Diablo Canyon NPP Probabilistic Risk Assessment Program

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

DiabloDiablo Canyon NPPCanyon NPPProbabilistic Risk Assessment ProgramProbabilistic Risk Assessment Program

Workshop InformationWorkshop InformationIAEA WorkshopIAEA Workshop City , Country

XX - XX Month, YearCity , Country

XX - XX Month, Year

LecturerLesson IV 3_11.2

LecturerLesson IV 3_11.2

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making 2

Risk Management and ItRisk Management and It’’s Applications Applicationat at Diablo Canyon NPP (DCPP) Diablo Canyon NPP (DCPP)

A process that evaluates the change in risk as a result of plant

changes in hardware, configuration, commitments,

processes, activities, and human and equipment performance.

The process uses risk- and performance-based methods as

opposed to traditional prescriptive methods.


Risk ManagementRisk Management

Motivation

US NRC plans to expand the use of PSA

Assessing changes to licensing basis

Assessing significance of findings

Enhance safety via systematic/integrated process

Reduce production interruption

Reduce operational cost


Definition of RulesDefinition of RulesPrescriptivePrescriptive--Based RulesBased Rules

These are rules that are based on arbitrary/judgmental assumptioThese are rules that are based on arbitrary/judgmental assumptions ns taken to assesstaken to assess adequacy of adequacy of plantplant response to certain bounding initiators. These arbitrary assumpresponse to certain bounding initiators. These arbitrary assumptions are often conservative tions are often conservative to account for the knowledge and model uncertainties. For examplto account for the knowledge and model uncertainties. For example, single failure criteria is a e, single failure criteria is a prescriptive rule which attempts to address the uncertainty abouprescriptive rule which attempts to address the uncertainty about equipment t equipment unavailabilityunavailability by by forcing at least two success paths for each function. forcing at least two success paths for each function.

DeterministicDeterministic--Based RulesBased RulesThese are rules which are purely based on the deterministic analThese are rules which are purely based on the deterministic analysis. For example, the amount ysis. For example, the amount of water required in the RWST for a PWR is usually based on the of water required in the RWST for a PWR is usually based on the amount of water that is amount of water that is required to allow for recirculation via the sump. And the amounrequired to allow for recirculation via the sump. And the amount of water is calculated based on t of water is calculated based on mechanistic calculationsmechanistic calculations..

ProbabilisticProbabilistic--Based RulesBased RulesThese are rules that are based on These are rules that are based on

probabilistic evaluation of the frequency of all possible initiaprobabilistic evaluation of the frequency of all possible initiatorstors

ANDAND

combination of deterministic and probabilistic evaluation of acccombination of deterministic and probabilistic evaluation of accident mitigating functions ident mitigating functions response to each (class of) initiators. response to each (class of) initiators. TheThe uncertainty in these rules can be statistically uncertainty in these rules can be statistically addressed. Defenseaddressed. Defense--inin--depth is an important consideration when implementing such rulesdepth is an important consideration when implementing such rules. .


Long Term Seismic Plan PSA in 1988 Long Term Seismic Plan PSA in 1988

LTSP is a full scope at power Level 1 PSA including External EveLTSP is a full scope at power Level 1 PSA including External Events nts

NRC staff issues SER on the NRC staff issues SER on the DCPPDCPP Level 1 PSA (NUREG/CRLevel 1 PSA (NUREG/CR--5726)5726)

DCPP IPE per Generic Letter 88DCPP IPE per Generic Letter 88--20 (Included Level 2 PSA) in 199120 (Included Level 2 PSA) in 1991

DCPP IPEEE model (Update of External Events) in 1993DCPP IPEEE model (Update of External Events) in 1993

Living PSA program including updates in 1995, 1997, and 2001 Living PSA program including updates in 1995, 1997, and 2001

DiabloDiablo Canyon Canyon NPP PSA ProgramNPP PSA ProgramProgram HistoryProgram History


Diablo Canyon Power Plant Diablo Canyon Power Plant PsaPsa ProgramProgram

PSA APPLICATIONS IMPLEMENTEDPSA APPLICATIONS IMPLEMENTEDMaintenance RuleMaintenance RuleConfiguration Risk Assessment (OnConfiguration Risk Assessment (On--line Maintenance)line Maintenance)Technical Specification OptimizationTechnical Specification OptimizationSevere Accident Management ProgramSevere Accident Management ProgramGeneration/Engineering SupportGeneration/Engineering SupportRiskRisk--Informed Informed InserviceInservice InspectionInspectionMotor Operated ValvesMotor Operated Valves

DCPP RISK MODEL PROGRAMDCPP RISK MODEL PROGRAMConfiguration Control ProgramConfiguration Control ProgramRiskRisk--Informed Application Projects Informed Application Projects PSA Model EnhancementsPSA Model Enhancements


Diablo Canyon Power Plant Risk Management Diablo Canyon Power Plant Risk Management ProgramProgram

Elements of Risk Management Program

Probabilistic Safety Assessment (PSA) information

PSA configuration controlPSA applications

Identification of safety enhancing/burden reducing applications

Risk significance evaluation

Expert panel & working groups

Post review of maintenance activities (risk curves)

Shutdown risk evaluation (ORAM Calculations)


Diablo Canyon Power Plant PSA Program Diablo Canyon Power Plant PSA Program Major Elements of PSA Configuration ControlMajor Elements of PSA Configuration Control

PSA configuration control procedure PSA configuration control procedure

PSA risk ranking procedurePSA risk ranking procedure

PSA risk assessment guidelinesPSA risk assessment guidelines

Periodic review of plant hardware and procedural changesPeriodic review of plant hardware and procedural changes

Periodic update of PSA Model subPeriodic update of PSA Model sub--modelsmodels


Diablo Canyon Power Plant PSA ProgramDiablo Canyon Power Plant PSA ProgramRisk Model Configuration Control ElementRisk Model Configuration Control Element

sequencing, Thermohydraulic

PSA INPUT &

FEEDBACK PATHS

System DesignChange -

Generic IndustryData - industry

system/equipmentfailure rates

Vendor Manuals -equipment operatingfeatures, failure modes

Design BasisDocuments -

system design basis,success criteria

FSAR - system designbasis, assumptions, successcriteria, Failure Modes and

Effects Analysis

TechnicalSpecifications -

allowed outage times,surveillance test

intervals

Plant OperatingProcedures - Normal

system alignments

Emergency OperatingProcedures - Accident

condition alignments, operatorrecovery actions

SurveillanceProcedures

system alignmentfor testing

MaintenanceProcedures - system

alignment formaintenance

EngineeringProcedures -other testing

Engineering Analysis -Room Heat-up Calcs,

Accident progression and

evaluations

Performance Data -plant specific system/

equipment failure rates,Maintenance Datafrequency/duration


DiabloDiablo Canyon Power Plant PSA ProgramCanyon Power Plant PSA ProgramRisk Insights ElementRisk Insights Element

Contributions to CDF by Initiator

24%

23%18%

11% 4%

1%

2%

17%

Loss of ASW or CCW (24%)Floods (23%)Loss of Offsite Power (18%)General Transients (Rx Trip, Turb Trip, etc.) (17%)LOCAs (Excessive, Large, Medium, Small, RCP Seal) (11%)Steam Generator Tube Rupture (4%)Interfacing System LOCAs (2%)Loss of One 125V DC Bus (1%)



Contributions to LERF by Initiator

66%

32%

2%

Steam Generator Tube Rupture (66%)Interfacing System LOCAs (32%)Other (2%)


IMPORTANT OPERATOR RECOVERY ACTIONSIsolate Ruptured Steam Generator

Reduce Unnecessary CCW Loads

Align Firewater as Backup Cooling to CCPs

480V Switchgear Vent (Reduce IY & BTC Room Temps)

Electric Power (offsite power, vital bus crosstie, DG)

Switchover to Cold Leg Recirculation

Initiation of Feed and Bleed Cooling

Trip RHR Pumps Following Small Break LOCA

TOP 10 SYSTEMS (RRW for Internal Events)

Auxiliary SaltwaterDiesel Generators

Component Cooling WaterRCS (PORVs & Seal LOCA)

Vital AC PowerResidual Heat RemovalNon-Vital Electric Power

Charging & SIAuxiliary Feedwater

Vital DC Power




Blends prescriptive and deterministic/probabilistic insights

Considers factors outside the scope of PSA analyses

Evaluates aggregate affects of all risk informed, performance based programs

Provides an overall sanity check


DiabloDiablo Canyon Power PlantCanyon Power PlantExpert Panel Members and ResponsibilitiesExpert Panel Members and Responsibilities

MEMBERSOperations- Licensed SRORisk and Reliability Supervisor (Chairperson)System Engineering SupervisorPreventative Maintenance Program Specialist

RESPONSIBILITIES1. Approve the criteria for assessing the risk significance of SSCs.2. Review and approve the risk significance assigned to SSCs.3. Maintain cognizance over the implementation of the Risk Management

Program and other risk-informed initiatives. 4. Adjust criteria for risk-informed programs as appropriate.


Diablo Canyon Power Plant PSA ProgramDiablo Canyon Power Plant PSA ProgramConclusionConclusion

ESSENTIAL ELEMENTS

Probabilistic Safety Assessment (PSA)

Deterministic insights

Expert Panel

Risk-Informed working group

Continuous performance feedback

Implementation strategies