edg auxiliary system (aaqib nazir)

8/18/2019 EDG Auxiliary System (Aaqib Nazir)

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NUCLEAR POWER PLANT

2014

EDG Auxiliary System

Aaqib NazirME-01

P I E A S


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ACKNOWLEDGEMENTS

All praises to The Allah Almighty who has created this world of knowledge for us. He is

The Gracious, The Merciful. He bestowed man with intellectual power and

understanding, and gave him spiritual insight, enabling him to discover his “Self” know

his Creator through His wonders, and conquer nature. Next to all His Messenger Hazrat

Muhammad (SAW ) Who is an eternal torch of guidance and knowledge for whole

mankind.

Many individuals have been supportive and instrumental in assisting me with this work,

and I owe them a debt of gratitude. I am deeply thankful to my respective teachers from

mechanical department especially respected Engr. Dr. Javed Hyder , whose continuous

guidance, feedback, advice and encouragements have been truly exceptional. I would

like to appreciate Pakistan Nuclear Regulatory Authority (PNRA) for their kind

cooperation in providing us the best faculty for the nuclear power plant systems

(N.P.P.S) course and their helping attitude inspired me greatly and helps me out. I would

also like to say thanks to all the staff from PNRA especially Dr. Ayub, Mr. Ahsan, Mr.

Moazzam, Mr. Bilal and also Mr. Waqas who always helped us and used to spend a lot

of time for sharing and discussing about the subject. Finally, it would not be justified if Idon’t mention the support of my session fellows. All of my friends have been very

encouraging and accommodating for me.


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Table of Contents1 System Description .................................................................................................................. 1

1.1 Component Boundaries ................................................................................................... 2

2 Diesel generator building ......................................................................................................... 4

2.1 Non-Safety Class .............................................................................................................. 5

3 Emergency Diesel Generator ................................................................................................... 5

3.1 Main Function .................................................................................................................. 6

3.2 Design Basis ...................................................................................................................... 6

3.3 Equipment Design ............................................................................................................ 7

3.4 Diesel Engine Efficiency ................................................................................................... 7

3.5 Disadvantage of Diesel Engine ......................................................................................... 9

3.6 Electrical Side of EDG ....................................................................................................... 94 Subsystem/ Auxiliary Subsystem of EDG ............................................................................... 10

4.1 EDG train ........................................................................................................................ 11

4.1.1 EDG Operating Characteristics ............................................................................... 11

4.2 EDG Train Boundaries .................................................................................................... 13

5 EDG Subsystem Description ................................................................................................... 14

5.1 Breaker ........................................................................................................................... 14

5.2 Air intake and Exhaust system ....................................................................................... 15

5.2.1 Design Basis ............................................................................................................ 15

5.2.2 System Description ................................................................................................ 15

5.2.3 General Description ............................................................................................... 15

5.2.4 Component Description ......................................................................................... 17

5.2.5 System Operation .................................................................................................. 17

5.2.6 Acceptance Criteria of Air intake and exhaust system .......................................... 18

5.2.7 Safety Evaluation ................................................................................................... 19

5.3 Air Starting System ......................................................................................................... 20

5.4 Fuel Oil System ............................................................................................................... 20

5.5 Instrumentation & Control ............................................................................................ 21

5.6 Lube Oil system .............................................................................................................. 21

5.7 COOLING WATER SYSTEM & WATER PREHEATING SYSTEM .......................................... 22

5.8 Generator Subsystem .................................................................................................... 23

5.9 Exhaust ........................................................................................................................... 23


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5.10 Diesel Subsystem ........................................................................................................... 24

6 Failure and Most Occurring Mode of EDG subsystem ........................................................... 24

6.1 Most Occuring Mode among EDG Subsystem ............................................................... 24

6.2 Most Failure Mode of EDG Subsystem .......................................................................... 25

6.3 Human Errors ................................................................................................................. 26


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TABLE OF FIGURES

Figure 1: Emergency Diesel Generator and subsystem ................................................................... 3

Figure 2: EDG Building Layout .......................................................................................................... 4

Figure 3: A typical generator installation supplying standby power [4] .......................................... 5

Figure 4: Diesel Engine Efficiency graph over gasoline Engine ........................................................ 8

Figure 5: Generalized EDG Subsystem Layout [5] ....................................................................... 11

Figure 6: Simplified EDG train schematic. ...................................................................................... 14

Figure 7: Events of EDG subsystem ................................................................................................ 24

Figure 8: Root cause distribution for complete CCF events .......................................................... 25


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Emergency Diesel Generator (EDG)

Auxiliary System

1 System Description

The EDGs are part of the class safety-related ac electrical power distribution system

providing reliable emergency power to electrical buses that supply the emergency core

cooling system (ECCS) and various other equipment necessary for safe shutdown of the

reactor plant. In general, each EDG configuration ensures that adequate electrical power

is available in a postulated loss-of-offsite power (LOSP), with, or without a concurrent

large break loss of coolant accident (LOCA). Gas turbine generators and hydroelectric

generators (used at some locations for emergency power) are not part of this study. High-

pressure core spray diesels are considered (for this study) to be a separate train of the

emergency ac power system. Diesel engines used for fire pumps and other non safety-

related backup generators are not included.

The EDGs are normally in standby, whether the plant is at power or shutdown. At least

one EDG is required by Technical Specifications to be aligned to provide emergency

power to safety related electrical buses in case of a LOSP to the plant. In some cases a

"swing" EDG is used to supply power to more than one power plant (but not

simultaneously). The result is that two power plants will have a total of only three EDGs:

one EDG dedicated to each specific power plant, and the third, a swing EDG, capable of

powering either plant. Electrical load shedding (intentional load removal) of the safety

bus and subsequent sequencing of required loads after closure of the EDG output breaker

is considered part of the EDG function.

The EDG system is automatically actuated by signals that sense either a loss of coolant

accident or a loss of, or degraded, electrical power to its safety bus. The control room

operator accomplishes manual initiation of the EDG system if necessary.


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diesel generators (namely water and air cooling) and experience-based recommendations

for approaching related new projects.

At the beginning of an additional diverse diesel generator installation project an extensive

external events analysis needs to be carried out to properly define the site-specific risks

(for example flooding, earthquake, tornado, shock wave, man-made hazards, extreme

ambient temperatures) [1]

Figure 1: Emergency Diesel Generator and subsystem


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2 Diesel generator building

The diesel generator building houses two identical slide-along diesel generators separated

by a three hour fire wall. These generators provide backup power for plant operation in

the event of disruption of normal power sources. The diesel generator building is

classified as non seismic and is designed as a structure subject to wind loads in

accordance with the Uniform Building Code. The building is not located adjacent to the

nuclear island and diesel generators supply only selected plant non-Safety-Related a.c.

loads. The building is a single storey steel framed structure with insulated metal siding.

The roof is composed of a metal deck supporting a concrete slab and serves as a

horizontal diaphragm to transmit lateral loads to sidewall bracing and thereby to the

foundation. The foundation consists of a reinforced concrete mat. [2]

Figure 2: EDG Building Layout


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2.1 Non-Safety Class

The diesel generator building is a non-safety related structure that houses the two

standby diesels engine powered generators and the power conversion cycle equipment and

auxiliaries. There is no safety-related equipment in the diesel generator building. The

diesel generator building is located on a separate foundation at a distance from the

nuclear island structures [3]

3 Emergency Diesel Generator

An Emergency Diesel Generator is a standby generator which may include

lighting, electric generators, fuel cells, uninterruptible power supplies and other

apparatus, to provide backup power resources in a crisis or when regular systems fail.

An emergency generator system is a very specific system with very specific equipment. It

consists of the generator, engine, exhaust system, engine electrical system, fuel system

and lubrication system.

Figure 3: A typical generator installation supplying standby power [4]


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3.1 Main Function

The emergency AC power system is installed only for emergency conditions; emergency

AC power system is an independent onsite medium-voltage power system to provide

adequate and reliable power for safety load and ensure the safe shutdown and accident

mitigation of the reactor, and prevent important equipment damage resulted from a loss

of offsite power

3.2 Design Basis

The emergency diesel generator set (genset) with its auxiliary systems shall have a good

starting and operating reliability as required. It is ensures by

Each genset should be installed in separated building

Two independent air starting systems which can start the genset independently

should be provided for each genset

The fuel storage system should be provided for each genset

The cooling water system should be provided for each genset.

In order to protect the diesel generator against mechanical damage from starting

and loading, provisions should be provided for cooling water and lubricating oil

heating and circulating during its standby condition.

During emergency condition, the genset can start automatically. The time from receiving

the starting signal to reaching the rated speed and voltage should be within l2s. Then the

load group will be loaded automatically according to a specified loading sequence. After

automatic loading sequence, some unimportant loads can be loaded manually by operatorin main control room according to the genset operating condition.


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3.3 Equipment Design

The genset shall be designed to withstand the following failures:

• Short circuit occurs on the three or two phases of the genset caused by external

fault for duration not less than 3 seconds.

• Operate at 115 percent of nominal speed for 5 seconds.

• Over voltage reach up to 1.4 times the nominal voltage at 50 Hz for 4 seconds.

3.4 Diesel Engine Efficiency

In Nuclear Power Plant, mostly Diesel Engine are preferred over Gasoline Engine

because of their efficiency and following reason

One positive aspect of the diesel engine is that they are thermally efficient.

The improved efficiency is caused by the relatively high compression ratios

The diesel engine is 54% thermally efficient, while gasoline engines are only

34%.

As a result of diesel engines thermally efficiency, they are able to achieve better

gas mileage because they produce greater horsepower output for fuel intake


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One main reason for the diesel engine’s excellent fuel economy is that it burns far

more air than fuel.

In a gasoline engine, it’s air intake is carefully restricted and controlled by the

carburetor for a 15:1 air to fuel ratio.

However, in the diesel engine, the air intake is unrestricted

The diesel engine compresses at a very high ratio of 14:1 to 25:1.

The higher the compression ratio, the more power is generated.

The main limiting factor to compression ratio is based on the knock limits of the

fuel.

Knock is the term used to describe the auto ignition that occurs when a fuel

ignites because the pressure in the cylinder is such that combustion occurs.

The knock limit of the fuel is determined by the point at which the engine begins

to shake.

The higher the knock limits, the higher the compression ratio, the more power is

generated.

The following graphs also show s the efficiency of the diesel engine over gasoline

engine.

Figure 4: Diesel Engine Efficiency graph over gasoline Engine


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3.5 Disadvantage of Diesel Engine

Diesel engine has following disadvantages over gasoline engine.

Components of diesel engines are usually heavier that those of gasoline engines

because of the additional structural strength needed to obtain the higher

compression ratio and power output.

They can emit large amounts of ozone-forming constituents and particulates.

Diesel engines are harder to start in cold weather conditions, because it is difficult

to get the temperature inside the cylinder up to the self-ignition temperature of the

diesel fuel

3.6 Electrical Side of EDG

Each diesel generator set has a continuous power capacity of 3400 kW ,short-time rating

of 3740 kW, power factor of 0.8 (lagged), rated voltage of 6.3 kV, three-phase. The

diesel generators are designed to reach rated speed and be ready to take loads within 12

seconds, to carry rated loads within 60 seconds after receipt of a starting signal to the

diesel engine, and to accept the emergency core cooling loads within the time stipulated

The requirement of voltage and frequency during loading of emergency diesel are:

Frequency should be more than 95% rated value (47.5Hz)

Load terminal voltage should be more than 75% rated value (4630V).

Frequency should be restored to within 2 percent (49Hz) of nominal, and voltage

should be restored to within 10 percent (5670V) of nominal within 60 percent of

each load-sequence time interval.

During the loading sequence, if largest single motor load isn't completely loaded

and reached up to its ratings, it can be reloaded continuously at the next loading

step.


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During recovery from transients caused by disconnection of the full load, the

speed of the diesel generator unit should not exceed the nominal speed plus 75

percent of the difference between nominal speed and the over-speed trip set point

Each diesel generator will be started automatically in any of the following

conditions

Safety injection signal

Under voltage on the 6 kV Class 1E buses (EMA, EMB).[LOOP]

Manual Starting Each diesel generator can be manually started either by a control switch

located on the main control board or by a control switch located on the diesel generator's

local control panel. A two position select switch (MCR/LOCAL), located on the control

panel in the main control room, is used to select the location control. Its position is

monitored by indicating lights in the main control room.

4 Subsystem/ Auxiliary Subsystem of EDG

This section contains a brief description of each of the subsystems that comprise the

emergency diesel generator. These descriptions are intended only to provide a general

overview of the most common EDG.A typical layout of a nuclear power plant application

includes the Emergency Diesel Genset with its main subsystems.

Breaker

Fuel Oil System

Air Starting System

Air intake and Exhaust System

cooling water system

Lubrication oil system

Instrumentation and control equipment

Ventilation system for Diesel Generator Building

Generator subsystem

Diesel Engine subsystem


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Figure 5: Generalized EDG Subsystem Layout [5]

4.1 EDG train

4.1.1 EDG Operating Charact erist ic s

The EDG train is part of the standby emergency onsite ac power system and is required to

be available as a reliable source of ac power in the event of a loss of normal ac power

during all plant modes (operating or shutdown). Normally, each plant has two safety-

related buses that power the electrical loads required for safe shutdown and emergency

conditions. These buses typically receive power from either the auxiliary or the startup

transformers, which are powered from the main generator or offsite power. In the event

of the loss of offsite power or the failure of the normal power to the individual safety-

related buses, an EDG train will provide a backup source of power to its associated

safety-related bus. The EDG train has sufficient capacity to power all the loads required

to safely shut the plant down or supply emergency core cooling system (ECCS) loads on


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a loss-of-coolant accident (LOCA). Plant-specific technical specifications identify the

requirements for the emergency ac power system operability under various plant

conditions.[11]

Instrumentation is provided in the control room to monitor EDG operation following an

automatic start signal. Control switches are also available to control EDG operation or

manually start the EDG if necessary. In addition, local manual controls are available in or

near the EDG room. Generally, any automatic start of the EDG train is considered an

emergency start regardless of whether the start was planned (i.e., surveillance test) or

unplanned (i.e., low-voltage condition).

An EDG train is required to automatically start upon indication of the following:

• A loss-of-coolant accident (safety injection signal)

•

A low-voltage condition on the safety-related bus.

A safety injection signal without a loss of offsite power will automatically start the EDG;

however, the EDG output breaker will not close. The EDG train will not supply power to

the safety-related bus for safety injection events unless a low-voltage condition exists.

The EDG will remain at rated speed and voltage with the output breaker open until

manually stopped. Should a LOCA occur during loss of offsite power, the bus is first

stripped of all loads (automatic load shedding), except for selected feeds for motor-

operated valves, and isolated from offsite power sources before the loading sequence

begins. After the bus is stripped of loads, the EDG output breaker automatically closes,

and the load sequencer automatically restarts selected equipment at a preset time interval

onto the affected safety-related bus.

A low-voltage condition on the safety-related bus requires automatic starting of the EDG

and closing of the output breaker to supply electrical power to designated equipment on

the affected bus. Should a loss of offsite power on any safety-related bus occur, the bus is

tripped of loads by a load-shedding scheme? Automatic loading of the safety-related bus

begins after the EDG has obtained rated speed and voltage and the EDG output breaker

has closed. During an under-voltage condition, the EDG train operates independently

without being in parallel with any other electrical power source. When normal power

again becomes available, the EDG train can then be paralleled with the grid, unloaded,

secured, and returned to standby condition.


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For most testing purposes, the EDG train is manually started, brought up to speed,

synchronized to the plant power system, and loaded. Normally, voltage is regulated

automatically. If offsite power is lost during parallel operation with the plant electrical

system, the EDG output breaker will open automatically via an under-frequency relay.

The under frequency relay protects the EDG from an over-load condition during parallel

operation. The under-frequency relay opens only the output breaker and is interlocked to

operate only in parallel operation. Once the output breaker has been opened by the under-

frequency relay, an undervoltage condition on the affected bus will exist, causing the

output breaker to reclose automatically. Operation of the EDG train from this point is

similar to the loss-of-offsite-power or under-voltage condition discussed earlier.

4.2 EDG Train Boundaries

The EDG train boundaries selected for this study are shown in Figure 6. These

boundaries are consistent with the boundaries identified in similar studies: NUREG-1032,

Evaluation of Station Blackout Accidents at Nuclear Power Plants and NUREG-2989.

The boundary of the EDG train includes the diesel engine, electrical generator, and

generator exciter, output breaker, load shedding and sequencing controls, EDG room

heating/ventilating subsystems (including combustion air), the exhaust path, lubricating

oil (with the device that physically controls the cooling medium, i.e., the nearest

isolation/control valve to the EDG boundary that is actuated on a start signal), fuel oil

subsystem (including all storage tanks permanently connected to the engine supply), and

the starting compressed air subsystem. All pumps, valves, valve operators, the power

supply breakers for the powered items, and associated piping for the above support

subsystems are inside the boundary of the EDG train.


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Figure 6: Simplified EDG train schematic.

5 EDG Subsystem Description

5.1 Breaker

The breaker subsystem includes the main EDG output breaker as well as the loading and

sequencing circuitry. The automatic load shedding and sequencing controls the order and


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timing of emergency loads that are loaded onto the safety-related bus. The purpose of this

equipment is to prevent the instantaneous full loading (ECCS loads during a LOCA vent)

the engine when the output breaker is closed.

5.2 Air intake and Exhaust system

The diesel generator air intake and exhaust system (DGAIES) provides the diesel engine

with combustion air from the outside. The combustion air passes through a filter, silencer,

and heater before being compressed by a turbocharger and cooled by the coolant system

before entering the individual cylinders for combustion.

The exhaust gas system collects the exhaust gas from the individual cylinders and

conveys them via the engine-mounted turbocharger, emissions equipment, and an exhaust

gas silencer to the outside [8]

5.2.1 Design B asis

The design of the system and EPGB establishes that the arrangement and location of the

combustion air intake and exhaust gas discharge are such that dilution and contamination

of the intake air will not prevent operation of the EDG at rated power output or cause

engine shutdown as a consequence of any metrological or accident condition. Each EDG

set has a separate, independent diesel engine combustion air and exhaust gas system

5.2.2 Sys tem Descr ip t ion

The diesel engine combustion air system provides the necessary combustion air for the

diesel engine, and the exhaust gas system provides a path for exhaust products of

combustion from the EDGs to the environment under all operating conditions

5.2.3 General Desc rip t ion

The combustion air for the diesel engine is taken directly from outside the EPGB via an

air duct located on the upper floor level (i.e., elevation +51 ft, 6 in) of the building inside


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the missile protection area. The air passes through a filter, inlet damper, silencer and

heater before entering the diesel engine turbocharger.

The turbocharger is operated by the kinetic energy of the exhaust gas and compresses the

combustion air, which then passes through an intercooler before entering the individual

cylinders. Compressed combustion air is supplied to the ejector of the crankcase

ventilation system. The air flow through the ejector creates a vacuum that removes

combustible vapors from the engine crankcase..

The intercooler is a heat exchanger, supplied with DGCWS to cool the intake air that has

been heated by compression. The cooled compressed air forces more air into each

cylinder during the intake portion of the combustion cycle, increasing the horsepower of

the engine. The compressed air is required for the EDG to meet its rated output. The

exhaust gas system, which consists of pipes, emission control equipment, and an exhaust

gas silencer, is insulated to reduce radiated heat in the EPGB to an acceptable level.

The layout of the main components (i.e., piping, filters, and valves) provides the space

required to permit inspection, cleaning, maintenance, and repair of the system

After Cooler


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5.2.4 Component Descr ip t ion

The system contains the following components:• Intake and exhaust silencers to attenuate the sound levels both in the EPGB and

outside the building to meet site requirements.

• Filter(s) to separate dirt from the injection stream remove dust and small particles

from the combustion air supply to the turbochargers.

• Pipes and ducting to route the air into the engine to minimize pressure drop, and

piping to route exhaust from the engine to meet backpressure specifications of the

engine manufacturer.

• Exhaust emission equipment to control exhaust emissions to meet federal, state,

and local emissions requirements.

• Sensor(s) to monitor exhaust gas temperature, and filter differential pressure to

alert the operators of abnormal conditions which may warrant operator action.

5.2.5 System Operation

The DGAIES supports the EDG and as such normal operation of the system is required

any time the EDG is running. During normal diesel engine operation, air flows from

outside the EPGB into the air duct and then through the air intake filter for particulate

removal and a silencer for noise reductions. The power of the diesel engine is raised by

compression of the combustion air in the engine-mounted turbocharger before the air

enters the cylinders. The exhaust gas heat is used to operate the turbocharger. The

exhaust gas flow is directed through the exhaust gas emissions equipment and silencer for

noise attenuation and then discharged to the outside.

5.2.5.1 Normal Operation

When the plant is operating under normal conditions, the EDGs are maintained in

standby. The air intake and exhaust system is maintained ready to support diesel

operation.


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5.2.5.2 Abnormal Operation

The combustion air and exhaust air systems are monitored and an alarm is sounded in the

MCR to alert the operator when a degraded condition exists. The intake filters are

monitored for differential pressure and an alarm sounds when a condition exists that

could affect the operability of the engine it supplies. The filter elements are replaceable

and in extreme conditions they could be replaced online. The temperature of the engine

exhaust gas is monitored to verify that the engine is operating as designed. An alarm is

sounded if the exhaust temperature exceeds established parameters which could damage

internal components of the engine or prevent the engine from meeting its design power

requirements. Heat generated by the engine combustion is maintained in a defined range

to allow the engine, turbocharger, and emissions equipment to function as designed.The exhaust system is equipped with a bypass valve and a bypass stack which provides

a safety-related exhaust path in the event that a system failure downstream restricts the

exhaust flow.

5.2.6 A cceptanc e Criter ia of Air intake and exh aust sy stem

A. Each diesel engine has an independent combustion air intake and exhaust system.

B.

The components are designed, fabricated, erected, and tested to acceptable quality

standards.

C. The system has boundary divisions between safety-related and nonsafety-related

sections.

D. Failures of any non-seismic Category 1 structure, system, or component (SSC) (or

failures of other non-seismic components or systems) will not affect the safety

functions of the system adversely.

E. Sections of the system important to safety are housed in or on a seismic Category

I structure.

F. The consequences of a single, active failure in an engine combustion air intake or

exhaust system will not lead to the loss of function of more than one diesel

generator.


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G. Instrumentation and control features permit operational testing of the system and

assure that normal protective interlocks do not preclude engine operation during

emergency conditions.

H. Sufficient space permits inspection, cleaning, maintenance, and repair of the

system.

5.2.7 Safety Evaluation

1. The safety-related portion of the combustion air system is located inside the

EPGB and meets the same safety objectives as the diesel engine itself. This

building is designed to withstand the effects of earthquakes, tornadoes,

hurricanes, floods, external missiles, and other natural phenomena. Sections 3.3,

3.4, 3.5, 3.7(B), and 3.8 provide the bases for the adequacy of the structural

design of these buildings.

2. The safety-related portion of the DGAIES is designed to remain functional after

an SSE. Sections 3.7(B).2 and 3.9(B provide the design loading conditions that

were considered. There are no high- or moderate-pressure lines in the EPGB

whose failure can affect the function of more than one DGAIES. Sections 3.5, 3.6

and 9.5.1 provide the hazards analyses to establish that a safe shutdown, as

outlined in Section 7.4, can be achieved and maintained.

3. The DGAIES for each diesel engine is independent of any other diesel engine’s

DGAIES. This precludes the sharing of any safety-related systems and

components that could prevent those systems or components from performing

required safety functions.

4. The four-division design of the EDG air system provides complete redundancy;

therefore no single failure compromises the EDG system safety functions. Vital power can be supplied from either onsite or offsite power systems, as described

in This meets the recommendation of NUREG/CR-0660 [7]

5. All the power supplies and control functions necessary for safe function of the air

handling system are Class IE


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5.3 Air Starting System

The starting air subsystem consists of those components required to start the EDG.

Typically, this system uses compressed air. The air start system provides compressed air

to the engine through a system of valves, relief valves, compressed gas cylinders, air

motor, and a distribution.

The diesel engine in CNPP uses compressed air for startup. There are two independent

starting air systems (for each Diesel Generator set) which provide the compressed air for

engine starting.

5.4 Fuel Oil System

The Fuel System ensures the supply of fuel from he fuel storage tank through the service

tank into the diesel engine. The fuel oil subsystem provides fuel oil from large external

storage tanks, having a capacity for several days of system operation, to a smaller day

tank for each engine. The day tank typically has capacity to operate the engine for 4 to 6

hours. Day tank fuel is supplied to the cylinder injectors, which inject the fuel to each

individual cylinder for combustion. Each Diesel Generator train has two Fuel Oil Storage

Tanks. The capacity of these tanks ensures that Diesel Generator can operate reliably for

14 days at rated power.

Air

compressor

two sta e


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During operation of Diesel Generator two fuel oil transfer pumps (back up of each other

continuously supply fuel oil to daily fuel tank. The capacity of daily oil tank ensures that

Diesel Generator can operate for 60 minutes at 1.1 times the rated power.

The diesel fuel oil system is an ESF system. It supplies diesel fuel for the auxiliary

feedwater pump diesel as well as the two site emergency diesel generators. Two

independent trains of fuel oil supply are provided. Each consists of an underground

storage tank, a transfer pump, and transfer piping. Each independent source of fuel

supplies the auxiliary feedwater pump day tank.

The day tank has sufficient capacity (500 gallons) to allow diesel operation at design

capacity (960 gpm at 3400 ft of head) for 10 hours. The minimum allowed level in the

AFW pump diesel fuel oil day tank per Technical Specifications is 450 gallons (69%) to

fulfill the operability requirements for train B of AFW. Each storage tank has sufficient

capacity to

5.5 Instrumentation & Control

The instrumentation and control I&C) subsystem components function to start, stop, and

provide operational control and protective trips for the EDG. Controls for the EDGs are a

mix of pneumatic and electrical devices, depending on the manufacturer. These function

to control the voltage and speed of the EDG. Various safety trips for the engine and

generator exist to protect the EDG. During the emergency start mode of operation, some

of these protective trips associated with the EDG engine are bypassed.

5.6 Lube Oil system

The lube oil circuit, featured with a level monitoring, is supplying the engine with

lubricating oil and dissipating heat into a cooling circuit.


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Lube oil system for the engine is a wet-sump forced feed system. The system can be

divided into following sub-systems:

Oil Conditioning Sub-System

Running Gear Oil Sub-System

Valve Gear Sub-System

Piston Cooling Oil Sub-System

Valve Seat Lubricating Sub-System

Pre Lubricating Oil Sub-System

5.7 COOLING WATER SYSTEM & WATER

PREHEATING SYSTEM

The cooling subsystem is a closed-loop water system that is integral to the engine and

generator, and has an external-cooling medium, typically, the plant emergency service

water. The pumps, heat exchangers, and valves are part of this system. The cooling water

jacket is part of the Engine subsystem.


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The diesel engine is cooled by two independent cooling circuits: the engine coolant

system (high temp.) and the charge air coolant system (low temp.). The heat for both

circuits is dissipated via external electrical fan cooling units, tube bundle heat exchangers

or plate heat exchangers. The coolant pump is engine driven.

The cooling water system is designed for 1000 hours continuous operation at rated load,

and 2 hour operation within 24 hours at 10% overload above rated load

5.8 Generator Subsystem

The generator subsystem consists of the generator casing, rotor, windings, and exciter.

These components all function to deliver electrical power to the output breaker.

5.9 Exhaust

The exhaust subsystem consists of the piping and valves installed to direct the engine

exhaust out of the building.

Air coolers, lube oil coolers;

fuel cooler etc

Circuit 1

Circuit 2


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5.10 Diesel Subsystem

The engine sub-system is the physical engine block and piece-parts internal to it. These

parts include pistons, crankshafts, turbochargers, cooling water jackets, and the governor.

The engine governor maintains correct engine speed by metering the fuel oil to each

cylinder injector

6 Failure and Most Occurring Mode of EDG

subsystem

6.1 Most Occuring Mode among EDG Subsystem Now we will see by graph which EDG subsystem is mostly used when EDG is under

operational. Figure 7 shows the distribution of the CCF events by EDG sub-system. The

highest number of events occurred in the instrumentation and control sub-system (41

events or 30 percent). The cooling, engine, fuel oil, and generator sub-systems are also

significant contributors. Together, these five subsystems comprise over 80 percent of the

EDG CCF events. The battery, exhaust, and lubricating oil subsystems are minor

contributors [9]

Figure 7: Events of EDG subsystem


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6.2 Most Failure Mode of EDG Subsystem

Now we will see which EDG subsystem is mostly fail. Fgure 6 how the distributions of

CCF events for subsystems for all events and complete CCF events by failure mode

Figure 8: Root cause distribution for complete CCF events

Cooling, engine, and fuel oil are most likely to result in fail-to-run. I&C, output breaker,

and starting air are most likely to result in fail-to-start. This does not shift significantly

between the set of all CCF events and the set of complete CCF events. Cooling and

engine become much less significant and I&C and fuel oil become much more

significant. The I&C contribution is consistent with the nature of that system since it

controls the EDG during operation and contains the shutdown controls.


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The fuel oil subsystem shifts from mostly fail-to-run to all fail-to-start between the all

CCF case and the complete CCF case. This is primarily due to most of the fuel oil fail-to-

run events involving minor leaks.

6.3 Human Errors

This category is worth mentioning. The instrumentation and control subsystem is

especially vulnerable to CCF from the human factor. Again, this is due to the complexity

and the function of instrumentation and control. Procedures, maintenance, and operations

all contribute to this root cause. The human error root cause category increases in

importance between all events and the set of complete CCF events. They also exhibit a

shift from an even number of fail-to-start and fail to-run events to more fail-to-start

events. The human errors contributing to this phenomenon include mis-positioned valves,

inadvertent switch operation, and a design modification error[10]


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References

[1] http://www.neimagazine.com/features/featurecooling-options-for-emergency-backup-

diesel-generators-4159521/

[2] http://www.onr.org.uk/new-reactors/reports/step3-ap1000-civil-engineering-externa-

hazards-assessment.pdf

[3] http://pbadupws.nrc.gov/docs/ML1117/ML11171A319.pdf

[4]http://www.aspenational.org/userfiles/file/Technical%20Papers/2011/ET

011February-TechPaper.pdf

[5]

http://www.mtuonsiteenergy.com/index.php?id=4517&L=0&tx_mcgbsecuredownload_

pi1%5Bfile%5D=media-all-site/pdf/en/brochure/3061871_OE_Brochure_NPP_2_14_lay_ES.pdf&tx_mcgbsecuredo

wnload_pi1%5BfullPath%5D=/fileadmin/fm-dam/mtu_onsite_energy/media-all-

site/pdf/en/brochure/3061871_OE_Brochure_NPP_2_14_lay_ES.pdf

[6] http://pbadupws.nrc.gov/docs/ML0705/ML070550033.pdf

[7] NUREG/CR-0660, “Enhancement of Onsite Emergency Diesel Generator

Reliability,” University of Dayton Research Institute for the U.S. NRC; UDR -TR-79-07;

February 1979.

[8] http://pbadupws.nrc.gov/docs/ML1307/ML13073A704.pdf

[9] http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6819/cr6819v1.pdf

[10] http://www.oecd-nea.org/nsd/docs/2000/csni-r2000-20.pdf

[11] http://nrcoe.inel.gov/resultsdb/publicdocs/SystemStudies/edg-system-description.pdf

edg auxiliary system (aaqib nazir)

Documents