ML032410087
| ML032410087 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 09/24/2003 |
| From: | Raghavan L NRC/NRR/DLPM/LPD3 |
| To: | Cayia A Nuclear Management Co |
| References | |
| FOIA/PA-2004-0282, TAC MC6184, TAC MC8438 | |
| Download: ML032410087 (15) | |
Text
September 24, 2003 Mr. Alfred J. Cayia Site Vice President Point Beach Nuclear Plant Nuclear Management Company, LLC 6610 Nuclear Road Two Rivers, WI 54241
SUBJECT:
POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 - EVALUATION OF RELIEF REQUEST MR 02-018-1 PERTAINING TO REACTOR VESSEL CLOSURE HEAD PENETRATION REPAIR (TAC NOS. MB6184 AND MB8438)
Dear Mr. Cayia:
By letter dated August 28, 2002, as supplemented by letters dated April 10 and July 31, 2003, the Nuclear Management Company, LLC (the licensee), submitted Relief Requests MR 02-018-1 and MR 02-018-2 for the Point Beach Nuclear Plant, Units 1 and 2, pertaining to reactor vessel closure head (RVCH) penetration repairs that may become necessary in the event that flaws requiring repair in the RVCH penetrations are discovered during upcoming inspections. The repair plan would reduce radiation exposures for control rod drive mechanisms (CRDM) penetration repair by instituting remote machine processes and ambient temperature temper bead welding (i.e., the repair weld would be performed with a machine Gas Tungsten Arc Welding (GTAW) weld head using the temper bead process using 50EF minimum preheat temperature). The Nuclear Regulation Commission (NRC) staff has previously addressed Relief Request MR 02-018-2 by separate correspondence dated September 10, 2003 (ADAMS Accession No. ML032310402).
In Relief Request MR 02-018-1, the licensee requests approval to utilize an alternative method to the temper bead welding requirements of the 1989 Edition of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section III, NB-4453, NB-4622, NB-5245, and NB-5330 for Reactor Pressure Vessel (RPV) Head-to-CRDM welds.
The requirements of paragraph QW-256 of ASME Code Section IX, and IWA-4000 of the 1998 Edition, 2000 Addenda of Section XI, are also applicable to the proposed repairs. As an alternative to these requirements, the licensee proposes to use requirements specified in to Attachment 1 of the licensees letter dated August 28, 2002, "Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique." The alternative would be used to make welds of P-No. 3, RVCH material to P-No. 43 CRDM nozzle material using F-No. 43 filler material.
The NRC staff has reviewed Relief Request MR 02-018-1. In the enclosed safety evaluation, the NRC staff concludes that the licensees proposed alternative to use GTAW ambient temperature temper bead welding for RPV head penetration nozzle J-groove weld repairs, during upcoming inspections, that do not include portions of remnant J-groove welds, as stated in Relief Request MR 02-018-1, provides an acceptable level of quality and safety. The NRC staffs authorization of this request does not remove or diminish the licensees responsibility to
A. Cayia assure that sound, defect free repair welds are placed into service. Therefore, pursuant to Section 10 CFR 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations, the NRC staff authorizes the proposed alternative to the GTAW-machine temper bead welding requirements of IWA-4500 and IWA-4530 of ASME Code Section XI at the Point Beach Nuclear Plant, Units 1 and 2.
The NRC staff also concludes in the enclosed safety evaluation that compliance with the ASME Code-required volumetric (radiographic testing) and progressive surface (liquid dye penetrant or magnetic particle testing) examinations of the repair weld would result in hardship without a compensating increase in the level of quality and safety, and that the licensees proposed alternative to perform a final surface examination (liquid penetrant inspection) and volumetric examination (ultrasonic inspection) provides reasonable assurance of structural integrity.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the proposed alternative is authorized for Point Beach Nuclear Plant, Units 1 and 2, for the fourth 10-year ISI interval.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and approved by the NRC staff remain applicable, including the third party review by the Authorized Nuclear Inservice Inspector.
Sincerely,
/RA/
L. Raghavan, Chief, Section 1 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-266 and 50-301
Enclosure:
Safety Evaluation cc w/encl: See next page
ML032410087 *Provided SE input by memo OFFICE PDIII-1/PM PDIII-1/LA EMCB/SC* OGC PDIII-1/SC NAME DSpaulding MMcAllister for SCoffin RHoefling LRaghavan RBouling DATE 09/17/03 09/16/03 08/27/03 09/24/03 09/24/03 Point Beach Nuclear Plant, Units 1 and 2 cc:
Jonathan Rogoff, Esquire Ms. Sarah Jenkins General Counsel Electric Division Nuclear Management Company, LLC Public Service Commission of Wisconsin 700 First Street P.O. Box 7854 Hudson, WI 54016 Madison, WI 53707-7854 Mr. Richard R. Grigg Nuclear Asset Manager President and Chief Operating Officer Wisconsin Electric Power Company Wisconsin Electric Power Company 231 West Michigan Street 231 West Michigan Street Milwaukee, WI 53201 Milwaukee, WI 53201 Mano K. Nazar Manager, Regulatory Affairs Senior Vice President Point Beach Nuclear Plant Nuclear Management Company, LLC Nuclear Management Company, LLC Prairie Island Nuclear Generating Plant 6610 Nuclear Road 1717 Wakonade Drive East Two Rivers, WI 54241 Welch, MN 55089 Mr. Ken Duveneck John Paul Cowan Town Chairman Executive Vice President & Chief Nuclear Town of Two Creeks Officer 13017 State Highway 42 Nuclear Management Company, LLC Mishicot, WI 54228 700 First Street Hudson, WI 54016 Chairman Public Service Commission of Wisconsin P.O. Box 7854 Madison, WI 53707-7854 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532-4351 Resident Inspectors Office U.S. Nuclear Regulatory Commission 6612 Nuclear Road Two Rivers, WI 54241 August 2003
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST MR 02-018-1 PERTAINING TO REACTOR VESSEL CLOSURE HEAD PENETRATION REPAIR NUCLEAR MANAGEMENT COMPANY, LLC POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-266 AND 50-301
1.0 INTRODUCTION
By letter dated August 28, 2002, as supplemented by letters dated April 10 and July 31, 2003, the Nuclear Management Company, LLC (the licensee), submitted Relief Requests MR 02-018-1 and MR 02-018-2 for the Point Beach Nuclear Plant, Units 1 and 2, pertaining to reactor vessel closure head (RVCH) penetration repairs that may become necessary in the event that flaws requiring repair in the reactor vessel closure head penetrations are discovered in upcoming inspections. The repair plan would reduce radiation exposures for control rod drive mechanisms (CRDM) penetration repair by instituting remote machine processes and ambient temperature temper bead welding [i.e., the repair weld would be performed with a machine gas tungsten arc welding (GTAW) weld head using the temper bead process using 50EF minimum preheat temperature].
In this safety evaluation, the Nuclear Regulation Commission (NRC) staff only addresses Relief Request MR 02-018-1.1 In Relief Request MR 02-018-1, the licensee requests approval to utilize an alternative method to the temper bead welding requirements of the 1989 Edition of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)
Section III, NB-4453, NB-4622, NB-5245, and NB-5330 for Reactor Pressure Vessel (RPV)
Head-to-CRDM welds. The requirements of paragraph QW-256 of ASME Code Section IX, and IWA-4000 of the 1998 Edition, 2000 Addenda of Section XI, are also applicable to the proposed repairs. As an alternative to these requirements, the licensee proposes to use requirements specified in Enclosure 1 to Attachment 1 of the licensees letter dated August 28, 2002, "Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique." The alternative would be used to make welds of P-No. 3, RVCH material to P-No.
P-No. 43 CRDM nozzle material using F-No. 43 filler material.
1 The NRC staff has previously addressed Relief Request MR 02-018-2 by separate correspondence dated September 10, 2003 (ADAMS Accession No. ML032310402). In Relief Request MR 02-018-2, the licensee requested relief from the requirement to characterize flaws that may exist in the remnants of the CRDM nozzle J-groove welds after the repair.
In its original letter dated August 28, 2002, the licensee requested relief only with respect to Point Beach Nuclear Plant, Unit 1. By supplemental letter dated April 10, 2003, the licensee expanded applicability of the relief request to include Unit 2, and provided supporting information for both units. By supplemental letter dated July 31, 2003, the licensee provided responses to the NRC staffs request for additional information pertaining to the April 10, 2003, supplemental submittal.
2.0 BACKGROUND
The inservice inspection (ISI) of the ASME Code Class 1, Class 2, and Class 3 components is to be performed in accordance with the ASME Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, and applicable edition and addenda as required by Section 10 CFR 50.55a(g) of Title 10 of the Code of Federal Regulations, 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 in part 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.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) will 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 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 code of record for the Point Beach Nuclear Plant, Units 1 and 2, fourth 10-year ISI interval is the 1998 edition of the ASME Code with addenda through 2000.
3.0 EVALUATION OF RELIEF REQUEST 3.1 ASME Code Requirements for Which Relief is Requested In its application for relief, by letter dated August 28, 2002, the licensee states:
ASME Section XI, paragraph IWA-4221, stipulates the following:
(a) "An item to be used for repair/replacement activities shall meet the applicable Owner's Requirements..."
(b) "An item to be used for repair/replacement activities shall meet the Construction Code specified..."
(c) "As an alternative to (b) above, the item may meet all or portions of the requirements of different Editions and Addenda of the Construction Code ... All or portions of later different Construction Codes may be used..."
The Construction Code for the Point Beach Unit[s] 1 [and 2] RVCH is ASME Section III, 1965 Edition. ... For the proposed repairs to the RVCH penetrations, paragraph N-528.2 of the 1965 Edition of Section III requires repairs be [subjected to] postweld heat treated [treatment] (PWHT) in accordance with paragraph N-532. The PWHT requirements set forth therein are not possible or practical to attain on a RVCH in containment without distortion of the head.
The proposed repairs will be conducted in accordance with the 1998 Edition of ASME Section XI, 2000 Addenda (as applicable), the 1989 Edition of Section III, no Addenda, and alternative requirements discussed below....
NMC [Nuclear Management Company] requests relief to use an ambient temperature temper bead method of repair as an alternative to the requirements of the 1989 Edition of ASME Section III, NB-4453, NB-4622, NB-5245, and NB-5330. The requirements of paragraph QW-256 of ASME Section IX, and IWA-4000 of the 1998 Edition, 2000 Addenda of Section XI, are also applicable to the proposed repairs.... As an alternative to these requirements, the requirements of, "Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique," (Enclosure 1 [to Attachment 1 of the licensees submittal]) will be used.
3.2 Licensees Proposed Alternative to Code and NRC Staff Evaluation Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee requests alternative repair techniques for Point Beach Nuclear Plant, Units 1 and 2, in the event that any flaws requiring repair in RVCH Penetrations are discovered during inspection. The licensee specifically states:
Nuclear Management Company (NMC) requests relief to use an ambient temperature temper bead method of repair as an alternative to the requirements of the 1989 Edition of ASME Section III, NB-4453, NB-4622, NB-5245, and NB-5330. The requirements of paragraph QW-256 of ASME Section IX, and IWA-4000 of the 1998 Edition, 2000 Addenda of Section XI, are also applicable to the proposed repairs.... As an alternative to these requirements, the requirements of, "Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique," (Enclosure 1 [to Attachment 1 of the licensees submittal]) will be used....
Repairs to RVCH penetration J-groove attachment welds, which are required when 1/8-inch or less of nonferritic weld deposit exists above the original fusion line, will be made in accordance with the requirements of IWA-4000 of the 1998 Edition, 2000 Addenda of ASME Section XI. The requirements of paragraphs NB-4622 and NB-5245, of the 1989 Edition of ASME Section III are also applicable to the contemplated repairs. Applicable alternatives to these requirements per the requirements of, "Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique," (Enclosure 1 [to Attachment 1 of the submittal]) will be used.
Specifically, alternatives are being proposed ... for articles, subarticles, paragraphs, and subparagraphs of ASME Section III, Section IX, and Section XI.
3.3 NRC Staff Evaluation The 1989 Edition of ASME Code Section III, paragraph NB-4622.11, Temper Bead Weld Repair to Dissimilar Metal Welds or Buttering states that whenever PWHT is impractical or impossible, limited weld repairs to dissimilar metal welds of P-No. 1 and P-No. 3 material or weld filler metal A-No. 8 (Section IX, QW-442) or F-No. 43 (Section IX, QW-432) may be made without PWHT or after the final PWHT provided the requirements of paragraphs NB-4622.11(a) through (g) are met.
The licensee has requested relief to use an ambient temperature temper bead method of repair as an alternative to the requirements of the 1989 Edition of ASME Code Section III, NB-4453, NB-4622, NB-5245, and NB-5330. The requirements of paragraph QW-256 of ASME Section IX, and IWA-4000 of the 1998 Edition, 2000 Addenda of Section XI, are also applicable to the proposed repairs. Portions of ASME Code Case N-638 as described herein have also been used as a template for this application. As an alternative to these requirements, the requirements of, "Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique," (Enclosure 1 to Attachment 1of the licensees submittal) are proposed.
The use of a GTAW temper bead welding technique to avoid the need for postweld heat treatment is based on research that has been performed by EPRI and other organizations. The research demonstrates that carefully controlled heat input and bead placement allow subsequent welding passes to relieve stress and temper the HAZ of the base material and preceding weld passes. Data presented in EPRI Report GC-111050 show the results of procedure qualifications performed with 300oF preheats and 500oF preheats, as well as with no preheat and postheat. From that data, it can be shown that adequate toughness can be achieved in base metal and HAZ with the use of a GTAW temper bead welding technique. The temper bead process has been shown effective by research, successful procedure qualifications, and many successful repairs performed since the technique was developed.
Many acceptable Procedure Qualification Records and Welding Procedure Specifications presently exist and have been utilized to perform numerous successful repairs. The use of the automatic or machine GTAW process utilized for temper bead welding allows more precise control of heat input, bead placement, and bead size and contour than the manual SMAW process required by subarticle NB-4622. The very precise control over these factors afforded by the alternative provides more effective tempering and eliminates the need to grind or machine the first layer of the repair.
IWB-3142.4 states that a component containing relevant conditions is acceptable for continued service if an analytical evaluation demonstrates the components acceptability. The licensees basis does not include an analytical evaluation for repair welds that, due to the radius of curvature of the RVCH, come into contact with remnant J-groove welds that are considered flawed. Therefore, this granting of relief applies only to repairs that do not include portions of the remnant J-groove weld.
The NRC staff approves the licensees proposed alternative, to utilize a temper bead weld procedure which obviates the need for PWHT, for repairs that do not include portions of the remnant J-groove weld.
The NRC staff has evaluated and approved, as discussed below, the following specific alternatives for subparagraphs of ASME Section III, subarticle NB-4622:
NB-4622.1 through NB-4622.8 all pertain to postweld heat treatment of welds including repair welds. In lieu of the requirements of these subparagraphs the licensee proposes to utilize a temper bead weld procedure, obviating the need for post weld stress relief.
NB-4622.9 establishes requirements for temper bead repairs to P-No. 1 and P-No. 3 materials and A-Nos. 1, 2, 10, or 11 filler metals. The subparagraph does not apply in this case because the proposed repairs will involve F-No. 43 filler metals.
NB-4622.10 establishes requirements for repair welding to cladding after PWHT. The subparagraph does not apply in this case because the proposed repair alternative does not involve repairs to cladding.
NB-4622.11 discusses temper bead weld repair to dissimilar metal welds or buttering and would apply to the proposed repairs as follows:
NB-4622.11(a) requires surface examination prior to repair in accordance with Article NB-5000. The proposed alternative will include surface examination prior to repair consistent with Article NB-5000.
NB-4622.11(b) contains requirements for the maximum extent of repair. The proposed alternative includes the same limitations on the maximum extent of repair.
NB-4622.11(c) discusses the repair welding procedure and welder qualification in accordance with ASME Section IX and the additional requirements of Article NB-4000.
The proposed alternative will satisfy these requirements... In addition, NB-4622.11(c) requires the welding procedure specification include the following requirements of NB-4622.11(c)(1) through NB-4622.11(c)(8), and NB-4622.11(d)(1) through NB-4622.11(d)(3), NB-4622.11(e) through NB-4622.11(g), NB-4453.4, NB-5330(b), and QW-256.
NB-4622.11(c)(1) requires the area to be welded be suitably prepared for welding in accordance with the written procedure to be used for the repair. The proposed alternative will satisfy this requirement.
NB-4622.11(c)(2) requires the use of the shielded metal arc welding (SMAW) process with covered electrodes meeting either the A-No. 8 or F-No. 43 classifications. The proposed alternative [utilizes] gas tungsten arc welding (GTAW) with bare electrodes meeting the F-No. 43 classifications.
NB-4622.11(c)(3) discusses requirements for covered electrodes pertaining to hermetically sealed containers or storage in heated ovens. These requirements do not apply because the proposed alternative uses bare electrodes that do not require storage in heated ovens since bare electrodes will not pick up moisture from the atmosphere.
NB-4622.11(c)(4) discusses requirements for storage of covered electrodes during repair welding. These requirements do not apply because the proposed alternative utilizes bare electrodes which do not require any special storage conditions to prevent the pickup of moisture from the atmosphere.
NB-4622.11(c)(5) requires preheat of the weld area and 11/2T or 5 inch band, whichever is less, to a minimum temperature of 350EF prior to repair welding and a maximum interpass temperature of 450EF. Thermocouples and recording instruments shall be used to monitor the metal temperature during welding. The proposed ambient temperature temper bead alternative does not require an elevated temperature preheat and interpass temperature. The use of a GTAW ambient temperature temper bead welding technique to avoid the need for preheat and postweld heat treatment is based on research that has been performed by EPRI [Electric Power Research Institute (EPRI Report GC-111050, "Ambient Temperature Preheat for Machine GTAW Temper Bead Applications," dated November 1998). The research demonstrates that carefully controlled heat input and bead placement allow subsequent welding passes to relieve stress and temper the HAZ [heat affected zone] of the base material and preceding weld passes. Data presented in the report show the results of procedure qualifications performed with 300EF preheats and 500EF post-heats, as well as with no preheat and post-heat. From that data, it is clear that equivalent toughness is achieved in base metal and HAZ in both cases. The ambient temperature temper bead process has been shown effective by research, successful procedure qualifications, and many successful repairs performed since the technique was developed. The RVCH preheat temperature will be essentially the same as the reactor building ambient temperature; therefore, RVCH preheat temperature monitoring in the weld region and using thermocouples is unnecessary and would result in additional personnel dose associated with thermocouple placement and removal. The maximum interpass temperature will be determined by calculation. The calculation is based on a typical inter-bead time interval of five minutes. The five minute inter-bead interval is based on: 1) the time required to explore the previous weld deposit with the two remote cameras housed in the weld head, 2) time to shift the starting location of the next weld bead circumferentially away from the end of the previous weld- bead, and 3) time to shift the starting location of the next bead axially to insure a 50% weld bead overlap required to properly execute the temper bead technique.
NB-4622.11(c)(6) establishes requirements for electrode diameters for the first, second, and subsequent layers of the repair weld and requires removal of the weld bead crown before deposition of the second layer. Because the proposed alternative uses weld filler metal much smaller than the 3/32, 1/8, and 5/32 inch electrodes required by sub-subparagraph NB-4622.11(c)(6), the requirement to remove the weld crown of the first layer is unnecessary and the proposed alternative does not include the requirement. On ferritic materials made with the SMAW process, the weld reinforcement crown is removed to allow heat from the second weld layer to penetrate to the untempered ferritic base metal below it. However, when repairs are performed to dissimilar materials using nonferritic weld metal and using a low heat input machine GTAW process, the heat from welding is much more controlled and heat from the second weld layer penetrates to the untempered ferritic base metal below it and tempers it. Therefore deletion of this requirement is acceptable.
NB-4622.11(c)(7) requires the preheated area to be heated from 450EF to 660EF for 4 hours0.167 days <br />0.0238 weeks <br />0.00548 months <br /> after a minimum of 3/16 inch of weld metal has been deposited. This postweld bake-out is performed to remove hydrogen that may have been introduced by the welding process. The proposed alternative does not require this heat treatment because the use of the low hydrogen GTAW temper bead procedure does not require the hydrogen bake-out. The proposed alternative temper bead procedure utilizes a welding process that is inherently free of hydrogen. The GTAW process relies on bare welding electrodes with no flux to trap moisture. An inert gas blanket positively shields the weld and surrounding material from the atmosphere and moisture it may contain. To further reduce the likelihood of any hydrogen evolution or absorption, the alternative procedure requires particular care to ensure the weld region is free of all sources of hydrogen. The GTAW process will be shielded with welding grade argon which typically produces porosity free welds. The F-No. 43 (ERNiCrFe-7) filler metal that would be used for the repairs is not subject to hydrogen embrittlement cracking.
NB-4622.11(c)(8) requires welding subsequent to the hydrogen bake-out of NB-4622.11(c)(7) be done with a minimum preheat of 100EF and maximum interpass temperature of 350EF. The proposed alternative limits the interpass temperature to 350EF (maximum) and requires the area to be welded be at least 50EF prior to welding.
These limitations have been demonstrated to be adequate to produce sound welds.
NB-4622.11(d)(1) requires a liquid penetrant examination after the hydrogen bake out described in NB-4622.11(c)(7). The proposed alternative does not require the hydrogen bake out because it is unnecessary for the very low hydrogen GTAW temper bead process.
NB-4622.11(d)(2) requires liquid penetrant and radiographic examinations of the repair welds and the preheated band after a minimum time of 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> at ambient temperature. Ultrasonic inspection is required if practical. The proposed alternative includes the requirement to inspect after a minimum of 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> at ambient temperature. Because the proposed repair welds are of a configuration that cannot be radiographed (due to limitations on access for source and film placement and the likelihood of unacceptable geometric unsharpness and film density), final inspection will be by liquid penetrant and ultrasonic examination. Also due to the repair configuration and accessibility, the weld and immediate surrounding area only will be liquid penetrant and ultrasonically examined.
NB-4622.11(d)(3 ) requires that all nondestructive examination be in accordance with NB-5000. The proposed alternative will comply with NB-5000 except that the progressive liquid penetrant examination required by NB-5245 will not be done. In lieu of the progressive liquid penetrant examination, the proposed alternative will use liquid penetrant and ultrasonic examination of the final weld.
NB-4622.11(e) establishes the requirements for documentation of the weld repairs in accordance with NB-4130. The proposed alternative will comply with this requirement.
The NRC staff concludes that this is appropriate and therefore acceptable.
NB-4622.11(f) establishes requirements for the procedure qualification test plate. The proposed alternative complies with those requirements.
NB-4622.11(g) establishes requirements for welder performance qualification relating to physical obstructions that might impair the welders ability to make sound repairs, which is pertinent to the SMAW manual welding process. The proposed alternative involves a machine GTAW process and requires welding operators be qualified in accordance with ASME Section IX. The use of a machine process eliminates any concern about obstructions, which might interfere with the welders abilities because all such obstructions will have to be eliminated to accommodate the welding machine.
Subparagraph NB-4453.4 of Section III requires examination of the repair weld in accordance with the requirements for the original weld. The welds being made in accordance with the proposed alternatives will be partial penetration welds as described by NB-4244(d) and will meet the weld design requirements of NB-3352.4(d). For these partial penetration welds, paragraph NB-5245 requires a progressive surface exam (PT, periodic test, or MT, materials test) at the lesser of 1/2 the maximum weld thickness or 1/2-inch, as well as on the finished weld. For the proposed alternative, the repair weld will be examined by a liquid penetrant and ultrasonic examination no sooner than 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after the weld has cooled to ambient temperature in lieu of the progressive surface exams required by NB-5245. The ultrasonic examination is a volumetric examination that has the capability to detect subsurface defects that may have been deposited by the welding process. The PT is a surface examination that not only has the capability of detecting both deposited weld defects such as incomplete fusion and slag but can also detect delayed cracking in the deposited weld since it is being performed no sooner than 48 hours2 days <br />0.286 weeks <br />0.0658 months <br /> after the welds are deposited. The NRC staff concludes that the volumetric examination coupled with a surface examination will provide a high level of confidence that the proposed welds are sound and defect free, therefore, deletion of the progressive PT is acceptable.
NB-5330(b) does not allow any cracks or incomplete penetration regardless of length.
Framtome's experience is that a weld anomaly often occurs at the intersection of the RVCH, the nozzle, and the first intersecting weld bead (triple point). The staffs review of published data indicates that this weld anomaly may in fact be incomplete penetration or cracking. The proposed alternative basis for use provides as a part of the basis for acceptable level of quality and safety, a fracture mechanics evaluation. By supplemental letter dated April 10, 2003, the licensee submitted calculation packages that supported its bases for Point Beach Nuclear Plant, Units 1 and 2. The NRC staff reviewed calculation package 32-5019398-00, PB-1 CRDM Nozzle IDTB Weld Anomaly Flaw Evaluations. The purpose of the analysis is to perform a fracture mechanics evaluation of a postulated weld anomaly in the Point Beach Nuclear Plant, Units 1 and 2, CRDM nozzle IDTB weld repair. The postulated weld anomaly is a 0.100 inch semi-circular flaw extending 360 degrees around the circumference at the triple point location where the Alloy 600 nozzle, Alloy 52/152, and low alloy steel RVCH materials converge.
The calculations showed that the maximum final flaw size would be 0.101 inches after 25 years of operation. The minimum fracture toughness margin was 9.57 which was three times greater than the required margin of 3.16. The margin on limit load was calculated to be 8.47 which was 2.5 times greater than the required margin of 3.0.
Whereas ASME Section XI allows for service related flaws to be evaluated for continued service, ASME Section III does not allow certain welding related defects to remain prior to placing the component back into service. The calculations submitted by the licensee
were submitted to the NRC staff to demonstrate that an acceptable level of quality and safety exists if a postulated 0.100 inch flaw were to exist as a result of the IDTB repair welding process. The licensee has a continuing responsibility to assure that sound repair welds are deposited, that the component is fit to return to service after repair, and that ASME Code requirements are met unless specific relief has been approved by the NRC staff. The NRC staff concludes that the calculations performed by the licensee demonstrate that sufficient margins exist to assure the deposited repair weld will remain structurally sound. The NRC staff does not grant relief from the acceptance criteria of NB-5330(b).
Paragraph QW-256 of ASME Code Section IX requires that the maximum interpass temperature during procedure qualification be no more than 100EF below that used for actual welding. The welding procedure specifies a maximum interpass temperature. of 350EF. The welding procedure was qualified with an interpass temperature less than 100EF. The procedure qualification requirements recommended in Code Case N-638 imposes a 150EF maximum interpass temperature during the welding of the procedure qualification. This requirement restricts base metal heating during qualification that could produce slower cooling rates that are not achievable during field applications.
However, this requirement does not apply to field applications as a 350EF maximum interpass temperature is a requirement in Section 3.0 of ASME Code Case N-638. The higher interpass temperature is permitted since it is a requirement of the ASME Code Case. Also, this temperature will not be achieved since test data presented in the request showed that thermocouples attached to a mock-up varied from the preheat by less than 15EF, so with a 50EF preheat, even the 150EF will not be achieved-- much less a 350EF maximum interpass temperature.
4.0 CONCLUSION
The NRC staff concludes that the licensees proposed alternative to use GTAW ambient temperature temper bead welding for RPV head penetration nozzle J-groove weld repairs, during upcoming inspections, that do not include portions of remnant J-groove welds, as stated in Relief Request MR 02-018-1, provides an acceptable level of quality and safety. This authorization does not remove or diminish the responsibility of the licensee to assure that sound, defect free repair welds are placed into service. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the proposed alternative to the GTAW-machine temper bead welding requirements of IWA-4500 and IWA-4530 of ASME Code Section XI at the Point Beach Nuclear Plant, Units 1 and 2.
The NRC staff also concludes that compliance with the Code-required volumetric and progressive surface (PT or MT) examinations of the repair weld would result in hardship without a compensating increase in the level of quality and safety, and that the licensee's proposed alternative to perform a final surface examination (liquid penetrant inspection) and volumetric examination (ultrasonic inspection) provides reasonable assurance of structural integrity.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), the NRC staff authorizes the proposed alternative for Point Beach Nuclear Plant, Units 1 and 2, for the fourth 10-year ISI interval.
All other requirements of the ASME Code, Sections III, IX, and XI, for which relief has not been specifically requested and approved herein by the NRC staff remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: E. Andruszkiewicz T. Steingass Date: September 24, 2003