ML22061A040
| ML22061A040 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 03/11/2022 |
| From: | James Danna NRC/NRR/DORL/LPL1 |
| To: | Rhoades D Constellation Energy Generation |
| Guzman R | |
| References | |
| EPID L-2021-LLR-0066 | |
| Download: ML22061A040 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON , D.C. 20555-0001 March 11, 2022 Mr. David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
NINE MILE POINT NUCLEAR STATION, UNIT 2 - RELIEF REQUEST ASSOCIATED WITH EXCESS FLOW CHECK VALVES (EPID L-2021-LLR-0066)
Dear Mr. Rhoades:
By letter dated September 8, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21251A491), as supplemented by letters dated November 15, 2021 (ADAMS Accession No. ML21320A049), and dated December 17, 2021 (ADAMS Accession No. ML21351A008) Exelon Generation Company, LLC (the licensee) submitted an alternative request GV-RR-10 to the U.S. Nuclear Regulatory Commission (NRC) for an alternative to specific inservice testing (IST) requirements in the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) at Nine Mile Point Nuclear Station, Unit 2 (Nine Mile Point 2), associated with the fourth 10-year IST Program interval. On February 1, 2022 (ADAMS Accession No. ML22032A333), Exelon Generation Company, LLC was renamed Constellation Energy Generation, LLC.
Specifically, pursuant to subparagraph (1) in paragraph (z), Alternatives to codes and standards requirements, of Section 55a, Codes and standards, in Part 50, Domestic Licensing of Production and Utilization Facilities, to Title 10, Energy, of the Code of Federal Regulations (10 CFR), the licensee requested to implement alternative request GV-RR-10 for the testing and schedule of excess flow check valves (EFCVs) at Nine Mile Point 2 on the basis that the proposed alternative will provide an acceptable level of quality and safety.
As set forth in the enclosed safety evaluation, the NRC staff has determined that proposed alternative GV-RR-10 provides an acceptable level of quality and safety for the proposed testing and schedule for the EFCVs at Nine Mile Point 2 listed in Table 1 of the enclosed safety evaluation. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements specified in 10 CFR 50.55a(z)(1) for alternative request GV-RR-10.
Therefore, the NRC staff authorizes the use of proposed alternative GV-RR-10 for the fourth 10-year IST program interval at Nine Mile Point 2, which began on January 1, 2019, and is scheduled to end on December 31, 2028.
D. Rhoades All other ASME OM Code requirements for which relief or an alternative were not specifically requested and approved as part of this request remain applicable.
If you have any questions, please contact the Nine Mile Point Nuclear Station Project Manager, Richard Guzman, at (301) 415-1030.
Sincerely, Digitally signed by James G. James G. Danna Date: 2022.03.11 Danna 13:58:26 -05'00' James G. Danna, Chief Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-410
Enclosure:
Safety Evaluation cc: Listserv
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST GV-RR-10 NINE MILE POINT NUCLEAR STATION, LLC CONSTELLATION ENERGY GENERATION, LLC NINE MILE POINT NUCLEAR STATION, UNIT 2 DOCKET NO. 50-410
1.0 INTRODUCTION
By letter dated September 8, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21251A491), as supplemented by letters dated November 15, 2021 (ADAMS Accession No. ML21320A049) and dated December 17, 2021 (ADAMS Accession No. ML21351A008), Exelon Generation Company, LLC (the licensee) submitted Alternative Request GV-RR-10 to the U.S. Nuclear Regulatory Commission (NRC) for an alternative to specific inservice testing (IST) requirements in the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) at Nine Mile Point Nuclear Station, Unit 2 (Nine Mile Point 2), associated with the fourth 10-year IST Program interval. On February 1, 2022 (ADAMS Accession No. ML22032A333), Exelon Generation Company, LLC was renamed Constellation Energy Generation, LLC.
Specifically, pursuant to subparagraph (1) in paragraph (z), Alternatives to codes and standards requirements, of Section 55a, Codes and standards, in Part 50, Domestic Licensing of Production and Utilization Facilities, to Title 10, Energy, of the Code of Federal Regulations (10 CFR), the licensee requested to implement alternative request GV-RR-10 for the testing and schedule of excess flow check valves (EFCVs) at Nine Mile Point 2 on the basis that the proposed alternative will provide an acceptable level of quality and safety. The Nine Mile Point 2 fourth 10-year IST program interval began on January 1, 2019, and is scheduled to end on December 31, 2028.
2.0 REGULATORY REQUIREMENTS The NRC regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating plants, state that throughout the service life of a boiling or pressurized water-cooled nuclear power facility, pumps and valves that are within the scope of the ASME OM Code must meet the IST requirements (except design and access provisions) set forth in the ASME OM Code and addenda that become effective subsequent to editions and addenda specified in 10 CFR 50.55a(f)(2) and (3) and that are incorporated by reference in 10 CFR 50.55a(a)(1)(iv),
to the extent practical within the limitations of design, geometry, and materials of construction of Enclosure
the components. The IST requirements for pumps and valves that are within the scope of the ASME OM Code but are not classified as ASME Boiler and Pressure Vessel Code (BPV Code)
Class 1, Class 2, or Class 3 may be satisfied as an augmented IST program in accordance with 10 CFR 50.55a(f)(6)(ii) without requesting relief under 10 CFR 50.55a(f)(5) or alternatives under 10 CFR 50.55a(z). This use of an augmented IST program may be acceptable provided the basis for deviations from the ASME OM Code, as incorporated by reference in 10 CFR 50.55a, demonstrates an acceptable level of quality and safety, or that implementing the Code provisions would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety, where documented and available for NRC review.
The NRC regulations in 10 CFR 50.55a(b)(3)(xi), OM condition: Valve Position Indication, state the following:
When implementing paragraph ISTC-3700, Position Verification Testing, in the ASME OM Code, 2012 Edition through the latest edition and addenda of the ASME OM Code incorporated by reference in paragraph (a)(1)(iv) of this section, licensees shall verify that valve operation is accurately indicated by supplementing valve position indicating lights with other indications, such as flow meters or other suitable instrumentation to provide assurance of proper obturator position for valves with remote position indication within the scope of Subsection ISTC including its mandatory appendices and their verification methods and frequencies.
In proposing alternatives, a licensee must demonstrate that the proposed alternatives provide an acceptable level of quality and safety (10 CFR 50.55a(z)(1)) or compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety (10 CFR 50.55a(z)(2)).
3.0 TECHNICAL EVALUATION
3.1 Licensees Alternative Request Applicable Code Edition The applicable Code of Record for the fourth IST Program interval at Nine Mile Point 2 is the 2012 Edition of ASME OM Code.
ASME Code Components Affected In its submittal, the licensee proposed alternative testing for the following EFCVs:
Table 1 Component ID Class Category System 2CMS*EFV10 2 C Containment Atmosphere Monitoring 2CMS*EFV1A 2 C Containment Atmosphere Monitoring 2CMS*EFV1B 2 C Containment Atmosphere Monitoring 2CMS*EFV3A 2 C Containment Atmosphere Monitoring 2CMS*EFV3B 2 C Containment Atmosphere Monitoring 2CMS*EFV5A 2 C Containment Atmosphere Monitoring 2CMS*EFV5B 2 C Containment Atmosphere Monitoring 2CMS*EFV6 2 C Containment Atmosphere Monitoring 2CMS*EFV8A 2 C Containment Atmosphere Monitoring 2CMS*EFV8B 2 C Containment Atmosphere Monitoring 2CMS*EFV9A 2 C Containment Atmosphere Monitoring 2CMS*EFV9B 2 C Containment Atmosphere Monitoring 2DER*EFV31 2 C Drywell Equipment Drains 2IAS*EFV200 2 C Instrument Air 2IAS*EFV201 2 C Instrument Air 2IAS*EFV202 2 C Instrument Air 2IAS*EFV203 2 C Instrument Air 2IAS*EFV204 2 C Instrument Air 2IAS*EFV205 2 C Instrument Air 2IAS*EFV206 2 C Instrument Air 2ISC*EFV12 2 C Reactor Vessel Instrumentation 2ISC*EFV16 2 C Reactor Vessel Instrumentation 2ISC*EFV19 2 C Reactor Vessel Instrumentation 2ISC*EFV9 2 C Reactor Vessel Instrumentation 2RCS*EFV44A 2 C Reactor Coolant System 2RCS*EFV44B 2 C Reactor Coolant System
Applicable Code Requirement
The IST requirements in the ASME OM Code, as incorporated by reference in 10 CFR 50.55a, related to this alternative request are as follows:
ASME OM Code, Subsection ISTC, Inservice Testing of Valves in Light-Water Reactor Nuclear Power Plants, paragraph ISTC-3510, Exercising Test Frequency, states that Active Category A, Category B, and Category C check valves shall be exercised nominally every 3 months, except as provided by paragraphs ISTC-3520, ISTC-3540, ISTC-3550, ISTC-3570, ISTC-5221 and ISTC-5222.
Paragraph ISTC-3522, Category C Check Valves, subparagraph (a) states, in part, During operation at power, each check valve shall be exercised or examined in a manner that verifies obturator travel by using the methods in paragraph ISTC-5221.
Paragraph ISTC-3522, subparagraph (c) states If exercising is not practicable during operation at power and cold shutdowns, it shall be performed during refueling outage.
Paragraph ISTC-3700, Position Verification Testing, states that Valves with remote position indicators shall be observed locally at least once every 2 years to verify that valve operation is accurately indicated. Where practicable, this local observation should be supplemented by other indications such as use of flow meters or other suitable instrumentation to verify obturator position.
3.2 Reason for Request The ASME OM Code (2012 Edition), Subsection ISTC, paragraph ISTC-3510, requires check valves to be exercised quarterly during plant operation. Further, paragraph ISTC-3522, subparagraph (c) requires if valve exercising is not practicable during plant operation and cold shutdown, it shall be performed during refueling outages. Based on past experience, the licensee stated that EFCV testing during inservice leakage testing can become the outage critical path and could possibly extend the outage if all EFCVs were to be tested during this time frame. The testing requires isolation of the instruments associated with each EFCV and opening of a drain valve to actuate the EFCV. Process fluid will be contaminated to some degree, requiring special measures to collect flow from the drain valve and also contributes to an increase in personnel radiation exposure. EFCVs are also required to be tested in accordance with ISTC-3700, which requires remote position verification at least once every 2 years.
The twenty six (26) EFCVs listed in Table 1 are normally open valves, which provide flow to safety-related instrumentation. Low-pressure EFCVs are safety-related active components designed to close in the event of an instrument line break outside of containment.
The licensee stated that the EFCVs are installed on instrument lines penetrating containment to minimize leakage in the event of an instrument line failure outside the containment in accordance with NRC Regulatory Guide 1.11. The EFCV is a spring-loaded check valve, with a position indication feature. Since the system is normally in a static condition, the valve flow restrictor is held open by the spring. When the valve is in its normal open position, the light indication is off. Any sudden increase in flow through the valve (i.e., line break) will result in a differential pressure across the valve which will overcome the spring and close the valve. This in turn, results in a change in position indication (light on). The valve is designed to allow some leakage past the seat in the closed position. This leakage will act to equalize pressure across the valve in the event the excess flow condition is corrected, thus allowing the spring to reopen the valve.
At Nine Mile Point 2, these low pressure EFCVs have installed position indication. Functional testing of valve closure and position verification are accomplished by connecting a temporary air supply and drain line to the EFCV, then venting the instrument side of the valve while the process side is under low pressure and observing a change in position indication and by
verifying that only a small amount of leakage (flow) exits through the vent. The testing of the EFCV requires the removal of the associated instrument or instruments from service.
The EFCVs are classified as ASME Code, Category C, and are also containment isolation valves. However, these valves are excluded from 10 CFR Part 50, Appendix J, Section III.C, leakage rate testing due to the size of the instrument lines; therefore, these EFCVs have no safety-related seat leakage criterion.
At Nine Mile Point 2, the internal design of the EFCV contains a flow restrictor which is spring-loaded and is, therefore, not designed with any type of pinned stem-to-disk connection, thus, making the EFCV at Nine Mile Point 2 non-susceptible to stem-to-disk separation. The field test procedure and the IST Program Plan will be revised to assure that each EFCV failure is entered into the corrective action program (CAP) and evaluated against performance criteria with appropriate corrective actions taken based on the failure analysis and trend in failures. If failures exceed the performance criteria of less than or equal to one failure during a 24-month rolling average, the IST Program Plan will require a cause evaluation and determination of additional testing requirements. The failed valves will be tested in the next refueling outage.
Industry experience, as documented in General Electric (GE) Topical Report NEDO-32977-A, Excess Flow Check Valve Testing Relaxation, dated June 2000, indicates the EFCVs have a very low failure rate. The licensee stated that the Nine Mile Point 2 test experience is consistent with the findings in the NEDO document. The NEDO document indicates that many reported test failures at other plants were related to test methodologies and not actual EFCV failures. An evaluation of the maintenance history and a comparison to the acceptance criteria in NEDO-32977-A concludes that Nine Mile Point 2 has demonstrated that the low-pressure EFCVs are highly reliable and that failures to isolate are very infrequent (4 out of approximately 286 tests in 22 years). The failure rate of the Unit 2 low-pressure EFCVs was also confirmed to be below the highest failure rates presented in NEDO-32977-A. Based on the high reliability of the EFCVs and the low failure rate, the licensee believes that ISTC-3700 position verification provides little to no added benefit to safety.
EFCV testing requires equipment setup and system reconfiguration. The licensee asserted that testing during refueling is costly and requires additional radioactive dose exposure with no increase in safety as compared to the proposed alternative for the EFCVs at Nine Mile Point 2.
3.3 Proposed Alternative The licensee stated that Nine Mile Point 2 is presently testing the referenced EFCVs, which are connected to the containment atmosphere, on a 24-month frequency. Under proposed Alternative Request GV-RR-10, Nine Mile Point 2 EFCVs will be tested on a representative sampling basis of approximately 20 percent every refueling outage, and all EFCVs will be tested at least once within a 10-year interval.
3.4 NRC Staff Evaluation The licensee's justification for Alternative Request GV-RR-10 is based on GE Nuclear Energy NEDO-32977-A, Excess Flow Check Valve Testing Relaxation, dated June 2000. The topical report provided (1) an estimate of steam release frequency (into the reactor building) due to a break in an instrument line concurrent with an EFCV failure to close, and (2) an assessment of the radiological consequences of such a release. The NRC staff reviewed NEDO-32977-A and issued a safety evaluation on March 14, 2000 (ADAMS Accession No. ML003691722). In its
evaluation, the NRC staff found that the test interval could be extended up to a maximum of 10 years. In conjunction with this finding, the NRC staff noted that each licensee that adopts the relaxed test interval program for EFCVs must have a failure feedback mechanism and a CAP to ensure EFCV performance continues to be bounded by the topical report results. Also, each licensee is required to perform a plant-specific radiological dose assessment, EFCV failure analysis, and release frequency analysis to confirm that they are bounded by the generic analyses of the topical report. In its response dated November 15, 2021, to an NRC staff request for additional information, the licensee described its actions to address the conditions specified in NEDO-32977-A related to EFCV failure rate and release frequency, failure feedback mechanism and CAP, and radiological dose assessment. The NRC staff reviewed the licensee's response related to the applicability of NEDO-32977-A, as well as conformance with the guidance regarding radiological dose assessment, EFCV failure rate, release frequency, and the proposed failure feedback mechanism and CAP.
The NRC staff reviewed the licensees description of the design of the EFCVs and plans to verify the remote position indication for the EFCVs in the supplemental information provided in the licensees letter dated December 17, 2021. For example, the licensee stated that the EFCVs are not designed with any type of pinned stem-to-disk connection such that they are not susceptible to stem-to-disk separation. The licensee described the functional testing and position verification of the EFCVs by connecting a temporary air supply and drain line, then venting the instrument side of the valve while the process side is under low pressure and observing a change in position and by verifying that only a small amount of flow exits through the vent. The staff considers the fundamental design of the EFCVs and position verification activity supports an extension of the ISTC-3700 test interval as supplemented by 10 CFR 50.55a(b)(3)(xi).
The licensee reported that the Nine Mile Point 2 test experience with the EFCVs is consistent with the reliable performance history documented in NEDO-32977-A. For example, Nine Mile Point 2 has demonstrated that the EFCVs are highly reliable with very infrequent failures. The licensee stated that the field test procedure and IST Program Plan will be revised to assure that each EFCV failure is entered into the CAP and evaluated against performance criteria with appropriate corrective actions taken based on the failure analysis and trend in failures. If failures exceed the performance criteria of less than or equal to one failure during a 24-month rolling average, the IST Program Plan will require a cause evaluation and determination of additional testing requirements. The licensee stated that any failed valves will be tested during the next refueling outage.
Based on its review, the NRC staff finds that the licensee has supported the proposed testing and schedule in Alternative Request GV-RR-10 for the EFCVs that meets the requirements of 10 CFR 50.55a(z)(1) by providing an acceptable level of quality and safety.
4.0 CONCLUSION
As indicated above, the NRC staff has determined that the proposed alternative GV-RR-10 as described in the licensees letters dated September 8, 2021, November 15, 2021, and December 17, 2021, provides an acceptable level of quality and safety for the proposed testing and schedule for the EFCVs at Nine Mile Point 2 listed in Table 1 of this safety evaluation.
Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1) for alternative GV-RR-10. Therefore, the NRC
staff authorizes the proposed alternative GV-RR-10 for the fourth 10-year IST program interval at Nine Mile Point 2, which began on January 1, 2019, and is scheduled to end on December 31, 2028.
All other ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a for which relief or an alternative was not specifically requested, and granted or authorized (as appropriate), in the subject request remain applicable.
Principal Contributor: G. Bedi, NRR Date: March 11, 2022
ML22061A040 *by safety evaluation dated OFFICE NRR/DORL/LPL1/PM NRR/DORL/LPL1/LA NRR/DEX/EMIB/BC(A)* NRR/DORL/LPL1/BC NAME RGuzman KEntz ITseng JDanna DATE 3/4/2022 3/7/2022 2/22/2022 3/11/2022