ML22273A041
| ML22273A041 | |
| Person / Time | |
|---|---|
| Issue date: | 06/07/2023 |
| From: | NRC/RES/DE/SGSEB |
| To: | |
| O'Donnell E | |
| Shared Package | |
| ML22273A011 | List: |
| References | |
| RG 1.61 Rev 2 DG-1364 | |
| Download: ML22273A041 (3) | |
Text
REGULATORY ANALYSIS DRAFT REGULATORY GUIDE DG-1364 DAMPING VALUES FOR SEISMIC DESIGN OF NUCLEAR POWER PLANTS (Proposed Revision 2 of Regulatory Guide 1.61)
- 1. Introduction This document presents an analysis of the U.S. Nuclear Regulatory Commissions (NRCs) determination of whether the NRC should expend resources to revise Regulatory Guide (RG) 1.61, Damping Values for Seismic Design of Nuclear Power Plants. It considers the potential benefits and costs to NRC staff and stakeholders. It does not consider the cost of implementation by existing licensees since that was covered by the Regulatory Analysis done for the rule(s) upon which the RG is based.
- 2. Statement of the Problem The NRC published Revision 1 of RG 1.61 in March 2007 to provide acceptable damping values for use in the seismic response analysis of Seismic Category I nuclear power plant structures, systems, and components (SSCs) in accordance with General Design Criterion 2, Design Bases for Protection Against Natural Phenomena, of Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50. Since the issuance of Revision 1 of RG 1.61, updated criteria related to the concrete properties and damping values for use in the development of in-structure response spectra have become available. Additionally, new criteria for new construction technologies have been developed. The NRC staff is considering revising RG 1.61 to address the updated and new damping criteria for use in seismic analysis and design of nuclear power plants structures.
- 3. Objective The objective of this regulatory action is to assess the need to update NRC guidance to applicants on updated damping values that the NRC staff finds acceptable for use in the seismic response analysis of seismic Category I nuclear power plant SSCs.
- 4. Identification and Analysis of Alternative Approaches The NRC staff considered the following alternative approaches:
- 1. Do not revise Regulatory Guide 1.61
- 2. Withdraw Regulatory Guide 1.61
- 3. Revise Regulatory Guide 1.61 Alternative 1: Do Not Revise Regulatory Guide 1.61 Under this alternative, the NRC would not revise or issue additional guidance, and the current guidance would be retained. If the NRC does not take action, then there would not be any changes in costs or benefit to the public and NRC. This alternative is considered the no-
action alternative and provides a baseline condition from which any other alternatives will be assessed. However, the no-action alternative would not address updated criteria related to the concrete properties and damping values for use in the development of in-structure response spectra that have become available since 2007.
Alternative 2: Withdraw Regulatory Guide 1.61 Under this alternative, the NRC would withdraw this regulatory guide. This would eliminate the only readily available guidance for applicants on damping values that the NRC staff finds acceptable for use in the seismic response analysis of seismic Category I nuclear power plant SSCs. Although this alternative would be less costly than revising the guide to address identified issues, it would leave stakeholders without guidance to address seismic design requirements found in 10 CFR Part 50, Appendix A, General Design Criterion 2, and Appendix S, Earthquake Engineering Criteria for Nuclear Power Plants, and 10 CFR Part 100, Appendix A, Seismic and Geologic Siting Criteria for Nuclear Power Plants.
Alternative 3: Revise Regulatory Guide 1.61 Under this alternative, the NRC would revise Regulatory Guide 1.61. This revision would address the problems identified above regarding the use of updated damping criteria for seismic analysis. By doing so, the NRC would ensure that the RG guidance available in this area is current and accurately reflects the staffs position.
The impact to the NRC would be the costs associated with preparing and issuing the regulatory guide revision. The impact to the stakeholders would be the voluntary costs associated with reviewing and providing comments to the NRC during the public comment period. The value to NRC staff and applicants would be the benefits associated with enhanced efficiency and effectiveness in using common guidance documents as the technical basis for license applications and other interactions between the NRC and its regulated entities.
- 5. Comparison of Alternatives The NRC compared the alternatives against each other with respect to safety and the NRCs and applicants resources.
With respect to safety, Alternatives 1 and 2 do not signify unsafe results since applicants would adopt methods that would be evaluated by NRC staff on a case-specific basis to establish its reasonable assurance of adequate protection of the public health and safety finding.
Alternative 3 would be superior to Alternatives 1 and 2 in that the NRC would issue a revised RG to include, where appropriate, updated damping criteria, thereby maintaining and potentially enhancing safety, improving clarity, and increasing uniformity in application reviews.
With respect to NRC resources, Alternative 3 represents the greatest initial cost to the NRC, which is attributable to the costs associated with preparing and issuing the RG. However, over the lifetime of the RG, the NRC staff estimates that the overall NRC cost of Alternative 3 is less than the overall cost of Alternative 1 due to the reduction in staff resources and schedule impacts associated with application reviews and requests for additional information (RAI) procedures. Alternative 2 is potentially the most expensive alternative for the NRC and applicants because, in the absence of NRC guidance, applicants would lack methods that the NRC staff has already approved for meeting a given set of regulations. In this case, applicants would need to develop their own methods for damping criteria and demonstrate their Page 2
effectiveness to the NRC. The NRC staff would be burdened by reviewing alternative methods, and this may result in issuing multiple RAIs to applicants that would in turn increase the review burden on staff and might impact schedules.
With respect to applicants resources, Alternative 3 results in the least cost when compared to Alternatives 1 and 2. Having a revised RG should reduce the need for RAIs and therefore the need for applicants to perform additional analyses to address them. Accordingly, costs to applicants associated with these additional activities are estimated to be lower with Alternative 3 than Alternative 1. Alternative 2 would be the most expensive alternative because eliminating the RG would require applicants to develop their own methods for damping criteria and demonstrate their effectiveness to the NRC, thereby increasing costs for applicants.
- 6. Decision Rationale Based on this regulatory analysis, the NRC staff concludes that revision of Regulatory Guide 1.61 is warranted. The action will address the problems identified above regarding the use of updated damping criteria for seismic analysis. It could also lead to cost savings for the industry, especially with regard to an applicants ability to prepare submittals to the NRC. An updated guide would potentially reduce staff review time and the need for requests for additional information, thus reducing costs to applicants and the NRC. The cost to the NRC in revising the RG and to applicants in adapting to a revised RG are deemed to be less than the benefits accrued by reducing the need for RAIs.
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