ML17263B168

Mupra: a Few Observations and Technical Challenges

ML17263B168
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Issue date:	09/20/2017
From:	NRC/RES/DRA
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MUPRA: A Few Observations and Technical ChallengesN. Siu and D. HudsonOffice of Nuclear Regulatory ResearchU.S. Nuclear Regulatory CommissionPresented at Special Session #2:MUPRA Advances, Issues, Impediments and PromiseANS International Topical Meeting on Probabilistic Safety Assessment (PSA 2017)Pittsburgh, PA; September 24

-28, 2017 2Multi-Unit Precursor EventsDatePlantDescription6/22/82Quad CitiesLOOP, Maintenance8/11/83SalemLOOP, Cloggedscreens7/26/84SusquehannaSBO, Bkrmis-aligned5/17/85Turkey PointLOOP, Brush fires7/23/87Calvert CliffsLOOP, Offsite t ree3/20/90VogtleLOOP, Truck hitsupport8/24/92Turkey PointLOOP, Hurricane12/31/92SequoyahLOOP, Switchyard fault10/12/93Beaver ValleyLOOP, Offsite fault6/28/96LaSalleTrip, Foreign material in SW Tunnel6/29/96Prairie IslandLOOP, HighwindsDatePlantDescription8/14/036 SitesLOOP, NE Blackout6/14/04Palo VerdeLOOP, Offsite fault9/25/04St. LucieLOOP, Hurricane5/20/06CatawbaLOOP, Switchyard fault3/26/09SequoyahLOOP, Bus fault4/16/11SurryLOOP, Tornado4/27/11Browns FerryLOOP, Winds/tornadoes8/23/11North AnnaLOOP, Earthquake3/31/13ANOLOOP/Trip, Load drop4/17/13LaSalleLOOP, Lightning5/25/14MillstoneLOOP, Offsite fault 3Some Other Old But Illustrative Events 3EventNotesEventNotesBrowns Ferry(BWR, 1975)Multi-unit cable fire; both units tripped. Narora(PHWR, 1993)Large TBexplosion and fire, smoke => U1/U2 MCR abandonment; U1 SBO,U2 cold shutdown. Greifswald(VVER, 1975)Electrical cable fire;U1 station blackout (SBO), U2 tripped.Shutdownused x-tie with U2Cooper(BWR, 1993)Extensive,extended flooding. Roads (one evacuation route) blocked.

Leakage through penetrations seals.Oconee(PWR, 1976)

U3 maintenance activity leads to large lake floodin common Turbine Building (TB); lost TD

-EFW.Blayais(PWR, 1999)Large storm causes LOOP (U2/U4),

flooding of U1/U2, affected site access.Doel(PWR, 1979)Large seawaterflood in common U1/U2 TB; both units tripped.Mihama(PWR, 2004)Large steam release in TB; also entered portions of control and intermediate buildings.Armenia(VVER, 1982)Electrical cable fire (multiple locations), smoke spread to U1 MCR,secondary explosionsand fire; U1 SBO, U2 tripped. Nogent(PWR, 2006)Large water leak lifts U2 TB floor, alsofloods U1 TB, enters ESW gallery through penetrations, CCW pump room through drainsChernobyl(RBMK, 1991)Large TB explosion and fire, partial roof collapse. Only U2 affected.Surry(PWR, 2006)Heavy rainfall floods Unit 1 TB and U2 ESGR through manhole and conduit penetrations 4Operational Experience ObservationsMany events caused by spatial (internal and external) hazardsSome events

-involve single units, and/or

-were terminated before serious plant impact,but mechanisms are relevant to MUPRAAll observed mechanisms and scenarios are relevant to (an d should, in principle, be captured by) single

-unit PRAAssumed defenses (e.g., seals, equipment qualification) and other screening factors may need re

-examination 5L3PRA OverviewProject objectives

-Develop state

-of-practice Level 3 PRA

-Extract new insights

-Enhance NRC PRA staff capability and expertise

-Demonstrate technical feasibility and cost of new Level 3 PRAsPlanned project scope

-All hazards

-All operational modes

-All major sourcesPlant: Vogtle 1&2 (special thanks to SNC for support) 6L3PRA Integrated Site Risk Approach*Logical combination of important single source scenarios (assumed symmetry)Inter-source dependencies (5 types)Parallel, independent search for scenarios*See ML17255A580 for details.

7New Tools to Aid SearchesOperational experience reports and other sources can spur (and temper) imaginationDatabase is massive and unstructured; how to

e fficiently identify, access, and analyze data?Recently completed scoping study (long

-term research)-Currently available technology (content analytics) can efficiently identify important target documents

-Increased subject matter expert involvement or more powerful machine learning tools would help in development of "industrial strength" applications ADDITIONAL SLIDES 9Multi-Unit Precursor EventsDatePlantTypeCCDP6/22/82Quad CitiesLOOP 1E-48/11/83SalemLOOP 1E-47/26/84Susquehanna SBO 2E-45/17/85Turkey PointLOOP 4E-57/23/87Calvert CliffsLOOP 5E-43/20/90VogtleLOOP 9E-48/24/92Turkey PointLOOP 2E-412/31/92SequoyahLOOP 2E-410/12/93Beaver ValleyLOOP 6E-56/28/96LaSalleTrip 7E-66/29/96Prairie IslandLOOP 5E-5DatePlantTypeCCDP8/14/036 Sites (NE Blackout)LOOP 4E-6 to 3E-56/14/04Palo VerdeLOOP 9E-6/4E-59/25/04St. LucieLOOP 1E-55/20/06CatawbaLOOP 9E-5/6E-53/26/09SequoyahLOOP 4E-64/16/11SurryLOOP 9E-5/7E-54/27/11Browns FerryLOOP 1E-58/23/11North AnnaLOOP 3E-4/6E-53/31/13ANOLOOP/TripYellow4/17/13LaSalleLOOP 1E-55/25/14MillstoneLOOP 2E-5/1E-5 10Inter-Source Dependencies