ML11279A037
| ML11279A037 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 09/29/2011 |
| From: | Swift P M Constellation Energy Nuclear Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC ME5789 | |
| Download: ML11279A037 (10) | |
Text
CENG.a joint venture ofConstellation eDFWEnergy* 0P.O. Box 63Lycoming, NY 13093NINE MILE POINTNUCLEAR STATIONSeptember 29, 2011U.S. Nuclear Regulatory CommissionWashington, DC 20555-0001ATTENTION:SUBJECT:Document Control DeskNine Mile Point Nuclear StationUnit No. 1; Docket No. 50-220Request to Utilize an Alternative to the Requirements of 10 CFR 50.55a(g) for theRepair of Control Rod Drive Housing Penetrations -Response to NRC Request forAdditional Information (TAC No. ME5789)REFERENCES:(a) Letter from J. E. Pacher (NMPNS) to Document Control Desk (NRC), datedMarch 25, 2011, Request to Utilize an Alternative to the Requirements of 10CFR 50.55a(g) for the Repair of Control Rod Drive Housing Penetrations for theRemainder of the License Renewal Period of Extended Operation(b) Letter from R. V. Guzman (NRC) to S. L. Belcher (NMPNS), dated August 11,2011, Request for Additional Information Regarding Nine Mile Point NuclearStation, Unit No. 1 -Relief Request No. I ISI-004 (TAC No. ME5789)Nine Mile Point Nuclear Station, LLC (NMPNS) hereby transmits supplemental information requested bythe NRC in support of a previously submitted request for alternative (No. 1ISI-004) under the provisionof 10 CFR 50.55a(a)(3). This 10 CFR 50.55a request, submitted in Reference (a), describes an alternativerepair strategy for Nine Mile Point Unit 1 Control Rod Drive (CRD) housing penetrations that includes avariation of the CRD housing penetration welded repair geometry specified in Boiling Water ReactorVessel and Internals Project (BWRVIP) report BWRVIP-58-A and variations from the requirements ofthe American Society of Mechanical Engineers (ASME) Code,Section XI, and ASME Code Case N-606-1. The supplemental information, provided in the Attachment to this letter, responds to the request foradditional information (RAI) documented in the NRC's letter dated August 11, 2011 (Reference b). Thisletter contains no new regulatory commitments.
Document Control DeskSeptember 29, 2011Page 2Should you have any questions regarding the information in this submittal, please contact John J. Dosa,Licensing Director, at (315) 349-5219.Very truly yours,Paul M. SwiftManager Engineering ServicesPMS/DEVAttachment:Nine Mile Point Unit I -Response to NRC Request for Additional InformationRegarding 10 CFR 50.55a Request Number 1 ISI-004cc: Regional Administrator, Region I, NRCProject Manager, NRCResident Inspector, NRC ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 1ISI-004Nine Mile Point Nuclear Station, LLCSeptember 29, 2011 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 11SI-004By letter dated March 25, 2011, Nine Mile Point Nuclear Station, LLC (NMPNS) submitted 10 CFR50.55a request number IISI-004 pursuant to 10 CFR 50.55a(a)(3). This 10 CFR 50.55a request describesan alternative repair strategy for Nine Mile Point Unit 1 (NMP1) Control Rod Drive (CRD) housingpenetrations that includes a variation of the CRD housing penetration welded repair geometry specified inBoiling Water Reactor Vessel and Internals Project (BWRVIP) report BWRVIP-58-A and variationsfrom the requirements of the American Society of Mechanical Engineers (ASME) Code,Section XI, andASME Code Case N-606-1. This attachment provides supplemental information in response to therequest for additional information (RAI) documented in the NRC's letter dated August 11, 2011. Eachindividual NRC request is repeated (in italics), followed by the NMPNS response.RAI -1American Society of Mechanical Engineers (ASME) Code, Section X7, 2004 Edition, no Addenda, IWA-4610(a) requires the use of thermocouples and recording instruments to monitor process temperatures.In Paragraph 5A of Relief Request No. 1ISI-004, the licensee requests relieffrom using thermocouples forinterpass temperature monitoring as specified in IWA-4610(a). In lieu of using thermocouples to monitorand verify process temperatures, the licensee proposes in Paragraph SB of the relief request to verifymaximum interpass temperature by performing heat transfer calculations or by performing temperaturemeasurement on a test coupon that is no thicker than the bottom head and control rod drive (CRD)housing wall thickness. The test coupon welding would use the maximum heat input permitted by theapplicable welding procedure specification.The measurement of interpass temperature in this application is critical for at least two reasons.Maintaining a maximum interpass temperature is critical to maintaining the corrosion resistance of thestainless steelfiller metal and base metal, and it is also critical in maintaining the notch toughness of thelow alloy steel reactor vessel material. Therefore, maintaining a maximum interpass temperature isabsolutely necessary; and since this cannot be done by direct measurement, all effort must beconcentrated on maintaining a correct maximum interpass temperature, and the use of both methods ofmaximum interpass temperature determination shown in Paragraph 5B of the relief request isimperative.In response to this question, please indicate if the licensee will modify its relief request to require bothheat transfer calculations and temperature measurement on a test coupon that is no thicker than thebottom head and CRD housing wall thickness to be performed. If both methods are not performed ordirect measurement of interpass temperature measurement is not made, please describe how anacceptable level of quality and safety can be maintained in this repair.ResponseAs stated in 10 CFR 50.55a Request Number 1ISI-004, submitted by NMPNS letter dated March 25,2011, direct interpass temperature measurement is impractical to perform during welding operations frominside the CRD housing penetration bore. Interpass temperature measurements cannot be accomplisheddue to the physical configuration and the inaccessibility of the weld region during welding. Thealternative proposed by NMPNS is to either perform heat flow calculations or measure the maximuminterpass temperature on a representative test coupon, but not both. This approach is consistent with theassociated requirements specified in ASME Code Case N-638-4, which the NRC has determined to be1 of7 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 1ISI-004conditionally acceptable in Regulatory Guide (RG) 1.147, Revision 16. RG 1.147, Revision 16 has beenincorporated into the NRC's regulations at 10 CFR 50.55a(b). The RG specifically states that if it isimpractical to perform interpass temperature measurements, then the provisions of 3(e)(2) [heat flowcalculations] or 3(e)(3) [measurement of maximum interpass temperature on a test coupon] may be used.For the NMP1 CRD housing internal weld repair, AREVA has prepared heat transfer calculations inaccordance with 3(e)(2) of Code Case N-638-4.Analyses have been performed by AREVA that compare the heat transfer calculation method with therepresentative test coupon/mockup interpass temperature measurement method. AREVA has successfullyperformed numerous inside diameter temper bead weld modifications on Control Rod Drive Mechanism(CRDM) nozzle penetrations in pressurized water reactor (PWR) closure heads. Determination ofinterpass temperature for these modifications involved either heat transfer calculations or mockuptemperature measurements, but not both. AREVA has also successfully performed PWR pressurizerheater nozzle sleeve inside diameter temper bead weld modifications. For these modifications, heattransfer calculations were performed according to the guidelines of Code Case N-638, and mockupinterpass temperature measurements were performed both with and without water backing. The results ofthese analyses, which were recently presented to the ASME Welding Subcommittee, demonstrate thatboth methods are suitable and conservative for ensuring that welding interpass temperature limits are notexceeded.Of the prior PWR work performed by AREVA, the CRDM nozzle penetration modifications represent asimilar configuration to the NMP 1 reactor vessel bottom head CRD housing internal weld repair, with thefollowing differences:" The NMP1 bottom head thickness is greater than a PWR reactor closure head thickness byapproximately one (1) inch, which provides a larger heat sink.* The NMP1 bottom head is filled with reactor coolant at the time of the repair, whereas the welding onthe PWR closure heads is performed without water backing. The NMP1 heat transfer calculationsconservatively ignore the beneficial cooling effects of the water backing.Consideration of the above differences provides additional margin to the maximum allowable interpasstemperature as determined in the NMPl heat transfer calculations.NMPNS agrees that maintaining the maximum interpass temperature below 350'F is critical inmaintaining the notch toughness in the reactor vessel low alloy steel material. When maintaining thenotch toughness of the low alloy steel, the focus of concern is elevated temperatures while performing theactual temper bead welding (i.e., during the first 3 layers of welding over P-No. 3 materials). Mockupsand calculations show that the temperature remains low during the first three layers of welding becausethe area surrounding the weld remains at low temperature until significant additional balance welding ofthe joint (i.e., the non-temper bead region) is completed. The welding procedure qualification wasperformed using the same tooling used in the field mockup, and demonstrated that notch toughness couldnot only be maintained, but improved.NMPNS also agrees that maintaining the maximum interpass temperature below 350'F is critical forcorrosion resistance of the stainless steel filler metal and base metal. In addition to the conservative nature2 of 7 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 11SI-004of the interpass temperature calculation, the following features contribute to maintaining the corrosionresistance of the stainless steel filler material:" Only "L" grade filler materials are being utilized for the repair. This significantly reduces thelikelihood of chromium carbides, the primary mechanism for sensitization.* The ambient temperature temper bead process uses low heat input techniques, minimizing times thatthe material is at the sensitization temperature.* The exposed stainless steel weld material will be subjected to rotary peening, which has proven toimpose compressive residual stresses on the surface.Welded and peened surfaces of fabricated sample coupons and full scale mockup samples have undergonetesting in accordance with American Society for Testing and Materials (ASTM) Standard G36 to validatecorrosion resistance.Based on the above discussion, an acceptable level of quality and safety can be maintained in theproposed repair by incorporating the heat transfer calculation inputs into the applicable process controldocuments, which will ensure that the maximum interpass temperature is not exceeded.RAI- 2ASME Code Case N-606-1, "Similar and Dissimilar Metal Welding Using Ambient Temperature MachineGTA W Temper Bead Technique for B WR [Boiling Water Reactor] CRD Housing Stub Tube Repairs,Section XM, Division 1, " Paragraph I(/) prohibits peening of the final weld layer. The licensee requestsrelief from this restriction to allow portions of the final weld surface and the heat affected zone in thelower CRD housing to be rotary peened after acceptance nondestructive evaluation (NDE) has beenperformed.Peening is a mechanical process which can crack or otherwise damage welds. It can also mask NDEmethods from identifying defects in a weld. Ifpeening is performed on a weld, the potential for creatingor masking defects exists and identification of defects in a weld is imperative. Therefore, NDE of the finalweld surface, both before peening and after peening, is the best method to identify defects in a weld.It is understood from the relief request that NDE will be performed prior to implementation of the rotarypeening process. Please indicate if NDE will be performed after peening. If so, please describe whattype of NDE will be performed to identify defects which may result from the peening process.ResponseNon-destructive examination (NDE), consisting of a remote ASME Code Section XI equivalent visual(VT-1) inspection, will be performed after completion of the rotary peening.The purpose of the peening is to induce a compressive stress in the new CRD housing weld and weld heataffected zone (HAZ) of the CRD housing base metal. The rotary peening tool used in this applicationconsists of a standard commercial roto-peening flapper driven by a belt driven electric motor. The flapper3 of 7 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 1ISI-004has embedded tungsten balls that perform the peening. This peening process is not capable of materialremoval, as demonstrated in the rotary peening developmental testing. Liquid penetrant (PT)examinations have been performed on the mockup used during the NMPI repair development,qualification, and demonstrations, both before and after the rotary peening. No surface defects wereidentified. Data from other AREVA repair projects also demonstrates that rotary peening does notproduce surface indications.PT and ultrasonic (UT) examinations are performed after final machining and weld crown removal butprior to rotary peening. The PT area includes the area to be rotary peened. The PT examination ensuresthat any relevant surface indications are identified prior to rotary peening. Relevant PT indications wouldbe evaluated for repair and PT examined again subsequent to making any repairs. Therefore, a PTexamination and subsequent repairs (if necessary) will have already been performed prior to rotarypeening such that the potential to mask defects is not a concern.The final step of the repair process requires post-rotary peening cleaning and visual inspection. AREVAhas developed a remote ASME Code Section XI equivalent visual (VT-1) inspection method for surfaceinspection of post-peened surfaces. This inspection will further validate that peening has not damaged theweld surface. The mockup qualification and demonstration on the entire area of interest was discernableto VT-I inspection quality standards. Various weld ripples and other landmarks were highly visible.Based on the above discussion, NMPNS concludes that visual inspection is an acceptable approach toverify that the final rotary peened surface is absent of defects, and that the repair process does not need toinclude a final PT examination of the rotary peened surface. An additional benefit is the personnel dosesavings (estimated to be 1.5 Rem) that is realized by not having to install the PT tool into the CRDhousing, perform the PT examination, and remove the PT tool.RAI -3In the second paragraph on page 1 of Attachment 2 to Relief Request No. 1ISI-004, it states, in part, "Inthe event that roll expansion does not seal the [Control Rod Drive Housing] penetration and stop theleak, a repair shall be performed based on BWR Vessel and Internals Project (BWRVIP)-58-A as depictedin Figure 1 with variations thereto as discussed and justified herein." Section 3 of BWRVIP-58-A, "BWRVessel and Internals Project, CRD Internal Access Weld Repair," discusses repair of CRD welds.Section 3.3 of BWRVIP-58-A discusses making a weld repair if water is leaking through a crack andstates that, "The welding is performed at a pressure (-60 psi) that would prevent leakage of water intothe cavity during the welding process. The pressure in the cavity is maintained during the weldingprocess by sealing at the CRD housing flange and at the nozzle bore plug. This hyperbaric-chamberenvironment must be maintained during an initial drying cycle when any residual moisture from the A WJ[Abrasive water jet] process or leakage is removed, and during the first three layers of welding to insurethe leak path is sealed."If this process or any other similar process is performed, then this weld is a dry underwater weld and assuch the rules of ASME Code, Section XU, IWA-4660, "Underwater Welding, "apply. The rules of Title10 of the Code of Federal Regulations (10 CFR), Section 50.55a(b)(2)(xii) also apply, in which case,permission to perform underwater welding must be sought from the NRC.4 of 7 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 1ISI-004If the licensee intends to implement the approach identified in Section 3.3 of BWRVIP-58-A, pleaseprovide a request, as identified above, consistent with 10 CFR 50.55a(b)(2)(xii) and indicate how thewelding process will be performed consistent with ASME Code, Section Xl, IWA-4660.ResponseThe relief request proposes to use ASME Code Case N-606-1 to implement the CRD housing insidediameter temper bead weld repair. This code case, which specifically addresses BWR CRD housing/stubtube repairs, requires all other requirements of IWA-4000, 1989 Edition with 1990 Addenda to be met.The ASME Code Section XI, 1989 Edition with 1990 Addenda, did not cover machine temper beadwelding or underwater welding. The NRC's conditional approval of Code Case N-606-1 that isdocumented in RG 1.147, Revision 16, also does not impose any conditions related to underwaterwelding.Code Case N-606-1, Paragraph 2.1 (b), states: "Consideration shall be given to the effects of welding in apressurized environment. If they exist, they shall be duplicated in the test assembly." The NMP1procedure qualification record (PQR) and repair test assembly were both designed to address welding in apressurized environment. In addition, Tables 3-1 and 3-2 below summarize how the welding process willbe performed consistent with ASME Code Section XI, IWA-4660 for dry underwater welding. Table 3-1addresses the procedure qualification additional essential variables listed in IWA-4662.1, and Table 3-2addresses the performance qualification variables listed in IWA-4662.2. These tables demonstrate that theNMP1 PQR meets all of the applicable technical requirements of IWA-4660 by following the procedurequalification instructions found in Code Case N-606-1.The RAI states that the rules of 10 CFR 50.55a(b)(2)(xii) also apply, in which case permission to performunderwater welding must be sought from the NRC. This regulation states:"The provisions in IWA-4660, "Underwater Welding," of Section XI, 1997 Addenda throughthe latest edition and addenda incorporated by reference in paragraph (b)(2) of this section, arenot approved for use on irradiated material".The BWRVIP has produced several documents pertaining to welding underwater on irradiatedcomponents. Specifically, BWRVIP-97-A, "Guidelines for Performing Weld Repairs to Irradiated BWRInternals," establishes a generic weldability boundary within which the effects of irradiation are benign.Within this boundary, BWRVIP-97-A states that the standard ASME Section IX weld procedurespecification (WPS) and PQR for non-irradiated material can be used. The NMP1 CRD housings are atthe bottom of the reactor vessel and are well within the generic weldability boundary. NRC acceptance ofBWRVIP-97-A is documented in the NRC safety evaluation transmitted to the BWRVIP by NRC letterdated June 30, 2008.Based on the BWRVIP-97-A guidance, NMPNS concludes that the NMP1 CRD housings may beconsidered non-irradiated material for the purpose of the proposed weld repair, and that a request forrelief from the requirements of 10 CFR 50.55a(b)(2)(xii) is not required.5 of 7 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 1ISI-004Table 3-1Assessment of Additional Essential Variables for Dry Underwater Welding Procedure QualificationEssential Additional Variable NMP1 CRD Housing(IWA-4662.1) PQR Internal RepairWelding procedure specifications for dry underwater Addressed -WPS/PQR meet Addressed -The fieldwelding shall be qualified in accordance with the the ASME Section IX Operation Instructions invokerequirements of Section IX for groove welds, requirements for groove the applicable WPS.welds.(1) A change in the method for underwater transport Not Applicable -There is no Not Applicable -There is noand storage of filler material (e.g., from sealed underwater transport of filler underwater transport of fillerpackages to exposed). material involved. The material involved. Theexposed filler material is exposed filler material iscontained outside the contained outside thepressurized chamber at all pressurized chamber at alltimes in a dry environment times in a dry environmentbelow the repair location, below the repair location.(2) Addition or deletion of waterproof or Not Applicable- No Not Applicable -Standardsupplementary coatings for the filler metal or a change supplementary coatings bare wire with noin the type of any waterproof or supplementary necessary or included, supplementary coatingscoatings. utilized.(3) A change in depth beyond that qualified in Addressed -Although the Addressed -Although theaccordance with Table IWA-4662.1-1. word "depth" is used, the word "depth" is used, thetechnical concern that is technical concern that isaddressed by IWA-4660 is addressed by IWA-4660 isthe pressure induced in order the pressure induced in orderto make dry underwater to make dry underwaterwelding possible. Depth welding possible. Depthtranslates into a specified translates into a specifiedrepair pressure of 60 psi repair pressure of 60 psi(+/- 14 psi) used for the entire (+/- 14 psi) used for the entirewelding process. welding process.(4) A change in the nominal background gas Addressed -Argon used as Addressed -Argon used ascomposition. background gas. background gas.(5) For SMAW [Shielded Metal Arc Welding] and Not Applicable -GTAW Not Applicable -GTAWFCAW [Flux-Cored Arc Welding], use of a larger (Gas Tungsten Arc Welding) utilized.diameter electrode than that used in qualification, utilized.(6) For P-No. 1 material, a decrease in the minimum Not Applicable -P-No. 3 Not Applicable -P-No. 3distance from the point of welding to the wetted material to P-No. 8 material material to P-No. 8 materialsurface in any direction, when the minimum distance used. used.is less than 6 in. (150 mm).(7) For P-No. I material, the supplementary essential Not Applicable -P-No. 3 Not Applicable -P-No. 3variables of Section XI apply to non-impact-tested material to P-No. 8 material material to P-No. 8 materialbase metal when the minimum distance from the point used. used.of welding to the wetted surface in any direction isless than 6 in. (150 mm).6 of 7 ATTACHMENTNINE MILE POINT UNIT 1RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATIONREGARDING 10 CFR 50.55a REQUEST NUMBER 1ISI-004Table 3-2Assessment of Variables for Dry Underwater Welding Performance QualificationVariable (IWA-4662.2) Welding Operator NMP1 CRD HousingQualification Internal Repair(a) A change in welding mode (i.e., dry chamber, dry Dry chamber welding used. Dry chamber welding used.spot, or habitat).(b) A change in the SFA specification AWS ASME SFA 5.9 classification ASME SFA 5.9 classification[American Welding Society] filler metal ER309L materials used. ER309L materials used.classification, or if not conforming to an AWS fillermetal classification, a change in the manufacturer'strade name for the electrode or filler metal.(c) Addition or deletion of supplementary coatings for N/A -Supplementary N/A -Supplementarythe filler metal or a change in the type of any coatings are not used. coatings are not used.supplementary coatings.(d) A change in depth beyond that qualified in Addressed -Although the Addressed -Although theaccordance with Table IWA-4662. 1-1. word "depth" is used, the word "depth" is used, thetechnical concern that is technical concern that isaddressed by IWA-4660 is addressed by IWA-4660 isthe pressure induced in order the pressure induced in orderto make dry underwater to make dry underwaterwelding possible. Depth welding possible. Depthtranslates into a specified translates into a specifiedrepair pressure of 60 psi repair pressure of 60 psi(+/- 14 psi) used for the entire (+/- 14 psi) used for the entirewelding process. welding process.(e) For SMAW and GMAW [Gas Metal Arc N/A -These processes are N/A -These processes areWelding], use of a larger diameter electrode than that not used. not used.used during performance qualification. I7 of 7