The benefits of using a risk-informed approach to resolve GSI-191

Timothy D. Sande, Gilbert L. Zigler, Ernie J. Kee, Bruce C. Letellier, C. Rick Grantom, Zahra Mohaghegh

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The emergency core cooling system (ECCS) and containment spray system (CSS) in a pressurized water reactor (PWR) are designed to safely shutdown the plant following a loss of coolant accident (LOCA). The assurance of long term core cooling in PWRs following a LOCA has a long history dating back to the NRC studies of the mid 1980s associated with Unresolved Safety Issue (USI) A-43. Results of the NRC research on boiling water reactor (BWR) ECCS suction strainer blockage of the early 1990s identified new phenomena and failure modes that were not considered in the resolution of USI A-43. As a result of these concerns, Generic Safety Issue (GSI) 191 was identified in September 1996 related to debris clogging of the ECCS sump suction strainers at PWRs. Although plants have taken steps to prevent strainer clogging (by increasing the screen area, for example), satisfactory closure of this issue has proved elusive due to long term cooling issues and the effect of chemical precipitates on head loss. Previous investigators have identified bounding scenarios using conservative inputs, methods, and acceptance criteria. The acceptance criteria are applied in a "pass/fail" fashion that ignores risk. That is, if the results are acceptable, the issue has been resolved. Otherwise, it is necessary to either redo the analysis with partial relaxation of analytical conservatisms or perform additional plant modifications to ensure that the acceptance criteria are met. This article describes a new approach to close out the GSI-191 issue by evaluating the risk associated with ECCS performance on post-LOCA core cooling as a basis to change the plant license. The approach includes an assessment of LOCA frequencies as a function of break size at locations along the reactor coolant system, as well as a full quantification of the uncertainties associated with LOCA frequencies and the generation, transport, accumulation, and subsequent impact of debris on ECCS performance. The overall frameworks for the deterministic and risk-informed approaches are summarized with emphasis on the risk-informed method. The differences between the deterministic approach taken in the past and the new risk-informed approach are described. Advantages and disadvantages between the two methods are described and contrasted for the GSI-191 issue. The South Texas Project (STP) GSI-191 risk-informed closure efforts are presented.

Original languageEnglish (US)
Title of host publication2012 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference, ICONE 2012-POWER 2012
PublisherAmerican Society of Mechanical Engineers (ASME)
Pages725-734
Number of pages10
Edition1
ISBN (Print)9780791844991
DOIs
StatePublished - Jan 1 2012
Externally publishedYes
Event2012 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference, ICONE 2012-POWER 2012 - Anaheim, CA, United States
Duration: Jul 30 2012Aug 3 2012

Publication series

NameInternational Conference on Nuclear Engineering, Proceedings, ICONE
Number1
Volume5

Other

Other2012 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference, ICONE 2012-POWER 2012
CountryUnited States
CityAnaheim, CA
Period7/30/128/3/12

ASJC Scopus subject areas

  • Nuclear Energy and Engineering

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