ML070520195
| ML070520195 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 02/26/2007 |
| From: | Gratton C NRC/NRR/ADRO/DORL/LPLIII-2 |
| To: | Marshall M NRC/NRR/ADRO/DORL/LPLIII-2 |
| Gratton C, NRR, DORL, 415-1055 | |
| References | |
| TAC MD3855, TAC MD3856 | |
| Download: ML070520195 (4) | |
Text
February 26, 2007 MEMORANDUM TO:
Michael L. Marshall, Jr., Chief Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation FROM:
Christopher Gratton, Sr. Project Manager/RA Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUBJECT:
BYRON STATION, UNIT NOS. 1 AND 2 - FACSIMILE TRANSMISSION OF DRAFT REQUEST FOR ADDITIONAL INFORMATION (TAC NOS. MD3855 AND MD3856)
The Nuclear Regulatory Commission (NRC) staff transmitted the attached facsimile containing questions to Mr. Darin Benyak of the Exelon Generation Company, LLC (the licensee), on January 31, 2007. The questions supported a conference call with the licensee held on February 8, 2007, regarding the request for relief dated February 14, 2006, for Byron Station, Unit Nos. 1 and 2. The questions were regarding the licensees request to employ risk-informed selection and examination criteria for certain pressure retaining welds.
During the February 8, 2007, conference call, the NRC staff made the following changes to the draft request for additional information (RAI): eliminated questions 1(a), 4(b) and 4(c), and added a new part to question 4, which now reads:
(b) Please provide a summary of how the changes to the PRA are developed and reviewed.
The change to question 1 was made because the licensee clarified during the conference call, and the NRC staff concurred, that the text in the submittal indicated that the analysis steps in the RAI were, in fact, performed. The NRC staff decided that there is no need for a description about how the steps were performed because the submittal states that the approved methodology was followed, the methodology states that these steps should be performed as is done in the endorsed methodology, and the submittal did not identify any deviation in these steps. The purpose of questions 4(b) and 4(c) was to gain confidence in the licensee's PRA update methodology through the evaluation of specific changes that the licensee had made. In lieu of responding to the questions, the licensee will provide a copy of its PRA update procedure in response to the new RAI 4(b).
This memorandum and the attached questions do not convey or represent an NRC staff position regarding the licensees request.
Docket Nos. 50-454 and 50-455
Attachment:
Draft Request for Additional Information sent January 31, 2007
February 26, 2007 MEMORANDUM TO:
Michael L. Marshall, Jr., Chief Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation FROM:
Christopher Gratton, Sr. Project Manager/RA Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUBJECT:
BYRON STATION, UNIT NOS. 1 AND 2 - FACSIMILE TRANSMISSION OF DRAFT REQUEST FOR ADDITIONAL INFORMATION (TAC NOS. MD3855 AND MD3856)
The Nuclear Regulatory Commission (NRC) staff transmitted the attached facsimile containing questions to Mr. Darin Benyak of the Exelon Generation Company, LLC (the licensee), on January 31, 2007. The questions supported a conference call with the licensee held on February 8, 2007, regarding the request for relief dated February 14, 2006, for Byron Station, Unit Nos. 1 and 2. The questions were regarding the licensees request to employ risk-informed selection and examination criteria for certain pressure retaining welds.
During the February 8, 2007, conference call, the NRC staff made the following changes to the draft request for additional information (RAI): eliminated questions 1(a), 4(b) and 4(c), and added a new part to question 4, which now reads:
(b) Please provide a summary of how the changes to the PRA are developed and reviewed.
The change to question 1 was made because the licensee clarified during the conference call, and the NRC staff concurred, that the text in the submittal indicated that the analysis steps in the RAI were, in fact, performed. The NRC staff decided that there is no need for a description about how the steps were performed because the submittal states that the approved methodology was followed, the methodology states that these steps should be performed as is done in the endorsed methodology, and the submittal did not identify any deviation in these steps. The purpose of questions 4(b) and 4(c) was to gain confidence in the licensee's PRA update methodology through the evaluation of specific changes that the licensee had made. In lieu of responding to the questions, the licensee will provide a copy of its PRA update procedure in response to the new RAI 4(b).
This memorandum and the attached questions do not convey or represent an NRC staff position regarding the licensees request.
Docket Nos. 50-454 and 50-455
Attachment:
Draft Request for Additional Information sent January 31, 2007 DISTRIBUTION:
PUBLIC LPL3-2 R/F RidsNrrDorl RidsNrrPMCGratton RidsNrrLAEWhitt RidsAcrsAcnwMailCenter RidsOgcRp RidsRgn3MailCenter RidsNrrDorlDpr ADAMS Accession Number: ML070520195 NRR-106 OFFICE LPL3-2/PM LPL3-2/LA LPL3-2/BC (A)
NAME CGratton:mw EWhitt MMarshall DATE 2/23/2007 2/23/2007 2/26/2007 OFFICIAL RECORD COPY
DRAFT REQUEST FOR ADDITIONAL INFORMATION RISK-INFORMED (RI) INSERVICE INSPECTION (ISI) RELIEF REQUEST THIRD TEN-YEAR ISI PROGRAM RELIEF REQUEST I3R-02 EXELON GENERATION COMPANY, LLC BYRON STATION UNITS 1 AND 2 (BYRON)
DOCKET NOS. 50-454 AND 50-455 The following questions are risk-related. The Nuclear Regulatory Commission (NRC) staff is continuing its review of your application and additional questions related to other aspects of this review may be necessary:
1.
The last paragraph on page 3 of 5 of relief request I3R-02 states that, "[t]he Consequence Evaluation, Degradation Mechanism, Risk Ranking, and Element Selection steps encompass the complete living program process applied under the Byron RI-SI program.
a) Please provide a description of what you did to implement the above living RI-ISI program commitment in preparation for your request to extend this program into the third 10-year ISI interval. Your description should specify those portions of the RI-ISI program process steps that were re-performed (e.g., scope definition, segment definition, consequence evaluation, failure probability estimation, element selection, etc.), and/or explain and justify what was done in lieu of re-performing those steps not re-performed.
b) Are the inspection locations in the RI-ISI program that has been developed for the third interval the same locations as those in the program approved in the NRC staff's February 5, 2002, safety evaluation? If not, please summarize the changes to the program and what caused those changes.
2.
Paragraph 4 on page 3 of 5 of your I3R-02 submittal states, "the original risk impact assessment is not a necessary element of the implementing process and is not required to be continually updated." The change in risk acceptance guidelines must continue to be met as the facility, PRA, and the risk-informed program change over time. Please provide the risk impact of implementing the RI-ISI program proposed for the third interval instead of the American Society of Mechanical Engineers inspection program that was replaced by risk-informed inservice inspection. (The NRC staff has concluded that it is an unnecessary burden to develop a new ASME inspection program when transitioning to a newer edition of the ASME code for the sole purpose of estimating the risk impact of a RI-SI program)
Attachment 3.
According to your submittal dated November 17, 2000, and the NRC staffs safety evaluation dated February 5, 2002, the Byron probabilistic risk assessment (PRA) had not undergone a peer review prior to development of the second interval's RI-ISI program. Instead, the submittal states that you used the results of the peer review on the sister plant Braidwood Station, Units 1 and 2, to address potential PRA quality issues. Please indicate when the peer review was performed on the Byron PRA.
Please provide the A and B level facts and observations from the Byron PRA peer review and the resolution of each observation or an explanation about why resolving the observation is not expected to significantly affect the proposed RI-ISI program.
4.
Risk-informed applications should be developed using a technically adequate PRA that is based on the as-built, as-operated, and as-maintained plant. Please provide the following:
a) The revision name or number, date, and base core damage frequency (CDF) and large early release fraction (LERF) of the Byron PRA model used to perform the risk ranking of pipe segments and change in risk evaluation in preparation for the third 10-year ISI interval.
b) A summary description of the significant changes to the PRA model not reported as a resolution to A and B level facts and observations from the peer review reported in response to RAI question #3. A significant change is a change that affects the risk-ranking of pipe segments or the change in risk evaluation in a substantial manner.
c) A summary of how the significant changes to the PRA provided in response to RAI
- 4b were developed and reviewed.
5.
The newer versions of the ASME Code have reduced the exempted portions of Auxiliary Feedwater piping from nominal pipe size (NPS) 4 to NPS 11/2. This reduction in exempted piping has caused other licensees to add ASME Class 2 and/or Class 3 Auxiliary Feedwater piping to the scope of their RI-ISI programs, and to implement their chosen RI-ISI methodology to classify, risk-rank, and to select, as necessary, additional locations for the next ISI interval. Please describe how you treated this issue in your RI-ISI program for the third 10-year ISI interval when you updated your code of record from the 1989 edition to the 2001 edition with 2003 addenda.
To ensure the review of this relief request remains on schedule, the NRC staff requests that you respond to this request for additional information by February 16, 2007.