ML082490050
| ML082490050 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  (NPF-087, NPF-089) |
| Issue date: | 09/18/2008 |
| From: | Markley M Plant Licensing Branch IV |
| To: | Blevins M Luminant Generation Co |
| Markley, M T, NRR/DORL/LP4, 301-415-5723 | |
| References | |
| TAC MD9215, TAC MD9216 | |
| Download: ML082490050 (7) | |
Text
September 18, 2008 Mr. M. R. Blevins Executive Vice President
& Chief Nuclear Officer Luminant Generation Company LLC ATTN: Regulatory Affairs P. O. Box 1002 Glen Rose, TX 76043
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION, UNITS 1 AND 2 - REQUEST FOR RELIEF B-8 (UNIT 1) AND B-6 (UNIT 2) FOR SECOND 10-YEAR INSERVICE INSPECTION INTERVAL FROM 10 CFR 50.55a INSPECTION REQUIREMENTS FOR REACTOR VESSEL HOT-AND COLD-LEG NOZZLE WELD EXAMINATIONS (TAC NOS. MD9215 AND MD9216)
Dear Mr. Blevins:
The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed and evaluated the information provided by Luminant Generation Company LLC (the licensee), in its letter dated July 10, 2008. The licensee requested approval of Relief Requests B-8 and B-6 for Comanche Peak Steam Electric Station (CPSES), Units 1 and 2, respectively, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(a)(3)(i). The relief requests relate to the examination of the reactor vessel hot-and cold-leg nozzle welds during the second 10-year inservice inspection (ISI) intervals at CPSES, Units 1 and 2.
Based on the proposed alternatives and information provided in the licensees submittal, the NRC staff has determined that requiring the licensee to qualify procedures, personnel, and equipment to meet the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code-required root mean square error (RMSE) for crack-depth sizing is not feasible at the present time. The licensees proposal of adding the difference between the ASME Code-required RMSE and the demonstrated RMSE to the measured through-wall extent, in addition to the use of the acceptance standards specified in Section IWB-3500 of the ASME Code, provides reasonable assurance of structural integrity. Additionally, the licensees proposal to use surface geometry profiling combined with eddy current examination provides reasonable assurance that the axial flaws in the presence of rough surfaces will be detected, thus providing an acceptable level of quality and safety.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the proposed alternative is authorized for the second 10-year ISI interval for CPSES Unit 1, which began on August 13, 2000, and ends on August 12, 2010, and the second 10-year ISI interval for CPSES Unit 2, which began on August 3, 2004, and ends on August 2, 2014.
M. The NRC staffs safety evaluation is enclosed.
Sincerely,
/RA/
Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-445 and 50-446
Enclosure:
Safety Evaluation cc w/encl: See next page
M. The NRC staffs safety evaluation is enclosed.
Sincerely,
/RA/
Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-445 and 50-446
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION:
PUBLIC LPLIV Reading RidsAcrsAcnw_MailCTR Resource RidsNrrDorlDpr Resource RidsNrrDciCpnb Resource RidsNrrDorlLpl4 Resource RidsNrrPMBSingal Resource RidsNrrLAJBurkhardt Resource RidsOgcRp Resource RidsRgn4MailCenter Resource MCox, EDO RIV CNove, NRR/DCI/CPNB ADAMS Accession No. ML082490050
(*) SE transmitted by Memo dated 8/27/08 OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/CPNB/BC OGC NRR/LPL4/BC NRR/LPL4/PM NAME BSingal JBurkhardt TChan (*)
RvHomlmes MMarkley BSingal DATE 9/12/08 9/11/08 8/27/08 9/16/08 9/18/08 9/18/08 OFFICIAL AGENCY RECORD
Comanche Peak Steam Electric Station (7/7/2008) cc:
Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 2159 Glen Rose, TX 76043-2159 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 612 E. Lamar Blvd., Suite 400 Arlington, TX 76011-4125 Mr. Fred W. Madden, Director Regulatory Affairs Luminant Generation Company LLC P.O. Box 1002 Glen Rose, TX 76043 Timothy P. Matthews, Esq.
Morgan Lewis 1111 Pennsylvania Avenue, NW Washington, DC 20004 County Judge P.O. Box 851 Glen Rose, TX 76043 Environmental and Natural Resources Policy Director Office of the Governor P.O. Box 12428 Austin, TX 78711-3189 Mr. Richard A. Ratliff, Chief Bureau of Radiation Control Texas Department of Health 1100 W. 49th Street Austin, TX 78756-3189 Mr. Brian Almon Public Utility Commission William B. Travis Building P.O. Box 13326 1701 N. Congress Avenue Austin, TX 78701-3326 Ms. Susan M. Jablonski Office of Permitting, Remediation and Registration Texas Commission on Environmental Quality MC-122 P.O. Box 13087 Austin, TX 78711-3087 Anthony P. Jones Chief Boiler Inspector Texas Department of Licensing and Regulation Boiler Division E.O. Thompson State Office Building P.O. Box 12157 Austin, TX 78711
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NOS. B-8 FOR UNIT 1 AND B-6 FOR UNIT 2 SECOND 10-YEAR INSERVICE INSPECTION INTERVAL LUMINANT GENERATION COMPANY LLC COMANCHE PEAK STEAM ELECTRIC STATION, UNITS 1 AND 2 DOCKET NOS. 50-445 AND 50-446
1.0 INTRODUCTION
By letter dated July 10, 2008 (Agencywide Document Access Management System (ADAMS),
Accession No. ML082000123), Luminant Generation Company LLC (the licensee) requested U.S. Nuclear Regulatory Commission (NRC) approval of Relief Requests B-8 and B-6 for Comanche Peak Steam Electric Station (CPSES), Units 1 and 2, respectively, which involve an alternative method of examination of the reactor vessel hot-and cold-leg nozzle welds during the second 10-year inservice inspection (ISI) intervals at both CPSES units.
2.0 REGULATORY REQUIREMENTS Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(g) specifies that ISI of nuclear power plant components shall be performed in accordance with the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section XI, except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest, given the consideration of the burden upon the licensee. In addition, 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Paragraph 10 CFR 50.55a(g)(5)(iii) states that if the licensee has determined that conformance with certain code requirements is impractical for its facility, the licensee shall notify the Commission and submit, as specified in Section 50.4, information to support the determinations.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that ISI of components and system pressure tests conducted during the first 10-year interval Enclosure
and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
3.0 TECHNICAL EVALUATION
3.1
Applicable Code Edition and Addenda
The Code of record for the second 10-year ISI program at CPSES, Units 1 and 2 is the ASME Code,Section XI, 1998 Edition through the 2000 Addenda. In addition, as required by 10 CFR 50.55a, ASME Code,Section XI, 1995 Edition with the 1996 Addenda is used for Appendix VIII, Performance Demonstration Initiative (PDI) for Ultrasonic Examination System.
3.2 Components for Which Relief is Requested The affected Class 1 Risk-Informed ISI (RI-ISI) Reactor Coolant piping welds are:
Code Category/Item No.
Description Weld Nos. (both units)
(pipe size in inches) 1-4100-1 (29")
1-4100-14 (27.5")
1-4200-1 (29")
1-4200-14 (27.5")
1-4300-1 (29")
1-4300-14 (27.5")
1-4400-1 (29")
R-A, R1.20 (formerly Code Category B-F, B5.10) 8 Nozzle-to-Safe End Butt Welds 1-4400-14 (27.5")
1-4100-2 (29")
1-4100-13 (27.5")
1-4200-2 (29")
1-4200-13 (27.5")
1-4300-2 (29")
1-4300-13 (27.5")
1-4400-2 (29")
R-A, R1.20 (formerly Code Category B-J, B9.11) 8 Circumferential Pipe Welds 1-4400-13 (27.5")
3.3
Applicable Code Requirement
Examination Category R-A, items R1.20 (formerly Code Categories B-F, B5.10 and B-J, B9.11 in the ASME Code,Section XI, 1998 Edition through the 2000 Addenda) specifies volumetric examination. This volumetric examination is to be conducted in accordance with Appendix VIII, Supplements 10 and 2 in the ASME Code,Section XI, 1995 Edition with the 1996 Addenda per 10 CFR 50.55a(g)(6)(ii)(C).
3.4 Licensee Proposed Alternative and Basis for Use 3.4.1 Relief from the 0.125 inches root mean square error (RMSE) depth-sizing requirement of Appendix VIII, Supplements 10 and 2 The licensee stated that a request for relief from the required RMSE depth sizing is needed because, to date, examination vendors have not met the established RMSE of 0.125 inches for depth sizing. The licensee proposes to use a contracted examination vendor that has demonstrated ability to meet a depth sizing qualification requirement with an RMSE of 0.189 inches instead of the 0.125 inches required for Supplement 10, an RMSE of 0.367 inches instead of the 0.125 inches required for Supplement 2, and an RMSE of 0.245 inches instead of the 0.125 inches for Supplements 10 and 2 combined, as per approved Code Case N-696.
The licensee states that in the event an indication is detected that requires depth sizing, the 0.120-inch difference between the required RMSE and the demonstrated RMSE will be added to the measured through-wall extent for comparison with applicable acceptance criteria. If the examination vendor demonstrates an improved depth-sizing RMSE prior to the examination, the excess of that improved RMSE over the 0.125-inch RMSE requirement, if any, will be added to the measured value for comparison with applicable acceptance criteria.
3.4.2 Relief from using only ultrasonic testing for Code-specified pipe weld inspections from the inside diameter surface in the presence of weld root and counter-bore surface conditions The licensee states that the examination vendor for the CPSES reactor vessel nozzle examinations has qualified for detection of circumferential flaws in accordance with Appendix VIII, Supplements 10 and 2, as demonstrated through the Electric Power Research Institute PDI Program, for nozzle-to-safe end and safe end-to-pipe welds examined from the inside diameter (ID) surface. The vendor is similarly qualified for detection of axial flaws provided the surface is machined or ground smooth with no exposed root reinforcement or counter-bore. Surface roughness may be present that could call into question the ultrasonic qualifications demonstrated for detection of axial flaws.
CPSES proposes using surface geometry profiling software (profilometry) in conjunction with a focused immersion ultrasonic transducer positioned to permit accurate profile data across the examination volume, to help the examiner confirm locations where the raw data indicates lack of transducer contact due to problematic surface geometry. Additionally, eddy current examination will be used to supplement ultrasonic examination for the nozzle-to-safe end or safe end-to-pipe welds having sufficient surface roughness to call into question the applicability of the ultrasonic examination qualification to detect axial flaws. Profilometry will be used to determine the surface areas, if any, where roughness may limit the ability of ultrasonic methods to be used effectively as qualified through performance demonstration.
To supplement the ultrasonic examinations for rough surface detection coverage, the licensee proposes to use the following eddy current techniques:
Up to two plus point probes applied circumferentially on the pipe inside surface in scan increments of 0.080 inches circumferentially (for axial flaws) and 0.25 inches axially.
Automated systems for data collection and analysis.
The target flaw size for the eddy current procedure is 0.28 inch, which is within the ASME Code linear flaw acceptance standards of 0.45 inches for austenitic material, and 0.625 inches for ferritic material (defined for the outside surface in the ASME Code, Table IWB-3514). All eight nozzle-to-safe end welds and all eight safe end-to-pipe welds will be examined.
The licensee states that the examination vendor has developed an eddy current technique to augment the ultrasonic examination method and provide increased sensitivity at the ID surface.
The eddy current technique was first used in the Virgil C. Summer (VC Summer) reactor vessel primary nozzle examinations of 2000. The procedure was refined after its first use in 2000 by applying it to the VC Summer hot-leg dissimilar metal weld section removed from service. The removed section had a number of primary water stress-corrosion cracking (PWSCC) flaws along with non-relevant indications resulting from metallurgical interface and surface geometry.
Using these actual flaws and geometric conditions in the removed section to refine the technique, the vendor developed a reliable flaw-screening criterion which allowed for the successful use of the procedure in the VC Summer 2002 and 2003 examinations.
Since that time, the technique has been successfully blind tested for the Swedish authority SQC (Swedish NDT Qualification Center) Kvalificeringscentrum AB under the program, "Qualification of Equipment, Procedure and Personnel for Detection, Characterization and Sizing of Defects in Areas in Nozzle to Safe End Welds at Ringhals Unit 3 and 4," by Hakan Soderstrand, dated July 10, 2003. The important qualification parameters (Reference SQC Qualification Report No. 019A/03) for eddy current in the SQC blind tests were as follows:
Defect types: fatigue and stress-corrosion cracks, surface initiated Tilt: +/- 10 degrees; Skew: +/- 10 degrees Detection target size: interdentritic stress-corrosion cracking (IDSCC) 6 millimeters (mm) (0.25 inches) long Flaws Location: within 10 mm (13/32 inches)
Length of the planar flaw within a 70 percent confidence level: +/- 9 mm (3/8 inches)
False call rate: less than or equal to 20 percent for the personnel qualification tests
The technique has also been used to supplement examination of portions of the relevant near-surface volumes during the last 15 domestic pressurized-water reactor (PWR) nozzle-to-pipe examinations conducted by the vendor.
The licensee states that ultrasonic examinations supplemented by eddy current examinations and profilometry will be conducted to the maximum extent practical and are subject to third-party review by the Authorized Nuclear Inservice Inspector.
The licensee states that use of ultrasonic profilometry and eddy current examination, with procedures and personnel qualified through the SQC blind tests to supplement Appendix VIIl qualified ultrasonic procedures and personnel for the nozzle-to-safe end and safe end-to-pipe welds provides additional assurance that surface-breaking flaws that may be present would be detected in the presence of potential surface roughness. The result is an equivalent or better level of quality and safety than that currently qualified to meet ASME Code requirements in accordance with 10 CFR 50.55a(a)(3)(i).
3.4.3 Duration of Proposed Alternative The proposed alternative is requested for the second 10-year ISI interval for CPSES Unit 1, which began on August 13, 2000, and ends on August 12, 2010, and the second 10-year ISI interval for CPSES Unit 2, which began on August 3, 2004, and ends on August 2, 2014.
4.0 STAFF EVALUATION 4.1 Relief from the 0.125-inch RMSE depth-sizing requirement of Appendix VIII, Supplements 10 and 2 ASME Code,Section XI, Appendix VIII, Supplement 10 states that examination procedures, equipment, and personnel are qualified for depth sizing when the RMSE of the flaw-depth measurements, as compared to true depths, do not exceed 0.125 inches. Supplement 2 also requires that the RMSE of the flaw depths estimated by ultrasonics, as compared with true depths, shall not exceed 0.125 inches. Code Case N-696, which combines the requirements of Supplements 10 and 2, states that Supplement 2 examination procedures, equipment, and personnel are qualified for depth sizing when the flaw depths estimated by ultrasonics, as compared with the true depth, do not exceed 0.125-inch root mean square, when they are combined with a successful Supplement 10 qualification. (Note: Code Cases N-695 and N-696 are identified as Acceptable ASME Code Section XI Code Cases per Revision 15 of the NRC Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability ASME Section XI, Division 1.)
The nuclear industry is in the process of qualifying personnel to Supplement 10 as implemented by the PDI program. However, for demonstrations performed from the inside surface of a pipe weld, personnel have been unsuccessful at achieving the ASME Code-required 0.125-inch RMSE flaw-depth sizing criterion. At this time, the staff acknowledges that achieving the 0.125-inch RMSE appears to not be feasible as personnel have only been capable of achieving an accuracy of 0.189-inch RMSE to size any detected flaws. The vendor contracted by the licensee has proposed to use an RMSE of 0.189 inches instead of the 0.125 inches required for Supplement 10, an RMSE of 0.367 inches instead of the 0.125 inches required for
Supplement 2, and an RMSE of 0.245 inches instead of the 0.125 inches for Supplements 10 and 2 combined, as per approved Code Case N-696. In the event an indication is detected that requires depth sizing, the 0.120-inch difference between the required RMSE and the demonstrated RMSE (0.245 inches - 0.125 inches = 0.120 inches) will be added to the measured through-wall extent. This total will then be assessed against the applicable acceptance criteria specified in Section IWB-3500 of the ASME Code for flaw evaluation.
Additionally, the licensee proposes that, if the examination vendor demonstrates an improved depth-sizing RMSE prior to the examination, the excess of that improved RMSE over the 0.125-inch RMSE requirement, if any, will be added to the measured value for flaw evaluation with applicable acceptance criteria specified in Section IWB-3500 of the ASME Code.
The staff finds that compliance with the ASME Code-required RMSE value is not feasible at this time and that adding the difference between the ASME Code-required RMSE and the demonstrated RMSE to the measured through-wall extent, in addition to the use of the acceptance standards specified in Section IWB-3500 of the ASME Code, provides reasonable assurance of structural integrity.
4.2 Relief from using only ultrasonic testing for Code-specified pipe weld inspections from the ID surface in the presence of weld root and counter-bore surface conditions The licensees contracted vendor did not fully meet the qualification requirements of ASME Code,Section XI, Appendix VIII, Supplements 10 and 2. The vendor has qualified for detection of circumferential flaws for nozzle-to-safe end and safe end-to-pipe welds examined from the ID surface. Similarly, the vendor is qualified for detection of axial flaws provided the surface is machined or ground smooth with no exposed root reinforcement or counter-bore. However, where surface roughness may be present, the ultrasonic qualifications demonstrated for detection of axial flaws is called into question due to the ultrasonic transducers lift-off from the rough surface/unfavorable ID geometry. The staff notes that the PDI program is not successful in qualifying examiners to detect axial flaws in the presence of rough surface. Therefore, the staff has determined that to fully comply with the subject ASME Code qualification requirement is not possible at this time.
The licensee proposed the use of surface geometry profiling software (profilometry) in conjunction with a focused immersion ultrasonic transducer positioned to permit accurate profile data across the examination volume to help the examiner confirm locations where the raw ultrasonic data indicates lack of transducer contact due to problematic surface geometry. The staff finds that the use of profilometry to confirm the presence of rough surfaces acceptable as it provides additional information as to the condition of the surface of the examination volume.
In addition to profilometry, the licensee proposed the use of eddy current examination to supplement to the ultrasonic examination for the nozzle-to-safe end and safe end-to-pipe welds having sufficient surface roughness to call into question the applicability of the ultrasonic examination qualification to detect axial flaws. Profilometry will confirm the presence of rough surfaces and the eddy current examination will assure the detection of surface breaking flaws.
The eddy current methodology to be used is similar to that used in VC Summers 2000, 2002 and 2003 refueling outages. The technique was refined based on examinations performed on a hot-leg dissimilar metal weld section removed from VC Summer during the 2000 refueling
outage. The removed section contained PWSCC flaws and non-relevant indications resulting from surface geometry and metallurgical interfaces. The licensees contracted vendor has used this technique to supplement examination of portions of the relevant near-surface volumes during the last 15 domestic PWR nozzle-to-pipe examinations. The staff finds that the licensees proposed alternative, which combines ultrasonic and eddy current techniques in examining for axial flaws in the presence of rough surfaces, will provide an acceptable level of detect ability and sensitivity. Therefore, the staff concludes that the licensees proposed alternative will provide reasonable assurance of the structural integrity of the subject welds.
5.0 CONCLUSION
Based on the above review, the staff has determined that requiring the licensee to qualify procedures, personnel, and equipment to meet the maximum error of 0.125-inch RMSE for crack-depth sizing is not feasible at the present time. The licensees proposal of adding the difference between the ASME Code-required RMSE and the demonstrated RMSE to the measured through-wall extent, in addition to the use of the acceptance standards specified in Section IWB-3500 of the ASME Code, provides reasonable assurance of structural integrity.
Additionally, the licensees proposal to use surface geometry profiling combined with eddy current examination provides reasonable assurance that the axial flaws in the presence of rough surfaces will be detected, thus providing an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the proposed alternative is authorized for the second 10-year ISI interval for CPSES Unit 1, which began on August 13, 2000, and ends on August 12, 2010, and the second 10-year ISI interval for CPSES Unit 2, which began on August 3, 2004, and ends on August 2, 2014. All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: C. Nove Date: September 18, 2008