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==Dear Mrs. Lacal:== | ==Dear Mrs. Lacal:== | ||
By letter dated July 17, 2019, as supplemented by letter dated February 19, 2020, Arizona Public Service Company (the licensee) requested the U.S. Nuclear Regulatory Commissions (NRCs) approval of Relief Request (RR) 64 for the third 10-year inservice inspection interval at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR 64, the licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 component welds. | By {{letter dated|date=July 17, 2019|text=letter dated July 17, 2019}}, as supplemented by {{letter dated|date=February 19, 2020|text=letter dated February 19, 2020}}, Arizona Public Service Company (the licensee) requested the U.S. Nuclear Regulatory Commissions (NRCs) approval of Relief Request (RR) 64 for the third 10-year inservice inspection interval at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR 64, the licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 component welds. | ||
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.55a(g)(5)(iii), the licensee requested relief on the basis that achieving the ASME Code-required examination coverage is impractical. | Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.55a(g)(5)(iii), the licensee requested relief on the basis that achieving the ASME Code-required examination coverage is impractical. | ||
The NRC staff has reviewed the licensees submittal and concludes, as set forth in the enclosed safety evaluation, that the proposed alternative in RR 64 has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Accordingly, the NRC staff determines that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) 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 RR 64 at Palo Verde, Unit 1 for the third 10-year inservice inspection interval, which commenced on July 18, 2008, and ended May 31, 2019. | The NRC staff has reviewed the licensees submittal and concludes, as set forth in the enclosed safety evaluation, that the proposed alternative in RR 64 has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Accordingly, the NRC staff determines that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) 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 RR 64 at Palo Verde, Unit 1 for the third 10-year inservice inspection interval, which commenced on July 18, 2008, and ended May 31, 2019. | ||
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==1.0 INTRODUCTION== | ==1.0 INTRODUCTION== | ||
By letter dated July 17, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19198A340), as supplemented by letter dated February 19, 2020 (ADAMS Accession No. ML20054A269), Arizona Public Service Company (the licensee), | By {{letter dated|date=July 17, 2019|text=letter dated July 17, 2019}} (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19198A340), as supplemented by {{letter dated|date=February 19, 2020|text=letter dated February 19, 2020}} (ADAMS Accession No. ML20054A269), Arizona Public Service Company (the licensee), | ||
submitted Relief Request (RR) 64 to the U.S. Nuclear Regulatory Commission (NRC) for the third 10-year inservice inspection (ISI) interval at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR 64, the licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 component welds. | submitted Relief Request (RR) 64 to the U.S. Nuclear Regulatory Commission (NRC) for the third 10-year inservice inspection (ISI) interval at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR 64, the licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 component welds. | ||
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii), | Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii), | ||
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Table 1. Examination Category B-A, Item No. B1.11, Limited Volumetric Examination Coverage Weld Examination Percent Coverage Weld Identification Material Limitation Achieved Vessel inlet and outlet Ferritic nozzles interfere with 1-10 80% | Table 1. Examination Category B-A, Item No. B1.11, Limited Volumetric Examination Coverage Weld Examination Percent Coverage Weld Identification Material Limitation Achieved Vessel inlet and outlet Ferritic nozzles interfere with 1-10 80% | ||
Steel scanning above and below the weld. | Steel scanning above and below the weld. | ||
By supplemental letter dated February 19, 2020, the licensee clarified the access limitation associated with the inlet and outlet. The six nozzles extend from the intermediate vessel shell to the upper vessel shell. Therefore, the nozzle-to-shell welds intersect and interrupt the circumferential weld between the upper and intermediate shells. The outlet nozzles are larger in diameter than the inlet nozzles, and they have protruding geometry into the inside of the vessel. | By supplemental {{letter dated|date=February 19, 2020|text=letter dated February 19, 2020}}, the licensee clarified the access limitation associated with the inlet and outlet. The six nozzles extend from the intermediate vessel shell to the upper vessel shell. Therefore, the nozzle-to-shell welds intersect and interrupt the circumferential weld between the upper and intermediate shells. The outlet nozzles are larger in diameter than the inlet nozzles, and they have protruding geometry into the inside of the vessel. | ||
The described geometric limitations create obstacles for performing the examination to the extent required by the ASME Code. | The described geometric limitations create obstacles for performing the examination to the extent required by the ASME Code. | ||
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: 4. Performance of plant walkdowns. | : 4. Performance of plant walkdowns. | ||
: 5. Performance of system pressure tests and associated visual examination. | : 5. Performance of system pressure tests and associated visual examination. | ||
Regarding the examination history of this weld, Table 2-A of the licensees supplemental letter dated February 19, 2020, describes the flaw geometry of nine detected and sized indications. | Regarding the examination history of this weld, Table 2-A of the licensees supplemental {{letter dated|date=February 19, 2020|text=letter dated February 19, 2020}}, describes the flaw geometry of nine detected and sized indications. | ||
The indications were dispositioned according to ASME Code, Section XI, 2001 Edition through 2003 Addenda. They were reconciled against previous examination results and were determined to be fabrication flaws, with no observed growth during service. | The indications were dispositioned according to ASME Code, Section XI, 2001 Edition through 2003 Addenda. They were reconciled against previous examination results and were determined to be fabrication flaws, with no observed growth during service. | ||
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welds, the NRC staff finds that the licensees RR is acceptable. | welds, the NRC staff finds that the licensees RR is acceptable. | ||
Based on the above discussion, the NRC staff determined that obtaining the ASME Code-required examination volume coverage for the subject pressurizer welds is impractical because of the stated limitations and that the modifications necessary to obtain the required coverage would impose a burden upon the licensee. The NRC staff determined that the volumetric examination performed to the maximum extent practical provides reasonable assurance of structural integrity of the welds for the following reasons: (1) the detected indications were not due to service-induced loads and were below the ASME Code allowable sizes; and (2) despite the limited coverages, the licensee examined regions of the welds most susceptible to service-induced degradation should it occur. | Based on the above discussion, the NRC staff determined that obtaining the ASME Code-required examination volume coverage for the subject pressurizer welds is impractical because of the stated limitations and that the modifications necessary to obtain the required coverage would impose a burden upon the licensee. The NRC staff determined that the volumetric examination performed to the maximum extent practical provides reasonable assurance of structural integrity of the welds for the following reasons: (1) the detected indications were not due to service-induced loads and were below the ASME Code allowable sizes; and (2) despite the limited coverages, the licensee examined regions of the welds most susceptible to service-induced degradation should it occur. | ||
In Section 8 of the enclosure to the licensees letter dated July 17, 2019, the licensee described one item in its corrective action program. The licensee performed examinations of welds 3-100-IR (inside radius) and 4-100-IR and reported a coverage of 95 percent, which meets the ASME Code requirement. However, during the closeout review, the licensee discovered that the equipment used to perform the examination was the same designed for the previous steam generators. After a modeling effort, the licensee stated that only 70 percent of the Code-required volume was achieved, as a result of using the older equipment and procedure. The licensee canceled the older procedure, and new equipment is now available to support proper performance of the examination in future intervals. This item is not a licensing issue, and therefore, will not be dispositioned in this SE. The NRC staff may refer this topic to NRC inspectors for future interactions with the licensee on this matter. | In Section 8 of the enclosure to the licensees {{letter dated|date=July 17, 2019|text=letter dated July 17, 2019}}, the licensee described one item in its corrective action program. The licensee performed examinations of welds 3-100-IR (inside radius) and 4-100-IR and reported a coverage of 95 percent, which meets the ASME Code requirement. However, during the closeout review, the licensee discovered that the equipment used to perform the examination was the same designed for the previous steam generators. After a modeling effort, the licensee stated that only 70 percent of the Code-required volume was achieved, as a result of using the older equipment and procedure. The licensee canceled the older procedure, and new equipment is now available to support proper performance of the examination in future intervals. This item is not a licensing issue, and therefore, will not be dispositioned in this SE. The NRC staff may refer this topic to NRC inspectors for future interactions with the licensee on this matter. | ||
3.3 Examination Category C-B, Pressure Retaining Nozzle Welds in Vessels, Item No. C2.21, Nozzle-to-Shell Weld 3.3.1 Components Affected Details of the steam generator welds under Examination Category C-B are shown in Table 3 of this SE, as obtained from the attachment to the licensees submittal dated July 17, 2019. | 3.3 Examination Category C-B, Pressure Retaining Nozzle Welds in Vessels, Item No. C2.21, Nozzle-to-Shell Weld 3.3.1 Components Affected Details of the steam generator welds under Examination Category C-B are shown in Table 3 of this SE, as obtained from the attachment to the licensees submittal dated July 17, 2019. | ||
Table 3. Examination Category C-B, Item No. C2.21, Limited Volumetric Examination Coverage Weld Examination Percent Coverage Weld Identification Material Limitation Achieved Weld geometry Austenitic incompatible with 42-100 Nickel probes. Austenitic 0% | Table 3. Examination Category C-B, Item No. C2.21, Limited Volumetric Examination Coverage Weld Examination Percent Coverage Weld Identification Material Limitation Achieved Weld geometry Austenitic incompatible with 42-100 Nickel probes. Austenitic 0% | ||
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3.3.3 ASME Code Requirement The ASME Code examination requirement is volumetric examination of essentially 100 percent of the weld length, as specified in Table IWC-2500-1, Examination Categories of the ASME Code, Section XI, Examination Category C-B. When 100 percent of the required volume cannot be examined due to interferences, obstructions, or geometrical configuration, ASME Code Case N-460 allows reduction of the examination volume to 90 percent or greater of the required volume. ASME Code Case N-460 has been approved for use without conditions in RG 1.147, Revision 19, which is incorporated by reference in 10 CFR 50.55a(a)(3)(ii). For Examination Category C-B, Item No. C2.21, the examination volume is defined in Figure IWC-2500-4 Nozzle-to-Vessel Welds, of ASME Code, Section XI. Table 3 of this SE summarizes the coverage the licensee achieved. | 3.3.3 ASME Code Requirement The ASME Code examination requirement is volumetric examination of essentially 100 percent of the weld length, as specified in Table IWC-2500-1, Examination Categories of the ASME Code, Section XI, Examination Category C-B. When 100 percent of the required volume cannot be examined due to interferences, obstructions, or geometrical configuration, ASME Code Case N-460 allows reduction of the examination volume to 90 percent or greater of the required volume. ASME Code Case N-460 has been approved for use without conditions in RG 1.147, Revision 19, which is incorporated by reference in 10 CFR 50.55a(a)(3)(ii). For Examination Category C-B, Item No. C2.21, the examination volume is defined in Figure IWC-2500-4 Nozzle-to-Vessel Welds, of ASME Code, Section XI. Table 3 of this SE summarizes the coverage the licensee achieved. | ||
3.3.4 Licensees Relief Request The licensee could not achieve the required examination coverage for the welds in Table 3 of this SE because of the limitations summarized in the table. The licensee did not attempt volumetric examinations on these welds in the third ISI interval, because they could not qualify an examination technique. | 3.3.4 Licensees Relief Request The licensee could not achieve the required examination coverage for the welds in Table 3 of this SE because of the limitations summarized in the table. The licensee did not attempt volumetric examinations on these welds in the third ISI interval, because they could not qualify an examination technique. | ||
Welds 41-114-IR and 41-115-IR for the steam generator main steam nozzle have a unique geometry not covered by ASME Code, Section XI, Figure IWC-2500-4. The steam line nozzle inner radius protrudes into the interior of the steam generator, as illustrated in Figure 1-4 of the attachment to the licensees letter dated July 17, 2019. Performance of this examination necessitates access to the interior of the steam generator, which represents significant risks to plant personnel. The licensee stated that, due to these limitations, complying with the ASME Code required examination coverage is impractical. The licensee is therefore requesting relief pursuant to 10 CFR 50.55a(g)(5)(iii). | Welds 41-114-IR and 41-115-IR for the steam generator main steam nozzle have a unique geometry not covered by ASME Code, Section XI, Figure IWC-2500-4. The steam line nozzle inner radius protrudes into the interior of the steam generator, as illustrated in Figure 1-4 of the attachment to the licensees {{letter dated|date=July 17, 2019|text=letter dated July 17, 2019}}. Performance of this examination necessitates access to the interior of the steam generator, which represents significant risks to plant personnel. The licensee stated that, due to these limitations, complying with the ASME Code required examination coverage is impractical. The licensee is therefore requesting relief pursuant to 10 CFR 50.55a(g)(5)(iii). | ||
3.3.5 Licensees Basis for Use The licensee performed a structural and fatigue analysis of the nozzle meant to demonstrate that ASME Class 1 and 2 design requirements were not exceeded. The licensee stated that there is no plant-specific or industry-wide operating experience indicating degradation at this weld. The licensee also mentioned the following plant activities that mitigate potential safety concerns associated with not achieving the required examination coverage. | 3.3.5 Licensees Basis for Use The licensee performed a structural and fatigue analysis of the nozzle meant to demonstrate that ASME Class 1 and 2 design requirements were not exceeded. The licensee stated that there is no plant-specific or industry-wide operating experience indicating degradation at this weld. The licensee also mentioned the following plant activities that mitigate potential safety concerns associated with not achieving the required examination coverage. | ||
: 1. Performance of the examination to the extent practical, achieving 80 percent coverage. | : 1. Performance of the examination to the extent practical, achieving 80 percent coverage. | ||
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3.3.6 Duration of Relief Request The licensee submitted RR 64 for the third 10-year ISI interval at Palo Verde, which began on July 18, 2008, and ended May 31, 2019. | 3.3.6 Duration of Relief Request The licensee submitted RR 64 for the third 10-year ISI interval at Palo Verde, which began on July 18, 2008, and ended May 31, 2019. | ||
3.3.7 NRC Staff Evaluation For welds 42-100 and 42-101, the licensee performed a preservice radiographic examination when the steam generators were replaced. The radiographic examination uncovered porosity indications that were determined to be acceptable according to ASME Code, Section III acceptance criteria. The NRC staff finds that subsurface, fabrication-induced flaws, such as those discovered during the preservice examination, pose low risk to the structural integrity of the component, since they will not likely grow during service. For welds 41-114-IR and 41-115-IR, there is no examination history. The unique geometry of these nozzles makes it impractical to perform the inner radius examinations without accessing the interior of the steam generator. Further, the licensee performed a fatigue and structural analysis of the nozzle as part of its technical basis for ensuring structural integrity of the nozzle. Finally, this same access issue was approved by the NRC for Palo Verde Unit 3 by letter dated December 4, 2019 (ADAMS Accession No. ML19331A608). | 3.3.7 NRC Staff Evaluation For welds 42-100 and 42-101, the licensee performed a preservice radiographic examination when the steam generators were replaced. The radiographic examination uncovered porosity indications that were determined to be acceptable according to ASME Code, Section III acceptance criteria. The NRC staff finds that subsurface, fabrication-induced flaws, such as those discovered during the preservice examination, pose low risk to the structural integrity of the component, since they will not likely grow during service. For welds 41-114-IR and 41-115-IR, there is no examination history. The unique geometry of these nozzles makes it impractical to perform the inner radius examinations without accessing the interior of the steam generator. Further, the licensee performed a fatigue and structural analysis of the nozzle as part of its technical basis for ensuring structural integrity of the nozzle. Finally, this same access issue was approved by the NRC for Palo Verde Unit 3 by {{letter dated|date=December 4, 2019|text=letter dated December 4, 2019}} (ADAMS Accession No. ML19331A608). | ||
Due to the limitations on the subject steam generator welds, the welds and their associated components would have to be physically modified or disassembled beyond their current design to comply with the ASME Code required examination coverage. The extensive effort that would be needed for such modifications presents a burden. The licensees RR includes periodic pressure testing, UT examination to the extent practical, and surface examination. Surface examination is required by Table IWC-2500-1, Examination Category C-B, Item No. C2.21. The licensee also credits routine leakage monitoring and plant walkdowns as additional mitigating factors. Since these activities all serve to verify structural integrity of the welds, the NRC staff finds that the licensees RR is acceptable. | Due to the limitations on the subject steam generator welds, the welds and their associated components would have to be physically modified or disassembled beyond their current design to comply with the ASME Code required examination coverage. The extensive effort that would be needed for such modifications presents a burden. The licensees RR includes periodic pressure testing, UT examination to the extent practical, and surface examination. Surface examination is required by Table IWC-2500-1, Examination Category C-B, Item No. C2.21. The licensee also credits routine leakage monitoring and plant walkdowns as additional mitigating factors. Since these activities all serve to verify structural integrity of the welds, the NRC staff finds that the licensees RR is acceptable. | ||
Latest revision as of 06:43, 23 September 2022
ML20114E325 | |
Person / Time | |
---|---|
Site: | Palo Verde |
Issue date: | 04/30/2020 |
From: | Jennifer Dixon-Herrity, Siva Lingam Plant Licensing Branch IV |
To: | Lacal M Arizona Public Service Co |
Lingam S, 301-415-1564 | |
References | |
EPID L-2019-LLR-0068 | |
Download: ML20114E325 (13) | |
Text
April 30, 2020 Mrs. Maria L. Lacal Executive Vice President/
Chief Nuclear Officer Mail Station 7602 Arizona Public Service Company P.O. Box 52034 Phoenix, AZ 85072-2034
SUBJECT:
PALO VERDE NUCLEAR GENERATING STATION, UNIT 1 - RELIEF REQUEST 64 FOR IMPRACTICAL EXAMINATIONS FOR THE THIRD 10-YEAR INSERVICE INSPECTION INTERVAL (EPID L-2019-LLR-0068)
Dear Mrs. Lacal:
By letter dated July 17, 2019, as supplemented by letter dated February 19, 2020, Arizona Public Service Company (the licensee) requested the U.S. Nuclear Regulatory Commissions (NRCs) approval of Relief Request (RR) 64 for the third 10-year inservice inspection interval at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR 64, the licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 component welds.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.55a(g)(5)(iii), the licensee requested relief on the basis that achieving the ASME Code-required examination coverage is impractical.
The NRC staff has reviewed the licensees submittal and concludes, as set forth in the enclosed safety evaluation, that the proposed alternative in RR 64 has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Accordingly, the NRC staff determines that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) 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 RR 64 at Palo Verde, Unit 1 for the third 10-year inservice inspection interval, which commenced on July 18, 2008, and ended May 31, 2019.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this RR remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
M. Lacal 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,
/RA/
Jennifer L. Dixon-Herrity, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-528
Enclosure:
Safety Evaluation cc: Listserv
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 64 IMPRACTICAL EXAMINATIONS FOR THE THIRD 10-YEAR INSERVICE INSPECTION INTERVAL ASME CODE, SECTION XI, EXAMINATION CATEGORIES B-A, B-D, AND C-B ARIZONA PUBLIC SERVICE COMPANY PALO VERDE NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. STN 50-528
1.0 INTRODUCTION
By letter dated July 17, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19198A340), as supplemented by letter dated February 19, 2020 (ADAMS Accession No. ML20054A269), Arizona Public Service Company (the licensee),
submitted Relief Request (RR) 64 to the U.S. Nuclear Regulatory Commission (NRC) for the third 10-year inservice inspection (ISI) interval at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR 64, the licensee requested relief from the examination coverage requirements of Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 component welds.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(5)(iii),
ISI program update: Notification of impractical ISI Code requirements, the licensee requested relief on the basis that achieving the ASME Code-required examination coverage is impractical.
2.0 REGULATORY EVALUATION
The regulations in 10 CFR 50.55a(g)(4), Inservice inspection standards requirement for operating plants, requires that, throughout the service life of a boiling or pressurized water-cooled nuclear power facility, components classified as ASME Code Class 1, 2, and 3 components meet the requirements, except the design and access provisions and preservice examination requirements, set forth in Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(a)(1)(ii) 12 months prior to the start of the 120-month interval, subject to the conditions listed in 10 CFR 50.55a(b)(2).
Enclosure
When conformance to these requirements is determined to be impractical, relief may be granted by the NRC pursuant to 10 CFR 50.55a(g)(5)(iii). Additionally, pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee must notify the NRC and submit, as specified in 10 CFR 50.4, Written communications, information to support the determination. Requests for relief made in accordance with 10 CFR 50.55a(g)(5)(iii), must be submitted to the NRC no later than 12 months after the expiration of the initial or subsequent 120-month inspection interval for which relief is sought.
Pursuant to 10 CFR 50.55a(g)(6)(i), Impractical ISI requirements: Granting of relief, the Commission will evaluate determinations of impracticality under 10 CFR 50.55a(g)(5),
Requirements for updating ISI programs. After its evaluation, the Commission may grant relief and may impose alternative requirements that are authorized by law, will not endanger life or property or the common defense and security, and are 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.
Based on the above and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the relief and the NRC staff to authorize it.
3.0 TECHNICAL EVALUATION
3.1. Examination Category B-A, Pressure Retaining Welds in Reactor Vessel, Item No. B1.11, Circumferential Shell Welds 3.1.1 Components Affected Details of the reactor pressure vessel weld under Examination Category B-A is shown below in Table 1, as obtained from the attachment to the licensees submittal dated July 17, 2019.
Table 1. Examination Category B-A, Item No. B1.11, Limited Volumetric Examination Coverage Weld Examination Percent Coverage Weld Identification Material Limitation Achieved Vessel inlet and outlet Ferritic nozzles interfere with 1-10 80%
Steel scanning above and below the weld.
By supplemental letter dated February 19, 2020, the licensee clarified the access limitation associated with the inlet and outlet. The six nozzles extend from the intermediate vessel shell to the upper vessel shell. Therefore, the nozzle-to-shell welds intersect and interrupt the circumferential weld between the upper and intermediate shells. The outlet nozzles are larger in diameter than the inlet nozzles, and they have protruding geometry into the inside of the vessel.
The described geometric limitations create obstacles for performing the examination to the extent required by the ASME Code.
3.1.2 Applicable ASME Code Edition and Addenda The ASME Code of record at Palo Verde for the third 10-year ISI interval is the 2001 Edition through the 2003 Addenda of ASME Code,Section XI.
3.1.3 ASME Code Requirement The ASME Code examination requirement is volumetric examination of essentially 100 percent of the weld length, as specified in Table IWB-2500-1, Examination Categories of the ASME Code,Section XI, Examination Category B-A. When 100 percent of the required volume cannot be examined due to interferences, obstructions, or geometrical configuration, ASME Code Case N-460, Alternative Examination Coverage for Class 1 and Class 2 Welds,Section XI, Division 1, allows reduction of the examination volume to 90 percent or greater of the required volume. ASME Code Case N-460 has been approved for use without conditions in Regulatory Guide (RG) 1.147, Revision 19, lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1, dated October 2019 (ADAMS Accession No. ML19128A244), which is incorporated by reference in 10 CFR 50.55a(a)(3)(ii). For Examination Category B-A, Item No. B1.11, the examination volume is defined in Figure IWB-2500-1, Vessel Shell Circumferential Weld Joints, of ASME Code,Section XI. Table 1 of this safety evaluation (SE),
summarizes the coverage the licensee achieved.
3.1.4 Licensees Relief Request The licensee could not achieve the required examination coverage for the weld in Table 1 of this SE because of the limitations summarized in the table. The licensee achieved 80 percent of the required examination volume. The licensee stated that due to the listed limitations, complying with the ASME Code-required examination coverage is impractical. The licensee is therefore requesting relief pursuant to 10 CFR 50.55a(g)(5)(iii).
3.1.5 Licensees Basis for Use The licensee stated that there is no plant-specific or industry-wide operating experience indicating degradation at this weld. According to the licensee, the required coverage could not be achieved without undue burden, increased radiation exposure, or damage to plant components. The licensee also mentioned the following plant activities that mitigate potential safety concerns associated with not achieving the required examination coverage:
- 1. Performance of the examination to the extent practical, achieving 80 percent coverage.
- 2. Performance of surface examinations, where applicable.
- 3. Performance of leakage monitoring.
- 4. Performance of plant walkdowns.
- 5. Performance of system pressure tests and associated visual examination.
Regarding the examination history of this weld, Table 2-A of the licensees supplemental letter dated February 19, 2020, describes the flaw geometry of nine detected and sized indications.
The indications were dispositioned according to ASME Code,Section XI, 2001 Edition through 2003 Addenda. They were reconciled against previous examination results and were determined to be fabrication flaws, with no observed growth during service.
3.1.6 Duration of Relief Request The licensee submitted RR 64 for the third 10-year ISI interval at Palo Verde, which began on July 18, 2008, and ended May 31, 2019.
3.1.7 NRC Staff Evaluation For reactor pressure vessel weld 1-10, the licensee achieved 80 percent of the required volumetric examination coverage. Due to the geometry limitations described in detail in the licensees supplemental letter, the weld and its associated components would have to be physically modified or disassembled beyond its current design to comply with the ASME Code-required examination coverage. The extensive effort that would be needed for such modifications presents a burden. The NRC staff finds these limitations to be an acceptable basis for impracticality of conforming to the requirements, and finds the modification necessary to achieve the required coverage constitutes a burden upon the licensee.
The licensee performed the required volumetric examination of the subject weld using ultrasonic testing (UT) to the extent practical and achieved the coverage shown in Table 1 of this SE. The licensee stated that nine recordable indications were detected during the examination of weld 1-10. The licensee also stated that previous examination records for this weld demonstrated that these flaws have been in existence and have shown no growth over the service life of the plant. Further, the license stated that the flaws were dispositioned according to ASME Code,Section XI rules and were found to be acceptable. Subsurface, fabrication-related flaws in welds are known to exist in nuclear plant components. These flaws do not pose a risk to structural integrity, as demonstrated by the ASME Code,Section XI acceptance criteria, and the fact that they are not growing. The NRC staff finds that, despite the limited coverage, the licensee adequately dispositioned the indications found in the weld.
The licensees alternative includes periodic pressure testing and UT examination to the extent practical. While the licensee proposed to perform surface examinations when required by ASME Code,Section XI, surface examination is not required by Section XI for Category B-A, Item No. B1.11 welds. The licensee also credits routine leakage monitoring and plant walkdowns as additional mitigating factors. The NRC staff finds that the licensee employed adequate measures to compensate for the missed coverage.
Based on the above discussion, the NRC staff determined that obtaining the ASME Code required examination volume coverage for weld 1-10 is impractical because of the stated limitations, and that the modifications necessary to obtain the required coverage would impose a burden upon the licensee. The NRC staff determined that the volumetric examination performed to the maximum extent practical provides reasonable assurance of structural integrity of the welds for the following reasons: (1) the detected indications were not due to service-induced loads and were below the ASME Code allowable sizes; and (2) despite the limited coverages, the licensee examined regions of the welds most susceptible to service-induced degradation should it occur.
3.2 Examination Category B-D, Full Penetration Welded Nozzles in Vessels - Inspection Program B, Item No. B3.110, Pressurizer Nozzle-to-Vessel Welds 3.2.1 Components Affected Details of the pressurizer nozzle-to-vessel welds under Examination Category B-D are shown
below in Table 2, as obtained from the attachment to the licensees submittal dated July 17, 2019.
Table 2. Examination Category B-D, Item No. B3.110, Limited Volumetric Examination Coverage Weld Nozzle Weld Examination Percent Coverage Identification Location Material Limitation Achieved Obstructing Pressurizer weld pads 5-9 Surge Nozzle to Ferritic Steel resulting from 65%
Head Weld pressurizer heater replacement Pressurizer Nozzle geometry 5-10 Spray Nozzle to Ferritic Steel incompatible with 81%
Head Weld ultrasonic probes 5-11 Pressurizer Nozzle geometry 5-12 Safety Nozzle to Ferritic Steel incompatible with 75%
5-13 Head Weld ultrasonic probes 5-14 3.2.2 Applicable ASME Code Edition and Addenda The ASME Code of record at Palo Verde for the third 10-year ISI interval is the 2001 Edition through the 2003 Addenda of ASME Code,Section XI.
3.2.3 ASME Code Requirement The ASME Code examination requirement is volumetric examination of essentially 100 percent of the weld length, as specified in Table IWB-2500-1 of the ASME Code,Section XI, Examination Category B-D. When 100 percent of the required volume cannot be examined due to interferences, obstructions, or geometrical configuration, ASME Code Case N-460 allows reduction of the examination volume to 90 percent or greater of the required volume. ASME Code Case N-460 has been approved for use without conditions in RG 1.147, Revision 19, which is incorporated by reference in 10 CFR 50.55a(a)(3)(ii). For Examination Category B-D, Item No. B3.110, the examination volume is defined in Figure IWB-2500-7, Nozzle in Shell or Head, of ASME Code,Section XI. Table 2 of this SE summarizes the coverage the licensee achieved.
3.2.4 Licensees Relief Request The licensee could not achieve the required examination coverage for the welds in Table 2 of this SE because of the limitations summarized in the table. The licensee achieved some percentage of the required examination volume as specified in Table 2 of this SE. The licensee stated that due to the listed limitations, complying with the ASME Code-required examination coverage is impractical. The licensee is therefore requesting relief pursuant to 10 CFR 50.55a(g)(5)(iii).
3.2.5 Licensees Basis for Use The licensee stated that there is no plant-specific or industry-wide operating experience indicating degradation at these welds. The licensee also mentioned the following plant activities that mitigate potential safety concerns associated with not achieving the required examination coverage.
- 1. Performance of the examination to the extent practical, achieving the coverage specified in Table 2 above.
- 2. Performance of surface examinations, where applicable.
- 3. Performance of leakage monitoring.
- 4. Performance of plant walkdowns.
- 5. Performance of system pressure tests and associated visual examination.
As stated in the licensees supplemental letter, no recordable indications were found during these examinations.
3.2.6 Duration of Relief Request The licensee submitted RR 64 for the third 10-year ISI interval at Palo Verde, which began on July 18, 2008, and ended May 31, 2019.
3.2.7 NRC Staff Evaluation For the pressurizer welds listed in Table 2 of this SE, the licensee achieved less than 90 percent of the required volumetric examination coverage due to weld pads resulting from pressurizer heater replacement. The NRC staff finds these limitations to be an acceptable basis for impracticality of conforming to the requirements, and finds the modification necessary to achieve the required coverage constitutes a burden upon the licensee.
The licensee performed the required volumetric examination of the subject welds using UT to the extent practical and achieved the coverages shown above in Table 2 of this SE. The NRC staff reviewed the examination diagrams and coverage sheets, which showed that the examined volumes included weld and base materials in the inner region where degradation is expected to occur (if it occurs). The licensee used 45- and 60-degree shear wave scanners, parallel and transverse to the weld, from both sides of the weld. The NRC staff finds that despite the limited coverages, the examinations were adequately performed.
The licensee stated that no recordable indications were noted in welds 5-9 through 5-14. Given that the inner surface of the welds was covered, the NRC staff finds that it is unlikely that service-induced degradation exists in these welds.
Due to the limitations on the subject pressurizer welds, the welds and their associated components would have to be physically modified or disassembled beyond their current design to comply with the ASME Code-required examination coverage. The extensive effort that would be needed for such modifications presents a burden. The licensees alternative includes periodic pressure testing and ultrasonic examination to the extent practical. While the licensee proposed to perform surface examinations when required by ASME Section XI, surface examination is not required by ASME Code,Section XI for Category B-D, Item No. B3.110 welds. The licensee also credits routine leakage monitoring and plant walkdowns as additional mitigating factors. Since these activities all serve to verify structural and leakage integrity of the
welds, the NRC staff finds that the licensees RR is acceptable.
Based on the above discussion, the NRC staff determined that obtaining the ASME Code-required examination volume coverage for the subject pressurizer welds is impractical because of the stated limitations and that the modifications necessary to obtain the required coverage would impose a burden upon the licensee. The NRC staff determined that the volumetric examination performed to the maximum extent practical provides reasonable assurance of structural integrity of the welds for the following reasons: (1) the detected indications were not due to service-induced loads and were below the ASME Code allowable sizes; and (2) despite the limited coverages, the licensee examined regions of the welds most susceptible to service-induced degradation should it occur.
In Section 8 of the enclosure to the licensees letter dated July 17, 2019, the licensee described one item in its corrective action program. The licensee performed examinations of welds 3-100-IR (inside radius) and 4-100-IR and reported a coverage of 95 percent, which meets the ASME Code requirement. However, during the closeout review, the licensee discovered that the equipment used to perform the examination was the same designed for the previous steam generators. After a modeling effort, the licensee stated that only 70 percent of the Code-required volume was achieved, as a result of using the older equipment and procedure. The licensee canceled the older procedure, and new equipment is now available to support proper performance of the examination in future intervals. This item is not a licensing issue, and therefore, will not be dispositioned in this SE. The NRC staff may refer this topic to NRC inspectors for future interactions with the licensee on this matter.
3.3 Examination Category C-B, Pressure Retaining Nozzle Welds in Vessels, Item No. C2.21, Nozzle-to-Shell Weld 3.3.1 Components Affected Details of the steam generator welds under Examination Category C-B are shown in Table 3 of this SE, as obtained from the attachment to the licensees submittal dated July 17, 2019.
Table 3. Examination Category C-B, Item No. C2.21, Limited Volumetric Examination Coverage Weld Examination Percent Coverage Weld Identification Material Limitation Achieved Weld geometry Austenitic incompatible with 42-100 Nickel probes. Austenitic 0%
42-101 Chromium weld material causes Alloy signal degradation.
Unique nozzle inner 41-114-IR Ferritic radius geometry 0%
41-115-IR Steel incompatible with ultrasonic probes.
3.3.2 Applicable ASME Code Edition and Addenda The ASME Code of record at Palo Verde for the third 10-year ISI interval is the 2001 Edition through the 2003 Addenda of ASME Code,Section XI.
3.3.3 ASME Code Requirement The ASME Code examination requirement is volumetric examination of essentially 100 percent of the weld length, as specified in Table IWC-2500-1, Examination Categories of the ASME Code,Section XI, Examination Category C-B. When 100 percent of the required volume cannot be examined due to interferences, obstructions, or geometrical configuration, ASME Code Case N-460 allows reduction of the examination volume to 90 percent or greater of the required volume. ASME Code Case N-460 has been approved for use without conditions in RG 1.147, Revision 19, which is incorporated by reference in 10 CFR 50.55a(a)(3)(ii). For Examination Category C-B, Item No. C2.21, the examination volume is defined in Figure IWC-2500-4 Nozzle-to-Vessel Welds, of ASME Code,Section XI. Table 3 of this SE summarizes the coverage the licensee achieved.
3.3.4 Licensees Relief Request The licensee could not achieve the required examination coverage for the welds in Table 3 of this SE because of the limitations summarized in the table. The licensee did not attempt volumetric examinations on these welds in the third ISI interval, because they could not qualify an examination technique.
Welds 41-114-IR and 41-115-IR for the steam generator main steam nozzle have a unique geometry not covered by ASME Code,Section XI, Figure IWC-2500-4. The steam line nozzle inner radius protrudes into the interior of the steam generator, as illustrated in Figure 1-4 of the attachment to the licensees letter dated July 17, 2019. Performance of this examination necessitates access to the interior of the steam generator, which represents significant risks to plant personnel. The licensee stated that, due to these limitations, complying with the ASME Code required examination coverage is impractical. The licensee is therefore requesting relief pursuant to 10 CFR 50.55a(g)(5)(iii).
3.3.5 Licensees Basis for Use The licensee performed a structural and fatigue analysis of the nozzle meant to demonstrate that ASME Class 1 and 2 design requirements were not exceeded. The licensee stated that there is no plant-specific or industry-wide operating experience indicating degradation at this weld. The licensee also mentioned the following plant activities that mitigate potential safety concerns associated with not achieving the required examination coverage.
- 1. Performance of the examination to the extent practical, achieving 80 percent coverage.
- 2. Performance of surface examinations, where applicable.
- 3. Performance of leakage monitoring.
- 4. Performance of plant walkdowns.
- 5. Performance of system pressure tests and associated visual examination.
Regarding examination history, the licensee did not attempt volumetric examinations on these welds in the third ISI interval, because they could not qualify an examination technique. When the steam generators were replaced, the licensee performed preservice radiographic testing on welds42-100 and 42-101. At that time, the licensee determined that found porosity indications were acceptable according to ASME Code,Section III acceptance criteria. The licensee performed surface examinations of this weld and found no indications.
3.3.6 Duration of Relief Request The licensee submitted RR 64 for the third 10-year ISI interval at Palo Verde, which began on July 18, 2008, and ended May 31, 2019.
3.3.7 NRC Staff Evaluation For welds42-100 and 42-101, the licensee performed a preservice radiographic examination when the steam generators were replaced. The radiographic examination uncovered porosity indications that were determined to be acceptable according to ASME Code,Section III acceptance criteria. The NRC staff finds that subsurface, fabrication-induced flaws, such as those discovered during the preservice examination, pose low risk to the structural integrity of the component, since they will not likely grow during service. For welds 41-114-IR and 41-115-IR, there is no examination history. The unique geometry of these nozzles makes it impractical to perform the inner radius examinations without accessing the interior of the steam generator. Further, the licensee performed a fatigue and structural analysis of the nozzle as part of its technical basis for ensuring structural integrity of the nozzle. Finally, this same access issue was approved by the NRC for Palo Verde Unit 3 by letter dated December 4, 2019 (ADAMS Accession No. ML19331A608).
Due to the limitations on the subject steam generator welds, the welds and their associated components would have to be physically modified or disassembled beyond their current design to comply with the ASME Code required examination coverage. The extensive effort that would be needed for such modifications presents a burden. The licensees RR includes periodic pressure testing, UT examination to the extent practical, and surface examination. Surface examination is required by Table IWC-2500-1, Examination Category C-B, Item No. C2.21. The licensee also credits routine leakage monitoring and plant walkdowns as additional mitigating factors. Since these activities all serve to verify structural integrity of the welds, the NRC staff finds that the licensees RR is acceptable.
4.0 CONCLUSION
As set forth above, the NRC staff concludes that it is impractical for the licensee to comply with the requirements of the ASME Code,Section XI, for the components in Examination Categories B-A, B-D, and C-B in RR 64 for Palo Verde, Unit 1. The NRC staff also concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Accordingly, the NRC staff has determined that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property or 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 the proposed alternative for the examination welds listed in RR 64 at Palo Verde, Unit 1 for the third 10-year ISI interval, which commenced on July 18, 2008, and ended on May 31, 2019.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this RR remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: M. Benson, RES D. Dijamco, NRR Date: April 30, 2020
ML20114E325 *by e-mail OFFICE NRR/DORL/LPL4/PM* NRR/DORL/LPL4/LA* NRR/DNRL/NVIB/BC* NRR/DORL/LPL4/BC NAME SLingam PBlechman HGonzalez JDixon-Herrity DATE 4/29/2020 4/29/2020 4/22/2020 4/30/2020