ML102000612
| ML102000612 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 07/27/2010 |
| From: | Markley M Plant Licensing Branch IV |
| To: | Edington R Arizona Public Service Co |
| Hall, J R, NRR/DORL/LPL4, 301-415-4032 | |
| References | |
| TAC ME2132 | |
| Download: ML102000612 (14) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 July 27,2010 Mr. Randall K. Edington Executive Vice President Nuclear/
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 NO. 46 RE: SECOND 10-YEAR INSERVICE INSPECTION PROGRAM INTERVAL (TAC NO. ME2132)
Dear Mr. Edington:
By letter dated July 17, 2009, as supplemented by letter dated May 27, 2010, Arizona Public Service Company (APS, the licensee) submitted Relief Request No. 46 (RR-46), requesting relief from certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) requirements at Palo Verde Nuclear Generating Station (Palo Verde), Unit 1, for the second 10-year inservice inspection (lSI) program interval, which ended on July 17, 2008.
RR-46 requests relief from certain examination requirements of ASME Code,Section XI, that the licensee considers to be impractical. In an e-mail dated March 12, 2010, the U.S. Nuclear Regulatory Commission (NRC) requested additional information concerning the APS submittal.
APS submitted its response by letter dated May 27,2010.
The NRC staff has reviewed the licensee's submittal and has determined that granting RR-46, Parts A through F, and Part G, for the hydrogen purge system (HPS) components, pursuant to paragraph 50.55a(g)(6)(i) of Title 10 of the Code of Federal Regulations (10 CFR) 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. Relief is granted for the second 10-year lSI program interval at Palo Verde, Unit 1, based on the determination that the examination coverage requirements are impractical for the subject components listed in RR-46, Parts A through F, and Part G, for the HPS components, and that the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject components.
In Part G of RR-46, APS requested relief for components associated with the chemical and volume control system (CVCS) charging pumps and the HPS. APS stated that relief is being requested from the ASME Code,Section XI, requirement for visual test level II (VT-2) examinations of 100 percent of the nitrogen supply lines and valves for the CVCS charging pumps due to access limitations. However, the NRC staff has determined that these nitrogen supply lines are not ASME Code components. Therefore, the nitrogen supply lines and valves are not covered by 10 CFR 50.55a and ASME Code,Section XI, requirements, and the staff is not authorized to grant relief for performing a limited scope VT-2 examination of these components under 10 CFR 50.55a(g)(6)(i).
R. Edington
- 2 A copy of the related Safety Evaluation is enclosed. All other ASME Code,Section XI, requirements for which relief has not been specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact Mr. Randy Hall at (301) 415-4032 or via e-mail at randy.hall@nrc.gov.
Sincerely, Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-528
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ON THE SECOND 10-YEAR INSERVICE INSPECTION INTERVAL RELIEF REQUEST NO. 46 ARIZONA PUBLIC SERVICE COMPANY, ET AL.
PALO VERDE NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. STN 50-528
1.0 INTRODUCTION
By letter dated July 17, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML092160398), Arizona Public Service Company (the licensee) submitted Relief Request No. 46 (RR-46) for Palo Verde Nuclear Generating Station (Palo Verde), Unit 1. In RR-46, the licensee requested relief from the examination requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section XI, for a number of ASME Code Class 1 and 2 components at Palo Verde, Unit 1.
The U.S. Nuclear Regulatory Commission (NRC) staff issued a request for additional information (RAI) by electronic mail (e-mail) dated March 12,2010 (ADAMS Accession 1\\10.
ML100710729), and the licensee responded to the RAI by letter dated May 27,2010 (ADAMS Accession No. ML101600454). The licensee provided further clarification bye-mail dated July 7,2010 (ADAMS Accession No. ML102000407). The staff reviewed and evaluated Parts A through G of the licensee's request pursuant to the provisions of Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(6)(i), on the basis that the inservice inspection code requirements were impractical for the subject components.
2.0 REGULATORY EVALUATION
Inservice inspection (lSI) of the ASME Code Class 1,2, and 3 components is to be performed in accordance with Section XI of the ASME Code, and applicable addenda, as required by 10 CFR 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). The regulation in 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if the licensee demonstrates that (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Enclosure
- 2 Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for
. Inservice Inspection of Nuclear Power Plant Components," 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 the first 1O-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code, which was incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The Code of record for the Palo Verde, Unit 1 second 1O-year interval lSI program, which ended on July 17, 2008, is the 1992 Edition of the ASME Code,Section XI, through the 1992 Addenda.
3.0 TECHNICAL EVALUATION
The information provided by the licensee in support of the request for relief from ASME Code requirements has been evaluated and the bases for disposition are documented below. For clarity, the licensee's request has been evaluated in several parts according to ASME Code,Section XI, Examination Category.
3.1 Component Identification RR-46 addresses the following ASME Code,Section XI, examination categories and item numbers covering examinations of ASME Code Class 1 and 2 components (the subject components) for the second 1O-year interval lSI program at Palo Verde, Unit 1. The following examination categories and item numbers are from Tables IWB-2500-1 (Class 1 components) and IWC-2500-1 (Class 2 components) of the 1992 Edition and 1992 Addenda of the ASME Code,Section XI.
ASME Code Class Examination Category Item Number(s)
Component Description 1
B-D B3.90 Reactor Vessel, Nozzle-to-Vessel Welds 1
B-H B8.20 Pressurizer, Integrally Welded Attachments 1
B-J B9.11 Piping, Nominal Pipe Size 4 inches (NPS 4) or Larger, Circumferential Welds 2
C-C C3.20 Piping, Integrally Welded Attachments 2
C-C C3.30 Pumps, Integrally Welded Attachments 2
C-F-1 C5.11 and C5.21 Piping Welds ~ 3/8 in. Nominal Wall Thickness for Piping> NPS 4, Circumferential Welds, and Piping Welds> 1/5 in. Nominal Wall Thickness for Piping ~ NPS 2 and s NPS 4, Circumferential Welds 2
C-H C7.30 and C7.70 Piping, Pressure retaining components, and Valves, Pressure retaining components
- 3 3.2
NRC Staff Evaluation
Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee submitted RR-46, requesting relief from the examination requirements of the ASME Code,Section XI, for the subject Class 1 and 2 components at Palo Verde, Unit 1. The 1992 Edition and 1992 Addenda of the ASME Code,Section XI, Articles IWB-2500 and IWC-2500 require that components be examined and tested as specified in Tables IWB-2500-1 and IWC-2500-1 of the ASME Code,Section XI.
Tables IWB-2500-1 and IWC-2500-1 define the examination requirements for Class 1 and 2 components, respectively. These tables specify, among other things, the examination techniques (volumetric, surface, and/or visual) and the examination boundary. For each of the subject components, the examination boundary is provided in the figure specified for that particular ASME Code,Section XI, item number in Tables IWB-2500-1 and IWC-2500-1. For volumetric and surface exams, the required examination boundary includes essentially 100 percent of the volume or area specified in the applicable figure listed in Tables IWB-2500-1 and IWC-2500-1.
In RR-46, the licensee stated that, for the subject components, the actual volumetric and/or surface examination coverage during the second 10-year interval lSI program at Palo Verde, Unit 1, was limited by component configuration and/or geometry, physical interferences, and/or accessibility issues. Based on these limitations, the licensee stated that it was unable to obtain essentially 100 percent examination coverage of the volume or area specified in the ASME Code,Section XI, for the subject components, and compliance with the examination requirements for the subject components would be impractical. The licensee conducted alternative limited examinations on the subject components to the extent practical. The details concerning the NRC staff's evaluation of RR-46, based on the licensee's stated impracticality of full ASME Code,Section XI, compliance and the alternative examinations for the subject components, are described in the following paragraphs.
Part A: Examination Category B-D, Item Number B3.90 - Reactor Vessel (RV)
Nozzle-to-Vessel Welds In Part A of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for examinations of RV Nozzle-to-Vessel Welds 1-15 and 1-18 at Palo Verde, Unit 1 (Examination Category B-D, Item Number B3.90). The licensee stated that the ASME Code,Section XI, as modified by ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 Welds,Section XI, Division 1," requires a volumetric examination of these welds, with a minimum coverage of 90 percent of the volume specified in Figure IWB-2500-7, as modified by ASME Code Case N-613-1, "Ultrasonic Examination of Full Penetration Nozzles in Vessels, Examination Category B-D, Item No's. B3.10 and B3.90, Reactor Nozzle-To-Vessel Welds, Figs. IWB-2500-7(a), (b), and (c)," for these welds. The NRC staff verified that the licensee's implementation of Code Cases N-460 and N-613-1 is authorized by Regulatory Guide (RG) 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1,"
October 2007. The licensee stated that the design of the RV outlet nozzle protrusion provided a geometric limitation to the ultrasonic scanning area. The examination robot and ultrasonic transducer sled are physically limited from achieving full ultrasonic scans by this protrusion.
The licensee provided figures illustrating where the limitations were documented in the vicinity of the nozzle-to-vessel protrusion, and a typical transducer sled scanning from the RV inside
- 4 diameter (ID). These figures illustrate the limitation caused by the nozzle protrusion. The licensee stated that ultrasonic scanning was performed on nozzle-to-vessel welds 1-15 and 1-18 to the fullest extent practical, resulting in a volumetric examination coverage of 98 percent for ultrasonic scans in the direction perpendicular to the weld centerline and 67 percent for ultrasonic scans in the direction parallel to the weld centerline. The overall combined examination volume coverage was 82.5 percent. The licensee stated that full compliance with the ASME Code,Section XI, examination requirements for these welds would require redesign and modification of the RV nozzle attachments in order achieve greater than 90 percent examination coverage.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of achieving full volumetric coverage of RV Nozzle-to-Vessel Welds 1-15 and 1-18, as discussed above, and agreed with the licensee's determination that the RV outlet nozzle protrusion did prevent the performance of ultrasonic scans with greater than 90 percent volumetric coverage. Therefore, the staff agreed with the licensee's determination that achieving the volumetric examination coverage required by the ASME Code,Section XI, is impractical for RV Nozzle-to-Vessel Welds 1-15 and 1-18. However, the staff noted that the licensee did not provide information concerning the results of the limited volumetric examinations for these welds. Therefore, in an RAI dated March 12, 2010, the staff requested that the licensee discuss the results of the limited volumetric examinations of RV Nozzle-to Vessel Welds 1-15 and 1-18. In its RAI response dated on May 27,2010, the licensee stated the volumetric examination of RV Nozzle-to-Vessel Weld 1-15 resulted in one indication. This indication was screened using the acceptance standards of the ASME Code,Section XI, IWB-3512 and was found to meet these acceptance standards. The licensee stated that the limited volumetric examinations of RV Nozzle-to-Vessel Welds 1-15 and 1-18 resulted in no unacceptable indications. The staff concluded that the licensee's RAI response was acceptable because the limited volumetric examinations of RV Nozzle-to-Vessel Welds 1-15 and 1-18 resulted in no unacceptable indications.
Based on the above, the NRC staff concluded that the ASME Code,Section XI, requirement to perform volumetric examinations of RV Nozzle-to-Vessel Welds 1-15 and 1-18, with essentially 100 percent coverage, is impractical for Palo Verde, Unit 1. The licensee's limited volumetric examinations provide reasonable assurance of continued structural integrity for RV Nozzle-to Vessel Welds 1-15 and 1-18 at Palo Verde, Unit 1.
Part B: Examination Category B-H, Item Number B8.20 - Pressurizer Integrally Welded Attachments In Part 8 of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for examinations of the pressurizer integrally welded attachments at Palo Verde, Unit 1 (Examination Category B-H, Item Number 88.20). The ASME Code,Section XI, requires surface examinations of these welds from both the outside surface and the inside surface of the welds, covering the surface area specified in the ASME Code,Section XI, Figure IWB-2500-13.
The licensee stated that the inside surface of one of the pressurizer attachment welds, Skirt Weld No. 5-1, is inaccessible due to high radiation, insulation, pressurizer heaters, and drain lines. Only the outside surface of this weld is accessible for examination. The licensee performed a surface examination using magnetic particle testing (MT), which achieved 100 percent coverage of only the outside surface of this weld. The licensee also performed an
- 5 ultrasonic examination of this weld from the outside surface, where it was accessible. The ultrasonic examination coverage was limited to 85 percent. The licensee provided figures illustrating the area of limitation that prevented the examination of this weld from the inside surface. The licensee stated that this weld was examined to the fullest extent practical and that obtaining the required examination coverage would require the redesign and modification of the pressurizer support skirt.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of achieving full examination coverage of this pressurizer attachment weld (Skirt Weld No. 5-1),
as discussed above, and determined that the licensee adequately described the limitation caused by the inaccessibility of this weld for the inside surface. Furthermore, the staff concluded that the licensee's best effort examinations, which included both the 100 percent outside surface examination and the supplemental volumetric examination, with 85 percent coverage, provided an acceptable alternative to the ASME Code,Section XI, examination requirements for this weld. The staff agreed with the licensee's determination that achieving surface examination coverage of this weld from both the inside surface and the outside surface, as required by the ASME Code,Section XI, is impractical for Skirt Weld No. 5-1. However, the staff noted that the licensee did not provide information concerning the results of the outside surface examination and the limited volumetric examination for this weld. Therefore, in an RAI dated March 12, 2010, the staff requested that the licensee discuss the results of these examinations. In its RAI response dated May 27, 2010, the licensee stated that the outside surface examination of Skirt Weld No. 5-1 resulted in no indications. The supplemental ultrasonic examination of this weld resulted in four indications that were screened using the acceptance standards of the ASME Code,Section XI, IWB-3516. These indications were found to be within the acceptable limits of IWB-3516. The licensee stated that the both the outside surface and supplemental volumetric examinations of Skirt Weld 5-1 resulted in no unacceptable indications. The staff concluded that the licensee's RAI response was acceptable because the outside surface examination and supplemental volumetric examination of Skirt Weld 5-1 resulted in no unacceptable indications.
Based on the above, the staff concluded that the ASME Code,Section XI, requirement to perform surface examinations of the subject pressurizer attachment weld (Skirt Weld No. 5-1) from both the outside surface and the inside surface of the weld is impractical for Palo Verde, Unit 1. The licensee's alternative examinations, which include a surface examination from just the outside surface and a limited volumetric examination, provide reasonable assurance of continued structural integrity for the subject pressurizer attachment weld at Palo Verde, Unit 1.
Part C: Examination Category B-J, Item Number B9.11 - Piping Nominal Pipe Size (NPS) 4 inches (in.) or Larger, Circumferential Welds In Part C of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for examinations of pipe-to-valve welds 23-4,23-6,24-14,24-16,24-19,24-6,25-4,25-6,26-17, 26-6, and pipe-to-tee weld 29-2 (the subject piping welds) at Palo Verde, Unit 1. All subject piping welds are Examination Category B-J, Item Number B9.11 welds. The ASME Code,Section XI, requires a volumetric examination and a surface examination for these welds, with a minimum surface examination coverage of 100 percent of the surface specified in Figure IWB-2500-8 and a minimum volumetric examination coverage of 90 percent of the volume specified in Figure IWB-2500-8 for these welds. The licensee stated that the subject
- 6 piping welds were credited with receiving only 50 percent volumetric examination coverage, based on the ASME Code,Section XI, Appendix VIII Performance Demonstration Initiative (PDI) criteria for ultrasonic examination systems, because access to these welds for ultrasonic scanning was limited to one side of the weld crown. The licensee provided a figure illustrating this weld configuration and the access limitation. This particular joint configuration contains a taper, where the connection on the restricted side of the weld transitions into the attached item (a fitting, valve, pump, etc.). The slope of this taper and the limited distance from the weld to the attached item does not allow room for the placement of the ultrasonic transducer. This prevents any meaningful axial scans from being performed from the tapered side of the weld.
The licensee stated that ultrasonic scanning was performed on the subject piping welds to the fullest extent practical and that obtaining the required volumetric examination coverage would require the redesign and modification of these welded joints.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of achieving full volumetric examination coverage for the subject piping welds, as discussed above, and agreed with the licensee's determination that the configuration of these welded joints prevented the performance of meaningful ultrasonic scans on the attachment side of the weld. Therefore, the staff agreed with the licensee's determination that achieving the volumetric examination coverage required by the ASME Code,Section XI, is impractical for the subject piping welds. However, the staff noted that the licensee did not provide information concerning the results of the limited volumetric examinations or the surface examinations for these welds.
Therefore, in an RAI dated March 12, 2010, the staff requested that the licensee discuss the results of the limited volumetric examinations and the surface examinations of the subject piping welds. In its RAI response dated May 27,2010, the licensee stated that both the limited volumetric and surface examinations of the subject piping welds resulted in no relevant indications. The staff concluded that the licensee's RAI response was acceptable because the limited volumetric and surface examinations of the subject piping welds resulted in no unacceptable indications.
Based on the above, the NRC staff concluded that the ASME Code,Section XI, requirement to perform volumetric examinations of the subject piping welds, with essentially 100 percent coverage, is impractical for Palo Verde, Unit 1. The licensee's surface examinations and limited volumetric examinations provide reasonable assurance of continued structural integrity for the subject piping welds at Palo Verde, Unit 1.
Part D: Examination Category C-C, Item Number C3.20 - Piping, Integrally Welded Attachments In Part D of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for examinations of two integrally welded support attachments to the high-pressure safety injection (HPSI) system discharge piping at Palo Verde, Unit 1 (Examination Category C-C, Item Number C3.20). The ASME Code,Section XI, requires 100 percent surface examinations for these welded attachments, covering the surface area specified in the ASME Code,Section XI, Figure IWC-2500-5. The licensee stated that Support No. SI-107-H-22 is located on the 4-inch diameter HPSI discharge line in the East Wrap of the auxiliary building. The licensee provided a figure illustrating the location and zone drawing for this support. This support is fabricated with two stainless steel shear lugs that are welded to the HPSI discharge piping. The licensee stated that one of the lugs is located inside the wall penetration and the other is accessible for
- 7 surface examination on only three sides. The examinations are limited by the location of these attachment welds with respect to the building wall and component support members. The licensee stated that it would cause undue burden to disassemble the support to make the inaccessible portion accessible when there have been no abnormal conditions noted at this location. The support components are welded so that disassembly would involve cutting and removing the welds and support components. The licensee stated that the attachment welds for these lugs were examined to the fullest extent practical and that obtaining the required surface examination coverage would be impractical because this would require the redesign and modification of these support components.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of obtaining the required examination coverage for these integrally welded attachments, as discussed above. The staff noted that the licensee did not provide sufficient information concerning the extent of surface examination coverage for these attachment welds or any information concerning the results of the limited surface examinations. Therefore, in an RAI dated March 12, 2010, the staff requested that the licensee provide further information concerning the extent of coverage that was obtained for these support attachment welds and discuss the results of these examinations. In its RAI response dated May 27, 2010, the licensee stated that Support SI-107-H-22 contains two lugs, one upstream and one downstream, welded to the "12 o'clock" position on the HPSI discharge piping. The upstream lug is located inside the wall penetration and is completely inaccessible because it is located behind the structural member of the support. Therefore, according the licensee, the surface examination coverage for this weld was 0.0 percent. The downstream lug has one end butting up against a structural member, making this end inaccessible. Therefore, the surface examination coverage for this weld was 83 percent. The licensee stated that no relevant indications were found during this examination. The staff concluded that the licensee's RAI response was acceptable because the RAI response adequately described the extent of surface examination coverage for the subject welded attachments and the results of the examinations. The staff agreed with the licensee's determination that obtaining the required examination coverage for the subject attachment welds is impractical because one is the welds is completely inaccessible due to its location relative to the structural member of the support and the other is accessible on only three sides.
Furthermore, the staff concluded that the licensee's alternative examination of these components was acceptable because these examinations, while limited in scope, resulted in no indications, with the potential for degradation of the upstream lug being monitored by the inspection of the downstream lug.
Based on the above, the NRC staff concluded that the ASME Code,Section XI, requirement to perform surface examinations of the HPSI piping support attachment welds, with essentially 100 percent coverage, is impractical for Palo Verde, Unit 1. The licensee's limited surface examinations provide reasonable assurance of continued structural integrity for the subject attachment welds at Palo Verde, Unit 1.
Part E: Examination Category C-C, Item Number C3.30 - Pumps, Integrally Welded Attachments In Part E of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for examinations of the integrally welded attachments to HPSI Pumps A and 8, at Palo Verde, Unit 1 (Examination Category C-C, Item Number C3.30). The ASME Code,Section XI, requires
- 8 100 percent surface examinations for these welded attachments, covering the surface area specified in the ASME Code,Section XI, Figure IWC-2500-5. According to the licensee, each HPSI pump has four integrally welded support lugs, with two lugs at the front of the pump and two lugs at the rear of the pump. The licensee provided a figure illustrating the locations and designations for the four support lugs on each of the HPSI pumps. According to the licensee, the examination area is limited for the front lugs on each pump. The front lug attachment welds are designated as Weld Nos. 116-1A and 116-1D for HPSI Pump A and 117-1A and 117-1D for HPSI Pump B. The licensee provided figures illustrating the actual front and rear support lugs.
For the rear lugs, complete access to the attachment weld is provided when the insulation is removed. For the front lugs, the bottom side of the attachment weld is inaccessible when the insulation is removed. Access to the bottom side of the attachment welds for the front lugs is restricted by the structural steel member that supports the lug. The licensee stated that the attachment welds for the support lugs on both HPSI pumps were examined to the fullest extent practical. The licensee stated that access to the rear lugs was not limited, and 100 percent surface examination coverage was obtained for the rear lug welds on both HPSI pumps.
However, the limited access to the front lugs, due to physical interference, resulted in a surface examination coverage of 78 percent for the front lug welds on both HPSI pumps. The licensee stated that a 100 percent surface examination of the front lug attachment welds would require that these welds be re-designed and modified. The licensee thus concluded that achieving the required surface examination coverage for these front lug welds would be impractical.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of achieving full surface examination coverage for the lug attachment welds on the HPSI pumps, as discussed above, and agreed with the licensee's determination that achieving the required 100 percent surface examination coverage for all of the lug attachment welds is impractical because access to the bottom side of the front lugs is restricted by a structural member.
However, the staff noted that the licensee did not provide information concerning the results of the surface examinations for these welds. Therefore, in an RAI dated March 12, 2010, the staff requested that the licensee discuss the results of the surface examinations of these attachment welds. In its RAI response dated May 27,2010, the licensee stated that acceptable small rounded indications were found on welds 116-1A, 116-'1 B, 116-1C, and 116-1D for HPSI Pump A; and 117-1D for HPSI Pump B. These indications were screened using the acceptance standards of the ASME Code,Section XI, IWC-3512 and all indications were found to meet these acceptance standards. The licensee stated that no indications were found on welds 117-1A, 117-1B, and 117-1DforHPSI Pump B. The staff concluded that the licensee's RAI response was acceptable because the limited surface examinations of the HPSI pump attachment welds resulted in no unacceptable indications.
Based on the above, the NRC staff concluded that the ASME Code,Section XI, requirement to perform surface examinations of the HPSI pump attachment welds, with essentially 100 percent coverage, is impractical for Palo Verde, Unit 1. The licensee's limited surface examinations provide reasonable assurance of continued structural integrity for the subject attachment welds at Palo Verde, Unit 1.
- 9 Part F: Examination Category C-F-1, Item Number C5.11 - Piping Welds>
3/8 in. Nominal Wall Thickness for Piping> NPS 4, Circumferential Welds, and Examination Category C-F-1, Item Number C5.21 - Piping Welds> 1/5 in.
Nominal Wall Thickness for Piping ~ NPS 2 and S NPS 4, Circumferential Welds In Part F of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for examinations of a number of Examination Category C-F-1, Item No. C5.11 and Item No.
C5.21 piping welds at Palo Verde, Unit 1. The complete list of Examination Category C-F-1 welds covered under this part of RR-46 is provided in the licensee's original submittal, dated July 17, 2009. For Examination Category C-F-1, Item Nos. C5.11 and C5.21 piping welds, the ASME Code,Section XI, requires a volumetric examination and a surface examination for these welds, with a minimum surface examination coverage of 100 percent of the surface area specified in Figure IWC-2500-7 and a minimum volumetric coverage of 90 percent of the volume specified in Figure IWC-2500-7. The licensee stated that the subject piping welds were credited with receiving only 50 percent volumetric examination coverage, based on the ASME Code,Section XI, Appendix VIII Performance Demonstration Initiative (POI) criteria for ultrasonic examination systems, because access to these welds for ultrasonic scanning was limited to one side of the weld crown. The licensee provided a figure illustrating this weld configuration and the access limitation. This particular joint configuration contains a taper, where the connection on the restricted side of the weld transitions into the attached item (i.e., a fitting, valve, pump, etc.). The slope of this taper and the limited distance from the weld to the attached item does not allow room for the placement of the ultrasonic transducer. This prevents any meaningful axial scans from being performed from the tapered side of the weld. The licensee stated that ultrasonic scanning was performed on the subject piping welds to the fullest extent practical and that obtaining the required volumetric examination coverage would require the redesign and modification of these welded joints.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of achieving full volumetric coverage for the subject piping welds, as discussed above, and agreed with the licensee's determination that the configuration of these welded joints prevented the performance of meaningful ultrasonic scans on the attachment side of the weld. Therefore, the staff agreed with the licensee's determination that achieving the volumetric examination coverage required by the ASME Code,Section XI, is impractical for the subject piping welds.
However, the staff noted that the licensee did not provide information concerning the results of the limited volumetric examinations or the surface examinations for these welds. Therefore, in an RAI dated March 12, 2010, the staff requested that the licensee discuss the results of the limited volumetric examinations and the surface examinations of the subject piping welds. In its RAI response dated May 27,2010, the licensee stated that both the limited volumetric and surface examinations of the subject piping welds resulted in no relevant indications. The staff concluded that the licensee's RAI response was acceptable because the limited volumetric and surface examinations of the subject piping welds resulted in no unacceptable indications.
Based on the above, the NRC staff concluded that the ASME Code,Section XI, requirement to perform volumetric examinations of the subject piping welds, with essentially 100 percent coverage, is impractical for Palo Verde, Unit 1. The licensee's surface examinations and limited volumetric examinations provide reasonable assurance of continued structural integrity for the subject piping welds at Palo Verde, Unit 1.
- 10 Part G: Examination Category C-H, Item Number C7.30 - Piping, Pressure Retaining Components and Examination Category C-H. Item Number C7.70 Valves, Pressure Retaining Components In Part G of RR-46, the licensee requested relief from the ASME Code,Section XI, requirements for visual test level II (VT-2) examinations of several Examination Category C-H, Item No. C7.30 and Item No. C7.70 components at Palo Verde, Unit 1. The licensee requested relief for components associated with the chemical and volume control system (CVCS) charging pumps and the hydrogen purge system (HPS). The CVCS charging pumps each have a suction stabilizer and pulsation dampener for system stability purposes. These components have a bladder and nitrogen system to moderate the fluid shock in the CVCS to maintain consistent operating characteristics. The licensee stated that relief is being requested from the ASME Code,Section XI, requirement for a VT-2 visual examination of 100 percent of the nitrogen supply lines and valves for the CVCS charging pumps due to access limitations. However, the NRC staff determined that these nitrogen supply lines are not ASME Code components.
Therefore, the nitrogen supply lines and valves are not covered by 10 CFR 50.55a and ASME Code,Section XI, requirements, and the staff is not authorized to grant relief for performing a limited scope VT-2 examination of these components under 10 CFR 50.55a(g)(6)(i).
The ASME Code,Section XI, Examination Category C-H requires that the HPS piping and valves at Palo Verde, Unit 1 be leak tested and receive a VT-2 visual examination. The licensee stated that a VT-2 qualified examiner employs a "snoop" method to detect escaping gas in the form of bubbles on the HPS piping. This method applies a liquid that forms bubbles if a gaseous substance leaks from the piping. The licensee stated that portions of the HPS piping within the containment penetrations are inaccessible for the application of "snoop" method, and the VT-2 examination is limited to the accessible portions of the HPS piping. The licensee stated that achieving 100 percent VT-2 examination coverage for the HPS piping would require the re-design and modification of wall penetrations to facilitate additional access. Therefore, according to the licensee, the ASME Code,Section XI, VT-2 examination requirements are impractical for the HPS piping at Palo Verde, Unit 1. In subsequent e-mail correspondence dated July 7, 2010, the licensee stated that the limited VT-2 examination of the HPS piping achieved a visual coverage of 17 feet (81 percent) of the HPS piping, with 4 feet (19 percent) of the piping being inaccessible due to the containment penetration configuration. The licensee also stated in this correspondence that the limited VT-2 examination of the HPS piping revealed no indications of leakage.
The NRC staff reviewed the information provided by the licensee concerning the impracticality of achieving full VT-2 visual examination coverage for the HPS piping, as discussed above, and agreed with the licensee's determination that access for VT-2 coverage of the HPS piping is restricted within the containment penetrations. Therefore, the staff agreed with the licensee's determination that achieving 100 percent VT-2 visual examination coverage of the HPS piping, as required by the ASME Code,Section XI, is impractical. The staff concluded that the licensee's alternative, consisting of a limited VT-2 examination of the HPS piping with 81 percent coverage provided reasonable assurance that the HPS piping would maintain its structural integrity because this examination, while limited in scope, did not detect any leakage of hydrogen gas from the piping.
- 11 Based on the above, the NRC staff concluded that the ASME Code,Section XI, requirement to perform a VT-2 visual examination of the HPS piping, with 100 percent coverage, is impractical for Palo Verde, Unit 1. The licensee's limited VT-2 visual examination provides reasonable assurance of continued integrity for the subject pressure retaining components at Palo Verde, Unit 1. As stated above, the licensee's request for relief for the CVCS charging pump nitrogen supply lines cannot be granted by the staff because the nitrogen supply lines are not ASME Code components.
4.0 CONCLUSION
Based on the above evaluation of RR-46, Parts A through G, the NRC staff concludes that the applicable ASME Code,Section XI, examination requirements are impractical for the subject Class 1 and 2 components at Palo Verde, Unit 1. Furthermore, the staff concludes that the licensee's alternative examinations provide reasonable assurance of structural integrity for the subject Class 1 and 2 components. The staff further concludes 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, RR-46, Parts A through F and Part G, for the HPS piping and valves only, is granted for the second 1O-year interval lSI program at Palo Verde, Unit 1. The staff cannot grant relief as requested in Part G for the CVCS charging pump nitrogen supply lines, pursuant to 10 CFR 50.55a(g)(6)(i), because these components are not subject to 10 CFR 50.55a and ASIVIE Code,Section XI, requirements. All other requirements of the ASME Code,Section XI, for which relief has not been specifically requested and approved, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: C. Sydnor Date: July 27,2010
R. Edington
- 2 A copy of the related Safety Evaluation is enclosed. All other ASME Code,Section XI, requirements for which relief has not been specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact Mr. Randy Hall at (301) 415-4032 or via e-mail at randy. hall@nrc.gov.
Sincerely, Ira!
Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-528
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv DISTRIBUTION:
PUBLIC RidsNrrPMPaloVerde Resource LPLIV r/f RidsNrrLAJBurkhardt Resource RidsAcrsAcnw_MailCTR Resource RidsOgcRp Resource RidsNrrDciCvib Resource RidsRgn4MailCenter Resource RidsNrrDorlDpr Resource LTrocine, EDO RIV RidsNrrDorlLpl4 Resource CSydnor, NRRIDCI/CVIB ADAMS Accession No.:
(*) Concurrence via SE OFFICE NRR/LPL4/PM NRR/LPL4/LA DCIICVIB/BC NRR/LPL4/BC NRR/LPL4/PM NAME JRHall JBurkhardt MMitchell o MMarkley JRHall DATE 7/23/10 7/22/10 7/12/10 7/27/10 7/27/10 OFFICIAL AGENCY RECORD