ML13338A284
| ML13338A284 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/22/2013 |
| From: | Sartain M D Dominion, Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 13-566, TAC MF2520 | |
| Download: ML13338A284 (8) | |
Text
009"Dominion Nuclear Connecticut, Inc. m5000 Dominion Boulevard, Glen Allen, VA 23060 DominEoNWeb Address: wwv.dom.com November 22, 2013U.S. Nuclear Regulatory Commission Serial No. 13-566Attention: Document Control Desk NLOS/WDC ROWashington, DC 20555 Docket No. 50-336License No. DPR-65DOMINION NUCLEAR CONNECTICUT, INC.MILLSTONE POWER STATION UNIT 2RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FORALTERNATIVE REQUEST RR-04-16 FOR THE USE OF ENCODED PHASEDARRAY ULTRASONIC EXAMINATION TECHNIQUES (PAUT) IN LIEU OFRADIOGRAPHY (TAC NO. MF2520)In a letter dated August 1, 2013, Dominion Nuclear Connecticut, Inc. (DNC) requestedrelief from the requirements of the American Society of Mechanical Engineers (ASME)Boiler and Pressure Vessel Code Section III for Millstone Power Station Unit 2(MPS2). Specifically, DNC requested approval to use encoded Phased ArrayUltrasonic Examination Techniques (PAUT) as an alternative to radiographicexamination to satisfy nondestructive examination requirements for ASME Class 2carbon steel circumferential pipe weld joint applications. In a letter dated October 1,2013, the Nuclear Regulatory Commission (NRC) transmitted a request for additionalinformation (RAI) to DNC related to the alternative request. DNC agreed to respondto RAI Questions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6 by November 25, 2013 and RAIQuestions 1, 3.b and 4 by February 28, 2014.The attachment to this letter contains DNC's response to RAI Questions 2, 3.a, 3.c,3.d, 3.e, 5, and 6.If you have any questions regarding this submittal, please contact Wanda Craft at(804) 273-4687.Sincerely,Mark D. SartainVice President -Nuclear Engineering and DevelopmentAttachment:Response to Request for Additional Information for Alternative Request RR-04-16Proposed Alternative to ASME Section III.Commitments made in this letter: NoneAw~2l Serial No. 13-566Docket No. 50-336Page 2 of 2cc: U.S. Nuclear Regulatory CommissionRegion I2100 Renaissance BlvdSuite 100King of Prussia, PA 19406-2713James S. KimProject ManagerU.S. Nuclear Regulatory CommissionOne White Flint North, Mail Stop 08 C2A11555 Rockville PikeRockville, MD 20852-2738NRC Senior Resident InspectorMillstone Power Station Serial No. 13-566Docket No. 50-336ATTACHMENTRESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR ALTERNATIVEREQUEST RR-04-16PROPOSED ALTERNATIVE TO ASME SECTION IIIMILLSTONE POWER STATION UNIT 2DOMINION NUCLEAR CONNECTICUT, INC.
Serial No. 13-566Docket No. 50-336Attachment, Page 1 of 5In a letter dated August 1, 2013, Dominion Nuclear Connecticut, Inc. (DNC) requestedrelief from the requirements of the American Society of Mechanical Engineers (ASME)Boiler and Pressure Vessel Code Section III for Millstone Power Station Unit 2 (MPS2).Specifically, DNC requested approval to use encoded Phased Array UltrasonicExamination Techniques (PAUT) as an alternative to radiographic examination to satisfynondestructive examination requirements for ASME Class 2 carbon steel circumferentialpipe weld joint applications. In a letter dated October 1, 2013, the Nuclear RegulatoryCommission (NRC) transmitted a request for additional information (RAI) to DNCrelated to the alternative request. This attachment provides DNC's response to RAIQuestions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6. DNC will respond to RAI Questions 1, 3.b and4 by February 28, 2014.Question 2The hardship associated with the use of radiographic testing was described as anincreased radiological dose to the people performing the inspections. What is theexpected reduction in radiological dose that would result from the use of ultrasonictesting in lieu of radiographic testing for the welds covered in RR-04-16?DNC ResponseThe hardship addressed in the alternative request was based on the safety riskassociated with performing radiographic examinations, which includes the plannedexposure and the potential for accidental exposure associated with transporting,positioning and exposing the radiation source required for the examination. Plannedexposure varies based on a number of factors such as source strength, set up time,local area dose rates, number of boundary guards required, and the potential forreexamination if repairs are required.Currently, a total of 55 radiography exams are included in the scope of the MPS2refueling outage 22 (2R22). This scope assumes examination of the 23 weldsassociated with the feedwater piping replacement project with PAUT being used in lieuof RT for 19 of those welds. Radiographic examination was performed on 24 weldsduring the last MPS2 refueling outage (2R21), which resulted in a total exposure of 251mrem. It is estimated that performing PAUT in lieu of RT on 19 of the 23 weldsassociated with the feedwater piping replacement project would result in a plannedexposure savings of approximately 50-100 mrem.Reducing the potential of accidental exposure is an equally important consideration.Accidental exposures can occur as a result of human error, equipment malfunction orinadequate boundary control. The potential for an accidental exposure is a function ofthe total number of radiographic examinations being performed during the outage.
Serial No. 13-566Docket No. 50-336Attachment, Page 2 of 5Therefore, removing 19 welds from the radiography scope provides a reduction in thepotential for an accidental exposure.Question 3The technical basis for the reliable detection and characterization of fabrication flawshas thus far assumed that the inspections will be conducted from both sides of the weld.The few experimental evaluations that have explored the reliability of single-sidedultrasonic testing (UT) suggest that detecting fabrication flaws, especially lack of fusiondefects, using single sided UT misses flaws found by inspections conducted from bothsides (see EPRI Report 1021181 page A-5 and the paper "An Empirical Study onUltrasonic Testing in Lieu of Radiography for Nuclear Power Plants" in the Proceedingsof the 9th international conference on NDE in relation to structural integrity for nuclearand pressurized components). As the technical basis for the detection andcharacterization of flaws from one side of the weld has not been established, thefollowing information on the single-sided examinations is required:a. Which welds described in RR-04-16, based on the current designs, would requiresingle-sided inspections and which welds would be inspected from both sides ofthe welds?c. As the replacement piping has not been installed, and it is possible to design thesystem to allow access to both sides of the weld. What would be the hardship orunusual difficulty and the expected increase in personnel radiation dose causedby designing the replacement Feedwater system to not require single-sidedultrasonic examinations for fabrication defects?d. It is possible for some components to be fabricated outside of containment in ashop setting. What would be the hardship or unusual difficulty and expectedincrease in radiation dose to personnel from performing radiography on the weldsthat require single-sided ultrasonic examinations in a low-radiation environment?e. What would be the hardship or unusual difficulty and expected increase inradiation dose to personnel that would be caused by performing radiography onlyon the welds that would require single-sided ultrasonic examinations?DNC Responsea. The following table lists the welds where UT is currently planned to be used tosatisfy the volumetric examination requirements. The column listed as accessidentifies the welds where the configuration allows the scanning to be performedfrom either both sides of the weld (dual) or only a single side.
I ISerial No. 13-566Docket No. 50-336Attachment, Page 3 of 5SG 1- A TrainID/Weld No. Configuration Size Access1A/AC-G-1 3-A 900 long radius (LR) elbow 18" SCH 60 (0.750" Dualto 900 LR elbow nominal wall)9Q0 LR elbow to 18" SCH 60 (0.750"1B/AC-G-1 2-A pipe at containment (CTMT) Dualpenetration nominal wall)18" SCH 60 (0.750"1C/N/A CTMT pipe to flue nominal wall) Single1 DIN/A Flue to pipe inside CTMVIT 18" SCH 60 (0.750" Singlenominal wall)1 E/AC-G-11-A Pipe to 900 LR elbow 18" SCH 60(0.750" Dualnominal wall)1 F/AC-G-10QA 900 LR elbow to 900 LR 18" SCH 60 (0.750" Dualelbow nominal wall)1 G/AC-G-09-A 900 LR elbow to pipe 18" SCH 60 (0.750" Dualnominal wall)1 H/AC-G-08-A Pipe to pipe 18" SCH 60 (0.750" Dualnominal wall)1 LIAC-G-1 6 6" auxiliary feedwater 6" (0.280" nominal Single1L/AC-G-16____ (AFW) nozzle to pipe wall) Single1M/AC-G-17 6" AFW pipe to LR elbow 6" (0.280" nominal Dual_____ _____ ____ _____ _____ _____ ____wall) _ _ _ _ _S, G-2- B TrainID/Weld No. Configuration Size Access2AIBC-G-14 Check valve to 18" SCH 60 (0.750" Single90° LR elbow nominal wall) Single900 LR elbow to900 L elbw to 18" SCH 60 (0.750"2B/BC-G-13 pipe at CTMT 18" SCH Dualpenetration nominal wall)18" SCH 60 (0.750" Dual2C/NA Pipe to Pipe nominal wall) Dual2D/NA CTMVIT pipe to flue 18" SCH 60 (0.750" Single2D/NA__TMTpipetoflue nominal wall) Single2E/N/A Flue to pipe inside 18" SCH 60 (0.750" SingleCTMT nominal wall) Single2F/BC-G-12 Pipe to 900 LR Elbow 18" SCH 60 (0.750" Dualnominal wall)
Serial No. 13-566Docket No. 50-336Attachment, Page 4 of 5SG-2- B TrainID/Weld No. Configuration Size Access2G/BC-G-1 1 90* LR elbow to vertical 18" SCH 60 (0.750" Dualpipe nominal wall)2K/BC-G-16 6" AFW nozzle to pipe 0.280" nominal wall Single2L/BC-G-17 6" AFW pipe to valve 0.280" nominal wall Singlec. The components of the weld joints are identified in the table. The associatedwelds have been designed to accommodate dual-sided examination to the extentpractical. Single-side examinations will be performed where piping connects toan existing nozzle or valve as these components are not scheduled forreplacement under the project. Replacement of these components to supportdual-sided examination would result in additional dose and added cost.Additionally, the containment penetration flue head configuration does not permitUT examination from both sides of the weld.d. Currently seven of the above listed welds are planned to be welded in the shopprior to installation. Four of the seven shop welds are identified as having single-side access for UT examination. Although the dose associated with RTexamination of these welds has not been quantified, qualitative experienceshows that the majority of the dose for a given RT exam is incurred by the RTcrew during the RT examination exposure process. Consequently, some dose isincurred for any RT examination, whether in the shop or in the field whereas,shop UT examination incurs no dose and presents no risk of accidentalexposure.e. The table provided in response to Question 3.a identifies 8 welds with limitedexamination access. As discussed in response to Question 2, the planned dosesavings is relatively small (50-100 mrem). However, the eight welds representone third of the total population of welds to be replaced. Reducing the populationof welds subject to RT examination provides a corresponding reduction in thepotential of an accidental exposure.Question 5The relief request defines the required examination zone as 100 percent of the weldvolume and the weld-to-base metal interface on each side. Does this examination zoneinclude Y2 inch or Y2 of the wall thickness or some other buffer area? Please provide adrawing of the examination area to be covered by the ultrasonic examinations. If a Y2inch or Y2 t buffer area around the weld is not to be used, please describe how theinspection procedure will conservatively include, in light of possible inner diameter and Serial No. 13-566Docket No. 50-336Attachment, Page 5 of 5outer diameter repairs, the entire volume of the weld and fusion zone in theexamination.DNC ResponseA sketch of the typical examination volume described in the request is included below.The intent of the examination is to detect flaws associated with the welding process,which will be located within the weld and the fusion zones of the weld to base metalinterface. The examination volume includes 100% of the weld volume and the weld tobase metal interface on each side of the weld. This volume will be used to calculatecoverage of the required examination volume. If the weld requires repair that extendsthe weld volume beyond the designed joint boundaries, the volume of the repairs will beincluded in the required examination volume. The progress of the weld process will betracked to determine if any repairs are made and compensated for in the scan plan. Noadditional buffer will be included in the volume examined.Weld / Examination VolumeQuestion 6Radiographic testing provides an archival-quality record of the examination that can bestored and interpreted after several decades. Encoded electronic data requires backupand proprietary data formats may become obsolete in the future. How will the ultrasonicresults be stored and protected from data loss and future changes in hardware andsoftware that could render the data unreadable?DNC ResponseThe electronic data files for the UT examinations will be stored as part of the archival-quality record. In addition to the electronic data, hard copy prints of the data will also beincluded as part of the record that allows viewing without the use of hardware orsoftware.