ML17263A059
| ML17263A059 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 10/06/2017 |
| From: | Robert Pascarelli Plant Licensing Branch IV |
| To: | Halpin E Pacific Gas & Electric Co |
| Singal B, 301-415-3016 | |
| References | |
| CAC MF9386, CAC MF9387, CAC MF9388, CAC MF9389, CAC MF9390, EPID L-2017-LLR-0011, EPID L-2017-LLR-0012, EPID L-2017-LLR-0013, EPID L-2017-LLR-0014, EPID L-2017-LLR-0111 | |
| Download: ML17263A059 (13) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. Edward D. Halpin Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424 October 6, 2017
SUBJECT:
DIABLO CANYON POWER PLANT, UNIT 2 - RELIEF REQUESTS NDE-SLH U2, NDE-LSL U2, NDE-LHC U2, NDE-LHM U2, AND NDE-ONV U2, TO ALLOW USE OF THE PROPOSED ALTERNATIVES DUE TO IMPRACTICALITIES TO IMPLEMENT REQUIREMENTS OF AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE, SECTION XI FOR REACTOR PRESSURE VESSEL WELDS FOR THE THIRD INSERVICE INSPECTION INTERVAL (CAC NOS. MF9386, MF9387, MF9388, MF9389, AND MF9390)
Dear Mr. Halpin:
By letter dated March 8, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17068A082), as supplemented by letter dated June 21, 2017 (ADAMS Accession No. ML17172A705), Pacific Gas & Electric Company (the licensee) submitted Relief Requests (RRs) NDE-SLH U2, NDE-LSL U2, NDE-LHC U2, NDE-LHM U2, and NDE-ONV U2 for relief from the requirements set forth in American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code},Section XI, for the Diablo Canyon Power Plant (DCPP), Unit 2, reactor pressure vessel (RPV) lower shell-to-bottom head circumferential, lower shell longitudinal, bottom head circumferential, bottom head meridional, and outlet nozzle-to-vessel welds.
Specifically, the licensee has proposed alternatives due to impracticalities encountered when attempting to implement the requirements of ASME Code,Section XI, for examination of the RPV welds during the DCPP, Unit 2, 191h refueling outage for the third inservice inspection interval. Pursuant to Title 1 O of the Code of Federal Regulations (10 CFR),
paragraph 50.55a(g)(5)(iii), the licensee requested relief on the basis that meeting the Code requirement would be impractical for the facility.
The U.S. Nuclear Regulatory Commission (NRG) staff reviewed the licensee's submittal and determined that (1) the applicable ASME Code,Section XI, examination requirements are impractical for the subject ASME Code Class 1 welds at DCPP, Unit 2, (2) the licensee's alternative examination coverages are consistent with those for which inspection relief has previously been granted, and (3) the NRG staff's qualitative stress and fracture toughness analyses and the licensee's inspection results provide reasonable assurance of structural integrity or leak tightness for the subject components. Granting relief pursuant to 1 O 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.
Accordingly, the NRC staff concludes, as set forth in the enclosed safety evaluation, that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Therefore, the NRC staff grants RRs NDE-SLH U2, NDE-LSL U2, NDE-LHC U2, NDE-LHM U2, and NDE-ONV U2, at DCPP, Unit 2, for the third 10-year inservice inspection interval, which started on March 13, 2006, and ended on June 2, 2016.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject requests for relief remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.
If you have any questions, please contact the Senior Project Manager, Balwant K. Singal, at 301-415-3016 or via e-mail at Balwant.Singal@nrc.gov.
Docket No. 50-323
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv Sincerely, Robert J. Pascarelli, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUESTS NDE-SLH U2, NDE-LSL U2, NDE-LHC U2, NDE-LHM U2, AND NDE-ONV U2 FOR THE THIRD INSERVICE INSPECTION PROGRAM
1.0 INTRODUCTION
PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON POWER PLANT, UNIT 2 DOCKET NOS. 50-323 By letter dated March 8, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17068A082), as supplemented by letter dated June 21, 2017 (ADAMS Accession No. ML17172A705), Pacific Gas & Electric Company (the licensee) submitted Relief Requests (RRs) NDE-SLH U2, NDE-LSL U2, NDE-LHC U2, NDE-LHM U2, and NDE-ONV U2 for relief from the requirements set forth in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code),Section XI, for the Diablo Canyon Power Plant (DCPP), Unit 2, reactor pressure vessel (RPV) lower shell-to-bottom head circumferential, lower shell longitudinal, bottom head circumferential, bottom head meridional, and outlet nozzle-to-vessel welds.
Specifically, the licensee has proposed alternatives due to impracticalities encountered when attempting to implement the requirements of ASME Code,Section XI, for examination of the RPV welds during the DCPP, Unit 2, 191h refueling outage for the third inservice inspection (ISi) interval, which started on March 13, 2006, and ended on June 2, 2016. Pursuant to Title 1 O of the Code of Federal Regulations (10 CFR), paragraph 50.55a(g)(5)(iii), "ISi program update:
Notification of impractical ISi Code requirements," the licensee requested relief on the basis that meeting the Code requirement would be impractical for the facility.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), "lnservice inspection standards requirement for operating plants," ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except design and access provisions and preservice examination requirements, set forth in ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during 120-month inspection intervals subsequent to the first inspection interval comply with the latest edition and addenda of the ASME Code incorporated by reference in 1 O CFR 50.55a(a) 12 months before the start of the 120-month inspection interval.
Enclosure The regulations in 1 O CFR 50.55a(g)(5)(iii) state that if licensees determine that conformance with an ASME Code requirement is impractical for its facility, the licensee must notify the U.S.
Nuclear Regulatory Commission (NRC) and submit information in support of its determination.
Determinations of impracticality must be based on the demonstrated limitations experienced when attempting to comply with the ASME Code requirements during the ISi interval for which the request is being submitted. Requests for relief must be submitted to the NRC no later than 12 months after the expiration of the 120-month inspection interval for which relief is sought.
The regulations in 10 CFR 50.55a(g)(6)(i), "Impractical ISi requirements: Granting of relief,"
state that NRC will evaluate determinations that ASME Code requirements are impractical.
NRC may grant such relief and may impose such alternative requirements as it determines 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.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Components Affected
The RRs address the following components for the third ISi interval at DCPP, Unit 2. The examination category and item numbers are from Table IWB-2500-1 of the ASME Code, 2001 Edition through 2003 Addenda.
Relief Request Component Weld No.
ASME Code ASME Code ASME Code Description Class Examination Item No.
Category NDE-SLH U2 RPV lower 10-201 1
8-A 81.11 shell-to-bottom head circumferential weld NDE-LSL U2 RPV lower shell 3-201A 1
8-A 81.12 longitudinal welds 3-2018 3-201C NDE-LHC U2 RPV bottom head 4-202 1
8-A 81.21 circumferential weld NDE-LHM U2 RPV bottom head 1-2028 1
8-A 81.22 meridional welds 1-202F NDE-ONV U2 RPV outlet WN22 1
B-D 83.90 nozzle-to-vessel welds WN158 WN202 WN338 3.2
Applicable Code Edition and Addenda
ASME Code,Section XI, 2001 Edition through 2003 Addenda.
3.3 ASME Code Requirements for which Reliefs are Requested The relief requests address the following examination requirements from Table IWB-2500-1 of the 2001 Edition of the ASME Code with 2003 Addenda.
Relief Request Component Examination Coverage Description Method NDE-SLH U2 RPV lower Volumetric Essentially 100% of the weld shell-to-bottom head length as shown in circumferential weld Fiqure IWB-2500-1 NDE-LSL U2 RPV lower shell Volumetric Essentially 1 00% of the weld longitudinal welds length as shown in Figure IWB-2500-2 NDE-LHC U2 RPV bottom head Volumetric Essentially 100% of the circumferential weld accessible weld length as shown in Fiqure IWB-2500-3 NDE-LHM U2 RPV bottom head Volumetric Essentially 100% of the meridional welds accessible weld length as shown in Figure IWB-2500-3 NDE-ONV U2 RPV outlet Volumetric Essentially 100% of the weld nozzle-to-vessel welds volume as shown in Figure IWB-2500-7(a) 3.4
Reason for Request
3.4.1 NDE-SLH U2 - RPV Lower Shell-to-Bottom Head Circumferential Weld The licensee stated that six core barrel support lugs limit access of the vendor's examination tool to a portion of the required examination volume for the RPV lower shell-to-bottom head circumferential weld. Providing access at these locations would require redesign of the core barrel supports and is impractical. The licensee also stated that consideration was given to examining the weld from the vessel outside surface. The bottom head and shell insulation in this area, however, are not designed to be removable and the close proximity of the insulated vessel to the concrete shield wall prohibits access. The licensee further stated that providing external access to the weld location would require redesign of the building concrete structure and the vessel insulation, and is impractical.
3.4.2 NDE-LSL U2 - RPV Lower Shell Longitudinal Welds Three of the six core barrel support lugs limit access of the vendor's examination tool to a portion of the required examination volumes for the three RPV lower shell longitudinal welds.
Since the reduced full coverage for the three RPV lower shell longitudinal welds was caused by the same six core barrel support lugs as stated above for the RPV lower shell-to-bottom head circumferential weld, the reason for request regarding these longitudinal welds is the same as that described in Section 3.4.1 of this safety evaluation (SE).
3.4.3 NDE-LHC U2 - RPV Bottom Head Circumferential Weld The licensee stated that bottom mounted instrumentation (BMI) tubes limit access of the vendor's examination tool to a portion of the required examination volume for the RPV bottom head circumferential weld. Providing access at these locations would require redesign of the BMI tube locations (i.e., the bottom vessel head, internals, and instrumentations all need to be redesigned), and is impractical. The licensee further stated that consideration was given to examining the weld from the vessel outside surface. It was determined, however, that the BMI bottom, which penetrate the bottom head, would still limit access for external examination of the weld.
3.4.4 NDE-LHM U2 - RPV Bottom Head Meridional Welds BMI tubes limit access of the vendor's examination tool to a portion of the required examination volumes for two of the six RPV bottom head meridional welds (Nos. 1-202B and 1-202F). Since the distribution of the BMI tubes is uniform over the RPV bottom head, the reason for request for these meridional welds in the bottom head is the same as that described in Section 3.4.3 of this SE for the RPV bottom head circumferential weld.
3.4.5 NDE-ONV U2 - RPV Outlet Nozzle-to-Vessel Welds The licensee stated that the outlet nozzle boss protrusion limits access of the vendor's examination to a portion of the required examination volume. Providing access at this location would require redesign of the RPV outlet nozzle configuration for the four outlet nozzles and is impractical. The licensee further stated that consideration was given to examining the welds from the vessel outside surface, but it was determined that vessel insulation in this area is not designed to be removable and the close proximity of the insulated vessel to the concrete shield wall prohibits access. Providing access at these locations would require redesign of the building concrete structure and the vessel insulation, and is impractical.
3.5 Proposed Alternative and Basis for Use 3.5.1 NDE-SLH U2 - RPV Lower Shell-to-Bottom Head Circumferential Weld The licensee stated that six core barrel support lugs prevent access to a portion of the length of the RPV lower shell-to-bottom head circumferential weld (No.10-201 ). The licensee calculated that the combined average volume coverage is 78.32 percent for this weld, using a procedure and techniques qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6. 1 3.5.2 NDE-LSL U2 - RPV Lower Shell Longitudinal Welds The licensee stated that access to the RPV lower shell longitudinal welds (Nos. 3-201 A, 3-201 B, and 3-201 C) is restricted by the three core barrel support lugs located at 60, 180, and 300 degrees. The licensee calculated that the combined average volume coverage is 80.1 O percent for each weld, using a procedure and techniques qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6.
3.5.3 NDE-LHC U2 - RPV Bottom Head Circumferential Weld The licensee stated that BMI penetration tubes prevent access to a portion of the length of the RPV bottom head circumferential weld (No. 4-202). The licensee calculated that the combined average volume coverage is 68. 77 percent for this weld, using a procedure and techniques qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VI 11, Supplements 4 and 6.
1 Using the 2001 Edition of the ASME Code Section X1 without Addenda is required by 10 CFR 50.55a(b)(2)(xv).
3.5.4 NDE-LHM U2 - RPV Bottom Head Meridional Welds The licensee stated that access to the RPV bottom head meridional welds (Nos. 1-202B and 1-202F} is restricted by the BMI penetration tubes. The licensee calculated that the combined average volume coverage is 70 percent for weld No. 1-202B and 79.5 percent for weld No. 1-202F, using a procedure and techniques qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6.
3.5.5 NDE-ONV U2 - RPV Outlet Nozzle-to-Vessel Welds With regard to the RPV outlet nozzle-to-vessel welds, the licensee stated that the nozzle boss protrusions prevent access to a portion of the length of the welds. The licensee calculated that the combined average volume coverage is 84.5 percent volume for each of welds WN22, WN158, WN202, and WN338, using a procedure and techniques qualified by demonstration to the 2001 Edition of the ASME Code without 2003 Addenda,Section XI, Appendix VIII, Supplements 4 and 6.
3.6 Duration of Proposed Alternative The relief requests are for the DCPP, Unit 2, third ISi interval, which began on March 13, 2006, and ended on June 2, 2016.
3.7
NRC Staff Evaluation
Pursuant to 10 CFR 50.55a{g){5}{iii), the licensee submitted five requests for relief from the examination requirements of the ASME Code,Section XI. The NRC staff evaluation of the licensee's requests for relief focused on: (1) whether the ASME Code requirement is impractical; (2) whether the imposition of the ASME Code required inspections would result in a burden to the licensee; and (3) whether the licensee's examination coverage provides reasonable assurance of structural integrity and leak tightness of the subject welds.
3.7.1 NDE-SLH U2 - RPV Lower Shell-to-Bottom Head Circumferential Weld As stated previously, ASME Code,Section XI, Table IWB-2500-1, Category B-A, Item B1.11 requires volumetric examination of essentially 100 percent of RPV circumferential shell welds.
The licensee is requesting relief from this requirement because the physical size of the transducer sled limits areas that can be examined around the core barrel support lugs without damaging the examination assembly.
In its letter dated March 8, 2017, the licensee stated, in part:
The examination used a combination of 45 degree angle search units with shear and longitudinal wave propagation. The sound beams from these transducers were directed in four orthogonal directions parallel and perpendicular to the weld in as close proximity to the six core barrel support lugs as the inspection device and transducer sled would allow. Scanning was conducted between and below the obstructing lugs with scan boundaries maximized by visually assisted positioning of the exam head.
The NRC staff reviewed the licensee's diagram of the RPV showing the location of the weld and the core barrel support lugs, as well as detailed drawings showing the areas around the lugs for which examination access is limited. The NRC staff concludes that the weld volume identified by the licensee is inaccessible, and, therefore, it is impractical for the licensee to comply with the specified requirement. Further, Section 3.4.1 of this SE indicates that providing access at these locations would require redesign of the core barrel supports. The NRC staff determined that this would be a burden on the licensee if the specified requirement was imposed. The NRC staff further determined that the examinations, which were performed during the third ISi interval, covered 78.32 percent of the weld, which was greater than 75.36 percent that was achieved for this weld during the second ISi interval (NRC staff letter dated June 25, 2007 (ADAMS Accession No. ML071620072)) due to improved design of the examination robot and control systems. The NRC staff finds that the ultrasonic testing (UT) procedure and techniques were qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6 in accordance with the requirements of 1 O CFR 50.55a(b)(2)(xv), "Section XI condition: Appendix VIII specimen set and qualification requirements."
Regarding the inspection results for this RPV component, by letter dated June 21, 2017, the licensee confirmed that no indications, which required flaw evaluations, were found for all five subject welds. Considering the axisymmetric geometry of the RPV lower head without significant interruptions (e.g., outlet and inlet nozzles) and the axisymmetric loading (pressure+ thermal+ weld residual stresses), the highly stressed area is likely to be evenly distributed along the entire lower shell-to-bottom head circumferential weld. On the material side, since the weld is located at a low fluence area, the lack of highly embrittled segments due to fluence variation along the weld caused the fracture toughness to be more evenly distributed along the circumferential weld. Therefore, inspection results of no indications for 78.32 percent of the weld are representative of the entire circumferential weld, and, based on this, the NRC staff concludes that the proposed inspection provides reasonable assurance of structural integrity or leak tightness of the subject weld.
3.7.2 NDE-LSL U2 - RPV Lower Shell Longitudinal Welds As stated previously, ASME Code,Section XI, Table IWB-2500-1, Category B-A, Item 81.12 requires volumetric examination of essentially 100 percent of RPV longitudinal shell welds. The licensee is requesting relief from this requirement because the physical size of the transducer sled limits areas that can be examined around three core barrel support lugs without damaging the examination assembly. The licensee stated that the examination used a combination of 45 degree angle search units with shear and longitudinal wave propagation. The sound beams from these transducers were directed in four orthogonal directions, parallel and perpendicular to the weld in as close proximity to the three core barrel support lugs as the inspection device and transducer sled would allow.
The NRC staff reviewed the licensee's diagram of the RPV showing the location of the welds and the core barrel support lugs, as well as detailed drawings showing the areas around the lugs for which examination access is limited. The NRC staff concludes that the weld volume identified by the licensee is inaccessible, and, therefore, it is impractical for the licensee to comply with the specified requirement. Further, Section 3.4.2 of this SE indicates that providing access at these locations would require redesign of the core barrel supports. The NRC staff determined that this would be a burden on the licensee if the specified requirement was imposed. The NRC staff further determined that the examinations, which were performed during the third ISi interval, covered 80.10 percent of the welds, which was slightly greater than 80.01 percent that was achieved for these welds during the second ISi interval (NRC staff letter dated June 25, 2007), due to improved design of the examination robot and control systems.
The NRC staff finds that the UT procedure and techniques were qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6 in accordance with the requirements of 1 O CFR 50.55a(b)(2)(xv).
Regarding the inspection results for this RPV component, by letter dated June 21, 2017, the licensee confirmed that no indications, which required flaw evaluations, were found for all five subject welds. Considering the axisymmetric geometry of the RPV lower shell without significant interruptions (e.g., outlet and inlet nozzles) and the axisymmetric loading (pressure+ thermal+ weld residual stresses), the highly stressed area is likely to be evenly distributed along the entire length of the three lower shell longitudinal welds. On the material side, since the upper portion of the welds, which are inspection accessible, received the most severe embrittlement due to the proximity to the core, they will have lower fracture toughness.
Therefore, inspection results of no indications for 80.1 O percent of the welds are representative of the worst segments of the three longitudinal welds, and, based on this, the NRC staff concludes that the proposed inspection provides reasonable assurance of structural integrity or leak tightness of the subject welds.
3.7.3 NDE-LHC U2 - RPV Vessel Bottom Head Circumferential Weld As stated previously, ASME Code,Section XI, Table IWB-2500-1, Category B-A, Item 81.21 requires volumetric examination of essentially 100 percent of the accessible length of RPV circumferential head welds. The licensee is requesting relief from this requirement because the physical size of the transducer sled limits areas that can be examined around BMI penetration tubes without damaging the examination assembly. The licensee stated that the examination used a combination of 45 degree angle search units with shear and longitudinal wave propagation. The sound beams from these transducers were directed in four orthogonal directions parallel and perpendicular to the weld in as close proximity to the BMI penetration tubes as the inspection device and transducer sled would allow.
The NRC staff reviewed the licensee's diagram of the RPV showing the location of the weld and the BMI penetration tubes, as well as detailed drawings showing the areas around the tubes for which examination access is limited. The NRC staff concludes that the weld volume identified by the licensee is inaccessible, and, therefore, it is impractical for the licensee to comply with the specified requirement. Further, Section 3.4.3 of this SE indicates that providing access at these locations would require redesign of the bottom vessel head, internals, and instrumentations. The NRC staff determined that this would be a burden on the licensee if the specified requirement was imposed. The ASME Code acknowledges the potential limitations of examining this weld by prescribing coverage for 100 percent of the accessible length, rather than 100 percent of the total length. The NRC staff further determined that the examinations, which were performed during the third 10-year ISi interval, covered 68.77 percent of the weld.
As stated by the licensee in its letter dated March 8, 2017, increased examination coverage was achieved during the third 10-year ISi interval as compared to the second 10-year ISi interval due to improved design of the examination robot and control systems. However, actual coverage achieved during the second 10-year ISi interval was not reported (ADAMS Accession No. ML16342A541 ). 2 The NRC staff finds that the UT procedure and techniques were qualified 2 "Technical Evaluation Report on the Second 10-Year Interval lnservice Inspection Program Plan:
Pacific Gas and Electric Company, Diablo Canyon Power Plant, Units 1 and 2, Docket Numbers 50-275 and 50-323," August 1998.
by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6 in accordance with the requirements of 10 CFR 50.55a(b)(2)(xv).
Regarding the inspection results for this RPV component, by letter dated June 21, 2017, the licensee confirmed that no indications, which required flaw evaluations, were found for all five subject welds. Since the BMI tubes are located at different level of proximity to the bottom head circumferential weld, it is highly likely that the inspection would cover some highly stressed locations. On the material side, since the weld is located at a low fluence area, the lack of highly embrittled segments due to fluence variation along the weld caused the fracture toughness to be more evenly distributed along the circumferential weld. Therefore, inspection results of no indications for 68.77 percent of the weld volume are representative of the entire circumferential weld, and, based on this, the NRG staff concludes that the proposed inspection provides reasonable assurance of structural integrity or leak tightness of the subject weld.
3.7.4 NDE-LHM U2 - Unit 2 RPV Bottom Head Meridional Welds As discussed previously, ASME Code,Section XI, Table IWB-2500-1, Category B-A, Item 81.22 requires volumetric examination of essentially 100 percent of the accessible length of RPV head meridional welds. The licensee is requesting relief from this requirement because the physical size of the transducer sled limits areas that can be examined around BMI penetration tubes without damaging the examination assembly. The licensee stated that the examination used a combination of 45 degree angle search units with shear and longitudinal wave propagation. The sound beams from these transducers were directed in four orthogonal directions parallel and perpendicular to the welds in as close proximity to the BMI penetration tubes as the inspection device and transducer sled would allow.
The NRG staff reviewed the licensee's diagram of the RPV showing the location of the welds and the BMI penetration tubes, as well as detailed drawings showing the areas around the tubes for which examination access is limited. The NRG staff concludes that the weld volume identified by the licensee is inaccessible, and, therefore, it is impractical for the licensee to comply with the specified requirement. Further, Section 3.4.4 of this SE indicates that providing access at these locations would require redesign of the bottom vessel head, internals, and instrumentations. The NRG staff determined that this would be a burden on the licensee if the specified requirement was imposed. The ASME Code acknowledges the potential limitations of examining this weld, by prescribing coverage for 100 percent of the accessible length, rather than 100 percent of the total length. The NRG staff further determined that the examinations, which were performed during the third 10-year ISi interval, covered 70 percent volume of weld No. 1-2028 and 79.5 percent volume of weld No. 1-202F, which were much greater than 39 percent that was achieved for these welds during the second 10-year ISi interval due to improved design of the examination robot and control systems (ADAMS Accession No. ML16342A541 ). The NRG staff finds that the UT procedure and techniques were qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6 in accordance with the requirements of 10 CFR 50.55a(b)(2)(xv).
Regarding the inspection results for this RPV component, by letter dated June 21, 2017, the licensee confirmed that no indications, which required flaw evaluations, were found for all five subject welds. Since the BMI tube that is close to bottom head meridional weld No. 1-2028 and the BMI tube that is close to weld No. 1-202F are at a different level of proximity to the weld, it is highly likely that the inspection would cover some highly stressed locations. On the material side, since the weld is located at a low fluence area, the lack of highly embrittled segments due to fluence variation along the welds caused the fracture toughness to be more evenly distributed along the meridional welds. Therefore, inspection results of no indications for 70 percent of weld No. 1-2028 and 79.5 percent of weld No. 1-202F are representative of the two meridional welds. Further, the other four bottom head meridional welds had received essentially 100 percent UT. Based on the above, the NRC staff concludes that the proposed inspection provides reasonable assurance of structural integrity or leak tightness of the subject welds.
3.7.5 NDE-ONV U2 - Unit 2 RPV Outlet Nozzle-to-Vessel Welds As discussed previously, ASME Code,Section XI, Table IWB-2500-1, Category B-D, Item 83.90 requires volumetric examination of essentially 100 percent of the weld volume as specified in Figure IWB-2500-7(a). The licensee is requesting relief from this requirement because the configuration of the outlet nozzle boss protrusion limits the approach of the transducer sled for parallel scans and portions of the perpendicular scans from the vessel inner diameter. The licensee stated that the examination used 45 degree angle search units directed perpendicular and parallel scans of the weld examination volume as close as the transducer sled would allow to the outlet nozzle boss protrusion.
The NRC staff reviewed the licensee's diagram of the RPV showing the location of the welds, as well as detailed drawings showing the areas around the nozzle boss protrusions for which examination access is limited. The NRC staff concludes that the weld volume identified by the licensee is inaccessible, and, therefore, it is impractical for the licensee to comply with the specified requirement. Further, Section 3.4.5 of this SE indicates that providing access at these locations would require redesign of the RPV outlet nozzle configuration for the four outlet nozzles. The NRC staff determined that this would be a burden on the licensee if the specified requirement was imposed. The NRC staff further determined that the examinations, which were performed during the third 10-year ISi interval, covered 84.5 percent of each of the outlet nozzle welds, which were much greater than 66 percent that was achieved for these welds during the second 10-year ISi interval due to improved design of the examination robot and control systems (ADAMS Accession No. ML16342A541 ). The NRC staff finds that the UT procedure and techniques were qualified by demonstration to the 2001 Edition of the ASME Code without Addenda,Section XI, Appendix VIII, Supplements 4 and 6 in accordance with the requirements of 10 CFR 50.55a(b}(2)(xv).
Regarding the inspection results for this RPV component, by letter dated June 21, 2017, the licensee confirmed that no indications, which required flaw evaluations, were found for all five subject welds. For each outlet nozzle, since the nozzle boss protrusion is of a 360 degree configuration around the nozzle, the inspection would cover the entire outlet nozzle-to-vessel weld length, though not the entire volume. Further, considering the axisymmetric geometry of the outlet nozzle, the axisymmetric loading (pressure+ thermal+ weld residual stresses), and the membrane and bending due to main coolant loop piping, it is highly likely that the inspection would cover some highly stressed locations. On the material side, again, since the inspection would cover the entire outlet nozzle-to-vessel weld length, though not the entire volume, it is highly likely that the inspection would cover some low fracture toughness locations. Therefore, inspection results of no indications for 84.5 percent of the weld for each outlet nozzle are representative of the entire nozzle weld, and, based on this, the NRC staff concludes that the proposed inspection provides reasonable assurance of structural integrity or leak tightness of the subject welds for the four outlet nozzles.
4.0 CONCLUSION
Based on the above evaluation, the NRC staff concludes that (1) the applicable ASME Code,Section XI examination requirements are impractical for the subject ASME Code Class 1 welds at DCPP, Unit 2, (2) the licensee's alternative examination coverages are consistent with those for which inspection relief has previously been granted, and (3) the NRC staff's qualitative stress and fracture toughness analyses and the licensee's inspection results provide reasonable assurance of structural integrity or leak tightness for the subject components. 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. Accordingly, the NRC staff concludes, as set forth in the above evaluation, that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5)(iii). Therefore, the NRC staff grants NDE-SLH U2, NDE-LSL U2, NDE-LHC U2, NDE-LHM U2, and NDE-ONV U2, at DCPP, Unit 2, for the third 10-year inservice inspection interval, which started on March 13, 2006, and ended on June 2, 2016.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject requests for relief remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.
Principal Contributors: Greg Oberson, NRR Simon Sheng, NRR Date: October 6, 2017
ML17263A059 OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA NAME BSingal PBlechman DATE 09/29/17 10/04/17
- SE via email dated 9/14/2017 NRR/DE/EVI B/BC*
NRR/DORL/LPL4/BC SRuffin RPascarelli 09/14/17 10/06/17