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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Download: ML17263B168 (10)

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MUPRA: A Few Observations and Technical Challenges N. Siu and D. Hudson Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Presented at Special Session #2:

MUPRA Advances, Issues, Impediments and Promise ANS International Topical Meeting on Probabilistic Safety Assessment (PSA 2017)

Pittsburgh, PA; September 24-28, 2017

2 Multi-Unit Precursor Events Date Plant Description 6/22/82 Quad Cities LOOP, Maintenance 8/11/83 Salem LOOP, Clogged screens 7/26/84 Susquehanna SBO, Bkr mis-aligned 5/17/85 Turkey Point LOOP, Brush fires 7/23/87 Calvert Cliffs LOOP, Offsite tree 3/20/90 Vogtle LOOP, Truck hit support 8/24/92 Turkey Point LOOP, Hurricane 12/31/92 Sequoyah LOOP, Switchyard fault 10/12/93 Beaver Valley LOOP, Offsite fault 6/28/96 LaSalle Trip, Foreign material in SW Tunnel 6/29/96 Prairie Island LOOP, High winds Date Plant Description 8/14/03 6 Sites LOOP, NE Blackout 6/14/04 Palo Verde LOOP, Offsite fault 9/25/04 St. Lucie LOOP, Hurricane 5/20/06 Catawba LOOP, Switchyard fault 3/26/09 Sequoyah LOOP, Bus fault 4/16/11 Surry LOOP, Tornado 4/27/11 Browns Ferry LOOP, Winds/tornadoes 8/23/11 North Anna LOOP, Earthquake 3/31/13 ANO LOOP/Trip, Load drop 4/17/13 LaSalle LOOP, Lightning 5/25/14 Millstone LOOP, Offsite fault

3 Some Other Old But Illustrative Events 3

Event Notes Event Notes Browns Ferry (BWR, 1975)

Multi-unit cable fire; both units tripped.

Narora (PHWR, 1993)

Large TB explosion and fire, smoke

=> U1/U2 MCR abandonment; U1 SBO, U2 cold shutdown.

Greifswald (VVER, 1975)

Electrical cable fire; U1 station blackout (SBO), U2 tripped.

Shutdown used x-tie with U2 Cooper (BWR, 1993)

Extensive, extended flooding. Roads (one evacuation route) blocked.

Leakage through penetrations seals.

Oconee (PWR, 1976)

U3 maintenance activity leads to large lake flood in 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 seawater flood 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 explosions and fire; U1 SBO, U2 tripped.

Nogent (PWR, 2006)

Large water leak lifts U2 TB floor, also floods U1 TB, enters ESW gallery through penetrations, CCW pump room through drains Chernobyl (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

4 Operational Experience Observations

• Many events caused by spatial (internal and external) hazards

• Some events

- involve single units, and/or

- were terminated before serious plant impact, but mechanisms are relevant to MUPRA

• All observed mechanisms and scenarios are relevant to (and should, in principle, be captured by) single-unit PRA

• Assumed defenses (e.g., seals, equipment qualification) and other screening factors may need re-examination

5 L3PRA Overview

• Project 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 PRAs

• Planned project scope

- All hazards

- All operational modes

- All major sources

• Plant: Vogtle 1&2 (special thanks to SNC for support)

6 L3PRA 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.

7 New Tools to Aid Searches

• Operational experience reports and other sources can spur (and temper) imagination

• Database is massive and unstructured; how to efficiently 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

9 Multi-Unit Precursor Events Date Plant Type CCDP 6/22/82 Quad Cities LOOP 1E-4 8/11/83 Salem LOOP 1E-4 7/26/84 Susquehanna SBO 2E-4 5/17/85 Turkey Point LOOP 4E-5 7/23/87 Calvert Cliffs LOOP 5E-4 3/20/90 Vogtle LOOP 9E-4 8/24/92 Turkey Point LOOP 2E-4 12/31/92 Sequoyah LOOP 2E-4 10/12/93 Beaver Valley LOOP 6E-5 6/28/96 LaSalle Trip 7E-6 6/29/96 Prairie Island LOOP 5E-5 Date Plant Type CCDP 8/14/03 6 Sites (NE Blackout)

LOOP 4E-6 to 3E-5 6/14/04 Palo Verde LOOP 9E-6/4E-5 9/25/04 St. Lucie LOOP 1E-5 5/20/06 Catawba LOOP 9E-5/6E-5 3/26/09 Sequoyah LOOP 4E-6 4/16/11 Surry LOOP 9E-5/7E-5 4/27/11 Browns Ferry LOOP 1E-5 8/23/11 North Anna LOOP 3E-4/6E-5 3/31/13 ANO LOOP/Trip Yellow 4/17/13 LaSalle LOOP 1E-5 5/25/14 Millstone LOOP 2E-5/1E-5

10 Inter-Source Dependencies