ML081330557
| ML081330557 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 06/27/2008 |
| From: | Russell Gibbs NRC/NRR/ADRO/DORL/LPLIII-2 |
| To: | Pardee C Exelon Generation Co |
| Wiebe, Joel NRR/DORL/LPL3-2, 415-6606 | |
| References | |
| RV-02C, RV-30E, RV-30F, TAC MD6682, TAC MD6683, TAC MD8150, TAC MD8151, TAC MD8241, TAC MD8242 | |
| Download: ML081330557 (8) | |
Text
June 27, 2008 Mr. Charles G. Pardee Senior Vice President and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
DRESDEN NUCLEAR POWER STATION UNITS 2 AND 3 - RELIEF REQUEST NO. RV-02C FROM 5-YEAR TEST INTERVAL FOR MAIN STEAM SAFETY VALVES (TAC NOS. MD8150 AND MD8151) AND QUAD CITIES NUCLEAR POWER STATION, UNITS 1 AND 2 - RELIEF REQUESTS NO. RV-30E AND RV-30F FROM 5-YEAR TEST INTERVAL FOR MAIN STEAM SAFETY VALVES (TAC NOS. MD6682, MD6683, MD8241, AND MD8242)
Dear Mr. Pardee:
By letter dated September 7, 2007, as supplemented by letter dated October 30, 2007, Exelon Generation Company, LLC (EGC, the licensee), submitted Relief Request (RR) No. RV-30E for Quad Cities Nuclear Power Station (QCNPS), Units 1 and 2. The licensee requested relief from the requirements of Title 10 of the Code of Federal Regulations, (10 CFR) Part 50, Section 55a, concerning a requirement in the American Society of Mechanical Engineers (ASME), Code for Operation and Maintenance of Nuclear Power Plants (OM Code). The RR involves a one-time extension to the ASME OM Code 5-year test interval for QCNPS, Unit 1 main steam safety valves (MSSVs) 1-0203-4C, 1-0203-4D, and 1-0203-4G and Unit 2 MSSVs 2-0203-4A, 2-0203-4C, 2-0203-4D, 2-0203-4G, and 2-0203-4H. By letter dated November 20, 2007, the Nuclear Regulatory Commission (NRC) granted relief for QCNPS, Unit 1 MSSV 1-0203-4D through May 2009, and for QCNPS, Unit 2 MSSV 2-0203-4A through March 2008. By letter dated March 6, 2008, the licensee withdrew RR-30E for QCNPS Unit 2 MSSVs 2-0203-4C, 2-0203-4D, 2-0203-4G, and 2-0203-4H because the valves were replaced during the March 2008, QCNPS, Unit 2 refueling outage. The licensee also stated that, when authorized, RR RV-30F (requested by the March 6, 2008, letter) would supercede the one-time RR RV-30E for Unit 1 MSSVs 1-0203-4C and 1-0203-4G because RR RV-30F would provide the necessary relief.
By letter dated February 8, 2008, as supplemented by letter dated April 18, 2008, EGC submitted RR No. RV-02C for Dresden Nuclear Power Station (DNPS), Units 2 and 3. The licensee requested relief from the requirements of 10 CFR 50.55a, concerning a requirement in the ASME OM Code. The RR involves an extension to the ASME OM Code 5-year test interval for all 16 DNPS MSSVs. EGC proposes a 6.5-year test interval as an alternative.
By letter dated March 6, 2008, as supplemented by letter dated April 18, 2008, EGC submitted RR No. RV-30F for QCNPS. The licensee requested relief from the requirements of 10 CFR 50.55a, concerning a requirement in the ASME OM Code. The RR involves an extension to the ASME OM Code 5-year test interval for all 16 QCNPS MSSVs. EGC proposes a 6.5-year test interval as an alternative.
The NRC staff has reviewed EGCs analyses in support of its requests for relief (RV-02C and RV-30F). The NRC staff has concluded that requiring compliance with the ASME OM Code 5-year test interval requirement for the above-mentioned valves would result in hardship because it would entail unnecessary personnel radiation exposure without a compensating increase in the level of quality and safety and that the proposed alternative provides reasonable assurance that the MSSVs are operationally ready.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the alternative 6.5-year test interval, requested by RR RV-02C, is authorized for DNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H and DNPS, Unit 3 MSSVs 3-0203-4A, 3-0203-4B, 3-0203-4C, 3-0203-4D, 3-0203-4E, 3-0203-4F, 3-0203-4G and 3-0203-4H for the remainder of the fourth 10 year inservice testing program intervals.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the alternative 6.5-year test interval, requested by RR RV-30F, is authorized for QCNPS, Unit 1 MSSVs 1-0203-4A, 1-0203-4B, 1-0203-4C, 1-0203-4D, 1-0203-4E, 1-0203-4F, 1-0203-4G and1-0203-4H and QCNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H for the remainder of the fourth 10-year inservice testing program intervals.
The staff has terminated the review of RR RV-30E for QCNPS Unit 1 MSSVs 1-0203-4C and 1-0203-4G because the alternative 6.5-year test interval, requested by RR RV-30F and authorized above, provides the necessary relief.
Sincerely,
/RA/
Russell Gibbs, Chief Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-237, 50-249, 50-254 and 50-265
Enclosure:
Safety Evaluation cc w/encls: See next page
ML081330557 *Prior concurrence via ML081150579 OFFICE LPL3-2/PM LPL3-2/LA DCI/CPTB/BC OGC LPL3-2/BC NAME JWiebe EWhitt JMcHale*
PMoulding RGibbs DATE 6/16/08 6/16/08 4 / 24 /08 6/18/08 6/27/08
Dresden and Quad Cities Nuclear Power Stations cc:
Corporate Distribution Exelon Generation Company, LLC Via e-mail Dresden Distribution Exelon Generation Company, LLC Via e-mail Quad Cities Distribution Exelon Generation Company, LLC Via e-mail Dresden Resident Inspector U.S. Nuclear Regulatory Commission Via e-mail Quad Cities Resident Inspector U.S. Nuclear Regulatory Commission Via e-mail Chairman Grundy County Board Via e-mail Illinois Emergency Management Agency Division of Disaster Assistance & Preparedness Via e-mail David C. Tubbs MidAmerican Energy Company Via e-mail Managing Senior Attorney MidAmerican Energy Company Via e-mail Chairman Rock Island County Board of Supervisors Via e-mail
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION EXTENSION OF MAIN STEAM SAFETY VALVE TEST FREQUENCY TO 6.5 YEARS EXELON GENERATION COMPANY, LLC DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3 REQUEST RV-02C, REVISION 0 DOCKET NOS. 50-237 AND 249 QUAD CITIES NUCLEAR POWER STATION, UNITS 1 AND 2 REQUEST RV-30F, REVISION 0 DOCKET NOS. 50-254 AND 50-265
1.0 INTRODUCTION
By letter to the Nuclear Regulatory Commission (NRC, the Commission) dated February 8, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML080420121), Exelon Generation Company, LLC (EGC, the licensee) submitted Request RV-02C, Revision 0, for Dresden Nuclear Power Station (DNPS), Units 2 and 3. By letter dated March 6, 2008 (ADAMS Accession No. ML080670433), EGC submitted Request RV-30F, Revision 0, for Quad Cities Nuclear Power Station (QCNPS), Units 1 and 2. Authorization of the alternative in each request was requested in accordance with Title 10 of the Code of Federal Regulations, (10 CFR) Part 50, Section 55a(a)(3)(ii) with respect to a requirement in the American Society of Mechanical Engineers (ASME), Code for Operation and Maintenance of Nuclear Power Plants (OM Code). EGC submitted additional information in a letter dated April 18, 2008 (ADAMS Accession No. ML081090634).
DNPS RR RV-02C, Revision 0, involves an extension to the ASME OM Code 5-year test frequency for DNPS, Unit 2 Main Steam Safety Valves (MSSVs) 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H; and DNPS, Unit 3 MSSVs 3-0203-4A, 3-0203-4B, 3-0203-4C, 3-0203-4D, 3-0203-4E, 3-0203-4F, 3-0203-4G and 3-0203-4H. QCNPS RR RV-30F, Revision 0, involves an extension to the ASME OM Code 5-year test frequency for QCNPS, Unit 1 MSSVs 1-0203-4A, 1-0203-4B, 1-0203-4C, 1-0203-4D, 1-0203-4E, 1-0203-4F, 1-0203-4G and 1-0203-4H; and QCNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H. EGC is proposing to extend the 5-year test frequency to 6.5 years.
The 1998 Edition through 2000 Addenda of the ASME OM Code is the current Code of Record for the DNPS Units 2 and 3 and QCNPS Units 1 and 2 inservice testing (IST) programs.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(f), Inservice Testing Requirements, ASME Code Class 1, 2, and 3 components must meet the requirements of the ASME OM Code and applicable addenda, except where alternatives have been authorized or relief has been requested by the licensee and granted by the Commission pursuant to paragraphs (a)(3)(i), (a)(3)(ii), or (f)(6)(i) of 10 CFR 50.55a. Section 50.55a(a)(3)(ii) of 10 CFR allows the Commission to authorize alternatives to ASME OM Code requirements upon a finding that compliance with certain specified requirements would result in hardship without a compensating increase in the level of quality and safety.
EGC requested authorization of an alternative in accordance with 10 CFR 50.55a(a)(3)(ii) to the 5-year test requirement in Mandatory Appendix I, Requirements for Inservice Testing of Nuclear Power Plant Pressure Relief Devices, Section I-1330, Test Frequencies, Class I Pressure Relief Valves, Paragraph (a), 5-Year Test Interval, of the 1998 Edition through 2000 Addenda of the ASME OM Code. Request RV-02C, Revision 0, involves extending the ASME OM Code 5-year test frequency to 6.5 years for DNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H; and DNPS, Unit 3 MSSVs 3-0203-4A, 3-0203-4B, 3-0203-4C, 3-0203-4D, 3-0203-4E, 3-0203-4F, 3-0203-4G and 3-0203-4H. RR RV-30F, Revision 0, involves extending the ASME OM Code 5-year test frequency to 6.5 years for QCNPS, Unit 1 MSSVs 1-0203-4A, 1-0203-4B, 1-0203-4C, 1-0203-4D, 1-0203-4E, 1-0203-4F, 1-0203-4G and 1-0203-4H; and QCNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H. EGC is requesting authorization of the alternative on the basis that compliance with this ASME OM Code requirement would result in hardship due to unnecessary personnel radiation exposure, without a compensating increase in the level of quality or safety.
The NRCs findings with respect to authorizing relief from the ASME OM Code 5-year test requirement are given below.
3.0 TECHNICAL EVALUATION
FOR DNPS REQUEST RV-02C, REVISION 0, AND QCNPS REQUEST RV-30F, REVISION 0 3.0.1 ASME OM Code Requirements ASME OM Code Mandatory Appendix I, Section I-1330(a), of the 1998 Edition through 2000 Addenda of the ASME OM Code requires that Class 1 pressure relief valves be tested at least once every 5 years.
3.0.2 Licensees Proposed Alternative EGC is proposing an alternative test frequency for DNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H; DNPS, Unit 3 MSSVs 3-0203-4A, 3-0203-4B, 3-0203-4C, 3-0203-4D, 3-0203-4E, 3-0203-4F, 3-0203-4G and 3-0203-4H; QCNPS, Unit 1 MSSVs 1-0203-4A, 1-0203-4B, 1-0203-4C, 1-0203-4D, 1-0203-4E, 1-0203-4F, 1-0203-4G and 1-0203-4H; and QCNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H. Specifically, EGC is proposing to extend the test frequency to 6.5 years. According to the licensee, the MSSVs will be refurbished to a like-new condition prior to the start of each 6.5-year test interval.
3.0.3 Licensees Basis for Relief EGC stated that the current DNPS and QCNPS ASME overpressure analyses assume that the MSSVs open to relieve pressure at the upper ASME limit of 3 percent of the MSSV set pressure. According to EGC, it is acceptable to extend the test frequency from 5 years to 6.5 years because IST as-found set pressure test results for the DNPS and QCNPS Dresser Model 3777Q MSSVs from May 1997 to present show that all MSSVs successfully passed the current technical specification (TS) as-found acceptance criteria of +/- 3 percent of set pressure. EGC stated that DNPS and QCNPS Dresser Model 3777Q MSSVs are tested and refurbished at the same facility, utilizing the same process. Furthermore, according to EGC, set pressure drift percentages indicate that in general, the MSSV set pressures tend to drift slightly downward; not upward.
EGC stated that extending the test interval to 6.5 years would reduce the minimum number of MSSVs tested over three refueling outages by four MSSVs per unit. According to EGC, without Code relief, the incremental outage work due to the inclusion of the 4 additional MSSVs would be contrary to the principles of as low as reasonably achievable, in that the removal and replacement of the 4 MSSVs over 3 refueling outages per unit will result in approximately 8 additional person-rem of cumulative radiation exposure at DNPS and 14 additional person-rem of cumulative radiation exposure at QCNPS. EGC concluded that this additional cumulative radiation exposure represents a hardship without a compensating increase in the level of quality or safety.
3.0.4 NRC Staffs Evaluation of Requests The NRC staff reviewed the Dresser Model 3777Q MSSV set pressure test summary results provided by the EGC to determine whether it is acceptable to extend the test frequency beyond the 5-year test frequency specified in the ASME OM Code. The MSSV set pressure test summary results show that the MSSVs passed the current TS acceptance criterion of +/- 3 percent of set pressure. The NRC staff finds that this test history demonstrates good performance.
The ASME developed Code Case OMN-17, Alternative Rules for Testing ASME Class 1 Pressure Relief/Safety Valves. The ASME has approved and plans to publish OMN-17 in the upcoming edition/addenda of the ASME OM Code. Code Case OMN-17 allows extension of the test frequency for safety valves from 60 months to 72 months plus a 6-month grace period. The code case imposes a special maintenance requirement to disassemble and inspect each safety and relief valve to verify that parts are free from defects resulting from the time-related degradation or maintenance-induced wear prior to the start of the extended test frequency. The purpose of this maintenance requirement is to reduce the potential for set pressure drift. The NRC staff has not approved use of Code Case OMN-17. However, consistent with the special maintenance requirement in Code Case OMN-17, EGC stated that each MSSV will be refurbished to a like-new condition prior to the start of each 6.5-year test interval. Critical components will be inspected for wear and defects, and the critical dimensions will be measured during the inspection. Components will be reworked to within the specified tolerance or replaced if found to be worn or outside of specified tolerances.
Since the unit must be shutdown and depressurized to remove the MSSVs for testing, this activity is normally accomplished during refueling outages that are scheduled approximately every 24 months. To comply with the ASME OM Code 5-year test frequency, a minimum of four of the eight MSSVs in each unit is required to be tested every refueling outage. Each MSSV would remain in service for two refueling outages (48 months). Extending the test frequency to 6.5 years would allow each MSSV to remain in service for three refueling outages (72 months).
This would reduce the minimum number of MSSVs that are required to be tested over a period of 3 refueling outages from 12 MSSVs to 8 MSSVs per unit. EGC estimates that the expected cumulative radiation exposure to remove and replace a single MSSV is approximately 2 to 3.5 person-rem. Therefore, extending the test frequency to 6.5 years would result in a reduction of the expected cumulative radiation exposure by approximately 8 to 14 person-rem for each unit over a period of 3 refueling outages. The NRC staff agrees that incurring 8 to 14 person-rem for each unit over a period of 3 refueling outages constitutes a hardship.
The NRC staff finds that the proposed alternative test frequency of 6.5 years for the DNPS and QCNPS Dresser Model 3777Q MSSVs is acceptable. Refurbishment to a like-new condition prior to the start of each 6.5-year test interval provides reasonable assurance that set pressure drift will be minimized. The performance history for DNPS and QCNPS supports this conclusion because the MSSV as-found set pressure test results passed the current TS acceptance criterion of +/- 3 percent of set pressure. Set pressure drift test results indicate that in general, MSSV set pressures tend to drift slightly downward, not upward. From an overpressure protection standpoint, set pressure drift in the downwards direction is conservative because the valve would tend to open sooner than required. Therefore, the additional time between tests required by the ASME OM Code should not impair the valves operational readiness.
Consequently, and in light of the hardship discussed above, the NRC staff agrees that requiring compliance with the specified ASME OM Code requirement would not provide a compensating increase in the level of quality and safety.
4.0 CONCLUSION
For the reasons stated above, the NRC staff has concluded that requiring compliance with the ASME OM Code 5-year test frequency for DNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H; DNPS Unit 3 MSSVs 3-0203-4A, 3-0203-4B, 3-0203-4C, 3-0203-4D, 3-0203-4E, 3-0203-4F, 3-0203-4G and 3-0203-4H; QCNPS, Unit 1 MSSVs 1-0203-4A, 1-0203-4B, 1-0203-4C, 1-0203-4D, 1-0203-4E, 1-0203-4F, 1-0203-4G and 1-0203-4H; and QCNPS, Unit 2 MSSVs 2-0203-4A, 2-0203-4B, 2-0203-4C, 2-0203-4D, 2-0203-4E, 2-0203-4F, 2-0203-4G and 2-0203-4H would result in a hardship due to unnecessary personnel radiation exposure, without a compensating increase in the level of quality and safety. The NRC staff also finds that the proposed alternative provides reasonable assurance that the subject valves are operationally ready. Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), DNPS Request RV-02C, Revision 0, and QCNPS Request RV-30F, Revision 0, are authorized for the remainder of the fourth 10-year IST program intervals.
Principal Contributor: S. Tingen, NRR Date: June 27, 2008