제제1717회원자력안전기술정보회의회원자력안전기술정보회의제제1717회원자력안전기술정보회의회원자력안전기술정보회의

신규원전신규원전 중대사고중대사고 대처설계대처설계

한국전력기술㈜한국전력기술㈜한국전력기술㈜한국전력기술㈜

원자력기술그룹원자력기술그룹 문문 영영 태태

ContentsContents

I. SA Design Features in APR1400

II. SA Design Features in EU-APR1400

III. SA Design Features in AP1000

IV. SA Design Features in US-APWR

V. SA Design Features in US-EPR

VI. Comparison of SA Design Features

1

I. SA Design Features in APR1400I. SA Design Features in APR1400

APR1400 Severe Accident Mitigation Featuresg

Containment Design

H d Miti ti S t (HMS)Hydrogen Mitigation System (HMS)

Safety Depressurization and Vent System (SDVS)

Cavity Flooding System (CFS)

Reactor Cavity Structure Designy g

Emergency Containment Spray Backup System (ECSBS)

2

Containment DesignContainment Design

Large dry pre-stressed li d i l tcylindrical concrete

containment with a steel liner plateplate

Reliable leak-tight barrier forReliable, leak tight barrier for approximately 24 hours following the onset of core gdamage under the more likely severe accident challenges by

i th t t i tensuring that containment stresses do not exceed FLC

3

Hydrogen Mitigation System (HMS)Hydrogen Mitigation System (HMS)

Limits hydrogen concentration in containment, generated from a 100% fuel clad-coolant reaction to less than 10 %100% fuel clad-coolant reaction, to less than 10 %PARs (Passive Autocatalytic Recombiners) and igniters

PARs : Distributed throughout the containment and control the hydrogen concentrationIgniters : Installed near the hydrogen discharge locations and control the possible rapid hydrogen releasep p y g

Igniter Igniter

4

PAR PAR

Safety Depressurization and Vent System (SDVS)Safety Depressurization and Vent System (SDVS)

Means to rapidly depressurize the primary system to 250 psia beforeprimary system to 250 psia before reactor vessel breach to prevent DCH following a severe accidentgMeans to depressurize RCS for Feed & Bleed operation following a TLOFW (T t l L Of F d W t )TLOFW (Total Loss Of Feed Water)Elimination of flow of hydrogen into IRWST through the manuallyIRWST through the manually opening of POSRVs and 3-way valvesFour POSRVs, twelve spargers and two 3-way motor operated valves

POSRVPOSRV 33--Way ValveWay Valve

5

Cavity Flooding System (CFS)Cavity Flooding System (CFS)

CFS is installed to minimize the corium-concrete attack and the generation of combustible gases (hydrogen & carbon monoxide)generation of combustible gases (hydrogen & carbon monoxide)CFS will assist with scrubbing fission products released from the core debris and molten corium-concrete interactionCFS consists of the HVT(Holdup Volume Tank), four MOVs and associated pipes

6

Reactor Cavity Structure DesignReactor Cavity Structure Design

Reactor cavity structure design minimizes challenges posed by DCH, MCCI and FCI ,Robust reinforced reactor cavity structure with large cavity volumeConvoluted flow path and core debris chamber room to decrease th t f j t d d b i th t h ththe amount of ejected core debris that may reach the upper containmentSufficient cavity floor area for corium debris spreading and coolingy p g gMinimum reinforced concrete thickness of 3 feet on the top of the containment embedded steel liner

7

Emergency Containment Spray Backup System (ECSBS)Emergency Containment Spray Backup System (ECSBS)

Alternate means of providing a containment spray in the event of a beyond design basis accident in which both CS and SC pumps, and/or the IRWST are unavailableand/or the IRWST are unavailablePiping connection to the dedicated ECSBS header line with 50 spray nozzlesAn effective means to prevent a catastrophic failure of the containment during severe accidentMultiple external water sources (reactor makeup water tankMultiple external water sources (reactor makeup water tank, demineralized water storage tank, fresh water tank, and raw water tank)

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II. SA Design Features in EU-APR1400II. SA Design Features in EU-APR1400

ERDS :ERDS : Emergency Reactor Depressurization System

SACSS

Depressurization System

HMS : HMS : Hydrogen Mitigation System

HMS

System

PECS : PECS : Passive Ex-vessel corium retaining and Coolingcorium retaining and Cooling System

SACSS :SACSS : Severe Accident

ERDS CFVS

SACSS :SACSS : Severe Accident Containment Spray System

CFVS :CFVS : Containment FilteredCFVS :CFVS : Containment Filtered Vent System

9

9PECS

SAM Strategy ConceptSAM Strategy Concept

The general design requirements for SAMS have characteristics as follows:characteristics as follows:

Safety Class 3Dedicated for severe accidentN+1 failure criteria

Dedicated SAM System and Actions would be implemented according to the SAM strategyimplemented, according to the SAM strategy

Recovery a steady state from a beyond DBAEntry condition of SA is defined by CET of 648.9 oCy yPrevention of High Pressure Melt Ejection and Direct Containment Heating by the ERDS & the convoluted path of reactor cavityreactor cavityHydrogen control by PARsPrevention of MCCI in the reactor cavity by the PECSK i th i t it f t i t b th SACSS & CFVSKeeping the integrity of containment by the SACSS & CFVS

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Emergency Reactor Depressurization System (ERDS)Emergency Reactor Depressurization System (ERDS)

RCS depressurization performed as the 1st step in SAM strategyas the 1st step in SAM strategyPurpose

To prevent high pressure meltTo prevent high pressure melt ejectionTo prevent steam generator tube

trupture

Two vent lines, common drain line to RDT rupture disk to SGline to RDT, rupture disk to SG compartmentIsolation and bleed valve inIsolation and bleed valve in series per pathEach line has 100% capacity for p yredundancy

11

Hydrogen Mitigation System (HMS)Hydrogen Mitigation System (HMS)

HMS consistes of Passive Autocatalytic Recombiners (PAR)PurposePurpose

To prevent the occurrence of Flame AccelerationTo prevent the occurrence of Deflagration-to Detonation TransitionTo prevent hydrogen explosion by keep the indexes of FA & DDT less than one over the containment

Description Equipment Tag No. Size Safety

ClassSeismic

Category

HR01A HR18A L SC 3 S1

PAR

HR01A ~ HR18A L SC-3 S1

HR01B ~ HR24B M SC-3 S1

HR01C ~ HR04C S SC-3 S1

Install in both containment and the IRWSTInside containment : 18 Larger PARs, 20 Medium PARs, 4 Small Pars

HR01C HR04C S SC 3 S1

Inside containment : 18 Larger PARs, 20 Medium PARs, 4 Small ParsInside IRWST : 4 Medium PARs

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Passive Ex-vessel corium retaining and Cooling System (PECS)Passive Ex-vessel corium retaining and Cooling System (PECS)

System FunctionT id i t ti i t hTo provide corium retention in core catcherTo provide coolability using water stored in IRWSTTo achieve a long term safe stateg

Design CriteriaProvision of sufficient corium coolabilityP i i f i t i i t t th i t ti b tProvision of corium retaining to prevent the interaction between hot corium and supporting structures of containmentInstallation of instruments for minitoringPassive actuationIndependence of flooding system

The PECS consists of a sacrificial concrete layer bodyThe PECS consists of a sacrificial concrete layer, body, cooling gap, supporting studs, downcomers, several monitors, and 2 train gravity cooling water supply sub-system.

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Passive Ex-vessel corium retaining and Cooling System (PECS)Passive Ex-vessel corium retaining and Cooling System (PECS)

Cooling WaterCorium-SM MixtureSacrificial Material (SM)Sacrificial Material (SM)Core Catcher BasinBasementStud

14

Severe Accident Containment Spray System (SACSS)Severe Accident Containment Spray System (SACSS)

The SACSS is a dedicated spray system for control of t i t i id tcontainment pressure in a severe accident

FunctionP d t t t l b i li tPressure and temperature control by spraying cooling waterReduction of concentrations of radioactive aerosols in containment atmospherepTo provide the function of long term cooling of the PECS

System ConfigurationConsists of two 100% trainsEach train consists of SA CS Pump (2), SA CS HX (2), SA CS Miniflow HX (2) Containment spray header piping valvesMiniflow HX (2), Containment spray header, piping, valves, controls, and instrumentation.Powered by dedicated AAC power supply systems

15

Severe Accident Containment Spray System (SACSS)Severe Accident Containment Spray System (SACSS)

SACSS

16

SA Dedicated CCW SA Dedicated ESW

Containment Filtered Vent System (CFVS)Containment Filtered Vent System (CFVS)

The CFVS consists of two vent trains with a common venturiscrubber as a passive component which will be located on Auxiliary Building.System Function

Protection of containment over-pressurization by filtered ventingProtection of containment over pressurization by filtered venting system as an alternative method when SACSS is unavailableMaintaining the containment integrity approximately 24 hours following the onset of core damagethe onset of core damage

Each train shall vent air from the containment atmosphere by the operator’s remotely opening of the containment isolation valve in h lthe main control room

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III. SA Design Features in AP1000III. SA Design Features in AP1000

In-vessel RetentionRetain core debris within the reactor vesselRetain core debris within the reactor vessel Ex-vessel coolingProvides reliable means of cooling damaged coreg gAP600 tests and analysis of IVR reviewed by U.S. NRCPrevents core-concrete interaction

High Pressure Core MeltEliminated with highly redundant and diverse ADVs

H d D t tiHydrogen DetonationPrevented by igniters

Steam ExplosionsSteam ExplosionsADS (Automatic Depressurization System) eliminates high pressure

18

pIVR eliminates low pressure

Reactor Coolant System DesignReactor Coolant System Design

19

In-Vessel Retention (IVR)In-Vessel Retention (IVR)

Severe Accident In-Vessel Retention

Cooling flow driven by natural circulationCooling water flow path in vessel/insulation annulusCore heat transferred through RV wallWater in containment removes heat from RVWater source is a IRWSTADS valves keep RCS pressure lowPassive containment coolingPassive containment cooling transfers heat out of containmentCore debris retained insideCore debris retained inside reactor vessel

20

IV. SA Design Features in US-APWRIV. SA Design Features in US-APWR

21

RCS Depressurization ValvesRCS Depressurization Valves

22

Schematic Diagram of the Arrangement of PSVs, SDVs, and DVsSchematic Diagram of the Arrangement of PSVs, SDVs, and DVs

V. SA Design Features in US-EPRV. SA Design Features in US-EPR

23

Severe Accident Depressurization ValvesSevere Accident Depressurization Valves

Dedicated valves preclude hi h RCShigh RCS pressure core melt ejection concerns

Manual actuation >Manual actuation > 1200℉(650℃)

Valve sizing ensures rapid g pdepressurization of RCSUS-EPR credits the availability of 1 of 2 100% depressurization trains

Goal is to ed e p ess e toGoal is to reduce pressure to < 20 bars (~300 psia) prior to RPV breach for all events

24

Core Melt Stabilization System (CMSS)Core Melt Stabilization System (CMSS)

CMSS protects integrity of containment basematcontainment basematCMSS designed to passively spread and stabilize moltenspread and stabilize molten core debrisCMSS features accomplish staged melt progression

In-vessel melt progressionControlled RPV failureControlled RPV failureMelt retention and conditioningMelt relocation and quenchingLong-term melt stabilizationLong term melt stabilization Spreading

25

Severe Accident Heat Removal System (SAHRS)Severe Accident Heat Removal System (SAHRS)

26

VI. Comparison of SA Design Features VI. Comparison of SA Design Features

APR1400 EU-APR1400 AP1000 US-APWR US-EPR

Hydrogen PAR(30)Igniter (10) PAR(46) Igniter(64) Igniter(20) PAR(47)

Reactor Core Reactor Reactor CoreMCCI

ReactorCavity Design

Core Catcher (PECS)

ReactorCavity Design

ReactorCavity Design

Core Catcher (CMSS)

Steam Structure Structure StructureSteam Explosion

Structure Design Dry Cavity Structure

DesignStructure Design Dry Cavity

HPME/DCH SDVS ERDS SA Depres. ADS SA Depres.HPME/DCH SDVS ERDS SA Depres.Valve ADS SA Depres.

Valve

IVR SAM N/A Mitigation SAM N/AIVR SAM N/A Feature SAM N/A

Containment P f

Large CTNT.ECSBS

Large CTNT.SACSS Large CTNT.

PCS Large CTNT. Large CTNT.SAHRS

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Performance ECSBS S CSSCFVS PCS a ge C SAHRS