ML040070449
| ML040070449 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 01/07/2004 |
| From: | John Nakoski NRC/NRR/DLPM/LPD2 |
| To: | Jamil D Duke Energy Corp |
| Nakoski J A, NRR/DLPM, 415-1068 | |
| References | |
| TAC MB8784 | |
| Download: ML040070449 (18) | |
Text
January 7, 2004 Mr. D. M. Jamil Catawba Nuclear Station Duke Energy Corporation 4800 Concord Road York, South Carolina 29745
SUBJECT:
CATAWBA NUCLEAR STATION, UNIT 1 RE: SECOND 10-YEAR INTERVAL INSERVICE INSPECTION PROGRAM PLAN REQUEST FOR RELIEF 02-002, REVISION 1 (TAC NO. MB8784)
Dear Mr. Jamil:
By letter dated August 15, 2002, Duke Power Company (the licensee) proposed its Second 10-Year Interval Inservice Inspection Program Plan Request for Relief 02-002 from the American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, for Catawba Nuclear Station, Unit 1. In response to a Nuclear Regulatory Commission (NRC) Request for Additional Information, the licensee revised the request for relief and provided additional information in a letter dated May 7, 2003. The NRC staff, with technical assistance from its contractor, the Pacific Northwest National Laboratory, has reviewed and evaluated the information provided by the licensee.
The enclosed Safety Evaluation contains the NRC staff's evaluation and conclusions. The NRC staff found the licensees Request for Relief 02-002, Revision 1 acceptable. The NRC staff concludes that the Code examination coverage requirements are impractical for the subject components listed in Request for Relief 02-002, Examination Categories B-F and B-J.
Furthermore, reasonable assurance of the structural integrity of the subject components has been provided by the examinations that were performed. Therefore, relief is granted pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g)(6)(i) for the second 10-year interval.
For Request for Relief 02-002 Category C-A, Residual Heat Removal Heat Exchanger Shell-to-Flange Weld 1BRHRHX-5-9, the NRC staff concludes that the Code volumetric requirement is a significant hardship without a compensating increase in quality and safety.
Furthermore, the NRC staff concludes that reasonable assurance of the structural integrity of the component has been provided based upon the examination previously performed.
Therefore, the licensees request for relief is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the second 10-year interval at Catawba Nuclear Station, Unit 1.
Sincerely,
/RA/
John A. Nakoski, Chief, Section 1 Project Directorate II Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-413
Enclosure:
As stated cc w/encl: See next page Furthermore, the NRC staff concludes that reasonable assurance of the structural integrity of the component has been provided based upon the examination previously performed.
Therefore, the licensees request for relief is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the second 10-year interval at Catawba Nuclear Station, Unit 1.
Sincerely,
/RA/
John A. Nakoski, Chief, Section 1 Project Directorate II Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-413
Enclosure:
As stated cc w/encl: See next page Distribution:
PUBLIC PDII-1 R/F BSmith, EDO TMcLellan SCoffin JNakoski RHaag,RII CHawes SPeters GHill(2)
ACRS ADAMS ACCESSION NO. ML040070049
- No Major Changes to SE OFFICE PDII-1/PM PDII-1/LA EMCB*
EMCB*
OGC PDII-1/SC NAME SPeters CHawes SCoffin TChan RHoefling JNakoski DATE 12/24/03 12/23/03 9/25/03 9/22/03 1/5/04 1/6/04 OFFICIAL RECORD COPY
Catawba Nuclear Station cc:
Lee Keller Regulatory Compliance Manager Duke Energy Corporation 4800 Concord Road York, South Carolina 29745 Ms. Lisa F. Vaughn Duke Energy Corporation Mail Code - PB05E 422 South Church Street P.O. Box 1244 Charlotte, North Carolina 28201-1244 Anne Cottingham, Esquire Winston and Strawn 1400 L Street, NW Washington, DC 20005 North Carolina Municipal Power Agency Number 1 1427 Meadowwood Boulevard P. O. Box 29513 Raleigh, North Carolina 27626 County Manager of York County York County Courthouse York, South Carolina 29745 Piedmont Municipal Power Agency 121 Village Drive Greer, South Carolina 29651 Ms. Karen E. Long Assistant Attorney General North Carolina Department of Justice P. O. Box 629 Raleigh, North Carolina 27602 NCEM REP Program Manager 4713 Mail Service Center Raleigh, NC 27699-4713 North Carolina Electric Membership Corporation P. O. Box 27306 Raleigh, North Carolina 27611 Senior Resident Inspector U.S. Nuclear Regulatory Commission 4830 Concord Road York, South Carolina 29745 Henry Porter, Assistant Director Division of Waste Management Bureau of Land and Waste Management Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201-1708 Mr. Michael T. Cash Manager - Nuclear Regulatory Licensing Duke Energy Corporation 526 South Church Street Charlotte, North Carolina 28201-1006 Saluda River Electric P. O. Box 929 Laurens, South Carolina 29360 Mr. Peter R. Harden, IV VP-Customer Relations and Sales Westinghouse Electric Company 6000 Fairview Road 12th Floor Charlotte, North Carolina 28210 Mary Olson Director of the Southeast Office Nuclear Information and Resource Service 729 Haywood Road, 1-A P. O. Box 7586 Asheville, N. C. 28802
Catawba Nuclear Station cc:
Mr. T. Richard Puryear Owners Group (NCEMC)
Duke Energy Corporation 4800 Concord Road York, South Carolina 29745 Richard M. Fry, Director Division of Radiation Protection North Carolina Department of Environment, Health, and Natural Resources 3825 Barrett Drive Raleigh, North Carolina 27609-7721 Mary Olson Director of the Southeast Office Nuclear Information and Resource Service 729 Haywood Road, 1-A P.O. Box 7586 Asheville, North Carolina 28802
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FOR SECOND 10-YEAR INTERVAL INSERVICE INSPECTION REQUEST FOR RELIEF 02-002, REVISION 1 FOR CATAWBA NUCLEAR STATION, UNIT 1 DUKE POWER COMPANY DOCKET NO. 50-413
1.0 INTRODUCTION
By letter dated August 15, 2002, Duke Power Company (the licensee) proposed its Second 10-Year Interval Inservice Inspection (ISI) Program Plan Request for Relief 02-002 from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, for Catawba Nuclear Station, Unit 1. In response to an NRC Request for Additional Information, the licensee revised the request for relief and provided additional information in a letter dated May 7, 2003.
The NRC staff, with technical assistance from its contractor, the Pacific Northwest National Laboratory (PNNL), has reviewed and evaluated the information provided by the licensee.
2.0 REGULATORY REQUIREMENTS ISI of the ASME Code Class 1, 2, and 3 components is performed in accordance with Section XI of the ASME B&PV Code and applicable addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if:
(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.
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 pre-service examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection (ISI) 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 ENCLOSURE conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code 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 applicable Code of record for the second 10-year ISI for Catawba Nuclear Station, Unit 1 is the 1989 Edition of the ASME Boiler and Pressure Vessel Code,Section XI.
3.0 TECHNICAL EVALUATION
The NRC staff adopts the evaluations and recommendations for granting reliefs contained in the Technical Letter Report (TLR), included as Attachment 1, prepared by PNNL. Attachment 2 lists each relief request and the status of approval.
Pressure Retaining Dissimilar Metal Welds in Vessel Nozzles - Pressurizer Safety Nozzles 1PZR-W4ASE, 1PZR-W4BSE, and 1PZR-WCSE The ASME Code,Section XI requires essentially 100 percent volumetric and surface examination of the subject pressure retaining Category B-F nozzle-to-pipe welds. The volumetric examinations must be performed using two beam path directions from both sides of the weld, when accessible. Scanning access for the subject welds was limited due to the design of the nozzle. The subject pressurizer safety valve nozzle material is SA-508 carbon steel and the safe end is SA-182, Grade F316L. The welds are 6.0 inches in diameter with a 0.96 inch wall thickness. The valve nozzle is designed with a taper such that examination of the weld is severely restricted when scanning from the nozzle side of the subject welds. For the licensee to achieve 100 percent volumetric coverage with two beam directions would require that the subject welds be completely redesigned and modified. This would place a significant burden on the licensee; therefore, the Code-required (essentially 100 percent) volumetric examinations are impractical.
The licensee achieved volumetric coverages of approximately 77.28 percent for Weld No.
1PZR-W4ASE, 86 percent for Weld No. 1PZR-W4BSE, and 82.03 percent for Weld No.
1PZR-W4CSE. The licensee was able to examine essentially 100 percent of the Code required examination volume from three scanning directions; however, on the fourth scan there was a limitation that resulted in less than 100 percent aggregate coverage from all scans. They also performed 100 percent of the Code-required surface examinations on these welds. No recordable indications were noted during the volumetric and surface examinations. Based on the impracticality of performing full volumetric examinations, and considering the coverages obtained during volumetric and surface examination in conjunction with recent full volumetric examinations on other Category B-F welds any significant patterns of degradation should have been detected. Therefore, the licensee has provided reasonable assurance of the continued structural integrity of the subject components.
Valve 1ND002A to Pipe Weld 1ND38-1 The ASME Code,Section XI requires essentially 100 percent volumetric coverage of Category B-J pressure retaining welds in piping using two beam path directions. The Code also requires a 100 percent surface examination. The Valve 1ND002A to Pipe Weld 1ND38-1 examination volume can not be examined to the extent required by the Code. The licensee has used the following ultrasonic methods to examine this weld:
45 degree shear wave from the pipe side
60 degree shear wave from the pipe side
60 degree longitudinal from the pipe side Due to the valve body taper the licensee was unable to scan the weld from the valve side of the weld. To achieve essentially 100 percent volumetric coverage of the subject weld from two beam directions, the licensee would have to redesign the valve body which would be a significant burden on the licensee. Therefore, the Code-required (essentially 100 percent) volumetric examination from two beam directions is impractical.
The licensee obtained 61.23 percent of the required examination volume. No known degradation mechanisms or industry failure experience has been experienced for these austenitic pipe-to-valve connections. The examinations performed by the licensee should have detected any significant patterns of degradation that might have occurred, providing reasonable assurance of the continued structural integrity of Weld 1ND38-1.
Pressure Retaining Welds in Vessels, Residual Heat Removal (RHR) Heat Exchanger Shell to Flange Weld 1BRHRHX-5-9 The ASME Code,Section XI requires essentially 100 percent volumetric examination of the length of the subject Code Class 2 vessel weld. However, complete examination is restricted by several factors, including the heat exchangers shell-to-flange configuration, the close proximity of the studs and nuts to the vessel outside surface, and internal vessel support plates.
The licensee would have to disassemble the residual heat exchanger vessel at the flange connection and separate the upper and lower halves of the shell to achieve the Code required examination coverage. As a result of disassembling the residual heat exchanger vessel plant personnel would be subject to a significant radiation dose. Therefore, imposition of the Code requirement would be a significant hardship on the licensee without a compensating increase in quality and safety.
The licensee obtained 56 percent volumetric coverage of the subject weld with radiography. In addition, to the limited radiographic examination of the subject weld, other Class 2 vessel shell welds were examined to the extent required by the Code and were free of recordable indications. The combination of limited radiographic examination on the subject weld and the examinations of other Class 2 vessel shell welds should have detected any significant patterns of degradation, therefore, providing reasonable assurance of continued structural integrity of the RHR Heat Exchanger Shell-to-Flange Weld 1BRHRHX-5-9.
4.0 CONCLUSION
The Catawba Nuclear Station, Unit 1 requests for relief to the Code requirements have been reviewed by the NRC staff with the assistance of its contractor, PNNL. The TLR provides PNNL's evaluation of these requests for relief. The NRC staff has reviewed the TLR and adopts the evaluation and recommendation for granting the licensees request for relief.
The NRC staff concludes that the ASME Code,Section XI volumetric examination requirements are impractical for Pressurizer Safety Nozzle-to-Safe End Welds 1PZR-W4ASE, 1PZR-WBSE and 1PZR-WCSE and Valve 1ND002A to Pipe Weld 1ND38-1. The NRC staff further concludes that reasonable assurance of the structural integrity of the subject components has been provided based on the examinations that were performed. Therefore, the licensees request for relief is granted pursuant to 10 CFR 50.55a(g)(6)(i) for the second 10-year ISI interval. All other requirements of the ASME Code,Section XI for which relief has not been specifically requested remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
The NRC staff concludes that the ASME Code,Section XI volumetric requirement is a significant hardship without a compensating increase in quality and safety for RHR Heat Exchanger Shell-to-Flange Weld 1BRHRHX-5-9. Furthermore, the NRC staff concludes that reasonable assurance of the structural integrity of the subject component has been provided based on the examination that was performed. Therefore, the licensees request for relief is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the second 10-year ISI interval. All other requirements of the ASME Code,Section XI for which relief has not been specifically requested remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Attachments: Technical Letter Report Summary of Relief Requests Principal Contributors: T. McLellan, EMCB D. Naujock, EMCB Date: January 7, 2004
TECHNICAL LETTER REPORT ON THE SECOND 10-YEAR INTERVAL INSERVICE INSPECTION REQUEST FOR RELIEF NO.02-002 FOR DUKE POWER COMPANY CATAWBA NUCLEAR POWER STATION, UNIT 1 DOCKET NUMBER: 50-413
1.0 INTRODUCTION
By letter dated August 15, 2002, the licensee, Duke Power Company, submitted Request for Relief 02-002, seeking relief from requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components. In response to an NRC Request for Additional Information (RAI), the licensee revised the request (RR 02-002, Revision 1) and provided further clarification in a letter dated May 7, 2003. This request is for the second 10-year inservice inspection (ISI) interval which started June 29, 1995 and will end June 29, 2005, at the Catawba Nuclear Power Station, Unit 1 (Catawba 1).
2.0 REGULATORY REQUIREMENTS Inservice inspection of the 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 (B&PV 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 at 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the U.S. Nuclear Regulatory Commission (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.
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 (ISI) 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 10-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 Catawba 1 second 10-year interval inservice inspection program, which began on June 29, 1995, is the 1989 Edition of Section XI of the ASME Boiler and Pressure Vessel Code, with no addenda.
ATTACHMENT 1 3.0 EVALUATION The Pacific Northwest National Laboratory (PNNL) has evaluated the subject request for relief, including information provided by Duke Power Company in support of the request. PNNLs evaluation and discussion of the relief request is provided below. The licensee submitted Request for Relief 02-002 by combining several Code Examination Categories. However, examination requirements and the bases for the requested relief may vary for different Categories. Therefore, for clarity this evaluation is divided into parts that correspond to the respective sections of the licensees relief request.
Part A evaluates the portion of the request pertaining to Examination Category B-F, Item B5.40, Pressure Retaining Dissimilar Metal Welds in Vessel Nozzles - Pressurizer Safety
- Nozzles, Part B evaluates the portion of the request pertaining to Examination Category B-J, Item B9.11, Pressure Retaining Welds in Piping, and Part C evaluates the portion of the request pertaining to Examination Category C-A, Item C1.10, Pressure Retaining Welds in Vessels, Residual Heat Removal (RHR) Heat Exchanger Shell to Flange Weld.
3.1 Request for Relief 02-002, Revision 1 (Part A), Examination Category B-F, Item B5.40, Pressure Retaining Dissimilar Metal Welds in Vessel Nozzles - Pressurizer Safety Nozzles Code Requirement: Examination Category B-F, Item B5.40, requires 100% volumetric and surface examination, as defined by Figure IWB-2500-8, of Class 1 pressure retaining dissimilar metal welds in the pressurizer. This request applies to pressurizer safety nozzle-to-safe end welds 1PZR-W4ASE, 1PZR-W4BSE, and 1PZR-W4CSE.
Licensees Code Relief Request: In accordance with 10CFR50.55a(g)(5)(iii), the licensee requested relief from the Code requirement to examine the subject welds using 2 beam paths, and to complete 100% coverage of the examination volume shown in Figure IWB-2500-8.
Licensees Basis for Relief Request (as stated):
Nozzle to Safe End Weld 1PZR-W4ASE Nozzle to Safe End Weld 1PZR-W4ASE cannot be examined from two beam path directions because the nozzle taper limits scanning from the nozzle side. This is a dissimilar metal weld joining a carbon steel nozzle to a stainless steel safe end.
Coverage is limited to 77.28% of the required examination volume. This percentage of coverage represents the aggregate from all scans performed on the weld. Each scan is considered 25% of the total examination volume because four scans are required. One axial scan from the safe end side covered 100% of the examination volume in one direction; one axial scan from the nozzle side covered 9.12% of the examination volume; two circumferential scans covered 100% of the examination volume in two opposing directions. Thus, the required exam volume was fully scanned from three of the four required directions but the fourth scan from the nozzle side caused the limitation that resulted in less than 100% aggregate coverage from all scans. In order to achieve more coverage the nozzle would have to be re-designed to allow scanning from both sides of the weld.
Nozzle to Safe End Weld 1PZR-W4BSE Nozzle to Safe End Weld 1PZR-W4BSE cannot be examined from two beam path directions because the nozzle taper limits scanning from the nozzle safe end. This is a dissimilar metal weld joining a carbon steel nozzle to a stainless steel safe end. Coverage is limited to 86% of the required examination volume. This %age of coverage represents the aggregate from all scans performed on the weld. Each scan is considered 25% of the total examination volume because four scans are required. One axial scan from the safe end side covered 100% of the examination volume in one direction; one axial scan from the nozzle side covered 44.00% of the examination volume; two circumferential scans covered 100% of the examination volume in two opposing directions. Thus, the required exam volume was fully scanned from three of the four required directions but the fourth scan from the nozzle side caused the limitation that resulted in less than 100% aggregate coverage from all scans. In order to achieve more coverage, the nozzle would have to be re-designed to allow scanning from both sides of the weld.
Nozzle to Safe End Weld 1PZR-W4CSE Nozzle to Safe End Weld 1PZR-W4CSE cannot be examined from two beam path directions because the nozzle taper limits scanning from the nozzle safe end. This is a dissimilar metal weld joining a carbon steel nozzle to a stainless steel safe end. Coverage is limited to 82.03% of the required examination volume. This %age of coverage represents the aggregate from all scans performed on the weld. Each scan is considered 25% of the total examination volume because four scans are required. One axial scan from the safe end side covered 100% of the examination volume in one direction; one axial scan from the nozzle side covered 28.15% of the examination volume; two circumferential scans covered 100% of the examination volume in two opposing directions. Thus, the required exam volume was fully scanned from three of the four required directions but the fourth scan from the nozzle side caused the limitation that resulted in less than 100% aggregate coverage from all scans. In order to achieve more coverage, the nozzle would have to be re-designed to allow scanning from both sides of the weld.
Licensees Proposed Alternative Examination (as stated):
The scheduled 10-year code examination was performed on the area/weld and resulted in the noted limited coverage of the required ultrasonic volume. No alternate examinations are planned for the areas/welds during the current interval Evaluation: The Code requires 100% volumetric and surface examination of the subject pressure retaining Category B-F nozzle-to-pipe welds. The volumetric examinations must be performed using two beam path directions from both sides of the weld, when accessible. Scanning access for the subject welds is limited due to the design of the nozzle. The subject pressurizer safety valve nozzle material is SA-508 carbon steel and the safe-end is SA-182, Grade F316L. The welds are 6.0 inches in diameter with a 0.96 inch wall thickness. The valve nozzle is designed with a taper such that examination of the weld is severely restricted when scanning from the nozzle side of the subject welds.
For the licensee to achieve 100% volumetric coverage with two beam directions would require that the subject welds be completely redesigned and modified. This would place a significant burden on the licensee; therefore, the Code-required 100% volumetric examinations are impractical.
As indicated in the licensees submittal, coverages of 77, 82, and 86% of the required examination volumes were obtained for the three welds. The licensee was able to examine 100% of the Code-required examination volume from three of the four required scanning directions and partial coverage in the fourth direction. Also the licensee performed 100% of the Code-required surface examinations on these welds. No recordable indications were noted during the volumetric and surface examinations.
In response to recent industry experience of primary water stress corrosion cracking (PWSCC) in dissimilar metal welds containing Inconel, the licensee has stated that the inside diameter of these welds has been clad with a very low carbon 304 stainless steel cladding that is resistant to PWSCC. PWSCC phenomena has been limited thus far to Inconel-buttered welds. The cladding that would be in contact with primary water does not contain Inconel.
Based on the impracticality of performing full volumetric examinations, and considering the coverages obtained during volumetric and surface examination in conjunction with recent full volumetric examinations on other Category B-F welds, it is believed that any significant patterns of degradation would have been detected. Therefore, reasonable assurance of the continued structural integrity of these components has been provided.
Pursuant to 10CFR50.55a(g)(6)(i), it is recommended that relief be granted.
3.2 Request for Relief 02-002, Revision 1 (Part B), Examination Category B-J, Item B9.11, Pressure Retaining Welds in Piping Code Requirement: Examination Category B-J, Item B9.11 requires essentially 100 %
volumetric and surface examination of the weld length, as defined by Figure IWB-2500-8(c), of Class 1 full penetration piping welds. Essentially 100 %, as clarified by ASME Code Case N-460, is greater than 90% coverage of the examination volume, or surface area, as applicable. In Paragraph III-4420, the Code further states that examinations be performed using a sufficiently long beam path to provide coverage of the required examination volume in two-beam path directions, and that the examination be performed from two sides of the weld, where practicable, or from one side of the weld, as a minimum.
Licensees Code Relief Request: In accordance with 10CFR50.55a(g)(5)(iii), the licensee requested relief from the Code requirement to examine Weld 1ND38-1 using two beam paths, and to complete 100 % coverage of the examination volume shown in Figure IWB-2500-8(c).
1.
Sketches provided by the licensee are not included in this report.
Licensees Basis for Relief Request (as stated):
Valve 1ND002A to Pipe Weld 1ND38-1 cannot be examined from two beam directions because the valve body taper limits scanning from the valve side. This is a similar metal weld joining a stainless steel valve to a stainless steel pipe. Coverage is limited to 61.23% of the required examination volume. This percentage of coverage represents the aggregate from all scans performed on the weld. One axial scan from the pipe side covered 54.885 of the examination volume in one direction; no axial scan was performed from the valve side. Two circumferential scans covered 100 % of the examination volume in two opposing directions. Thus, the required exam volume was fully scanned from only the two circumferential directions. The partial scan from one axial direction and none from the other caused the limitation that resulted in less than 100 % aggregate coverage from all scans. In order to achieve more coverage the valve configuration would have to be re-designed to allow scanning from both sides weld.
Licensees Proposed Alternative Examination (as stated):
No additional examinations are planned during the current interval for Weld 1ND38-1.
The scheduled 10-year code examination was performed on the reference area / weld and resulted in the noted limited coverage of the required ultrasonic volume. No alternate examinations or testing is planned for the area/ weld during the current inspection interval.
Evaluation: The Code requires essentially 100 % volumetric coverage of Category B-J pressure retaining welds in piping using two beam path directions. The subject valve to pipe weld examination volume can not be examined to the extent required by Figure IWB-2500-8(c) of Section XI. The licensee has used the following ultrasonic methods to examine this weld:
45 degree shear wave from the pipe side 60 degree shear wave from the pipe side 60 degree longitudinal from the pipe side The licensee was not able to scan the weld from the valve side of the weld due to the valve body taper. The shear wave examinations from the pipe side are adequate to detect flaws on the same side (e.g. pipe side of the weld). The licensee then performed a supplemental 60 degree longitudinal wave examination in an attempt to examine the far side (valve side of the weld).
For the licensee to achieve essentially 100 % volumetric coverage of this weld from two beam directions would require that the valve body be completely removed and redesigned which would place a significant burden on the licensee. Therefore, the Code-required 100 % volumetric examination from two beam directions is impractical.
As shown on the sketches1 provided by the licensee, an aggregate coverage of approximately 61% of the required examination volume and 100 % of the Code-required surface examinations on these welds was obtained. Recent round-robin trials for ultrasonic examination of stainless steel on the far side of the weld (e.g. the examination sound beam must pass through the weld), show that many of these configurations may not be reliably inspected with current technology (reference NUREG/CR Report CR-4908 Ultrasonic Inspection Reliability for Intergranular Stress Corrosion Cracks and NUREG/CR Report CR-5068 Piping Inspection Round Robin). However, longitudinal wave techniques similar to that used by the licensee were shown in these trials to provide the best possible detection results for this examination configuration. Further, no known degradation mechanisms or industry failure experience has been experienced for these austenitic pipe-to-valve connections. While the licensee cannot meet the Code-required 100% volumetric examination requirement from two beam path directions, the licensee has performed volumetric examinations to the extent practical based upon component geometry. The volumetric examinations performed by the licensee should have detected any significant patterns of degradation that might have occurred, providing reasonable assurance of the continued structural integrity of Weld 1ND38-1. Therefore, pursuant to 10CFR50.55a(g)(6)(i), it is recommended that relief be granted.
3.3 Request for Relief 02-002, Revision 1 (Part C), Examination Category C-A, Item C1.10, Pressure Retaining Welds in Vessels, Residual Heat Removal (RHR) Heat Exchanger Shell-to-Flange Weld Code Requirement: Examination Category C-A, Item C1.10, requires essentially 100%
volumetric examination of the weld length, as defined in Figure IWC-2500-1, for Class 2 nozzle-to-vessel welds. Essentially 100%, as clarified by ASME Code Case N-460, is greater than 90% coverage of the examination volume, or surface area, as applicable.
Licensees Code Relief Request: In accordance with 10CFR 50.55a(g)(5)(iii), the licensee requested relief from the Code requirement to examine essentially 100% of the weld volume required by Figure IWC-2500-1 for Residual Heat Removal (RHR) Heat Exchanger Shell-to-Flange Weld 1BRHRHX-5-9.
Licensees Basis for Relief Request (as stated):
This weld was radiographed to provide more exam volume coverage than was possible with ultrasonic examination. During the radiograph examination of Residual Heat Removal Heat Exchanger Shell to Flange Weld 1BRHRHX-5-9, 100% coverage of the required examination volume could not be obtained. The examination coverage was limited to 55.90%. Limitations were caused by the heat exchangers shell-to-flange configuration. In order to achieve more coverage, the heat exchanger would have to be disassembled at the flange connection and the upper and lower sections of the vessel separated allowing access for the placement of the radiographic film on the inside surface of the weld, which is impractical. Ultrasonic examination of this weld and adjacent base metal would also require the disassembly of the flange connection; which is impractical.
2.
Drawings and descriptions provided by the licensee are not included in this report.
Licensees Proposed Alternative Examination (as stated):
The scheduled 10-year code examination was performed on the reference area / weld and resulted in the noted limited coverage of the required ultrasonic volume. No alternate examinations or testing is planned for the area/ weld during the current inspection interval.
Evaluation: The Code requires essentially 100% volumetric examination of the length of the subject Code Class 2 vessel welds. However, as described in the licensee's basis, complete examinations are restricted by several factors, including the heat exchangers shell-to-flange configuration, the close proximity of the studs and nuts to the vessel outside surface, and internal vessel support plates. The licensee would have to disassemble the residual heat exchanger vessel at the flange connection and separate the upper and lower halves of the shell to achieve greater examination coverage and would result in a significant radiation dose to plant personnel. Therefore, imposition of this requirement would result in a significant hardship or unusual difficulty without a compensating increase in quality and safety.
Drawings and descriptions included in the licensees submittal2 clearly show that examination of the subject RHR vessel flange weld has been performed to the extent practical, with the licensee obtaining substantial volumetric (56%) coverage for most of this weld.
As described in the licensees submittal, ultrasonic examination of this weld would require that the flange assembly be disassembled. Limited radiographic (RT) examination of the RHR heat exchanger shell-to-flange weld was performed. Complete radiographic examination of the weld was not possible due to internal vessel divider plates, the external geometric configuration and limited access to the examination external surface due to the flange bolting configuration. Each of these specific examination interferences limited the radiographic examination of the required volume as discussed in the following paragraphs.
Internal Vessel Divider Plates The vessels internal divider plates are designed in a T configuration. The internal divider plates come in contact with the examination area in three separate locations, which completely obstruct examination coverage of the weld and the required 0.5 inch of base metal on each side of the weld. At three locations the internal divider plate obstructs a total of approximately 10 linear inches of the circumferential examination area due to the divider plate thickness and the angle through which the radiation from the source had to penetrate the divider plate to image the examination area on the opposite side.
External Shell to Flange Configuration and Flange Bolting The flange weld is in close proximity to the flange bolting surface. The close proximity of the studs and nuts to the outside surface of the vessel in conjunction with the nearness of the flange face restricted the placement of the RT film for complete examination coverage. During the examination, the radiographic film holders and backing leads were placed behind the bolting material, on the outside surface of the vessel and then slid onto the flange taper to the fullest extent possible. This provided for examination coverage of the required 0.5 inch base metal on the shell side of the weld and 0.625 inches of the total 0.875 inch wide weld. The required 0.5 inch of base metal on the flange side, and an average of 0.25 inch of the weld were not recorded on the film.
In addition to the limited radiographic examination of this weld, other Class 2 vessel shell welds were examined to the extent required by the Code and there has been no recorded degradation of these components. The limited radiographic examination on this weld in conjunction with examinations of other Class 2 vessel shell welds should detect any significant patterns of degradation that may occur, providing reasonable assurance of continued structural integrity of these vessels. Requiring the licensee to disassemble the RHR vessel to achieve the required Code coverage would place a significant hardship or unusual difficultly on the licensee without a compensating increase in quality or safety. Therefore, based on the examination coverages obtained and the examinations of other Class 2 vessels, it is recommended that the alternative be authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the second 10-year inservice inspection interval.
4.0 CONCLUSION
S The PNNL staff has reviewed the licensees submittal and concludes that the Code examination coverage requirements are impractical for the pressurizer safety nozzle-to-safe-end and Class 1 piping welds listed in Request for Relief No.02-002, Revision 1 (Parts A and B of this report, respectively). Further, reasonable assurance of the structural integrity of the subject components has been provided by the examinations that were performed. Therefore, pursuant to 10 CFR 50.55a(g)(6)(i), it is recommended that these portions of the relief request be granted for the second 10-year interval at Catawba 1, which is scheduled to end on June 29, 2005.
For RHR heat exchanger Weld 1BRHRHX-5-9, it has been determined that in order to comply with the specified Code volumetric examination requirements, the RHR heat exchanger would have to be disassembled, placing a significant hardship or unusual difficultly on the licensee with no compensating increase in quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3(ii), it is recommended that Request for Relief 02-002, Revision 1, (Part C of this report), be authorized for the remainder of the Catawba 1 second 10-year inspection interval.
CATAWBA NUCLEAR POWER STATION, UNIT 1 Page 1 of 1 Second 10-Year ISI Interval TABLE 1
SUMMARY
OF RELIEF REQUESTS Relief Request Number PNNL TLR Sec.
System or Component Exam.
Category Item No.
Volume or Area to be Examined Required Method Licensee Proposed Alternative Relief Request Disposition 02-002, Revision 1 Part A 3.1 Pressurizer Nozzle-to-pipe Welds B-F B5.40 100% volumetric and surface examination of Class 1 pressure retaining dissimilar metal welds in the pressurizer; Welds 1PZR-W4ASE, 1PZR-W4BSE, and 1PZR-W4CSE Volumetric and Surface Use achieved 77%
and 86% volumetric coverage(s)
Granted 10 CFR 50.55a(g)(6)(i) 02-002, Revision 1 Part B 3.2 Piping Welds B-J B9.11 100% volumetric and surface examination of Class 1 pressure retaining welds in piping; Weld IND38-1 Volumetric and Surface Use achieved 61%
volumetric coverage Granted 10 CFR 50.55a(g)(6)(i) 02-002, Revision 1 Part C 3.3 RHR Heat Exchanger Shell Weld C-A C1.10 100% of the Pressure Retaining Welds in Class 2 Vessels; Weld 1BRHRHX-5-9 Volumetric Use achieved 56%
volumetric coverage Authorized 10 CFR 50.55a(a)(3)(ii)
ATTACHMENT 2