An Assessment for Five Severe Accident Risks: An ...

1 NUREG-1150 Vol. 1An Assessment for FiveSevereAccident Risks: An Assessment for nuclear Power PlantsFinal Summary nuclear RegulatoryCommissionOffice of nuclear regulatory ResearchAVAILABILITY NOTICEA vailability of Reference Materials Cited in NRC PublicationsMost documents cited in NRC publications will be available from one of the followingsources:1. The NRC Public Document Room, 2120 L Street, NW, Lower Level, Washington, DC205552. The Superintendent of Documents, Government Printing Office, Box 37082,Washington, DC 20013-70823. The National Technical Information Service, Springfield, VA 22161 Although the listing that follows represents the majority of documents cited in NRC publica-tions, it is not intended to be documents available for inspection and copying for a fee from the NRC PublicDocument Room include NRC correspondence and internal NRC memoranda; NRC Office ofInspection and Enforcement bulletins, circulars, information notices, inspection and Investi-gation notices; Licensee Event Reports; vendor reports and correspondence; Commissionpapers.

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4 1 Severe Accident Risks: An Assessment for nuclear Power PlantsFinal Summary ReportManuscript Completed: October 1990 Date Published: December 1990 Division of Systems ResearchOffice of nuclear regulatory nuclear regulatory CommissionWashington, DC 20555 ABSTRACTThis report summarizes an Assessment of the risksfrom Severe accidents in five commercial nuclearpower plants in the United States. These risks aremeasured in a number of ways, including: theestimated frequencies of core damage accidentsfrom internally initiated accidents and externallyinitiated accidents for two of the plants; theperformance of containment structures undersevere Accident loadings; the potential magnitudeof radionuclide releases and offsite consequencesof such accidents; and the overall risk (theproduct of Accident frequencies and conse-quences).

5 Supporting this summary report are alarge number of reports written under contract toNRC that provide the detailed discussion of themethods used and results obtained in these report was first published in February 1987as a draft for public comment. Extensive peerreview and public comment were received. As aresult, both the underlying technical analyses andthe report itself were substantially changed. Asecond version of the report was published in June1989 as a draft for peer review. Two peer reviewsof the second version were performed. One wassponsored by NRC; its results are published as theNRC report NUREG-1420. A second wassponsored by the American nuclear Society(ANS); its report has also been completed and isavailable from the ANS. The comments by bothgroups were generally positive and recommendedthat a final version of the report be published assoon as practical and without performing anymajor reanalysis.

6 With this direction, the NRCproceeded to generate this final version of I of this report has three parts. Part Iprovides the background and objectives of the as-sessment and summarizes the methods used toperform the risk studies. Part II provides a sum-mary of results obtained for each of the five plantsstudied. Part III provides perspectives on the re-sults and discusses the role of this work in thelarger context of the NRC staff's 150 CONTENTSPageAbstract .. iiiAcknowledgments .. xvPART I INTRODUCTION AND SUMMARY OF METHODS1. INTRODUCTION .. Background . Objectives . Scope of Risk Analyses . Structure of NUREG-1150 and Supporting Documents .1-42. SUMMARY OF METHODS .. Introduction . Accident Frequency Estimation . Methods .. Products of Accident Frequency Analysis.

7 Accident Progression, Containment Loading, and Structural Response Analysis .. Methods . Products of Accident Progression, Containment Loading, and Structural ResponseAnalysis . Analysis of Radioactive Material Transport .. Methods . Products of Radioactive Material Transport Analysis . Offsite Consequence Analysis .. Methods . Products of Offsite Consequence Analysis . Uncertainty Analysis . Formal Procedures for Elicitation of Expert Judgment . Risk Integration . Methods . Products of Risk Integration .2-26 PART I SUMMARY OF PLANT RESULTS3. SURRY PLANT RESULTS .. Summary Design Information .. Core Damage Frequency Estimates .. Summary of Core Damage Frequency Estimates . Important Plant Characteristics (Core Damage Frequency) . Important Operator Actions.

8 Important Individual Events and Uncertainties (Core Damage Frequency) . Containment Performance Analysis .. Results of Containment Performance Analysis .. Important Plant Characteristics (Containment Performance) .. Source Term Analysis .. Results of Source Term Analysis .. Important Plant Characteristics (Source Term) .. Offsite Consequence Results .. Public Risk Estimates .. Results of Public Risk Estimates .. Important Plant Characteristics (Risk) ..4. PEACH BOTTOM PLANT RESULTS .. Summary Design Information .. Core Damage Frequency Estimates .. Summary of Core Damage Frequency Estimates . Important Plant Characteristics (Core Damage Frequency) .. Important Operator Actions .. Important Individual Events and Uncertainties (Core Damage Frequency).

9 Containment Performance Analysis .. Results of Containment Performance Analysis .. Important Plant Characteristics (Containment Performance) .. Source Term Analysis .. Results of Source Term Analysis .. Important Plant Characteristics (Source Term) .. Offsite Consequence Results .. Public Risk Estimates .. Results of Public Risk Estimates .. Important Plant Characteristics (Risk) ..5. SEQUOYAH PLANT RESULTS .. Summary Design Information .. Core Damage Frequency Estimates .. Summary of Core Damage Frequency Estimates .. Plant Characteristics (Core Damage Frequency) ..Important Operator Actions ..Important Individual Events and Uncertainties (Core Damage Frequency) .. Containment Performance Analysis .. Results of Containment Performance Analysis.

10 Important Plant Characteristics (Containment Performance) .. Source Term Analysis .. Results of Source Term Analysis .. Important Plant Characteristics (Source Term) .. Offsite Consequence Results .. Public Risk Estimates .. Results of Public Risk Estimates .. Important Plant Characteristics (Risk) ..6. GRAND GULF PLANT RESULTS .. Summary Design Information .. Core Damage Frequency Estimates .. Summary of Core Damage Frequency Estimates .. Important Plant Characteristics (Core Damage Frequency) .. Important Operator Actions .. Important Individual Events and Uncertainties (Core Damage Frequency). Containment Performance Analysis .. Results of Containment Performance Analysis .. Important Plant Characteristics (Containment Performance) .. Source Term Analysis.