ML16358A156
| ML16358A156 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/2017 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Shared Package | |
| ML16358A194 | List: |
| References | |
| DG-1285 RG 1.174, Rev 3 | |
| Download: ML16358A156 (3) | |
Text
Template Revised October 18, 2012 REGULATORY ANALYSIS DRAFT REGULATORY GUIDE DG-1285 AN APPROACH FOR USING PROBABILISTIC RISK ASSESSMENT IN RISK-INFORMED DECISIONS ON PLANT-SPECIFIC CHANGES TO THE LICENSING BASIS (Proposed Revision 3 of Regulatory Guide 1.174, dated May 2011)
- 1.
Statement of the Problem The U.S. Nuclear Regulatory Commission (NRC) is considering revising Regulatory Guide (RG) 1.174, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis. Revision 3 of RG 1.174 would use precise language to assure that users interpret and implement the defense-in-depth philosophy consistently. The Commission originally directed staff to perform this revision in SRM-SECY-11-0014, Staff Requirements - SECY-11-0014 - Use of Containment Accident Pressure in Analyzing Emergency Core Cooling System and Containment Heat Removal System Pump Performance in Postulated Accidents, dated March 2011. Other changes include the introduction of language related to the transitioning from large release frequency and conditional containment failure probability to core damage frequency and large early release frequency for new reactors; introduction of language related to the containment performance expectations for new reactors; and clarification to modifications related to guidance on the treatment of uncertainty, combining risk results, and the nature of the acceptance guideline boundaries.
The NRC published Revision 2 of RG 1.174 in May 2011. Revision 2 provides a general discussion of the NRC defense-in-depth philosophy and defines a set of seven elements that are used to evaluate whether proposed risk-informed licensing basis changes maintain defense-in-depth. The defense-in-depth guidance in Revision 2 to RG 1.174 is not entirely clear and can be misinterpreted. Users can also implement the guidance inconsistently.
The NRC staff initiated the effort to develop Revision 3 of RG 1.174 in 2011. In May 2012, staff made available a proposed draft of the revision (published as Draft Regulatory Guide DG-1285) for public review and comment. At the time, the staff was already engaged in efforts to address issues related to defense-in-depth under Near-Term Task Force Recommendation 1 and the Risk-Management Regulatory Framework. Because of these competing priorities, the agency postponed the effort to develop Revision 3 of RG 1.174. In March 2016, the Commission directed the staff to expeditiously complete Revision 3 to RG 1.174 to improve the clarity of the guidance (see SRM-SECY-15-0168, Staff Requirements - SECY-15-0168 -
Recommendations on Issues Related to Implementation of a Risk Management Regulatory Framework). In response to this Commission direction, the staff reinitiated the effort to develop Revision 3 of RG 1.174.
- 2.
Objective The objective of this regulatory action is to 1) revise the guidance on defense-in-depth using precise language to assure consistent interpretation and implementation of the NRC defense-in-depth philosophy, 2) incorporate changes related to the transitioning from large release frequency and conditional containment failure probability to large early release frequency for new reactors, 3) incorporate changes related to new language on containment performance expectations for new reactors, 4) incorporate changes related to guidance on the
Page 2 treatment of uncertainty, combining risk results, the nature of the acceptance guideline boundaries, and 5) incorporate language on defense-in-depth from other NRC guidance documents.
- 3.
Alternative Approaches The NRC staff considered the following alternative approaches:
- 1. Do not revise RG 1.174
- 2. Withdraw RG 1.174
- 3. Revise RG 1.174 Alternative 1: Do Not Revise RG 1.174 Under this alternative, the NRC would not revise RG 1.174 and would retain the current version of the regulatory guide. This alternative is considered the no-action alternative and provides a baseline condition from which the staff will assess any other alternatives. The no-action alternative results in no additional costs to the public, licensees, or the NRC. However, this alternative also means no potential new benefits to the public, licensees, or the NRC and the identified concerns with the current version of the regulatory guide would not be addressed.
The NRC staff would continue to review each application on a case-by-case basis. This could result in inconsistent interpretation and application of the guidance.
Alternative 2: Withdraw RG 1.174 Under this alternative the NRC would withdraw RG 1.174. This would eliminate the problems identified above regarding the regulatory guide. It would also eliminate the only readily available description of the methods the NRC staff considers acceptable for demonstrating compliance with 10 CFR 50.90, Application for amendment of license, construction permit, or early site permit, and 10 CFR 50.92, Issuance of amendment, as related to applications involving the use of probabilistic risk assessment in risk-informed decisions on plant-specific changes to the licensing basis. Withdrawing the regulatory guide would be less costly than revising it; however, it would also mean that users would not have access to important regulatory guidance.
Alternative 3: Revise RG 1.174 Under this alternative, the NRC would revise Regulatory Guide 1.174. This revision would incorporate the latest information in the defense-in-depth guidance, supporting guidance, and review practices. Revising RG 1.174 would help ensure that NRC staff, the industry, and the public have access to the most current guidance available that accurately reflects the agencys position.
The impact to the NRC would be the costs associated with preparing and issuing the regulatory guide revision. The impact to the public would be the voluntary costs associated with reviewing and providing comments to NRC during the public comment period. The benefit to NRC staff and its applicants would be enhanced efficiency and effectiveness in using a common guidance document as the technical basis for license applications and other interactions between the NRC and its regulated entities.
Page 3 Conclusion Based on this regulatory analysis, the NRC staff concludes that revision of Regulatory Guide 1.174 is warranted. The action will enhance the efficiency and effectiveness of related regulatory reviews. It could also lead to cost savings for the industry, especially with regard to applications that impact defense-in-depth.