ML103481146
| ML103481146 | |
| Person / Time | |
|---|---|
| Issue date: | 06/28/2011 |
| From: | Correia R NRC/RES/DRA |
| To: | Bradley B Nuclear Energy Institute |
| Drouin, Mary RES/DRA 301-251-7574 | |
| References | |
| RG-1.200 | |
| Download: ML103481146 (4) | |
Text
June 28, 2011 Mr. Biff Bradley, Director Risk Assessment Nuclear Generation Division Nuclear Energy Institute 1776 I Street, Suite 400 Washington DC 20006
Dear Mr. Bradley:
In this past year, in various forums, comments and concerns with regard to the U.S. Nuclear Regulatory Commission (NRC) expectations on Probabilistic Risk Analysis (PRA) technical acceptability (as it is related to risk-informed activities) have been brought to our attention.
These comments and concerns are noted in your letters of March 3, 2010, and May 20, 2010, titled Draft Industry Strategy Paper for Regulatory Guide 1.200 Revision 2 Implementation (ML100640558) and NRC March 12th Meeting Regarding Future Expansion of Regulatory Guide 1.200 (ML101440329), respectively, and have also been discussed in various public meetings (e.g., March 19, 2010; June 3, 2010; October 13, 2010; January 6, 2011; May 18, 2011) on risk-informed activities.
Generally, the comments and concerns have included the following:
Considerable challenges remain for implementation of Revision 2 of Regulatory Guide (RG) 1.200, and insufficient time was provided to address these challenges.
The staff has increased regulatory expectations with regard to PRA technical acceptability in support of risk-informed applications for operating reactors.
The staffs plans for expansion of RG 1.200 do not properly reflected the regulatory requirements of 10 CFR 50.71(h) for new reactors, and further expansion should be limited until well after the first new plants are operating.
To achieve stable and mature implementation of new PRA standards, the standards should be piloted before they are finalized and endorsed by the staff.
The staff position has been that the confidence in the information derived from a PRA is an important issue and that accuracy of the technical content must be sufficient to justify the specific results and insights that are used to support the regulatory decision under consideration. This position is articulated in several NRC documents, particularly in RG 1.200.
CONTACT:
Mary Drouin, RES/DRA 301-251-7574
NRC has and will continue to implement this position. For example, transition to the new risk-informed fire protection program relies on PRA, and therefore, needs an appropriately capable PRA that may differ from a PRA that would support a temporary change to an allowed outage time for a low risk component.
Moreover, in anticipation of risk-informed applications for new reactors, understanding NRCs PRA expectations prior to development of the licensees site-specific, plant-specific PRA is a significant benefit. A PRA standard endorsed by NRC clearly communicates these expectations and helps in achieving regulatory stability.
Risk-informed activities have been part of the NRC regulatory structure for over 20 years. Risk assessments or applications of parts of PRA technology provide a substantial basis for these and numerous other risk-informed initiatives and applications. In light of this and a 30-year PRA experience, PRA technology is mature and standards have been published and endorsed without pilot studies. However, pilots have a role, and that role is in the implementation of the standard to ensure a common and clear understanding of the standard. The pilots that were conducted for the Level 1/LERF PRA standard for internal events and internal flood are a good demonstration. The results from the pilots provided insights where certain language was unclear or ambiguous. In this regard, we will continue to support pilot applications, and we encourage industry to submit requests for pilots.
Regarding the PRA standard, it is essential that the standard is written at the what to do level.
The PRA standard should clearly and succinctly state what is required for a base PRA; it should not provide guidance (e.g., methods and data) for how to construct a PRA model. The technology is sufficiently mature for the standard to address the various hazards and operating conditions for what constitutes an acceptable base PRA for all risk levels and for both operating and pre-operational reactors. Moreover, like all other technologies, PRA technology also will continue to evolve and improve as new knowledge and experience is gained. However, that does not mean that the methodology should not be used today and must wait years for a study before a standard can be developed. This position is further confirmed by the Advisory Committee on Reactor Safeguards as noted in their February 17, 2011, letter (ML110460631) where they state that Elements of methods, modeling techniques, and data for the analyses of internal initiating events continue to evolve, 30 years after performance of the first full-scope plant-specific PRAs. It is likely that a similar evolution of fire analysis methods and data will continue through short term (1-4 years) and longer-term research programs. However, the often-cited concerns regarding additional needed research should not preclude use of the fire PRA models for rational decision making. Consequently, improvements to the methodology should not affect the writing of the standard. Methodology and data issues should be addressed in supporting documents whether developed by NRC or industry. Example of such supporting documents include NUREG-1855 (Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decision Making), NUREG/CR-6595 (An Approach for Estimating the Frequencies of Various Containment Failure Modes and Bypass Events), NUREG/CR-6823 (Handbook of Parameter Estimation for Probabilistic Risk Assessment), and NUREG/CR-6850 (EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities). With this approach, the PRA standard remains unchanged.
The staff position on PRA technical acceptability (as defined in RG 1.200) is consistent with the Commissions PRA Policy Statement. Moreover, as part of the policy statement, the Commission noted that PRA applications should be implemented in a consistent and predictable
manner that promotes regulatory stability and efficiency. The PRA standards play a critical role in this endeavor; however, there are other equally important elements that promote regulatory stability and efficiency. These other key elements include, for example, application-specific RGs (e.g., RG 1.174, RG 1.177, RG 1.178 and RG 1.200) supporting technical guidance reports (e.g., NUREGs, industry technical documents); and peer review guidance. Consequently, to achieve stability and efficiency, it is important to understand how each of the elements work together, such that both NRC and industry can properly prioritize and focus resources.
We have initiated an effort to determine how best to address standards and other needed guidance for the various risk-informed activities. This effort will address both operating and new reactors. We also plan to interact closely with all stakeholders on this effort. The goal is to provide the agency with the necessary information to better prioritize activities so that we can ensure that we (both NRC and stakeholders) can appropriately focus our resources. Moreover, it is not always necessary that NRC take the lead in evaluating and resolving each issue. There are times that resolution should be undertaken for example, by industry or under a cooperative agreement. Finally, efforts will not be limited to, and may not even emphasize new standards.
Efforts to clarify and improve the consistency of existing standards, provide up to date technical guidance and to pilot the standards and guidance should be prioritized to make sure any expenditure of resources improves the industries risk-informed activities. However, there are standards efforts underway that have a high priority which need to be completed. These efforts include addressing the concerns with Addendum B of the ASME/ANS PRA Standard (NRC comments are being forwarded to ASME and American Nuclear Standards Institute as part of their public review and comment process), and issuing the standard for new advanced light water reactors and for low power and shutdown conditions.
Clear and continuous communication between industry, NRC, and other stakeholders is the most effective and efficient means of addressing issues, and we will continue to engage and interact as appropriate. If you have any questions, please contact Mary Drouin at (301) 251-7574.
Sincerely,
/RA/
Richard P. Correia, Director Division of Risk Analysis Office of Nuclear Regulatory Research
ML103481146 OFFICE RES/DRA/PRB Tech Editor RES/DRA/PRB NRO/DSRA NRR/DRA RES/DRA NAME M. Drouin J. Zabel (via email)
G. DeMoss C. Ader (via email)
M. Cheok R. Correia DATE 6/16/11 4/28/11 5/5/11 06/24/11 06/27/11 06/27/11