ML073100991

Relief Requests 07-001-RR and 07-002-RR Regarding Weld Repairs

ML073100991
Person / Time
Site:	Crystal River
Issue date:	11/15/2007
From:	Boyce T NRC/NRR/ADRO/DORL/LPLII-2
To:	Young D Florida Power Corp
Bailey S , NRR/ADRO/DORL, 415-1321
References
TAC MD5498, TAC MD5499
Download: ML073100991 (20)

Text

November 15, 2007 Mr. Dale E. Young, Vice President Crystal River Nuclear Plant (NA1B)

ATTN: Supervisor, Licensing & Regulatory Programs 15760 W. Power Line Street Crystal River, Florida 34428-6708

SUBJECT:

CRYSTAL RIVER UNIT 3 - RELIEF REQUESTS #07-001-RR AND #07-002-RR REGARDING WELD REPAIRS (TAC NOS. MD5498 AND MD5499)

Dear Mr. Young:

By letter dated April 12, 2007, as supplemented by letters dated September 13 and October 23, 2007, the Florida Power Corporation (the licensee) requested Nuclear Regulatory Commission (NRC) staff review and approval of Relief Requests (RRs) #07-001-RR and #07-002-RR to allow weld repairs during the upcoming refueling outage at Crystal River Unit 3 (CR-3). The proposed RRs provide alternatives to the requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI.

The NRC staff has reviewed the licensees submittal and determined that #07-001-RR and

1. 07-002-RR, as supplemented, will provide an acceptable level of quality and safety.

Therefore, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Paragraph 50.55a(a)(3)(i), the NRC staff authorizes the use of the #07-001-RR and #07-002-RR for weld repairs at CR-3. The effective period of these RRs is the third 10-year inservice inspection interval, which ends in August 2008.

The bases for the NRC staffs conclusions are contained in the enclosed Safety Evaluation. If you have any questions regarding this issue, please contact Stewart Bailey at (301) 415-1321 or snb@nrc.gov.

Sincerely,

/RA/

Thomas H. Boyce, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-302

Enclosure:

Safety Evaluation cc w/enclosure: See next page

November 15, 2007 Mr. Dale E. Young, Vice President Crystal River Nuclear Plant (NA1B)

ATTN: Supervisor, Licensing & Regulatory Programs 15760 W. Power Line Street Crystal River, Florida 34428-6708

SUBJECT:

CRYSTAL RIVER UNIT 3 - RELIEF REQUESTS #07-001-RR AND #07-002-RR REGARDING WELD REPAIRS (TAC NOS. MD5498 AND MD5499)

Dear Mr. Young:

By letter dated April 12, 2007, as supplemented by letters dated September 13 and October 23, 2007, the Florida Power Corporation (the licensee) requested Nuclear Regulatory Commission (NRC) staff review and approval of Relief Requests (RRs) #07-001-RR and #07-002-RR to allow weld repairs during the upcoming refueling outage at Crystal River Unit 3 (CR-3). The proposed RRs provide alternatives to the requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI.

The NRC staff has reviewed the licensees submittal and determined that #07-001-RR and

1. 07-002-RR, as supplemented, will provide an acceptable level of quality and safety.

Therefore, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Paragraph 50.55a(a)(3)(i), the NRC staff authorizes the use of the #07-001-RR and #07-002-RR for weld repairs at CR-3. The effective period of these RRs is the third 10-year inservice inspection interval, which ends in August 2008 The bases for the NRC staffs conclusions are contained in the enclosed Safety Evaluation. If you have any questions regarding this issue, please contact Stewart Bailey at (301) 415-1321 or snb@nrc.gov.

Sincerely,

/RA/

Thomas H. Boyce, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-302

Enclosure:

Safety Evaluation cc w/enclosures: See next page Distribution:

PUBLIC LPL2-2 R/F RidsNrrDorlLpl2-2 RidsNrrPMSBailey RidsOgcRp RidsNrrLABClayton (Hard Copy)

RidsAcrsAcnwMailCenter RidsRgn2MailCenter RidsNrrDciCpnb RidsNrrDorlDpr WKoo ADAMS ACCESSION NO.: ML073100991 NRR-106 OFFICE LPL2-2/PM LPL2-2/LA CPNB/BC OGC LPL2-2/BC NAME SBailey BClayton TChan NLO GMizuno TBoyce DATE 11/15/07 11/14/07 11/05/07 11/14/07 11/15/07 OFFICIAL RECORD

Florida Power Corporation Crystal River Nuclear Plant, Unit 3 cc:

Mr. R. Alexander Glenn Associate General Counsel (MAC-BT15A)

Florida Power Corporation P.O. Box 14042 St. Petersburg, Florida 33733-4042 Mr. Michael J. Annacone Plant General Manager Crystal River Nuclear Plant (NA2C) 15760 W. Power Line Street Crystal River, Florida 34428-6708 Mr. Jim Mallay Framatome ANP 1911 North Ft. Myer Drive, Suite 705 Rosslyn, Virginia 22209 Mr. William A. Passetti, Chief Department of Health Bureau of Radiation Control 2020 Capital Circle, SE, Bin #C21 Tallahassee, Florida 32399-1741 Attorney General Department of Legal Affairs The Capitol Tallahassee, Florida 32304 Mr. Craig Fugate, Director Division of Emergency Preparedness Department of Community Affairs 2740 Centerview Drive Tallahassee, Florida 32399-2100 Chairman Board of County Commissioners Citrus County 110 North Apopka Avenue Inverness, Florida 34450-4245 Mr. Stephen J. Cahill Engineering Manager Crystal River Nuclear Plant (NA2C) 15760 W. Power Line Street Crystal River, Florida 34428-6708 Mr. Jon A. Franke Director Site Operations Crystal River Nuclear Plant (NA2C) 15760 W. Power Line Street Crystal River, Florida 34428-6708 Senior Resident Inspector Crystal River Unit 3 U.S. Nuclear Regulatory Commission 6745 N. Tallahassee Road Crystal River, Florida 34428 Ms. Phyllis Dixon Manager, Nuclear Assessment Crystal River Nuclear Plant (NA2C) 15760 W. Power Line Street Crystal River, Florida 34428-6708 David T. Conley Associate General Counsel II - Legal Dept.

Progress Energy Service Company, LLC Post Office Box 1551 Raleigh, North Carolina 27602-1551 Mr. Daniel L. Roderick Vice President, Nuclear Projects &

Construction Crystal River Nuclear Plant (SA2C) 15760 W. Power Line Street Crystal River, Florida 34428-6708 Mr. David Varner Manager, Support Services - Nuclear Crystal River Nuclear Plant (SA2C) 15760 W. Power Line Street Crystal River, Florida 34428-6708

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUESTS #07-001-RR, REVISION 0, AND #07-002-RR, REVISION 0 CRYSTAL RIVER NUCLEAR PLANT, UNIT 3 FLORIDA POWER CORPORATION DOCKET NO. 50-302

1.0 INTRODUCTION

By letter dated April 12, 2007, as supplemented by letters dated September 13 and October 23, 2007, the Florida Power Corporation (FPC, or the licensee) submitted two relief requests (RRs) to be implemented during the upcoming refueling outage at the Crystal River Nuclear Plant, Unit 3 (CR-3). The RRs were requested pursuant to Title 10 to the Code of Federal Regulations (10 CFR) Part 50, Paragraph 50.55a(a)(3)(i), on the basis that they provide an acceptable level of quality and safety.

In #07-001-RR, the licensee sought relief from the requirements of Article IWA-4500 of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),

Section XI, 1989 Edition, to perform weld repairs on pressurizer nozzle and thermowell penetrations. The licensee proposed to perform the repair utilizing a half-nozzle or a full penetration repair method, as applicable, with a remotely operated weld tool using the machine Gas Tungsten Arc Welding (GTAW) process, and an ambient temperature temper bead method with 50o F minimum preheat temperature and no post-weld heat treatment (PWHT), as described in Code Case N-638-1. The Nuclear Regulatory Commission (NRC) has conditionally approved the use of Code Case N-638-1.

In #07-002-RR, the licensee sought relief from the requirements of Paragraph IWA-3300 of the ASME Code,Section XI, to fully characterize the existing flaws left in the J groove weld of the nozzle, and instead proposed to use the worst-case assumptions to conservatively estimate the size and orientation of flaws for the flaw-growth evaluations.

2.0 REGULATORY EVALUATION

The requirements of 10 CFR 50.55a(g) specify that inservice inspection (ISI) of nuclear power plant components shall be performed in accordance with the requirements of the ASME Code,Section XI, except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). It states in 10 CFR 50.55a(a)(3) that alternatives to the requirements of paragraph 10 CFR 50.55a(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.

In accordance with 10 CFR 50.55a(g)(4)(ii), licensees are required to comply with the requirements of the latest edition and addenda of the ASME Code incorporated by reference in the regulations 12 months prior to the start of subsequent 120-month ISI program interval.

ASME Code cases approved by the NRC provide an acceptable voluntary alternative to the mandatory ASME Code provisions. The requirements in 10 CFR 50.55a were amended to incorporate Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, by reference, and state the requirements governing the use of Code cases. ASME Code Cases N-638-1 and N-416-2 have been approved for use as indicated in RG 1.147.

Paragraph 10 CFR 50.55a(g)(5)(iii) states that, if the licensee has determined that conformance with certain Code requirements is impractical for its facility, the licensee shall notify the Commission and submit information to support the determinations, as specified in 10 CFR 50.4.

The Code of record for the CR-3 third 10-year ISI interval is the 1989 Edition of the ASME Code, with no addenda. The CR-3 third 10-year ISI interval ends in August 2008.

3.0 TECHNICAL EVALUATION

3.1 Relief Request #07-001-RR, Revision 0 3.1.1 System/Components for Which Relief is Requested a) Name of component:

Pressurizer lower level instrument, sampling and vent nozzle penetrations and thermowell penetration. There are three (3) lower level instrument nozzle penetrations, one (1) sampling nozzle penetration and one (1) thermowell penetration in the shell of the pressurizer. There is one (1) vent nozzle penetration in the upper head of the pressurizer.

b) Function:

The nozzles, thermowell and penetration welds serve as a portion of the pressure boundary for the pressurizer.

c) ASME Code Class:

The pressurizer nozzle penetrations and thermowell penetrations are ASME Code Class 1.

d) Category:

Examination Category B-E, Pressure Retaining Partial Penetration Welds in Vessels, Item No. B4.11 for the modified vent nozzle penetration and original penetration, and Item No. B4.13 for the modified lower level instrumentation, sample nozzle and thermowell penetrations and original penetrations.

Category B-P Items B15.20 and B15.21 also apply to the modified locations.

3.1.2 Current Code Requirement and Relief Request The activity is considered a replacement governed by ASME Code,Section XI. ASME Code,Section XI, 1989 Edition, IWA-7320, states that welding required for the installation of an item to be used for replacement shall be performed by welders who are qualified, and by using procedures that are qualified, in accordance with ASME Code,Section IX, and the additional heat treating and impact tests required by IWB-4000 shall be used. ASME Code,Section XI, IWB-4000, does not apply as it is limited to repairs to heat exchanger tube or tubesheet bore hole plugging. ASME Code,Section XI, IWA-7510, requires all procedures for installation of items to be used for replacement shall be in accordance with IWA-4100. ASME Code,Section XI, 1989 Edition, IWA-4120(a), requires repairs to be made in accordance with the owners design specification and the original construction code of the component or system.

Later editions and addenda of the construction code or of ASME Code,Section III, either in their entirety or portions thereof, and Code cases may be used. If repair welding cannot be performed in accordance with these requirements, the applicable alternative requirements of IWA-4500 and IWB-4000 may be used for Class 1 components. As stated above, IWB-4000 is not applicable for this activity.

In accordance with 10 CFR 50.55a(a)(3)(i), the licensee requested relief from the following portion of ASME Code,Section XI, IWA-4120(a), and its referenced IWA-4500 to perform pressurizer nozzle and thermowell penetration repairs: If repair welding cannot be performed in accordance with these requirements, the applicable alternative requirements of IWA-4500 and IWB-4000 may be used for Class 1 components.

In lieu of performing the repair using the alternative welding techniques described in IWA-4500, the licensee proposed to perform a portion of the repair with a remotely operated weld tool, utilizing the GTAW process and the ambient temperature temper bead method with 50º F minimum preheat temperature and no post weld heat treatment, as described in Code Case N-638-1. The licensee requested the use of the Code case in its entirety, except for deviations as listed in Table 1, of the attachment to the April 12, 2007, application. The description of the proposed alternative is provided in the following section.

The licensee proposed to use Code Case N-416-2 to perform a system leak test in lieu of a hydrostatic pressure test. Since this Code case has been previously approved by the NRC, no Code relief is required. However, Code Case N-416-2 stipulates the use of the 1992 Edition of the ASME Code,Section III, for nondestructive examination (NDE) of welded repairs and ASME Section XI for visual examination (VT-2) of welded repairs in conjunction with the system leakage test. Consequently, the licensee adopted the 1992 Edition of ASME Code,Section III and Section XI, for NDE, visual examination, and system leak test associated with this replacement, instead of the ASME Code, 1989 Edition referenced in the CR-3 ASME Section XI Repair and Replacement Program. The conditional approval requirements for Code Case N-638-1, as specified in RG 1.147 Revision 14, will also be applicable for the ultrasonic examination of the weld pads.

The licensee determined that the proposed alternative will provide an acceptable level of quality and safety, while allowing significant dose reductions.

3.1.3 Alternate Criteria for Acceptability The licensee plans to perform pressurizer nozzle and thermowell penetration repairs as follows:

1. Removal of a portion of the existing nozzle and thermowell.

2. Application of weld pad (or weld buildup) using F-No. 43 to the pressurizer shell and upper head (P-No. 1, Group 2) base material.

3. Machining the weld pad and bore to accept the new half nozzle/complete thermowell (P-No. 43).

4. Installing the replacement half nozzle/complete thermowell by using conventional manual GTAW and a J groove partial penetration weld.

The proposed alternative to the applicable portion of ASME Code,Section XI, involves the use of the ambient temperature temper bead repair described in Code Case N-638-1. The licensee proposed to use this methodology only for the weld pad application, which is the second step of the repair process.

Table 1 of the April 12, 2007, submittal describes those areas where the proposed methodology deviates from the requirements of the original construction code, ASME Section XI, or Code Case N-638-1.

3.1.4 Basis for Relief The licensees basis for the relief is that the use of an ambient temperature temper bead welding process provides an equivalent, acceptable level of quality and safety when compared to the temper bead welding process required by ASME Code Sections XI and III, while offering substantial savings in accumulated radiation dose. In support of this conclusion, the licensee described the process, the technical justification for the differences between the two techniques, and the expected dose savings. The licensees description is as follows:

(1) Description of the process Figures 1 and 2 [of the April 12, 2007, submittal] provide a general overview of the nozzle and thermowell configurations.

a) The existing piping will be cut away from the nozzle/penetration and the nozzle/thermowell cut close to the pressurizer shell or upper head, as applicable. The nozzle/thermowell will then be ground flush with the pressurizer shell or upper head, as applicable. The area around the nozzle/thermowell will be prepared for the application of the weld pad by grinding smooth and performing a surface examination (PT [penetrant tested] or MT [magnetic particle tested]) and ultrasonic examination of the area to be welded and the 5 inch wide band surrounding the weld area.

b) A weld pad is applied to the surface of the pressurizer shell or upper head, as applicable, using the ambient temperature temper bead weld process and GTAW method as described in Code Case N-638-1. The weld pad is applied as a weld buildup centered on the existing opening.

c) The weld pad is prepared suitable for NDE. The pad and its HAZ

[heat-affected zone] below the pad are volumetrically examined (UT) to the extent practical. The weld pad and a 5 inch wide band of the pressurizer shell or upper head, as applicable, surrounding the weld pad are also surface examined (PT or MT). The examinations and acceptance criteria are in accordance with ASME Section III, 1992 Edition, no Addenda, NB-5000.

Ultrasonic examination, before and after welding, of the full parent material thickness beneath the weld pad, to the extent practical, is performed to discern laminar type indications therein. Laminar type indications observed will be recorded and evaluated to assure the structural integrity of the modified configuration is not adversely affected.

d) The center of the weld pad is ground or machined to re-establish a free path into the Pressurizer penetration. The outer portion of the remaining existing nozzle is removed by machining into the Pressurizer shell or upper head, as applicable. The entire thermowell is removed by machining. The weld pad is prepared to accept the new nozzle/thermowell using a J groove partial penetration weld.

e) The new nozzle/thermowell is inserted and welded using conventional welding and NDE techniques (manual GTAW and progressive PT). Note that this weld is in full ASME construction code compliance and relief from code requirements is not required.

(2) Justification a) As low as reasonably achievable (ALARA)

Experience gained from the performance of similar repairs/modifications at other plants indicates that remote automated repair methods reduce the radiation dose to repair personnel and still provide acceptable levels of quality and safety. CR-3 estimates the dose saved by not providing access, installing heating pads and performing the preheat and post weld heat treatment required by the construction code would be approximately 4.8 to 7.2 REM per location.

b) Procedure Qualification Results of procedure qualification work undertaken to date on low alloy steel base material indicate that the ambient temperature temper bead process produces sound and tough welds. Industry experience also indicates that the GTAW temper bead process can produce acceptable welds on P-No.3 Group No. 3 as well as P-No.1 Group No. 2 ferritic steel base materials. AREVA NP (AREVA) has qualified the welding process and procedures for this specific application in accordance with Code and Code Case requirements.

AREVA has also performed welding procedure qualifications using machine GTAW ambient temperature temper bead welding on low alloy steel P-No.3 Group No. 3 base materials in accordance with Code Case N-638-1. These qualifications were also performed at room temperature under similar conditions as the current application. The results of similar procedure qualification work indicate that the process produces sound and tough welds.

Other welding procedure qualification work can be compared to the current process. Specifically, the existing Code Case N-638-1 qualifications have also been performed on P-No. 3 Group No. 3 base materials, which have a higher hardenability and propensity for hydrogen embrittlement than the Pressurizer shell and upper head base material (P-No. 1 Group No. 2). These qualifications use the same F-No. 43 filler material (Alloy 52 AWS Class ERNiCrFe-7). This filler material or similar F-No. 43 filler material, Alloy 52M AWS Class ERNiCrFe-7A, will be used in this application with the same low heat input controls. These qualifications did not include a post weld heat soak. The successful qualification of the ambient temperature temper bead welding process demonstrates that the proposed alternative provides an acceptable level of quality and safety.

As previously noted, AREVA has successfully performed a machine GTAW procedure qualification using the same test assembly base material, SA-516 Gr. 70, P-No.1 Group No. 2 base material, as the Pressurizer shell/upper head. Alloy 52 AWS Class ERNiCrFe-7, F-No. 43, filler metal was used. This filler material or similar filler material, Alloy 52M, ERNiCrFE-7A, F-No. 43, will be used for this activity.

c) Weld Quality The proposed alternative repair technique has been demonstrated as an acceptable method for performing Pressurizer nozzle repairs. The ambient temperature temper bead technique has been approved by the ASME committee per Code Case N6381. The ambient temperature temper bead technique has also been previously approved by the NRC as having an acceptable level of quality and safety and used successfully at several utilities (Three Mile Island, CR-3, Millstone, St. Lucie, ANO

[Arkansas Nuclear One], South Texas Project and other facilities). This Code Case has been conditionally approved in Regulatory Guide 1.147, Revision 14. This conditional approval indicates that the methodology is capable of producing quality in-situ repairs.

As documented in EPRI [Electric Power Research Institute] Report GC-111050, research shows that carefully controlled heat input and bead placement allow subsequent welding passes to relieve stress and temper the heat affected zone (HAZ) of the base material. The use of the machine GTAW temper bead process will allow precise control of heat input, bead placement, and bead size and contour as compared to the SMAW [small metal ark weld] process. The very precise control over these factors afforded by the machine GTAW process provides effective tempering of the HAZ.

The machine GTAW temper bead process uses a welding process that is inherently free of hydrogen. The GTAW process relies on bare welding electrodes and bare wire filler metal with no flux to introduce moisture.

An inert gas blanket provides shielding for the weld and surrounding metal, which protects the region during welding from the atmosphere and any moisture it may contain and typically produces porosity free welds. In accordance with the weld procedure qualification, welding grade argon is used for the inert gas blanket. To further reduce the likelihood of any hydrogen evolution or absorption, specific controls will be used to ensure the welding electrodes, filler metal and weld region are free of all sources of hydrogen. Argon flow rates are adjusted to assure adequate shielding of the weld without creating a venturi affect that might draw oxygen or water vapor from the ambient atmosphere into the weld.

Typically preheat and post weld heat treatment are used to mitigate the effects of the solution of atomic hydrogen in ferritic materials prone to hydrogen embrittlement cracking. The susceptibility of ferritic steels is directly related to their ability to transform to martensite with appropriate heat treatment. The P-No. 1 Group No. 2 material of the Pressurizer is able to produce martensite from heating and cooling cycles associated with welding, however it is much less susceptible to martensite formation than P-No. 3 Group No. 3 base material.

d) Maximum Preheat & Interpass Temperature Measurement Due to the location of the repair and area radiation dose rate, the placement of thermocouples for monitoring weld interpass temperature is determined to be not beneficial based on dose savings. Therefore, thermocouples are not planned for use to monitor interpass temperature during welding. The location of the Pressurizer ensures that its temperature will be above 50°F prior to welding. The maximum interpass temperatures measured during the Procedure Qualifications were less than 160°F. Temperature measurements, using a contact pyrometer, on the three upper level instrumentation nozzle weld pads in 2003 were less than 150°F.

[In its supplemental information letters dated September 13 and October 23, 2007, FPC stated that the measurement of preheat and interpass temperature will be measured by using a calibrated contact pyrometer or infrared thermometer. Interpass temperature will be monitored for the first three temper bead layers for each of the weld pads.

On the first weld pad, the interpass temperature measurements will be taken every three to five passes. On Subsequent weld pads, the interpass temperature will be monitored every six to ten passes.]

e) Examination All examinations will be performed in accordance with ASME Section III, 1992 Edition, NB-5000 as specified in Code Case N-416-2, using personnel qualified in accordance with IWA-2300 and/or NB-5500.

The area to be welded, plus a 5 inch surrounding band, will be surface examined (PT or MT) both prior to and following welding. All post weld exams will be performed on the completed weld no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of the third temper bead layer. The entire volume of the weld pad, to the extent practical, will be scanned from the face of the pad, using examination angles of 0°, 45° RL [refracted longitudinal], 60° RL and an OD [outside diameter] creeping wave. The examination volume shall include the weld-deposited material and the ferritic vessel HAZ.

Ultrasonic examination, before and after welding, of the full parent material thickness beneath the weld pad, to the extent practical, will be performed to discern laminar type indications therein. Laminar type indications observed will be recorded and evaluated to assure the structural integrity of the modified configuration is not adversely affected.

Because this is a surface application of the temper bead process, there will be minimal impact to the volume of the Pressurizer shell/upper head in the area surrounding the weld. Since this weld is applied to the surface of the Pressurizer shell/upper head only, there is no additional useful information that can be gained by a volumetric examination of the area surrounding the weld. The weld and HAZ below will be post weld volumetrically examined to the extent possible. This reduction in the post welding inspection will provide additional dose reduction for this repair while still ensuring sound weld metal is deposited and that the process has not introduced flaws in the base material.

f) Post Weld Examination 48 Hours Minimum After Completion of the Third Temper Bead Layer Code Case N-638-1 and IWA-4534(b) impose a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> delay between completion of welding and returning to ambient temperature and final NDE. The 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> delay provides time for delayed hydrogen cracking to occur. Code Case N-638-1 requires the machine or automatic GTAW process to be used thereby eliminating the use of welding processes requiring flux for shielding.

As discussed [in the above discussion of weld quality], the machine GTAW temper bead process uses a welding process that is inherently free of hydrogen and consistently delivers low-hydrogen welds.

Furthermore, past industry experience with the use of the machine or automatic GTAW process has resulted in no detection of hydrogen cracking after the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold NDE or subsequent in-service inspections.

EPRI Report 1013558, Temperbead Welding Applications, 48 Hour Hold Requirements for Ambient Temperature Temperbead Welding, Technical Update, December 2006, provides justification for reducing the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time on P-No. 3 Group No. 3 ferritic steel base material to start after completion of the third temper bead layer instead of the currently specified hold time in Code Case N-638-1 and IWA-4534(b). Report 1013558 addresses microstructural issues, hydrogen sources, tensile stress and temperature, and diffusivity and solubility of hydrogen in steels.

Also, as discussed [in the above discussion of weld quality], the Pressurizer shell/upper head ferritic steel is P-No. 1 Group No. 2 carbon steel material, not P-No. 3 Group No. 3 low alloy steel. The P-No. 1 Group No. 2 HAZ is less susceptible to hydrogen induced cracking than P-No. 3 Group No. 3 due to its lower hardenability and propensity to produce untempered martensite.

There is currently an ASME Section XI action to incorporate the revised NDE hold requirement into existing Code Case N-638-3 which is the current published version. This change has been approved by the Main Committee and Board on Nuclear Codes and Standards and will be included in N-638-4.

g) Corrosion The automated repair method described above leaves an area of ferritic carbon steel at the outside diameter (OD) of the nozzle/thermowell [inside diameter (ID) of the nozzle/thermowell penetration bore] exposed to the primary coolant. The effect of corrosion on the exposed area, including both the reduction in Pressurizer wall thickness and the release rates of Iron (Fe) to the primary coolant is evaluated by AREVA NP and concurred with by CR-3. The analysis shows that the total corrosion is insignificant when compared to the thickness of the Pressurizer shell/upper head. It is also concluded that the total estimated Fe release is significantly less than the total Fe release from all other sources. CR-3 has determined that the expected extremely low rate of material loss and Fe release rates will provide an acceptable level of safety.

h) Stresses A stress analysis of the modified weld configuration is performed. The stress analysis demonstrates that the modified nozzle configuration complies with the criteria of NB-3000, ASME Section III, 1989 Edition, no Addenda, using design and service conditions applicable to the Pressurizer.

Therefore, based on the discussion above, CR-3 has determined that the proposed alternative provides an acceptable level of quality and safety while reducing radiation exposure to as low as reasonably achievable.

3.1.5 Documentation

The licensee stated that use of the Code cases and this RR will be documented on the NIS-2 Form for the repair.

3.1.6 Implementation Schedule:

The licensee requested this RR for repairs made during the third 10-year ISI interval, and it is only applicable to the repairs to the pressurizer lower level instrument, sampling and vent nozzles, and thermowell penetrations. The third 10-year ISI interval ends in August 2008.

3.1.7 Staff Evaluation In #07-001-RR, the licensee sought relief from the requirements of Article IWA-4500 of the ASME Code,Section XI, 1989 Edition, to perform weld repairs on pressurizer nozzles and thermowell penetrations. ASME Code,Section XI, 1989 Edition, IWA-4120(a) requires that weld repairs be made in accordance with the owners design specification and the original construction code of the component or system. Later Code editions and addenda of the construction code, or of ASME Code,Section III, may be used. If repair welding cannot be performed in accordance with these requirements, the applicable alternative requirements of IWA-4500 and IWB-4000 of ASME Code,Section XI, may also be used for Class 1 components.

The licensee proposed to perform the repair utilizing a half-nozzle or full penetration repair method, as applicable with a remotely operated weld tool, using the machine GTAW process, and the ambient temperature temper bead method with 50o F minimum preheat temperature and no PWHT, as described in Code Case N-638-1. In RG 1.147, Revision 14, the NRC conditionally approved the use of Code Case N-638-1. The conditions consist of (1) UT examinations shall be demonstrated for the repaired volume using representative samples that contain construction type flaws and (2) the acceptance criteria of NB-5330 of ASME Code,Section III, edition and addenda approved in 10 CFR 50.55a apply to all flaws identified within the repaired volume. The licensee stated in its submittal that these conditions will be applied for the ultrasonic examination of the weld pads.

Code Case N-638-1 provides for the use of machine GTAW with ambient temperature preheat and no PWHT when draining the vessel is impractical for operational or radiological reasons.

Although draining the CR-3 pressurizer is not impractical (i.e., it can be drained), the methodology of N-638-1 can be applied to obtain a significant reduction in radiation dose for the reasons stated in Section 3.1.4.2.a of this safety evaluation. The licensee stated that the reduction of radiation dose to repair personnel is estimated to be about 4.8 to 7.2 REM per repair location. With a proposed repair of 6 locations, the total reduction in radiation dose would amount to about 28.8 to 43.2 REM, which is a significant dose reduction. Therefore, the use of Code Case N-638-1 is consistent with the principle of ALARA.

Paragraph IWA-4533(b) of the ASME Code,Section IX, requires that preheating and interpass temperature be monitored using thermocouples and recording instruments. The licensee initially intended to calculate the interpass temperature based on prior interpass temperature results and experience gained therefrom. However, in its response to the staffs requests for additional information, the licensee stated that it will use calibrated contact pyrometers or infrared thermometers to measure the preheat and interpass temperatures as an alternative to the Code requirement. The licensee will measure the interpass temperature for the first three layers of each weld repair. On the first weld repair location, the interpass temperature measurements will be taken every three to five passes. For subsequent weld repair, the interpass temperature will be measured every six to ten passes. Code Case N-638-1 requires that, for the welding of the pressurizer, the preheat temperature shall be at least 50o F prior to depositing the first weld layer. For the first three layers, the interpass temperatures shall be at least 50o F but less than 150o F. The interpass temperature of each remaining layer shall be at least 50o F but less than 350o F prior to depositing the subsequent weld layers. The preheat temperature required for this welding is 50o F. This temperature is to be maintained on a weldment inside a building that normally is above this temperature. Therefore, preheat measurement by this alternate method is acceptable. The maximum interpass temperatures required for this welding (150o F for the first three layers, and a maximum interpass temperature of 350o F for the balance of welding), can easily be measured with this type of device. Also, the large mass of the pressurizer coupled with the low heat input GTAW process should help to ensure that the maximum interpass temperature will not be exceeded, and with the alternate temperature measurement methods a close control will be maintained on these temperatures.

Therefore, this type of temperature measurement will provide an acceptable level of quality and safety.

To accomplish the repair, the licensee will utilize the half-nozzle or full penetration repair method, as applicable. These methods have been successfully employed in the past at other nuclear power plants. The repair is accomplished by removing the existing piping from the nozzle followed by cutting the nozzle/penetration close to the pressurizer shell or upper head.

The nozzle/penetration will then be ground flush with the pressurizer shell or upper head. The surface area around the nozzle/penetration will be prepared for the application of the weld pad by grinding the surface smooth. The area prepared for welding will be surface (PT or MT) and ultrasonically (UT) examined, which would include a 5 inch wide band surrounding the weld area. The weld pad will be applied to the surface of the pressurizer shell or upper head using the ambient temperature temper bead weld process and GTAW method as described in Code Case N-638-1. The weld pad made of Alloy 52/52m filler metal will be applied as a weld buildup centered on the existing nozzle/penetration opening, and the weld pad surface will be prepared for NDE. The pad and its HAZ below the pad will be volumetrically examined (via UT) to the extent practical. The weld pad and a 5 inch wide band of the pressurizer shell surrounding the weld pad will be also surface examined (PT or MT). The surface and ultrasonic examinations and acceptance criteria will meet the requirements of Article NB-5000 of the ASME Code,Section III, 1992 Edition, with no addenda. Therefore, the examinations are acceptable. In addition, ultrasonic examination, before and after welding, of the parent material beneath the weld pad, to the extent practical, will be performed to detect laminar type indications if present in the base material. Laminar-type indications, if detected, will be recorded and evaluated to ensure that the structural integrity of the weld repair is not affected. This is acceptable because the ultrasonic examination will verify that weld buildup is not applied in close proximity to the laminations in the base material and thus the structural integrity of the weld repair is ensured.

The center of the weld pad will be ground or machined to re-establish a free path into the pressurizer nozzle penetration. The outer portion or the full length of the remaining existing nozzle will be removed by machining into the pressurizer shell or upper head. The weld pad will be prepared to accept the new nozzle using a J groove, partial penetration weld made of Alloy 52/52m. The new nozzle made of Inconel 690 material will be inserted and welded using ASME Code-approved welding methods such as manual GTAW and inspected by progressive PT.

Code Case N-638-1 and IWA-4534(b) require a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> delay for the performance of final NDE after completion of welding and returning the component to ambient temperature. The purpose of this 48-hour delay is to minimize the occurrence of delayed hydrogen cracking. The licensee proposed to perform the final NDE after a minimum of 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of the third temper bead layer.

The licensee provided the following justification to support the proposed alternative:

(1) The welds produced by machine GTAW temper bead welding process as specified in Code Case N-638-1 are inherently free of hydrogen. This is also supported by past industry experience.

(2) EPRI Report 1013558 performed a technical evaluation regarding the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time requirements for ambient temperature temper bead welding. The results of this study supported the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time after completion of the third temper bead layer.

(3) The pressurizer shell or upper head ferritic steel is P-No.1/Group No.2 carbon steel material. This material is less susceptible to hydrogen-induced cracking than the P-No. 3/Group No.3 low alloy steel due to its lower hardenability and propensity to produce untempered martensite.

(4) The ASME Section XI Code Committee is currently taking action to incorporate the revised NDE hold time requirement into the new version of Code Case N-638.

The staff has determined that the licensees proposed alternative hold time for final NDE is acceptable based on the low susceptibility of the material to hydrogen-induced cracking and based on the licensees use of machine GTAW temper bead welding process for the in repair.

Based on the above, the NRC staff finds the licensees proposed weld repair process acceptable for the repair of pressurizer nozzle and thermowell penetrations. This is based on the fact that the repair process utilizes remotely operated weld tool, employing the machine GTAW temper bead method with 50o F minimum preheat temperature, and no PWHT, as described in Code Case N-638-1. Code Case N-638-1 has been previously approved by the NRC. In addition, the NRC has previously approved the use of remote machine processes to perform weld repairs. Such weld repairs have been successfully accomplished at CR-3 and other nuclear power plants. As a result, the NRC staff concludes that the licensee has proposed an alternative to the requirements of IWA-4120(a) and IWA-4500 of the ASME Code,Section XI, that provides an acceptable level of quality and safety.

3.2 Relief Request #07-002-RR, Revision 0 3.2.1 System/Components for Which Relief is Requested a) Name of component:

Pressurizer lower level instrument, sampling and vent nozzle penetrations, and thermowell penetration. There are three (3) lower level instrument nozzle penetrations, one (1) sampling nozzle penetration and one (1) thermowell penetration in the shell of the pressurizer and one (1) vent nozzle penetration in the upper head of the pressurizer.

b) Function:

The nozzles, thermowell and penetration welds serve as the pressure boundary for the pressurizer.

c) ASME Code Class:

The pressurizer, nozzle penetrations, and thermowell penetrations are ASME Code Class 1.

d) Category:

Examination Category B-E, Pressure Retaining Partial Penetration Welds in Vessels; Item No. B4.11 for the modified vent nozzle penetration and original penetration, and Item No. B4.13 for the original and modified lower level instrumentation and sample nozzle penetrations, and the original and modified thermowell penetration.

Category B-P Items B15.20 and B15.21 also apply to the modified locations.

3.2.2 Current Code Requirement and Relief Request The activity is considered a replacement governed by ASME Code,Section XI. The 1989 Edition of the ASME Code,Section XI, IWA-7320, states welding required for the installation of an item to be used for replacement shall be performed by welders who are qualified, and by using procedures that are qualified, in accordance with ASME Code,Section IX, and using the additional heat treating and impact tests required by IWB-4000.

ASME Code,Section XI, IWB-4000, does not apply as it is limited to repairs to heat exchanger tube or tubesheet bore hole plugging. ASME Code,Section XI, IWA-7510, requires all procedures for installation of items to be used for replacement shall be in accordance with IWA-4100. ASME Code,Section XI, 1989 Edition, IWA-4120(a), requires repairs to be made in accordance with the owners design specification and the original construction code of the component or system. Later editions and addenda of the construction code or of ASME Code,Section III, either in their entirety or portions thereof, and Code cases may be used. If repair welding cannot be performed in accordance with these requirements, the applicable alternative requirements of IWA-4500 and IWB-4000 may be used for Class 1 components. As stated above, IWB-4000 is not applicable for this activity.

In accordance with the provisions of ASME Code,Section XI, 1989 Edition, IWA 4120(c), the licensee will use the 1992 Edition of ASME Code,Section XI, IWA-4310. IWA-4310 requires, in part, that, Defects shall be removed or reduced in size in accordance with this Paragraph.

Furthermore, IWA-4310 allows that,... the defect removal and any remaining portion of the flaw may be evaluated and the component accepted in accordance with the appropriate flaw evaluation rules of ASME Section XI. ASME Code,Section XI, IWA-3300 requires characterization of flaws detected by inservice examination.

The licensee is requesting relief from ASME Code,Section XI, IWA-3300. The licensee assumed that flaws in the original pressurizer lower level instrument, sampling, or vent nozzle to pressurizer shell/upper head J groove weld, and thermowell to pressurizer shell weld will not be removed. Instead of fully characterizing the existing cracks, the licensee proposed to utilize worst-case assumptions to conservatively estimate the crack extent and orientation. The licensee determined that the proposed alternative will provide an acceptable level of quality and safety, while allowing significant dose reductions.

3.2.3 Alternate Criteria for Acceptability In accordance with 10 CFR 50.55a(a)(3)(i), the licensee proposed alternatives to the requirements of IWA-3300. The planned repair for the subject pressurizer nozzles and thermowell does not include removal of any flaws assumed to be present in the remaining J groove partial penetration welds. Therefore, IWA-4310 requires the cracks to be evaluated using the appropriate flaw evaluation rules of ASME Code,Section XI. The licensee does not plan to perform additional inspections to characterize the cracks. Thus, the actual dimensions of any remaining flaws will not be fully determined. Instead of fully characterizing the existing cracks, the licensee will utilize worst-case assumptions to conservatively estimate the crack extent and orientation. The postulated crack extent and orientation will then be evaluated using the rules of IWB-3600.

3.2.4 Basis for Relief The licensee provided the following basis for relief:

CR-3 plans to perform Pressurizer nozzle and thermowell penetration repairs as follows:

1. Removal of a portion of the existing nozzle and thermowell.

2. Application of a weld pad or weld buildup (F-No. 43) to the Pressurizer shell/upper head (P-No 1, Group No. 2) base material.

3. Machining the weld pad and bore, as required, to remove the outer portion of the nozzle within the bore and the complete thermowell, and to accept the new half nozzle/complete thermowell (P-No. 43).

4. Installing the replacement half nozzle/complete thermowell by using conventional manual gas tungsten arc welding (GTAW) and a J groove partial penetration weld.

The original nozzle(s) and weld(s) and the original thermowell to Pressurizer weld will no longer function as Pressurizer vessel pressure boundary. However, the possible existence of cracks in these welds mandates that the potential for flaw growth be evaluated. The requirements of IWA-4310 allow two options for determining the disposition of discovered cracks. The subject cracks are either removed as part of the repair process or left as-is and evaluated per the rules of IWB-3600. The repair design and the inaccessibility of the inside of the Pressurizer dictated that the inside weld and nozzle portion and the original thermowell to Pressurizer weld be left intact inside the Pressurizer.

The assumptions of IWB-3500 are that the cracks are fully characterized to be able to compare the calculated crack parameters to the acceptable parameters provided in IWB-3500. In the alternative being proposed, the acceptance of the postulated crack is calculated based on the two inputs of expected crack orientation and the geometry of the welds.

Typically, an expected crack orientation is evaluated based on prevalent stresses at the location of interest. Using worst case (maximum) assumptions with the geometry of the as-left weld, the postulated crack is assumed to begin at the intersection of the Pressurizer shell/upper head inner surface and the Pressurizer nozzle/thermowell penetration bore and propagate into the Pressurizer shell/upper head carbon steel. The depth and orientation are worst-case assumptions for cracks that may occur in the remaining J groove partial penetration weld configuration. It is assumed that the as-left condition of the remaining J groove weld includes degraded or cracked weld material.

Fracture mechanics analyses are performed. The analyses determine if degraded J groove weld material could remain in the vessel, with no examination to size any flaws that might remain following the repair. Since the hoop stresses in the J groove weld are higher than the axial stresses, the preferential direction for cracking is axial, or radial relative to the nozzle/thermowell. It is postulated that a radial crack in the Alloy 182 weld metal would propagate by Primary Water Stress Corrosion Cracking (PWSCC) through the weld to the interface with the carbon steel shell/upper head. It is fully expected that such a crack would then blunt and arrest at the weld-to-shell/upper head interface.

Ductile crack growth through the Alloy 182 material would tend to relieve the residual stresses in the weld as the crack grew to its final size and blunted.

Although residual stresses in the shell/upper head material are low, it is assumed that a small flaw could initiate in the carbon steel material and grow by fatigue. It is postulated that the small flaw in the shell/upper head would combine with a large stress corrosion crack in the weld to form a radial corner flaw that would propagate into the carbon steel shell/upper head by fatigue crack growth under cyclic loading conditions. Residual stresses are determined and are included in the analysis.

Flaw evaluations are performed for a postulated radial corner crack. Hoop stresses are used since they are perpendicular to the plane of the crack. The life of the repair is determined based on fatigue crack growth and crack growth per year of operation. It has been calculated as 40 years of additional service. The final flaw size meets the fracture toughness requirements of the ASME Code using an upper shelf value of 200 ksi for ferritic materials. The results of this analysis indicate that it is acceptable to leave the postulated cracks in the attachment weld (J groove) for the remaining life of the component.

An additional evaluation is performed to determine the potential for debris damage resulting from a cracked J groove partial penetration weld. As noted above, radial cracks are postulated to occur in the weld due to the dominance of the hoop stress at this location. The occurrence of transverse cracks that could intersect the radial cracks is considered remote. There are no identified forces that would drive a transverse crack. Only thermal and welding residual stresses could cause a transverse crack to grow. However, the presence of radial cracks limits the growth potential of the transverse cracks. The radial cracks would relieve the potential transverse crack driving forces. Hence, it is unlikely that a series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged. Even though highly unlikely, the analysis assumes worst case configurations of debris are generated by a cracked weld.

The analysis concludes that there is an insignificant probability of damage to any Reactor Coolant System (RCS) or Pressurizer component resulting from debris generated because of a cracked weld.

The cited evaluations will provide an acceptable level of safety and quality in insuring that the Pressurizer shell remains capable of performing its design function with flaws existing in the original J groove weld.

Justification for Granting Relief Removal of the cracks in the existing J groove partial penetration welds would incur excessive radiation dose for repair personnel. With the installation of the new pressure boundary welds previously described, the original function of the J groove partial penetration welds is no longer required. It is well understood that the cause of the cracks in the subject J groove welds is Primary Water Stress Corrosion Cracking (PWSCC). As shown by industry experience, the carbon steel shell of the Pressurizer impedes crack growth by PWSCC. CR-3 believes the alternative described will provide an acceptable level of quality and safety when compared to the code requirements in IWB-3500 to characterize the cracks left in service. Using flaw tolerance techniques as was done on previous pressurizer instrument nozzle repair efforts at CR-3, it will be demonstrated that the assumed worst case crack size will not grow to an unacceptable depth into the Pressurizer shell/upper head carbon steel base material over the life of the repair. Thus, the Pressurizer shell/upper head can be accepted per the requirements of IWA-4310.

3.2.5 Implementation Schedule:

The licensee requested this relief for the third 10-year ISI interval, and only to be applied to the repairs of the pressurizer lower level instrument, sampling and vent nozzles and the thermowell penetration. The third 10-year ISI interval ends in August 2008.

3.2.6 Staff Evaluation The licensee submitted #07-002-RR, for implementation during the upcoming refueling outage at CR-3. In this RR, the licensee indicated that, in accordance with ASME Code,Section XI, 1989 Edition, paragraph IWA-4120(c), it will use the 1992 Edition of ASME Code,Section XI, paragraph IWA-4310. The staff finds this acceptable, pursuant to 10 CFR 50.55a(g)(4)(iv),

provided that all related requirements are met.

The licensee also sought relief from the requirements of paragraph IWA-3300 of the ASME Code,Section XI, which requires characterization of flaws detected by inservice examination.

Instead, the licensee proposed to use the worst-case assumptions to conservatively estimate the size and orientation of flaws. To accomplish this goal, the licensee performed a fracture mechanics evaluation to determine if degraded J groove weld material could remain in the vessel with no examination to size any flaws that might remain following the repair. The evaluation assumed that a radial crack in the Alloy 182 weld metal would propagate by PWSCC through the weld to the interface with the carbon steel material (shell/upperhead). Such a crack will blunt and arrest at the weld-to-shell/upperhead interface. Ductile crack growth through the Alloy 182 material would tend to relieve the residual stresses in the weld as the crack grew to its final size and blunted at the interface. Although residual stresses in the shell/upperhead material are low, the licensees evaluation assumed that a small flaw could initiate in the carbon steel material and grow by fatigue. It also postulated that the small flaw in the shell/upperhead would combine with a large stress corrosion crack in the weld to form a radial corner flaw that would propagate into the carbon steel shell/upperhead by fatigue crack growth under cyclic loading conditions. The life of the repair was determined based on fatigue crack growth and crack growth per year of operation. The life of the repair was calculated to provide 40 years of additional service. The final flaw size was determined to meet the fracture toughness requirements of the ASME Code using an upper shelf fracture toughness value of 200 ksi/in for ferritic materials. The results of the licensees analysis are documented in AREVA NP documents 32-9043166-000, 32-9043167-000 and 32-5029133-01. The analysis indicated that it is acceptable to leave the postulated cracks in the attachment weld (J groove) for the remaining life of the component.

The NRC staff finds the licensee flaw evaluation approach acceptable because the licensee has utilized the worst-case assumptions to estimate the crack extent and orientation. Further, the NRC staff has previously approved this flaw evaluation approach for use at other nuclear power plants that have successfully repaired nozzles using the half-nozzle or full penetration repair method.

The potential of corrosion mechanisms affecting the pressurizer nozzles and thermoweld penetrations were evaluated by the licensee. This evaluation was performed because the repair configuration leaves portions of the carbon steel material inside the pressurizer penetrations exposed to the primary reactor coolant. The exposure of the carbon steel material is caused by the existence of a small gap at the junction between the original (Alloy 600) and new (Alloy 690) nozzles. The analysis evaluated the long-term impact of the newly exposed carbon steel material to the reactor coolant. The results of the licensees analysis are documented in AREVA document 51-5029172-02. The analysis concluded that the corrosion rate and release of iron into the reactor coolant system are negligible. The NRC staff concurs with the licensees evaluation results that the long-term impact on exposed carbon steel material to reactor coolant is negligible because operating history of domestic power plants includes many cases where localized exposure of carbon steel to reactor coolant has been confirmed to be very low, on the order of 0.001 to 0.002 inch per year.

According to the licensee, the removal of cracks in the existing J groove partial penetration welds would incur excessive radiation dose for repair personnel. With the installation of the new pressure boundary welds previously described in #07-001-RR, the original function of the J groove partial penetration welds is no longer required. It is well understood that the cause of the cracks in the subject J groove welds is PWSCC. As shown by industry experience, the carbon steel material of the pressurizer shell/upperhead impedes crack growth by PWSCC.

Therefore, the alternative described in the licensees submittal will provide an acceptable level of quality and safety when compared to the Code requirements in IWB-3500 to characterize the cracks left in service. Using flaw tolerance techniques, it has been demonstrated that the assumed worst-case crack size will not grow to an unacceptable depth into the pressurizer shell/upperhead carbon steel base material over the life of the repair.

The NRC staff finds the licensees evaluation in support of #07-002-RR acceptable. This is based on the fact that the licensee has assumed a conservative initial crack size and has demonstrated that the assumed worst-case crack size will not grow to an unacceptable depth into the pressurizer shell/upperhead carbon steel base material over the life of the repair.

Furthermore, the long-term impact on exposed carbon steel material to reactor coolant is negligible because operating history of domestic power plants includes many cases where localized exposure of carbon steel to reactor coolant has been confirmed to be very low. As a result, the NRC staff concludes that the licensee has proposed an alternative to the requirements of IWA-3300 of ASME Code,Section XI, that provides an acceptable level of quality and safety.

4.0 CONCLUSION

Based on the information provided in the licensees submittal, as supplemented, the NRC staff has determined that the licensee has proposed acceptable alternatives to the requirements of ASME Code,Section XI. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the licensees proposed alternatives in #07-001-RR and #07-002-RR are authorized for the repair of pressurizer nozzle and thermowell penetrations, because they provide an acceptable level of quality and safety. The effective period of these RRs is the third 10-year inservice inspection interval, which ends in August 2008. All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested and approved, remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: William Koo Date: November 15, 2007