ML080880012

Request for Additional Information Related to LAR to Revise TS 3.7.8, Essential Service Water System, and TS 3.8.1, AC Sources - Operating, for One-time Completion Time Extension Re Underground Piping

ML080880012
Person / Time
Site:	Callaway
Issue date:	03/31/2008
From:	Thadani M NRC/NRR/ADRO/DORL/LPLIV
To:	Naslund C Union Electric Co
Thadani, M C, NRR/DORL/LP4, 415-1476
References
TAC MD7252
Download: ML080880012 (7)

Text

March 31, 2008 Mr. Charles D. Naslund Senior Vice President and Chief Nuclear Officer Union Electric Company Post Office Box 620 Fulton, MO 65251

SUBJECT:

CALLAWAY PLANT, UNIT 1 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO LICENSE AMENDMENT REQUEST FOR ONE-TIME EXTENSION OF COMPLETION TIME FOR INOPERABLE ESSENTIAL SERVICE WATER SYSTEM (TAC NO. MD7252)

Dear Mr. Naslund:

By application dated October 31, 2007, as supplemented by letter dated February 21, 2008, Union Electric Company (the licensee) requested the U.S. Nuclear Regulatory Commission (NRC) staff approval of a one-time change to the Technical Specifications (TS) for its Callaway Plant.

The proposed change would revise the TS to extend the completion time (CT) associated with an inoperable Essential Cooling Water train from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days, applicable once per train, and to be implemented prior to December 31, 2008. The licensee also proposed to eliminate the second CT applicable to TS 3.8.1, Condition B in accordance with the NRC staff-approved TS Task Force (TSTF) traveler TSTF-439.

The NRC staff has reviewed the information provided in your submittal and determined that additional information is required in order to complete its review. Please provide a response to the enclosed questions by May 15, 2008, to facilitate the continuation of the review by the NRC staff. In the absence of your response by the requested date, the NRC staff may proceed to deny your request pursuant to Title 10 of the Code of Federal Regulations, Part 2, Section 108, for not responding to this request within the time specified by the NRC staff.

If there are any questions, please contact me at (301) 415-1476, or e-mail mct@nrc.gov.

Sincerely,

/RA/

Mohan C. Thadani, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-483

Enclosure:

As stated cc w/encl: See next page

ML (*) memo dated OFFICE NRR/LPL4/PM NRR/LPL4/LA DSS/APLA/BC NRR/LPL4/BC NAME MThadani, JBurkhardt MRubin (*) THiltz DATE 3/31/08 3/31/08 3/24/08 3/31/08 Callaway Plant, Unit 1 (November 2007) cc:

John ONeill, Esq. Mr. H. Floyd Gilzow Pillsbury Winthrop Shaw Pittman LLP Deputy Director for Policy 2300 N. Street, N.W. Department of Natural Resources Washington, D.C. 20037 P.O. Box 176 Jefferson City, MO 65102-0176 Mr. Tom Elwood, Supervising Engineer Regulatory Affairs and Licensing Mr. Rick A. Muench, President and CEO AmerenUE Wolf Creek Nuclear Operating Corporation P.O. Box 620 P.O. Box 411 Fulton, MO 65251 Burlington, KA 66839 Mr. Les H. Kanuckel, Manager Certrec Corporation Quality Assurance 4200 South Hulen, Suite 422 AmerenUE Fort Worth, TX 76109 P.O. Box 620 Fulton, MO 65251 Technical Services Branch Chief FEMA Region VII Mr. Luke Graessle, Manager 2323 Grand Boulevard, Suite 900 Regulatory Affairs Kansas City, MO 64108-2670 AmerenUE P.O. Box 620 Kathleen Logan Smith, Executive Director Fulton, MO 65251 and Kay Drey, Representative, Board of Mr. Scott Maglio Directors Assistant Manager, Regulatory Affairs Missouri Coalition for the Environment AmerenUE 6267 Delmar Blvd., Suite 2E P.O. Box 620 St. Louis, City, MO 63130 Fulton, MO 65251 Mr. Lee Fritz, Presiding Commissioner U.S. Nuclear Regulatory Commission Callaway County Courthouse Resident Inspector Office 10 East Fifth Street 8201 NRC Road Fulton, MO 65251 Steedman, MO 65077-1302 Mr. Keith G. Henke, Planner III Missouri Public Service Commission Division of Community and Public Health Governor Office Building Office of Emergency Coordination 200 Madison Street Missouri Department of Health and P.O. Box 360 Senior Services Jefferson City, MO 65102-0360 930 Wildwood Drive P.O. Box 570 Regional Administrator, Region IV Jefferson City, MO 65102 U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Mr. Scott Clardy, Director Arlington, TX 76011-4005 Section for Environmental Public Health Missouri Department of Health and Senior Services 930 Wildwood Drive P.O. Box 570 Jefferson City, MO 65102

P.O. Box 116 Director, Missouri State Emergency Jefferson City, MO 65102-0116 Management Agency

OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR ADDITIONAL INFORMATION RELATED TO ESSENTIAL SERVICE WATER UNION ELECTRIC COMPANY CALLAWAY PLANT DOCKET NO. 50-483 By application dated October 31, 2007, as supplemented by letter dated February 21, 2008, Union Electric Company (the licensee) requested the U.S. Nuclear Regulatory Commission (NRC) staff approval of a one-time change to the Technical Specifications (TS) for its Callaway Plant. The NRC staff has reviewed the information provided in your submittal and determined that additional information is required in order to complete its review. Please provide a response to the following request for additional information (RAI) questions by May 15, 2008, to facilitate the continuation of the review by the NRC staff:

1. The NRC staff asked for substantive justification that the known deficiencies in the probabilistic risk assessment (PRA) model, identified from peer reviews and identified to the NRC staff in the submittal, would not significantly impact the application. In response, to address the Scientech gap assessment against the American Society of Mechanical Engineers internal events standard, the licensee restated that it "believed" these gaps would not invalidate the risk insights for this application, then argued that since the existing PRA results were already greater than the Regulatory Guide 1.177 guidelines for permanent changes, the gaps would not result in any further significant increase in the risk.

Please submit specific information which qualitatively discusses the substance of the deficient items and adequately justifies that these deficiencies or gaps do not impact the risk results of this application.

2. The NRC staff asked for discussion and justification of the truncation level for this application. The licensee's response identified the use of pre-solved cutsets to generate the application risk results. The staff is concerned that the use of pre-solved cutsets for this application may not be adequate to obtain an accurate assessment of the configuration-specific risk level. Specifically, the service water unavailability and random failure probability, coincident with the unavailability or failure of the backup normal service water system (identified in other RAI responses as credited in the model),

represents a very unlikely failure mode, which may not appear in many cutsets above truncation. Regenerating the cutsets with the service water train out-of-service to reflect the actual configuration during the proposed extended completion time (CT) could result in many more cutsets generated above the nominal truncation level, resulting in an increase in the configuration-specific risk. This can be an especially significant problem if the nominal unavailability and random failure probability result in large numbers of cutsets just below the truncation level. In addition, initiating events, such as loss-of-service water, are more likely to occur when one of the two trains is

out-of-service. This frequency increase may not be reflected in the pre-solved cutsets, and, therefore, the risk contribution from such initiators would not be reflected in the results.

Please provide risk results which avoid this potential non-conservatism by regenerating cutsets for the specific configuration(s) expected as result of the changes requested and addressing the increased likelihood of the loss-of-service water initiating event.

3. The NRC staff requested the licensee to address initiating events not included in its risk assessment model, including fires, floods, seismic events, and other external events.

The licensee identified proposed compensatory measures, to include walkdowns of the operable service water train, fire and flood watches in rooms identified as risk important in the licensee's internal flooding, seismic margin, and fire protection evaluations, and evaluation of transient combustibles within 20 feet of the operable service water train.

The staff is unable to conclude that these sources of risk will not be potentially significant while the plant configuration has one service water header unavailable.

(a) With regard to seismic risk, there is no risk mitigation provided by the compensatory measure of walkdowns of rooms identified as risk-important in a seismic margins analysis. Please provide a summary of the relationship between the results of the seismic margins analyses which it identified in its response with the specific configuration of the plant when it is reliant upon a single service water header. The seismic ruggedness of the remaining operable service water system should be addressed to justify that a seismic event is not likely to cause damage to this system. The qualitative information should be adequate for the NRC staff to conclude that seismic risk is not significant for this application.

Otherwise, additional quantified estimates should be provided to characterize the risk impact.

(b) With regard to internal flooding, the NRC staff agrees that the compensatory measure of verifying the availability of flood mitigation equipment for the protected train is beneficial. However, the NRC staff needs to understand the significant contributors to internal flooding risk, how these could potentially impact the remaining operable protected train of equipment, or otherwise result in increased reliance upon that equipment, and either conclude that the risk of these scenarios is not significant or that compensatory measures are in place to mitigate these events. Please provide adequate qualitative information for the NRC staff to determine whether the internal flooding risk is not significant for this application. Otherwise, please provide additional quantified estimates enable the NRC staff to characterize the risk impact.

(c) Similar to internal fires, the compensatory measures identified for walkdowns and monitoring of transient combustibles is a benefit. The staff must understand the significant contributors to fire risk, how these could potentially impact the remaining operable protected train of equipment or otherwise result in increased reliance upon that equipment, and either conclude that the risk of these scenarios is not significant or that compensatory measures are in place to mitigate these events. Please provide adequate qualitative information for the NRC staff to determine whether the fire risk is not significant for this application.

Otherwise, provide additional quantified estimates to characterize the risk impact.

(d) Please discuss the impact of this proposed TS change on other external events (i.e., hazardous material leaks, transportation events, high winds and tornadoes, etc.). Although weather-related loss-of-offsite power was addressed (and credited in the risk analyses), there is no discussion of high winds with regard to any unique vulnerabilities during the time the service water header is out of service, the vulnerability of the backup normal service water system to high winds, or other discussion to characterize the site with regard to this source of risk. Other external events were not discussed at all.

4. The NRC staff previously requested the licensee to address sources of uncertainty in the risk analyses which may be significant for this application. In response, the licensee stated, without justification or basis, that the assumptions applied and the use of point estimates of mean values would not invalidate the risk analyses. For the specific areas identified by the NRC staff as examples of key assumptions, the licensee identified the methodologies used in the risk analyses, but did not provide any assessment as to the impact of uncertainties associated with these assumptions on the application.

The purpose of this RAI was to request the licensee to review the important PRA assumptions and elements of the model which are especially relevant to the risk of the plant configuration with one service water header unavailable, to characterize the impact of these uncertainties, and to develop and present its basis as to why these sources of uncertainty do not adversely impact the results of the risk analyses relevant to the NRC staff decision to accept a 14-day extended CT. Please provide a more specific technical justification for your conclusions that the uncertainties do not affect the risk analyses.

With regard specifically to equipment repair credit, please identify what equipment repairs are credited, the numerical value and basis for such credit, and the specific impact to the risk metrics for this application. (Note that the NRC staff position does not permit PRA credit for repair and restoration of any equipment subject to the extended CT to be used in the calculation of the risk metrics.)