ML070470306
| ML070470306 | |
| Person / Time | |
|---|---|
| Site: | WM-00011 |
| Issue date: | 02/28/2007 |
| From: | Jennifer Davis NRC/NMSS/DHLWRS |
| To: | Mccullum R Nuclear Energy Institute |
| References | |
| Download: ML070470306 (7) | |
Text
February 28, 2007 Rodney McCullum Director, Used Fuel Projects Nuclear Energy Institute 1776 I Street, NW, Suite 400 Washington, DC 20006-3708
SUBJECT:
U.S. NUCLEAR REGULATORY COMMISSION RESPONSES TO NUCLEAR ENERGY INSTITUTE AND ELECTRIC POWER RESEARCH INSTITUTE TECHNICAL COMMENTS ON STAFF GUIDANCE
Dear Mr. McCullum:
The purpose of this letter is to summarize the discussions between the U. S. Nuclear Regulatory Commission (NRC) staff and Nuclear Energy Institute (NEI) and Electric Power Research Institute (EPRI), concerning technical comments by NEI and its consultant EPRI, on the NRC staff guidance document (Ref. 1). NEI/EPRI presented these technical comments, to the NRC Advisory Committee on Nuclear Waste, at the December 2006 meeting in Rockville, MD (Ref. 2). NRC staff also discussed these technical comments at a public meeting, with NEI/EPRI on January 30, 2007 (Ref. 3).
NRC appreciates NEI/EPRIs efforts in reviewing and providing comments on the Interim Staff Guidance 01 (ISG-01) methodology, and meeting with the staff to provide additional clarification of the comments. As stated at the public meeting (Ref. 3), NRC has considered the NEI/EPRI comments to determine the need for a revision to ISG-01. We have concluded that ISG-01 provides clear guidance to the staff, and does not need revision at this time.
As we discussed in the meeting (Ref. 3), NRC will continue to review the implementation of the ISG-01 methodology, and revise the guidance, if necessary. If NEI or its consultants have performed analyses relevant to the ISG-01 methodology, we would appreciate your sharing that information with us.
The following summarizes our responses to your comments on ISG-01 methodology:
- 1. Part 63 is a risk-informed and performance-based regulation, in which safety is demonstrated through a preclosure safety analysis (PCSA). Unlike other NRC regulations, including other NRC performance-based regulations, the PCSA in Part 63 is based on evaluation of event sequences, not on an individual structure, system, or component (SSC),
as a way to demonstrate compliance with performance objectives.
As a result, the performance-based requirements in Part 63 necessarily rely on a demonstration of compliance that is different than is used for reactor licensing. Specifically, in reactor regulations, seismic design or performance requirements are directly related to the characteristics of a safe shutdown earthquake (10 CFR Part 50, Appendix S), which is
R. McCullum also used as the design basis for each of the safety-related SSCs. In contrast, Part 63 does not specify seismic nor other design bases for SSCs, but instead requires consideration of credible event sequences and their potential consequences. Thus, performance-based requirements in Part 63 necessarily result in a different type of metric for compliance demonstration (i.e., design bases resulting from DOEs safety strategy and PCSA analyses).
- 2. The ISG-01 staff guidance provides one method for verifying compliance with Part 63, for seismically initiated event sequences. It is not expected that conformance with this guidance will result in more stringent seismic design requirements for Yucca Mountain surface facilities than for reactors.
A. In addition to the seismic hazard, the surface facilities at Yucca Mountain, NV, will be designed to natural hazards that could affect safety, including high winds, tornadoes, and floods. In addition, designs will also include shielding and confinement requirements, any or all of which may govern the final design.
B. It is generally expected that an event sequence will have more than one important to safety (ITS) SSC; thus, even though an individual ITS SSC may not yield failure probabilities less than 1 in 10,000 during a preclosure period, the combination of the failure probabilities of several of the ITS SSCs in the event sequence will lead that event sequence to below the Category 2 limit, as illustrated in the example calculation provided in ISG-01, Appendix B.
C. As discussed in the ISG, the U.S. Department of Energy (DOE) can choose alternative Limit States [e.g., American Society of Civil Engineers (ASCE) standard ASCE/SEI 43-05 Limit State A - Large Permanent Distortion (Short of Collapse), versus Limit State D - Essentially Elastic], for calculating the fragilities of ITS SSCs, if sufficient technical basis is provided. In contrast, performance of SSCs for reactors is evaluated at Level D, which is the most conservative.
D. Part 63 allows DOE to comply with regulations by demonstrating that the consequences meet the performance objectives specified in 10 CFR 63.111. Reactor regulations do not allow this alternative demonstration of compliance.
- 3. ISG-01 provides NRC staff with an example methodology, to review seismically initiated event sequences, in the context of the PCSA. As we discussed at the January 30, 2007, meeting, PCSA uses a top-down approach to identify ITS SSCs, by a systematic analysis of hazards at the geologic repository operations area, including a comprehensive identification of potential events, resulting event sequences, and potential consequences. Thus, the ISG-01 methodology is facility-based, and not component/sequence-based.
- 4. Evaluation of failure probabilities of SSCs, considering fragilities, is limited to ITS SSCs, for Category 2 event sequences, only, and thus is not resource-intensive.
ISG-01 does not require evaluation of all SSCs in the facility. Only those SSCs, in the Category 2 event sequences, that are relied on to prevent or mitigate potential dose consequences exceeding the Part 63 performance objectives, will be evaluated. As a first step, a single ITS SSC may be considered, instead of all SSCs in an event sequence. If the
R. McCullum performance of the ITS SSC does not meet the compliance requirements, then the fragilities of other components in the event sequences can be combined.
- 5. The ISG-01 methodology is staff guidance consistent with Part 63, and does not impose any standards, or alternative-design requirements, on DOE. The rule provides DOE with flexibility to choose any methods to comply with the performance objectives for event sequences, based on frequency evaluation, or dose-consequence calculations. For compliance with Part 63, based on frequency evaluation, DOE may optimize their PCSA, by choosing to rely on specific SSCs, for safety, that afford it the greatest overall benefit in performance, design, cost, and function.
- 6. The ISG-01 scope does not include:
A. An iterative design process that DOE is expected to have gone through, during the PCSA, to arrive at the final design, submitted in the license application; B. Potential mitigative actions, risk-reduction strategies, and use of non-seismic factors, that DOE may consider, in PCSA, with appropriate justification; C. Review methodologies for consequence analysis; and D. DOEs method for the development of the probabilistic seismic hazard assessment and the site-specific seismic hazard for Yucca Mountain.
- 7. The essential element of the methodology (i.e., convolving the seismic hazard and fragility curve to determine failure probability of an ITS SSC), is state-of-the art for evaluating performance of an SSC, based on the consensus industry standard ASCE/SEI 43-05, developed by ASCE. For example, for the mixed-oxide fuel fabrication facility at the Savannah River Site in South Carolina, a methodology similar to the one outlined in the ISG-01 was used to demonstrate performance of selected SSCs beyond seismic design levels.
For an event sequence, where more than one SSC is relied on to meet the performance objective, the ISG-01 uses the same approach to calculate event sequence frequency. For this case, the combined fragility of the multiple SSCs is convolved with the seismic hazard curve, instead of the fragility curve for a single SSC.
- 8. Uncertainty (in the tails of distributions for the seismic hazard curve or for ITS SSC fragility curves), should be supported by technical bases, within the context of finding of reasonable assurance.
- 9. Part 63 requires screening criteria for categorization of event sequences (e.g., Category 2 event sequences as those that have at least one chance in 10,000 of occurring during preclosure period). ISG-01 does not impose such screening criteria.
Again, NRC appreciates NEI/EPRIs efforts in providing comments on the ISG-01 methodology, and discussing them during the January 30, 2007, public meeting. We hope that the discussions at the January 2007 public meeting, summarized here, have resolved technical
R. McCullum concerns and clarified your understanding of the risk-informed performance-based approach developed in ISG-01 for the seismic hazard.
If you have any questions about this letter, please contact Mahendra Shah, of my staff, at (301) 415-8537, or by e-mail, at mjs3@nrc.gov.
Sincerely Yours,
/RA/
Jack R. Davis, Deputy Director Division of High-Level Waste Repository Safety Office of Nuclear Material Safety and Safeguards
References:
- 1. U.S. Nuclear Regulatory Commission, Interim Staff Guidance, HLWRS-ISG-01, Review Methodology for Seismically Initiated Event Sequences, September 29, 2006, issued by NRC, Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste Repository Safety.
- 2. Nuclear Energy Institute/Electric Power Research Institute, Presentation to the NRC Advisory Committee on Nuclear Wastes 175th Meeting, on December 12, 2006.
- 3. U.S. Nuclear Regulatory Commission, Public Meeting between NRC staff and Nuclear Energy Institute and its consultant Electric Power Research Institute representatives, on January 30, 2007.
cc: See attached list.
Letter to Rodney McCullum from Jack Davis dated: February 28, 2007 cc:
A. Kalt, Churchill County, NV A. Elzeftawy, Las Vegas Paiute Tribe R. Massey, Churchill/Lander County, NV J. Treichel, Nuclear Waste Task Force I. Navis, Clark County, NV W. Briggs, Ross, Dixon & Bell E. von Tiesenhausen, Clark County, NV R. Murray, DOE/OCRWM G. McCorkell, Esmeralda County, NV G. Runkle, DOE/Washington, D.C.
R. Damele, Eureka County, NV S. Bokhari, DOE/RW L. Marshall, Eureka County, NV S. Gomberg, DOE/Washington, D.C.
A. Johnson, Eureka County, NV D. Curran, Harmon, Curran, Spielberg &
Eisenberg, L.L.P.
S. Schubert, Sen. Reids Office R. Dyer, DOE/OCRWM M. Yarbro, Lander County, NV J. Espinoza, GAO J. Donnell, DOE/OCRWM A. Gil, DOE/OCRWM M. Baughman, Lincoln County, NV W. Boyle, DOE/OCRWM L. Mathias, Mineral County, NV M. Ulshafer, DOE/OCRWM J. Saldarini, BSC S.A. Wade, DOE/OCRWM M. Henderson, Cong. J. Gibbons Office C. Hanlon, DOE/OCRWM D. Swanson, Nye County, NV T. Gunter, DOE/OCRWM M. Simon, White Pine County, NV A. Benson, DOE/OCRWM E. Sproat, DOE/OCRWM N. Hunemuller, DOE/OCRWM D. Cornwall, NV Congressional Delegation P. Harrington, OPM&E T. Story, NV Congressional Delegation M. Mason, BSC R. Herbert, NV Sen. Reids Office S. Cereghino, BSC M. Murphy, Nye County, NV B. Gattoni, Burns & Roe R. Lambe, NV Congressional Delegation E. Mueller, Esmeralda County, NV K. Kirkeby, NV Congressional Delegation J. Gervers, Clark County, NV R. Loux, State of NV D. Beckman, BSC/B&A S. Frishman, State of NV J. Raleigh, SNL S. Lynch, State of NV J. Kennedy, Timbisha Shoshone Tribe P. Guinan, Legislative Counsel Bureau B. Durham, Timbisha Shoshone Tribe R. Clark, EPA R. Arnold, Pahrump Paiute Tribe R. Anderson, NEI J. Birchim, Yomba Shoshone Tribe
cc: (Continued)
R. McCullum, NEI R. Holden, NCAI S. Kraft, NEI C. Meyers, Moapa Paiute Indian Tribe J. Kessler, EPRI C. Dahlberg, Fort Independence Indian Tribe D. Duncan, USGS D. Vega, Bishop Paiute Indian Tribe K. Skipper, USGS Egan, Fitzpatrick, Malsch, PLLC W. Booth, Engineering Svcs, LTD J. Leeds, Las Vegas Indian Center C. Marden, BNFL Inc. J. C. Saulque, Benton Paiute Indian Tribe J. Bacoch, Big Pine Paiute Tribe of the Owens C. Bradley, Kaibab Band of Southern Paiutes Valley P. Thompson, Duckwater Shoshone Tribe R. Joseph, Lone Pine Paiute-Shoshone Tribe T. Kingham, GAO L. Tom, Paiute Indian Tribes of Utah D. Feehan, GAO E. Smith, Chemehuevi Indian Tribe E. Hiruo, Platts Nuclear Publications D. Buckner, Ely Shoshone Tribe G. Hernandez, Las Vegas Paiute Tribe V. Guzman, Walker River Paiute K. Finfrock, NV Congressional Delegation D. Eddy, Jr., Colorado River Indian Tribes P. Johnson, Citizen Alert M. Boyd, Public Citizen M. Williams, DOE/OCRWM J. Wells, Western Shoshone National Council J. Williams, DOE/Washington, DC D. Crawford, Inter-Tribal Council of NV A. Robinson, Robinson-Seidler I. Zabarte, Western Shoshone National Council M. Plaster, City of Las Vegas S. Devlin S. Rayborn, Sen. Reids Office G. Hudlow L. Lehman, T-REG, Inc. D. Irwin, Hunton & Williams B.J. Garrick, NWTRB P. Golan, DOE T. Feigenbaum, BSC M. Rice, Lincoln County, NV M. Urie, DOE G. Hellstrom, DOE J. Brandt, Lander County S. Joya, Sen. Ensigns Office R. Holland, Inyo County M. Gaffney, Inyo County B. Sagar, CNWRA L. Desell, RW/DOE V. Trebules, RW/DOE P. Nair, SNL R. Warther, DOE/OCRWM B. Neuman, Carter Ledyard & Milburn L.L.P.
Connie Simkins, Lincoln County E. Bonano, SNL S.A. Orrell, SNL
R. McCullum concerns and clarified your understanding of the risk-informed performance-based approach developed in ISG-01 for the seismic hazard.
If you have any questions about this letter, please contact Mahendra Shah, of my staff, at (301) 415-8537, or by e-mail, at mjs3@nrc.gov.
Sincerely Yours,
/RA/
Jack R. Davis, Deputy Director Division of High-Level Waste Repository Safety Office of Nuclear Material Safety and Safeguards
References:
- 1. U.S. Nuclear Regulatory Commission, Interim Staff Guidance, HLWRS-ISG-01, Review Methodology for Seismically Initiated Event Sequences, September 29, 2006, issued by NRC, Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste Repository Safety.
- 2. Nuclear Energy Institute/Electric Power Research Institute, Presentation to the NRC Advisory Committee on Nuclear Wastes 175th Meeting, on December 12, 2006.
- 3. U.S. Nuclear Regulatory Commission, Public Meeting between NRC staff and Nuclear Energy Institute and its consultant Electric Power Research Institute representatives, on January 30, 2007.
cc: See attached list.
Distribution:
HLWRS r/f HLWRS Staff ML070470306 OFC HLWRS HLWRS HLWRS HLWRS NAME MShah SRohrer RJohnson SWhaley DATE 2/20/07 2/28/07 2/16/07 2/16/07 OFC HLWRS OGC TechEd HLWRS NAME TMcCartin MZobler EKraus JDavis DATE 2/21/07 2/26/07 2/13/07 2/27/07 OFFICIAL RECORDS COPY