chapter 6: special safety systems module a: reliability … library/20044214.pdf · 2011. 9....

CANDU OverviewDr. George Bereznal page 6A-1

CHAPTER 6: SPECIAL SAFETY SYSTEMS

MODULE A: RELIABILITY CONCEPTS

~

Chapter 6: Speolal Safety SystemsModule A: Reliability Concepts

MODULE OBJECTIVES:

At the end of this module, you will be able to describe the following for a CANDU reactor:

1. define the four Special Safety Systems;

2. explain the Increasing levels of safety provided by the Safety Systems in case of process systemfailures;

3. explain the -significance of the eight main reliability principles and hO;N a two out of three logicimplements these principles.

:ANDU Overview Chapter 6: Special Safety Systems::.:.1/'• ..::G:.::.:eOtpe:::J&:;.:B::::e:.:re.::.zn::::8/~ .z:.p:::lage;t;;...;:6;,.:.A_.2=-- ,. Module A: Reliability Concepts

EmergencyCooling

1ST lEVEL OFSAFETY

(ACCIDENTPREVENTION)

2ND lEVEL OFSAFETY

(ACCIDENTMITIGATION)

3RO lEVEL OFSAFETY

(ACCIDENTACCOMMODATION)

---------

---------

Emergency Shutdown

EmergencyContainment

OPERATION WITHOUTFAILURE

(HIGH nUALlTY PROCESSSYSTEMS)

FAILSAFE(L1KELY FAILURES)

NO

------------------------ EFFECT •, ON

ANTICIPATED UNSAFE SOSl PUBLICPROCESS FAILURES ~

OTHER PROCESS~

OR ~SYSTEM ACTION SOS2(LESS L1KEI,Y FAILURES)

ACTION------------------____~_ISEVERE PROCESS .. 50S10RSOS2

~FAILURE -LOC ACTION CONTAIN· ...

(UNLIKELY FAILURES) -.f ~MENT

Eel,

--

NTRODUCTION

;peclal Safety Systems

• Mitigate the consequences of aserious process failure requiringreactor shutdown, decay heatremoval and/or retention ofreleased radioactivity.

• Do not perform any activefunctions in the normal operationof the plant: they are said to be'poised' to prevent unsafeconsequences of plant operationunder abnormal or accidentconditions.

• The four special safety systemsare:

=> shutdown system number 1

=> shutdown system number 2

=> emergency core cooling system

=> containment system.

• The reactor may not be operated without all of thespecial safety systems being available.

>ystems which provide services, such as electricallower, cooling water, and air to the special safetyiystems are referred to as safety support systems.

, - ' .. " ,..._~ .. "., ... 1 r- ... ,..:............ ,..i.......

~

;ANDU OverviewIr. George Bereznal page 6A·3

Chapter 6: Special Safely SystemsModule A: Reliability concepts

4E

4D

4F

+90Vcc

3E

3D

3F

This chain of the SOS

Clutch

4E

4D

4F

o Relay

:z: Relay Contact

-90Vcc

3F

3E

3D

48Vcc

10

2D

3D

-0

-0

In order to reduce the number of unnecessary firings, atwo out of three logic is used by each of the shutdownsystems.

Each shutdown parameter Is related to threemeasuring devices, and each of these devices isassociated with one of three electrical chains of theshutdown system.

When a reading passes Its setpoint, a relay logic acts to open the electric circuit.Is then said to be "opened". Trip setpoints may be fixed or variable.

Two such chains of an SOS must be opened for the firing of the SOS.

• Redundancy

• Independence

• Diversity

• Periodic Testing

• Fall Safe

• Operational Surveillance

• Preventive Maintenance

• Predictive Maintenance

•

•

•

•

~ELlABILITY PRINCIPLES

rwo OUT OF THREE LOGIC

INDU Overview~ George 8ereznel page 68·1


MODULE B: SHUTDOWN SYSTEM #1

Chapter 6: Special Safety SystemsModule 8: Shutdown System #1

MODULE OBJECTIVES:

At the end of this module, you will be able to describe the following features of a CANDU reactor:

1. The function, reactivity worth, insertion time, methods of insertion and testing of the shutdown rods;

2. The main types of trip parameters used for SDS1;

3. The role of the Reactor Regulating System in withdrawing the shutdown rods.

I4NDU Overview'. Georpe Seremal

~TRODUCTION

page 68-2

.,Chapter 6: Special Safety Systems

Module 8: Shutdown System #1

• Each CANDU reactor has two reactor shutdown systems, SDS1 and SDS2, completely independent ofeach other. They are also very different by design and by their intervention mode.

• Each of the shutdown systems must be able, by itself, to stop the neutron chain reaction during anyaccident condition.

• A further requirement Is that the safety analyses used to show this capacity must be performed withpart of the system impaired. For SDS1, the two most effective rods, on a total of 32, are assumed to stayout of core. For SDS2, the most effective injection line out of eight is assumed dead.

• Each shutdown system is environmentally qualified to the most severe conditions under which it isrequired to function.

• Each shutdown system meets an unavailability target of less than 1X10~.

• The two shutdown systems incorporate the principles of redundancy, diversity, testability andseparation throughout their design.

• The two shutdown systems are independent of the regulating and process systems.

:ANDU OvelVlewIf. GeOrge Bereznel page 6B - 3

Chapter 6: Special Safety SystemsModule B: Shutdown System #1

iHUTDOWN SYSTEM NUMBER 1

.._~.

III '11.111"'" _ZOi 1.t,.. III

,.-""

..

,~+--I--+-+-1f-It-Hf-+- 1'-1'-+-+---1i·1-++-t-t--iI-tt-iHI-+-+-++-t---t

·I-++-t-t--il-tl-HI-+-+-++-t---tf--t--,io;"rlh~ '71 """';-1

O~ ~~,(~B ~~ ~~~~• [] u' []

(I~ (0) (. err,~o~»)'at<:lj-+-1--l'1-+-+-1--+'...![¥-c ~ ;-"'f[]"-jl-t-+--+---i

( I ~•f--t-t-t--tc~"r";--[ 0 '[,!,J'c><:""o-t--t--t--i"1-+"'"aoj-t4lW;.L-H-';.rtrr~t+'iIi(llj:s-+--l"I-+-~-+-+--;d[J..---it-r±[]rlt-[;:I:Jrl-+-"i'''---11--1

o}--,--{ -{a

[] 0 0..1-+--:ablJ!J-I-f--IT!-'(!kT-*i-¥--i-Ir--:]~" (Xl 0 [J [J co C-L--'-l

"l-+--+- ( i ( ~

"f--t-t-t--i~-.=[]' 0 []"I--+-+~(I~""'(o~))-¥~( '"*' e--'T,'-,.,.l~o)""'-.!°","<--I--+---I

[ 0 []to t-+-~o~""',,--1,--o~~rl=-~(-"j.~~~'-O~~r-±~]~o:-t--l11 i '--1---1al-++-t-t--j-tt-jHI-+-+-++-t---t..1-++-t-t--i-tt-1HI-+-+-++-t-l..I-++-t-t-i-tt-HI-+-+-++-t-l

Iji

-10

•

2.0IA

-----1--..

sa REACT.MIY WORTH

1~ 1~ IA I~

11M!! (.J

...

32 Shutdown rods of cadmium and stainless steel

reactivity worth is -60 to -70 mk;

spring assisted gravity drop; fully inserted in 2 seconds.

.+-===----

II'",'"

••

•

-70

Shutdown Rods Insertion and Reactivity Worth.

-- , ,'. ,..._~ .• u •• _, r-_ ... :..."' ..... ..:......

~.

AfiDU Overviewr. Geo/pe Sereznal page 68 - 4

'llJW'Chapter 6: Special Safely Systems

Module S: Shutdown System #1

,0S1 TRIP PARAMETERS

• ensure reactor power level Is under CONTROL.

• ensure that ability to COOL the fuel Is maintained

Trip Parameter Trip Condition TypicalSetpoint

Neutron Power HIGH 120%FP

Rate Log Neutron Power HIGH 10%/sec

Heat Transport System Flow LOW 21 kg/sec(channel flow)

Heat Transport System HIGH 10.7 MPaPressure (ROH)Heat Transport System LOW 8.5 MPaPressure

Pressurizer Level LOW 2.5 m-

Steam Generator Level LOW 12 m

Steam Generator Feedline LOW 5.1 MPaPressure

Moderator Level HIGH 9.5 m

Moderator Level LOW 8.5 m

;ANDU Overview'r. George 8ereznal paga 68·5

Chapter 6: Special Safety SystemsModule 8: Shutdown System #1

SHUTDOWN ROD WITHDRAWAL AND DROP TEST

• Normal withdrawal is controlled by the Reactor Regulating System.

• The shutdown rods are withdrawn as soon as the trip signal has been cleared and the trip has beenreset by the operator.

• All shutdown rods are withdrawn simultaneously.

• Withdrawal of the shutdown rods is interrupted if:

=> control is switched to manual, or

=> the flux power error is excessive, or

=> the reactor Is tripped.

=> if the log-rate exceeds 7 percent per second.

• The computer monitors the withdrawal time and, if it is greater than normal, the 'shutdown rod stuck'signal is generated.

• An individual rod may be selected for manual control at any time for drop testing or drive.

• A partial drop test facility is provided in the clutch circuit to allow the operation of each shutdown rod tobe checked during reactor operation.

• Withdrawal of the rods by banks in the manual modo is possible when the automatic control is notavailable.

... __ • ,'I .. ~, ~_,..r... ,... ,..,,:......

\@:ANDU OverviewIr. George Bereznal page BC - 1


MODULE C: SHUTDOWN SYSTEM #2

Chapter 6: Special Safety SystemsModule C: Shutdown System #2

MODULE OBJECTIVES:


1. The function, reactivity worth and Insertion time of SDS2 liquid poison;

2. The main operating features of the liquid poison injection system;

3. The main types of trip parameters used for SDS2.

ANDU Overviewr. George Bereznal page IlC - 2


IJTRODUCTION

Shuto"Unitt

.. .' ..-. ~ " .

".lIlldown SYlltm no. 1

Slllddhtn 'pl,," flO. 2

DS2 uses a liquid polson injection system.

tecall the following key requirements for the Reactor Shutdown Systems:

• Each CANDU reactor has two emergency shutdown systems, SDS1 and SDS2, completely independentof each other. They are also very different by design and by their intervention mode.

• Each of the shutdown systems must be able, by Itself, to stop the neutron chain reaction during anyaccident condition.

• The two shutdown systems incorporate theprinciples of redundancy, diversity, testabilityand separation throughout their design.

o met these requirements and method ofhutdown that was as different as possible from thehutdown rods used In SDS1 is required.

""~ .. I-.' ...... ~.'.~---- • '.,', ._.__ ~"

~

ANDU Overviewr. GeO/Jl!l Semmsl page 6C - 3

Chapter 6: Special Safety SystemsModule C: Shutdown SYstem #2

"QUID POISON INJECTION SYSTEM

."

·'00

t'1Cr-------'--------...,------

, .. f-- --...,--------.:.---:.-----

-300

-3"

-300

'he method chosen incorporates the following features:

• liquid polson;

• horizontal orientation of both trip measuringdevices and of polson Injection assemblies;

• three Independent channels signal theopening of fast-acting valves which releasehigh pressure helium to inject gadoliniumpoison into the moderator.

-350 L----r---r----r----..---....----.l0,' '0 100

TRANSIENT 11MI!' II)'000 ooסס, ooסס0'

CANOU OvervfewDr. Ge0!P8 Bereznal page 6C-4


SHUTDOWN SYSTEM NUMBER 2

REACTMTY DECK

I+----"..

,.......-t:I<r-_._...;P"'AE:::8S:::UA;:::E8A::;:lAH::-..:=CE:::lINE:::..-----,

ORANANDFULMBMOM""""" TANI<IIlYALVESf«)RMALlYa.oSED)

F

SMt1'llNQPUMP

SAMPLJNQ RE'1'\IANLNEI 'TO POISONT-.tvALWSNOAMALLY Q.08E01

0lJ1Cl( OI'ENmVALVEll.

SAMPlECANISTER

HElJ\IIaupPl.YT_

high pressure helium supplies energy for rapid poison injection;

four quick opening valves In two successive pairs

valves are air-to-close,sprlng-to-open

eight polson tanks,

polyethylene floatingball to prevent backnowof poison and Injectionof helium Into thecalandrla

IIquid-to-liquid Interfaceat the ball Isolation valvethat Is normally open

four rows of eightinjection jets on eachnozzle

•

••

•

••

:ANDU OverviewIf. George Bereznal page 6C- 5

Chapter 6: Special Safety SystenisModule C: Shutdown System #2

>DS2 TRIP PARAMETERS

• ensure reactor power level Is under CONTROL

• ensure that ability to COOL the fuel Is maintained

• ensure CONTAINMENT Is maintained

Item Trip Parameter Detector

a. Neutron Power Vertical In-Core Detectors

b. Rate Log Neutron Power Ion Chambers

c. Heat transport system Flow Differential Pressure Transmitter

d. Heat transport system Pressure Pressure Transmitter.

e. Reactor building Pressure Differential Pressure Transmitter

f. Reactor building Pressure Differential Pressure Transmitter

g. Steam generator Level Differential Pressure Transmitter on each boiler

h. Steam generator Feedllne Pressure Pressure Transmitter on Individual Feedlines

I. Moderator Level Differential Pressure Transmitter

:ANDU Overviewlr. George BereU/al pag? 6D· 1

Chapter 6: Special Safety SystemsModule D: Emergency Core Coolinp System


MODULE D: EMERGENCY CORE COOLING SYSTEM

MODULE OBJECTIVES:


1. The functional requirements for Emergency Core Cooling;

2. The equipment and operation of the ECC systems during the injection phase;

3. The equipment and operation of the ECC systems during the recovery phase;

4. The operation of the process systems during a loss of coolant accident.

~:J~:'

CANDU OverviewDr. Ge0l'll!! BereU/al

"L.;:.>

page 60-2Chapter 6: Special Safety Systems

Module D: Emergency Core Coolll1tJ System

t

-----REACTOR •

INITW. PHASE OF ECIS INJECTION(One 01 _ ryatem, II applied to a parllculanllllon)

---'-·,------------1

""""'::1_........ ItQAIT~ I,OW

. f

~ I

-I--------------------j

j! tI

INTRODUCTION

The system Is required to maintain or re-establishCOOLING of the fuel and fuel channels for specifiedlo~s-of-coolantaccidents so as to limit the releaseof fission prodUCts from the fuel and maintain fuel:hannel integrity.

Emergency core cooling Is Initiated when the heattransport system pressure drops to aoredetermlned value and either the high reactorJulldlng pressure, or a sustained low reactor outlet1eader pressure conditioning signal Is activated.

!\fter reestablishing sufficient cooling of the fuel,:he system Is capable of providing sufficient:oollng flow for a period of four months to prevent'urther damage to the fuel. This Is accomplished by''eclrculatlng (recovering) the coolant mixturejJscharglng from the accident location, back to the1eat transport system.

l':CONTAINMENT RECOVERY SUMP

........_......_-_.~--_ .._--_...._.._--------------_.._-_.._----

CANDU Oll8f\llewDr, G!Of!l!! Ber8znal page 6D-3

Chapter 6: Special Safety SystemsModule D: Emergency Core Cooling System

DEMlNEfIAUZ!CWAT!R

AfACTOl1BUILDING

FlOOD LEVa

RESERVE WATER TANK

--.J'--,. WATER.- TANKS

TO SHIELD TO GROUP 2 TOCOOU\O FEEDWATEA MODERATOR

SYSTEM

.......,

....TANKS

DEMINEAAUZroWATER

SYSTEM DESCRIPTION

The emergency core cooling system suppliescoolant to the reactor headers In the event of aloss-of-coolant accident. In'espectlve of thebreak size or location, the emergency coolantIs directed to all reactor headers.

The system operation Is divided Into twostages: the injection stage and the recoverystage. The injection stage Is provided by twohigh pressure gas tanks located outside thereactor building and connected via a valvestation to the top of four water tanks locatedInside 'the reactor building. The water tankoutlets are jointed by a distribution headerFrom which two separate lines symmetricallyFeed all the reactor headers.

In the recovery stage, the recovery pumps:Iraw water from the fuelling machine vault~oor, and discharge It Into the reactor headers(Ia the emergency core cooling heat!xchangers. The recovery stage begins when:he emergency core cooling system water:anks are depleted. The water subsequently!scapes from the break In the heat transportsystem, falls to the floor and Is recirculated by:h~ recovery pumps. The recovery stage)rovldes a long term heat sink.

- -, ~ - '. . ..'--

~.

CANDU OverviewDr. George Beremal page 6D- 4

Chapter 6: Special Safety SystemsModule D: Emergen()y Core Cooling System

PROCESS SYSTEM OPERATIONS

Following a loss-of-coolant accident, the heat transport pressure drops at a rate dependent on the size of thebreak. The time from the loss-of-coolant accident until the heat transport pressure reaches the injectionpressure Is known as the blowdown period.

The main steam safety valves are opened on the loss-of-coolant signal, to provide a rapid cooldown of thesteam generators, commonly referred to as steam generator crash cooldown. This reduces the transfer ofheat from the secondary side to the primary side during the initial period of emergency core cooling injectionarid allows the steam generators to provide a long-term heat sink for 'small' breaks during steady stateemergency core cooling operation.

For scenarios involving a small loss-of-coolant accident and the loss of the emergency core cooling, a steameenerator crash cooldown depressurizes the heat transport system and reduces the stress on pressuretubes. ,During the full sequence of emergency core cooling operation, decay heat removal is by transfer of heat tothe steam generators or by discharge of fluid through the break. The latter mode predominates for the largebreaks; the former mode predominates for small breaks.

;ANDU Overview>r, George BereU/sl page 6E-1


MODULE E: CONTAINMENT SYSTEM

Chapter 6: Special Safety SystemsModule E: Containment System

MODULE OBJECTIVES:


1. ihe functional requirements for the Containment System;

2. The equipment and operation of the Containment System.

';;ANDU OVfJrvlew".. GfJ0fll!! BfJreznfJl page 1St:. 2

Chapter 6: Spe-:ial Safety SystemsModule t:: Containment System

'.

,"

.:

'"Call:lndria'assembly

__-Dousing sprayheader

Main primary---system pumps

----Boilers

Dousing watersupply

INTRODUCTION

The basic function of the containment system Isto form a continuous pressure-confining envelopeilbout the reactor core and the heat transportsystem In order to limit the release to the external~nvlronment of radioactive material resulting fromm accident.

"n accident which causes a release of radioactivenaterlal to containment mayor may not beilccompanled by a rise In containment pressure.

ro achieve this overall function, the containmentsystem Includes ,the., following related safetylunctlons:

I Isolation: to ensure closure of all openings inthe containment when an accident occurs.

Pressure/activity reduction: to control andassist In reducing the Internal pressure andthe Inventory of free radioactive materialreleased Into containment by an accident.

, Hydrogen control: to limit concentrations ofhydrogen/deuterium within containment afteran accident to prevent potential detonation.

• Monitoring: to monitor conditions withincontainment and the status of containmentequipment, before, during and after anaccident.

:ANDU Ollllrvlewr. George Semmel page 6E - 3

Chapter 6: Special Safety SystemsModule E: Containment System

'he containment structure also serves the following functions:

limits the release of radioactive materials from the reactor to the environment during normal operations,

provides external shielding against radiation sources within containment during normal operations andafter an accident,

protects reactor systems against external events such as tornados, floods, etc,

CONTAINMENr STRUCTURE

VENTILATIONFILTER 173120 FRlI

t:,

! ...,•

t•t

RII AIR COOLERS73110/17311

DOUSING SYSTiM.l3oI310183431_J

• ••t t

~I

, PP

,"

. _-=,",.:"~7'l:--m----Irt<=l:~~~~,---'t'---'i:-·- ,

•' ..

~:::n:'~~ l><O><I..~ SPENT FUEL

VENT AI RSUPl'LV_c:r9~Cj

chapter 6: special safety systems module a: reliability … library/20044214.pdf · 2011. 9....

Documents