ML063070602
| ML063070602 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 11/20/2006 |
| From: | Terao D NRC/NRR/ADRO/DORL/LPLIV |
| To: | Muench R Wolf Creek |
| Donohew J N, NRR/DORL/LP4, 415-1307 | |
| References | |
| ET 06-0027, I2R-34, I2R-35, I2R-36, I2R-37, I2R-38, TAC MD0290 | |
| Download: ML063070602 (9) | |
Text
November 20, 2006 Mr. Rick A. Muench President and Chief Executive Officer Wolf Creek Nuclear Operating Corporation Post Office Box 411 Burlington, KS 66839
SUBJECT:
WOLF CREEK GENERATING STATION - RELIEF REQUEST I2R-36 FOR THE SECOND 10-YEAR INTERVAL INSERVICE INSPECTION (TAC NO. MD0290)
Dear Mr. Muench:
By letter dated March 2, 2006 (ET 06-0011), supplemented by letter dated July 12, 2006 (ET 06-0027), Wolf Creek Nuclear Operating Corporation (the licensee) submitted Relief Request (RR) I2R-36 for its second 10-year inservice inspection (ISI) program interval at Wolf Creek Generating Station (WCGS). Included with the submittal were the following five RRs:
I2R-34, I2R-35, I2R-36, I2R-37, and I2R-38. This letter only addresses RR I2R-36.
In the enclosed safety evaluation (SE), the Nuclear Regulatory Commission (NRC) staff has evaluated the information provided by the licensee for the proposed second 10-year ISI interval RR I2R-36 for WCGS. Based on the SE, the staff concludes that it is impractical for the licensee to meet the applicable American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code requirements. Therefore, granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. The NRC staff grants relief and imposes alternative requirements in accordance with paragraph 50.55a(g)(6)(i) of Title 10 of the Code of Federal Regulations for the second 10-year ISI interval for WCGS. All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Sincerely,
/RA/
David Terao, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-482
Enclosure:
Safety Evaluation cc w/encl: See next page
November 20, 2006 Mr. Rick A. Muench President and Chief Executive Officer Wolf Creek Nuclear Operating Corporation Post Office Box 411 Burlington, KS 66839
SUBJECT:
WOLF CREEK GENERATING STATION - RELIEF REQUEST I2R-36 FOR THE SECOND 10-YEAR INTERVAL INSERVICE INSPECTION (TAC NO. MD0290)
Dear Mr. Muench:
By letter dated March 2, 2006 (ET 06-0011), supplemented by letter dated July 12, 2006 (ET 06-0027), Wolf Creek Nuclear Operating Corporation (the licensee) submitted Relief Request (RR) I2R-36 for its second 10-year inservice inspection (ISI) program interval at Wolf Creek Generating Station (WCGS). Included with the submittal were the following five RRs:
I2R-34, I2R-35, I2R-36, I2R-37, and I2R-38. This letter only addresses RR I2R-36.
In the enclosed safety evaluation (SE), the Nuclear Regulatory Commission (NRC) staff has evaluated the information provided by the licensee for the proposed second 10-year ISI interval RR I2R-36 for WCGS. Based on the SE, the staff concludes that it is impractical for the licensee to meet the applicable American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code requirements. Therefore, granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. The NRC staff grants relief and imposes alternative requirements in accordance with paragraph 50.55a(g)(6)(i) of Title 10 of the Code of Federal Regulations for the second 10-year ISI interval for WCGS. All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Sincerely,
/RA/
David Terao, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-482
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION PUBLIC RidsNrrDorl RidsNrrPMJDonohew RidsRgn4MailCenter (GMiller)
LPLIV r/f (CHaney/JLubinski) RidsNrrLALFeizollahi MMitchell, CVIB RidsAcrsAcnwMailCenter RidsNrrDorlDpr RidsOgcRp GCheruvenki, CVIB RidsNrrDorlLpl4 (DTerao) JLamb, EDO RIV ADAMS Accession No.: ML063070602 OFFICE NRR/LPL4/PM NRR/LPL4/LA LPL4/PM CVIB/BC OGC NRR/LPL4/BC NAME JDonohew LFeizollahi RCureton MMitchell JRund NLO w/comments Dterao DATE 11/20/06 11/20/06 11/17/06 8/8/06 11/7/06 11/20/06 OFFICIAL AGENCY RECORD
Wolf Creek Generating Station cc:
Jay Silberg, Esq. Chief, Radiation and Asbestos Control Pillsbury Winthrop Shaw Pittman LLP Section 2300 N Street, NW Kansas Department of Health Washington, D.C. 20037 and Environment Bureau of Air and Radiation Regional Administrator, Region IV 1000 SW Jackson, Suite 310 U.S. Nuclear Regulatory Commission Topeka, KS 66612-1366 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 Vice President Operations/Plant Manager Wolf Creek Nuclear Operating Corporation Senior Resident Inspector P.O. Box 411 U.S. Nuclear Regulatory Commission Burlington, KS 66839 P.O. Box 311 Burlington, KS 66839 Supervisor Licensing Wolf Creek Nuclear Operating Corporation Chief Engineer, Utilities Division P.O. Box 411 Kansas Corporation Commission Burlington, KS 66839 1500 SW Arrowhead Road Topeka, KS 66604-4027 U.S. Nuclear Regulatory Commission Resident Inspectors Office/Callaway Plant Office of the Governor 8201 NRC Road State of Kansas Steedman, MO 65077-1032 Topeka, KS 66612 Attorney General 120 S.W. 10th Avenue, 2nd Floor Topeka, KS 66612-1597 County Clerk Coffey County Courthouse 110 South 6th Street Burlington, KS 66839 February 2006
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST I2R-36 FOR THE SECOND 10-YEAR INTERVAL INSERVICE INSPECTION WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION DOCKET NO. 50-482
1.0 INTRODUCTION
By letter dated March 2, 2006 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML060720056), as supplemented by letter dated July 12, 2006 (ADAMS Accession No. ML062000312), Wolf Creek Nuclear Operating Corporation (the licensee) submitted Relief Request (RR) I2R-36 for its second 10-year inservice inspection (ISI) program interval at Wolf Creek Generating Station (WCGS). Included with the submittal were the following five RRs: I2R-34, I2R-35, I2R-36, I2R-37, and I2R-38. This safety evaluation (SE) only addresses RR I2R-36.
2.0 REGULATORY EVALUATION
ISI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Class 1, 2, and 3 components are performed in accordance with applicable editions and addenda of Section XI of the ASME Code, Rules for Inservice Inspection of Nuclear Power Plant Components, as required by Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g), except where specific relief has been granted by the Nuclear Regulatory Commission (NRC) pursuant to 10 CFR 50.55a(g)(6)(i) where code requirements are impractical. Paragraph 10 CFR 50.55a(g)(6)(i) indicates that NRC 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 giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2 and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month
interval, subject to the limitations and modifications listed therein. The ASME Code of record for the WCGS second 10-year ISI interval is the 1989 Edition, with no addenda.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Requirement ASME Code,Section XI, 1989 Edition, with no addenda, Figure IWC-2500-1, Examination Category C-A Full Penetration Bonnet Flange to Channel Welds of the Residual Heat Exchanger, Code Item Number C1.10, requires that ultrasonic testing (UT) must be conducted on each side of the weld equal to a distance of one-half of the flange thickness adjacent to the weld for the flange side, and one-half of the channel thickness adjacent to the weld for the channel side.
3.2 System/Component(s) for which Relief is Requested The licensee requested relief for the following ASME Code,Section XI, Category C-A full penetration bonnet flange to channel welds of the residual heat exchanger:
Code Item Number C1.10 - Bonnet Flange to Channel Welds of the Residual Heat Exchanger.
3.3 Licensees Proposed Alternative and Basis for Requesting Relief (as stated in the licensees letter dated March 2, 2006):
- 3. Applicable Code Requirement ASME Section Xl, Figure IWC-2500-1 1989 Edition with no addenda requires volumetric examination of a minimum volume of base material on each side of the weld equal to a distance of 1/2 inch for the shell circumferential weld [one-half of the flange thickness adjacent to the weld for the flange side, one-half of the channel thickness adjacent to the weld for the channel side] (Code Item C1.10).
The Wolf Creek Nuclear Operating Corporation (WCNOC) second ten-year interval inservice inspection program plan also implements Code Case N-460, which is endorsed by the NRC in Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability ASME Section Xl, Division 1." Code Case N-460 states in part, when the entire examination volume or area cannot be examined due to interference by another component or part geometry, a reduction in examination coverage on any Class 1 or Class 2 weld may be accepted provided the reduction in coverage for that weld is less than 10 percent."
NRC Information Notice (IN) 98-42, "Implementation of 10 CFR 50.55a(g)
Inservice Inspection Requirements," termed a reduction in coverage of less than 10 percent to be essentially 100 percent." IN 98-42 states in part, The NRC has adopted and further refined the definition of "essentially 100 percent" to mean "greater than 90 percent"... has been applied to all examinations of welds or other areas required by ASME Section XI.
- 4. Impracticality of Compliance The examination of the subject components is limited by the configuration of the flange design and the location of flange bolting. As shown on the attached figures [in the licensees March 2, 2006, submittal], the proximity of the bolting to the bonnet flange to channel weld limits the scans from the flange side of the weld. Complete perpendicular coverage was achieved; however, the parallel coverage was limited on the flange side of the weld. Although a small amount of scanning was able to be performed on the flange side, parallel coverage was conservatively credited only to the channel side of the weld. This yields a composite coverage of the required examination volume of 75%.
Removal of the bolting to allow for complete coverage would be needed to meet the Code requirements. This would result in a considerable increase of radiological exposure to WCNOC personnel as, during refueling outages, this component is located in an area classified as a "high radiation area." The dose rates around this component generally range from 15 to 50 millirem per hour. It is estimated that it would take approximately 40 additional man-hours to remove the bolting, perform the additional examination and replace the bolting. The amount of dose received by personnel during this time would be a considerable burden to WCGS.
- 5. Burden Caused by Compliance The design configuration restrictions of the bonnet flange of the RHR [residual heat remover] heat exchanger at Wolf Creek Generating Station (WCGS) make the Code required examination coverage requirements impractical. The bolting is located so that circumferential scanning for axial flaws is limited on the flange side of the weld. To examine essentially 100% of the Code required volume would require removal and replacement of the bolting, causing Wolf Creek personnel to receive an additional amount of radiological dose, likely well in excess of one man-Rem.
- 6. Proposed Alternative and Basis for Use Proposed Alternative The following alternatives are proposed in lieu of the required examination coverage of essentially 100 percent:
- 1. Ultrasonic Testing (UT) of the subject weld was performed to the maximum extent practical during the second ten-year interval.
- 2. Pressure test VT-2 visual examinations were performed as required by Code Category C-H during the second ten-year interval. No evidence of leakage was identified for this component.
4 Basis for Use The basis for use of this alternative is that it provides the best examination coverage practical within the limitations of the current configuration. Based on the percentage of the examination volume completed, and the lack of any indications detected, there is a high level of confidence in the continued structural integrity of the weld. WCNOC does not believe that there is an increased level of safety or quality commensurate with the amount of increased dose required to complete this examination.
It should be noted that the Channel-to-Head weld of this RHR heat exchanger was examined with 100% coverage achieved, and no indications were detected.
- 7. Duration of Proposed Alternative The second ten-year ISI interval which began September 3, 1995, and ended September 2, 2005.
Precedents Comanche Peak Steam Electric Station Letter, dated March 10, 2005, Docket No. 50-446, "Relief Requests B-12, B-13, B-14, and C-8 to the Unit 2 Inservice Inspection (ISI) from 1986 Edition of ASME Code,Section XI, No Addenda," and the associated NRC Safety Evaluation Report dated July 8, 2005 (TAC No. MC6405) 4.0 STAFF EVALUATION ASME Code,Section XI, 1989 Edition, and no Addenda, Figure IWC-2500-1, Examination Category C-A Full Penetration Bonnet Flange to Channel Welds of the Residual Heat Exchanger, Code Item Number C1.10, requires that UT must be conducted on each side of the weld equal to a distance of one-half of the flange thickness adjacent to the weld for the flange side, and one-half of the channel thickness adjacent to the weld for the channel side.
As stated in its application for relief and discussed above in the section on the licensees basis for requesting relief from the ASME Code, the licensee explained that (1) examination of the subject components is limited by the configuration of the flange design and the location of flange bolting, and (2) removal of the bolting to allow for complete coverage would be needed to meet the Code requirements resulting in a considerable increase in personnel radiation exposure. Therefore, the licensee concluded that it was impractical to meet the applicable ASME Code requirement. Based on its review of the relief requested, the NRC staff agrees with the licensee that it is impractical for the licensee to meet the applicable ASME Code requirements.
In its letter dated March 2, 2006, the licensee stated that no indications were identified in the subject welds during the previous preservice and ISI UT examinations, and complete coverage of the subject welds was not achieved during these UT examinations.
5 To effectively evaluate the licensees proposed alternative, the staff, in an electronic mail dated May 9, 2006, requested that the licensee provide additional information regarding the following issues associated with the relief request.
(1) Type of weld metal that was used for the subject welds.
(2) State of stress that is present in the uninspected portion of the welds.
The licensee, in its letter dated July 12, 2006, provided responses to the staffs request for additional information (RAI). The following section provides information regarding the responses from the licensee and the corresponding staff evaluation.
4.1 Type of Weld Metal that was Used for the Subject Welds In its response to the staffs RAI, the licensee, in a letter dated July 12, 2006, stated that carbon/low-alloy steel weld metal was used for all the subject welds.
4.2 State of Stress that is Present in the Uninspected Portion of the Welds In its response to the staffs RAI, the licensee, in a letter dated July 12, 2006, stated that the uninspected portion of the weld is a low-stress region. The licensee stated that the subject welds have a very large flaw tolerance and they experience mild-duty cycle. The volume of the subject welds where degradation would be first expected to occur was examined to the ASME Code,Section XI, requirements. These welds are subject to pressure visual testing (VT-2) during every outage and this test would detect any through-wall leakage in the subject welds.
Since no flaws were detected in the subject welds, the licensee concluded that the proposed alternative examination provides reasonable assurance of structural integrity.
The staff reviewed the licensees responses to the RAIs and finds that the licensees technical basis for the reduction in the examination volume is acceptable for the following reasons:
(1) The base metal and weld metal were extensively examined during construction, preservice inspection, and prior inservice inspections. These examinations indicated no flaws which required evaluation per the ASME Code.
(2) The low-alloy steel bonnet flange to channel welds of the residual heat exchanger are classified as ferritic welds. Unlike stainless-steel welds or nickel-alloy welds, these ferritic welds are less likely to experience aging degradation due to intergranular stress-corrosion cracking near the heat-affected zone region of the weld area.
(3) The uninspected portion of the weld is a low-stress region and, therefore, service-induced flaws are less likely to occur in the volume near the weld that was excluded from the UT examinations. The licensee conducted UT examinations on the volume of the subject welds where service-induced cracking is more likely to occur. Since UT examinations thus far did not identify any cracking in the inspected region, the staff concludes that there is no reason to expect service-induced degradation in the uninspected regions of the subject
6 welds. Furthermore, the licensees pressure test VT-2 examinations during every refueling outage did not identify any through-wall leakage in these welds.
Therefore, the staff concludes that there is no active service-induced degradation in the subject welds.
Based on the above evaluation, the NRC staff concludes that the prior UT examinations and VT-2 and pressure tests of the subject welds did not identify any unacceptable flaws (per the ASME Code,Section XI criteria), the location of the uninspected region of the welds is a low-stress region, and this region is less prone to any service-induced cracking. Based on these conclusions, the NRC staff finds that the licensees proposed alternative will identify degradation in these welds in a timely manner so that corrective actions can be taken by the licensee to maintain the structural integrity of the subject welds. Based on this and the impracticality of meeting the applicable ASME Code requirements, the NRC staff concludes that the requested relief may be granted to the licensee for the second 10-year interval in accordance with 10 CFR 50.55a(g)(6)(i).
5.0 CONCLUSION
Based on the above discussion, the staff concludes that it is impractical for the licensee to meet the applicable code requirements. Therefore, granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. The proposed RR I2R-36 is granted for the second 10-year ISI interval for WCGS. All other requirements of the ASME Code, Sections III and XI, for which relief has not been specifically requested, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: Ganesh S. Cheruvenki Date: November 20, 2006