RS-23-068, Response to Request for Additional Information for Quad Cities Relief Request I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell
| ML23118A312 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 04/28/2023 |
| From: | Simpson P Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RS-23-068 | |
| Download: ML23118A312 (1) | |
Text
Constellation~
4300 Winfield Road Warrenville, IL 60555 April 28, 2023 RS-23-068 630 657 2000 Office 10 CFR 50.55a(z)(1)
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Quad Cities Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-30 NRC Docket No. 50-265
Subject:
Response to Request for Additional Information for Quad Cities Relief Request I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges
References:
- 1. Letter from P.R. Simpson (Constellation Energy Generation, LLC) to U.S.
Nuclear Regulatory Commission, "Submittal of Supplement to Sixth lnservice Inspection Interval Relief Request I6R-11 Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges," dated April 24, 2023 (ADAMS Accession No. ML23114A378)
- 2. Email from R. Kuntz (U.S. Nuclear Regulatory Commission) to R. Steinman (Constellation Energy Generation, LLC),
Subject:
"Request for Additional Information RE: Quad Cities, Unit 2, Alternative Request I6R-11," dated April 28, 2023 In Reference 1, Constellation Energy Generation, LLC (CEG) submitted relief request I6R-11 for repair(s) of the reactor pressure vessel head to shell flanges. This request applies to the sixth 10-year interval which began on April 2, 2023 and is required by 10 CFR 50.55a(g)(4) to comply with the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, 2017 Edition.
In Reference 2, the NRC requested additional information that is needed to complete review of the proposed relief request. The attachment to this letter provides the additional information requested.
U.S. Nuclear Regulatory Commission April 28, 2023 Page 2 There are no regulatory commitments contained within this letter. Should you have any questions concerning this letter, please contact Ms. Rebecca L. Steinman at 630-657-2831.
Respectfully, Patrick R. Simpson Sr. Manager Licensing Constellation Energy Generation, LLC
Attachment:
Response to Request for Additional Information for Quad Cities Alternative I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges cc:
Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
ATTACHMENT Response to Request for Additional Information for Quad Cities Alternative I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges Page 1 of 5 REQUEST FOR ADDITIONAL INFORMATION ALTERNATIVE REQUEST I6R-11 PROPOSED ALTERNATIVES FOR A TEMPER BEAD WELD REPAIR OF THE MATING SURFACES OF THE REACTOR PRESSURE VESSEL HEAD AND SHELL FLANGES CONSTELLATION ENERGY GENERATION, LLC QUAD CITIES NUCLEAR POWER STATION, UNIT 2 DOCKET NO. 50-265 BACKGROUND By letter dated April 24, 2022 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML23114A378), Constellation Energy Generation, LLC (CEG), submitted alternative I6R-11 which requested approval of proposed alternatives for examination requirements for repairs of the reactor pressure vessel head to shell flanges at Quad Cities Nuclear Power Station (QCNPS) Unit 2.
Alternative request I6R-11 specifically pertains to the planned weld repair(s) using ambient temperature temper bead (ATTB) welding in accordance with the requirements of American Society of Mechanical Engineers (ASME) Code Case N-638-10. As an alternative to performing the required nondestructive examinations (NDE) at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completion of the third tempering layer, CEG proposes performing the NDE after completion of the repair(s). CEG is also requesting an alternative to the requirement to perform a volumetric examination of the welded region(s).
REGULATORY BASIS QCNPS implements ASME Code Case N-638-10 "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [gas tungsten arc welding] Temper Bead Technique,Section XI, Division 1" within the stations sixth interval inservice inspection (ISI) program. Code Case N-638-10 is approved in Regulatory Guide (RG) 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, Revision 20, Table 1. This Code Case is an approved alternative to ASME Code,Section XI, IWA-4400 to use an automatic or machine gas GTAW temper bead technique to repair certain materials.
The proposed repair(s) will be performed by using ATTB welding in accordance with ASME Code Case N-638-10. Paragraph 4(a)(2), of Code Case N-638-10 requires the final NDE be performed 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completion of the third tempering layer.
In accordance with Code Case N-638-10, Paragraph 4(a)(2), examination of the welded region shall include both volumetric and surface examination methods.
RAI-1 REQUEST Provide additional information (e.g., schematic drawings, diagrams, photographs, and/or description) regarding how thickness, geometry, and orientation of the reactor vessel flanges prevent volumetric examinations.
ATTACHMENT Response to Request for Additional Information for Quad Cities Alternative I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges Page 2 of 5 Discuss the maximum extent to which the volumetric and surface examinations of the mating surfaces between the reactor pressure vessel head and shell flanges can be performed in accordance with Code Case N-638-10, Paragraph 4(a)(2); provide an assessment of how the proposed alternative will result in an acceptable level of quality and safety comparable to performance of the NDE required by code.
CEG Response Based on ASME Section III, 1965 Edition, the volumetric examination requirement would be ultrasonic examination based on N-322, examination of forgings and bars. Per N-322.1(a) forgings shall be examined in accordance with ASTM A388-59, "Recommended Practice for Ultrasonic Testing and Inspection of Heavy Steel Forgings," using the longitudinal-beam technique. A388, Paragraph 6.2, "Longitudinal Testing," and subparagraphs state establishment of the test sensitivity is by either adjusting the back reflection to approximately 75% of full screen from the opposite side of the forging or adjusting the instrument controls from a specified signal from a flat bottom hole in a standardized reference block.
Inspection is performed by monitoring the back reflection for any significant reduction in amplitude.
Based on the configuration of the anticipated area of the flange which may need to be repaired and the surface from which the exam would be performed, no parallel surfaces exist which would allow the examiner to either establish a back wall or utilize a back wall response for monitoring to determine if responses would need to be recorded.
The reactor vessel head configuration does not allow examination from the outside surface looking in toward the area that may need to be repaired and based on the surface geometry from the O-ring grooves, examination cannot be performed from the flange surface. As shown in Figure RAI-1a, the configuration of the reactor vessel does not allow examination in the area that may need to be repaired based on not having the ability to monitor a back wall signal to use as a comparison for recording.
The anticipated repair is not a full volume material or weld repair. The expected degradation mechanism is high pressure steam leakage over the Inconel clad mating surface of the low alloy steel reactor vessel flange to head flange. The most likely degradation extent expected is a thinning or gouging of the existing Inconel cladding material. The repair activities will be to remove service induced defects, reweld/build up the mating surface, and re-machine to allow for proper sealing surfaces for the O-rings as designed. As such, the depth of the repair work should be constrained to the cladding thickness and possibly a limited amount of low alloy steel flange material beneath.
Surface exams will be performed progressively as the weld build up is applied through to the finished machined surface. Original Construction Code longitudinal exams would have been performed to determine laminar defects or delamination of the cladding material application to allow for adequate ultrasonic (UT) examination of the flange to vessel weld. Physical geometry, extreme and varied thicknesses, and interferences such as stud holes or landings would prevent shear wave UT or other volumetric examination from being used from the mating surface or from either perpendicular surface (i.e., flange sides).
UT shear or surface wave applications for near surface defects in the weld repair areas would not provide an increase in detection of service or weld induced defects greater than the proposed progressive surface examination alternative.
ATTACHMENT Response to Request for Additional Information for Quad Cities Alternative I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges Page 3 of 5 In addition, radiography (RT) can also not be used based on the overall thickness of the RPV head flange (31") and the configuration of the vessel flange (the top of the flange surface does not have a corresponding opposite surface). To perform RT, the positioning of the film would be placed on the flange surface shown in Figure RAI-1b and there is no practical place to put the source to perform an achievable radiographic image. Based on the thickness of the repair area being significantly thinner than the overall thickness of the flange, the possibility of having adequate resolution to identify or characterize any indications in the repair would not be achievable.
Based on the above discussion, it is concluded that the proposed alternative of progressive surface examination will provide an acceptable level of quality and safety compared to the volumetric examination required by Code Case N-638-10.
ATTACHMENT Response to Request for Additional Information for Quad Cities Alternative I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges Based on configuration a longitudinal exam would not be able to be performed from this surface and achieve a back reflection Potential repair area (see Figure DRAl-1 b)
Based on configuration a longitudinal exam would not be able to be performed from this surface and achieve a back reflection Figure RAI-la: Reactor Head and Vessel Closure Page 4 of 5
ATTACHMENT Response to Request for Additional Information for Quad Cities Alternative I6R-11, Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges Areas in the RPV flange that do not have parallel surfaces and will not allow scanning to be performed Figure RAI-1 b: Simplified Flange Configuration Page 5 of 5