr was continuously measured by effluentmonitors installed at the stacks. The air containing 85Krwas introduced in the chambers in which a NaI(Tl)

scintillation counter or a plastic scintillation counter wasinstalled to measure the high-level and the low-levelconcentration, respectively.

Airborne 129I concentration was continuouslymeasured by effluent monitors. 129I in the airborneeffluent was absorbed in a charcoal filter activated withEDTA (ethylene diamine tetraacetic acid) which iseffective for both the inorganic and organic forms. Alow energy gamma-spectrometer directly determined129I activity on the charcoal filter. 129I in liquid effluentwas measured by a low energy gamma spectrometerafter chemical precipitation as PdI2.

Liquid effluents have been discharged in batch modethrough a pipeline stretching about 3.7 km from theshoreline into the sea. Radioactivity concentrations inthe liquid effluent were measured for each discharge toconfirm that they are less than the limit. The length ofthe discharge pipeline was 1.8 km until the new 3.7 kmpipeline was installed in 1990.

Environmental monitoringThe radiological environmental monitoring program

of TRP was based on the environmental safetyassessment for licensing of the TRP and the Guidelinefor Environmental Radiological Monitoring, publishedby the Nuclear Safety Commission (NSC).2 Theprograms are shown in Tables 1 and 2, and themeasurement and sampling locations are shown in Figs2 and 3.


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Table 1. Terrestrial environmental monitoring program around the TRPSampling MeasurementItem Location Frequency Nuclide Method

Air absorbed dose rate in site: 9off site: 3

Continuously Gamma-ray NaI(Tl)

Cumulative dose in site: 15off site: 25

Quarterly Gamma-ray TLD

Airborne dust in site: 3off site: 4

Weekly Gross α, β90Sr, 137Cs, 239,240Pu

ZnS(Ag), GMRadiochemical +spectrometry

Iodine in site: 1off-site: 3

Weekly 131I Spectrometry

Rare gas in site: 1off site: 3

Continuously 85Kr GM

Humidity off site: 2 Weekly 3H LSCRain water in site: 1 Monthly 3H LSCFallout in site: 1 Monthly Gross β GMDrinking water in site: 1

off site: 3Quarterly Gross β, L3H GM, LSC

Leafy vegetable off site: 3 Quarterly 90Sr, 131I, 137Cs,239,240Pu

Radiochemical +spectrometry

Polished rice off site: 3 Annually 14C,90Sr

Benzene synthetic +LSC,Radiochemical +spectrometry

Milk off site: 3 Quarterly 90Sr, 131I Radiochemical +spectrometrySurface soil

Cultivated soil

in site: 2off site: 3off site: 4

Quarterly

Annually

90Sr, 137Cs, 239,240Pu

129I


NAARiver water off site: 4 Semi-annually Gross β, 3H GM, LSCRiverbed sediments off site: 4 Semi-annually Gross β GM

TLD: Thermoluminescent dosimeter.GM: Geiger-Müller counter.LSC: Liquid scintillation counter.NAA: Neutron activation analysis.

For the terrestrial environment, the air absorbedgamma-radiation dose rate and the cumulative dose weremeasured to estimate the external exposures originatedmainly from 85Kr. Air dust, drinking water andagricultural products were measured for estimating theinternal exposures from 3H, 14C, 90Sr, 131I, 137Cs and239,240Pu. 90Sr, 137Cs and 239,240Pu in surface soil andriverbed sediments were measured to observe the long-term accumulation. Because the maximum airconcentrations of radionuclides were estimated at about2 km southwest of the TRP in the safety assessment, themeasurement and sampling points were mainly locatedin a radius of 10 km in conjunction with the emergencymonitoring program.

For the marine environment, radionuclides in marineproducts such as fish, shellfish and seaweed weremeasured for estimating the internal exposures mainlyfrom 90Sr, 137Cs and 239,240Pu. Seawater and seabedsediments were measured to observe the long-termvariation and accumulation of 3H, 90Sr, 137Cs and239,240Pu. Gamma- and beta-radiation doses weremeasured to estimate the external exposures toradioactive contaminations on beach sand and fishingboats. The main observation area for marineenvironment was sited around the discharge port,offshore the TRP. This area was extended to 20 kmnorth and south to get “control” data.

External exposure dose rates from 85Kr weremeasured by automatic monitoring systems, called“monitoring station” and a “monitoring post”.


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Table 2. Marine environmental monitoring program around the TRPItem Sampling Measurement

Location Frequency Nuclide MethodSeawater Surrounding surface of

discharge port: 5Quarterly Gross β, 3H, GM, LSC,

Offshore Tokai Works: 2 Semi-annually 90Sr, 106Ru, 134Cs, 137Cs,144Ce, 239,240Pu


20 km North fromdischarge point: 1

Annually

Surrounding surface ofdischarge port: 5

Seabed sediments Offshore Tokai Works: 2 Semi-annually 90Sr, 106Ru, 134Cs, 137Cs,144Ce, 239,240Pu


20 km North fromdischarge point: 1

Beachwater 4 Semi-annually Gross β, 3H, GM, LSC,90Sr, 106Ru, 134Cs, 137Cs,144Ce, 239,240Pu


Beachsand 4 Quarterly Gamma and betaabsorbed dose rates

NaI(Tl), Plastic

Fish 2 Quarterly 90Sr, 106Ru, Radiochemical +spectrometryShellfish 2 Quarterly 134Cs, 137Cs,Seaweed 3 Quarterly 144Ce, 239,240PuFishing net 1 Quarterly Gamma and beta

absorbed dose ratesNaI(Tl), plastic

Fishing boat decksurface

1 Quarterly Gamma and betaabsorbed dose rates

NaI(Tl), plastic

Plastic: Plastic scintillator.

A monitoring station had a low-level and a high-level air absorbed dose rate monitors, a beta gasmonitor, and samplers for airborne dust, iodine, 3H and14C enclosed in a small housing. A monitoring post hada low-level and a high-level air absorbed dose ratemonitors. The low-level monitor was a NaI(Tl)scintillation monitor (Aloka ADR-122) with an energycompensation circuit, and the high-level monitor was apressurized ion chamber (Aloka RIC-328R). Eachmonitoring station or post had both monitors.

The measured data of air absorbed dose rates andbeta gas concentrations were automatically transmittedto the environmental monitoring facility in JNC TokaiWorks at every one-minute. Data compilation, storage,statistics and reporting were processed by computersystems.

The cumulative air absorbed dose was measured byCaSO4(Tm) type thermoluminescent dosimeters (TLD,Matsushita UD-200S). There were three TLDs at eachmonitoring point, and were exchanged by new onesevery three months. The total absorbed gamma-dose forthis period was measured at the monitoring facility.

Environmental samples were periodically collectedat the sampling locations. Airborne dust and iodinesamples were collected on a glass fiber filter (Advantec

HE-40T) and a charcoal filter (Advantec CHC-50)activated with EDTA, respectively. These filters wereexchanged with new ones after one week of sampling,and allowed to decay the short-lived radionuclides to alow level. Gross α and β radioactivities were measuredfor weekly filters, and quarterly composite filters wereinvestigated for radionuclides by gamma spectrometers.131I was determined from weekly charcoal filters.

Airborne 3H was absorbed in columns filled withmolecular sieves to separate the chemical form of HTOand HT. Tritiated water (HTO) in the air was absorbedin the first column, and then dried air was introducedinto the Pd catalyst column to oxidize the HT form of3H, which, namely HTO, was absorbed in the finalcolumn.3 These samples were recovered as water vaporby heating the molecular sieve columns at 400 °C. 3Hconcentrations in the samples were measured by liquidscintillation counters (Aloka LSC-LB3).

Airborne 14C in the chemical form of CO2 wasabsorbed in 3M NaOH solutions and made Na2CO3precipitate with NH4Cl, and then the precipitate wasconverted to C6H6 by a benzene synthesizer for liquidscintillation counting (Packard 2560 TR/XL, 2260XL).


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Fig. 2. Terrestrial monitoring locations around the TRP

Gamma-emitters such as 131I and 137Cs weremeasured by gamma-spectrometry with Ge detectors(MCA: EG&G MCA7700) after adequate pretreatmentof the samples. Samples of surface soil, riverbedsediments, seabed sediments and beach sands were driedin a low temperature oven and sieved to less than 2 mmdiameter with a mesh. Agricultural and marine productswere dried at 200 °C and burned to ash at 450 °C inelectrical furnaces.

To measure alpha and beta emitters such as 239,240Puand 90Sr, the nuclides were separated by radiochemicalprocesses.

For 239,240Pu, 236Pu or 242Pu was added into asample to compensate for a loss of plutonium by theanalysis flow. After leaching by HNO3, plutonium wasseparated by anion ion exchange and thenelectrodeposited on a steel disk. 239,240Pu is determinedby alpha spectrometry with Si detectors (MCA: EG&GMCA7700).

For 90Sr, samples were leached with HNO3, andstrontium and calcium were co-precipitated with oxalicacid and then transformed to carbonates. 90Y wasseparated by a milking method after waiting forradioactive equilibrium (about 2 weeks) and then 90Sr

was determined using a low background beta counter(Aloka LBC-453, Tennelec/Nucleus LB4110).

For measuring 14C in polished rice grain, the grainwas completely resolved in a pressurized combustionchamber filled with oxygen, in which CO2 wasproduced. CO2 was converted to C2H2 in a reaction ofmelted lithium with water, and then C6H6 wassynthesized by polymerization of C2H2. C6H6 wasmixed with a liquid scintillator and then 14C wasmeasured by a liquid scintillation spectrometer.

To investigate the long-term accumulation of 129I,soil samples were collected from agricultural fields at 1,2, 3, and 8 km southwest (SW) of the TRP. AnnuallySW is the most frequent wind direction in the area. Soilsamples were dried at low temperature. The samples ofthe 4 points were mixed into one sample for eachlocation, and then they were sieved to a particlediameter of less than 2 mm. Then, they were combustedat 1,000 °C in a quart glass column in which a mixed gasof oxygen and hydrogen continuously flowed. Iodinefrom the soil was completely transformed to theelemental form and then absorbed in a charcoal bed atthe end of the column. The elemental iodine wasrecovered and purified by solvent extraction and then


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packed into a quart glass ampoule. Because 129I emitslow energy beta particles, the neutron activation analysismethod was applied to measure very low-levelradioactivity of 129I in the environmental samples.About 80-minute 1014 n.cm–2.s–1 thermal neutron fluxwas enough to measure the present background level.129I was changed to 128I and 130I by nuclear reactionswith neutrons, and these nuclides were measurable by agamma-spectrometer.

Mathematical models using for estimating theconcentration of radionuclides

Figure 4 shows the exposure pathways considered inthe dose assessment. Mathematical models were used toevaluate the concentrations of radionuclides in thepathways, the intake of radionuclides by an individual,and the effective dose. Concentration of radionuclide inthe air was calculated by ORION-II computer codetogether with the observed meteorological data.4

The annual statistics of meteorological data observed atJNC Tokai Works were given as one of the input data, tocalculate the annual average concentration in the air.

The air concentration of pollutants continuouslydischarged from a point source is calculated by theGaussian plume model:

σ+−+

σ−−

σ−σπσ=χ

22

22

22

2)(exp

2)(exp

2exp2),,(

zz

y

HzHz

yUzy

Qzyx(1)

where χ(x,y,z) is the concentration of radionuclide at(x,y,z) point (Bq.m–3), Q is the discharge rate ofradionuclide (Bq.s–1), σy is the parameter of horizontaldiffusion width of the plume (m), σz is the parameter ofvertical diffusion width of the plume (m), U is the windspeed at discharge height (m.s–1), and H is the dischargeheight (m).

Fig. 3. Marine monitoring locations offshore the TRP


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Fig. 4. Exposure pathways to man in assessing effective dose due to radionuclides discharged from the TRP

Because one of sixteen separated direction has a fan-shaped sector area in the angle of 22.5 degree, theannual average fluctuation of wind direction in the samesector of the angle was considered to be uniform.Radioactive plumes may have passed either in the centerof the direction concerned or near the adjacentdirections. As the horizontal distribution ofconcentration has the Gaussian normal distribution, thedistribution may extend to the adjacent directions.Therefore, the annual average concentration at the pointof interest considered the contributions from the winddirection concerned and the adjacent directions.

Equation (1) is the basic equation to calculate theconcentration of stable and inert gas in the surface air.To apply the equation for radioactive materials, somemodifying factors should be included. Radiologicaldecay, deposition onto ground surface and theresuspension of deposited materials are the typicalexample of them. The resuspension of depositedradionuclides resulted in increased concentrations in theair. This phenomenon can be estimated by the ORION-IIcode. However, since detailed observations have not

been conducted in this area, resuspension was notconsidered in the assessment.

The concentrations of radionuclides in agriculturalproducts were calculated with adequate transfercoefficients. Almost constants used here were obtainedfrom the site-specific data and the published data of theUnited States Nuclear Regulatory Commission.5

For 129I, the fraction of deposited material retainedon vegetations and the deposition velocity on groundsurface were obtained by field measurements.6Concentrations of radionuclides in rice, leafy vegetableand pasture grass were calculated by Eq. (2). Theconcentration of radionuclide in vegetation wascalculated for both pathways of direct deposition ontovegetation and the root uptake of radioiodine depositedonto the ground:

( )

λ

λ−−+λλ−−χ= P

tBY

trvC bE

eEdII)exp(1()exp(1 (2)

where CI is the concentration of radionuclide invegetation (Bq.kg–1), χ–I is the annual average


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concentration of radionuclide in surface air (Bq.m–3), vdis the deposition velocity (m.s–1), r is the fraction ofdeposited material retained on vegetation, λE is theeffective removal rate constant (s–1), te is the time thatvegetation is exposed to radionuclides during thegrowing season (s), Y is the agricultural productivity byunit area (kg.m–2), B is the transfer factor of radio-nuclide from soil to vegetation (Bq.kg–1 [Bq.kg–1]–1),λ is the radiological decay constant (s–1), tb is the timeof long-term accumulation of radioiodine in soil (s), andP is the effective surface density of soil (kg.m–2).

The deposition velocity (vd) was investigated byfield measurements of iodine isotopes in the surroundingenvironment of the TRP. Values for total apparentdeposition, including both dry and wet depositions, wereestimated as 0.76±0.19 cm.s–1 and 0.50±0.18 cm.s–1,respectively, i.e., 0.73±0.19 cm.s–1 onto the cultivatedground surface for 129I discharged from the TRP, and0.69±0.58 cm.s–1 onto the pasture grass for 131I afterChernobyl nuclear accident in 1986.7 Theseinvestigations showed that a total deposition velocity of1 cm.s–1 onto ground surface and vegetations couldreasonably be set for iodine isotopes.

The value r for radioiodine was obtained by the fieldmeasurements of 129I discharged from the TRP.6 It wasestimated with both the measured concentrations of 129Iin polished rice grain, leafy vegetable and pasture grass,and the concentration in the air calculated by thediffusion model together with the discharge and themeteorological monitoring data. Because theconcentrations of 129I in vegetations were less than thedetection limit, the values for rice, leafy vegetables andpasture grass were estimated to be less than 0.01, 0.2and 0.3, respectively. ORION-II computer code usedthose equations and constants for calculating theconcentrations of radionuclides in the air andagricultural food products.

The concentration of radionuclide in seawater can beestimated by the diffusion equation like that for theatmospheric diffusion. Diffusion equation used forcalculation of concentration of radionuclide in seawater

was introduced by the field experiments offshore JNCTokai Works.8,9

The experimental equation is:10,11

α= x

YuuHY

qC 4erf (3)

where C is the concentration of radionuclide in seawater(Bq.m–3), q is the discharge rate of radionuclide(Bq.s–1), u is the current speed (m.s–1), 0.1, H is thevertical mixing layer (m), 4.6, Y is the horizontal widthof vertical mixing layer (m), 2, α is the experimentallyobtained constant, 0.1415, x is the distance from thedischarge point (m), and erf is the error function:

∫ −=y

tty0

2 d)exp(2)(erf πConstants in Eq. (3) were obtained from the

diffusion experiments offshore JNC Tokai Works.10,11The concentrations of radionuclides in fish, seaweed

and mollusca were calculated by bioaccumulationfactors and concentrations in the seawater where marineorganisms live. The bioaccumulation factors shown inTable 3 were adopted from the results of investigationsperformed in the Tokai coastal area for falloutradionuclides produced by atmospheric explosiontests.12,13 The value for plutonium was taken from theinvestigations done about discharged plutonium fromthe Sellafield reprocessing plant to the Irish sea.12,13

Dose assessmentThe external exposures from radioactive cloud were

calculated by three-dimensional integrations of pointkernels in the Gaussian plume. Because 85Kr ispractically only one airborne radionuclide dischargedfrom a reprocessing plant to be considered as externalexposure, the KR85G computer code was used for thecalculations.14

Table 3. Bioaccumulation factors (in Bq.g–1 per Bq.cm–3) of radionuclides used for estimation of public dose from ingestionof marine organisms

Element Fish Red seaweed Brown seaweed Shellfish Cephalopod CrustaceanHSr

Zr, NbRuI

CsCePu

13

5050303050

100

120

30020001000

10600

3000

120

1000500

200030

6003000

15

4030060

9200200

13050

200302090

400

12

5080

31030

200


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Equation (4) shows the basic equation for gamma-cloud dose calculation:

( )∫ ∫ ∫= ∞ ∞

∞−

∞ −0 0

2 ddd),,(χµπ4)µexp(

1 µ zyxzyxrBrr

aEKD (4)

where D is the air-kerma rate (mGy.h–1), K1 is theconversion factor from absorbed energy to air-kermarate (dis.m3.mGy [MeV.Bq.h]–1), 0.446, E is theeffective gamma-energy of 85Kr (MeV.dis–1), 2.21.10–3,µa is the linear absorption factor of gamma-ray in the air(m–1), 3.84.10–3, µ is the linear attenuation factor ofgamma-ray in the air (m–1), 1.11.10–2, r is the distancefrom the point (x,y,z) in radioactive cloud to the point ofreceptor (m), B(µr) is the build-up factor of gamma-rayin the air, and χ(x,y,z) is the concentration of 85Kr at thepoint (x,y,z) in the radioactive cloud (Bq.m–3).

The annual effective dose was calculated bysumming up the contributions from the wind directionconcerned and all other wind directions.

According to the ICRP 1990 recommendations, skindose has to be included in the effective dose with thetissue weighting factor of 0.01.1

As 85Kr is primarily a beta-emitting nuclide, the skindose was solely estimated in the environmentalassessment of the TRP for licensing. In the latestassessment in 2000, the skin dose was included in theeffective dose with the tissue weighting factor. Thefraction of effective dose by beta rays was about 17% ofthe total effective dose from 85Kr. The fraction waschanged year by year according to the variation of themeteorological condition. In 2001, the fraction wasabout 10% of total external effective dose from airborne85Kr.

External exposures from radionuclides dischargedinto the sea were calculated for beach sand, fishing netsand fishing boats. It was considered that those materialswere contaminated with radionuclides discharged intothe sea and then individuals of public or fisher personswere exposed to them.

Internal exposures were considered for inhalation ofradionuclides in the air, and oral intake of radionuclidesin agricultural and marine products. Estimated doseswere the 50 years committed effective dose for areference man after 1-year intake of radionuclides.

The inhalation of radionuclides via humanrespiratory tracts, can be calculated by:

INHINHINH DFMD χ= 25.365 (5)where DINH is the effective dose by inhalation(mSv.y–1), MINH is the breathing rate (m3.d–1), χ– is theaverage concentration of radionuclide in the surface air

(Bq.m–3), and DFINH is the effective dose factor forinhalation (mSv.Bq–1).

The oral intake (ingestion) of radionuclides viahuman digestive organs, can be calculated by:

INGFINGING DFCMFD 25.365= (6)where DING is the effective dose by ingestion (mSv.y–1),MFING is the daily food consumption (kg.d–1), CF is theconcentration of radionuclide in food (Bq.kg–1), andDFING is the effective dose factor for ingestion(mSv.Bq–1).

The effective dose conversion factors given in theICRP database were applied in the calculations.15

Results and discussion

The annual discharges from the TRP are shown inFigs 5 and 6. The maximum discharged fractions to thedischarge limits, set in the safety manual of the TRP,were 20%, 0.96%, 16% and 59% for 85Kr, 3H, 14C and129I in airborne effluent, respectively, and 2.6% and4.8% for 3H and Pu(α) in the liquid effluent,respectively. In the effluents monitoring program, othershort half-lived radionuclides such as 95Zr/95Nb,106Ru/106Rh, 131I, 134Cs and 144Ce/144Pr were included,but they were not measurable in the effluents becausethe short lived radionuclides decayed into negligiblelevel before reprocessing.

The behavior of 3H, 14C, 85Kr and 129I in theairborne effluent was investigated from themeasurement of the nuclides in the operation of theTRP, as follows:

For 3H, a part of 3H in the spent fuel was trapped aszirconium compound in the cladding material of anuclear fuel. Approximately 80% of the remainder wastransferred to the extraction–separation process and theother flows to the off-gas treatment. In the extraction–separation process, almost all of 3H dissolvent wastransferred to the high radioactive waste concentration,and only a part of 3H was directly sent to for acidrecovery. Most of the former 3H, however, was sent tothe acid recovery as tritiated water vapor (HTO) duringthe evaporation–concentration step. After the acidrecovery, some 3H in the acid was returned toreprocessing. The 3H in airborne effluent dischargedfrom the stacks of the TRP to the atmosphere wasestimated to be less than 1% of the total throughput,because the off-gas treatment process removed most ofthe 3H. Approximately 70–80% of 3H discharged fromthe main stack of the TRP was in the chemical form ofHTO.


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Fig. 5. Annual discharges of radionuclides in airborne effluents from the TRP

Fig. 6. Annual discharges of radionuclides in liquid effluents from the TRP

The amount of 3H discharged to the sea wasestimated to be about 20–40% of the total throughput.

For 14C, only a very small amount of 14C in spentfuels was released to shearing most of it was released todissolving. The chemical form of 14C in spent fuels wasestimated as free element and carbon oxides. These wereoxidized to CO2 by the dissolving process. Some part of14C was trapped by the caustic scrubbers using NaOHsolution installed at the dissolver off-gas and the vesseloff-gas treatment, and the residual 14C was discharged

to the atmosphere. The amount of 14C discharged fromthe main stack was 4.1–6.5 GBq for every ton ofreprocessed uranium fuel. 14C trapped by the causticscrubbers was transferred to the low active liquid wastevessel. The amount of 14C transferred was 5.4–9.6 GBqfor every ton of reprocessed uranium fuel. The lowactive liquid waste was concentrated by evaporators, andmost of the 14C in the liquid waste was transferred intoconcentrated solutions and not to the marine dischargeeffluents.


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At the Tokai Vitrification Demonstration Facility(TVF), 14C was discharged from sub-2 stack of the TRP.The amount was estimated as approximately 0.6 GBqfor every package of vitrified product.16 The throughputof 14C at the TRP was estimated to be 11.9–15.5 GBqfor every ton of reprocessed uranium fuel. The fractionof airborne 14C discharged was 34–45% of thethroughput.

85Kr was essentially always totally discharged fromthe spent fuel at the shearing and dissolving processes.

For 129I, almost all of 129I shifted into the gaseousphase during dissolution of spent fuels, and wasabsorbed by the acid and alkaline scrubbers during theoff-gas treatment. The scrubbers removed approximately99% of 129I in dissolver off-gas, and less than 0.2% of itwas further trapped by high efficiency particulate filters(HEPA) before discharge. In a series of measurementsfrom 1975 to 1977 at the Sellafield plant the chemicalcomponents of discharged 129I were reported as 21–97%inorganic, 2–54% organic and 0.04–14% elemental.17At the TRP, the ratio of inorganic to organic compoundsin the airborne effluent was estimated to be 2 to 3.18

In the environmental monitoring program, short-termincreases of air absorbed dose rate, rare gasconcentration in the air and 3H concentration in theseawater were observed as the effects of effluentdischarges from the normal operation of the TRP.

The most significant source of artificialradionuclides in the environment has been atmosphericnuclear explosions. In the late 1970s and early 1980s,the effects of Chinese atmospheric nuclear explosionswere clearly found at JNC Tokai Works. After theexplosion test in October 1980, the amount of falloutwas increased for the reason of rain-wash as theradioactive plume arrived. Various short-livedradionuclides including 131I were measured in the air,agricultural products, and human hairs. A lot of hotparticles including 137Cs and plutonium were found onthe ground and on the roof of buildings.

Domestic and foreign accidents discharged someradionuclides into the environment, and they weremeasured by the environmental monitoring program atJNC Tokai Works.

The accident at the Chernobyl nuclear power plant inthe former Soviet Union showed significant effects onthe environmental monitoring in 1986.7,19 The specialmonitoring at JNC Tokai Works was started on May 3,1986 and closed on June 23, 1986. In the period, variouskinds of radionuclides including short-livedradionuclides were detected in the surroundingenvironment of the TRP. In the air samples, 131I, 132I,134Cs and 137Cs were detected and the maximumconcentrations were 0.41 Bq.m–3, 0.041 Bq.m–3,0.022 Bq.m–3 and 0.056 Bq.m–3, respectively.19 In milksamples 131I, 134Cs and 137Cs were detected and the

maximum concentrations were 14 Bq.l–1, 1.2 Bq.l–1 and2.4 Bq.l–1, respectively.

The nuclear explosion tests and the Chernobylaccident influenced the environmental monitoringaround the TRP, but the sources of radionuclides werefar from the site. The following two cases were verydifferent from those foreign events.

In the fire and explosion accident at thebituminization demonstration facility of the TRP onMarch 11, 1997, radionuclides were released from the90 m high stack (sub-1 stack), and through the brokenwindows and doors to the air. The released radionuclidesand the amounts were estimated as 1–4 GBq of 137Cs,0.1–0.4 GBq of 134Cs and 0.001–0.002 GBq of Pu (α).20By the emergency environmental radiologicalmonitoring, it was found that some radionuclides such as134Cs, 137Cs, 238Pu and 239,240Pu were detected mainlyin the air dust and soil samples near the facility on thesite, but there were no significant environmental effectsfrom the accident. The maximum concentrations of134Cs, 137Cs, 238Pu and 239,240Pu in the airborne dustcollected in the site were 1.6 Bq.m–3, 16 Bq.m–3,5.1.10–3 Bq.m–3 and 1.9.10–3 Bq.m–3, respectively. Themaximum public dose of 0.02 mSv was estimated withthe amounts of the released radionuclides and themathematical model.

The Japanese first criticality accident was broken outat the nuclear fuel fabrication plant operated by JCOCo., Ltd. at about 6 km northwest of JNC Tokai Workson September 30, 1999. The accident occurred byunlawful handling of 20% enriched uranium in theprecipitation tank that was not criticality safe. Two ofthe three workers over exposed were killed by theaccident.

The residents in the radius of about 350 m wereevacuated to the community center at about 1 km southof the plant. Extensive radiation monitoring wasconducted under the emergency monitoring centeroperated by the Ibaraki local government. JNC TokaiWorks cooperated during the monitoring with themonitoring center. In the accident, the radiation sourcerelated to public exposures was the precipitation tank inwhich a chain reaction of enriched uranium occurred.Direct and scattered neutron and gamma-radiations wereemitted from the tank and noble gases and radioiodineelements were released to the environment through theventilation of the plant. Short-lived radionuclides suchas 24Na, 91Sr, 131I, 133I, 135I, 138Cs and 140Ba weredetected in air dusts, soil and leafy vegetables. Gammaexposure dose rates measured at 13 locations in and offJNC Tokai Works were temporarily increased by noblegases. The maximum air dose rate detected by JNC’smonitoring system was 1.6 µGy.h–1 as one-minuteaverage at ST-2 monitoring station that was locatedabout 2 km east-south-east of JCO plant.21 The airborne


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concentrations of 131I and 133I collected at ST-2 duringSeptember 30 and October 5 were 4.1.10–10 Bq.cm–3and 1.3.10–9 Bq.cm–3, respectively, as the averageconcentrations during the sampling period. Theindividual doses to the public were estimated as 0.01–21 mSv mainly given by direct and scattered neutronand gamma-radiations.22,23

Tables 4, 5 and 6 show the summary of variationranges of monitoring data in the recent 11 years between1992 and 2002, when the influences of atmosphericexplosion tests and the Chernobyl accident have beendecreased. The variation ranges were the same as theenvironmental radioactivity level observed at otherlocations of Japan.24,25 The concentrations of 129I in soilwith the annual and cumulative airborne discharges of129I are shown in Fig. 7. Airborne discharges have beencontrolled effectively since 1980s by the installation ofsilver-impregnated zeolite (AgX) filters in the off-gastreatment process and the adjustment of pH of thesolution to decrease the volatility of iodine. Theconcentrations of 129I in soil were different fromlocation to location. They gradually decreased in orderof 2 km southwest (SW), 3 km SW, 1 km SW and 8 kmSW of the TRP.

Despite some radiological fluctuations that havebeen observed in the environment as shown above, theenvironmental radiological monitoring had not shownany significant effects on the surrounding environmentdue to the operation of the TRP.

This assessment with the actual monitoring data wasalso supported by the estimated effective dosescalculated by mathematical models. The estimatedannual individual doses due to discharges of radioactiveeffluents from the TRP are summarized in Figs 8 and 9.Figure 8 shows the external effective dose, and Fig. 9the internal 50-year committed effective dose. Theinternal exposures from airborne effluents since 1992are larger than those before. This is because the effluentmonitoring of 14C was started in the fall of 1991, and thedoses were not included in the contribution of 14C untilthat year.

The results show that the annual effective dose wasaround 1 µSv for the hypothetical critical individualaround the TRP. This is only 0.1 percentile of the annualeffective dose limit of 1 mSv for the publicrecommended by the ICRP.1

Table 4. Ranges of variation of terrestrial environmental radiological monitoring data during the recent 11 years (1992 to 2002)Item Nuclide Range Number of data

Air absorved dose rate Gamma-ray 0.031 – 0.048 µGy.h–1 576Cumulative dose Gamma-ray 40 – 120 µGy.(3 months)–1 639

Gross α <0.02 – 0.095 mBq.m–3 903Gross β <0.7 – 0.83 mBq.m–3 90390Sr <0.01 mBq.m–3 301137Cs <0.007 mBq.m–3 301

Airborne dust

239,240Pu <0.0001 mBq.m–3 301Iodine 131I <0.2 mBq.m–3 527Rare gas 85Kr <7 kBq.m–3 528Humidity 3H <4 – 8.4 Bq.l–1 264Rain water 3H <4 – 7.0 Bq.l–1 132Fallout Gross β <4 – 65 Bq.m–2 132

Gross β <0.04 – 0.09 Bq.l–1 176Drinking water3H <4 Bq.l–1 17690Sr <0.04 – 0.34 Bq.kg–1 33131I <1 Bq.kg–1 132137Cs <0.08 Bq.kg–1 33

Leafy vegetables

239,240Pu <0.0002 Bq.kg–1 3314C 0.24 – 0.29 Bq.g–1 C 33Rice90Sr <0.04 Bq.kg–1 3390Sr <0.02 – 0.088 Bq.l–1 26Milk131I <0.2 Bq.l–1 10590Sr <0.08 – 13 Bq.kg–1 55137Cs 2.8 – 47 Bq.kg–1 55

Surface soil

Cultivated soil239,240Pu129I

0.052 – 0.91 Bq.kg–10.0027 – 0.023 Bq.kg–1

5544

Gross β <0.04 – 0.21 Bq.l–1 88River water3H <4 – 4.6 Bq.l–1 88

Riverbed sediments Gross β 440 – 720 Bq.kg–1 88


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Table 5. Ranges of variation of marine environmental radiological monitoring dataduring the recent 11 years (1992 to 2002)

Item Nuclide Range Number of dataGross β <0.04 Bq.l–1 993H <4 – 93 Bq.l–1 9990Sr <0.002 – 0.0033 Bq.l–1 22106Ru <0.02 Bq.l–1 22134Cs <0.008 Bq.l–1 22137Cs <0.004 – 0.0043 Bq.l–1 22144Ce <0.02 Bq.l–1 22239,240Pu <0.00002 Bq.l–1 22

Seawater

Seabed sediments 90Sr <0.08 – 0.13 Bq.kg–1 88106Ru <6 Bq.kg–1 88134Cs <1 Bq.kg–1 88137Cs <0.8 – 1.7 Bq.kg–1 88144Ce <6 Bq.kg–1 88239,240Pu 0.17 – 1.0 Bq.kg–1 88

Beach water Gross β <0.04 – 0.072 Bq.l–1 883H <4 – 11 Bq.l–1 8890Sr <0.002 – 0.0035 Bq.l–1 44106Ru <0.02 Bq.l–1 44134Cs <0.008 Bq.l–1 44137Cs <0.004 – 0.0047 Bq.l–1 44144Ce <0.02 Bq.l–1 44239,240Pu <0.00002 – 0.00012 Bq.l–1 44

Table 6. Ranges of variation of marine environmental radiological monitoring dataduring the recent 11 years (1992 to 2002)

Item Nuclide Range, Bq.kg–1 Number of data90Sr <0.02 88106Ru <0.8 88134Cs <0.2 88137Cs 0.059 – 0.21 88144Ce <0.8 88

Fish

239,240Pu <0.002 8890Sr <0.02 78106Ru <0.8 78134Cs <0.2 78137Cs <0.04 – 0.062 78144Ce <0.8 78

Shellfish

239,240Pu <0.002 – 0.0030 7890Sr <0.02 – 0.097 132106Ru <0.8 132134Cs <0.2 132137Cs <0.04 – 0.13 132144Ce <0.8 132

Seaweed

239,240Pu <0.002 – 0.0081 132

Conclusions

The radiological effects to the regional environmentdue to the operation of the TRP during about a quartercentury, were assessed with both actual radiationmonitoring data and mathematical model calculations.

In the environmental radiological monitoring,temporarily increases were detected for gamma air

absorbed dose rates due to 85Kr discharges and 3Hconcentrations in the seawater. These, however, are notsignificant effects on the environment and the public.The concentration levels of the most radionuclides in theregional environment around the TRP were the same asin other locations of Japan. The concentration levels of129I in the cultivated soil were too low to be measuredby standard radiochemical analysis.


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Fig. 7. Annual and cumulative discharges of 129I to the atmosphere and concentrations of 129I in cultivated soil

Fig. 8. Estimated effective dose due to external exposures to the public around the TRP

Fig. 9. Estimated committed effective dose due to internal exposures to the public around the TRP


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It means that this level was the background at thattime and was mainly due to the fallout of radionuclidesproduced by past atmospheric nuclear explosions.

The estimated annual effective dose from theradionuclides in the effluents was around 1 µSv, ofwhich about 90% of the dose was given by 85Kr and 14Cfor the external and the internal exposure pathways,respectively.

The regional environmental effects due to theoperation of the TRP were found insignificant accordingto the actual environmental monitoring data and the doseassessment by mathematical models.

References

1. ICRP, Publication 60, 1990.2. NSC (Nuclear Safety Commission of Japan): Guideline for

Environmental Radiological Monitoring, 1989, revised in 2000 (inJapanese).

3. K. SHINOHARA, Hoken Butsuri, 18 (1983) 231 (in Japanese).4. K. SHINOHARA, T. ASANO, O. NARITA, PNCT N8410 87 17

(1987) in Japanese.5. USNRC, Regulatory Guide 1.109, Revision 1, 1977.6. K. SHINOHARA, Donen Giho, 7 (1991) 118 (in Japanese).7. J. ISHIDA, N. MIYAGAWA, H. WATANABE, T. ASANO,

Y. KITAHARA, J. Environ. Radioact., 7 (1988) 17.8. JAERI, JAERI-5014, 1965 (in Japanese).9. JAERI, JAERI-5014, 1967 (in Japanese).

10. T. NOMURA, Y. KISHIMOTO, A. HIRAYAMA, S. FUKUDA,K. IWASAKI, Proc. Symp. on the Behaviour of Tritium in theEnvironment, International Atomic Energy Agency, 1979, p. 257.

11. K. SHINOHARA, T. ASANO, Health Phys., 62 (1992) 58.12. M. KURABAYASHI, S. FUKUDA, Y. KUROKAWA, Proc. 3 rd

Seminar of Marine Ecology, Nuclear Energy Agency, 1980, p.335.

13. N. HAYASHI, H. KATAGIRI, Y. MARUO, K. SHINOHARA, Proc. 3 rdIntern. Conf. on Nuclear Fuel Reprocessing and WasteManagement, Japan Atomic Industrial Forum, 1991, p. 247.

14. Y. KITAHARA, O. NARITA, T. ASANO, Y. KISHIMOTO, PNCT 84181-44, 1981 (in Japanese).

15. ICRP, The ICRP Database of Dose Coefficients, 1991.16. Y. NAGASATO, T. YAMAGUCHI, H. FUJITA, E. OMORI, JNC

TN8410 2001-021, 2001 (in Japanese).17. UNSCEAR, 1982 Report, 1982.18. E. OMORI, T. SUTO, T. SHIMIZU, N. SUGIYAMA, A. TAKAYA,

A. KOYAMA, H. NAKAMURA, A. MAKI, T. YAMANOUCHI, JNCTN8410 99-002, 1999 (in Japanese).

19. M. KINOSHITA, PNCT N8420 86-10, 1986 (in Japanese).20. M. NAKANO, H. WATANABE, T. SHIMIZU, N. MIYAGAWA,

S. MORITA, H. KATAGIRI, H. ISHIGURO, J. Radioanal. Nucl.Chem., 243 (2000) 319.

21. K. SHINOHARA et al., JNC TN8440 2001-004, 2001 (in Japanese).22. K. FUJIMOTO, Y. YAMAGUCHI, A. ENDO, Proc. 28 th NIRS

Seminar on Environmental Research, 2001, p. 186 (in Japanese).23. T. MOMOSE, N. TSUJIMURA, T. TASAKI, K. KANAI,

O. KURIHARA, N. HAYASHI, K. SHINOHARA, J. Radiation Res., 42(Suppl.) (2001) 95.

24. K. HASHIMOTO, S. HIROTA, Y. KANARI, Y. HIRAI, Proc. 8 thIntern. Conf. on Low-level Measurements of Actinides and Long-lived Radionuclides in Biological and Environmental Samples,2000, p. 29.

25. http://www.kankyo-hoshasen.go.jp/

environmental monitoring and public dose assessment around the tokai reprocessing plant

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