ML14094A051
| ML14094A051 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 04/30/2014 |
| From: | Meena Khanna Plant Licensing Branch 1 |
| To: | Pacilio M Exelon Generation Co |
| Ennis R, NRR/DORL/LPLI-2, 415-1420 | |
| References | |
| TAC MF2509, TAC MF2510 | |
| Download: ML14094A051 (8) | |
Text
{{#Wiki_filter:UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 30, 2014 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
PEACH BOTTOM ATOMIC POWER STATION, UNITS 2 AND 3- SAFETY EVALUATION OF RELIEF REQUEST 01A-VRR-3 REGARDING THE FOURTH 10-YEAR INTERVAL OF THE INSERVICE TESTING PROGRAM (TAC NOS. MF2509 AND MF251 0)
Dear Mr. Pacilio:
By letter dated July 29, 2013, Exelon Generation Company, LLC (Exelon, the licensee) submitted relief request 01 A-VRR-3 to the Nuclear Regulatory Commission (NRC). Exelon proposed an alternative to certain inservice testing (1ST) requirements of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code), for Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3. Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) Section 50.55a(a)(3)(i), Exelon requested to extend the test interval for certain safety valves and safety relief valves on the basis that the proposed alternative provides an acceptable level of quality and safety. The subject relief request is for the fourth 10-year interval of the 1ST program at PBAPS, Units 2 and 3. The NRC staff has completed its review of the subject relief request as documented in the enclosed Safety Evaluation (SE). Our SE concludes that the proposed alternative will provide an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(a)(3)(i) and is in compliance with the ASME OM Code requirements. Therefore, the NRC staff authorizes the proposed alternative for the remainder of the fourth 10-year 1ST interval at PBAPS, Units 2 and 3. All other ASME OM Code requirements for which relief was not specifically requested and approved remain applicable.
M. Pacilio If you have any questions concerning this matter, please contact the PBAPS Project Manager, Mr. Richard Ennis, at (301) 415-1420. Sincerely,
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Meena K. Khanna, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-277 and 50-278
Enclosure:
Safety Evaluation cc w/encl: Distribution via ListServ
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST FOR THE FOURTH 10-YEAR INTERVAL OF THE INSERVICE TESTING PROGRAM EXELON GENERATION COMPANY. LLC PEACH BOTTOM ATOMIC POWER STATION, UNITS 2 AND 3 DOCKET NOS. 50-277 AND 50-278
1.0 INTRODUCTION
By letter dated July 29, 2013, (Agencywide Documents Access and Management System Accession No. ML13211A054) Exelon Generation Company, LLC (Exelon, the licensee) submitted relief request 01 A-VRR-3 to the Nuclear Regulatory Commission (NRC). Exelon proposed an alternative to certain inservice testing (1ST) requirements of the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code), for Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3. Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) Section 50.55a(a)(3)(i), Exelon requested to extend the test interval for certain safety valves (SVs) and safety relief valves (SRVs) on the basis that the proposed alternative provides an acceptable level of quality and safety. The subject relief request is for the fourth 10-year interval of the 1ST program at PBAPS, Units 2 and 3. The fourth 1ST interval for PBAPS, Units 2 and 3, began on August 15, 2008, and is currently scheduled to end on August 14, 2018.
2.0 REGULATORY EVALUATION
Section 50.55a(f), "lnservice Testing Requirements," of 10 CFR requires, in part, that 1ST of certain ASME Boiler and Pressure Vessel Code (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 by the NRC pursuant to paragraphs (a)(3)(i) or (a)(3)(ii) of 10 CFR 50.55a. The requirements in 10 CFR 50.55a(a)(3) state, in part, that alternatives to the requirements of paragraph (f) may be used, when authorized by the NRC, if the applicant demonstrates that: (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Section 50.55a authorizes the NRC to approve alternatives and to grant relief from ASME Code requirements upon making necessary findings. Enclosure
3.0 TECHNICAL EVALUATION
3.1 Licensee's Alternative Request 01 A-VRR-3 Applicable Code and Addenda The applicable ASME OM Code edition and addenda for P8APS, Units 2 and 3, is the 2001 Edition through the 2003 Addenda. Applicable Code Requirements ISTC-3200, "lnservice Testing," states, "lnservice testing in accordance with this Subsection shall commence when the valves are required to be operable to fulfill their required function(s) (See ISTA-11 00)." ISTC-5240, "Safety and Relief Valves," states, "Safety and relief valves shall meet the inservice test requirements of Mandatory Appendix 1." Mandatory Appendix I, Paragraph 1-1320 (a), states: Class 1 pressure relief valves shall be tested at least once every 5 years, starting with initial electric power generation. No maximum limit is specified for the number of valves to be tested within each interval; however, a minimum of 20 percent of the valves from each valve group shall be tested within any 24-month interval. This 20 percent shall consist of valves that have not been tested during the current 5-year interval, if they exist. The test interval for any individual valve shall not exceed 5 years. ASME OM Code Case OMN-17, "Alternate Rules for Testing ASME Class 1 Pressure Relief/Safety Valves," from the 2009 Edition of ASME OM Code, allows an extended test interval of 6 years, for testing these relief valves, plus an additional 6-months grace period provided the licensee disassembles and inspects each valve after as-found set-pressure testing to verify that valve parts are free of defects resulting from time-related degradation or service-induced wear. Alternative testing is requested for the following Class 1, Category C, SVs and SRVs: RV-2-02-070A SV RV-3-02-070A SV RV-2-02-0708 SV RV-3-02-0708 SV RV-2-02-071 A SRV RV-3-02-071 A SRV RV-2-02-071 8 SRV RV-3-02-071 8 SRV RV-2-02-071 C SRV RV-3-02-071 C SRV RV-2-02-071 D SRV RV-3-02-071 D SRV RV-2-02-071 E SRV RV-3-02-071 E SRV RV-2-02-071 F SRV RV-3-02-071 F SRV RV-2-02-071 G SRV RV-3-02-071 G SRV RV-2-02-071 H SRV RV-3-02-071 H SRV RV-2-02-071 J SRV RV-3-02-071J SRV RV-2-02-071 K SRV RV-3-02-071 K SRV RV-2-02-071 L SRV RV-3-02-071 L SRV
Reason for Request
The licensee provided the following reason for the request: Section ISTC-3200, "lnservice Testing," states that inservice testing shall commence when the valves are required to be operable to fulfill their required function(s). Section ISTC-5240, "Safety and Relief Valves," directs that safety and relief valves meet the inservice testing requirements set forth in Appendix I of the ASME OM Code. Appendix I, Section l-1320(a) of the ASME OM Code states that Class 1 pressure relief valves shall be tested at least once every 5 years, starting with initial electric power generation. This section also states a minimum of 20 percent of the pressure relief valves are tested within any 24-month interval and that the test interval for any individual valve shall not exceed 5 years. The required tests ensure that the SRVs/SVs, which are located on each of the main steam lines between the reactor vessel and the first isolation valve within the drywell, will open at the pressures assumed in the safety analysis. The SRVs/SVs have shown acceptable test history at PBAPS, Units 2 and 3 as described in Section 5 [of the relief request]. However, given the current 24-month operating cycle for each PBAPS unit, Exelon Generation Company, LLC (Exelon) is required to remove and test approximately half of the SRVs/SVs every refueling outage in order to ensure that all valves are removed and tested in accordance with the ASME OM Code requirements. This ensures compliance with the ASME OM Code requirements for testing Class 1 pressure relief valves within a 5 year interval. With the current 5 year interval, PBAPS is required to remove all 13 SRVs/SVs over 2 refuel cycles (i.e., 4 years). Approval of extending the test interval to 6.5 years would reduce the number of SRVs/SVs removed during an individual outage, such that the full scope of 13 SRVs/SVs are replaced over 3 refuel cycles (i.e., 6 years). Without Code relief, the incremental outage work due to the inclusion of the additional 2-3 Main Steam SRVs/SVs per outage would be contrary to the principle of maintaining radiation dose As Low As Reasonably Achievable (ALARA). The removal and replacement of the additional2- 3 Main Steam SRVs/SVs per outage without Code relief results in an additional exposure of approximately 2Y2- 4 Rem each outage. In accordance with 10 CFR 50.55a(a)(3)(i), Exelon requests approval of an alternative to the 5 year test interval requirements of ASME OM Code, Appendix I, Section l-1320(a) for the SRVs/SVs at PBAPS, Units 2 and 3. Exelon requests that the test interval be increased from 5 years to 6.5 years. All other requirements of the applicable ASME OM Code would be met. Proposed Alternative and Basis for Use The licensee proposed the following alternative and the basis for its use: As an alternative to the Code required 5-year test interval per Appendix I,
paragraph l-1320(a), Exelon proposes that the subject Class 1 pressure relief valves be tested at least once every three refueling cycles (approximately 6 years/72 months) with a minimum of 20% of the valves tested within any 24-month interval. This 20% would consist of valves that have not been tested during the current 72-month interval, if they exist. The test interval for any individual valve would not exceed 72 months except that a 6-month grace period is allowed to coincide with refueling outages to accommodate extended shutdown periods and certification of the valve prior to installation. After as-found set-pressure testing, the valves shall be disassembled and inspected to verify that parts are free of defects resulting from time-related degradation or service induced wear. As-left set-pressure testing shall be performed following maintenance and prior to returning the valve to service. Each valve shall have been disassembled and inspected prior to the start of the 72-month interval. Disassembly and inspection performed prior to the implementation of Code Case OMN-17 may be used. The relief valve testing and maintenance cycle at PBAPS consists of removal of the SRV/SV complement requiring testing and transportation to an off-site test facility. Upon receipt at the off-site facility the valves are subject to an as-found inspection and set-pressure testing. Prior to the return of a complement of SRVs/SVs for installation in the plant, the valves are disassembled and inspected to verify that internal surfaces and parts are free from defects or service induced wear prior to the start of the next test interval. During this process, anomalies or damage are identified for resolution. Damaged or worn parts, springs, gaskets and seals are replaced as necessary. Following reassembly, the valve's set pressure is recertified. This existing process is in accordance with ASME OM Code Case OMN-17 paragraphs (d) and (e). Exelon has reviewed the as-found set point test results for all of the SRVs/SVs tested since 2000 as detailed in Table 1 [of the relief request]. Since 2000, the PBAPS, Units 2 and 3 SRVs/SVs have a history of 96 as-found lift tests. Of these 96 tests, 99% have been found within a +1-3% tolerance. During the PBAPS Fall 2012 Unit 2 refueling outage, one of the main steam SVs (SIN 1095) as-found lift pressure was identified to be 3.4% above the setpoint. An expanded scope removal of the other SV was performed with a satisfactory lift (the S/N 1093 as-found test (November 2012) was exactly at set pressure). An investigation was performed regarding the one valve that lifted outside of a +l-3% tolerance. It was identified that the previous certification practices were not using currently best known practices; procedure enhancements have been implemented to prevent future recurrence. Additionally, PBAPS has implemented enhanced subcomponent replacement and testing criteria to provide further assurance of repeatable as-found lift results. Accordingly, the proposed alternative of increasing the test interval for the subject Class 1 pressure relief valves from 5 years to 3 fuel cycles (approximately 6 years/72 months) would continue to provide an acceptable level of quality and safety while restoring the operational and maintenance flexibility that was lost when the 24-month fuel cycle created the unintended consequences of
more frequent testing. This proposed alternative will continue to provide assurance of the valves' operational readiness and provides an acceptable level of quality and safety pursuant to 10 CFR 50.55a(a)(3)(i). 3.2 NRC Staff Evaluation The ASME Code requires that the reactor pressure vessel be protected from overpressure during upset conditions by self-actuated SVs. As part of the nuclear pressure relief system, the size and number of SRVs and SVs are selected, such that peak pressure in the nuclear system will not exceed the ASME Code limits for the Reactor Coolant Pressure Boundary (RCPB). At PBAPS, the SRVs are Target Rock three-stage pilot operated safety/relief valves (11 SRVs per unit). The SVs are Dresser spring-loaded safety valves (2 SVs per unit). The SRVs and SVs are located on the main steam lines between the reactor vessel and the first isolation valve within the drywell. The SRVs can actuate by either of two modes: the safety mode or the depressurization mode. In the safety mode, the pilot disc opens when steam pressure at the valve inlet expands the bellows to the extent that the hydraulic seating force on the pilot disc is reduced to zero. Opening of the pilot stage allows a pressure differential to develop across the second stage disc which opens the second stage disc, thus venting the chamber over the main valve piston. This causes a pressure differential across the main valve piston which opens the main valve. The SVs are spring-loaded valves that actuate when steam pressure at the inlet overcomes the spring force holding the valve disc closed. This satisfies the ASME Code requirement. The proposed changes do not impact the depressurization mode function of the SRVs. ASME OM Code, Mandatory Appendix I requires that Class 1 pressure relief valves be tested at least once every 5 years. However, Mandatory Appendix I does not require that pressure relief valves be disassembled and inspected prior to the start of the 5 year test interval. In lieu of the 5-year test interval, the licensee proposed to implement ASME OM Code Case OMN-17, which allows a test interval of 6 years plus a 6-month grace period. The ASME Committee on OM developed Code Case OMN-17 and published it in the 2009 Edition of OM Code. ASME OM Code Case OMN-17 imposes a special maintenance requirement to disassemble and inspect each pressure relief/safety valve to verify that parts are free from defects resulting from time-related degradation or maintenance-induced wear prior to the start of the extended test interval. The purpose of this maintenance requirement is to reduce the potential for SV/SRV set-point drift. ASME OM Code Case OMN-17 has not been added to Regulatory Guide 1.192, "Operation and Maintenance Code Case Acceptability, ASME OM Code," or included in 10 CFR 50.55a by reference. However, the NRC has allowed licensees to use OMN-17, provided all requirements in the Code Case are met. Consistent with the special maintenance requirement in ASME OM Code Case OMN-17, each SV/SRV at PBAPS is disassembled and inspected to verify that internal surfaces and parts are free from defects or service-induced wear prior to the start of the next test interval. During this process, anomalies or damage are identified for resolution. Damaged or worn parts, springs, gaskets and seals are replaced as necessary. Following reassembly, the valve's set pressure is recertified. This existing process is in accordance with ASME OM Code Case OMN-17, paragraphs (d) and (e). Furthermore, ASME OM Code Case OMN-17 is performance-based, in that it requires that the SVs/SRVs be tested more frequently if test failures occur. For example, ASME OM Code Case
OMN-17 requires that two additional valves be tested when a valve in the initial test group exceeds the set pressure acceptance criteria. All remaining valves in the group are required to be tested if one of the additional valves tested exceeds its set pressure acceptance criteria. Therefore, the SV/SRV test frequency would be equivalent to the current test frequency, if test failures occur. The licensee has provided test data since 2000 to show that the subject valves have historically exhibited very limited susceptibility to time-related degradation or set-point drift. The licensee plans to implement a disassembly and inspection program in conjunction with the extended test interval, as required by ASME OM Code Case OMN-17. Based on the historical performance of the set-point testing of SVs/SRVs and the disassembly and inspection of the SVs/SRVs after as-found set-pressure testing and prior to use, the NRC staff finds that implementation of the ASME OM Code Case, OMN-17, for the testing of the designated SVs/SRVs, in lieu of the requirements of the 2001 Edition of the ASME OM Code through the 2003 Addendum and the Mandatory Appendix I, Section 1320 of the ASME OM Code, provides an acceptable level of quality and safety.
4.0 CONCLUSION
As set forth above, the NRC staff determines that the proposed alternative described in relief request 01A-VRR-3 provides an acceptable level of quality and safety for the SVs/SRVs listed in Section 3.1 above. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(a)(3)(i) and is in compliance with the ASME OM Code requirements. Therefore, the NRC staff authorizes the proposed alternative for the remainder of the fourth 10-year 1ST interval at PBAPS, Units 2 and 3. All other ASME OM Code requirements for which relief was not specifically requested and approved in the subject request remain applicable. Principal Contributor: J. Huang Date: April 30, 2014
ML14094A051 *concurrence via e-mail OFFICE LPL 1-2/PM LPL 1-2/LA EPNB/BC LPL 1-2/BC NAME REnnis ABaxter Tlupold* MKhanna DATE 4/29/14 4/28/14 2/25/14 4/30/14}}