ML20216A539
| ML20216A539 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 08/06/2020 |
| From: | Jennifer Dixon-Herrity Plant Licensing Branch IV |
| To: | Lacal M Arizona Public Service Co |
| Lingam S, 301-415-1564 | |
| References | |
| EPID L 2020 LLR 0045 | |
| Download: ML20216A539 (10) | |
Text
August 6, 2020 Mrs. Maria L. Lacal Executive Vice President/
Chief Nuclear Officer Arizona Public Service Company P.O. Box 52034, Mail Station 7605 Phoenix, AZ 85072-2034
SUBJECT:
PALO VERDE NUCLEAR GENERATING STATION, UNIT 2 - RELIEF REQUEST 65 FOR INSPECTION OF REACTOR PRESSURE VESSEL BOTTOM MOUNTED INSTRUMENT NOZZLES AND PRESSURIZER SURGE LINE WELD OVERLAY (EPID L-2020-LLR-0045)
Dear Mrs. Lacal:
By letter dated March 27, 2020, as supplemented by letter dated March 30, 2020, Arizona Public Service Company (the licensee) requested the U.S. Nuclear Regulatory Commissions (NRCs) approval of Relief Request 65 for inservice inspection examinations for the reactor pressure vessel bottom mounted instrumentation nozzles and a pressurizer surge line nozzle weld overlay from the Unit 2 spring of 2020 refueling outage (2R22) to the next refueling outage (2R23) in the fall of 2021 due to the COVID-19 pandemic at Palo Verde Nuclear Generating Station (Palo Verde), Unit 2. Relief Request 65 requested an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section XI and Code Cases N-722-1, Additional Examinations for PWR [Pressurized Water Reactors] Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 MaterialsSection XI, Division 1 and N-770-2, Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated With UNS [Unified Numbering System] N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation ActivitiesSection XI, Division 1, as required by Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a, for Palo Verde, Unit 2.
Pursuant to 10 CFR 50.55a(z)(2), the licensee has determined that complying with the specified 10 CFR 50.55a and ASME Code requirements to inspect the reactor pressure vessel bottom mounted instrumentation nozzles and the pressurizer surge line nozzle full structural weld overlay would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety, noting that reducing the number of contractors brought onsite during the 2R22 refueling outage will reduce the risk of spreading the coronavirus to Palo Verde personnel who safely operate the plant.
The NRC staff has reviewed the licensees submittal and concludes, as set forth in the enclosed safety evaluation, that the proposed alternative in Relief Request 65 has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Accordingly, the NRC staff determines that granting relief pursuant to 10 CFR 50.55a(z)(2) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the
M. Lacal requirements were imposed on the facility. Therefore, the NRC grants the use of proposed alternative for the examination of welds listed in Relief Request 65 at Palo Verde, Unit 2 for the inservice inspection of the reactor pressure vessel bottom mounted instrumentation nozzles and the pressurizer surge line nozzle full structural weld overlay from refueling outage 2R22 (spring of 2020) to refueling outage 2R23 (fall of 2021), due to the COVID-19 pandemic.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject request for relief remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact the Project Manager, Siva P. Lingam, at 301-415-1564 or by e-mail to Siva.Lingam@nrc.gov.
Sincerely, Jennifer L. Dixon- Digitally signed by Jennifer L.
Dixon-Herrity Herrity Date: 2020.08.06 07:30:39 -04'00' Jennifer L. Dixon-Herrity, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-529
Enclosure:
Safety Evaluation cc: Listserv
ML20216A539 *by e-mail OFFICE NRR/DORL/LPL4/PM* NRR/DORL/LPL4/LA* NRR/DNRL/NPHP/BC* NRR/DORL/LPL4/BC*
NAME SLingam PBlechman MMitchell JDixon-Herrity DATE 8/5/20 8/5/2020 7/30/20 8/6/2020 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 65 DEFER ASME CODE INSERVICE INSPECTION OF BOTTOM MOUNTED INSTRUMENTATION NOZZLES AND SURGE LINE WELD OVERLAY DUE TO COVID-19 PANDEMIC ARIZONA PUBLIC SERVICE COMPANY PALO VERDE NUCLEAR GENERATING STATION, UNIT 2 DOCKET NO. 50-529
1.0 INTRODUCTION
By letter dated March 27, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20088A533), as supplemented by letter dated March 30, 2020 (ADAMS Accession No. ML20090L944), Arizona Public Service Company (APS, the licensee),
requested an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI and Code Cases N-722-1, Additional Examinations for PWR [Pressurized Water Reactors] Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 MaterialsSection XI, Division 1 and N-770-2, Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated With UNS [Unified Numbering System] N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation ActivitiesSection XI, Division 1, as required by Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a, Codes and standards, for Palo Verde Nuclear Generating Station (Palo Verde), Unit 2.
Pursuant to 10 CFR 50.55a(z)(2), Hardship without a compensating increase in quality and safety, the licensee submitted this alternative requesting U.S. Nuclear Regulatory Commission (NRC) approval to defer the scheduled Palo Verde, Unit 2 inservice inspection (ISI) examinations for the reactor pressure vessel (RPV) bottom mounted instrumentation (BMI) nozzles and a pressurizer surge line nozzle weld overlay from the spring of 2020 refueling outage (2R22) to the next refueling outage (2R23) in the fall of 2021 due to the COVID-19 pandemic. The licensee has concluded that complying with the specified 10 CFR 50.55a and ASME Code requirements to inspect the RPV BMI nozzles and the pressurizer surge line nozzle full structural weld overlay would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety, noting that reducing the number of Enclosure
contractors brought onsite during the 2R22 refueling outage will reduce the risk of spreading the COVID-19 virus to Palo Verde personnel who safely operate the plant.
Verbal Authorization was provided on March 31, 2020 (ADAMS Accession No. ML20091M199).
2.0 REGULATORY EVALUATION
Compliance with 10 CFR 50.55a, ASME Code,Section XI and Code Case N-722-1 requires visual examination of the RPV BMI nozzle penetrations every other outage and Code Case N-770-2 requires the pressurizer nozzle surge line weld overlay be examined in 2R22 by qualified staff.
Adherence to Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, 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 preservice examination requirements, set forth in ASME Code,Section XI.
The regulations in 10 CFR 50.55a(z) state, in part:
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) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety.
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.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request, and the NRC to authorize, the alternative requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Licensees Relief Request 3.1.1 ASME Code Affected Components The affected components at Palo Verde, Unit 2, are 61 RPV BMI nozzle penetrations under ASME Code Class 1, Examination Category B-P, Item Number 15.80. The subject weld joins the RPV BMI nozzle to the RPV.
The other affected components are ASME Code Class 1, PWR pressure retaining dissimilar metal piping and vessel nozzle butt welds containing Alloy 82/182 with full structural weld overlay, weld 5-34-OL, which encapsulates weld 5-34 (pressurizer surge nozzle-to-safe end weld) and the adjacent weld 20-1 (safe end-to-surge line weld). These welds are defined in
Code Case N-770-2 as inspection Item F-1, Cracked butt weld reinforced by full structural weld overlay of Alloy 52/152 materials.
3.1.2 Applicable Code Edition and Addenda The current Code of record for the fourth 10-year ISI interval at Palo Verde, Unit 2 is ASME Code,Section XI, 2013 Edition. Palo Verde, Unit 2 entered the fourth inspection interval on November 1, 2018, and currently, the ASME Code,Section XI, 2013 Edition is utilized for Appendix VIII, Performance Demonstration for Ultrasonic Examinations.
3.1.3 Applicable Code Requirement ASME Code Case N-722-1, as required by 10 CFR 50.55a, requires visual examination of the RPV BMI nozzle penetrations every other outage in order to detect leakage as a result of primary water stress corrosion cracking operating experience (OE).
ASME Code Case N-770-2, as required by 10 CFR 50.55a, defines the inspection category for the full structural overlay as Item F-1 and includes examination of weld overlays on a sample basis. Sample size should include 25 percent of the population of these weld overlays and shall be examined once each inspection interval. The 25 percent sample shall consist of the same welds in the same sequence during successive intervals to the extent practical provided the 25 percent sample contains the welds that experience the highest operating temperature in the inspection item. Those welds not included in the 25 percent sample shall be examined prior to the end of the mitigation evaluation period if the plant is to be operated beyond that time.
3.1.4 Reason for Request Pursuant to 10 CFR 50.55a(z)(2), the licensee submitted this alternative requesting NRC approval to defer the scheduled Palo Verde, Unit 2 ISI examinations for the RPV BMI nozzles and a pressurizer surge line nozzle weld overlay from refueling outage 2R22 to the 2R23 refueling outage in the fall of 2021 due to the COVID-19 pandemic. The licensee stated that complying with the specified 10 CFR 50.55a and ASME Code requirements to inspect the RPV BMI nozzles and the pressurizer surge line nozzle full structural weld overlay would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety, noting that reducing the number of contractors brought onsite during the 2R22 refueling outage will reduce the risk of spreading the coronavirus to Palo Verde personnel who safely operate the plant.
The U.S. Federal Government made a declaration of emergency due to COVID-19, pursuant to the Stafford Act, on March 13, 2020, while the U.S. Center for Disease Control has determined that COVID-19 poses a serious public health risk. Due to the COVID-19 pandemic, APS has enacted guidelines to limit outside contractors, including those that perform examinations for the ISI program, in order to minimize the potential of inadvertently spreading the COVID-19 virus to Palo Verde personnel. The licensees outage scope was modified to reduce the number of outside contractors accessing Palo Verde site owner-controlled area by approximately 300. The licensee was able to defer many ISI examinations to the 2R23 refueling outage within the existing APS ISI programmatic controls, except for the two ISI examinations addressed by this alternative. These ISI examinations are for Code Case N-722-1 visual examination of the RPV BMI nozzle penetrations and Code Case N-770-2 volumetric examination of the pressurizer surge line nozzle weld overlay. Palo Verde site personnel do not have the equipment and qualifications to perform RPV BMI nozzle and pressurizer surge line nozzle weld overlay
examinations. Due to the potential spread of COVID-19 to Palo Verde personnel, the licensee has identified the performance of RPV BMI and pressurizer surge line nozzle weld overlay examinations as a hardship without a compensating increase in the level of quality and safety in accordance with 10 CFR 50.55a(z)(2). The licensee is proposing to delay the examinations for one refueling cycle to the 2R23 refueling outage in the fall of 2021.
3.1.5 Proposed Alternative and Basis for Use The licensee is proposing to extend the scheduled Palo Verde, Unit 2 ISI examinations for the RPV BMI nozzles and a pressurizer nozzle surge line weld overlay from refueling outage 2R22 to refueling outage 2R23 in the fall of 2021 due to COVID-19 issues.
RPV BMI Inspection Regarding OE, the previous RPV BMI inspection for Palo Verde, Unit 2 was performed in the spring of 2017 during refueling outage 2R20 with no relevant indications. To date there have been no observed RPV BMI leaks in Palo Verde, Unit 2. Palo Verde, Unit 3 had a leaking RPV BMI nozzle in 2013 but was attributed to a fabrication defect. No other Unit 3 RPV BMI nozzles had indications based on ultrasonic and eddy current examinations. Since primary water stress corrosion cracking can also be attributed to material condition, the heat numbers for the RPV BMI nozzles used in Palo Verde, Units 2 and 3 were reviewed. Palo Verde, Unit 2 was made from one heat number, which was a different heat number from Palo Verde, Unit 3. As part of the design, each RPV BMI nozzle has an anti-ejection collar to prevent nozzle ejection. In addition, the licensee monitors the sump for leakage to prevent structural loss of the bottom head. The licensee would investigate the increased leakage and has the ability to shut down the unit in a controlled manner prior to a nozzle failure, if unacceptable increased leakage were to occur.
The licensee indicated in its letter dated March 27, 2020, that the RPV BMI nozzles are in a locked high radiation area. Dose rates in the area are 1000 millirem per hour or greater. To enter the area, personnel must wear a restraint harness and climb down an approximately 45-foot ladder. Confined space permits and an emergency plan must also be in place prior to entering. Entry windows in the insulation must be opened to obtain access. Only a small subset of nozzles and limited access could be obtained. For dose and coverage concerns, a robot is used that can travel along the RPV insulation. Due to personnel safety, dose and visual limitations, no alternative inspections of the nozzles or the general area were determined to be practical during refueling outage 2R22. Currently APS does not have the internal capability and equipment to perform the inspection and this must be done by the vendor. The four contractors needed to perform the RPV BMI inspections traveled to states that have confirmed cases of COVID-19.
Pressurizer Weld Overlay Inspection The licensee indicated in its letter dated March 27, 2020, that overall, weld 5-34-OL is scheduled to be examined three times in the fourth interval. Weld 5-34 OL examination frequency is based on the Design Report PV-23Q-405, which currently uses the time for a circumferential flaw in the dissimilar metal weld to reach the structural overlay thickness. The postulated time to reach the minimum allowable overlay thickness is 3 years for the dissimilar metal weld and 4 years for the similar metal safe end-to-pipe weld. The last examination performed on weld 5-34-OL was in 2017 and documented in Report 17-UTE-2017. No flaws
were detected in the overlay or in the base metal of the dissimilar and similar metal welds during the April 2017 examination.
The licensee also indicated that the 3-year life for weld 5-34 and 4-year life for weld 20-1 are based on a conservative analysis. The crack growth evaluation of pressurizer surge nozzle weld overlay applies the design fatigue cycles for each year of operation and assumes 360 degrees of the base metal is flawed through 75 percent of the weld. The fatigue calculation assumes 12.5 heatup and cooldown cycles per year, while it was documented in Surveillance Test Work Orders 4915281 and 4788084 for 73ST-9RC02, Reactor Coolant System Transient and Operational Cycles, that five heatup and five cooldown cycles were actually performed during Palo Verde, Unit 2 Operating Cycles 20 and 21. The fatigue evaluation for the pressurizer surge nozzle overlay, concludes that circumferential flaws in the dissimilar metal weld takes 3 years to reach the overlay and circumferential flaws in the stainless steel weld takes 4 years to reach the overlay.
In its supplemental letter dated March 30, 2020, the licensee indicated that further evidence of cyclic fatigue conservatism is presented by the evaluation for environmentally assisted fatigue screening that was conducted for license renewal. The study determined sentinel locations for environmentally assisted fatigue and usage factor (Uen) for a number of components. For the pressurizer surge nozzle overlay and the hot-leg surge nozzle, the sentinel location for the hot-leg surge nozzle contains a Uen of 7.58, where pressurizer surge nozzle overlay contains a Uen of 2.28. The analysis of the hot-leg surge nozzle is bounding for the pressurizer surge nozzle overlay. The analysis for the hot-leg surge nozzle results in a design cumulative Uen of 0.4949, whereas the 60-year usage factor utilizing projected cycle count based on actual plant data for Palo Verde, Unit 2 hot-leg nozzle is 0.0948 Uen. Thermal cycles projected by the end of life for Palo Verde, Unit 2 pressurizer surge nozzle overlay are bounded by the design cycles documented in fracture mechanics evaluation.
The licensee further indicated in its supplement that based on the above considerations of the number of cycles and 60-year life for Level A and B service loads and transients, it can be said that the pressurizer surge line weld overlay with a fatigue life of 3 years to reach the overlay inside diameter from a 75 percent cracked pipe is conservative by a factor of 4.
The licensee indicated in its letter dated March 27, 2020, that due to the conservative nature of the calculation and three previous inservice examinations detecting no inservice flaws in the original base metal and welds, it is not expected that a crack would exceed critical flaw size by 2R23 refueling outage scheduled for fall 2021. No known industry experience exists for flaw propagation or failure of an Alloy 82/182 weld that has been mitigated with a full structural weld overlay. In addition, APS monitors the sump for leakage to prevent structural loss of the surge line.
The licensee further indicated that postponing the weld 5-34-OL examination will not result in a reduction in safety or quality. Currently, no site staff at Palo Verde have the ASME Code,Section XI, Appendix VIII certification to perform the weld overlay examination. To perform the examination, a contractor was required to travel to Palo Verde. In light of the travel recommendations that exist from the COVID-19 pandemic and risk to examiners traveling pose to themselves and site personnel, performance of the pressurizer surge nozzle weld 5-34-OL is considered a hardship per 10 CFR 50.55a(z)(2).
Duration of Proposed Alternative The duration of the request is until completion of the next scheduled refueling outage, scheduled for the fall of 2021.
3.2 NRC Staff Evaluation RPV BMI Inspection For the 61 RPV BMI nozzle penetrations, OE for the Palo Verde, Unit 2 RPV BMI nozzles shows that there have been no leaks, and the last visual inspection of the RPV BMI nozzles in 2017 revealed no relevant indications. Palo Verde, Unit 3 had a leaking RPV BMI nozzle in 2013 but was attributed to a fabrication defect. No other Palo Verde, Unit 3 RPV BMI nozzles had indications based on ultrasonic and eddy current examinations. In addition, the Palo Verde, Unit 2 RPV BMI nozzle material is of a different heat than that of the Palo Verde, Unit 3 RPV BMI nozzles and, therefore, the same material condition may not be present in the Palo Verde, Unit 2 RPV BMI nozzles. The licensee is also crediting enhanced leakage monitoring with the capability of detecting unidentified leakage of 0.1 gallons per minute (gpm) or greater, and plant procedures, which require taking appropriate action to identify and address the source of the leak, including, if necessary, shutting down the unit in a controlled manner, as providing adequate protection against a nozzle failure as outlined in the licensees letter dated March 30, 2020. The NRC staff found the licensees evaluation of the OE at Palo Verde, Unit 2 that recorded no flaws or leaks at the RPV BMI nozzles based on previous examinations provides sufficient justification to support the requested alternative. In addition, the NRC staff finds that the Palo Verde, Unit 2 enhanced leakage monitoring and actions required by plant procedures provide reasonable assurance of adequate safety to defer the ISI examinations of the RPV BMI nozzles by one refueling outage.
Pressurizer Weld Overlay Inspection For the pressurizer surge line nozzle weld overlay (5-34-OL) of dissimilar metal weld (5-34) and similar metal weld (20-1), OE shows that the preemptive Alloy 52 weld overlay installed in 2008 had no indications of flaws during phased array ultrasonic examinations performed in 2008, 2011, 2014, and 2017. In addition, these same ultrasonic examinations recorded no indications in the outer 25 percent of the underlying Alloy 82/182 material of weld 5-34-OL. The licensee is also crediting enhanced leakage monitoring with the capability of detecting unidentified leakage of 0.1 gpm or greater, and plant procedures, which require taking appropriate action to identify and address the source of the leak, including, if necessary, shutting down the unit in a controlled manner, as providing adequate protection against a failure at the weld overlay location as outlined in the licensees letter dated March 30, 2020. The licensee also stated there is additional margin in the ISI examination interval due to the previous conservative fatigue crack growth analysis used to initially determine the examination frequency of the weld overlay, as clarified in the licensees letter dated March 30, 2020. The fatigue crack growth analysis is conservative and includes all sources of thermal fatigue transients, with conservative transient estimates that are well above actual plant operating conditions as discussed in the licensees letter dated March 30, 2020. Based on the above considerations of number of cycles and 60-year life for Level A and B service loads and transients, it can be said that the pressurizer surge line weld overlay with a fatigue life of 3 years to reach the overlay inside diameter from a 75 percent cracked pipe is conservative by a factor of 4. The NRC staff found the licensees evaluation of the conservatisms in the fatigue crack growth evaluation and review of past inspection results provides sufficient justification to support the requested alternative. In
addition, the NRC staff finds that the enhanced Palo Verde, Unit 2 leakage monitoring and actions required by plant procedures provides reasonable assurance of adequate safety to defer the ISI examinations of the surge line nozzle weld overlay for one refueling outage.
Summary Based on the results of the information provided above, the NRC staff finds that (1) there is reasonable assurance of adequate protection based on the OE of the RPV BMI nozzles, which show no recorded indications, and the enhanced leakage monitoring with the capability of detecting 0.1 gpm of unidentified leakage and the associated actions required by plant procedures for deferring the ISI examination until the 2R23 refueling outage in the fall of 2021 for the 61 RPV BMI nozzle penetrations, (2) there is reasonable assurance of adequate protection based on the inspection history of the weld overlay, which shows no recorded indications, conservatisms in the licensees fatigue crack growth analysis for the pressurizer surge line nozzle weld overlay, and the enhanced leakage monitoring with the capability of detecting 0.1 gpm of unidentified leakage and the associated actions required by plant procedures for deferring the ISI examination for the pressurizer surge line nozzle weld overlay until 2R23 refueling outage in the fall of 2021, and (3) the licensees hardship justification is acceptable.
4.0 CONCLUSION
As set forth above, the NRC staff concludes that the proposed alternative in Relief Request 65 has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
Accordingly, the NRC staff determines that granting relief pursuant to 10 CFR 50.55a(z)(2) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Therefore, the NRC grants the use of proposed alternative for the examination of welds listed in Relief Request 65 at Palo Verde, Unit 2 for the ISI of the RPV BMI nozzles and the pressurizer surge line nozzle full structural weld overlay from refueling outage 2R22 (spring of 2020) to refueling outage 2R23 (fall of 2021), due to the COVID-19 pandemic All other requirements in ASME Code,Section XI for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: J. Honcharik Date: August 6, 2020