ML051220568
| ML051220568 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 06/22/2005 |
| From: | Richard Laufer NRC/NRR/DLPM/LPD1 |
| To: | Shriver B Susquehanna |
| Guzman R | |
| References | |
| TAC MC2450, TAC MC2451, TAC MC2594 | |
| Download: ML051220568 (20) | |
Text
June 22, 2005 Mr. Bryce L. Shriver President-PPL Generation PPL Susquehanna, LLC Two North Ninth Street, GENTW15 Allentown, PA 18101-1179
SUBJECT:
SUSQUEHANNA STEAM ELECTRIC STATION, UNIT 1 - RELIEF FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS, BOILER AND PRESSURE VESSEL CODE (ASME CODE), SECTION XI, APPENDIX VIII, SUPPLEMENT 11, REQUIREMENTS AND CODE CASES N-504-2 AND N-638 REQUIREMENTS (TAC NOS. MC2450, MC2451 AND MC2594)
Dear Mr. Shriver:
By letter dated March 26, 2004 (PLA-5741), as supplemented by letter dated April 7, 2004 (PLA-5743), PPL Susquehanna, LLC (PPL or the licensee) submitted Relief Request No. 30, requesting relief from ASME Code,Section XI requirements related to the qualification for examination of overlay repaired austenitic piping welds for weld N1B at Susquehanna Steam Electric Station, Unit 1 (SSES-1). By letter dated April 8, 2004 (PLA-5744), PPL requested that the March 26, 2004 (PLA-5741) Relief Request seeking relief for N1B from inspection qualification requirements also be extended to seek the same relief for weld N2J.
In addition, by letter dated March 26, 2004 (PLA-5740) for Relief Request No. 29, as supplemented by letter dated April 7, 2004 (PLA-5743), and by letter dated April 8, 2004 (PLA-5744) for Relief Request No. 31, as supplemented by letter dated December 17, 2004 (PLA-5842), PPL requested relief from certain requirements in ASME Code,Section XI, Code Cases N-504-2 and N-638. Relief Requests Nos. 29 and 31 were needed to support a full structural weld overlay repair on the N1B outlet and N2J inlet recirculation system nozzles at SSES-1. PPL proposed to perform the weld overlay repair with Alloy 52 filler material utilizing the machine gas tungsten arc welding process and an ambient temperature temper bead method with 50 EF minimum preheat temperature and no post-weld heat treatment.
The applications above requested approval of relief requests in support of the SSES-1 refueling and inspection outage to complete an inservice inspection repair plan to the N1B and N2J reactor pressure vessel nozzle to safe-end welds. On April 16, 2004, the NRC staff completed its review of the subject relief requests, determined that the proposed alternatives would provide an acceptable level of quality and safety, and granted verbal authorization for the subject alternatives pursuant to 10 CFR 50.55a(a)(3)(i).
B. Shriver A copy of our safety evaluation is enclosed. If you have any questions, please contact your Project Manager, Rich Guzman, at (301) 415-1030.
Sincerely,
/RA/
Richard J. Laufer, Chief, Section 1 Project Directorate I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-387
Enclosure:
Safety Evaluation cc w/encl: See next page
B. Shriver A copy of our safety evaluation is enclosed. If you have any questions, please contact your Project Manager, Rich Guzman, at (301) 415-1030.
Sincerely,
/RA/
Richard J. Laufer, Chief, Section 1 Project Directorate I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-387
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION:
PUBLIC PDI-1 RF RLaufer RGuzman MOBrien OGC ACRS GHill (2) WKoo TChan MShanbaky, RI DLPM DPR ACCESSION NO.: ML051220568 *SEs provided. No major changes made.
OFFICE PDI-1/PM PDI-2/LA EMCB/SC* OGC PDI-1/SC NAME RGuzman SLittle for TChan KKannler RLaufer MO'Brien DATE 6/2/05 5/16/05 8/9/04, 4/19/05 6/17/05 6/22/05 OFFICIAL RECORD COPY
Susquehanna Steam Electric Station, Units 1 and 2 cc:
Britt T. McKinney Michael H. Crowthers Sr. Vice President and Supervising Engineer Chief Nuclear Officer Nuclear Regulatory Affairs PPL Susquehanna, LLC PPL Susquehanna, LLC 769 Salem Blvd., NUCSB3 Two North Ninth Street, GENPL4 Berwick, PA 18603-0467 Allentown, PA 18101-1179 Robert A. Saccone Steven M. Cook General Manager - Nuclear Operations Manager - Quality Assurance PPL Susquehanna, LLC PPL Susquehanna, LLC 769 Salem Blvd., NUCSB3 769 Salem Blvd., NUCSB2 Berwick, PA 18603-0467 Berwick, PA 18603-0467 Aloysius J. Wrape, III Luis A. Ramos General Manager - Performance Community Relations Manager, Improvement and Oversight Susquehanna PPL Susquehanna, LLC PPL Susquehanna, LLC Two North Ninth Street, GENPL4 634 Salem Blvd., SSO Allentown, PA 18101-1179 Berwick, PA 18603-0467 Terry L. Harpster Bryan A. Snapp, Esq General Manager - Plant Support Assoc. General Counsel PPL Susquehanna, LLC PPL Services Corporation 769 Salem Blvd., NUCSA4 Two North Ninth Street, GENTW3 Berwick, PA 18603-0467 Allentown, PA 18101-1179 Gregory F. Ruppert Supervisor - Document Control Services General Manager - Nuclear Engineering PPL Susquehanna, LLC PPL Susquehanna, LLC Two North Ninth Street, GENPL4 769 Salem Blvd., NUCSB3 Allentown, PA 18101-1179 Berwick, PA 18603-0467 Richard W. Osborne Rocco R. Sgarro Allegheny Electric Cooperative, Inc.
Manager - Nuclear Regulatory Affairs 212 Locust Street PPL Susquehanna, LLC P.O. Box 1266 Two North Ninth Street, GENPL4 Harrisburg, PA 17108-1266 Allentown, PA 18101-1179 Director - Bureau of Radiation Protection Walter E. Morrissey Pennsylvania Department of Supervising Engineer Environmental Protection Nuclear Regulatory Affairs P.O. Box 8469 PPL Susquehanna, LLC Harrisburg, PA 17105-8469 769 Salem Blvd., NUCSA4 Berwick, PA 18603-0467
Susquehanna Steam Electric Station, Units 1 and 2 cc:
Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 35, NUCSA4 Berwick, PA 18603-0035 Regional Administrator, Region 1 U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Board of Supervisors Salem Township P.O. Box 405 Berwick, PA 18603-0035 Dr. Judith Johnsrud National Energy Committee Sierra Club 443 Orlando Avenue State College, PA 16803
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST NOS. 29, 30, AND 31, FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE, SECTION XI, APPENDIX VIII, SUPPLEMENT 11, AND CODE CASES N-504-2 AND N-638 REQUIREMENTS PPL SUSQUEHANNA, LLC ALLEGHENY ELECTRIC COOPERATIVE, INC.
SUSQUEHANNA STEAM ELECTRIC STATION, UNIT 1 DOCKET NO. 50-387
1.0 INTRODUCTION
By letter dated March 26, 2004 (Agency Documents Access and Management System (ADAMS) Accession No. ML040960439), as supplemented by letter dated April 7, 2004 (ADAMS Accession No. ML041000283), PPL Susquehanna, LLC (PPL or the licensee) submitted Relief Request No. 30, requesting relief from the American Society of Mechanical Engineers, Boiler and Pressure Vessel Code (ASME Code),Section XI requirements related to the qualification for examination of overlay repaired austenitic piping welds for weld N1B at Susquehanna Steam Electric Station, Unit 1 (SSES-1). By letter dated April 8, 2004 (ADAMS Accession No. ML041040011), PPL requested that the March 26, 2004 Relief Request seeking relief for N1B from inspection qualification requirements also be extended to seek the same relief for weld N2J.
In addition, by letter dated March 26, 2004 (ADAMS Accession No. ML040960442) for Relief Request No. 29, as supplemented by letter dated April 7, 2004 (ADAMS Accession No. ML041000283), and by letter dated April 8, 2004 (ADAMS Accession No. ML041040011) for Relief Request No. 31, as supplemented by letter dated December 17, 2004 (ADAMS Accession No. ML050140139), PPL requested relief from certain requirements in ASME Code,Section XI, Code Cases N-504-2 and N-638. Relief Requests Nos. 29 and 31 were needed to support a full structural weld overlay repair on the N1B outlet and N2J inlet recirculation system nozzles at SSES-1. PPL proposed to perform the weld overlay repair with Alloy 52 filler material utilizing the machine gas tungsten arc welding process and an ambient temperature temper bead method with 50 EF minimum preheat temperature and no post-weld heat treatment.
The applications above requested approval of relief requests in support of the SSES-1 refueling and inspection outage to complete an inservice inspection repair plan to the N1B and N2J
reactor pressure vessel nozzle to safe-end welds. On April 16, 2004, the NRC staff completed its review of the subject relief requests, determined that the proposed alternatives would provide an acceptable level of quality and safety, and granted verbal authorization for the subject alternatives pursuant to 10 CFR 50.55a(a)(3)(i).
2.0 REGULATORY EVALUATION
In accordance with 10 CFR 50.55a(g)(4), ASME Code, Class 1, 2, and 3 components must meet the requirements set forth in ASME Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plants Components, to the extent practical within the limitations of design, geometry, and materials of components construction. The regulations require that all inservice examinations and system pressure tests conducted during the first 10-year interval, and subsequent intervals, comply with the requirements in the latest edition and addenda of ASME Code,Section XI, incorporated by reference in 10 CFR 50.55a(b) on the date 12 months prior to the start of the 10-year interval. For SSES-1, the 1989 edition to ASME Code,Section XI, is the applicable edition for the current second 10-year inservice inspection (ISI) interval.
In accordance with 10 CFR 50.55a(g)(6)(ii)(C)(1), the implementation of Supplements 1 through 8, and 10 through 11 of Appendix VIII to Section XI, 1995 edition with the 1996 addenda of the ASME Code is required on a phased schedule ending on November 22, 2002.
Supplement 11 was required to be implemented by November 22, 2001. Additionally, 10 CFR 50.55a(g)(6)(ii)(C)(2) requires licensees implementing the 1989 edition and earlier editions of paragraph IWA-2232 of Section XI of the ASME Code to implement the 1995 edition with the 1996 addenda of Appendix VIII and supplements to Appendix VIII of Section XI of the ASME Code. Pursuant to 10 CFR 50.55a(g)(4)(iv), ISI items may meet the requirements set forth in subsequent editions and addenda of the ASME Code that are incorporated by reference in 10 CFR 50.55a(b), subject to the limitations and modifications listed therein, and subject to Commission approval. Portions of editions and addenda may be used provided that related requirements of the respective editions and addenda are met.
Pursuant to 10 CFR 50.55a(a)(3) alternatives to requirements may be authorized by the Nuclear Regulatory Commission (NRC) if the licensee demonstrates that: (i) the proposed alternatives provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The licensee submitted the subject relief requests, pursuant to 10 CFR 50.55a(a)(3)(i), as a proposed alternative to the implementation of ASME Code,Section XI, Appendix VIII, Supplement 11, for the remaining portion of the second 10-year ISI interval and of the ASME Code Cases (CCs) N-638 and N-504-2 for the performance of weld overlay repair of two nozzle-to-safe-end welds (N1B and N2J) for the remaining portion of the second 10-year ISI interval.
3.0 TECHNICAL EVALUATION
The NRC staff has reviewed the licensees regulatory and technical analysis in support of its request for relief from ASME Code,Section XI requirements related to the qualification for examination of overlay repaired austenitic piping welds and ASME CCs N-638 and N-504-2 for the performance of weld overlay repair of two nozzle-to-safe-end welds, N1B and N2J.
The detailed evaluation below supports the conclusion that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by the operation in the proposed manner, (2) such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the relief will not be inimical to the common defense and security or to the health and safety of the public.
3.1 Relief from ASME Code,Section XI, Appendix VIII, Supplement 11 Requirements for Reactor Pressure Vessel Nozzle-to-Safe-end welds N1B and N2J 3.1.1 ASME Code Requirements The Code requirements for which the relief is requested are contained in ASME Code,Section XI, Appendix VIII, Supplement 11, 1995 edition with 1996 addenda, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds.
3.1.2 System/Components for which Relief is Requested The requested relief from the ASME Code,Section XI, Appendix VIII, Supplement 11 requirements applies to the ultrasonic examination of two reactor pressure vessel nozzle-to-safe-end welds (N1B and N2J).
3.1.3 Licensees Proposed Alternative and Basis As an alternative to ASME Code,Section XI, Appendix VIII, Supplement 11 requirements, the licensee proposes the use of the qualification process as administered by the Electric Power Research Institute (EPRI), Performance Demonstration Initiative (PDI) Program, for ultrasonic examination of overlay repaired piping welds. The proposed alternative will be implemented through the EPRI administered PDI Program. The bases for the proposed alternative are discussed below:
Paragraph 1.1(d)(1) requires that all base metal flaws be cracks. As illustrated below
[see figure in the submittal (ADAMS Accession No. ML040960439)], implanting a crack requires excavation of the base material on at least one side of the flaw. While this may be satisfactory for ferritic materials, it does not produce a useable axial flaw in austenitic materials because the sound beam, which normally passes only through base material, must now travel through weld material on at least one side, producing an unrealistic flaw response. To resolve this issue, the PDI program revised this paragraph to allow use of alternative flaw mechanisms under controlled conditions. For example, alternative flaws shall be limited to when implantation of cracks precludes obtaining an effective ultrasonic response, flaws shall be semi-elliptical with a tip width of less than or equal to 0.002 in., and at least 70 percent of the flaws in the detection and sizing test shall be cracks and the remainder shall be alternative flaws.
Relief is requested to allow closer spacing of flaws provided they did not interfere with detection or discrimination. The existing specimens used to-date for qualification to the Tri-party (NRC/BWROG [Boiling Water Reactor Owners Group]/EPRI) agreement have a flaw population density greater than allowed by the current [ASME] Code requirements. These samples have been used successfully for all previous
qualifications under the Tri-party agreement program. To facilitate their use and provide continuity from the Tri-party agreement program to Supplement 11, the PDI Program has merged the Tri-party test specimens into their weld overlay program. For example:
the requirement for using IWA-3300 for proximity flaw evaluation in paragraph 1.1(e)(1) was excluded, instead indications will be sized based on their individual merits; paragraph 1.1(d)(1) includes the statement that intentional overlay fabrication flaws shall not interfere with ultrasonic detection or characterization of the base metal flaws; paragraph 1.1(e)(2)(a)(1) was modified to require that a base metal grading unit include at least 1 (one) in. of the length of the overlaid weld, rather than 3 (three) in.; paragraph 1.1(e)(2)(a)(3) was modified to require sufficient unflawed overlaid weld and base metal to exist on all sides of the grading unit to preclude interfering reflections from adjacent flaws, rather than the 1 (one) in. requirement of Supplement 11; paragraph 1.1(e)(2)(b)(1) was modified to define an overlay fabrication grading unit as including the overlay material and the base metal-to-overlay interface for a length of at least 1 (one) in., rather than the 6 sq. in. requirement of Supplement 11; and, paragraph 1.1(e)(2)(b)(2) states that overlay fabrication grading units designed to be unflawed shall be separated by unflawed overlay material and unflawed base metal-to-overlay interface for at least 1 (one) in. at both ends, rather than around its entire perimeter.
Additionally, the requirement for axially oriented overlay fabrication flaws in paragraph 1.1(e)(1) was excluded from the PDI Program as an improbable scenario. Weld overlays are typically applied using automated gas tungsten arc welding techniques with the filler metal being applied in a circumferential direction. Because resultant fabrication induced discontinuities would also be expected to have major dimensions oriented in the circumferential direction, axial overlay fabrication flaws are unrealistic.
The PDI program paragraph 2.0, allowing the overlay fabrication and base metal flaw tests to be performed separately. The requirement in paragraph 3.2(b) for reporting all extensions of cracking into the overlay is omitted from the PDI Program because it is redundant to the RMS calculations performed in paragraph 3.2(c) and its presence adds confusion and ambiguity to depth sizing as required by paragraph 3.2(c). This also makes the weld overlay program consistent with the Supplement 2 depth sizing criteria.
These changes are contained in [ASME] Code Case N-653. A comparison between the 1995 Edition and 1996 Addenda of Supplement 11, [ASME] Code Case N-653, and the PDI Program is enclosed [in the submittal] as supporting documentation. The first (left) column identifies the [ASME] Code requirements, while the second (middle) column identifies the changes made by the [ASME] Code Case.
There are, however, some additional changes that were inadvertently omitted from the
[ASME] Code Case. The most important change is paragraph 1.1(e)(2)(a)(1) where the phrase and base metal on both sides was inadvertently included in the description of a base metal grading unit. The PDI program intentionally excludes this requirement because some of the qualification samples include flaws on both sides of the weld. To avoid confusion, several instances of the term cracks or cracking were changed to the term flaws because of the use of alternative flaw mechanisms. Additionally, to avoid confusion, the overlay thickness tolerance contained in paragraph 1.1(b) last sentence, was reworded and the phrase and the remainder shall be alternative flaws
was added to the next to last sentence in paragraph 1.1(d)(1). Additional editorial changes were made to the PDI program to address an earlier request for additional information. The above changes are identified by bold print in the third (right) column of the enclosure [in the submittal].
3.1.4 NRC Staffs Evaluation The domestic nuclear utilities created the PDI to implement performance demonstration requirements contained in Appendix VIII of Section XI of the ASME Code. To this end, the PDI has developed a program for qualifying equipment, procedures, and personnel for examinations of weld overlays in accordance with the ultrasonic testing (UT) criteria of Appendix VIII, Supplement 11. Prior to the Supplement 11 program, EPRI maintained a performance demonstration program for weld overlay qualification under the Tri-party Agreement.1 Instead of having two programs with similar objectives, the NRC staff recognized the PDI Program for weld overlay qualifications as an acceptable alternative to the Tri-party Agreement.2 The PDI Program does not fully comport with the existing requirements of Supplement 11. PDI presented the differences at public meetings in which the NRC participated.3, 4 The differences are in flaw location within test specimens and fabricated flaw tolerances. The changes in flaw location permitted using test specimens from the Tri-party Agreement, and the changes in fabricated flaw tolerances provide UT acoustic responses similar to the responses associated with intergranular stress-corrosion cracking.
There are differences between the PDI Program and Supplement 11. The differences identified in the following Supplement 11 paragraphs: 1.1(b), 1.1(d)(1), 1.1(e)(1), 1.1(e)(2),
1.1(e)(2)(a)(1), 1.1(e)(2)(a)(2), 1.1(e)(2)(a)(3), 1.1(e)(2)(b)(1), 1.1(e)(2)(b)(2), 1.1(e)(2)(b)(3),
1.1(f)(1), 1.1(f)(3), 1.1(f)(4), 2.0, 2.1, 2.2(d), 2.3, 3.1, 3.2(a), 3.2(b) and 3.2(c) are evaluated below:
Paragraph 1.1(b) of Supplement 11 states limitations to the maximum thickness for which a procedure may be qualified. The ASME Code states that, The specimen set must include at least one specimen with overlay thickness within minus 0.10-inch to plus 0.25-inch of the maximum nominal overlay thickness for which the procedure is applicable. The ASME Code requirement addresses the specimen thickness tolerance for a single specimen set, but is confusing when multiple specimen sets are used. The PDI proposed alternative states that the specimen set shall include specimens with overlay not thicker than 0.10-inch more than the minimum thickness, nor thinner than 0.25-inch of the maximum nominal overlay thickness for 1
The Tri-party Agreement is between NRC, EPRI, and the Boiling Water Reactor Owners Group (BWROG), Coordination Plan for NRC/EPRI/BWROG Training and Qualification Activities of NDE (Nondestructive Examination) Personnel, July 3, 1984.
2 Letter from William H. Bateman to Michael Bratton, Weld Overlay Performance Demonstration Administered by PDI as an Alternative for Generic Letter 88-01 Recommendations, January 15, 2002, (ML020160532).
3 Memorandum from Donald G. Naujock to Terence Chan, Summary of Public Meeting Held January 31 - February 2, 2002, with PDI Representatives, March 22, 2002, (ML010940402).
4 Memorandum from Donald G. Naujock to Terence Chan, Summary of Public Meeting Held June 12 through June 14, 2001, with PDI Representatives, November 29, 2001, (ML013330156).
which the examination procedure is applicable. The proposed alternative provides clarification on the application of the tolerance. The tolerance is unchanged for a single specimen set; however, the proposed alternative clarifies the tolerance for multiple specimen sets by providing tolerances for both the minimum and maximum thicknesses. The proposed wording eliminates confusion while maintaining the intent of the overlay thickness tolerance. Therefore, the NRC staff finds this PDI Program alternative maintains the intent of the Supplement 11 requirements and is acceptable.
Paragraph 1.1(d)(1) requires that all base metal flaws be cracks. PDI determined that certain Supplement 11 requirements pertaining to location and size of cracks would be extremely difficult to achieve. For example, flaw implantation requires excavating a volume of base material to allow a pre-cracked coupon to be welded into this area. This process would add weld material to an area of the specimens that typically consists of only base material, and could potentially make ultrasonic examination more difficult and not representative of actual field conditions. In an effort to satisfy the requirements, PDI developed a process for fabricating flaws that exhibit crack-like reflective characteristics. Instead of all flaws being cracks, as required by Paragraph 1.1(d)(1), the PDI weld overlay performance demonstrations contain at least 70% cracks with the remainder being fabricated flaws exhibiting crack-like reflective characteristics. The fabricated flaws are semi-elliptical with tip widths of less than 0.002 inches. The licensee provided further information describing a revision to the PDI Program alternative to clarify when real cracks, as opposed to fabricated flaws, will be used:
Flaws shall be limited to the cases where implantation of cracks produces spurious reflectors that are uncharacteristic of actual flaws. The NRC has reviewed the flaw fabrication process, compared the reflective characteristics between actual cracks and PDI fabricated flaws, and found the fabricated flaws for this application provide assurance that the PDI Program meets the intent of the Supplement 11 requirements. Therefore, the NRC staff finds the proposed alternative to the Supplement 11 requirements acceptable.
Paragraph 1.1(e)(1) requires that at least 20% but not less than 40% of the flaws shall be oriented within +/-20 degrees of the axial direction (of the piping test specimen). Flaws contained in the original base metal heat-affected zone satisfy this requirement; however, PDI excludes axial fabrication flaws in the weld overlay material. PDI has concluded that axial flaws in the overlay material are improbable because the overlay filler material is applied in the circumferential direction (parallel to the girth weld); therefore, fabrication anomalies would also be expected to have major dimensions in the circumferential direction. The NRC staff finds, based upon engineering judgment, that this approach to implantation of fabrication flaws is reasonable for meeting the intent of the Supplement 11 requirements. Therefore, the NRC staff concludes that the PDI application of flaws oriented in the axial direction is acceptable.
Paragraph 1.1(e)(1) also requires that the rules of IWA-3300 shall be used to determine whether closely spaced flaws should be treated as single or multiple flaws. PDI treats each flaw as an individual flaw and not as part of a system of closely spaced flaws. PDI controls the flaws going into a test specimen set such that the flaws are free of interfering reflections from adjacent flaws. In some cases this permits flaws to be spaced closer than what is allowed for classification as a multiple set of flaws by IWA-3300, thus potentially making the performance demonstration more challenging than the existing requirements. Hence, the NRC staff concludes that PDI control for closely spaced flaws is acceptable.
Paragraph 1.1(e)(2) requires that specimens be divided into base metal and overlay grading units. The PDI Program adds clarification with the addition of the word fabrication and ensures flaw identification by ensuring all flaws will not be masked by other flaws with the addition of, Flaws shall not interfere with ultrasonic detection or characterization of other flaws.
the PDI alternative provides clarification and assurance that the flaws are identified. Therefore, the NRC staff finds the PDI alternative to the Supplement 11 requirements is acceptable.
Paragraph 1.1(e)(2)(a)(1) requires that a base grading unit shall include at least 3 inches of the length of the overlaid weld, and the base grading unit includes the outer 25% of the overlaid weld and base metal on both sides. The PDI Program reduced the criteria to 1 inch of the length of the overlaid weld and eliminated from the grading unit the need to include both sides of the weld. The proposed change permits the PDI Program to continue using test specimens from the existing weld overlay program which have flaws on both sides of the welds. These test specimens have been used successfully for testing the proficiency of personnel for over 16 years. The weld overlay qualification is designed to be a near-side (relative to the weld) examination, and it is improbable that a candidate would detect a flaw on the opposite side of the weld due to the sound attenuation and re-direction caused by the weld microstructure.
However, the presence of flaws on both sides of the original weld (outside the PDI grading unit) may actually provide a more challenging examination, as candidates must determine the relevancy of these flaws, if detected. The NRC staff determined, based on engineering judgment, that PDI use of the 1-inch length of the overlaid weld base grading unit and elimination from the grading unit, and the need to include both sides of the weld, as described in the PDI Program alternative, is an acceptable alternative to the Supplement 11 requirements.
Therefore, the NRC staff finds the proposed alternative acceptable.
Paragraph 1.1(e)(2)(a)(2) requires, when base metal cracking penetrates into the overlay material, that a portion of the base grading unit shall not be used as part of the overlay grading unit. The NRC staff finds that the PDI Program adjusts for the changes in Paragraph 1.1(e)(2)(a)(2) and conservatively states that when base metal flaws penetrate into the overlay material, no portion of it shall be used as part of the overlay fabrication grading unit. The NRC staff finds that the PDI Program also provided clarification by the addition of the term flaws for cracks and the addition of fabrication to overlay grading unit. The NRC staff concludes that the PDI Program alternative provides clarification and conservatism and, therefore, is acceptable.
Paragraph 1.1(e)(2)(a)(3) requires that for unflawed base grading units, at least 1 inch of unflawed overlaid weld and base metal shall exist on either side of the base grading unit. This is to minimize the number of false identifications of extraneous reflectors. The PDI Program stipulates that unflawed overlaid weld and base metal exists on all sides of the grading unit and flawed grading units must be free of interfering reflections from adjacent flaws which addresses the same concerns as the ASME Code. Hence, the NRC staff concludes that the PDI application of the variable flaw-free area adjacent to the grading unit meets the intent of the Supplement 11 requirements and is, therefore, acceptable.
Paragraph 1.1(e)(2)(b)(1) requires that an overlay grading unit shall include the overlay material and the base metal-to-overlay interface of at least 6 square inches. The overlay grading unit shall be rectangular, with minimum dimensions of 2 inches. The PDI Program reduces the base metal-to-overlay interface to at least 1 inch (in lieu of a minimum of 2 inches) and
eliminates the minimum rectangular dimension. This criterion is necessary to allow use of existing examination specimens that were fabricated in order to meet NRC Generic Letter (GL) 88-01 (Tri-party Agreement, July 1984). This criterion may be more challenging to meet than that of the ASME Code because of the variability associated with the shape of the grading unit.
Based on engineering judgment, the NRC staff concludes that PDI application of the grading unit is an acceptable alternative to the Supplement 11 requirements and is acceptable.
Paragraph 1.1(e)(2)(b)(2) requires that unflawed overlay grading units shall be surrounded by unflawed overlay material and unflawed base metal-to-overlay interface for at least 1 inch around its entire perimeter. The PDI Program redefines the area by noting unflawed overlay fabrication grading units shall be separated by at least 1 inch of unflawed material at both ends and sufficient area on both sides to preclude interfering reflections from adjacent flaws. The NRC staff determined that the relaxation in the required area on the sides of the specimens, while still ensuring no interfering reflections, may provide a more challenging demonstration than required by the ASME Code because of the possibility for having a parallel flaw on the opposite side of the weld. Therefore, based on engineering judgment, the NRC staff concludes that the PDIs application is an acceptable alternative to the Supplement 11 requirements.
Paragraph 1.1(e)(2)(b)(3) requirements are retained in the PDI Program. In addition, the PDI Program requires that initial procedure qualifications contain three times the number of flaws required for a personal qualification. To qualify new values of essential variables, the equivalent of at least one personal qualification set is required. The NRC staff concludes that PDIs additions enhance the ASME Code requirements and are, therefore, acceptable because it provides for a more stringent qualification criteria.
Paragraph 1.1(f)(1) requirements are retained in the PDI Program, with the clarification change of the term flaws for cracks. In addition, the PDI Program includes the requirements that sizing sets shall contain a distribution of flaw dimensions to verify sizing capabilities. The PDI Program also requires that initial procedure qualification contain three times the number of flaws required for a personal qualification. To qualify new values of essential variables, the equivalent of at least one personal qualification set is required. The NRC staff concludes that PDI additions enhance the ASME Code requirements and are, therefore, acceptable because it provides a more stringent qualification criteria.
Paragraphs 1.1(f)(3) and 1.1(f)(4) requirements are clarified by the PDI Program by replacing the term cracking with flaws because of the use of alternative flaw mechanisms. The NRC staff concludes that this clarification in the PDI Program meets the intent of the ASME Code requirements and is acceptable.
Paragraph 2.0 requirements are retained in the PDI Program alternative. In addition, the PDI Program provides clarification that the overlay fabrication flaw test and the base metal flaw test may be performed separately. The NRC staff concludes that this clarification in the PDI Program meets the intent of the ASME Code requirements and is acceptable.
Paragraphs 2.1 and 2.2(d) requirements are clarified by the PDI Program by the addition of the terms metal and fabrication. The NRC staff determined that the clarifications provide acceptable classification of the terms they are enhancing. Therefore, the NRC staff concludes that the PDI Program meets the intent of the ASME Code requirements and is acceptable.
Paragraph 2.3 requires that, for depth sizing tests, 80% of the flaws shall be sized at a specific location on the surface of the specimen identified to the candidate. This requires detection and sizing tests to be performed separately. The PDI revised the weld overlay program to allow sizing to be conducted either in conjunction with, or separately from, the flaw detection test. If performed in conjunction with detection and the detected flaws do not meet the Supplement 11 range criteria, additional specimens will be presented to the candidate with the regions containing flaws identified. Each candidate will be required to determine the maximum depth of flaw in each region. For separate sizing tests, the regions of interest will also be identified and the maximum depth and length of each flaw in the region will similarly be determined. In addition, PDI stated that grading units are not applicable to sizing tests, and that each sizing region will be large enough to contain the target flaw, but small enough such that candidates will not attempt to size a different flaw. The NRC staff determined that the above clarification provides a basis for implementing sizing tests in a systematic, consistent manner that meets the intent of Supplement 11. Based on engineering judgment, the NRC staff concludes that the PDI method is acceptable.
Paragraph 3.1 requires that examination procedures, equipment and personnel (as a complete ultrasonic system) are qualified for detection or sizing of flaws, as applicable, when certain criteria are met. The PDI Program allows procedure qualification to be performed separately from personnel and equipment qualification. Historical data indicate that, if ultrasonic detection or sizing procedures are thoroughly tested, personnel and equipment using those procedures have a higher probability of successfully passing a qualification test. In an effort to increase this passing rate, PDI has elected to perform procedure qualifications separately in order to assess and modify essential variables that may affect overall system capabilities. For a procedure to be qualified, the PDI Program requires three times as many flaws to be detected (or sized) as shown in Supplement 11 for the entire ultrasonic system. The personnel and equipment are still required to meet the Supplement 11 requirement; therefore, the PDI Program criteria exceeds the ASME Code requirements for personnel, procedures, and equipment qualification.
Therefore, the NRC staff concludes that the PDI Program criteria is acceptable.
Paragraph 3.2(a) requirements are clarified by the PDI Program by replacing the term cracking with flaws because of the use of alternative flaw mechanisms. The NRC staff concludes that this clarification in the PDI Program maintains the intent of the ASME Code requirements, and is acceptable.
Paragraph 3.2(b) requires that all extensions of base metal cracking into the overlay material by at least 0.10-inch are reported as being intrusions into the overlay material. The PDI Program omits this criterion because of the difficulty in actually fabricating a flaw with a 0.10-inch minimum extension into the overlay, while still knowing the true state of the flaw dimensions.
However, the PDI Program requires that cracks be depth-sized to the tolerance specified in the ASME Code which is 0.125 inches. Since the ASME Code tolerance is close to the 0.10-inch value of Paragraph 3.2(b), any crack extending beyond 0.10 inch into the overlay material would be identified as such from the characterized dimensions. The NRC staff determined that reporting of an extension in the overlay material is redundant for performance demonstration testing because of the flaw sizing tolerance. Therefore, the NRC staff concludes that PDI omission of highlighting a crack extending beyond 0.10 inch into the overlay material is acceptable.
Paragraph 3.2(c) is renumbered to Paragraph 3.2(b) in the PDI Program. The NRC staff concludes that this PDI Program change is administrative in nature and is, therefore, acceptable.
Based on the above evaluation, the NRC staff has determined that the licensees proposed alternative to use the PDI Program for the ultrasonic examination of overlay repaired piping welds is acceptable, because it will provide an acceptable level of quality and safety.
3.2 Relief for Weld Overlay Repair of Reactor Pressure Vessel Nozzle-to-Safe-end welds N1B and N2J 3.2.1 Code Requirements The licensees proposed repair plan consists of the use of CCs N-504-2 and N-638 to implement a weld overlay repair of the subject welds. A weld overlay repair has been designed consistent with the requirements of NUREG-0313, Revision 2 (which was implemented by GL 88-01), ASME CC N-504-2, and ASME Code,Section XI, Paragraph IWB-3640, 1989 edition with Appendix C (1989 addenda). The SSES-1 Code of Record is ASME Code,Section XI, 1989 edition. SSES-1 is currently in the second 10-year ISI interval. The original code of construction for the reactor vessel nozzle is ASME Code,Section III, 1968 edition up to and including 1970 summer addenda. The safe end was fabricated and installed to the ASME Code,Section III, 1974 edition with the summer 1974 addenda.
The weld overlay will extend around the full circumference of the safe end to nozzle location in accordance with NUREG-0313, Rev. 2, CC N-504-2, and GL 88-01. The overlay length will extend across the projected indication intersection with the outer pipe surface. The design thickness and length will be computed according to ASME CC N-504-2 and ASME Code,Section XI, Paragraph IWB-3640,1989 edition with Appendix C (1989 addenda). The overlay completely covers the defect location and other areas containing Alloy 182 material with the highly corrosion resistant Alloy 52 material. Approximately twelve layers of weld material are to be applied for the N1B weld overlay and ten layers of weld material are to be applied for the N2J weld overlay. The final number of layers will be determined based on the number of layers needed to meet the thickness requirement of each overlay. A temper bead welding approach will be used for this repair because it will be necessary to weld on the P3 Group 3 low alloy steel (LAS) nozzle material. ASME CC N-638 will be applied because it provides for machine GTAW temper bead weld repairs to P3 Group 3 materials at ambient temperature using dissimilar materials and without need for PWHT. The temper bead approach was selected because temper bead welding supplants the requirement for PWHT of heat affected zones (HAZs) in welded LAS material. Temper bead techniques produce excellent toughness and ductility in heat affected zones of the LAS.
3.2.2 System/Components for which Relief is Requested The requested relief applies to the proposed weld overlay repair of two reactor pressure vessel nozzle-to-safe-end welds (N1B and N2J).
3.2.3 Licensees Proposed Alternative
Exceptions to ASME CC N-504-2, Paragraph (b):
ASME CC N-504-2, paragraph (b) requires that the weld overlay metal shall be low carbon (0.035% maximum) austenitic stainless steel. Alloy 52, a nickel-based filler material has been selected in place of low carbon austenitic stainless steel.
Exception to CC N-504-2, Paragraph (e):
ASME CC N-504-2, paragraph (e) requires as-deposited delta ferrite measurements of at least 7.5 FN (ferritic number) for the weld overlay. These measurements will not be performed for this overlay, as the nickel-based filler material, is a fully austenitic material, containing no ferrite.
Exception to ASME CC N-638, Paragraph 1(a):
ASME CC N-638, paragraph 1(a) requires the maximum area of an individual weld based on the finished surface shall be 100 square inches. The area for the temper bead weld in this weld overlay design will be approximately 300 square inches for the N1B weld overlay and 150 square inches for the N2J weld overlay.
3.2.4 Licensees Bases for Licensee Proposed Alternative The bases for the proposed alternative are discussed below:
Exception to ASME CC N-504-2, Paragraph (b):
Alloy 52 was selected for the weld overlay material. This material is designated as UNS N06052 and F-No. 43. Alloy 52 with its high chromium content provides a high level of resistance to intergranular stress-corrosion cracking (IGSCC) consistent with the requirement of the code case.
Exception to ASME CC N-504-2, Paragraph (e):
Ferrite measurement requirements were developed for weld deposits of the 300 series stainless steels that require delta ferrite to develop resistance to IGSCC. Welds of Alloy 52 or Alloy 152 are 100% austenitic and contain no delta ferrite due to the high nickel composition (approximately 60% nickel and low iron content). Alloy 52 with its high chromium content provides a high level of resistance to IGSCC consistent with the purpose for the delta ferrite requirements for stainless steels of the code case.
Exception to ASME CC N-638, Paragraph 1(a):
ASME CC N-638 specifies a limit of 100 square inches for a temper bead weld. Because of the diameter of nozzles N1B (30 3/32 inches) and N2J (14 1/4 inches), this restriction would limit the weld overlay length to 1 1/16 inches and 2 1/4 inches, respectively, on the LAS nozzle materials. This distance could be justified as adequate axial length to provide for load redistribution from the weld overlay back into the nozzle without violating applicable stress limits of ASME Code,Section III for primary local and bending stresses and secondary peak stresses.
However, this axial length will not permit a complete examination of the outer 25% of the nozzle thickness as required by ASME CC N-504-2. In order to perform a qualified exam of the
required volume, the axial length of the overlay on the LAS nozzle will be extended to 3 1/8 inches for the N1B weld overlay and 2 5/8 inches for the N2J weld overlay, encompassing areas of 300 square inches and less than 150 square inches, respectively, for the temper bead welds.
PPL has requested relief from this restriction such that the overlay covers a LAS surface area of 300 square inches for the N1B weld and less than 150 square inches for the N2J weld. The reason for the relief is to allow a configuration which permits PPL to ultrasonically inspect the area involving the crack region from the nozzle side of the weld as required by Paragraph 4.0(b) of ASME CC N-504-2.
There have been a large number of temper bead weld overlay repairs applied to nozzle-to-safe-end welds in the nuclear industry. For the most part, these have involved smaller diameter components, and have generally been able to be performed while meeting the 100 square inches requirement of ASME CC N-638. However, at least two nozzle-to-safe-end welds have exceeded this limit. These include the nozzle-to-safe-end repair at V. C. Summer, where a nozzle butter was applied to a nominal 30-inch diameter, 3-inch thick nozzle using the temper bead process (this repair involved approximately 300 square inches), and the Three Mile Island surge nozzle, where a weld overlay repair was extended onto the nozzle so as to avoid producing a high stress concentration at the toe of the overlay (this repair involved greater than 200 square inches).
ASME CC N-432 has always allowed temper bead welding on LAS nozzles without limiting the temper bead weld surface area to 100 square inches. The two additional conditions required by ASME CC N-432 that are not required by ASME CC N-638 are that the temper bead repair have preheat when applied and that the procedure qualification be performed on the same specification type, grade and class of material as the component being welded in the field. The first of these requirements would present a severe man-rem radiation burden to PPL when performing this repair. The second condition could readily be met. It is principally for the man-rem exposure reason that ASME CC N-638 was selected for performing this repair. ASME CC N-638 is more restrictive than ASME CC N-432 when the size of the repair is considered.
The ASME Code committees have recognized that the 100 square inches restriction on the overlay surface area may be excessive and a draft code case is currently in progress within ASME Code,Section XI to increase the area limit to 500 square inches. The code case currently has the designation RRM 00-04 and attempts to combine the features of ASME CCs N-432 and N-638 into a single code case. The EPRI report that supports the draft code case examined the issue of residual stresses and of cracking associated with the weld overlay application. It concluded that the residual stresses were not detrimentally changed and that the tempering effects of the repair were not affected by the size of the overlay.
The issue of cracking and/or distortion of the weld and base metal was not specifically addressed in the code case development work. Since the nozzle-to-safe-end weld and the weld overlay are fabricated from austenitic materials with very high inherent toughness, no cracking is expected to occur due to the shrinkage associated with the weld overlays. With respect to the LAS, as was noted above, many temper bead weld overlays have been applied in the nuclear industry to these nozzle-to-safe-end locations. In no instance has there been any reported cracking due to the weld overlay application. The stiffness and high toughness
inherent in the LAS nozzle is expected to protect against any cracking and severely limit any distortion that might occur in the LAS nozzle. PPL will be measuring and evaluating axial shrinkage for impact on the nozzle and safe end materials and the piping system in accordance with ASME CC -504-2.
3.2.5 NRC Staffs Evaluation During the 13th refueling outage at SSES-1, flaws resulting from IGSCC were found in two reactor pressure vessel nozzle-to-safe-end welds (N1B and N2J). The licensee submitted two relief requests (RR-29 and RR-31) to support the weld overlay repair of the degraded welds. In RR-29 and RR-31, the licensee proposed a repair plan which consists of the use of ASME CCs N-504-2 and N-638, with exceptions, for a full structural weld overlay repair on the N1B outlet and N2J inlet recirculation system nozzles. The NRC staff notes that both ASME CCs are approved for use by the NRC in Regulatory Guide 1.147 without limitations or modifications.
The details of the exceptions and proposed alternatives are described in paragraph 3.2 of this safety evaluation.
ASME CC N-504-2 allows the use of weld overlay repair by deposition of weld reinforcement on the outside surface of the pipe in lieu of mechanically reducing the defect to an acceptable flaw size. However, the subject ASME CC is designed for weld overlay repair of austenitic stainless steel piping. Therefore, the material requirements regarding the carbon content limitation (0.035% maximum) and the delta ferrite content of at least 7.5 FN as delineated in ASME CC N-504-2, paragraphs (b) and (e) apply only to austenitic stainless steel weld overlay materials to ensure its resistance to IGSCC. These requirements are not applicable to Alloy 52, a nickel-based material which the licensee will use for the weld overlay repairs. The NRC staff notes that both nozzle-to-safe-end welds (N1B and N2J) are dissimilar metal welds made of Alloy 182 material. In addition, the weld overlay design requires a portion of the weld overlay to extend onto the LAS nozzle. For material compatibility in welding, the NRC staff considers that Alloy 52 is a better choice of filler material than austenitic stainless steel material for this weld joint configuration.
Alloy 52 contains about 30% chromium which would provide excellent resistance to IGSCC in the reactor coolant environment. This material is identified as F-No. 43 Grouping for Ni-Cr-Fe, classification UNS N06052 Filler Metal and has been previously approved by the NRC staff for similar applications. Therefore, the licensees proposed use of Alloy 52 for the weld overlay repair as an alternative to the requirements of ASME CC N-504-2, paragraphs (b) and (e) is acceptable as it will provide an acceptable level of quality and safety.
ASME CC N-638 allows the use of machine GTAW with ambient temperature preheat and no PWHT when draining the vessel is impractical. ASME CC N-638, paragraph 1(a) limits the size of the repair to 100 square inches maximum. However, because of the diameter of the nozzles (N1B is 30 3/32 inches and N2J is 14 1/4 inches) this restriction would limit the weld overlay length to 1 1/16 inches for the N1B nozzle and 2 1/4 inches for the N2J nozzle on the LAS nozzle material. These distances could be justified as adequate axial length to provide for load redistribution from the weld overlay back into the nozzle without violating the applicable stress limits of ASME Code,Section III for primary local and bending stresses and secondary peak stresses. However, this axial length will not permit a complete ultrasonic inspection of the area involving the crack region from the nozzle side of the weld as required by paragraph 4.0(b) of
ASME CC N-504-2. Therefore, the axial length of the overlay on the LAS nozzle will be extended to 3 1/8 inches for the N1B nozzle and 2 5/8 inches for the N2J weld overlay, encompassing areas of approximately 300 square inches and 150 square inches, respectively, for the temper bead welds. As a result, PPL has requested relief from the 100 square inches weld restriction.
ASME CC N-638 limits the size of the repair to a maximum of 100 square inches and a depth not greater than 1/2 the ferritic base metal thickness. The final weld surface areas requested in these relief requests are significantly larger than that allowed by the ASME Code. Some of the reasons for these limits are distortion of weld and base metal, cracking in weld and base metal and large residual stresses.
The issue of cracking and/or distortion of the weld and base metal were not specifically addressed in the code case development work. Since the nozzle-to-safe-end welds and the weld overlays are fabricated from austenitic materials with inherent toughness, no cracking in the overlays is expected to occur due to the shrinkage associated with the weld overlay. With respect to the LAS, many temper bead weld overlays have been applied in the nuclear industry to these nozzle to safe end locations. In no instance has there been any reported cracking due to the weld overlay application. The stiffness and high toughness inherent in the LAS nozzle is expected to protect against any cracking and limit any distortion that might occur in the LAS nozzle. PPL will be measuring and evaluating axial shrinkage for impact on the nozzle and safe end materials and on the piping system in accordance with ASME CC N-504-2. Also, any cracking which might occur should be detected by the final NDE of the weld overlay.
Since laboratory testing and field experience have been documented qualifying the temper bead weld overlay repair for nozzle-to-safe-end welds and these efforts and experience have demonstrated that the remedy provides a quality, sound repair to these joints, the NRC staff concludes that the nozzle-to-safe-end weld overlay repairs discussed in SSES-1 RR-29 and RR-31 can be applied to these nozzles without detrimental effects.
It should be noted that this relief is granted only for these specific nozzle repairs. If the licensee wishes to perform these types of repairs on other product forms (pipe, plate, forging, casting, etc.), thicknesses, diameters, ratios of thickness of overlay to original wall thickness or materials, a separate relief will have to be requested for each application.
Based on the above evaluation, the NRC staff has determined that the licensees proposed alternatives to the requirements of ASME CCs N-504-2 and N-638 for weld overlay repair of the subject welds are acceptable, because they will provide an acceptable level of quality and safety.
4.0 CONCLUSION
The NRC staff has reviewed PPLs submittal and determined that the proposed alternative to use the PDI program will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the use of the proposed alternative for the remainder of the second 10-year ISI interval. The NRC staff has also determined that PPL has provided an acceptable alternative to certain requirements of ASME CCs N-504-2 and N-638.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(i) PPLs proposed alternative is authorized for the
weld overlay repair of N1B outlet and N2J inlet recirculation system nozzles at SSES-1.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the authorized nuclear inservice inspector.
Principal Contributor: W. Koo Date: