ML20127B042
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'o UNITED STATES
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..e NOV 1 41983 MEMORANDUM FOR: George Lear, Chief Structural & Geotechnical Engineering Branch, DE FROM:
Robert J. Bosnak, Chief Mechanical Engineering Branch, DE
SUBJECT:
MILLSTONE UNIT 3 PROBABILISTIC SAFETY STUDY Reference 1: Report from Northeast Nuclear Energy Company, " Millstone Unit 3 Prcbabilistic Safety Study", dated August 1983 The Mechanical Engineering Branch has reviewed the Millstone Unit 3 Probabilistic Safety Study (Reference 1). We have reviewed the information pertaining to the analysis of the component fragility and its associated seismic risk as presented in Section 2.5, Appendix 2-I, Appendix A and Appendix 2-J.
Attached are our comments of the Millstone Unit 3 seismic' risk analysis which are based on a preliminary review of Reference 1.
Because of the short schedule for review, we feel that a L
close interaction between the contractor and the staff is necessary for
-completing this review. Since we have not yet had this interaction, our i.
review is neither final nor necessarily complete.
otg t J. Bosnak, Chief Mechanical Engineering Branch Division of Engineering
Attachment:
As stated cc:
R. Vollmer J. Knight H..Brammer N. Chokshi Y. Li
Contact:
Yueh-Li C. Li, DE:l!EB, x24417 7"21itIcoal g
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MECHANICAL ENGINEERING BRANCH EVALUATION Millstone Unit 3 Probabilistic Safety Study 1.
It is not clear that the applicant has considered the possible
. failure of non-safety related structures or equipment which could impact.on Lsafety-related items. The applicant is requested to provide a description of the procedure of evaluating the effects of failures of non-safety related structures or equipment on safety-related structures, equipment, and safety-related-piping systems and components and their supports.
2.
It is not clear how the applicant has considered the possible failure of pipirg systems and components due to differential movement or tilting of structures.
In addition, it is not clear how the applicant has considered the failure modes of buried piping
.which may be influenced by geotechnical parameters, e.g., soil amplification. The applicant is requested to confirm that these effects have been considered and included in its evaluation.
3.
It is not clear that the applicant has considered design and construction errors in its seismic fragility analysis. The staff feels that design and construction errors (e.g., concerns of IE 1
Bulletin No. 79-14, Seismic Analyses for As-Built Safety-Related Piping: System, problems identified in various Independent Design Verification Programs) may become important in the seismic fragility analysis for piping systems and components. Therefore, the effects of design and construction should be considered in the 5
seismic fragility analysis.
4.
The definitions of the component failure modes considered in the applicant's seismic fragility analysis need to be clarified.
Section 4.2 and Table 2.5.1-2A do not clearly define all the possible failure modes which were considered for the many individual components such as piping systems, pumps, valves, piping system supports, other mechanical components and their supports including the reactor pressure vessel support. The applicant is requested to provide this information.
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