MODIFICATIONS TO A MODIFICATIONS TO A PRA MODEL TO PRA MODEL TO ADDRESS MULTIPLE ADDRESS MULTIPLE SPURIOUS OPERATIONS SPURIOUS OPERATIONS (MSOs)(MSOs).

Presented at the ANS PSA Presented at the ANS PSA 2008 Topical Meeting2008 Topical Meeting

September 7–11, 2008September 7–11, 2008

Knoxville, TennesseeKnoxville, Tennessee

Richard Anoba, Anoba Richard Anoba, Anoba Consulting Services, LLCConsulting Services, LLC

David Miskiewicz, David Miskiewicz, Progress Energy Progress Energy Carolinas, IncCarolinas, Inc

IntroductionIntroduction

• Increasing use of PRAs to develop Increasing use of PRAs to develop Fire PRA Models for NFPA-805 Fire PRA Models for NFPA-805 ApplicationApplication

• Increasing demands to address fire-Increasing demands to address fire-induced multiple spurious induced multiple spurious operations (MSOs)operations (MSOs)

What is a MSO?What is a MSO?

• A MSO is unique to fire initiating events A MSO is unique to fire initiating events such that it involve fire-induced failure of such that it involve fire-induced failure of multiple electric-powered components that multiple electric-powered components that lead to undesired end stateslead to undesired end states

• Spurious closure/opening of MOVs, AOVs, Spurious closure/opening of MOVs, AOVs, SOVs, etc due to fire-induced hot short.SOVs, etc due to fire-induced hot short.

• Spurious starting/stopping of pumps, etc Spurious starting/stopping of pumps, etc due to fire-induced hot shortdue to fire-induced hot short

Simplified Hot Short ModelSimplified Hot Short Model

How do we model MSOs?How do we model MSOs?

• NUREG/CR-6850

• ANS Fire PRA Standard

• Expert Panel Reviews

• Fire Safe Shutdown Analysis (Appendix R)

• No specific “how to” guidance

Modeling ChallengesModeling Challenges

• PRA model alone will not capture all possible MSOs

• Apendix R captures single spurious Apendix R captures single spurious operationoperation

• Expert panel can capture additional Expert panel can capture additional MMSOs based on Appendix R safe SOs based on Appendix R safe shutdown functions and systemsshutdown functions and systems

Modeling ChallengesModeling Challenges

• Requires commprehensive review of all Requires commprehensive review of all inputs/guidance plus creativity of PRA inputs/guidance plus creativity of PRA analystanalyst

• The modeling of MSOs in the PRA model The modeling of MSOs in the PRA model presents some unique issues that the PRA presents some unique issues that the PRA analysts must deal withanalysts must deal with

• Fault tree is a static model, while a fire Fault tree is a static model, while a fire scenario is time-dependentscenario is time-dependent

Modeling ChallengesModeling Challenges

• The duration of a hot short event that The duration of a hot short event that causes the MSO might be on the order causes the MSO might be on the order of 10 to 20 minutes after which the of 10 to 20 minutes after which the fire-induced fault becomes a short-to-fire-induced fault becomes a short-to-groundground

• At this point power is removed from At this point power is removed from the component and the hot short event the component and the hot short event is terminated. is terminated.

Modeling ChallengesModeling Challenges

• Competing MSO failure modes for Competing MSO failure modes for the same component may be the same component may be mutually exclusivemutually exclusive

• Alternatively, MSO failure modes Alternatively, MSO failure modes that have to occur later in time may that have to occur later in time may be invalidbe invalid

NUREG/CR-6850 NUREG/CR-6850 Component Selection (Key Component Selection (Key MSO Steps)MSO Steps)

• The NFPA-805 project typically The NFPA-805 project typically includes a task to develop the includes a task to develop the component list to be considered for component list to be considered for inclusion into the Fire PRA model using inclusion into the Fire PRA model using NUREG/CR-6850NUREG/CR-6850

• Identify electrically dependent Identify electrically dependent components in the PRA model and in components in the PRA model and in Appendix R.Appendix R.

NUREG/CR-6850 NUREG/CR-6850 Component Selection (Key Component Selection (Key MSO Steps)MSO Steps)

• Reconciliation of differences between Reconciliation of differences between the Appendix R Analysis and the PRAthe Appendix R Analysis and the PRA

• Addition of components whose potential spurious actuations (considering multiples) could challenge the event mitigation capability..

NUREG/CR-6850 NUREG/CR-6850 Component Selection (Key Component Selection (Key MSO Steps)MSO Steps)• Addition of instrumentation important to Addition of instrumentation important to

human responsehuman response

• Inclusion of components whose failure, Inclusion of components whose failure, by itself, could cause high consequence by itself, could cause high consequence events as defined in the NUREG/CR-6850events as defined in the NUREG/CR-6850

• Addition of components identified by the Addition of components identified by the expert panel review teamexpert panel review team

Expert Panel ReviewsExpert Panel Reviews

• Focus on Appendix R or Safe Focus on Appendix R or Safe Shutdown functions and systems (2 Shutdown functions and systems (2 Spurious operations)Spurious operations)

• Many identified MSOs are also Many identified MSOs are also applicable to Fire PRAapplicable to Fire PRA

• PRA analyst needs to expand focus to PRA analyst needs to expand focus to PRA functions and systemsPRA functions and systems

A - Loss of Reactivity A - Loss of Reactivity ControlControl

• 1- Boron Dilution1- Boron Dilution

• 2- Uncontrolled Cooldown2- Uncontrolled Cooldown

B - Loss of Reactor B - Loss of Reactor Coolant System (RCS) Coolant System (RCS) Inventory ControlInventory Control• 1- Reactor Coolant Pump Seal LOCA1- Reactor Coolant Pump Seal LOCA

• 2- Stuck Open Pressurizer PORV2- Stuck Open Pressurizer PORV

• 3- Spurious Opening of Head/High Point Vents3- Spurious Opening of Head/High Point Vents

• 4- Spurious Opening of Letdown Line4- Spurious Opening of Letdown Line

• 5- Diversion flowpaths for RWST inventory5- Diversion flowpaths for RWST inventory

• 6- Pump dead head6- Pump dead head

C- Excessive RCS C- Excessive RCS InjectionInjection

• 1- Spurious HPI injection in excess 1- Spurious HPI injection in excess of letdown capability with failure of of letdown capability with failure of Pressurizer PORVPressurizer PORV

D- Loss of RCS D- Loss of RCS Pressure ControlPressure Control

• 1- Spurious Auxiliary Pressurizer Spray1- Spurious Auxiliary Pressurizer Spray

• 2- Spurious Pressurizer Heater 2- Spurious Pressurizer Heater ActuationActuation

• 3- Spurious Start of RCP with 3- Spurious Start of RCP with subsequent pump heatsubsequent pump heat

• 4- Spurious normal Pressurizer spray 4- Spurious normal Pressurizer spray with RCPs runningwith RCPs running

E- RCS OvercoolingE- RCS Overcooling

• 1- Spurious Turbine Bypass Valve actuation1- Spurious Turbine Bypass Valve actuation

• 2- Failure of MSIVs to close with spurious 2- Failure of MSIVs to close with spurious opening of downstream opening of downstream condenser/atmospheric dump valvescondenser/atmospheric dump valves

• 3- Spurious opening of MSIV bypass valve3- Spurious opening of MSIV bypass valve

• 4- Failure to isolate SG Blowdown Valves4- Failure to isolate SG Blowdown Valves

F- Loss of Decay Heat F- Loss of Decay Heat RemovalRemoval

• 1- Spurious isolation of MFW flow 1- Spurious isolation of MFW flow pathpath

• 2- Spurious start of AFW system2- Spurious start of AFW system

G- Loss of Support G- Loss of Support SystemSystem

• 1- Loss of Electrical Power1- Loss of Electrical Power

• 2- Loss of Component Cooling Water 2- Loss of Component Cooling Water SystemSystem

• 3- Loss of Salt Water Cooling System3- Loss of Salt Water Cooling System

• 4- Loss of HVAC4- Loss of HVAC

• 5- Loss of Instrument Air5- Loss of Instrument Air

Characterization and Characterization and Evaluation of MSOs Evaluation of MSOs

• A- MSO already addressed in the PRAA- MSO already addressed in the PRA

• B- MSO from Appendix R excluded since PRA function not B- MSO from Appendix R excluded since PRA function not impactedimpacted

• C- New MSO from various steps in the component selection C- New MSO from various steps in the component selection tasktask

• D - New MSO from Appendix RD - New MSO from Appendix R

• ..

Characterization and Characterization and Evaluation of MSOs Evaluation of MSOs

• E - New MSO from expert panel E - New MSO from expert panel reviewreview

• F - MSO from Appendix R and F - MSO from Appendix R and incorporated into the PRAincorporated into the PRA

RCS System RCS System Pressurizer PORVs and Pressurizer PORVs and Vent ValvesVent Valves

Safety Injection System - Safety Injection System - Recirculation Sump ValvesRecirculation Sump Valves

Component Cooling Component Cooling Water SystemWater System

Safety Injection System - Safety Injection System - High Head InjectionHigh Head Injection

Example MSO EvaluationExample MSO Evaluation

Example MSO Evaluation

System MSO Combination MSO Category Safe Shutdown Function Category Impacted

PRA Model Modification Required

RCS Spurious opening of 1RC-114 and failure to close 1RC-113

D B3 Yes

RCS Spurious opening of 1RC-905 and 1RC-900

E B3 Yes

SI Spurious opening 1SI-300 and 1SI-310

E B5 Yes

CCW Spurious closure of 1CC-99 and 1CC-113

A B1 No

CVCS Spurious opening of 1CS-291 and 1CS-292

A B (PRA function - Isolation of RWST)

No

Spurious Opening of Spurious Opening of Pressurizer PORVs Causes Pressurizer PORVs Causes Small LOCASmall LOCA

Spurious Opening of Spurious Opening of Reactor Vessel or Reactor Vessel or Pressurizer Vent Valves Pressurizer Vent Valves Causes Small LOCACauses Small LOCA

Spurious Opening of SG Spurious Opening of SG Blowdown Valves Causes Blowdown Valves Causes Uncontrolled Secondary Uncontrolled Secondary DepressurizationDepressurization

SummarySummary

• Although, the PRA already Although, the PRA already addresses many of the MSO issues, addresses many of the MSO issues, there remain a handful of issues there remain a handful of issues that require model modificationthat require model modification

• Extensive modifications to the PRA Extensive modifications to the PRA model may be required to model may be required to adequately address MSOadequately address MSO

SummarySummary

• Time-dependent nature of a fire Time-dependent nature of a fire scenario can cause mutually exclusive scenario can cause mutually exclusive failure mode combinations and/or failure mode combinations and/or invalid failure modes. These need to be invalid failure modes. These need to be addressed.addressed.

• New failure scenarios may require New failure scenarios may require additional supporting deterministic additional supporting deterministic analysesanalyses