ML063070602

Wolf Creek Generating Station - Relief Request I2R-36 for the Second 10-year Interval Inservice Inspection (TAC No. MD0290)

ML063070602
Person / Time
Site:	Wolf Creek
Issue date:	11/20/2006
From:	Terao D NRC/NRR/ADRO/DORL/LPLIV
To:	Muench R A 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, 2006Mr. Rick A. MuenchPresident 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 THESECOND 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 hasevaluated 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 intervalfor WCGS. All other requirements of the ASME Code, Sections III and XI, for which relief hasnot been specifically requested, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.Sincerely,/RA/David Terao, ChiefPlant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor RegulationDocket No. 50-482

Enclosure:

Safety Evaluation cc w/encl: See next page November 20, 2006Mr. 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 THESECOND 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 hasevaluated 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 intervalfor WCGS. All other requirements of the ASME Code, Sections III and XI, for which relief hasnot 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 RegulationDocket No. 50-482

Enclosure:

Safety Evaluation cc w/encl: See next pageDISTRIBUTION PUBLIC LPLIV r/f RidsAcrsAcnwMailCenterRidsNrrDorl(CHaney/JLubinski)

RidsNrrDorlDpr RidsNrrDorlLpl4 (DTerao)RidsNrrPMJDonohewRidsNrrLALFeizollahi RidsOgcRp JLamb, EDO RIVRidsRgn4MailCenter (GMiller)MMitchell, CVIB GCheruvenki, CVIBADAMS Accession No.: ML063070602OFFICENRR/LPL4/PMNRR/LPL4/LALPL4/PMCVIB/BCOGCNRR/LPL4/BCNAMEJDonohewLFeizollahiRCuretonMMitchellJRund NLO w/commentsDterao DATE11/20/0611/20/0611/17/068/8/0611/7/0611/20/06OFFICIAL AGENCY RECORD February 2006Wolf Creek Generating Station cc:Jay Silberg, Esq.

Pillsbury Winthrop Shaw Pittman LLP 2300 N Street, NW Washington, D.C. 20037Regional Administrator, Region IVU.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011Senior Resident InspectorU.S. Nuclear Regulatory Commission P.O. Box 311 Burlington, KS 66839Chief Engineer, Utilities DivisionKansas Corporation Commission 1500 SW Arrowhead Road Topeka, KS 66604-4027Office of the GovernorState of Kansas Topeka, KS 66612Attorney General120 S.W. 10 th Avenue, 2 nd FloorTopeka, KS 66612-1597County ClerkCoffey County Courthouse 110 South 6 th StreetBurlington, KS 66839Chief, Radiation and Asbestos Control Section Kansas Department of Health and Environment Bureau of Air and Radiation 1000 SW Jackson, Suite 310 Topeka, KS 66612-1366Vice President Operations/Plant ManagerWolf Creek Nuclear Operating Corporation P.O. Box 411 Burlington, KS 66839Supervisor LicensingWolf Creek Nuclear Operating Corporation P.O. Box 411 Burlington, KS 66839U.S. Nuclear Regulatory CommissionResident Inspectors Office/Callaway Plant

8201 NRC Road Steedman, MO 65077-1032 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATIONRELATED TO RELIEF REQUEST I2R-36FOR THE SECOND 10-YEAR INTERVAL INSERVICE INSPECTIONWOLF CREEK NUCLEAR OPERATING CORPORATIONWOLF CREEK GENERATING STATIONDOCKET NO. 50-48

21.0INTRODUCTION

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.

2.0REGULATORY EVALUATION

ISI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel CodeClass 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 (includingsupports) 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 recordfor the WCGS second 10-year ISI interval is the 1989 Edition, with no addenda.

3.0TECHNICAL EVALUATION

3.1ASME Code RequirementASME Code,Section XI, 1989 Edition, with no addenda, Figure IWC-2500-1, ExaminationCategory 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.3.2System/Component(s) for which Relief is RequestedThe licensee requested relief for the following ASME Code,Section XI, Category C-A fullpenetration bonnet flange to channel welds of the residual heat exchanger:Code Item Number C1.10 - Bonnet Flange to Channel Welds of the Residual HeatExchanger.3.3Licensee's Proposed Alternative and Basis for Requesting Relief (as stated in thelicensee's letter dated March 2, 2006):3.Applicable Code RequirementASME Section Xl, Figure IWC-2500-1 1989 Edition with no addenda requiresvolumetric 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-yearinterval 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 orother areas required by ASME Section XI.' 4.Impracticality of ComplianceThe examination of the subject components is limited by the configuration of theflange design and the location of flange bolting. As shown on the attached figures [in the licensee's 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 meetthe 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 ComplianceThe design configuration restrictions of the bonnet flange of the RHR [residualheat 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 UseProposed AlternativeThe following alternatives are proposed in lieu of the required examinationcoverage of essentially 100 percent:1.Ultrasonic Testing (UT) of the subject weld was performed to themaximum extent practical during the second ten-year interval.2.Pressure test VT-2 visual examinations were performed as required byCode Category C-H during the second ten-year interval. No evidence of leakage was identified for this component. 4Basis for UseThe basis for use of this alternative is that it provides the best examinationcoverage 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 exchangerwas examined with 100% coverage achieved, and no indications were detected.7.Duration of Proposed AlternativeThe second ten-year ISI interval which began September 3, 1995, and endedSeptember 2, 2005.PrecedentsComanche Peak Steam Electric Station Letter, dated March 10, 2005, DocketNo. 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)4.0STAFF EVALUATIONASME Code,Section XI, 1989 Edition, and no Addenda, Figure IWC-2500-1, ExaminationCategory 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 licensee's basisfor 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 thesubject welds during the previous preservice and ISI UT examinations, and complete coverage of the subject welds was not achieved during these UT examinations. 5To effectively evaluate the licensee's proposed alternative, the staff, in an electronic mail datedMay 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 staff's request foradditional information (RAI). The following section provides information regarding the responses from the licensee and the corresponding staff evaluation.4.1Type of Weld Metal that was Used for the Subject WeldsIn its response to the staff's RAI, the licensee, in a letter dated July 12, 2006, stated thatcarbon/low-alloy steel weld metal was used for all the subject welds.4.2State of Stress that is Present in the Uninspected Portion of the WeldsIn its response to the staff's RAI, the licensee, in a letter dated July 12, 2006, stated that theuninspected 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 licensee's responses to the RAIs and finds that the licensee's technicalbasis 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 heatexchanger 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 6welds. Furthermore, the licensee's pressure test VT-2 examinations duringevery 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 andVT-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 licensee's 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).

5.0CONCLUSION

Based on the above discussion, the staff concludes that it is impractical for the licensee to meetthe 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