ML090690154
| ML090690154 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 03/26/2009 |
| 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 MD8328 | |
| Download: ML090690154 (17) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 March 26, 2009 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 2 - RELIEF REQUEST NO. 38 RE: SECOND 10-YEAR INSERVICE INSPECTION PROGRAM INTERVAL (TAC NO. MD8328)
Dear Mr. Edington:
By letter dated March 14, 2008, as supplemented on November 14,2008, Arizona Public Service Company (APS, the licensee) submitted Relief Request No. 38 (RR-38) to the U.S.
Nuclear Regulatory Commission (NRC), 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 2, for the second 1O-year inservice inspection (lSI) program interval, which ended on March 17,2007. NRC approval of RR-38 would authorize relief from certain weld examination requirements of ASME Code,Section XI that are considered impractical. In a letter dated September 24, 2008, the NRC requested additional information concerning the APS submittal. APS submitted its response and withdrew Part A of the relief request, which it subsequently determined to be unnecessary, by letter dated November 14,2008.
Based on the information in the licensee's submittals, the NRC staff has determined that granting RR-38, Parts B through F, pursuant to paragraph 50.55a(g)(6)(i) of Title 10 of the Code of Federal Regulations is authorized by law and will not endanger life or property, or the common defense and security, and is othelWise in the public interest given 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 1O-year lSI program interval at Palo Verde, Unit 2, based on the determination that the examination coverage requirements are impractical for the subject welds listed in RR-38, Parts B through F, and that the examinations performed to the extent practical provide reasonable assurance of structural integrity of the welds.
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 of my staff at (301) 415-4032 or via email at randy.hall@nrc.gov.
Sincerely, Michael 1. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-529
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 INSERVICE INSPECTION RELIEF REQUEST NO. RR-38 ARIZONA PUBLIC SERVICE COMPANY, ET AL.
PALO VERDE NUCLEAR GENERATING STATION, UNIT 2 DOCKET NO. STN 50-529
1.0 INTRODUCTION
The U.S. Nuclear Regulatory Commission (NRC) staff, with technical assistance from its contractor, the Pacific Northwest National Laboratory (PNNL), has reviewed and evaluated the information provided by Arizona Public Service Company (the licensee) in its letter dated March 14, 2008 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML080920639), which proposed its second 1O-year inservice inspection (lSI) interval program plan Request for Relief No. RR-38 for Palo Verde Nuclear Generating Station (Palo Verde), Unit 2. The NRC staff issued a request for additional information (RAI) by letter dated September 24,2008 (ADAMS Accession No. ML082610134), and the licensee responded to the RAI in a letter dated November 14, 2008 (ADAMS Accession No. ML083370163). The staff also requested additional clarification in an electronic mail message dated February 6,2009 (ADAMS Accession No. ML090370861). The licensee provided the requested information in an electronic mail message dated March 4, 2009 (ADAMS Accession No. ML090690082). This safety evaluation (SE) discusses the results of the NRC staff's review. Attachment 1 to this SE lists each individual part of the relief request and the status of approval.
2.0 REGULATORY REQUIREMENTS Inservice inspection (lSI) of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components is to be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code (Code), and applicable addenda, as required by Title 10 of the Code of Federal Regulations (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 at 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, 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 ASME Code of record for Palo Verde, Unit 2 second 10-year interval lSI program, which ended on March 17, 2007, is the 1992 Edition through the 1992 Addenda, of Section XI of the ASIVIE Code.
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 Request for Relief 38, Part A, ASME Code,Section XI, Examination Category B-A, Item B1.22, Pressure Retaining Welds in Reactor Vessel (RPV)
ASME Code Requirement ASME Code,Section XI, Examination Category B-A, Item B1.22 requires essentially 100 percent VOlumetric examination of the "accessible length" of meridional head welds on the reactor pressure vessel (RPV), as defined by ASME Code,Section XI, Figure IWB-2500-3.
When implementing the above requirement, the ASME Code Committees considered various obstacles (e.g., control rod drives, RPV support skirt, instrument lines, etc.) that may prevent VOlumetric examination of the full length of these welds. For these reasons, the examinations are limited to the accessible length of the meridional RPV head welds.
As a result of the NRC RAI, the licensee stated that 100 percent of the accessible length was inspected. Therefore, relief is not required. As a result, the licensee subsequently withdrew this portion of RR-38 in its letter dated November 14, 2008. Therefore, RR-38, Part A will not be discussed further in this SE.
3.2 Request for Relief 38, Part B, ASME Code,Section XI, Examination Category B-O, Item B3.11 0, Full Penetration Welded Nozzles in Vessels ASME Code Requirement ASME Code,Section XI, Examination Category B-O, Item B3.11 0 requires 100 percent volumetric examination, as defined by ASME Code,Section XI, Figures IWB-2500-7(a) through (d), as applicable, of ASME Code Class 1 pressurizer (PZR) nozzle-to-vessel
- 3 welds. ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 Welds,Section XI, Division 1," as an alternative approved for use by the NRC in Regulatory Guide (RG) 1.147, Revision 15, "I nservice Inspection Code Case Acceptability, ASME Section XI, Division 1," states that a reduction in examination coverage due to part geometry or interference for any ASME Code Class 1 and 2 weld is acceptable provided that the reduction is less than 10 percent (i.e., greater than 90 percent examination coverage is obtained).
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent volumetric examination of pressurizer (PZR) Nozzle to-Vessel Welds 5-10 and 5-13.
Licensee's Basis for Relief Request (as stated)
[PZR] Nozzle Zone 5 welds 5-10 and 5-13 were limited to an average of 83 [percent] [ASME] Code volume coverage because of limited access based on geometric constraints of the nozzle. The radius portion of the nozzle and the curvature of the [PZR] head limited some angles of sound to portions of the inside diameter. The examiner performed a coverage calculation that identified that the examination did not achieve >90 [percent]
coverage. All accessible surfaces were scanned in multi directions to obtain the maximum coverage within the available configuration and transducer/equipment used.
Licensee's Proposed Alternative Examination The licensee did not propose any additional examinations as an alternative to the ASME Code requirements. However, the licensee examined the subject welds to the extent practical.
NRC Staff Evaluation
The ASME Code requires 100 percent VOlumetric examination of full penetration welded nozzles and inside radius sections in ASME Code Class 1 vessels. However, examinations of PZR spray and safety nozzle-to-vessel welds, designated by the licensee as Welds 5-10 and 5-13, respectively, are limited by the design geometry of the PZR upper head. In order to increase volumetric coverage, the subject nozzle-to-vessel welds would require re-design and modification. This would create a significant burden on the licensee; therefore, the ASME Code-required 100 percent volumetric examinations are impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, examinations of the subject nozzle-to-vessel welds have been performed to the extent practical with the licensee obtaining volumetric coverage of approximately 83 percent on each of the subject welds. The spray nozzle is a 4-inch outside diameter (00) nominal pipe size (NPS), SA-541, Grade B carbon steel forging welded to the
- 4 SA-533, Grade B carbon steel upper PZR head. Similarly, the 6-inch 00 NPS forged safety nozzle is SA-541, Grade B carbon steel welded to the PZR upper head. The nozzles are of the "set-in" design, which essentially makes the welds concentric rings aligned parallel with the nozzle axes in the through-wall direction of the head (shell).
This design geometry limits ASME Code-required ultrasonic angle beam examinations to be performed only from the shell side of the welds. In addition, the forging blend radii of the nozzles also prevent scanning due to the curvature in these areas.
The ultrasonic examinations on these PZR carbon steel nozzle welds included O-degree longitudinal, and 45-, 60- and 70-degree shear waves from the shell side, including most of the weld and base materials near the inside surface of the vessel, which are the highest regions of stress and where one would expect degradation sources to be manifested should they occur. Although ultrasonic scans were primarily limited to the head side only, recent studies have found that inspections conducted through carbon steel are equally effective whether the ultrasonic waves have only to propagate through the base metal, or have to also propagate through the carbon steel weldment. 1 Therefore, it is expected that the ultrasonic techniques employed by the licensee would detect structurally significant flaws that might occur on either side of the subject welds due to the fine-grained carbon steel microstructures in these materials. No unacceptable indications were noted during the examinations.
The licensee has shown that it cannot meet the ASME Code-required 100 percent volumetric examination coverage for the subject nozzle-to-vessel welds due to their design. The NRC staff finds that the Code-required examinations are impractical for these welds, for the reasons stated above. However, based on the volumetric coverage obtained, it is reasonable to conclude that, if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that were performed. In addition, the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject welds.
3.3 Request for Relief 38, Part C, ASME Code,Section XI, Examination Category B-H, Item B8.20, Integral Attachments for Vessels ASME Code Requirement ASME Code,Section XI, Examination Category B-H, Item B8.20 requires essentially 100 percent surface examination of integrally welded supports on the PZR, as defined by ASME Code,Section XI, Figures IWB-2500-13, -14, or -15, respectively. The examination must be performed on accessible inside diameter (10) and 00 surfaces of the weld. If the weld is a full penetration configuration as shown in IWB-2500-14, a VOlumetric examination may be used in lieu of the surface examination. "Essentially 100 percent," as clarified by ASIVIE Code Case N-460, is greater than 90 percent coverage of the examination volume, or surface area, as applicable. ASME Code Case N-460 has been approved for use by the NRC in RG 1.147, Revision 15.
P. G. Heasler and S. R. Doctor, 1996. Piping Inspection Round Robin, NUREG/CR-5068, PNNL-10475, U.S. Nuclear Regulatory Commission, Washington, DC.
- 5 Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent surface examination of PZR integral support skirt Weld 5-1.
Licensee's Basis for Relief Request (as stated)
The [PZR-to-Skirt] weld (5-1) is inaccessible for surface examination from the inside due to radiation, insulation, heaters, and drain lines. A surface examination was performed [on the] outside surface and an ultrasonic examination was performed from the outside surface to augment the surface examination. The examination was limited to 50 [percent coverage] for the surface examination and approximately 57 [percent]
[ASME] Code volume coverage for the volumetric examination, due to the configuration. Scanning could only be performed from the skirt side.
Licensee's Proposed Alternative Examination The licensee performed a VOlumetric examination from the outside surface to augment the limited surface examination.
NRC Staff Evaluation
The ASME Code requires essentially 100 percent surface examination of both the inside (i.e., the side inside the skirt) and outside surfaces of PZR main support skirt Weld 5-1.
However, examination on the inside surface is restricted due to the geometry of the PZR bottom head, heater nozzle penetrations, and other appurtenances. To gain access for examination, the support skirt weld and PZR bottom head would require extensive design modifications or replacement. Imposition of this requirement would create a significant burden on the licensee; therefore, the ASME Code-required examination on the inside surface is impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, surface examinations of the PZR support skirt weld have been performed to the extent practical with the licensee obtaining 100 percent examination on the outside surface. While PZR skirt attachment Weld 5-1 is not a full penetration design, as described in ASME Code,Section XI, IWB-2500-14, the licensee conducted an augmented volumetric examination of the weld and inside surface region, as performed from the outside surface, and obtained additional volumetric coverage of approximately 50 percent. This volumetric examination used both 45-and 60-degree shear waves applied from the skirt side of the weld. A portion of the blend radius between the PZR head and support skirt was inaccessible for examination. The licensee reported that the pressurizer skirt weld has a mid-wall construction slag inclusion. The slag was detected ultrasonically during interval one and evaluated to be acceptable for continued operation.
The slag was re-examined in intervals one and two and has not changed in size. No unacceptable indications were observed during the performance of these examinations.
- 6 The licensee has shown that it cannot meet the ASME Code-required surface examination coverage on both inside and outside surfaces of the subject weld due to limited access caused by the PZR bottom head geometry, heater penetrations, and other instrument lines and insulation in this area. The NRC staff finds that the Code required examinations are impractical for this weld, for the reasons stated above.
However, based on the 100 percent examination coverage obtained on the outside surface of the weld and the volumetric examination performed to augment the inspection, it is reasonable to conclude that, if significant service-induced degradation had occurred, evidence of it would have been detected. In addition, the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject welds.
3.4 Request for Relief 38. Part D. ASME Code,Section XI, Examination Category 8-J, Items 89.11, Pressure Retaining Welds in Piping ASME Code Requirement ASME Code,Section XI, Examination Category 8-J, Item 89.11, requires essentially 100 percent volumetric and surface examinations, as defined by ASME Code, Figures IW8-2500-8, for piping circumferential welds 4-inch NPS, and greater, in diameter. "Essentially 100 percent," as clarified by ASIVIE Code Case N-460, is greater than 90 percent coverage of the examination volume, or surface area, as applicable.
ASME Code Case N-460 has been approved for use by the NRC in RG 1.147, Revision 15.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent volumetric examination of the ASME Code, Class 1 piping welds shown in Table 3.4.1.
Table 3.4.1 - ASME Code,Section XI, Examination Category 8-J ASME Code Item Weld Identification Weld Configuration Nominal Pipe Size (NPS),
Thickness (T) (inches) 89.11 22-11 Pipe-to-Valve 16 NPS, 1.594 T 89.11 23-4 Pipe-to-Valve 14 NPS, 1.406 T 89.11 23-6 Pipe-to-Valve 14 NPS, 1.406 T 89.11 24-6 Pipe-to-Valve 14 NPS, 1.406 T 89.11 24-14 Pipe-to-Valve 14 NPS, 1.406 T 89.11 24-16 Pipe-to-Valve 14 NPS, 1.406 T 89.11 24-19 Pipe-to-Valve 14 NPS, 1.406 T 89.11 25-4 Pipe-to-Valve 14 NPS, 1.406 T 89.11 25-6 Pipe-to-Valve 14 NPS, 1.406 T 89.11 26-6 Pipe-to-Valve 14 NPS, 1.406 T
- 7 Table 3.4.1 - ASME Code,Section XI, Examination Category B-J ASME Code Item Weld Identification Weld Configuration Nominal Pipe Size (NPS),
Thickness (T) (inches)
B9.11 26-17 Pipe-to-Valve 14 NPS, 1.406 T B9.11 29-2 Pipe-to-Tee 4 NPS, 0.532 T B9.11 29-3 Pipe-to-Tee 4 NPS, 0.531 T Licensee's Basis for Relief Request (as stated)
Several [ASME Code,Section XI,] Category B-J and C-F-1 butt welds were only accessible from one side of the weld due to configuration problems. Only 50 [percent] [ASME] Code volume coverage was credited due to single sided examination of austenitic stainless steel welds e.g.;
obstruction from valves.
Licensee's Proposed Alternative Examination The licensee did not propose any additional examinations as an alternative to the ASIVIE Code requirements. However, the licensee examined the subject welds to the extent practical.
!\\IRC Staff Evaluation The ASIVIE Code requires essentially 100 percent volumetric and surface examination for selected ASME Code,Section XI, Examination Category B-J pressure retaining welds in piping. The volumetric examination must be applied from both sides of the weld to maximize coverage. Full ASME Code-required surface examinations were conducted for all of the subject welds. However, volumetric examinations are limited by the pipe-to valve/tee geometry of the welds, which restricts scanning to the pipe side only. To gain access for examination, the welds would require major design modifications. Imposition of this requirement would create a significant burden on the licensee; therefore, the ASME Code-required 100 percent volumetric examinations from both sides of the welds are impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, access for examination of the subject welds is limited to the pipe side only due to the cast materials of the valve and the extreme tapers caused by the valve-to-pipe and pipe-to-tee weld configurations (see Table 3.4.1 above). The ultrasonic methods employed for these welds have been qualified through the industry's performance demonstration initiative (POI), which meets ASME Code, Appendix VIII requirements.
These methods have been qualified for flaws located on the near-side of the welds; far side detection of flaws is considered to be a "best effort." For this reason, the licensee has taken credit for completing only 50 percent of the ASME Code-required inspection volume on each of the subject piping welds.
The licensee's ultrasonic methods included 45-and 60-degree, as applicable, refracted longitudinal waves (L-waves), which have been shown to provide enhanced detection on
- 8 the far-side of austenitic stainless steel welds. 2,3 Although these L-wave techniques could potentially provide coverage well beyond the near-side of the welds, the licensee has only taken credit for obtaining 50 percent volumetric coverage. A review of the typical weld cross-sectional information indicates that limited volumetric coverage on the far-side of the welds has also been obtained by the licensee. The licensee reported that the welds with coverage limitations have no flaw indications. Several welds have ultrasonic geometrical indications caused by 10 or 00 surface conditions; however, no service-induced defects have been identified in these welds.
The licensee has shown that it cannot meet the ASME Code-required 100 percent volumetric examination coverage for the subject piping welds due to their design and ultrasonic access restrictions. The NRC staff finds that the Code-required examinations are impractical for these welds, for the reasons stated above. Although the ASME Code-required coverage could not be obtained, the ultrasonic methods employed would have provided full volumetric coverage for the near-side of the welds and limited volumetric coverage for the weld fusion zone and base materials on the opposite side of the welds. Based on the aggregate coverage obtained for the subject welds, and considering the licensee's performance of ultrasonic techniques used to maximize this coverage, it is reasonable to conclude that if significant service-induced degradation were occurring, evidence of it would have been detected by the examinations that were performed. In addition, the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject welds.
3.5 Request for Relief 38, Part E, ASME Code,Section XI, Examination Category C-C, Items C3.20 and C3.30, Integral Attachments for Vessels, Piping, Pumps and Valves ASME Code Requirement ASME Code,Section XI, Examination Category C-C, Items C3.20 and C3.30 require 100 percent surface examinations, as defined by Figure IWC-2500-5, of integrally welded attachments to ASME Code, Class 2 piping and pumps, respectively.
"Essentially 100 percent," as clarified by ASME Code Case N-460, is greater than 90 percent coverage of the examination volume, or surface area, as applicable. ASIVIE Code Case N-460 has been approved for use by the NRC in RG 1.147, Revision 15.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent surface examination of integrally welded attachment SI-107-H-022 on the safety injection piping system and integrally welded attachments 116-1 Band 116-1 C on High Pressure Safety Injection (HPSI) Pump A.
F. V. Ammirato, X. Edelmann, and S.M. Walker, Examination of Dissimilar Metal Welds in BWR Nozzle-to Safe End Joints, 8th International Conference on NDE in the Nuclear Industry, ASM International, 1987.
3 P. Lemaitre, T.D. Koble, and S.R. Doctor, PISC 11/ Capability Study on Wrought-to-Wrought Austenitic Steel Welds: Evaluation at the Level of Procedures and Techniques, Effectiveness of Nondestructive Examination Systems and Performance Demonstration, PVP-Volume 317, NDE-Volume 14, ASME, 1995.
- 9 Licensee's Basis for Relief Request (as stated)
The integral attachment for component support SI-1 07-H-022 consists of two shear lugs, one on each side of a support member, just before the pipe enters a wall penetration. One of the lugs is inside the wall penetration and the other lug is accessible on 3 sides of the lug. The remaining side is very close to the structural member and is not accessible for surface examination. When only one lug is considered,
[ASME] Code [surface] coverage changes to approximately 81 [percent].
It would cause an undue burden on the plant to disassemble the support to make the inaccessible portion accessible when there have been no abnormal conditions noted at this location.
The integral attachment for component supports 116-1 Band 116-1 C consist of a three-sided support lug with the bottom of the lugs sitting on a structural member, limiting access to a portion of the bottom weld and adjacent base material. [ASME] Code coverage is limited to approximately 72 [percent] due to configuration. All support lugs on the HPSI pumps (8) were examined during the second interval and there have been no abnormal conditions noted at these locations. It would cause an undue burden on the plant to disassemble the support or remove the pump to allow access to the inaccessible portion of the attachment.
Licensee's Proposed Alternative Examination The licensee did not propose any additional examinations as an alternative to the ASME Code requirements. However, the licensee examined the subject welds to the extent practical.
NRC Staff Evaluation
The ASME Code requires essentially 100 percent surface examination of the length of the subject piping integrally welded attachment and pump supports on the safety injection system. However, ASME Code,Section XI, paragraph IWC-1223 states that integral attachments that are inaccessible due to being encapsulated by guard pipe are exempt from examination. Complete examinations were restricted by interference from a wall penetration and structural steel on piping support SI-107-H-022, and the design of the support lug welds 116-1B and 116-1C on HPSI Pump A. To gain access for examination, the piping support and pump lugs would require major design modifications. Imposition of this requirement would create a significant burden on the licensee; therefore, the ASM E Code-required 100 percent surface examinations are impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, examinations of the subject integral attachment welds have been performed to the extent practical with the licensee obtaining surface coverage of approximately 81 percent on the non-exempt portion of the piping support and 72 percent on the pump
- 10 lugs. The liquid penetrant (PT) examinations on integrally welded attachments for piping component support SI-1 07-H-022 were obstructed due to a permanently installed structural steel member and a portion of the support being located within a wall penetration. A structural steel member adjacent to the pump causes an access limitation to the underside of Welds 116-1 Band 116-1 C on the front support lugs for HPSI Pump A. No restrictions exist on the rear support lugs and the licensee completed the examinations of the rear support lug welds to the full ASME Code extent. The licensee indicated that the piping weld examinations have reported no recordable indications, and that the pump lug welds do not have any rejectable dye penetrant indications. The lug welds have acceptable recordable indications caused by surface conditions (rough as-welded surface condition). No service-induced defects have been identified in these welds.
The licensee has shown that it cannot meet the ASME Code-required surface examination coverage for the subject integrally welded attachments due to access restrictions caused by the presence of structural steel components and proximity to a wall penetration. The NRC staff finds that the Code-required examinations are impractical for these integrally welded attachments, for the reasons stated above.
Based on the surface coverage obtained, it is reasonable to conclude that, if significant service-induced degradation had occurred in the subject welds, evidence of it would have been detected by the examinations performed. In addition, the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject welds.
3.6 Request for Relief 38. Part F, ASME Code,Section XI, Examination Category C-F-1, Items C5.11 and C5.21, Pressure Retaining Welds in Austenitic Stainless Steel or High Alloy Piping ASME Code Requirement ASIVIE Code,Section XI, Examination Category C-F-1, Items C5.11 and C5.21 require 100 percent VOlumetric and surface examinations, as defined by ASME Code, Figure IWC-2500-7, of selected ASME Code, Class 2 austenitic stainless steel or high alloy piping welds. "Essentially 100 percent," as clarified by ASME Code Case N-460, is greater than 90 percent coverage of the examination volume, or surface area, as applicable. ASIVIE Code Case N-460 has been approved for use by the NRC in RG 1.147, Revision 15.
- 11 Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required volumetric examinations of the high alloy piping welds shown in Table 3.6.1.
Table 3.6.1 - ASME Code,Section XI, Examination Category C-F-1 ASME Code Item Weld Identification Weld Configuration Nominal Pipe Size (NPS),
Thickness (T) (inches)
C5.11 77-7 Pipe-to-flange 12 NPS, 0.406 T C5.11 77-14 Pipe-to-valve 12 NPS, 1.125 T C5.11 84-12 Pipe-to-valve 24 NPS, 0.562 T C5.11 85-46 Pipe-to-valve 20 NPS, 0.375 T C5.11 77-27 Pipe-to-valve 12 NPS, 1.312 T C5.11 70-121 Pipe-to-valve 16 f\\lPS, 1.420 T C5.21 77-16 Pipe-to-valve 12 NPS, 1.125 T C5.21 84-3 Pipe-to-valve 20 NPS, 0.375 T C5.21 106-1 Pipe-to-pump 4 NPS, 0.337 T C5.21 106-21 Pipe-to-valve 4 NPS, 0.438 T C5.21 106-64 Pipe-to-valve 2 NPS, 0.344 T C5.21 106-68 Pipe-to-tee 2 NPS, 0.344 T C5.21 107-1 Pipe-to-pump 4 NPS, 0.337 T C5.21 107-11 Pipe-to-valve 4 I\\IPS, 0.337 T C5.21 110-17 Pipe-to-valve 2 NPS, 0.344 T C5.21 110-52 Pipe-to-tee 2 NPS, 0.344 T C5.21 115-13 Pipe-to-penetration 3 NPS, 0.438 T C5.21 115-20 Pipe-to-valve 3 NPS, 0.438 T C5.21 118-49 Pipe-to-valve 3 I\\IPS, 0.438 T C5.21 119-52 Pipe-to-valve 3 NPS, 0.438 T C5.21 119-53 Pipe-to-valve 2 NPS, 0.344 T Licensee's Basis for Relief Request (as stated)
Several categories [ASME Code,Section XI,] B-J and C-F-1 butt welds were only accessible from one side of the weld due to configuration problems. Only 50 percent [ASME] Code volume coverage was credited due to single sided examination of austenitic stainless steel welds e.g.;
obstruction from valves.
- 12 Licensee's Proposed Alternative Examination The licensee did not propose any additional examinations as an alternative to the ASME Code requirements. However, the licensee examined the subject welds to the extent practical.
NRC Staff Evaluation
The ASME Code requires essentially 100 percent volumetric and surface examination for selected ASME Code,Section XI, Examination Category C-F-1 pressure retaining welds in piping. The volumetric examination must be applied from both sides of the weld to maximize coverage. Full ASME Code-required surface examinations were conducted for all of the subject welds. However, volumetric examinations are limited by the geometry of the welds, which restricts scanning to the pipe side only. To gain access for examination, the welds would require major design modifications. Imposition of this requirement would create a significant burden on the licensee; therefore, the ASME Code-required 100 percent volumetric examinations from both sides of the welds are impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, access for examination of the subject welds is limited to the pipe side only due to the cast materials of the valve and the extreme tapers caused by the valve-to-pipe, pipe-to-tee, pipe-to-pump, and pipe-to-penetration weld configurations (see Table 3.6.1 above). The ultrasonic methods employed for these welds have been qualified through the industry's POI, which meets ASME Code, Appendix VIII requirements. These methods have been qualified for flaws located on the near-side of the welds; far-side detection of flaws is considered to be a "best effort." For this reason, the licensee has taken credit for completing only 50 percent of the ASME Code-required inspection volume on each of the subject piping welds.
However, depending on the piping wall thickness (see Table 3.6.1), the licensee's ultrasonic methods included 45-, 60- and 70-degree, shear or refracted longitudinal waves (L-waves), which have been shown to provide enhanced detection on the far-side of austenitic stainless steel welds.
4
,5 Although these L-wave techniques could potentially provide coverage beyond the near-side of the welds, the licensee has only taken credit for obtaining 50 percent volumetric coverage. A review of the typical weld cross sectional information indicates that limited volumetric coverage on the far-side of the welds has been obtained by the licensee. The licensee reported that the welds with coverage limitations have no flaw indications. Several welds have ultrasonic geometrical indications caused by 10 or 00 surface conditions, however, no service-induced defects have been identified in these welds.
4 Ammirat0f, F.V., X. Edelmann, and S.M. Walker, Examination of Dissimilar Metal Welds in BWR Nozzle-to Safe End Joints, 8t International Conference on NDE in the Nuclear Industry, ASM International, 1987.
5 Lemaitre, P., T.o. Koble, and S.R. Doctor, PISC III Capability Study on Wrought-to-Wrought Austenitic Steel Welds: Evaluation at the Level of Procedures and Techniques, Effectiveness of Nondestructive Examination Systems and Performance Demonstration, PVP-Volume 317, NDE-Volume 14, ASME, 1995.
- 13 The licensee has shown that it cannot meet the ASME Code-required 100 percent volumetric examination coverage for the subject piping welds due to their design and ultrasonic access restrictions. The NRC staff finds that the Code-required examinations are impractical for these welds, for the reasons stated above. Although the ASME Code-required coverage could not be obtained, the ultrasonic methods employed would have provided full volumetric coverage for the near-side of the welds and limited volumetric coverage for the weld fusion zone and base materials on the opposite side of the welds. Based on the aggregate coverage obtained for the subject welds, and considering the licensee's performance of ultrasonic techniques used to maximize this coverage, it is reasonable to conclude that if significant service-induced degradation were occurring, evidence of it would have been detected by the examinations that were performed. In addition, the examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject welds.
4.0 CONCLUSION
S The staff has reviewed the licensee's submittal and concludes that the ASME Code examination coverage requirements are impractical for the subject welds listed in RR-38, Parts B through F.
Furthermore, imposition of these ASME Code requirements would create a burden on the licensee. The staff further determined that based on the volumetric and/or surface coverage obtained on the subject welds contained in RR-38, Parts B through F, it is reasonable to conclude if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that were performed. Furthermore, the staff concluded that examinations performed to the extent practical provide reasonable assurance of structural integrity of the subject welds. Therefore, for the welds contained in RR-38, Parts B through F, relief is granted, pursuant to 10 CFR 50.55a(g)(6)(i), for the second lSI interval at Palo Verde, Unit 2.
The staff has determined that granting RR-38, Parts B through F, 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 given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
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 Inservice Inspector.
Principal Contributors: Thomas K. McLellan Carol A. Nove Date:
I"larch 26, 2009
Attachment:
Summary of Relief Requests
PALO VERDE NUCLEAR STATION, UNIT 2 Page 1 of 1 Second 10-Year lSI Interval ATTACHMENT
SUMMARY
OF RELIEF REQUESTS TLR Relief Request RR System or Exam.
Volume or Area to be Required Licensee Proposed Relief Request Number Sec.
Component Category Item No.
Examined Method Alternative Disposition RR-38 3.1 RPV head B-A B1.22 100% of accessible Class 1 Volumetric None Withdrawn by (part A) welds meridional head welds licensee RR-38 3.2 PZR nozzle-B-D B3.110 100% of Class 1 nozzle-to-Volumetric Use volumetric Granted (Part B) vessel welds to-vessel coverage(s) achieved 10 CFR welds 50.55a(g)(6)(i)
RR-38 3.3 Integrally B-H B8.20 100% of selected Class 1 Surface Use surface coverage Granted welded component supports (Part C) achieved with augmented 10 CFR attachments volumetric examination 50.55a(g)(6)(i)
RR-38 3.4 Piping welds B-J B9.11 100% of selected Class 1 Volumetric Use volumetric Granted (Part D) piping welds and coverage(s) achieved 10 CFR Surface 50.55a(g)(6)(i) 3.5 Integrally RR-38 C-C C3.20 100% of selected Class 2 Surface Use surface coverage(s)
Granted welded (Part E)
C3.30 component supports achieved 10 CFR attachments 50.55a(g)(6)(i)
Piping Welds C-F-1 C5.11 RR-38 3.6 100% of selected Class 2 Volumetric Use vOlumetric Granted (Part F)
C5.21 piping welds in high alloy and coverage(s) achieved 10 CFR systems Surface 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 of my staff at (301) 415-4032 or via email at randy.hall@nrc.gov.
Docket No. STN 50-529
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv DISTRIBUTION:
PUBLIC LPLIV rtf RidsAcrsAcnw_MailCTR Resource RidsNrrDciCpnb Resource RidsNrrDorlDpr Resource RidsNrrDorlLpl4 Resource ADAMS Accession No.: ML090690154 OFFICE NRR/LPL4/PM NRR/LPL4/LA NAME
.IBurkhardt ("")
.IRHall ("")
DATE 3/11 109 3/11/09 Sincerely, IRAJ Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation RidsNrrPMPaloVerde Resource RidsNrrLAJBurkhardt Resource RidsOgcRp Resource RidsRgn4MailCenter Resource EGuthrie, EDO RIV
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(**) See rrevious concurren ce DCI/CVIB/BC OGC NRR/LPL4/BC MMitchell (*)
DRoth (NLO) ("")
MMarkley 3/20109 3/2/09 3/26/09 OFFICIAL AGENCY RECORD