ML20219A202
| ML20219A202 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 09/01/2020 |
| From: | Nancy Salgado Plant Licensing Branch III |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| Wiebe J | |
| References | |
| EPID L-2019-LLR-0116 | |
| Download: ML20219A202 (10) | |
Text
September 1, 2020 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO)
Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
CLINTON POWER STATION, UNIT 1 - PROPOSED ALTERNATIVE I4R-05 TO THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE (EPID L-2019-LLR-0116)
Dear Mr. Hanson:
By letter dated December 16, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19350C642), as supplemented by letter dated April 1, 2020 (ADAMS Accession No. ML20092L027), Exelon Generation Company, LLC (the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) for the use of an alternative to certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code),Section XI, requirements at Clinton Power Station (CPS), Unit 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee proposed alternate system pressure tests with associated VT-2 visual examination for combustible gas control piping on the basis that compliance with the specified ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the proposed alternative I4R-051 provides reasonable assurance of structural integrity of combustible gas control piping. The NRC staff finds that complying with the requirements of the ASME Code,Section XI, 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 the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC authorizes the use of Relief Request I4R-05 at CPS, Unit 1, for the fourth 10-year inservice inspection (ISI) interval which commenced on July 1, 2020, and is currently scheduled to end on June 30, 2030.
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.
1 The other requests contained in the licensees December 16, 2019, letter have been or will be addressed by separate correspondence
B. Hanson If you have any questions, please contact the Senior Project Manager, Joel S. Wiebe, at (301) 415-6606 or Joel.Wiebe@nrc.gov.
Sincerely, Digitally signed by Nancy L.
Nancy L. Salgado Salgado Date: 2020.09.01 13:43:12 -04'00' Nancy L. Salgado, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-461
Enclosure:
Safety Evaluation cc: ListServ
ML20219A202 *via email OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA* NRR/DNRL/NPHP/BC* NRR/DORL/LPL3/BC*
NAME JWiebe SRohrer MMitchell NSalgado DATE 8/ 10 /2020 8/ 6 /2020 7/20/2020 9/1/2020 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATE SYSTEM PRESSURE TESTS FOR COMBUSTIBLE GAS CONTROL PIPING EXELON GENERATION COMPANY, LLC CLINTON POWER STATION, UNIT 1 DOCKET NO. 50-461
1.0 INTRODUCTION
By letter dated December 16, 2019, (Agencywide Documents and Access Management System (ADAMS) Accession No. ML19350C642), with supplement dated April 1, 2020 (ADAMS Accession No. ML20092L027), Exelon Generation Company, LLC (the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code),Section XI, Table IWC-2500-1, and Subarticle IWC-5200, for the fourth 10-year inservice inspection (ISI) interval at Clinton Power Station (CPS), Unit 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee proposed alternate system pressure tests with associated VT-2 visual examination for combustible gas control piping on the basis that compliance with the specified ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
2.0 REGULATORY EVALUATION
Adherence to Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4), which states, in part, that ASME Code Class 1, 2, and 3 components will meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI.
Paragraph 10 CFR 50.55a(z) states, in part, that alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a, or portions thereof, may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that: (1) The proposed alternative would provide an acceptable level of quality and safety; or (2)
Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Enclosure
Based on the above, and subject to the following technical evaluation, the U.S. Nuclear Regulatory Commission (NRC) staff finds that regulatory authority exists for the licensee to request the use of an alternative and the NRC to authorize the use of the proposed alternative.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Component(s) Affected The affected ASME Code components are the ASME Code, Class 2, combustible gas control (HG) piping to and from hydrogen recombiners 0HG01SA and 0HG01SB. The HG piping is required to be inspected periodically per Examination Category C-H, Item No. C7.10 in Table IWC-2500-1 of the ASME Code,Section XI.
The seamless HG piping is fabricated with carbon steel, American Society of Testing and Materials (ASTM) A-106, Grade B, and/or ASME SA-106, Grade B. The 2-inch and smaller diameter piping is Schedule 80 thickness and the 2.5-inch diameter piping is Schedule 40 thickness.
The HG system maintains the hydrogen concentration in the drywell and containment below the ignition level. Relief Request I4R-05 is applicable to a portion of the HG piping and associated components that control and direct flow from the containment to hydrogen recombiners 0HG01SA and 0HG01SB and back to the containment.
The HG piping and components requiring VT-2 visual examination are listed below.
Lines associated with hydrogen recombiner 0HG01SA in flow path starting inside the containment just before containment penetration 1MC-71 and ending inside containment just past containment penetration 1MC-72 are: 1HG01A-2 inch, 1HG07A-3/4 inch, 1HG01B-2 1/2 inch, 1HG11A-3/4 inch, 0HG03A-2 inch, 0HG03B-2 inch, 0HG04A-2 inch, 0HG04B-2 inch, 0HG02A-2 1/2 inch, 1HG12A-3/4 inch, 1HG02B-2 inch, and 1HG08A-3/4 inch.
Valves associated with hydrogen recombiner 0HG01SA in flow path starting inside the containment just before containment penetration 1MC-71 and ending inside containment just past containment penetration 1MC-72 are: 1HG012-2 inch, 1HG016-3/4 inch, 1HG001-2 inch, 1HG020-3/4 inch, 1HG002-2 inch, 2HG002-2 inch,2HG003-2 inch, 1HG003-2 inch, 1HG021-3/4 inch, 1HG004-2 inch, 1HG017-3/4 inch, and 1HG013-2 inch.
Hydrogen recombiner 0HG01SA.
Lines associated with hydrogen recombiner 0HG01SB in flow path starting inside the containment just before containment penetration 1MC-166 and ending inside containment just past containment penetration 1MC-62 are: 1HG03A-2 inch, 1HG09A-3/4 inch, 1HG03B-3 inch, 0HG01B-2 inch, 0HG01A-2 inch, 0HG02A-2 inch, 0HG02B-2 inch, 1HG04A-2 1/2 inch, 1HG04B-2 inch, and 1HG010A-3/4 inch.
Valves associated with hydrogen recombiner 0HG01SB in flow path starting inside the containment just before containment penetration 1MC-166 and ending inside containment just past containment penetration 1MC-62 are: 1HG014-2 inch, 1HG018-3/4 inch, 1HG005-2 inch, 1HG006-2 inch, 2HG006-2 inch, 2HG007-2 inch, 1HG007-2 inch, 1HG008-2 inch, 1HG019-3/4 inch, and 1HG015-2 inch.
Hydrogen recombiner 0HG01SB.
3.2 Applicable Code Edition The fourth 10-year ISI interval program is based on the 2013 Edition of the ASME Code,Section XI.
3.3 Applicable Code Requirement Item No. C7.10 of the ASME Code,Section XI, Table IWC-2500-1, Examination Category C-H, requires all ASME Code, Class 2, pressure-retaining components to be subjected to a system leakage test and an associated VT-2 visual examination in accordance with the ASME Code,Section XI, paragraph IWC-5220. This pressure/system leakage test is to be conducted once each inspection period. Article IWC-5000 permits the use of a pneumatic test for ISI of ASME Code, Class 2, components in accordance with paragraph IWA-5211(c).
3.4 Reason for Request In its letter dated December 16, 2019, the licensee stated that performing a VT-2 visual examination of the HG piping in accordance with the ASME Code,Section XI, would require applying a leak detection solution to the safety-related HG piping and components to locate leakage. The licensee further stated that performing this examination would pose significant personnel safety hazards, as most of this piping requires working at high elevations, requiring either a ladder or scaffold to reach the subject piping. Also, the examination would require removal of pipe insulation. The licensee estimated that the HG piping associated with hydrogen recombiner 0HG01SA is 550 linear feet and the HG piping associated with hydrogen recombiner 0HG01SB is 1050 feet in length. According to the licensee, examining the HG piping associated with 0HG01SB will result in an estimated radiation exposure of 150 to 200 millirem. The licensee contended that performing the required VT-2 visual examination would not be consistent with as-low-as-reasonably-achievable (ALARA) radiation exposure practices. Therefore, the licensee requested relief from the performance of system leakage tests and VT-2 visual examination per Table IWC-2500-1 for the HG piping, valves and components associated with hydrogen recombiners 0HG01SA and 0HG01SB.
3.5 Proposed Alternative As an alternative to the examination requirements of Table IWC-2500-1, the licensee proposed to perform leak rate tests using dry air in the HG piping associated with hydrogen recombiners 0HG01SA and 0HG01SB based on the following two plant surveillances: (1) local leak rate testing (LLRT) CPS 9861.02 Datasheet D041 for containment penetration 1MC071/1MC072 -
Hydrogen Recombiner 0HG01SA, and (2) LLRT CPS 9861.02 Datasheet D033 for containment penetration 1MC062/1MC166 - Hydrogen Recombiner 0HG01SB.
3.6 Basis for Use In its letter dated December 16, 2019, the licensee stated that CPS 9861.02, Datasheets D033 and D04,1 specify procedures to perform the system leakage test to determine the potential leakage rate from the subject piping with associated components and potential leakage through affected boundary valve internals and mechanical connections. These datasheets require three separate leak rate tests (i.e., Test Sets A, B, and C) for the HG piping associated with the A and B hydrogen recombiner trains as follows:
Test set A for the 'A' hydrogen recombiner train tests piping and components on the inlet line from the open-ended piping in the containment to motor-operated containment isolation valve 1HG001 as shown in LLRT CPS 9861.02D041, P&ID MO5-1063-1. This test is associated with containment penetration IMC-71/72.
Test set A for the 'B' hydrogen recombiner train tests piping and components on the outlet line from the open-ended piping in the containment to motor-operated containment isolation valve 1HG008 as shown in LLRT CPS 9861.02D033, P&ID MO5-1063-1, and MO5-2063-1. This test is associated with containment penetration IMC-062.
Test set B for the 'A' hydrogen recombiner train tests piping and components on the outlet line from motor-operated containment isolation valve 1HG004 to the open-ended piping in the containment as shown in LLRT 9861.02D041, P&ID MO5-1063-1. This test is associated with containment penetration IMC-71/72.
Test set B for the 'B' hydrogen recombiner train tests piping and components on the inlet line from motor-operated containment isolation valve 1HG005 to the open-ended piping in the containment as shown in LLRT 9861.02D033, P&ID MO5-1063-1, and MO5-2063-1. This test is associated with containment penetration IMC-166.
Test set C for both hydrogen recombiner trains tests piping and components on the inlet and outlet lines from the open-ended inlet piping in the containment, through the respective hydrogen recombiner (i.e., 0HG01SA or 0HG01SB) to the open-ended outlet piping in the containment, respectively.
The licensee stated that the pressure for each test is maintained between 9.1 pounds per square inch gauge (psig) and 9.9 psig. The hold time is a minimum of 15 minutes from stabilization of test pressure. The licensee further stated that pressure stabilization can be declared when the measured flow rate is stable for a period of approximately five minutes.
According to the piping design, the maximum operating pressure of the subject piping is nine psig and the maximum design pressure is 15 psig.
The licensee has established administrative leakage limits for each train to prompt further examinations and/or evaluations. Train 'B' has an administrative leakage limit of 500 standard cubic centimeters per minute (sccm) and Train 'A' has an administrative leakage limit of 1000 sccm. Normal system flow is 50 standard cubic feet per minute (scfm), which is 1.4 million sccm. The accuracy of the pressure measuring instrumentation is +/- 0.15 psig and the accuracy of the flow measuring instrumentation is +/- 2 percent of full scale.
The licensee further stated that any leakage detected is included in the overall secondary containment bypass pathway limit of 28,882 sccm, or 0.08 times the maximum allowable containment atmospheric leak rate at the calculated peak accident pressure. The licensee used the administrative leakage limits in LLRT procedure CPS 9861.02, Datasheets D033 and D041, to evaluate and trend the test results to prevent potential challenges to the overall secondary containment bypass pathway leakage limit.
The licensee stated that if the leak rate exceeds its administrative limits, it will evaluate the test results and determine whether the leakage is due to through-wall leakage in the pressure boundary. In that situation, the licensee will quantify all valve seat leakage and perform VT-2
visual examinations of all mechanical joints associated with the train in question with a leak detection solution. The licensee stated that it will correct any leakage identified and run the leak test again. If the licensee determines that leakage above its administrative limits may be attributed to a through-wall pressure boundary leak, the licensee will perform a VT-2 visual examination of the entire piping run with a leak detection solution. The licensee stated that if through-wall pressure boundary leakage from a safety-related component is discovered, it will repair or replace the component or piping in accordance with the applicable requirements of the ASME Code,Section XI. The licensee indicated that if the safety-related pressure boundary is shown to be not leaking, the examination will be considered acceptable for that inservice inspection period.
The licensee stated that the volume tested by these surveillances encompasses all piping and components requiring testing under the ASME Code,Section XI for these portions of the HG system. The licensee further stated that these surveillances are performed every ISI period to comply with the frequency required in the ASME Code,Section XI, Table IWC-2500-1. The test pressure used is consistent with the pressure requirements of Table IWC-2500-1. The licensee indicated that, as a minimum, the testing performed during this surveillance will provide the same level of quality and safety as the pressure testing and VT-2 visual examination requirements of Table IWC-2500-1.
3.7 Duration of Proposed Alternative The licensee requested relief for the fourth 10-year ISI Interval which commenced on July 1, 2020, and is scheduled to end on June 30, 2030.
4.0 NRC STAFF EVALUATION By letter dated August 23, 2012, as supplemented by letter dated February 8, 2013 (ADAMS Accession Nos. ML12236A405 and ML13039A389, respectively), the licensee submitted relief request I3R-09 to perform the same system leakage testing of the subject piping for the third 10-year ISI interval. By letter dated April 18, 2013 (ADAMS Accession No. ML13107A099), the NRC approved Relief Request I3R-09. The supplement date February 8, 2013 contains the licensees LLRT procedure CPS 9861.02, Datasheets D033 and D041. The NRC staff reviewed these two datasheets to evaluate Relief Request I4R-05.
As stated above, the HG piping is periodically inspected per the requirements of Examination Category C-H, Item No. C7.10, in Table IWC-2500-1 of the ASME Code,Section XI. Table IWC-2500-1 requires a VT-2 visual examination of the pressure-retaining boundary during a system leakage test conducted in accordance with ASME Code,Section XI, IWC-5220. IWC-5220 specifies that the system leakage test be conducted each ISI period at the system pressure obtained while the system, or portion of the system, is in service performing its normal operating function or at the system pressure developed during a test conducted to verify system operability (e.g., to demonstrate system safety function or satisfy technical specification surveillance requirements).
The licensee stated that the maximum operating pressure of the subject piping and components is nine psig and the maximum design pressure is 15 psig. The NRC staff confirmed that these pressure values are consistent with section 6.2.1.1.3.1 of the plants updated safety analysis report (ADAMS Accession No. ML17038A445), which states that the containment design pressure is 15 psig and the calculated accident pressure is 6.97 psig, with a short-term pressure
peak of 9.22 psig occurring in the wetwell region below the hydraulic control unit floor during pool swell.
The NRC staff recognizes that performing the ASME Code-required VT-2 visual examination of the HG piping and associated components during the system leakage test would need to apply a leak detection solution to detect air leakage. The NRC staff further recognizes that performing the VT-2 visual examination of the subject piping would pose significant safety hazards to personnel as examination of most of this piping would require working at high elevations and expose personnel to an estimated radiation of 150 to 200 millirem. The NRC staff finds that the ALARA considerations and personnel safety will cause hardship for the licensee.
The NRC staff notes that, as an alternative, the licensees proposed leak test per CPS 9861.02 and associated troubleshooting procedures will require appropriate actions to ensure that any source of leakage is correctly identified and dispositioned. The NRC staff determines that CPS 9861.02 specifies that for the system leakage test, the pressure inside the HG piping is considered stable between 9.1 psig and 9.9 psig, the pressure measuring instrumentation has an accuracy of +/-0.15 psig, and the flow measuring instrumentation has an accuracy of +/-2 percent of full scale. As such, the NRC staff finds that procedures in CPS 9861.02 are adequate to (1) detect leakage in the subject HG system piping, and (2) distinguish leakage from the gasket and motor-operated containment isolation valve seat versus leakage from through-wall pressure boundary leakage. Therefore, the NRC staff finds that the proposed alternative is acceptable because based on the licensees description it will effectively identify through-wall pressure boundary leakage based on the stability of the pressure reading.
The licensee stated that in addition to the procedures in CPS 9861.02, if through-wall pressure boundary leakage above the administrative limit is identified, it will perform a VT-2 visual examination with a leak detection solution applies to the entire piping run. The NRC staff finds this is acceptable because this action is consistent with the requirements of the ASME Code,Section XI, IWC-5200.
The NRC staff determines that the structural integrity of the HG piping will not likely to be significantly affected by pressure and thermal loading because of low operating pressure and low (i.e., ambient) temperature. The deadweight loads are low because the pipe carries hydrogen, not water. The interior of the pipe is not under corrosive environment because hydrogen is not corrosive. The licensee stated in its February 8, 2013, supplemental response as part of Relief Request I3R-09 , that there does not seem to be a trend that would indicate active degradation in the subject piping based on system leakage tests performed during the second ISI interval. In the supplement dated April 1, 2020, the licensee reported that its administrative leakage limits were not exceeded during system leakage tests performed in the third ISI interval. Therefore, the NRC staff finds that there is a low probability of an active degradation mechanism that would challenge the structural integrity the HG piping.
The NRC staff recognizes that the gaskets in the valves and flanges may degrade as a result of aging. However, the NRC does not believe the leakage from valves and flanges are expected to challenge the functionality or structural integrity of the subject piping. If the gaskets in the valves or flanges do degrade and leakage does occur, the periodic system leakage tests would identify the degradation and the licensee would be required to take correction actions in accordance with Relief Request I4R-05.
Therefore, the NRC staff finds that the proposed alternative will provide reasonable assurance of structural integrity of the HG piping and associated components because (1) the licensee will
perform a system leakage test on the HG piping every ISI period, (2) if leakage is detected, the licensee will use the leak detection solution to identify the leaking location and take corrective actions, (3) the HG piping does not have an active degradation mechanism that would affect its structural integrity, and (4) the loading on the HG piping is not significant.
5.0 CONCLUSION
The NRC staff determines that the proposed alternative provides reasonable assurance of structural integrity of HG piping. The NRC staff finds that complying with the requirements identified in Section 3.3 above, 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 the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC authorizes the use of Relief Request I4R-05 at CPS, Unit 1, for the fourth 10-year ISI interval which commenced on July 1, 2020, and is scheduled to end on June 30, 2030.
All other requirements in the ASME Code,Section XI, for which relief was not specifically requested and approved in this proposed alternative remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: J. Tsao Date: September 1, 2020