ML112900885
| ML112900885 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 11/21/2011 |
| From: | Jacob Zimmerman Plant Licensing Branch III |
| To: | Pacilio M Exelon Generation Co, Exelon Nuclear |
| Zimmerman J | |
| References | |
| TAC ME4985, I3R-07 | |
| Download: ML112900885 (8) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 21, 2011 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
CLINTON POWER STATION, UNIT NO. 1-RELIEF REQUEST 13R-07 ASSOCIATED WITH THE THIRD 10-YEAR INSERVICE INSPECTION INTERVAL (TAC NO. ME4985)
Dear Mr. Pacilio:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated November 5, 2010 (Agencywide Documents Access and Management System Accession No. ML103090572), as supplemented by letter dated August 19, 2011 (Accession No. ML112311215), Exelon Generation Company, LLC (the licensee), submitted Relief Request (RR) 13R-07 for the third 10-year inservice inspection (lSI) interval for the Clinton Power Station (CPS), Unit NO.1.
Specifically, pursuant to Title 10 of the Code ofFederal Regulations (10 CFR) Section 50.55a(a)(3)(ii}, the licensee requested approval to use an alternative to the American Society of Mechanical Engineers (ASME) Code,Section XI, requirements on the basis that complying with the specified requirement would result in hardship or unusual difficulty.
The NRC has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the licensee's proposed alternative to perform a pressure decay test for the instrument air piping supplying all eight main stream isolation valves every refueling outage in accordance with surveillance procedure, CPS-9061.11, "Instrument Air Check Valve Operability and Pipe Pressure Test," would provide reasonable assurance of leak tightness. In addition, compliance with ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the 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)(ii). Therefore, the NRC staff authorizes the proposed alternative at CPS for the third 10-year lSI interval.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and approved, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
M. Pacilio
- 2 If you have any questions, please contact the CPS Project Manager, Nicholas DiFrancesco, at 301-415-1115.
Sincerely, CJ)/.
JtbIZimL:::-
Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-461
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 FOR RELIEF REQUEST 13R-07 ON THE THIRD 10-YEAR INSERVICE INSPECTION INTERVAL EXELON GENERATION COMPANY. LLC CLINTON POWER STATION. UNIT NO.1 DOCKET NO. 50-461
1.0 INTRODUCTION
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated November 5, 2010 (Agencywide Documents Access and Management System Accession No. ML103090572), as supplemented by letter dated August 19, 2011 (Accession No. ML112311215), Exelon Generation Company, LLC (the licensee), submitted Relief Request (RR) 13R-07, for the third 10 year inservice inspection (lSI) interval for the Clinton Power Station (CPS), Unit No.1. The second 10-year lSI interval for CPS ended on June 30, 2010.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(a)(3)(ii), the licensee requested approval to use the proposed alternative to the American Society of Mechanical Engineers (ASME) Code,Section XI, requirements on the basis that complying with the specified requirement would result in hardship or unusual difficulty without a compensation increase in the level of quality and safety.
2.0 REGULATORY EVALUATION
Section 50.55a(g) of 10 CFR requires that the lSI of ASME Code Class 1, 2, and 3, components be performed in accordance with Section XI and applicable addenda, except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
According to 10 CFR 50.55a(a)(3), alternatives to the requirements of paragraph 10 CFR 50.55a(g) may be used when authorized by the NRC if an applicant demonstrates that the proposed alternatives would provide an acceptable level of quality and safety, or if the specified requirement that would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3, components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection (lSI) of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The Enclosure
- 2 regulations require that the lSI of components and system pressure tests, conducted during the first 1 O-year interval and subsequent intervals, comply with the requirements in the latest edition and Addenda of Section XI of the ASME Code, incorporated by reference in 10 CFR SO.SSa(b),
12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable code of record for the third 10-year lSI interval for CPS is the 2004 Edition (No Addenda) of the ASME Code,Section XI. The proposed alternative is sought for the third 10-year lSI interval which is scheduled to end on June 30,2020.
The NRC staff has reviewed the licensee's proposed alternative, RR 13R-07, pursuant to 10 CFR SO.SSa(a)(3)(ii), that the alternative would provide reasonable assurance of leak tightness when compliance to ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
3.0 TECHNICAL EVALUATION
3.1 RR 13R-07 The RR 13R-07 requests approval of an alternative to the requirement of the ASME Code,Section XI, in regard to pressure testing Class 3 IA piping supplying all eight main steam isolation valves (MSIVs). The licensee proposed to perform a pressure decay test in lieu of the visual examination during pressure testing of the instrument air piping. In accordance with the CPS Inservice Test Program, a pressure decay test to verify the operability of each MSIV's air supply components, including instrument air piping, check valves, and accumulators, will be conducted using surveillance procedure, CPS-9061.11, "Instrument Air Check Valve Operability and Pipe Pressure Test."
3.1.1 System/Component(s) for Which Relief is Requested Class 3 IA piping and components (lines, valves and accumulators) are supplying IA to all eight MSIVs. The piping is %-inch to 2-inch diameter austenitic stainless steel.
3.1.2 ASME Code Requirements The 2004 Edition of the ASME Code,Section XI, paragraph IWD-S200, states that Class 3 pressure retaining components shall be tested at the frequency stated in, and visually examined by, the methods specified in Table IWO-2S00-1, Examination Category O-B. Table IWO-2S00-1 requires performance of VT -2 visual examination during system pressure tests. This pressure test is required to be conducted once each inspection period.
Examination Categories:
Class 3 - D-B, All Pressure Retaining Components.
Item Nos.:
Class 3 - 02.10, Pressure Retaining Components.
3.1.3 Basis for Requesting Relief Pursuant to 10 CFR SO.SSa(a)(3)(ii), the licensee requested relief on the basis that compliance with the specified ASME Code,Section XI, requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Performance of a VT-2 visual examination would require applying a leak detection solution to surfaces of large
- 3 amount of piping and components, many of which are located in elevated dose rate areas with limited access. VT-2 visual inspections would expose the test crew to additional radiation exposure of 0.5 rem, and industrial safety challenges without a compensating increase in the level of quality and safety.
The surveillance procedure, CPS-9061.11, verifies operability of MSIV closure capability and check valve repositioning in the IA supply lines to all eight MSIVs. The surveillance is performed for each individual MSIV as a requirement of the CPS Inservice Testing Program. One specific test under this surveillance is the pressure decay test of the accumulators of the MSIV air supply components. The pressure decay test is performed by pressurizing and isolating these accumulators and associated piping at nominal operating pressure. The decay in pressure is then monitored through calibrated pressure measuring instrumentation. If any pressure decay acceptance criterion is exceeded, the surveillance identifies appropriate troubleshooting steps to perform including application of soap solution to the surface of the component to locate leakage.
The pressure decay test performed as part of surveillance procedure CPS-9061.11, identifies any degradation of the Class 3 IA supply piping to the MSIVs and associated isolation check valves. The volume tested by this surveillance encompasses all piping and components requiring testing under the ASME Code,Section XI, for the portions of the IA system. The surveillance is also performed each 24-month refueling cycle, which is a greater frequency than that required in Table IWD-2S00-1, and the test pressure is consistent with the pressure requirements of this table. Thus, the testing performed during this surveillance will provide the same level of quality and safety as the pressure testing and VT-2 visual examination of Table IWD-2S00-1. The VT-2 visual examination described in Table IWD-2S00-1, which is performed once per inspection period, would not provide an increase in safety, system reliability, or structural integrity.
3.1.4 Proposed Alternate Examination As an alternative to the VT-2 visual examination requirements of Table IWD-2S00-1, CPS will perform a pressure decay test on the lSI Class 3 IA piping supplying all eight MSIVs as required in surveillance procedure, CPS-9061.11, "Instrument Air Check Valve Operability and Pipe Pressure Test."
3.2 NRC Staff's Evaluation of Proposed Alternative The 2004 ASME Code,Section XI, Table IWD-2S00-1, requires a system leakage test of pressure retaining components (such as th~ MSIV accumulators), including the associated piping each inspection period, and a VT-2 visual examination during the system leakage test to detect evidence of leakage from the pressure retaining components. The ASME Code further states that the contained fluid in the system, which is air, shall serve as the pressurizing medium.
As an alternative to the system leakage test and associated VT -2 visual examination requirements of IWD-2S00-1, the licensee proposes to perform a pressure decay test on the lSI Class 3 IA piping supplying all eight MSIVs. The licensee's surveillance is performed in accordance with procedure CPS-9061.11, "Instrument Air Check Valve Operability and Pipe Pressure Test," which verifies operability of the MSIV IA supply system. This procedure requires performance of a pressure decay test by isolating and pressurizing the MSIV accumulators including their associated piping to the nominal operating pressure and monitoring the pressure
- 4 decay to ensure leak-tight integrity of the components. The pressure test wilt be performed at normal operating pressure, which is 110 psig to the Instrument Air system supplying the MSIV.
The licensee's pressure decay test was described in detail in their request for additional information response letter. The licensee stated that:
Design calculations determined that each MSIV would need 35 gallons of air to close an MSIV following the failure of the normal air supply. The sizing of MSIV air system piping is based on continuous leakage of one standard cubic foot per hour (SCFH) at the minimum air pressure of 100 psig [pounds per square inch gauge]. Each MSIV has an air accumulator that is slightly oversized at 39 gallons to provide additional margin. The pressure decay test acceptance criterion is based upon leakage equaling one-half of the assumed one SCFH continuous leakage, or 0.5 SCFH. This equates to a pressure drop of 0.0242 psi [pounds per square inch] per minute. For a 63 minute test, the total pressure drop would be 1.5 psig. The 63 minute test duration is based on the resolution of the instrument used for the test and the time necessary to obtain conclusive and reliable results.
If the pressure drop measured during the test exceeds 1.5 psig, the affected piping will be inspected using a soapy liquid leak detecting solution to locate any leakage. Leakage that is located will be corrected until satisfactory results are obtained. If through-wall leakage from a safety related component is discovered, the component will be repaired or replaced in accordance with the applicable ASME Code requirements.
The NRC staff considers this leakage criterion based on pressure decay to be an acceptable alternative to the ASME Code-required VT-2 visual examination of the pressure boundary, as the proposed test ensures an adequate supply of instrument air to close the MSIVs that provide reasonable assurance of leak tightness of the subject components. In addition, the proposed alternative offers further conservatism as reflected in the frequency of surveillance being once every 24 months as opposed to the ASME Code required VT-2 visual examination frequency of once every 40 months.
The NRC staff concludes that the licensee's basis for requesting relief is reasonable as VT-2 visual inspections would require the application of leak detection solution to a large area of piping all of which are located in areas of elevated dose rates. The NRC staff finds that the licensee's proposed alternative would provide reasonable assurance of leak tightness while achieving as low as reasonably achievable goals and that compliance to ASME Code requirements that would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
4.0 CONCLUSION
As set forth above, the NRC staff determines that the licensee's proposed alternative to perform pressure decay test for the IA piping supplying all eight MSIVs every refueling outage in accordance with surveillance procedure, CPS-9061.11, "Instrument Air Check Valve Operability and Pipe Pressure Test," would provide reasonable assurance of leak tightness and compliance to ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes
- S that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR SO.SSa(a)(3)(ii). Therefore, the NRC staff authorizes the proposed alternative at CPS for the third 10-year 151 interval. All other ASME Code,Section XI, requirements for which relief was not specifically requested and approved remains applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: Margaret Audrain Charles Norton Date of issuance:
November 21, 2011
ML112900885 NRR-028
- by memo dated OFFICE LPL3*2/PM LPL3*2/PM LPL3-2/PM DCI/CPNB/BC LPL3-2/BC NAME BHarris SRohrer(BTully for)
NDiFrancesco TLupold*
JZimmerman DATE 1118/11 11/18/11 11/21/11 9130111 11121111