ML071790313

Safety Evaluation of EPRI Report, Technical Basis for Part Circumference Weld Overlay Repair of Vessel Internal Core Spray Piping (BWRVIP-34)

ML071790313
Person / Time
Site:	Fermi
Issue date:	06/27/2007
From:	Matthew Mitchell NRC/NRR/ADES/DCI/CVIB
To:	Libra R DTE Energy
John Honcharik (301) 415-1157
References
BWRVIP-34, TR-108198
Download: ML071790313 (30)

Text

June 27, 2007 Rick Libra, BWRVIP Chairman DTE Energy Fermi Nuclear Plant (M/S 280 OBA) 6400 N. Dixie Highway Newport, MI 48166-9726

SUBJECT:

SAFETY EVALUATION OF PROPRIETARY EPRI REPORT, BWR VESSEL AND INTERNALS PROJECT, TECHNICAL BASIS FOR PART CIRCUMFERENCE WELD OVERLAY REPAIR OF VESSEL INTERNAL CORE SPRAY PIPING (BWRVIP-34)

Dear Mr. Libra:

The Nuclear Regulatory Commission (NRC) staff has completed its review of the Electric Power Research Institute (EPRI) proprietary report, BWR Vessel and Internals Project, Technical Basis for Part Circumference Weld Overlay Repair of Vessel Internal Core Spray Piping (BWRVIP-34), dated May 1997. This report was submitted for NRC staff review and approval by letter dated May 22, 1997, and supplemented by letters dated March 30, 1998, November 1, 2004, and July 18, 2006. The BWRVIP also submitted the non-proprietary version of this report by letter dated May 22, 1997.

The BWRVIP-34 report provides a generic weld repair concept that includes design basis and design requirements for a part circumference weld overlay repair for internal core spray piping; the technical basis and methodology for evaluation of core spray leakage when part circumference overlay repairs are applied; the materials and welding qualification performed to demonstrate this repair technique; and the evaluation performed to confirm the inspectability of part circumference overlay repairs.

The NRC staff has reviewed your submittal and the staffs safety evaluation is attached.

The staff requests that the BWRVIP submit the-A version of the BWRVIP-34 report within 180 days of receipt of this letter. Please contact John Honcharik of my staff at (301) 415-1157 if you have any further questions regarding this subject.

Sincerely,

/RA/

Matthew A. Mitchell, Chief Vessels & Internals Integrity Branch Division of Component Integrity Office of Nuclear Reactor Regulation

Enclosure:

Safety Evaluation cc: BWRVIP Service List

June 27, 2007 Rick Libra, BWRVIP Chairman DTE Energy Fermi Nuclear Plant (M/S 280 OBA) 6400 N. Dixie Highway Newport, MI 48166-9726

SUBJECT:

SAFETY EVALUATION OF PROPRIETARY EPRI REPORT, BWR VESSEL AND INTERNALS PROJECT, TECHNICAL BASIS FOR PART CIRCUMFERENCE WELD OVERLAY REPAIR OF VESSEL INTERNAL CORE SPRAY PIPING (BWRVIP-34)

Dear Mr. Libra:

The Nuclear Regulatory Commission (NRC) staff has completed its review of the Electric Power Research Institute (EPRI) proprietary report, BWR Vessel and Internals Project, Technical Basis for Part Circumference Weld Overlay Repair of Vessel Internal Core Spray Piping (BWRVIP-34), dated May 1997. This report was submitted for NRC staff review and approval by letter dated May 22, 1997, and supplemented by letters dated March 30, 1998, November 1, 2004, and July 18, 2006. The BWRVIP also submitted the non-proprietary version of this report by letter dated May 22, 1997.

The BWRVIP-34 report provides a generic weld repair concept that includes design basis and design requirements for a part circumference weld overlay repair for internal core spray piping; the technical basis and methodology for evaluation of core spray leakage when part circumference overlay repairs are applied; the materials and welding qualification performed to demonstrate this repair technique; and the evaluation performed to confirm the inspectability of part circumference overlay repairs.

The NRC staff has reviewed your submittal and the staffs safety evaluation is attached.

The staff requests that the BWRVIP submit the -A version of the BWRVIP-34 report within 180 days of receipt of this letter. Please contact John Honcharik of my staff at (301) 415-1157 if you have any further questions regarding this subject.

Sincerely,

/RA/

Matthew A. Mitchell, Chief Vessels & Internals Integrity Branch Division of Component Integrity Office of Nuclear Reactor Regulation

Enclosure:

Safety Evaluation cc: BWRVIP Service List DISTRIBUTION:

DCI R/F PPatnaik AValentine CMoyer WCullen JWhite, RI

GHopper, RII DHills, RIII WJones, RIV ADAMS ACCESSION NO.: ML071790313 OFFICE DCI/CVIB DCI/CVIB DD/DCI NAME JHoncharik MMitchell WBateman DATE 6/14/2007 6/15/2007 6/27/2007 OFFICIAL RECORD COPY

cc:

Randy Stark, EPRI BWRVIP Integration Manager Raj Pathania, EPRI BWRVIP Mitigation Manager Ken Wolfe, EPRI BWRVIP Repair Manager Larry Steinert, EPRI BWRVIP Electric Power Research Institute P.O. Box 10412 3420 Hillview Ave.

Palo Alto, CA 94303 Paul J. Davison BWRVIP Executive Oversight Committee PSEG Nuclear, LLC Salem/Hope Creek Nuclear Station 11 Yubas Ave.

Burlington, NJ 08016 Bob Geier, Technical Chairman BWRVIP Assessment Committee Exelon Corporation Cornerstone II at Cantera 4300 Winfield Rd.

Warrenville, IL 60555 Denver Atwood, Technical Chairman BWRVIP Repair Focus Group Southern Nuclear Operating Co.

Post Office Box 1295 40 Inverness Center Parkway (M/S B031)

Birmingham, AL 35242-4809 Jeff Goldstein, Technical Chairman BWRVIP Mitigation Committee Entergy Nuclear NE 440 Hamilton Ave. (M/S K-WPO-11c)

White Plains, NY 10601 Charles J. Wirtz, Chairman Technical Chairman BWRVIP Integration Committee FirstEnergy Corp.

Perry Nuclear Power Plant (M/S A250) 10 Center Road Perry, OH 44081 Amir Shahkarami, Executive Chairman BWRVIP Integration Committee Exelon Corporation Cornerstone II at Cantera 4300 Winfield Rd.

Warrenville, IL 60555-4012 Robert Carter, EPRI BWRVIP Assessment Manager Jeff Landrum, EPRI BWRVIP Inspection Manager EPRI NDE Center P.O. Box 217097 1300 W. T. Harris Blvd.

Charlotte, NC 28221 Richard Anderson, Executive Chairman BWRVIP Assessment Committee Vice President, Nuclear FirstEnergy Service Co.

Perry Nuclear Power Plant (M/S A-PY-290) 10 Center Road Perry, OH 44081 Joe Donahue BWRVIP Executive Oversight Committee V. P., Nuclear Engineering & Services Progress Energy, Inc.

410 S. Wilmington St. (M/S PEB6)

Raleigh, NC 27601-1849 Dennis Madison BWRVIP Executive Oversight Committee Site Vice President Southern Nuclear Operating Co.

Edwin I. Hatch Nuclear Plant US Hwy 1 N Baxley, GA 31515-2010

U. S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION SAFETY EVALUATION OF EPRI PROPRIETARY REPORT TR-108198 BWRVIP VESSEL AND INTERNALS PROJECT, TECHNICAL BASIS FOR PART CIRCUMFERENCE WELD OVERLAY REPAIR OF VESSEL INTERNAL CORE SPRAY PIPING (BWRVIP-34)

1.0 INTRODUCTION

1.1 Background

By letter dated May 22, 1997, the Boiling Water Reactor Vessel and Internals Project (BWRVIP) submitted for staff review and approval the Electric Power Research Institute (EPRI) proprietary and non-proprietary versions of Report TR-108198, BWR Vessel and Internals Project, Technical Basis For Part Circumference Weld Overlay Repair of Vessel Internal Core Spray Piping (BWRVIP-34), dated May 1997. It was supplemented by letters dated March 30, 1998, November 1, 2004, and July 18, 2006, in response to the staffs request for additional information (RAI) by letters dated December 14, 1997, October 7, 2004, and March 16, 2006, respectively. The BWRVIP-34 report provides a generic weld repair concept that includes design basis and design requirements for a part circumference weld overlay repair for internal core spray piping; the technical basis and methodology for evaluation of core spray leakage when part circumference overlay repairs are applied; the materials and welding qualification performed to demonstrate this repair technique; and the evaluation performed to confirm the inspectability of part circumference overlay repairs.

The BWRVIP-34 report was submitted as a means of exchanging information with the staff for the purpose of supporting generic regulatory improvements related to the repair of core spray piping. The review of this report was suspended in 1998 due to the staffs concerns related to weldability of irradiated piping. The BWRVIP has since developed guidance for performing weld repairs on irradiated piping, as documented in Guidelines for Performing Weld Repairs to Irradiated BWR Internals (BWRVIP-97), November 2001. The staff is currently reviewing BWRVIP-97. Therefore, all applicable information, guidance, and discussions of weldability of irradiated materials previously mentioned in the BWRVIP-34 report will be addressed during the review of BWRVIP-97.

1.2 Purpose The staff reviewed the BWRVIP-34 report to determine whether it will provide an acceptable technical justification for the repair of the subject safety-related reactor vessel (RV) internal components. The proposed repair follows the American Society of Mechanical Engineers (ASME) Code Case N-504, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1. The review assessed the design objectives, structural evaluation, system evaluation, materials, fabrication and installation considerations, as well as inspection and testing requirements.

ENCLOSURE 1.3 Organization of this Report Because the BWRVIP-34 report is proprietary, this safety evaluation (SE) was written to not repeat proprietary information contained in the report. The staff does not discuss, in any detail, the provisions of the guidelines or the parts of the guidelines which it finds acceptable. A brief summary of the contents of the subject report is given in Section 2 of this SE, with the evaluation presented in Section 3. The conclusions are summarized in Section 4.

The presentation of the evaluation is structured according to the organization of the BWRVIP-34 report.

2.0

SUMMARY

OF BWRVIP-34 REPORT The BWRVIP-34 report addresses the following topics in this order:

Component Descriptions and Typical System Configurations - Identifies welds that are considered candidates for underwater part circumferential weld overlay repairs and provides drawings of the configurations of typical core spray internal piping.

Weld Overlay Design Basis - Defines assumptions, criteria and the methodology for performing the underwater part circumferential weld overlay piping.

Leakage Calculation for Part Circumference Weld Overlays - Specifies the methodology to be used to determine leakage through the unrepaired cracks in the part circumferential weld overlay repairs during normal and accident conditions.

Irradiation Effects on Weldability - Discusses the effects of helium content in the material to be welded, and the effect that boron impurities (which transmutates under high radiation flux to produce helium) in the base material have on weldability. It should be noted that based on the development of BWRVIP-97, which addresses weldability of irradiated materials, all discussions and guidance on this issue will be addressed in BWRVIP-97.

Materials and Welding Qualification - Describes the welding materials and processes used, stress corrosion and sensitization tests to be performed, and evaluations of ferrite levels and mechanical properties to be performed prior to installing the part circumferential weld overlay repairs.

Inspection of Core Spray Internal Piping Weld Overlays - Reviews the inspection requirements detailed in the latest revision of BWRVIP-03, Reactor Pressure Vessel and Internals Examination Guidelines.

3.0 STAFF EVALUATION Core spray line/sparger cracking due to intergranular stress corrosion cracking (IGSCC) was first detected in 1978 during routine in-vessel visual examinations. The staff issued Bulletin 80-13, Cracking in Core Spray Spargers, dated May 12, 1980, which required augmented inspections of the core spray lines/spargers to detect cracking. BWR licensees have been performing these augmented inspections, and have continued to find cracking in the core spray lines/spargers. Licensees have repaired or replaced the cracked core spray components.

The repair options have been limited to installation of welded straps or specially designed clamps. The industry finds the current repair/replacement options economically viable for planned repair or replacement. However, these options, when utilized as a contingency repair, can have economic disadvantages. A plant owner must commit to a potential repair for planning purposes, or accept the risk of a significant outage extension if cracking that requires repair is discovered prior to startup. In response to these concerns, the BWRVIP repair committee has proposed weld overlay repairs that would have a significant economic advantage as a contingency repair.

3.1 Section 2.0 - Components Description and Typical System Configurations This section identifies the welds on the internal core spray piping that are accessible for underwater, part circumferential weld repair. The welds that are considered accessible and within the scope of this report include welds P2, P3, P4a, P4B, P4c, P4d, P5, P6 P7, P8a and P8b as defined in Figure 2-1 of the BWRVIP-34 report. There are certain plant-specific differences in geometry of the core spray piping and in clearances between the piping and major components, i.e., the RV and core shroud. These plant-specific differences are likely to be inconsequential as far as the development of a generic weld repair concept. The report, instead of considering these plant-specific differences, considered the core spray piping geometry at one specific plant as a common geometry. Therefore, BWRVIP-34 requires that the differences in clearances must be addressed on a plant-specific basis while implementing the weld repair concept presented in this report. The staff finds this section adequately describes the applicable locations that are accessible for this type of weld repair, and that plant-specific clearances must be addressed on a plant-specific basis because these clearances play a role in determining the thickness and length of a part circumference weld overlay as discussed in Section 3 of the BWRVIP-34 report.

3.2 Section 3.0 - Weld Overlay Design The design of the core spray piping weld overlay repairs is restricted by the space limitations of the piping being located close to the RV wall or the core shroud, thereby necessitating a partial weld overlay with less than 360 degrees around the circumference of the pipe. Due to this limited access, the part circumference (less than 360 degrees) weld overlay repair has to be designed to have the required structural capability for repairing an assumed 360 degree crack around the circumference of the pipe. The design of the weld overlay repair is intended to meet the BWRVIP core spray design criteria in BWRVIP-19 report, Internal Core Spray Piping and Sparger Repair Design Criteria, and is based on the guidance in the ASME Code and Code Case N-504.

In response to the staffs Supplemental RAI 3-1 in the October 7, 2004, letter and other RAIs, the BWRVIP provided a general statement in its letter dated July 18, 2006, to address the staff's concern about compliance with the current editions of the ASME Code and associated Code Cases approved by the staff. The BWRVIP agreed to modify the BWRVIP-34 report to include a preamble to ensure the overlay design will be in accordance with the current NRC-approved version of the ASME Code and Code Cases. The staff finds adding this preamble acceptable because it ensures that the overlay design will be in accordance with the current NRC-approved version of the ASME Code and Code Cases. In addition, the preamble includes guidance for the use of the Z-factor (correction factor-Z that is used as a stress multiplier for welds fabricated using flux) as appropriate, considerations for designing the length of the overlay repair, evaluation of the effects of residual stresses and water backing, evaluation of the effects of the weld overlay on other welds and components, and the inclusion of a maximum limit on ferrite content (maximum ferrite number (FN) of 12 FN). These other aspects of the preamble have been found acceptable and will be discussed later in the SE.

The following is the preamble which will be included in the BWRVIP-34 report.

The design analysis documented in this report was developed in 1997 and is generally consistent with Section XI of the ASME Boiler and Pressure Vessel Code (Code) in place at that time. Since that time, a number of changes have been made to the Code which will affect some of the details in the analyses. While the general design principles documented in the report are still valid, any analyses used in the design of core spray weld overlay repairs shall be in accordance with the latest Edition and Addenda of the ASME Code including Section IX and Section XI as identified in the Owners ISI Inspection Plan and with applicable Code Cases (e.g., N-516 and N-504-2) that are endorsed in Regulatory Guide 1.147. Further, Code Cases N-504-2 and N-516 are referenced throughout this report. The reader should understand that these Cases have since been revised and, in part, incorporated into Section XI. The reader must use the requirements of, and the Cases applicable to, the Edition and Addenda of Section XI identified in the Owners ISI Inspection Plan.

Section 3.2 includes an example where the design approach used in the report differs from the Code requirements. The analysis in Section 3.2 does not incorporate a Z-factor correction as required by the Code for flux welds such as SMAW and FCAW welds. However, any future design would need to include that correction should the applicable Code so require.

Also note that, in applying Code Case N-504-2, special care must be taken in designing the length of the weld overlay repair for each application taking into account both fatigue and IGSCC considerations. The minimum required length of the part-circumference weld overlay is to be determined by analytical demonstration of the effective transfer of longitudinal loads across the defect location by means of shear load transfer between the base metal and the weld overlay material. Code Case N-504-2 does not explicitly define methods for demonstrating that such transfer is adequate to meet applicable Code requirements.

In addition, note that Code Case N-504-2 implements the requirements of NUREG-0313, Rev. 2 and Generic Letter (GL) 88-01. Code Case N-504-2 paragraphs (g) (1), (2) and (3) address the effects of residual stresses in the repair welds, and the effects of water backing in the repaired welds and the effects of the weld overlay on other welds, components, supports, restraints, etc., in the system. Increases in loadings due to weight and shrinkage effects are addressed.

Finally note that, in response to an NRC RAI, the BWRVIP has agreed that the delta ferrite content of weld overlay material for this application shall not exceed 12 FN.

To assure the structural integrity of the core spray system, Section 3.0 of BWRVIP-34 presented methods for determining the thickness and length of part circumference weld overlays fabricated using the automatic flux cored arc welding (FCAW) and the manual shielded metal arc welding (SMAW) processes. The FCAW process produces high toughness welds as demonstrated in Appendix H of the BWRVIP-34 report, whereas the SMAW process produces lower toughness welds as illustrated in Appendix I of the report.

For the FCAW weld overlay, the BWRVIP-34 report provided a methodology and an example analysis using this methodology. The methodology used is based on the structural strength of the overlay using a net section plastic collapse methodology similar to that provided in Appendix C of Section XI to the ASME Code. This method considers only membrane and bending stresses acting on the pipe and not secondary stresses such as expansion stresses.

Secondary stresses were not included in the analysis because, for high toughness material, plastic collapse is the anticipated failure mechanism and the secondary stresses are assumed to relax before failure. The example analysis uses a safety factor of 2.77 on primary loads for normal operating and upset conditions, and a safety factor of 1.39 for emergency and faulted conditions. The staff finds the application of the net section plastic collapse methodology for determining the thickness of the FCAW weld overlay acceptable because it is based on the methodology in Appendix C of Section XI to the ASME Code (current edition of ASME Code approved by the staff, as stated in the revised preamble).

The flaw evaluation methodology for piping described in Appendix C of Section XI to the ASME Code does not require the use of a Z-factor for gas tungsten arc welds and gas metal arc welds because these welds are fabricated without the use of flux. However, the FCAW process uses flux in the fabrication of welds. The composition of the flux varies from one heat/lot to another and has a significant effect on the notch toughness values of the weld metal. In the staffs October 7, 2004, letter, Supplementary RAI 3-1(b) requested the BWRVIP to provide the justification for not using the Z-factor approach for FCAW welds in the flaw evaluation methodology. In response, the BWRVIPs letter dated November 1, 2004, referred to the proposed preamble and stated that all welding activities including weld design will be in accordance with the ASME Code or with ASME Code cases N-516 and N-504-2, as appropriate. However, instead of following the current version of the ASME Code and using the Z-factor approach for FCAW welds, the analysis in the BWRVIP-34 report took some exceptions to the ASME Code based on the fact that measured material properties exceeded the strength parameters assumed by the ASME Code. In a letter dated March 16, 2006, the staff issued Supplementary RAI 3-4 requesting the BWRVIP to provide further justification for why the Z-factor approach is not needed for the welds fabricated using flux. The staff requested that the justification include the strength parameters assumed by the ASME Code and the measured material properties, including their reliability and applicability. In a letter dated July 18, 2006, the BWRVIP responded that designs of overlays should incorporate a Z-factor if it is required by the current ASME Code. To further clarify the issue, the BWRVIP included a statement concerning the use of the Z-factor in the revised preamble to the report proposed earlier in response to Supplementary RAI 3-1 and other RAIs. The revised preamble is presented in the beginning of Section 3.2 of this SE where the response to Supplementary RAI 3-1 is evaluated. The staff finds the response acceptable because it ensures that the current version of ASME Code will be followed in the design of part circumferential weld overlay repair of core spray piping.

For the SMAW weld overlay, the BWRVIP-34 report provided a similar methodology and an example analysis. The methodology used is also based on the structural strength of the overlay using a net section plastic collapse methodology. However, the staff notes that for the SMAW weld overlay, the anticipated failure mechanism is unstable crack extension that would occur at loads lower than the plastic collapse loads. Therefore, the low toughness SMAW welds should be analyzed by elastic-plastic fracture mechanics methodology. However, these welds can be analyzed by the net section plastic collapse methodology with appropriate correction factors applied. The BWRVIP uses the Z-factor correction approach specified in Appendix C of Section XI to the ASME Code. The technical basis for this approach is discussed in Reference 9 of the BWRVIP-34 report (Reference 5.1 of this SE). Since failure of a SMAW weld overlay is anticipated to occur at lower overall strain levels, secondary stresses such as expansion stresses may not be relaxed and have to be included in the analysis.

The BWRVIP-34 report includes expansion stresses with a safety factor of 1.0 along with the primary membrane and bending stresses, and the associated safety factors mentioned in the preceding paragraph. This analysis approach is similar to the methodology in Appendix C of Section XI to the ASME Code. The correction factor (Z) is introduced as a stress multiplier.

For the SMAW weld, Z = 1.15{1 + 0.013(pipe OD - 4)}.

Reference 5.1 made two modifications to the above-mentioned Z-factor approach based on NRC staff comments: (a) the allowable flaw depth should be limited to 60% of the wall thickness, and (b) the Z-factor should be computed using pipe outside diameter (OD) = 24 inches for pipe sizes less than 24 inches. The second modification was intended to account for uncertainties in determining the thermal expansion stresses for smaller pipe sizes. With these modifications, the Z-factor for a 6-inch core spray pipe would be 1.45 instead of 1.2 as reported in Section 3.2 of the BWRVIP-34 report. In the staffs October 7, 2004, letter, Supplementary RAI 3-1(a) requested that the BWRVIP should explain why these two modifications to the Z-factor are not included in the design for the SMAW weld overlay. In response, the BWRVIP stated that when applying these repairs, the Z-factor will be per Section XI of the then currently approved ASME Code. The staff finds this response acceptable because it ensures the use of Z-factors will be in accordance with the then current NRC approved version of the ASME Code, specifically Appendix C of Section XI (which accounts for the modifications to the Z-factor).

The staff also notes that Z-factors used in the BWRVIP-34 report is consistent with the 1998 Edition of the ASME Code.

On Page 3-4 of the BWRVIP-34 report, stress-ratio (SR) is defined as (Pm + Pb + Pe /SF)/Sm, where Pm is the primary membrane stress, Pb is the primary bending stress, Pe is the expansion stress, SF is the safety factor and Sm is the design stress intensity at temperature.

However, this SR is different from SR of (Pm + Pb)/Sm resulting from a series of derivations shown on Page 3-5 of the BWRVIP-34 report. In a letter dated October 7, 2004, the staff requested in Supplementary RAI 3-1(c) that the BWRVIP confirm that the design tables (Tables 3-1 to 3-4) for the weld overlay repair were obtained by employing (Pm + Pb)/Sm without considering the Z-factor of Appendix C of Section XI of the ASME Code. In response, the BWRVIP confirmed that the design tables in the report were developed without considering the Z-factor, but that future repair designs will be in accordance with the current NRC-approved Code Editions. In a letter dated March 16, 2006, the staff issued Supplementary RAI 3-5 suggesting that BWRVIP include this response to Supplementary RAI 3-1(c) in Section 3.3 of the report. In a letter dated July 18, 2006, the BWRVIP response stated that it agrees with the staff suggestion, and proposed to add the following paragraph at the end of Section 3.2 of the BWRVIP-34 report:

Note that while the example analysis included here does not incorporate a Z-factor based on the assumption of high toughness weld metal, any repair design utilizing the methods described in this report should incorporate Z-factor if required by the Owners Edition and Addenda of Section XI as limited by 10 CFR 50.55a. In general, for an SMAW or FCAW overlay, a Z-factor correction would be required.

The staff finds the response acceptable because it ensures that Z-factor will be used if required by the applicable version of the ASME Code.

In Section 3.0, the weld overlay design did not consider the effect of IGSCC on the structural integrity of the repair for the case where the weld overlay is applied to a through-wall flaw, nor did it consider the effect of fatigue crack growth on the structural integrity of the repair for the case where the weld overlay is applied to a surface flaw. In the staffs October 7, 2004, letter, Supplementary RAI 3-1(d) requested that the BWRVIP revise the report to include information regarding (1) the recommended level of inspection effort in classifying a flaw as a through-wall flaw or a surface flaw, and (2) the additional weld overlay thickness to account for IGSCC and fatigue crack growth for through-wall and surface flaws. In its letter dated November 1, 2004, the BWRVIP response stated that no additional thickness is required to account for IGSCC because the overlay weld is fabricated from austenitic stainless steel having low carbon content (0.02 wt% max) and minimum FN value of 7.5. The staff finds this response acceptable because field experience has shown that such weld material is resistant to IGSCC. It should be noted that the BWRVIP proposed a FN range of 7.5 to 12, which provides sufficient delta ferrite content to minimize IGSCC, but limits the delta ferrite to prevent thermal aging of the stainless steel. Therefore, no additional inspection effort is warranted as far as IGSCC growth is concerned. However, through-wall and surface flaws may grow by fatigue and detailed flaw characterization would be required. Thus, fatigue crack growth would warrant additional inspection effort. The staffs concern about fatigue crack growth and inspection has been addressed by the revised preamble to the report submitted in the BWRVIP letter dated July 18, 2006. The revised preamble stated that Code Cases N-504-2 and N-516 that are endorsed in Regulatory Guide 1.147 (RG) will be followed in the design of part circumference weld overlay repair of core spray piping. Code Case N-504-2 requires the licensee to consider potential flaw growth due to fatigue and identifies the specific nondestructive examination of the repair. Therefore, the staff finds that its concern about fatigue cracking of the repair is satisfactorily addressed.

In Section 3.0, it is not clear that the determination of the required weld overlay length, according to the formula presented on Page 3-8 of the BWRVIP-34 report, is appropriate to ensure shear transfer between the weld overlay and the piping. Therefore, in the staffs letters dated October 7, 2004, and March 16, 2006, Supplementary RAI 3-1(e) and Supplementary RAI 3-6, respectively, requested the BWRVIP to provide additional information on why the determination of the required weld overlay length is appropriate to ensure shear transfer between the overlay and the piping. The BWRVIP letters dated November 1, 2004, and July 18, 2006, stated that neither Code Case N-504-2 nor Section XI of the ASME Code explicitly address the manner in which shear transfer is calculated. However, the BWRVIP provided the following explanation for how shear was accounted for in the example calculation in the BWRVIP-34 report:

The lengths calculated by the methods shown on page 3-8 were determined based upon net section collapse methods as included in Appendix C of ASME Section XI.

The assumed membrane stress was taken as 0.1 Sm rather than 0.5 Sm however, based upon analysis results of internal/external pressure differential magnitude. This pressure stress magnitude is very small (a few hundred psi). The length is also a function of overlay length in the circumferential direction (angle of coverage), and of the underlying wall thickness. Length is calculated for each side of the weld (considering the radius and wall thickness on each side of a repair location), and for both levels A/B and C/D conditions. The more conservative result is used. It should also be noted that the flow stress in shear is 1/2 of the flow stress in tension, and this effect is included in the calculation.

The staff finds the BWRVIP explanation adequate in accounting for shear in the example calculation presented in the BWRVIP-34 report. In addition, the staff notes that based on the response to Supplementary RAI 3-5 in BWRVIP letter dated July 18, 2006, the BWRVIP-34 report would also require the use of Z-factor correction in determining the overlay length as required by the ASME Code. Therefore, the staff finds the BWRVIP methodology on accounting for shear transfer acceptable. The BWRVIP has also included an appropriate discussion in the revised preamble to the BWRVIP-34 report to ensure that shear is adequately addressed in core spray weld overlay designs. The preamble is presented at the beginning of Section 3.2 of this SE.

The weld overlay design methodology presented in the BWRVIP-34 report follows the requirements of ASME Section XI Code Case N-504, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1, April 30, 1992. However, according to USNRC RG 1.147, Revision 13, dated June 2003, the NRC-approved Code Case N-504-2, dated March 1997, supersedes Code Case N-504. The following is a discussion on how the weld overlay design satisfies the requirements of Code Case N-504-2.

a.

Requirement (g)(2) of Code Case N-504-2 states For repaired welds, the evaluation shall consider residual stresses produced by the weld overlay with other applied loads on the system. The evaluation shall demonstrate that the requirements of IWB-3640 are satisfied for the design life of the repair, considering potential flaw growth due to fatigue and IGSCC. In the staffs letter dated October 7, 2004, Supplementary RAI 3-2(a) requested the BWRVIP to provide an equivalent evaluation for weld overlay repairs of the internal core spray piping. The evaluation should include weld overlay design on a pipe/coupling weld joint. In response, the BWRVIP letter dated November 1, 2004, stated that all repairs will be performed in accordance with the currently-approved ASME Code or with Code Cases N-516 or N-504-2, as appropriate.

The staff finds the response acceptable because the licensee will be performing this evaluation at the time of the weld overlay repair.

b.

Requirement (g)(3) of ASME Section XI Code Case N-504-2 states The evaluation of other welds and components in the system [i.e., internal core spray system] shall consider potential increases in loading, including shrinkage effects, due to all weld overlays in the system, and shall identify and record the magnitude and location of the maximum shrinkage stress developed. These welds and components shall meet the applicable stress limits of the Construction Code [Section III to the ASME Code]. In the staffs letter dated October 7, 2004, Supplementary RAI 3-2(b) requested the BWRVIP to provide the maximum shrinkage stress produced due to weld overlay repair, and ensure that welds and components of the common internal core spray system meet the applicable stress limits of Section III to the ASME Code. In response, the BWRVIP stated that the maximum shrinkage stress is determined by evaluation of actual repair configuration, the measured shrinkage, number of repairs applied to a specific piping system, and the actual configuration of the repaired piping system. The BWRVIP further stated that the evaluation of the shrinkage stress will be performed after repair application as required by Supplement 1 of GL 88-01. The staff finds the response acceptable because the licensee will be estimating the maximum shrinkage stress after the actual weld overlay repair. Additionally, in a letter dated July 18, 2006, the BWRVIP stated that it will include the consideration of potential increases in loading, including the evaluation of shrinkage stresses in the preamble to the BWRVIP-34 report.

The preamble is presented at the beginning of Section 3.2 of this SE, which the staff found acceptable.

Based on the above evaluation, the weld overlay design will include the requirements of Code Case N-504-2 during the licensees implementation of the BWRVIP-34 weld overlay repair.

Section 3.1.2, Design Criteria, of the BWRVIP-34 report mentions that the length of an overlay is determined by requiring that the stresses in the overlay meet the net section plastic collapse requirements for shear transfer between the overlay and the piping. In the staffs letter dated December 14, 1997, RAI 1 recommended that the inspectability of defects in the base metal be considered in designing the length of an overlay. The length of an overlay should be large enough so that the growth of the defects in the base metal heat-affected zones can be adequately monitored to ensure that cracking will not affect the integrity of the overlay.

In response to RAI 1, in a letter dated March 30, 1998, the BWRVIP stated that Section 3.1.2 of BWRVIP-34 requires that the minimum length provide sufficient structural reinforcement.

However, the BWRVIP acknowledged that additional length may be required to allow for effective inspection. This additional length is determined by the specific inspection technique and process to be used, and should be determined prior to application. The BWRVIP will revise the report to reflect this additional consideration for weld overlay minimum length. The staff finds the response acceptable because it addresses an important additional criterion for determining appropriate minimum weld overlay length, and will be included in the -A version of the BWRVIP-34 report.

In the staffs letter dated December 14, 1997, RAI 10 requested that the BWRVIP describe the residual stress distribution in the overlay weld and the cracked piping, particularly at the inside diameter (ID) surface of the pipe, and at the root of the overlay/seal weld adjacent to a through-wall crack. Compressive residual stresses on the ID surface of the component are desirable in resisting crack initiation and growth, and are recommended in NUREG-0313, Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping, Revision 2, January 1988. In its letter dated March 30, 1998, the BWRVIPs response stated that the residual stresses at the inside surface of the uncracked ligament will depend strongly on the extent of the part circumference repair, which is a variable in this technique. The design basis for this repair is that the underlying crack extends entirely around the circumference and is completely through the pipe wall. This is consistent with the standard design basis in Section 4 of NRC NUREG-0313, Revision 2. The BWRVIP concluded that, for this design basis, residual stresses at the inside surface are not relevant, and were not determined since an open crack is assumed at the inside surface.

The BWRVIP further stated that at the interface between the base metal and the weld overlay material, the residual stresses in the overlay material are expected to be tensile unless the overlay is very thick. Since the overlay repair itself is part circumference in extent, the residual stress distribution within the weld metal and at the interface between the weld metal and base metal is expected to vary with position, reflecting the asymmetry of the repair. No credit for any residual stress improvement is taken in the design basis for such repairs. Demonstration of IGSCC resistance is tied to the material properties of the weld metal.

The staff considers the residual stresses on the inside surface to be relevant because a crevice may be present under the weld overlay. Field experience indicates that IGSCC can initiate at a crevice even though the material is not sensitized. In the staffs letter dated October 7, 2004, Supplementary RAI 3-3(a) requested the BWRVIP to provide the residual stresses at the inside surface of core spray piping to be repaired by a weld overlay. In its letter dated November 1, 2004, the BWRVIPs response stated that the residual stresses developed on the inside surface due to the weld overlay application will depend on the extent of the overlay around the circumference, and the residual stresses will be developed per the requirements of Code Case N-504-2 on a component-specific, repair-specific basis. The staff finds the response acceptable because the licensee will be estimating the residual stresses at the time of the actual weld overlay repair in accordance with the applicable Code Case.

In the staffs letter dated October 7, 2004, Supplementary RAIs 3-3(b) and (c) requested the BWRVIP to discuss whether any crevices may be introduced on the outside surface of the repaired core spray piping along the periphery of the weld overlay. Since IGSCC can be enhanced due to the presence of any crevice, the staff also requested that the BWRVIP provide an explanation for not performing crevice corrosion tests on weld coupons with a simulated crevice condition. In its letter dated November 1, 2004, the BWRVIPs response stated that crevices may form on the OD surface of the repaired core spray piping along the periphery of the weld overlay, but any IGSCC will be arrested at the structural overlay interface with the core spray pipe due to the high IGSCC resistance of the overlay material. The staff acknowledges that the overlay weld material is required to have low carbon and adequate ferrite contents and, therefore, it is IGSCC resistant. However, IGSCC could initiate at a crevice if residual tensile stresses are present and penetrate the core spray piping wall, away from the repaired crack location, without entering the structural overlay. In other words, the weld overlay repair could introduce new IGSCC-susceptible locations in the core spray piping.

In a letter dated March 16, 2006, the staff issued Supplementary RAI 3-8 requesting the BWRVIP to evaluate the possibility of cracking of core spray piping at IGSCC-susceptible locations (i.e., weld overlay periphery) introduced by the weld overlay repair. In its letter dated July 18, 2006, the BWRVIP agreed with the staff that if a crevice were formed due to poor weld fusion or undercut at the weld overlay periphery, the IGSCC-susceptibility of the piping would be increased. However, the BWRVIP noted that workmanship standards of Sections XI and III of the ASME Code do not allow for lack of fusion or cracks and limit undercut to no greater than 1/32-inch. These standards effectively eliminate the creation of a crevice at the weld toe.

The BWRVIP further stated that while crevices at weld toes are not expected to occur, the Core Spray Repair Design Criteria in BWRVIP-19-A require that the repair designer specify periodic inspections of the repair that are consistent with the intent of BWRVIP-18-A, BWR Core Spray Internals Inspection and Flaw Evaluation Guidelines. These inspections would periodically interrogate the overlays and would detect any cracking in a timely manner. To ensure that the area of interest is addressed properly, the BWRVIP proposed to add the following paragraph to Section 7 (Inspection of Core Spray Internal Piping Weld Overlays) of the BWRVIP-34 report:

In accordance with BWRVIP-19-A (Internal Core Spray Piping and Sparger Repair Design Criteria), the repair designer is responsible for specifying inspections of the weld overlay repair consistent with the intent of BWRVIP-18-A (BWR Core Spray Internals Inspection and Flaw Evaluation Guidelines). In defining these inspections, specific consideration should be given to the possibility of crack initiation in any crevice-like areas that may be created at the periphery of the overlay due to weld undercut. Cracks initiated at these locations may be difficult to detect using visual techniques and ultrasonic inspection may be required. In the event that UT is chosen for future, periodic inspections, it may be useful to perform a baseline UT inspection immediately subsequent to installation of the repair.

The staff finds the BWRVIP response acceptable because the proposed paragraph does include adequate guidance for inspecting IGSCC-susceptible locations resulting from weld overlay repairs of core spray piping. The BWRVIP shall include this paragraph in the -A version of the BWRVIP-34 report as suggested.

In addition to the extent of the part circumference weld overlay repair, residual stresses also depend on the underwater welding procedure used. Since the residual stresses produced by underwater welding are different from those produced by in-air welding, the staff, in its letter dated October 7, 2004, issued Supplementary RAI 3-3d requesting that the BWRVIP consider the underwater welding process when determining the residual stress distribution. In its letter dated November 1, 2004, the BWRVIPs response stated that underwater welding will slightly affect the residual stresses, and therefore the staffs concern about underwater welding and residual stress will be addressed by the revised preamble to the report. The revised preamble stated that Code Cases N-516 and N-504-2 will be followed for underwater welding and residual stress determination. The BWRVIP also stated that in general, OD welding with a water-solid ID and fast cooling are beneficial to producing improved ID and through-wall residual stresses.

The staff notes that OD welding with a water-solid ID is different than underwater welding of core spray piping where both ID and OD are exposed to water. However, the staff accepts the BWRVIP response because the licensee will be evaluating the residual stresses at the time of the actual weld overlay repair using Code Cases N-516 and N-504-2, and will take into consideration the effects of the core spray piping ID and OD being exposed to water during welding.

The staff finds that the BWRVIP has adequately addressed the design of the weld overlay repair by presenting acceptable methods to be used in determining the length and thickness of a part circumference weld overlay to assure the structural integrity of the core spray piping system.

3.3 Section 4.0 - Leakage Calculation for Part Circumference Weld Overlay The BWRVIP-34 report discusses how, in some weld overlay repairs, access restrictions limit the circumferential extent of the repair to less than 360-degrees. Because the repair extends around only a part of the circumference, some portion of the original component is assumed to be left with a through-wall crack through which some amount of core spray flow could leak into the annulus, thus removing such leakage flow from the emergency core cooling system (ECCS) capacity of the system. A method for predicting the magnitude of such leakage was developed to allow plants to evaluate the ECCS penalty that they would have to take if such repairs were applied.

The BWRVIP-34 report provides guidance on core spray leakage calculation methods and leakage assessment criteria for the core spray piping and the core spray spargers. Utilities have been performing leakage rate calculations by either using standard fluid equations or developing computer programs. The guidance on leak rate calculation methods provided in the BWRVIP-34 report is based on the EPRI Pipe Crack Evaluation Computer Program. This guidance does not differ from common industry practice.

The staff notes that the amount of leakage calculated is plant-specific and includes leakage from the T-box vent hole, the thermal sleeve and nozzle safe end ID slip fit, and unrepaired and repaired flaws. The staff believes that all leakage should be considered in the loss of coolant accident (LOCA) analysis and evaluated for plant-specific acceptability. The BWRVIP-34 report provides examples of evaluating total system leakage for normal and accident operations. Both examples stress the importance of performing plant-specific LOCA analyses to demonstrate that the total leakage from the core spray line does not cause unacceptable increases in peak cladding temperature for any licensing basis accident. The staff finds this guidance acceptable because it demonstrates a comprehensive approach for consideration of total system leakage.

3.4 Section 5.0 - Irradiation Effects on Weldability Section 5 discusses irradiation effects on the weldability of the internal core spray piping based on on-going work sponsored by the BWRVIP. The BWRVIP has developed guidance for performing weld repairs on highly irradiated materials in the form of the BWRVIP-97 report, Guidelines for Performing Weld Repairs to Irradiated BWR Internals, November 2001.

In response to the staffs RAIs on weldability of irradiated material, the BWRVIP proposed in its letter dated November 1, 2004, to replace Section 5.0 of the BWRVIP-34 report with a reference to the BWRVIP-97 report. The staff finds this appropriate since it will consolidate the guidance in one report. The staff is currently reviewing the BWRVIP-97 report. Therefore, all applicable information, guidance, and discussions of weldability of irradiated materials previously mentioned in the BWRVIP-34 report will be addressed during the review of the BWRVIP-97 report.

The following are applicable RAIs which are related to core spray partial weld overlay repair (Section 5.0 of the BWRVIP-34 report) that will be addressed during the review of BWRVIP-97, since section 5.0 of the BWRVIP-34 report will now reference the BWRVIP-97 report:

a.

Supplemental RAI 97-9 from NRC letter dated March 18, 2004, with the BWRVIP response in a letter dated July 25, 2005 b.

RAI 97-1 from NRC letter dated January 8, 2003, with the BWRVIP response in a letter dated July 25, 2005 c.

Supplemental RAI 97-10 from NRC letter dated March 18, 2004, with the BWRVIP response in a letter dated July 25, 2005 d.

Supplemental RAI-1 from NRC letter dated August 7, 2006, and the BWRVIP response in letter dated October 5, 2006 e.

Supplemental RAI 97-11 from NRC letter dated March 18, 2004, with the BWRVIP response in a letter dated July 25, 2005 f.

RAI 5-4 from NRC letter dated October 7, 2004, and the BWRVIP response in a letter dated November 1, 2004 g.

Supplemental RAI-2 from NRC letter dated August 7, 2006, and the BWRVIP response in a letter dated October 5, 2006 h.

Supplemental RAI 6-3(a) in NRC letter dated October 7, 2004, and the BWRVIP response in a letter dated November 1, 2004 i.

Supplemental RAI 7-1 from letter dated October 7, 2004, and the BWRVIP response in letters dated November 1, 2004, and July 25, 2005 (renumbered to RAI 34-7.1) j.

Supplemental RAI A-4 from NRC letter dated October 7, 2004, and the BWRVIP response in letters dated November 1, 2004, and July 25, 2005 (renumbered to RAI 34-A-4) 3.5 Section 6.0 - Materials and Welding Qualification In Section 6, the BWRVIP states that the composition of the welding electrodes has been selected with a focus on maximizing the ferrite level, and thereby maximizing the IGSCC resistance of the weld overlay. Appendix J of the BWRVIP-34 report is the recommended underwater electrode procurement specification. The acceptable range of ferrite content is specified as 8-20 ferrite number (FN) for the FCAW process and 8-25 FN for the SMAW process. Based on the results of laboratory test data, it appears that these welds, especially welds with high ferrite contents, are likely to experience the effects of low-temperature thermal aging. In its letter dated December 14, 1997, the staffs RAI 3 requested that the BWRVIP provide a discussion regarding potential degradation of the welds by low-temperature thermal aging when the ferrite content is at the high end of the specified range. The RAI also requested that the BWRVIP discuss the need to lower the maximum acceptable ferrite content of the repair welds. In its letter dated March 30, 1998, the BWRVIP response referred to the literature related to thermal aging of Grades CF-3, CF-8, and CF-8M cast stainless steels at BWR operating temperature. The staff notes that the thermal aging behavior of austenitic stainless steel weld metals is different than that of cast stainless steels [see References 5.2 and 5.3].

Unaged austenitic stainless steel weld metal has a significantly lower resistance to stable crack growth than unaged cast stainless steel. In addition, the welding process affects fracture toughness of stainless steel welds. Welds fabricated using the SMAW process have a lower fracture toughness than those made using the FCAW process as reported in Section 6.4 of the BWRVIP-34 report. Therefore, in its letter dated October 7, 2004, the staffs RAI 6-1a requested the BWRVIP to discuss low-temperature thermal aging of the SMAW welds when the ferrite content of the weld is in the range of 20-25 FN and include an evaluation of the need to lower the maximum acceptable ferrite content of the repair welds.

In its letter dated November 1, 2004, the BWRVIP refered to the Argonne National Laboratory (ANL) research results for the long-term (>100,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />) thermal aging of cast stainless steel Grades CF-3 and CF-8 at 288EC; the results showed that thermal aging is expected to produce a 50% reduction in the room temperature Charpy impact energy of materials with 10% ferrite and an 80% decrease for material with 25% ferrite. The BWRVIP further stated that because of the high initial values of room temperature impact strength of Grades CF-3 and CF-8 materials, even a large decrease in this measure of toughness does not reduce the overall toughness of the overlay repair to unsatisfactory levels. In addition, the BWRVIP proposes to modify the BWRVIP-34 report to place an upper limit of 17 FN for this underwater welding activity. The BWRVIP also states that it was difficult to produce underwater welds with a FN value above 5, and very specific chemistry requirements have been recommended for the welding electrodes to ensure that underwater weld deposits produce a FN above 5. The staff notes that with the use of the recommended electrodes, the BWRVIP appears to be successful in fabricating underwater weld deposits with FN close to 17 (see Table G-6 in the BWRVIP-34 report). The staff notes that the thermal aging results for the Grades CF-3 and CF-8 materials are not applicable to overlay weldments because the ferrite morphology and distribution in the weldments are different than that in CF-3 and CF-8 castings. In addition, unaged austenitic stainless steel weld metal, especially when welds are made using SMAW process, has a significantly lower resistance to stable crack growth than unaged cast stainless steel.

The staff provides the following discussion on the thermal aging results for Type 308 SS welds by Reference 5.3. The welds were fabricated by SMAW process with a ferrite content of 12%

by volume. The results show that aging of these welds at 343EC for 20,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> caused a significant increase in the ductile-to-brittle transition temperature measured at 68-J level, an increase from -25 to 60EC. The staff notes that the weld overlay repair will be exposed to lower temperatures (288EC). However, the proposed upper limit of 17 FN for the underwater welding activity could make the weld overlay repair susceptible to thermal aging. Therefore, in a letter dated March 16, 2006, the staff issued Supplementary RAI 6-5 requesting the BWRVIP to evaluate thermal aging of a weld overlay repair made with 17FN weld metal. In its letter dated July 18, 2006, the BWRVIP takes a conservative position of limiting the delta ferrite in the weld overlay to 12 FN instead of 17 FN. The BWRVIP has included an appropriate discussion in the revised preamble to BWRVIP-34 report to limit the delta ferrite in the weld overlay to 12FN.

The preamble is presented at the beginning of Section 3.2 of this SE. The staff finds this response acceptable because lower ferrite contents and lower operating temperature (288EC) would provide large margins against thermal aging. It should be noted that based on the responses to this and other RAIs, the BWRVIP proposed a FN range of 7.5 to 12, which provides sufficient delta ferrite content to minimize IGSCC, but limits the delta ferrite to prevent thermal aging of the stainless steel. The BWRVIP shall clarify in the -A version of the BWRVIP-34 report that the ferrite content of the weld shall be within the range of 7.5 to 12 FN.

In its letter dated October 7, 2004, the staffs supplementary RAI 6-1(b) requested that the BWRVIP discuss whether low-temperature thermal aging behavior of the SMAW welds fabricated underwater is different than those fabricated in air. In its letter dated November 1, 2004, the BWRVIP response noted that underwater welding actually suppresses the FN, primarily due to the rapid quenching and lack of time for ferrite to form. Consequently, the welds produced underwater will have less tendency than those produced in air to undergo low-temperature thermal aging. The staff agrees with the BWRVIP that since underwater welding produces a lower FN, the thermal aging susceptibility is reduced, because thermal aging susceptibility is directly proportional to FN values.

Section 6.1 of the BWRVIP-34 report includes Type 312 stainless steel weld metal in a group of materials that were selected for evaluation. This material was not referenced in Section 3.0 Weld Overlay Design Basis. In RAI 4 to its letter dated May 22, 1997, the staff requested that the BWRVIP discuss the service experience with Type 312 stainless steel weld metal in the BWR environment including its susceptibility to IGSCC. In its letter dated March 30, 1998, the BWRVIP stated that Type 312 stainless steel weld metal is a two phase micro-duplex stainless steel with nominal composition of 30% chromium (Cr), 9% nickel (Ni), and 0.15% carbon (C)

[Reference 5.4]. This alloy composition produces a two-phase weld deposit with substantial percentages of ferrite, on the order of 15-25%. The BWRVIP refered to a figure in the paper in Reference 5.5 for predicting the susceptibility of a given alloy to IGSCC in the BWR environment as a function of ferrite and carbon contents. In summary, the BWRVIP stated that the IGSCC resistance of duplex stainless steels has been studied extensively in the laboratory, in theoretical investigations, and in coupon or pipe tests. The BWRVIP also stated that these results confirm the field observations that IGSCC in duplex stainless steel weld metal or castings is rare. The BWRVIP contended that these results support the conclusion that Type 312 stainless steel weld metal can be used successfully for underwater core spray pipe weld overlays in the BWR environment. Finally, the BWRVIP stated that the report will be revised to specifically discuss Type 312 material. The staff notes that the BWRVIP does not present any laboratory test results, field experience, or performance predictions related specifically to IGSCC resistance of Type 312 weld metal. The staff reviewed Figures 5 and 6 in Reference 5.5 as suggested in the response to RAI 4, but finds that these figures may not be applicable to Type 312 stainless steel because the carbon content (0.15 wt%) of Type 312 stainless steel is more than two times the maximum carbon content (0.07 wt%) considered in that paper. In Supplementary RAI 6-2(a) to its letter dated October 7, 2004, the staff requested the BWRVIP to provide service experience with Type 312 weld metal including its susceptibility to IGSCC. In addition, in Supplementary RAI 6-2(b), the staff requested that the BWRVIP discuss the effect of low-temperature thermal aging on mechanical properties of Type 312 stainless steel welds and suggested that these properties should be considered for the design of weld overlay repair with Type 312 welds. In its letter dated November 1, 2004, the BWRVIP response stated that Type 312 SS weld metal will not be considered for the underwater weld overlay application due to its high carbon content. The staff finds the response acceptable because it eliminates its concern about aging degradation of underwater weld overlay fabricated with Type 312 weld metal. Therefore, the BWRVIP will delete any reference to Type 312 stainless steel weld metal as it applies to the use in the weld overlay repair.

As mentioned, heat input during weld repair is one of the parameters that affects cracking susceptibility of neutron-irradiated stainless steel components due to helium embrittlement.

High heat input welding processes generate high temperatures in a larger volume of the component being repaired and, therefore, would cause more cracking due to helium embrittlement as compared to low heat input processes. In Supplementary RAI 6-3(a) to its letter dated October 7, 2004, the staff requested the BWRVIP to include a recommendation for heat input for the FCAW and the SMAW weld overlay repairs in the BWRVIP-34 report. In its letter dated November 1, 2004, the BWRVIP response proposes to remove the discussion on weldability of irradiated stainless steel from the BWRVIP-34 report and refer to the BWRVIP-97 report. The staff finds the response acceptable because it will be evaluating the issue of heat input as its relates to weldability of irradiated material when it reviews the BWRVIP-97 report.

Since the heat input varies with welding position, in Supplementary RAI 6-3(b) to its letter dated October 7, 2004, the staff requested the BWRVIP to explain why no mechanical tests were performed on weld coupons fabricated using the FCAW process in the vertical (3G) position; and on SMAW weld coupons fabricated in the horizontal (2G), vertical (3G), and overhead (4G) positions at a depth of 50 feet. In its letter dated November 1, 2004, the BWRVIP response stated that all welding activities will be in accordance with Code Cases N-516 and N-504-2, as appropriate. The staff finds the response acceptable because Code Case N-516-3 requires that the wet underwater welding procedure be qualified in different welding positions at a qualified depth.

In Supplementary RAI 6-3(c) to its letter dated October 7, 2004, the staff requested the BWRVIP to explain why shrinkage values for weld test coupons that were fabricated in 2G, 3G, and 4G positions at a depth of 50 feet were not measured. In its letter dated November 1, 2004, the BWRVIP response stated that all welding activities will be in accordance with Code Cases N-516 and N-504-2, as appropriate. The staff finds the response acceptable because Code Case N-504-2 requires that shrinkage effects due to all weld overlays in the system be considered in determining the magnitude and location of the maximum shrinkage stress developed in the system being repaired.

In order to be consistent with other BWRVIP repair design procedures, such as the BWRVIP-16, Internal Core Spray Piping and Sparger Replacement Design, and BWRVIP-19 reports, the staff issued Supplementary RAI 6-4 in its letter dated October 7, 2004, recommending that the BWRVIP include the following requirements in Section 6.0, Materials and Welding Qualification, of the BWRVIP-34 report:

Repair and replacement designs for plants which are not designed and constructed in accordance with ASME Section III (and components not subject to Section XI) must meet the individual plant safety analysis report and other plant commitments for RPV internals mechanical design, as stated in Section 6. In that instance, materials must meet the requirements of ASME code cases, ASME Section II specifications, American Society for Testing and Materials (ASTM) specifications, or other material specifications that have been previously approved by the staff. Otherwise, it is recognized that a repair or replacement design that uses a material not meeting these criteria must be submitted to the NRC for approval on a plant specific basis.

In its letter dated November 1, 2004, the BWRVIP response stated that all repairs to core spray piping (including the weld overlays described in the BWRVIP-34 report) are required to be designed and fabricated in accordance with relevant BWRVIP Repair Design Criteria (in this case, the BWRVIP-16 and BWRVIP-19 reports) and BWRVIP Material Guidelines (the BWRVIP-84 report). The BWRVIP further stated that the requirements suggested by the staff are required by Section 3.2 of the BWRVIP-84 report. The staff finds the response acceptable because the BWRVIP has the design requirements specified in other applicable reports. In a letter dated March 16, 2006, the staff issued Supplementary RAI 6-5 requesting the BWRVIP to reference these other reports in Section 6.0 of the BWRVIP-34 reort. In its letter dated July 18, 2006, the BWRVIP agreed with the staff and proposed to include the following paragraph as an introduction to Section 6.0 to the report.

Subsequent to the initial publication of this report, the BWRVIP published a Material Guideline (BWRVIP-84, Reference 15) that provides material specifications for use in repairs to BWR internals. Any core spray weld overlay repair design must be consistent with the requirements of BWRVIP-84 as well as the Core Spray Repair Design Criteria (Reference 13).

The staff finds the response acceptable because BWRVIP will be incorporating a recommendation to use the BWRVIP-19 and BWRVIP-84 report guidelines in the BWRVIP-34 report as requested. It should be noted that the BWRVIP letter dated November 1, 2004, stated that the design basis for the part circumference weld overlay repair of core spray piping is for a permanent repair and it is addressed in the Core Spray Repair Design Criteria (BWRVIP-19-A) which the staff has approved by NRC letter dated March 8, 2006.

The staff finds that the BWRVIP has adequately addressed the materials to be used and the welding qualifications to be performed for the weld overlay repairs by assuring that the ASME Code requirements, including Code Cases N-504-2 and N-516, will be met.

3.6 Section 7.0 - Inspection of Core Spray Internal Piping Weld Overlays Section 7.0 refers to the BWRVIP-03 report for the underwater ultrasonic examinations of core spray overlay mockups. Some of the mockups contained controlled, artificial defects.

The results of the mockup examinations presented in Section 7.0 support the conclusion that the partial weld overlay repairs cannot be examined in the as-welded condition. However, these partial weld overlay repairs can be inspected by qualified personnel with improvements of the weld surface condition to meet the existing standards for piping overlays. Therefore, the staff finds it acceptable that these part circumference weld overlays will be inspected by qualified personnel with improvements of the weld surface condition to meet existing standards for piping overlay (EPRI report NP-4720-LD, Examination of Weld -Overlaid Pipe Joints, October 1986).

In reviewing the inspectability of these partial weld overlay repairs, the NRC notes that References 5.6 and 5.7 found underbead weld cracking, but did not find weld toe cracking in a Type 304 stainless steel specimen containing entrapped helium and repaired by a gas metal arc weld overlay. In Supplementary RAI 7-1 to its letter dated October 7, 2004, the staff requested that the BWRVIP explain whether the inspection methods considered in Section 7.0 are qualified for detecting and sizing underbead cracking. In its letters dated November 1, 2004, and July 25, 2005 (renumbered to RAI 34-7.1), the BWRVIP response stated that the issue of inspection of welds to irradiated material is addressed in the BWRVIP-97 report and not in the BWRVIP-34 report because the discussion on inspection of highly irradiated material is already included in the BWRVIP-97 report. The staff finds this acceptable, and therefore will continue the review of the ability of the inspection methods for detecting and sizing underbead cracking in irradiated material during the review of the BWRVIP-97 report.

3.7 Appendices The appendices (A through L) to the BWRVIP-34 report provide the weld qualification parameters, testing and test results for the SMAW and FCAW processes, which demonstrate that these welding processes could be used for weld overlay repairs of core spray piping, and meet the ASME Code requirements. In addition, the appendices provide recommended guidelines for procuring welding electrodes for use with the SMAW and FCAW processes in an underwater environment. The staff generally finds that these appendices adequately address the weld qualification and weld material requirements to assure satisfactory weld overlay repairs can be applied on core spray piping. Specific issues are discussed below for some of the applicable appendices.

3.7.1 Appendix A This appendix describes the mockup testing performed to evaluate weld bead sequencing, the extent of the weld overlay, and verification of any crack extension into the weld overlay repair.

The mockups consisted of butt welds in flat pipe cylinders butted together with no gap to simulate cracks. The mockups were coated with zinc oxide to determine the effects on weldability with FCAW. In RAI 5 to letter dated May 22, 1997, the staff requested additional information on flat cylinders, seal weld, and zinc oxide coating as discussed in Appendix A.

In its letter dated March 30, 1998, the BWRVIP clarified the fabrication details of these mockups. The BWRVIP stated that stainless steel (Type 304) mockups discussed in Appendix A were manufactured with 3/8-inch plate and 6-inch schedule 40 pipe (cylinders). All mockups simulated a through-wall circumferential crack by butting two sections of the plate or pipe together. Welding was completed transverse to the crack on the pipe mockups and directly over the crack with the plate material. The term flat pipe cylinders refers to pipe sections welded in the flat position with manipulation of the weld head along the axis of the pipe.

The BWRVIP-34 report states that a seal weld is the first weld bead that completely closes the crack. These welds were evaluated for variations in welding conditions that may arise due to limitations in accessibility or manipulation of equipment.

The BWRVIP-34 report states that a zinc oxide coating was applied prior to butting the plates together, which assured a complete coverage of the plates and simulated crack. Seal welds were applied directly over the crack and adjacent to crack. No modification of the welding was necessary due to the zinc oxide coating. No effort was made to closely duplicate the details of the zinc deposition, which occurs in some operating BWRs. However, the fact that welding over the heavy galvanized layer was possible provides an initial indication that the process should be successful in plants with zinc deposits.

The staff finds the results of the mockup testing in Appendix A provide confirmation that welding over cracks can be accomplished, even if the core spray piping is coated with zinc oxide.

However, in Supplementary RAI A-1 to its letter dated October 7, 2004, the staff requested that the BWRVIP discuss whether weld overlay repair will leave a crevice geometry in the core spray piping wall underneath the weld. In its letter dated November 1, 2004, the BWRVIP response stated that a crevice geometry will be present in the core spray wall underneath the weld overlay, but any IGSCC, if present, will be arrested in the structural portion of the weld overlay interfacing with the underlying material of core spray piping. The staff finds this acceptable because the weld overlay material is IGSCC resistant due to its low carbon content and minimum FN value of 7.5. Therefore, any IGSCC present at the crevice would not propagate into the overlay material and would not challenge the integrity of weld overlay repair.

3.7.2 Appendix B Appendix B describes the qualification test parameters used for the automated FCAW process using 308L weld material. In addition, Appendix B states that the test specimens from the qualification welds were made using the FCAW process at a depth 50 feet. However, in Appendix D.1, the specimens for constant extension rate testing (CERT) tests for FCAW process were made at a depth of 30 feet. Underwater weld depth has an effect on the welding arc characteristics and occurrence of weld defects. Increasing the depth can increase the occurrence of weld defects. Therefore, the CERT tests on coupons fabricated at 30 feet may not bound the test results on coupons fabricated at 50 feet. In Supplementary RAI A-3 to its letter dated October 7, 2004, the staff requested that the BWRVIP discuss whether CERT test results for coupons fabricated at 30 feet depth can be used as a bounding value for assessing the corrosion behavior of welds that will be made at 50 feet. In its letter dated November 1, 2004, the BWRVIP response stated that ferrite levels were not affected by depth or pipe wall thickness for underwater welding and therefore the CERT results at 30 feet can be used for welds to be made at a depth of 50 feet. The heat sink is basically the same based on the quantity of water the test specimens were fabricated in and therefore the weld residual stresses would be the same. The BWRVIP further states that the only reason tests were conducted on coupons fabricated at various depths was the level of difficulty in fabricating specimens at 50 feet (hyperbaric chamber) and 30 feet (open dive tank).

However, the staff notes that welding at increasing depths will also increase the number of weld defects. In its letter dated March 16, 2006, the staff requested that the BWRVIP discuss how the increased number of weld defects would affect the CERT test results, and that the BWRVIP-34 report should include guidelines about the use of dry (underwater welding in a dry chamber or habitat that displaces water around the material to be welded) and wet underwater welding for overlay repair in the -A version of the report. In its letter dated July 18, 2006, the BWRVIP response stated that Code Case N-516 recognizes the fact that depth may have some effect on the mechanical properties of welds and requires that the Owner perform welding qualifications for production welds under the same conditions for which the in-plant weld will be performed within certain specified tolerances. These conditions include depth for wet welding and pressure for habitat (dry underwater) welding. In addition, the same welding process must be used for the qualification and the actual repair activity. Consequently, since qualification specimens are fabricated from welds performed under representative conditions (defined by the ASME Code) with the same welding process, the material properties will be accurately representative of the repair weld. The staff agrees with the BWRVIP conclusion that Code Case N-516 does take into account the effect of depth on weld qualification. The BWRVIP further states that since the qualification parameters are adequately addressed by the ASME Code, additional discussion of wet versus dry welding in the -A version of the BWRVIP-34-A report is not required. The staff notes that Code Case N-516-3, dated April 8, 2002, does provide guidelines for welding procedure qualifications and welder performance qualifications for both dry and wet underwater welding, so no additional discussion is needed in the -A version of the BWRVIP-34 report.

3.7.3 Appendix D This Appendix provides the results of the CERT tests conducted on FCAW and SMAW welds in order to evaluate IGSCC susceptibility of stainless steel filler metals welded underwater in a BWR environment.

In reviewing these results, the staff noted that in Tables D-3 and D-6, the CERT results have shown that a specimen tested in water takes a longer time to fail than a specimen tested in air.

However, the reported percentage reduction in area of the specimen tested and failed in water is significantly less than that of the specimen tested and failed in air. In its letter dated March 30, 1998, the BWRVIP discussed why the CERT tests results in Table D-3 and D-6 indicated that a longer time to failure occurred with the specimens tested in the water environment, even though a lower percent area reduction was recorded for these specimens.

The BWRVIP provided the CERT test recording charts and concluded that the welds are not susceptible to environmental embrittlement, since there was a lack of secondary cracking, and overall time to failure for all the specimens tested in water was greater than specimens tested in air. The results indicated that both specimens experienced fully ductile failures and that the variations were a result of inclusions or defects in the weld and were not due to environmental embrittlement. Test specimens were archived and are available for further metallographic evaluation if additional information is required. Time to failure could be directly related to defects, grain structure and grain size.

In the staffs review of the test results for coupons 16.1A and 16.1B, it was noted that the ferrite content is low on the weld cover pass when using the electrodes coated with the Cr-Al enamel waterproof coating. In its letter dated March 30, 1998, the BWRVIP response to RAI 11(b) clarified that the term cover passes used in these mockups are additional weld passes on the groove weld, which increased the volume of weld metal necessary to obtain the required test specimens. The ferrite number for the CERT test specimens was measured on the final weld surface of the groove weld. The FN recorded was between 4 to 6 across the length of the weld.

The BWRVIP further stated that at the time the test matrix was completed, a FN value of 4-6 was typical for an underwater SMAW weld. The FN value in the intermediate and root passes was not measured in this test report. A later test evaluation with the same electrode and coating measured the FN value on the cross section of the specimen. A FN value of 6.1 was measured near the root and a FN value of 5.2 to 7.1 was measured on intermediate passes.

The early low ferrite results led to development of electrodes with enhanced chemistry, which produced as-deposited weldments with higher delta ferrite values. This additional electrode development has achieved a FN value of 8 to 15.

The staff notes that Section D.2 of Appendix D to the BWRVIP-34 report notes a significant reduction (60%) in ductility (percent reduction in cross sectional area) of SMAW welds fabricated and tested in water as compared to those fabricated in water but tested in air. In Supplementary RAI A-2 (a) to its letter dated October 7, 2004, the staff requested that the BWRVIP discuss whether the fracture toughness test results for the SMAW welds reported in Appendix I of the BWRVIP-34 report may be similarly affected. In its letter dated November 1, 2004, the BWRVIP response stated that the fracture toughness results should not be influenced by testing conducted underwater versus testing conducted in air. The staff agrees that the fracture toughness results should not be affected by testing underwater versus in air, especially since the welds tested underwater have not shown any susceptibility to environmental embrittlement.

As mentioned above, the results presented in Section D.2 of Appendix D to the BWRVIP-34 report indicate that the SMAW welds that are fabricated and tested in water have inferior mechanical properties to those fabricated in water but tested in air. Therefore, in Supplementary RAI A-2 (b) to its letter dated October 7, 2004, the staff requested that the BWRVIP-34 report include a recommendation that the design of weld overlay repair of internal core spray piping use mechanical properties (e.g., yield strength and tensile strength) determined by welds fabricated and tested underwater. In its letter dated November 1, 2004, the BWRVIP response stated that all requirements of Code Case N-516 will be met and, therefore, the required mechanical properties will be used in the design, and therefore will be representative of these weldments.

However, Code Case N-516 refers to determination of only Charpy energy for filler metal qualification and not of yield strength and tensile strength of the weldment. Therefore, in a letter dated March 16, 2006, the staff requested that the BWRVIP address the mechanical properties of yield strength and tensile strength because they are needed to determine the design stress intensity, Sm, used for determination of overlay thickness (see Section 3.4 of the BWRVIP-34 report). The staff also requested that the BWRVIP address whether the proposed high-ferrite contents (17 FN) would affect the material properties of the FCAW and SMAW welds fabricated and tested underwater. In a letter dated July 18, 2006, the BWRVIP further clarified that the mechanical properties testing is required by Code Case N-516. Code Case N-516 refers back to Section XI of the ASME Code, which mandates a procedure qualification that requires the suggested mechanical testing. Per the ASME Code, the tests are performed on samples removed from a weld that is deposited at the appropriate depth in the water environment using the welding process that will be used in the field application. With respect to the ferrite content, the BWRVIP stated that any effect of high ferrite levels on the material properties of the as-deposited weld will be measured in the ASME Code required weld procedure qualification testing. Potential future degradation caused by ferrite will be controlled by limiting the ferrite level to 12 FN as stated in the preamble to the BWRVIP-34 report.

The staff finds this acceptable because samples that are tested will be removed from representative weldments and the ferrite content will be limited to reduce potential degradation.

3.7.4 Appendices F and G Appendix F provides the material specifications for 308L weld material for automatic FCAW, while Appendix G provides the material specifications for 309L, 316L and other stainless steel weld material for manual SMAW.

In Appendices F and G, the reported ferrite content in the test coupons depends on the instrument that was used for the measurement. The reported FN readings measured by the Magne-Gage are much higher than those measured by ferritescope. In RAI 6 to its letter dated May 22, 1997, the staff requested that the BWRVIP provide an explanation of the differences in FN readings measured by the two instruments, and discuss which instrument provides a more reliable reading. In its letter dated March 30, 1998, the BWRVIP stated that the FN value in the test coupons was measured with two instruments; Magne-Gage and ferritescope.

The Magne-Gage is primarily used in the lab and is restricted to small specimens oriented in the flat position. The specimens are prepared in accordance with Appendix A (filler metal specification SFA 5.4) to the ASME Code,Section II. The Magne-Gage is the standard for Quality Assurance Test Reports from the consumable weld material manufacturers.

The Magne-Gage utilizes a true magnetic reading established by a dial reading at the point the magnet is pulled free of the specimen. In contrast, the ferritescope is a portable instrument that allows FN readings in all positions and does not require coupon preparation (as-welded condition). Unlike the Magne-Gage, an AC or DC current is applied across the surface of the component to obtain an electromagnetic indication of the FN value. The Magne-Gage actually measures the FN value over some depth into the coupon, whereas the ferritescope obtains a reading at the surface of the coupon.

The ferritescope was used to get a quick reading in the field during welding operations, primarily to evaluate experimental electrodes. The Magne-Gage was used on the same weldments at a later date for a more accurate reading. The Magne-Gage results were used for final assessment of weld acceptability. Therefore, since the more accurate reading from the Magne-Gage instrument is used to verify the quality of the ferritescope (used in the field), the staff finds that the FN values obtained are reliable.

3.7.5 Appendix J Appendix J provides requirements for procurement of welding electrodes utilized for the FCAW and SMAW processes in an underwater environment. For the chemical requirements of the weld material, Appendix J allows the FN value to be determined either by chemical analysis or by a magnetic measuring instrument. In its letter dated March 30, 1998, the BWRVIP clarified that it was not the intent of the Appendix J to allow acceptance of the FN value by using the chemical analysis of the weld material in lieu of direct measurement of the as-deposited weld materials. The candidate weld materials are selected based on chemical analysis and certified mill test report (CMTR) FN values, but the actual performance of this material in the underwater application must be demonstrated in the as-welded condition by measurement of delta ferrite (possibly during procedure qualifications rather than for each underwater repair). The staff finds this acceptable, because the FN values will be measured for each of the weld materials used in the as-welded condition (either during the procedure qualifications or in the field).

3.7.6 Appendix K Appendix K addresses the ability to inspect the weld overlay repair by using mockups welded with the FCAW and SMAW processes. In its letter dated March 30, 1998, the BWRVIP provided clarification of the term nearly-as-welded to be a surface that has been modified only by knocking off slag and weld spatter with no intentional alteration of the weld surface quality.

However, the nearly-as-welded condition was still too rough to permit effective inspection.

Regarding the acceptable surface quality for inspection of a weld overlay, the BWRVIP stated that the specimens were not able to be examined effectively until the surface had been improved to meet the criteria for an acceptable surface quality as specified in Reference 14 of the BWRVIP-34 report, EPRI NP-4720-LD, Examination of Weld-Overlaid Pipe Joints, dated October 1986. The BWRVIP further stated that the actual overlay thickness should be designed to accommodate the surface preparation necessary for UT inspection and that the BWRVIP-34 report will be revised to reflect this explanation. The staff finds this acceptable since these guidelines have been found to be effective in weld overlay repair of BWR recirculation piping. The results of this testing on mockups show that ultrasonic inspection of the weld overlay repair can be performed to detect lack of bond, porosity, and any potential crack extension from the core spray piping material into the weld overlay repair.

4.0 CONCLUSION

S The NRC staff has reviewed the BWRVIP-34 report and the supplemental information that was transmitted to the staff by letters dated March 30, 1998, November 1, 2004, and July 18, 2006, and found that the report, as modified and clarified to incorporate the staffs comments above, is acceptable for providing guidance for permanent or temporary underwater part circumference weld overlay repairs of core spray piping. Therefore, the staff has concluded that licensee implementation of the guidelines in the BWRVIP-34 report, as modified to incorporate the resolution of the RAIs as discussed in this SE, will provide an acceptable technical basis for designing underwater part circumference weld overlay repairs of the components addressed in the BWRVIP-34 report based on the following.

Section 2.0 of the BWRVIP-34 report described the applicable locations that are accessible for this part circumference weld overlay repair, and that plant-specific clearances must be addressed on a plant-specific basis because these clearances play a role in determining the thickness and length of this type of repair.

Section 3.0 of the BWRVIP-34 report provided the methodology and an example analysis of designing a part circumference weld overlay repair using FCAW and SMAW processes to meet the BWRVIP core spray design criteria in the BWRVIP-16 and BWRVIP-19 reports, and the requirements in Appendix C of Section XI to the ASME Code and Code Cases N-504-2 and N-516. The structural strength of the weld overlay (including length and thickness of the weld) will be determined by using a net section plastic collapse evaluation methodology, and the use of the Z-factor correction in the current version of the ASME Code for weld overlays fabricated with welding processes using flux. In addition, each licensee will perform this evaluation and shall also consider residual stresses (taking into account underwater welding with the piping ID and OD exposed to water during welding) and shrinkage stresses produced by the weld overlay to ensure that the welds and components meet the applicable stress limits of Section III of the ASME Code. Each licensee shall consider potential flaw growth due to fatigue and IGSCC, and identify the specific nondestructive examination of the weld overlay repair. The BWRVIP-34 provided an acceptable method for accounting for shear transfer between the weld overlay and the piping. Each licensee will also determine, prior to performing the weld overlay, any additional length to the weld repair to allow for an effective inspection. The weld overlay repair will use the workmanship standards of Sections XI and III of the ASME Code to minimize the creation of a crevice at the toe of the weld repair, and BWRVIP-19-A will require the licensee to specify periodic inspections of the repair that are consistent with the BWRVIP-18-A guidelines in order to detect any cracking in the weld overlay in a timely manner.

Section 4.0 of the BWRVIP-34 report provided guidance on performing core spray leakage calculations and leakage assessment criteria which will be performed for each plant-specific application to demonstrate that the total leakage from the core spray piping does not cause unacceptable increases in peak cladding temperature for any licensing basis accident.

Section 5.0 of the BWRVIP-34 report will reference the BWRVIP-97 report for guidance on weldability of core spray piping (irradiated stainless steel).

Section 6.0 of the BWRVIP-34 report identified the testing necessary to demonstrate the adequacy of materials and welding processes for underwater welding of core spray piping. The qualification of the underwater welding activities will be in accordance with Code Cases N-516 and N-504-2, and will be qualified for the appropriate welding positions at the required depth. Materials used for the weld repair will be selected in accordance with the guidelines of BWRVIP-84. The report also included results of a demonstration for two welding processes (FCAW and SMAW). The BWRVIP-34 report will also specify that weld material shall have a delta ferrite content between 7.5 to 12 FN to minimize IGSCC and thermal aging susceptibility.

Section 7.0 of the BWRVIP-34 report demonstrated that the part circumference weld overlays cannot be inspected in the as-welded condition, but can be inspected by qualified personnel with improvements of the weld surface condition. Therefore, the staff finds it acceptable that these part circumference weld overlays will be inspected by qualified personnel with improvements of the weld surface condition to meet existing standards for piping overlay (EPRI report NP-4720-LD, Examination of Weld -Overlaid Pipe Joints, October 1986).

The staff notes that the BWRVIP-34 report provided, for information, the results of mockup testing to demonstrate that the SMAW and FCAW processes could be used for these weld overlay repairs and would be able to meet the applicable ASME Code requirements. However, the ASME Code requirements for weld procedure and welder qualifications still apply, and would be required to be performed by the licensee when implementing these BWRVIP-34 report guidelines. In addition, the requirements and testing specified in Code Cases N-516 and N-504-2 that are endorsed in RG 1.147 must be performed. These tests include:

Ferrite determination of the weld deposit.

Fracture toughness testing for each material type deposited underwater.

Determine IGSCC susceptibility using CERT tests of the weld deposit.

Sensitization tests of the heat affected zone (HAZ) (ASTM A-262, Practices A and E).

Weld procedure specification qualification tests including mechanical testing specified in Section IX of the ASME Code.

In addition, when welding on irradiated core spray piping, the guidelines in the BWRVIP-97 report shall also be implemented, including any additional mockup testing or helium content determination.

The staff notes that Section 8.0 of the BWRVIP-34 report states, The structural adequacy of such repairs has been demonstrated, as has the IGSCC resistance of weld overlay materials in the as applied condition, for two underwater welding processes: automatic remote flux cored arc welding (FCAW) and manual shielded metal arc welding (SMAW). In addition, Section 6.4 of the BWRVIP-34 report states, The design thickness of the weld overlay repair for core spray piping depends upon the expected properties of the as deposited weld overlay....In particular, the fracture toughness and the mechanical properties of the weld deposit must be determined, since these properties have a strong impact on the weld overlay design. Therefore, based on these BWRVIP-34 report guidelines, if licensees intend to use a welding process other than SMAW or FCAW, they must perform the qualification tests required by Section IX of the ASME Code and Code Cases N-516, and additional testing as outlined in the BWRVIP-34 and BWRVIP-97 reports in order to ensure that weld properties are obtained for use in the determination of the size (length and depth) of the part circumference weld overlay.

The modifications, clarifications, and supplemental information that were provided in response to the staffs RAIs, as addressed in Section 3 of this SE, are summarized below. The staff requests that these modifications, clarifications, and supplemental information be incorporated in the -A version of the BWRVIP-34 report.

a.

In response to Supplemental RAI question No. 3-1 in the staff's October 7, 2004, letter, the BWRVIP provided a general statement in its letter dated July 18, 2006, to address the staff's concern about compliance with the current editions of the ASME Code.

The BWRVIP agreed to modify the BWRVIP-34 report to include a preamble to ensure the overlay design will be in accordance with the current NRC-approved version of the ASME Code and Code Cases. In addition, the preamble includes the use of the Z-factor, consideration for designing the length of the overlay repair, evaluation of the effects of residual stresses and water backing, the effects of the weld overlay on other welds and components, and the inclusion of a maximum limit on ferrite content of 12 FN.

It should be noted that based on the responses to this and other RAIs, the BWRVIP proposed a FN range of 7.5 to 12, which provides sufficient delta ferrite content to minimize IGSCC, but limits the delta ferrite to prevent thermal aging of the stainless steel. The BWRVIP shall clarify in the -A version of the BWRVIP-34 report that the ferrite content of the weld shall be within the range of 7.5 to 12 FN.

b.

In response to RAI question No. 3-1(c) in the staffs letter dated October 7, 2004, and Supplemental RAI question No. 3-5, the BWRVIP agreed with the staffs recommendation that the example analysis in the BWRVIP-34 report did not use a Z-factor, but a Z-factor should be used for a repair when required by the ASME Code.

The BWRVIP will add a paragraph at the end of Section 3.2 of the BWRVIP-34 report as addressed in its letter dated July 18, 2006, regarding Supplemental RAI question No. 3-5.

c.

In response to RAI question No. 1 in the staffs letter dated March 30, 1998, the BWRVIP agreed with the staffs recommendation that additional length of the weld overlay may be required to allow effective inspection. Therefore, the BWRVIP agreed to modify Section 3.1.2 in the BWRVIP-34 report accordingly.

d.

In response to RAI question No. 3-8 in the staffs letter dated July 18, 2006, the BWRVIP proposed to modify Section 7 of the BWRVIP-34 report to provide guidance for inspecting IGSCC-susceptible locations resulting from weld overlay repair of the core spray piping.

e.

In response to RAIs on weldability of irradiated material in the staff's letters dated January 8, 2003, March 18, 2004, and October 7, 2004, the BWRVIP proposed in its letter dated November 1, 2004, to replace Section 5.0 of the BWRVIP-34 report with a reference to the BWRVIP-97 report for all welding on highly irradiated materials and to address all the staff's comments during the review of the BWRVIP-97 report. This is appropriate and will consolidate the guidance in one report. Therefore, the BWRVIP will revise Section 5.0 of the BWRVIP-34 report as addressed in its letter dated November 1, 2004, to state that all welding on highly irradiated materials shall be in accordance with the BWRVIP-97 report.

f.

In response to the staffs Supplementary RAI question No. 6-2(b) in its letter dated November 1, 2004, the BWRVIP proposed that Type 312 stainless steel weld metal will not be considered for the underwater weld overlay application. Therefore, the BWRVIP will delete any reference to Type 312 stainless steel weld metal as it applies to the use in the weld overlay repair.

g.

In response to Supplementary RAI question No. 3-8 in the staffs letter dated March 16, 2006, the BWRVIP agreed with the staff's recommendation to include the use of the BWRVIP-19 and BWRVIP-84 report guidelines concerning repair and replacement designs and material specifications. Therefore, the BWRVIP will modify Section 6.0 of the BWRVIP-34 report, as addressed in its letter dated July 18, 2006, regarding Supplementary RAI 3-8.

h.

In response to RAI question No. 8 in the staff's letter dated March 30, 1998, the BWRVIP agreed with the staff's recommendation that the term nearly-as-welded condition requires further explanation. The BWRVIP agreed to revise the BWRVIP-34 report to further define this term, and state that the actual overlay thickness should be designed to accommodate the surface preparation necessary for UT inspection.

The BWRVIP-34 report is considered by the staff to be acceptable for licensee usage, as modified and approved by the staff, anytime during either the current operating term or during the extended license period. If it is determined during the course of implementing these repair guidelines that implementation cannot be achieved as described in the guideline or that meaningful results are not obtained, then the staff requests that the user notify the BWRVIP with sufficient details to support development of alternative actions. These notifications, as well as planned actions by the BWRVIP, should be summarized and reported to the NRC. It should be noted that a licensee is responsible for reviewing regulatory requirements for repairs to this system. If the repair is an alternative repair to that specified in the regulations, i.e.,

10 CFR 50.55a, the licensee will need to pursue the appropriate regulatory action.

5.0 REFERENCES

5.1 ASME Section XI Task Group for Piping Flaw Evaluation 1986. Evaluation of Flaws in Austenitic Stainless Steel Piping, Journal of Pressure Vessel Technology, August 1986.

5.2 Hale, G. E. and S. J. Garwood 1990. Effect of Aging on Fracture Behavior of Cast Stainless Steel and Weldments, Material Science and Technology, 6, March 1990, pp.

230-235.

5.3 Alexander, K. B., et al. 1990. Microscopical Evaluation of Low Temperature Aging of Type 308 Stainless steel Weldments, Material Science and Technology, 6, March, pp.

314-320.

5.4 ASM 1980. Properties and Selection: Stainless Steels, Tool Materials and Special-Purpose Metals, Volume 3, Metals Handbook, Ninth Edition, American Society for Metals, p. 9 5.5 Hughes, N. R., et al. 1982. Intergranular Stress Corrosion Cracking Resistance of Austenitic Stainless Steel Castings, Stainless Steel Castings, ASTM STP 756, 5.6 Kanne, W. R., et al. 1993. Metallographic Analysis of Helium-Embrittlement Cracking of Repair Welds in Nuclear Reactor Tanks, Materials Characterization, Vol. 30, 1993, pp.

23-34.

5.7 Goods, S. H., and C. W. Karfs 1991. Helium-Induced Weld Cracking in Low Heat Input GMA Weld Overlays, Welding Research Supplement, May 1991, pp. 123-s to 132-s.