ML16224A771

Proposed Revisions to 10 CFR Parts 50 and 100 and Proposed Regulatory Guides Relating to Seismic Siting and Earthquake Engineering Criteria

ML16224A771
Person / Time
Issue date:	02/14/1992
From:	Ward D Advisory Committee on Reactor Safeguards
To:	Selin I NRC/Chairman
References
Download: ML16224A771 (3)

Text

D920214 The Honorable Ivan Selin Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555

SUBJECT:

PROPOSED REVISIONS TO 10 CFR PARTS 50 AND 100 AND PROPOSED REGULATORY GUIDES RELATING TO SEISMIC SITING AND EARTHQUAKE ENGINEERING CRITERIA During the 382nd meeting of the Advisory Committee on Reactor Safeguards, February 6-8, 1992, we completed our initial review of those proposed revisions to reactor siting regulations that deal with seismology, geology, and earthquake engineering. These matters were considered also during meetings of our Extreme External Phenomena Subcommittee on December 10, 1991, and February 5, 1992. During these meetings, we had the benefit of discussions with representatives of the NRC staff and the industry.

The proposed revisions are to be submitted to the Commission as part of a package intended to decouple siting from plant design.

Our report of January 15, 1992, provided comments on those portions of the package relating to the nonseismic revisions to 10 CFR Parts 50 and 100 and to the source term. The specific revisions covered by this report are those referenced at the end of this report.

The existing requirements in 10 CFR Part 100 and its Appendix A remain in effect for all plants licensed prior to the effective date of the proposed revisions. For future plants and sites, the seismic siting portion of Part 100 will be included in a new Subpart B (the existing requirements will become Subpart A). In addition, a new Appendix B will be referenced in Subpart B. This new appendix will contain much less detailed requirements than those in Appendix A. The identification and characterization of seismic sources and procedures for the selection of a Safe Shutdown Earthquake (SSE) will be covered in a new Regulatory Guide DG-1015, and the engineering criteria for seismic design of structures, systems, and components will be in a new Appendix S to 10 CFR Part

50.

These relocations of various requirements within the body of regulations and guidance serve two purposes: (1) criteria for seismic design of a plant, now in Part 100, are moved to Part 50, where they belong. And (2), many requirements in Appendix A, that were state of the art when the appendix was written in 1973, are being brought up to date and are being removed from the regulations and placed in a regulatory guide where they can be more easily kept up to date in the future. We commend the staff for this proposed reorganization. It should make the licensing process more rational, and perhaps simpler, and will have no adverse effect on risk.

In addition to the proposed reorganization, two of the proposed changes to the content of the regulations deserve comment. The proposed Appendix S to Part 50 redefines the Operating Basis Earthquake (OBE) in a way that leads to more rational consideration of the OBE in design and operation. Studies are being made to ensure that the proposed changes will not lead to significant increases in risk. We believe that this change is a step in the right direction. Two new Regulatory Guides, DG-1017 and DG-1018, have been proposed to provide guidance on inspections, evaluations, shutdown, and restart, following the occurrence of an earthquake greater than the OBE at a plant.

The other change is a more significant departure from current requirements. Proposed Appendix B to Part 100 requires that the SSE ground motion be determined "using both probabilistic and deterministic approaches." The staff does not claim that this new requirement will have any significant effect on safety. The staff does believe, however, that a probabilistic approach will make it easier to determine an SSE ground motion in the face of unknowns or uncertainties, and that the resulting value will be more robust and resistant to challenge. In our view, that would argue for the use of a probabilistic approach, not for the use of a dual approach.

Although we are not convinced that the proposed dual approach is either necessary or desirable, we have no objection to the staff proposing and publishing it for public comment.

In summary, we have no reservations or concerns at this time that would argue against publication for comment of the several proposed revisions considered in our review. We note, however, that the documents considered were not in final form. Some had not yet been edited, others were still being modified by the staff, and none had yet been reviewed by the Committee to Review Generic Requirements.

If substantial changes are made in any of these documents before they are submitted to you, we expect the staff to inform us of them.

Sincerely, David A. Ward Chairman

References:

1. Memorandum dated October 11, 1991, from Themis P. Speis, Nuclear Regulatory Commission, for Raymond F. Fraley, Advisory Committee on Reactor Safeguards,

Subject:

Proposed Revision of 10 CFR Part 100, Reactor Site Criteria, Revisions to 10 CFR Part 50, New Appendix B to 10 CFR Part 100 and Appendix S to 10 CFR Part 50, and Associated Regulatory Guides (Draft Predecisional), enclosing:

a. Draft Revision to 10 CFR Part 50

b. Revised Part 100, Reactor Site Criteria

c. Proposed Revisions to Regulatory Guide 4.7, "General Site Suitability Criteria for Nuclear

Power Stations"

2. Memorandum dated January 21, 1992, from Lawrence C. Shao, Nuclear Regulatory Commission, for Raymond F. Fraley, Advisory Committee on Reactor Safeguards,

Subject:

Revision of Appendix A to 10 CFR Part 100 -- Geological and Seismological Siting Criteria for Nuclear Power Plants, enclosing:

a. Draft 10 CFR Part 100, Appendix B, Criteria for The Seismic and Geologic Siting of Nuclear Power Plants After [Effective Date]

b. Draft 10 CFR Part 50, Appendix S, Earthquake Engineering Criteria for Nuclear Power Plants

c. Draft Regulatory Guide DG-1015, Identification and Characterization of Seismic Sources, Expected Maximum Earthquakes and Ground Motion

d. Draft Regulatory Guide DG-1016, Second Proposed Revision 2 to Regulatory Guide 1.12, Nuclear Power Plant Instrumentation for Earthquakes

e. Draft Regulatory Guide DG-1017, Pre-Earthquake Planning and Immediate Nuclear Power Plant Operator Post-Earthquake Actions

f. Draft Regulatory Guide DG-1018, Restart of a Nuclear Power Plant Shut Down By A Seismic Event

g. Proposed Revision 3, Standard Review Plan 2.5.2, Vibratory Ground Motion