NMP1L3485, Proposed Alternative Associated with a Weld Overlay Repair to the Torus
| ML22342B229 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 12/08/2022 |
| From: | David Gudger Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NMP1L3485 | |
| Download: ML22342B229 (1) | |
Text
200 Exelon Way Kennett Square, PA 19348 www.exeloncorp.com
NMP1L3485
December 8, 2022
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63 NRC Docket No. 50-220
Subject:
Proposed Alternative Associated with a Weld Overlay Repair to the Torus
In accordance with 10 CFR 50.55a, Codes and standards, paragraph (z)(1), Constellation Energy Generation, LLC (CEG) is requesting relief from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components. This alternative is associated with a weld overlay repair to the torus and is being submitted as a contingency repair at this time. This alternative applies to the third ten-year Containment Inservice Inspection (CISI) interval, which began on August 23, 2019, for the Nine Mile Point Nuclear Station, Unit 1. The third ten-year CISI interval complies with the ASME Boiler and Pressure Vessel Code,Section XI, 2013 Edition.
There are no regulatory commitments in this letter.
CEG requests approval of this relief request by December 8, 2023.
If you have any questions concerning this letter, please contact Tom Loomis at (610) 765-5510.
Respectfully,
David T. Gudger Senior Manager - Licensing & Regulatory Affairs Exelon Generation Company, LLC
Attachment:
- 1) Relief Request I5R-10, Revision 0
Proposed Alternative Associated with a Weld Overlay Repair to the Torus December 8, 2022 Page 2
cc: Regional Administrator, Region I, NRC NRC Senior Resident Inspector, NMP Project Manager NRC, NMP A. L. Peterson, NYSERDA
Attachment 1
10 CFR 50.55a Relief Request I5R-10, Revision 0 Proposed Alternative for Weld Overlay Repair of a Class MC Component Nine Mile Point Nuclear Station, Unit 1 10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 1 of 8)
Proposed Alternative for Weld Overlay Repair of a Class MC Component In Accordance with 10 CFR 50.55a(z)(1)
- 1. ASME Code Component(s) Affected
Code Class: Classified as Code Class MC for application of the ASME Boiler and Pressure Vessel Code,Section XI, Subsection IWE
Description:
Primary Containment Vessel Torus Shell in BWR Mark I Containment Design Pressure: 35 psig (Internal Pressure), 1 psig (External Pressure)
Design Temperature: 205° F Material: ASTM A-201, Gr. B (Firebox)
Specified Minimum Ultimate Tensile Strength: 60,000 psi Nominal Plate Thickness: 0.46 in. (Specified Minimum Thickness for Design)
Diameter of the Torus: 27-0 (Inside Diameter)
Original Construction ASME Section III, 1965 Edition, Subsection B, Code: Requirements for Class B Vessels
2. Applicable Code Edition and Addenda
The following table identifies the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV)Section XI Code of Record for performing repair/replacement activities on Class MC components at Nine Mile Point Nuclear Station, Unit 1:
PLANT INTERVAL EDITION START END Nine Mile Point Nuclear Third Station, Unit 1 Containment 2013 August 23, 2019 August 22, 2029 ISI Interval
3. Applicable Code Requirements
3.1 IWA-4411 states, in part, that welding and installation shall be performed in accordance with the Owners Requirements and the Construction Code of the item.
3.2 IWE-5221(a) requires that a pneumatic leakage test be performed in accordance with IWE-5223 following repair/replacement activities performed by welding, prior to returning the component to service. The requirements of IWE-5221 are as follows:
10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 2 of 8)
IWE-5221 General (a) Except as noted in IWE-5224, a pneumatic leakage test shall be performed in accordance with IWE-5223 following repair/replacement activities performed by welding or brazing, prior to returning the component to service.
(b) The following are exempt from the requirements of this Article:
(1) attachments (e.g., as defined in NE1132) and nonpressureretaining items (2) welding or brazing on pressureretaining portions of components, when the remaining wall thickness after metal removal is at least 90% of the minimum design wall thickness
4. Reason for Request
Constellation Energy Generation, LLC (CEG) performs examinations of the Nine Mile Point, Unit 1 containment torus shell plate in accordance with Table IWE-2500-1, Examination Category E-C. If these examinations detect excessive wall thickness loss that cannot be accepted in accordance with IWE-3122.3, Acceptance by Engineering Evaluation, the torus shell plate must be corrected by a repair/replacement activity in accordance with IWE-3122.2 to the extent necessary to meet the Construction Code and Owners Requirements.
The proposed alternative in this request will allow weld overlay repairs to be performed on the exterior surface of the torus in lieu of performing underwater weld repairs or draining the torus to allow access to perform weld repairs on the interior surface of the torus.
This request also includes an alternative to the pneumatic leakage test requirements of IWE-5221 following the installation of a weld overlay repair performed on the torus. This alternative is requested to avoid having to perform a pneumatic leakage test in accordance with IWE-5221 following weld overlay repairs that do not penetrate through the pressure boundary.
- 5. Proposed Altern ative and Basis for Use
5.1 In lieu of the requirements of IWA-4411 that welding be performed in accordance with requirements of the Construction Code and Owners Requirements, CEG proposes an alternative to perform one or more weld overlay repairs on the exterior surface of the containment torus in accordance with the following requirements.
5.1.1 General Requirements
(a) The requirements of IWA-4000 shall be met, except as noted in this proposed alternative.
(b) Weld overlay repairs are limited to correcting unacceptable erosion, corrosion, cavitation or pitting on the interior surfaces of the containment torus shell.
(c) The weld overlay shall not be performed more than once in a single location.
10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 3 of 8)
(d) The material beneath the surface to which the weld overlay is to be applied shall be ultrasonically examined in accordance with IWA-2232 to verify no crack-like defects exist. Use of this alternative shall not be used for repair of cracking or crack-like defects.
(e) The existing average wall thickness and the rate, extent, and configuration of degradation to be reinforced by the weld overlay shall be determined.
The adjacent area shall be examined ultrasonically to verify that the overlay will encompass the entire unacceptable area. The extent of degradation requiring repair shall be evaluated to ensure that there are no other unacceptable locations within the surrounding area that could affect the integrity of the overlaid torus shell plate. The dimensions of the surrounding area to be evaluated shall be determined, considering the type of degradation present. The effect of the overlay on the torus shell plate and any remaining degradation shall be evaluated in accordance with IWA -
4160.
(f) Dimensions and details shown in Figure 1 of ASME Code Case N -561-3 apply to the alternative proposed in 5.1 of this request.
5.1.2 General Design Requirements
(a) Unless otherwise established by theoretical analysis, the full thickness of the weld overlay shall extend a distance of at least s in each direction beyond the area predicted, over the design life of the overlay to infringe upon the required thickness prescribed by the Construction Code, where
R = outer radius of the component = 162.46 in.
tnom = 0.46 in.
s = 3/4Rtnom = 6.5 in.
When applicable to satisfy the minimum s dimension, the overlay may be extended over adjacent compatible carbon steel weld and base metal that is not experiencing unacceptable wall thinning.
(b) Edges of the weld overlay shall be tapered to the existing torus shell plate surface at a maximum angle ( in Figure 1) of 45 deg, except as specified in 5.1.4(c)(4). Final configuration of the overlay shall permit the examinations and evaluations required by this alternative.
(c) The thickness shall be sufficient to maintain the required thickness for the predicted life of the overlay, and, except for the tapered edges, the overlay shall have a uniform thickness. The overlay surface finish may be as-welded or smoother.
(d) The tensile strength of the weld filler metal used for the overlay shall be at least that specified for the base metal to which it is applied.
10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 4 of 8)
(e) The predicted maximum degradation of the overlaid torus shell plate and the overlay over the design life of the overlay shall be considered in the design. The predicted degradation of the torus shell plate shall be based on in-situ inspection data obtained from previous torus shell examinations, and/or from engineering evaluations documenting the basis for the expected corrosion rate. If the weld overlay is predicted to become exposed to the corroding medium, the predicted degradation of the overlay shall be based upon established data for base metals or weld metals with similar chemical composition to that of the filler metal used for the weld overlay.
(f) The effects of the weld overlay on the dynamic analysi s of the torus shall be addressed in the weld overlay design.
5.1.3 Design
The design of weld overlays not prequalified by 5.1.4 shall be in accordance with the applicable requirements of the Construction Code or NE -3000 and shall consider the weld overlay as an integral portion of the torus shell plate upon which it is applied (not as a weld). The allowable stress values of the base metal shall apply to the design of the deposited weld metal. The following factors shall be considered in the design and application of the overlay:
(a) Effects of shrinkage on the torus shell, if any.
(b) Stress concentrations caused by application of the overlay or resulting from existing and predicted torus shell internal surface configuration.
5.1.4 Prequalified Design
Application of weld overlays on the torus shell plate need not comply with the requirements of 5.1.3, provided all of the following conditions are met:
(a) The General Design Requirements of 5.1.2 shall be met.
(b) The distance between toes of adjacent overlays shall not be less than 3/4Rtnom, and the distance X between the toe of an overlay and the branch reinforcement limit for an adjacent nozzle shall be no less than 21/2Rtnom.
(c) The finished overlay shall be rectangular in shape, and shall comply with the following:
(1) The overlays shall be aligned parallel with or perpendicular to the axis of the torus shell;
(2) Corners shall be rounded with radii not less than the overlay thickness;
(3) The average thickness of the overlayed area u shall be at least 1/8 in.;
(4) The maximum angle of taper, ( in Figure 1) shall not exceed 30 deg.;
10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 5 of 8)
(5) The maximum area of the weld overlay excluding tapered edges shall not exceed 576 in2 which includes s. The dimension and area of base metal below the required thickness shall not exceed that defined by:
Lmax(in.) = 0.11D + 1.84 = 0.11(27 x 12) + 1.84 = 37 in.
Amax(in.2) = 0.455D - 0.8 = 0.455(27 x 12) - 0.8 = 146 in2
Where
Amax = maximum area of base metal predicted to degrade below the required thickness over the remaining life of the overlay, in.2
Lmax = maximum axial dimension of base metal predicted to degrade below the required thickness over the remaining life of the overlay, in.
5.1.5 Temper Bead Welding Technique
At locations where the weld overlay repair will be performed on surfaces backed by water, the qualification, application, examination, and repair requirements of the temper bead welding technique described in the IWA-4610 and IWA-4680 (2017 Edition) shall be met, except as follows:
(a) In lieu of the requirement of IWA-4681(b), the maximum area of an individual weld based on the finished surface over the ferritic material shall be 1,300 in.2, except as specified in 5.1.4(c)(5), and the thickness of the weld overlay W shall not be greater than the ferritic base metal nominal thickness.
5.1.6 Installation
(a) The entire surface area to which the weld overlay is to be applied shall be examined using the liquid penetrant or magnetic particle method, with acceptance criteria in accordance with NE -2500 and NE-5300 (2013 Edition) for the product form (base metal or weld) involved.
(b) If through-wall repairs are necessary as a result from application of the weld overlay, they shall be accomplished by sealing with weld metal using a qualified weld procedure suitable for open-root welding. This weld shall be examined in accordance with 5.1.6(a). In addition, the first layer of overlay over the repaired area shall be examined in accordance with 5.1.6(a).
(c) Overlay weld metal shall be de posited using a groove-welding procedure qualified in accordance with Section IX and IWA -4610 and IWA-4680 (2017 Edition). The qualified minimum thickness specified in the weld procedure does not apply to the weld overlay or associated base metal repairs.
10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 6 of 8)
(d) The surface of the weld overlay may be prepared by machining or grinding, as necessary, to permit performance of surface examinations required by 5.1.7 and any subsequent inservice examinations.
5.1.7 Examination
(a) The completed weld overlay shall be examined using the liquid penetrant or magnetic particle method in accordance with IWA-2220 (2013 Edition) and shall satisfy the surface examination acceptance criteria for welds in NE-5300 (2013 Edition).
(b) The weld overlay, including the existing torus shell plate upon which it is applied, shall be examined to verify acceptable wall thickness using an ultrasonic thickness measurement method in accordance with the ASME Boiler and Pressure Vessel Code,Section XI, 2013 Edition, Mandatory Appendix I.
5.1.8 In-Service Examination
Each weld overlay shall be examined using an ultrasonic thickness measurement method during each of the two subsequent fuel cycles following installation to establish the expected life of the weld overlay repair. Subsequent examinations shall be scheduled prior to exceeding 1/2 of the expected life of the repair.
5.2 In lieu of the requirement of IWE-5221, CEG proposes to perform a pneumatic leakage test in accordance with IWE -5223 following installation of a weld overlay repair only at locations where the weld overlay repair is performed to correct a through-wall defect, or when pressure boundary integrity is not maintaine d during the welding process.
5.3 The proposed alternative in 5.1 is justified for the following reasons:
5.3.1 The proposed alternative is based on requirements in ASME Code Case N -561-3, which is approved for use in Table 1 of NRC Regulatory Guide 1.147, Revision
- 20. Although this case is applicable to Class 2 and high-energy Class 3 carbon steel piping experiencing internal wall thinning from localized erosion, corrosion, and cavitation or pitting, its use is acceptable for Class MC applications for the following reasons:
(a) The containment torus shell is constructed from A -201, Gr. B Firebox material, which is a carbon steel P1 material;
(b) The containment torus design pressure is consider ably lower than the high energy limit of 275 psig;
(c) The containment torus weld overlay repairs are proposed for internal wall thinning from localized erosion, corrosion, and cavitation or pitting; 10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 7 of 8)
(d) NRC Regulatory Guide 1.26, Revision 3 does not specifically address applicable quality standards for metal containment pressure vessels; however, NUREG-0800, 3.2.2, Quality Group B includes both Class 2 components and metal containment components. Application of weld overlay requirements similar to those approved for Class 2 containment pressure boundary piping using Code Case N -561-3 are suitable for Class MC components that perform the same containment pressure boundary function.
5.3.2 The proposed alternative includes requirements for the design and installation of weld overlays.
5.3.3 The proposed alternative includes requirements for performing ambient temperature temper bead welding using shielded metal arc welding in accordance with requirements of IWA-4680 in the ASME Boiler and Pressure Vessel Code,Section XI, 2017 Edition. These requirements shall be met for all weld overlays installed on surfaces where the interior side of the surface is below the torus water level.
5.3.4 The proposed alternative includes requirements for post-installation examination and subsequent inservice inspections to ensure that continued corrosion on the affected area will not challenge the integrity of the containment torus for the life of the weld overlay repair.
5.3.5 The proposed alternative includes post-installation pressure testing requirements for applications where weld overlays are installed to correct through-wall defects, or for through-wall conditions resulting from application of the weld overlay.
5.3.6 The proposed alternative limits the use of weld overlay repairs to applications where wall thickness loss due to internal erosion, corrosion, cavitation or pitting have occurred, and prohibits the use of weld overlay repairs for cracking or crack-like defects. The alternative requires ultrasonic examination of the material to be overlaid to confirm the absence of any cracking or crack-like defects in the area requiring repair.
5.3.7 There are no specific requirements in the Construction Code or ASME Section III, Subsection NE for the design and installation of weld overlays, so use of an approved alternative, based on requirements in an NRC approved ASME Code Case, is desired in lieu of performing underwater weld repairs or draining the containment torus to permit weld repairs on the torus interior surfaces.
5.3.8 CEG has determined that a weld overlay of as large as 1,300 in2 could be required for some torus repairs. CEG has determined that an overlay of up to 1,300 in2 will not affect the containment design basis loads or the dynamic analysis of the torus. The justification for the alternative to IWA-4681(b), allowing an individual weld area not greater than 1,300 in2 is supported by Electric Power Research Institute Report, Justification for Extension of Temper Bead Limit to 1,000 Square Inches for WOL of P1 and P3 Materials, EPRI, Palo Alto, CA:
2010, 1021073. This report provided a basis for increasing the allowable size of a temper bead weld overlay from 500 in2 to 1,000 in2, but the report also 10 CFR 50.55a Relief Request I5R-10 Revision 0 (Page 8 of 8)
concluded that increasing the area of the temper bead WOL area over the ferritic material does indeed improve the ID residual stresses and the report concluded that the investigation produced no unexpected or unacceptable results that would preclude the use of the temper bead process for weld overlays up to and beyond 1,000 in2.
5.3.9 Use of the proposed alternative will avoid the need to perform underwater welding on any submerged torus shell surfaces or would avoid the need to drain the containment torus to provide access for performing weld repairs on the torus shell interior.
5.4 The proposed alternative to IWE-5221 in 5.2 is justified because the alternative is consistent with requirements in IWA-4540(b)(3) for Class 1, 2, and 3 components. The proposed alternative is also consistent with 10 CFR 50, Appendix J, IV, A. which requires a Type A or B test only following a major modification of the containment.
The proposed alternative does include a requirement to perform a post-repair pressure test in accordance with IWE-5221 in the event that the weld overlay is being performed to correct a through-wall defect, or if the containment pressure boundary integrity is not maintained during the welding process.
5.5 All other requirements of the ASME Code,Section XI, 2013 Edition for which an alternative has not been requested, shall be met, including the involvement of the Authorized Nuclear Inservice Inspector.
5.6 For the reasons stated above, the proposed alternative provides an acceptable level of quality and safety, as required by 10 CFR 50.55a(z)(1).
6. Duration of Proposed Alternative
The proposed alternative is requested for use during the current (3rd) Containment Inservice Inspection Interval, currently scheduled to end on August 22, 2029.
7. Precedents
None.