RA-23-0018, Relief Request (RA-23-0018) to Utilize Code Case N-853 PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking Section XI, Division 1
| ML23124A384 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/04/2023 |
| From: | Snider S Duke Energy Carolinas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-23-0018 | |
| Download: ML23124A384 (1) | |
Text
Steven M. Snider Vice President Oconee Nuclear Station Duke Energy ON01VP l 7800 Rochester Hwy Seneca, SC 29672 o: 864.873.3478 f: 864.873.4208 Steve.Snider@duke-energy.com Serial: RA-23-0018 10 CFR 50.55a May 4, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 OCONEE NUCLEAR STATION, UNIT NOS. 1, 2 AND 3 DOCKET NOS. 50-269, 50-270, 50-287 / RENEWED LICENSE NOS. DPR-38, DPR-47 AND DPR-55
SUBJECT:
Relief Request (RA-23-0018) to Utilize Code Case N-853 PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking Section XI, Division 1 with Deviations Ladies and Gentlemen:
Pursuant to 10 CFR 50.55a(z)(1), Duke Energy Carolinas, LLC (Duke Energy) hereby submits Relief Request RA-23-0018 requesting U.S. Nuclear Regulatory Commission (NRC) approval to use an alternative to the defect removal requirements of American Society of Mechanical Engineers (ASME) Code,Section XI, Article IWA-4000 at Oconee Nuclear Station Units 1, 2 and 3 (ONS). Specifically, Duke Energy proposes to use ASME Code Case N-PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking Section XI, Division 1 with the deviations described herein. The Enclosure contains details regarding this request.
This submittal contains no new regulatory commitments. To support work in the ONS Unit 1 refueling outage currently scheduled in October 2024, Duke Energy requests approval of this relief request prior to that outage. If you have questions concerning this request, please contact Ryan Treadway, Director Nuclear Fleet Licensing, at (980) 373-5873.
Sincerely, Steven M. Snider Site Vice President Oconee Nuclear Station
Enclosure:
Relief Request RA-23-0018
U.S. Nuclear Regulatory Commission RA-23-0018 Page 2 cc:
(all with Enclosure unless otherwise noted)
L. Dudes, Regional Administrator USNRC Region II J. Nadel, USNRC Resident Inspector - ONS S. Williams, NRR Project Manager - ONS
Enclosure RA-23-0018 ENCLOSURE Duke Energy Carolinas, LLC Relief Request RA-23-0018
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 1 of 12
1.0 ASME Code Components Affected
1.1 Oconee Nuclear Station (ONS) Unit 1 - Code Class 1:
Three 1A Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds (1-PHA-13, 1-PHA-14, & 1-PHA-15).
Four (4) Cold Leg RTE Mounting Boss Alloy 600 Nozzle Welds (1-PIA1-12, 1-PIA2-12, 1-PIB1-12, & 1-PIB2-12).
1.2 ONS Unit 2 - Code Class 1:
Four (4) Cold Leg RTE Mounting Boss Alloy 600 Nozzle Welds (2-PIA1-12, 2-PIA2-12, 2-PIB1-12, & 2-PIB2-12).
1.3 ONS Unit 3 - Code Class 1:
Three 3B Hot Leg RTE Mounting Boss Alloy 600 Nozzle Welds.
(3-PHB-13, 3-PHB-14, & 3-PHB-15).
Two 3B Hot Leg Flow Meter Alloy 600 Nozzle Welds.
(* Nearest Nozzle Butt Welds 3-RC-286-11 & 3-RC-286-58V).
Four (4) Cold Leg RTE Mounting Boss Alloy 600 Nozzle Welds (3-PIA1-9, 3-PIA2-9, 3-PIB1-11, & 3-PIB2-9).
One 3B1 Cold Leg Level Tap Alloy 600 Nozzle Weld.
(* Nearest Nozzle Butt Weld 3-50-37-1).
Three Cold Leg Drain Alloy 600 Nozzle Welds.
(3PIA1-10, 3-PIA2-10, 3-PIB2-10).
Note *: Small Bore Piping (1 NPS) Nozzle Welds are not given explicit weld IDs on the original Drawings. These five specific Small Bore Nozzle Welds are located by the nearest documented branch connection butt weld.
Materials of construction for all locations referenced above are:
Reactor Coolant System Piping (RCS) - SA-106 Grade C (P-No. 1)
Alloy 600 Nozzle - SB-166 UNS N06600 (P-No. 43)
Alloy 82/182 Dissimilar Metal Weld (DMW) - ERNiCr-3, Spec. SFA 5.14 /
ENiCrFe-3, Spec. SFA 5.11 (F-No. 43) 2.0 APPLICABLE CODE EDITION AND ADDENDA The code of record for the current 5th Inservice Inspection (ISI) interval for ONS Units 1, 2, and 3 is the American Society of Mechanical Engineers (ASME) Code,Section XI, 2007 Edition with the 2008 Addenda (Reference 8.1). All units are currently in the 5th ISI interval with a scheduled end date of July 14, 2024.
The applicable ASME Section XI code of record for the 6th ISI interval at ONS Units 1, 2, and 3 was determined in accordance with the requirement of 10 CFR 50.55a(g)(4)(ii),
which states, in part, that successive 120-month inspection intervals must comply with
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 2 of 12 the requirements of the latest edition and addenda of the Code incorporated by reference in paragraph (a) of this section 18 months before the start of the 120-month inspection interval. The 5th ISI Interval for ONS 1, 2, and 3 is scheduled to end on July 14, 2024.
Therefore, the 6th ISI Interval code of record for ONS 1, 2, and 3 complies with the requirements of the latest edition and addenda of the Code incorporated by reference in 10 CFR 50.55a (Reference 8.2) on January 15, 2023, which is ASME Section XI, 2019 Edition (Reference 8.3). The current scheduled start date of the 6th ISI interval for ONS Units 1, 2, and 3 is July 15, 2024 with a scheduled end date of July 14, 2034.
The code of construction for ONS 1, 2, and 3 is B31.7, 1969 Edition, and was later reconciled to the ASME Code,Section III, 1983 Edition, no Addenda.
American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Code Case N-722-1 as conditioned by 10 CFR 50.55a (Reference 8.4).
American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Code Case N-853 (Reference 8.5).
3.0 APPLICABLE CODE REQUIREMENTS Code Case N-722-1 (as conditioned by 10 CFR 50.55a) requires that piping hot leg/cold leg full penetration welds susceptible to Primary Water Stress Corrosion Cracking (PWSCC) be inspected in accordance with Table 1 of the Code Case as part of the ISI program. Duke Energy has decided to preemptively mitigate/repair selected nozzle butt welds on the reactor coolant system (RCS) piping, utilizing a welded reinforcing pad and replacement nozzle.
ASME Code,Section XI (References 8.1 and 8.3), Article IWA-4000 provides requirements for repair replacement activities:
IWA-4421 states, in part:
Defects shall be removed or mitigated in accordance with the following requirements...
IWA-4422.1(a) states, in part:
A defect is considered removed when it has been reduced to an acceptable size...
IWA-4422.1(b) states, in part:
Alternatively, the defect removal area and any remaining portion of the defect may be evaluated, and the component accepted in accordance with the appropriate flaw evaluation provisions of Section XI...
Article IWA-4000 does not provide specific guidance for the repair or mitigation of defects in dissimilar metal welds. Furthermore, the NRC in 10 CFR 50.55a paragraph (xxv)(A) prohibits the use of the provisions in IWA-4340, "Mitigation of Defects by Modification, when using the ASME Code, 2001 Edition through 2010 Addenda. For ASME Code, 2011 and later editions, the NRC in 10 CFR 50.55a paragraph (xxv)(B) allows use of the provisions in IWA-4340 subject to conditions. However, per IWA-4340 of the 2019 Edition of ASME Section XI (Reference 8.3), modification is prohibited for Class 1 items.
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 3 of 12 4.0 REASON FOR REQUEST The welds identified in Section 1.0 are unmitigated full penetration welds fabricated from materials susceptible to PWSCC, (Figures 1a and 1b). As these welds are unmitigated, there exists the potential that flaws may develop at these locations and result in leakage.
In accordance with Code Case N-722-1, these welds require frequent visual examination for the identification of any RCS leakage.
4.1 Alternative Repair Technique Duke Energy is proposing to apply a welded reinforcing pad on the Outer Diameter (OD) of the RCS piping using PWSCC resistant nickel Alloy 52M (ERNiCrFe-7A) filler metal. The new weld pad is welded using the machine Gas Tungsten Arc Welding (GTAW) Ambient Temperature Temper Bead (ATTB) welding technique.
Duke Energy is proposing to attach a PWSCC resistant nozzle to the new weld pad with a full penetration nozzle corner weld using a non-temper bead manual welding technique, using PWSCC resistant nickel Alloy 52M filler metal, or with a "J" groove partial penetration weld as described in ASME Code Case (CC) N-853. The welded pad is designed and installed in accordance with CC N-853 except that the replacement nozzle material is UNS S31600 or UNS N06690.
ONS received approval applicable to the 5th ISI interval via NRC safety evaluation dated February 26, 2020 (Reference 8.14) to preemptively apply a mitigation/repair using the rules of CC N-853 with a PWSCC resistant nozzle attached to the new weld pad with a full penetration nozzle corner weld (Figure 3) using a non-temper bead manual welding technique, using PWSCC resistant nickel Alloy 52M filler metal, or with a "J" groove partial penetration weld as described in CC N-853 (Figure 2). The welded pads are to be designed and installed in accordance with CC N-853 except that the replacement nozzle material is UNS S31600 or UNS N06690. The new welded pad provides a full structural primary pressure boundary repair that takes no structural credit for either the existing 82/182 weld or the Alloy 600 nozzle material.
Therefore, Duke Energy is requesting relief applicable to the 6th ISI interval under 10 CFR 50.55a(z)(1) from the defect removal requirements of ASME Code,Section XI, Article IWA-4000. The identified welds are mitigated by a repair/replacement activity that meets the requirements of CC N-853 with the alternative nozzle material and weld joint geometry described herein. The repair/replacement activity provides an acceptable level of quality and safety.
4.2 Alternative Acceptance Criteria ONS received approval applicable to the 5th ISI interval via NRC safety evaluation dated February 7, 2022 (Reference 8.15) to use ASME Code,Section XI, IWB-3514 (Reference 8.3) as an alternative acceptance criteria for acceptance and disposition of defects detected during ultrasonic testing (UT) of the stress corrosion cracking resistant Alloy 52M weld pad in lieu of the ASME Code,Section III, NB-5330 criteria specified in CC N-853.
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 4 of 12 ASME CC N-853 specifies that the volumetric examination of the pad repair material shall be in accordance with the construction code or Section III with acceptance criteria in NB-5330. The ASME Code,Section III acceptance standards are written for a range of fabrication flaws, including lack of fusion, incomplete penetration, cracking, slag inclusions, porosity, and concavity. However, experience and fracture mechanics have demonstrated that many of the flaws that would be rejected using the ASME Code,Section III acceptance criteria do not have a significant effect on the structural integrity of the component. These inspection criteria are derived on the basis of a radiographic (RT) examination, which does not have the granularity of current ultrasonic techniques. Therefore, any flaw identified by RT would be presumed to be unacceptable. That is why the NB-5330 inspection criteria, under Fabrication, does not allow any identified crack-like indications, regardless of size, orientation, depth, cause, or significance to the structural adequacy of the overall weld pad. Many flaws that are not detected with radiography have a high likelihood of being detected with UT, depending on its orientation. If identified by the more sensitive UT method, the RT-based acceptance criteria would require the removal of the defect and the weld pad repaired and re-inspected. This could significantly alter the beneficial residual stress pattern and produce a less optimal final, stress field protecting the RCS pressure boundary.
Therefore, Duke Energy is also requesting relief applicable to the 6th ISI interval under 10 CFR 50.55a(z)(1) to utilize alternative acceptance criteria for volumetrically inspecting the weld pad that provides an acceptable level of quality and safety.
5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE 5.1 Proposed Alternative for Repair is as Follows:
Figure 1a and Figure 1b provide sketches of the existing nozzle configurations described in Section 1. The Alloy 600 nozzle and Alloy 82/182 weld are materials with known susceptibility to PWSCC. The replacement of PWSCC susceptible material with material that is resistant to PWSCC provides for an acceptable level of quality and safety. The PWSCC susceptible material, at the identified locations, is currently unmitigated. Application of a PWSCC resistant branch connection weld metal buildup reduces the risk of a flaw propagating through the pressure boundary.
The PWSCC resistant branch connection weld metal buildup is designed in accordance with CC N-853 as modified herein. CC N-853 has been reviewed by the NRC and is approved for Unconditional Use (References 8.6 and 8.7). Two optional deviations may be taken to CC N-853 as follows: a) the new nozzle material may be manufactured from UNS S31600 material instead of UNS N06690, and b) the new nozzle may be attached by a full penetration nozzle corner weld instead of a partial penetration J groove weld. Reference 8.8 provides the technical basis supporting the use of CC N-853.
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 5 of 12 5.2 The Basis for the Proposed Repair Alternative is as Follows:
CC N-853 requires the use of UNS N06690 material for the replacement nozzle.
Duke Energy proposes as an option to use UNS S31600 material for the replacement nozzle. UNS S31600 material is used in many applications for elevated temperature reactor coolant piping at ONS. UNS S31600 is an austenitic stainless steel that has demonstrated operating experience as PWSCC resistant. The applicable ASME Code allowable stresses and material properties for UNS S31600 is used in the design of the replacement nozzle. The reason for the requested use of UNS S31600 is that UNS S31600 is a more readily available material, given the strict ASME Code Class 1 requirements for materials, and the small volume of material required.
CC N-853 requires the use of a partial penetration J groove weld for the attachment of the new nozzle to the reinforcing weld metal buildup. The partial penetration J groove weld is one of many Code approved configurations for attachment of nozzles to piping. Figure 2 provides a sketch of the Code Case configuration. Duke Energy proposes to optionally use a full penetration nozzle corner weld to join the new nozzle to the weld reinforcing pad. The technical basis for CC N-853 (Reference 8.8) includes reference for the use of full penetration nozzle welds.
The full penetration nozzle corner weld configuration shown in Figure 3 is in agreement with ASME Code,Section III, Figure NB-4244(b)-1 detail (a) (Reference 8.9). The full penetration corner weld is examined in accordance with Reference (Reference 8.9) and CC N-853. The reason for the requested optional use of the nozzle corner weld detail (detail (a) of Figure NB-4244(b)-1) is that field conditions of access and interferences may result in situations where the corner weld is preferable to the J-groove weld, based on dose exposure and installation sequence.
Additionally, use of a full penetration corner weld eliminates the small pocket area at the base of the nozzle which over time collects contaminants and create a radiological hot spot in the RCS piping.
In summary, Duke Energy is requesting relief under 10 CFR 50.55a(z)(1) from the ASME Code,Section XI defect removal requirements of IWA-4000. The repair/replacement activity follows the requirements stated in CC N-853 and modified herein. The requested relief from IWA-4000 is based on the use of CC N-853 (with the noted deviations / exceptions) that provides an alternative with an acceptable level of quality and safety. The subject welds are mitigated or repaired by application of a PWSCC resistant reinforcing pad and attachment of a PWSCC resistant nozzle.
The use of CC N-853 as guidance for the repair/replacement activity provides an acceptable level of quality and safety.
5.3 Proposed Alternative Acceptance Criteria is as Follows:
In lieu of the NB-5330 acceptance criteria for Fabrication, it is proposed to use the preservice examination acceptance criteria of IWB-3514 for the welded pad material and Heat Affected Zone (HAZ).
For acceptance of the weld pad after installation, Duke Energy will follow CC N-853, Section 3, paragraph (d)(3). If the results of the examination are acceptable under
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 6 of 12 NB-5330, Duke Energy will follow the CC N-853 required subsequent inservice inspection for that weld pad (i.e., visual examination).
If a defect is detected in a weld pad that is rejectable under NB-5330 but acceptable under IWB-3514, Duke Energy will perform a subsequent, one-time volumetric examination of that weld pad during the first or second refueling outage following installation. If the volumetric examination shows no indication of crack growth or new cracking, the weld pad is placed into a population (per unit) to be examined on a sample basis. Twenty-five percent of this population shall be added to the ISI program and shall be examined volumetrically once each inspection interval with the following inspection attributes.
The examination is considered a best effort examination obtaining the maximum coverage available, knowing beforehand that the examination will have reduced coverage due to the nozzle obstruction.
If the defect is located within the weld pad volume that is completely removed as part of nozzle replacement activities, the defect will be considered to have been removed, and no further evaluation is required.
If the defect is located in the weld pad volume that cannot be sufficiently interrogated in the future due to the existence of the nozzle, the defect will be removed by weld repair as confirmed by subsequent volumetric examination.
The one-time examination is of sufficient volume, and area, such that the previously identified and dispositioned defect will be adequately interrogated to determine any in-service growth. The one-time examination will not include the entire weld pad volume.
The one-time volumetric examination will use the same or equivalent procedures, equipment, and personnel qualifications as the initial fabrication examination.
The applicability of these provisions are limited solely to the N-853 weld pads, and not any other components evaluated to IWB-3514 acceptance criteria.
The 25% inspection population is defined as only those CC N-853 weld pads that required this alternative to disposition an identified defect. All other CC N-853 weld pads that were acceptable, either by the presence of no defects, or acceptable using NB-5330 criteria, will not be included in this population.
If during the subsequent, one-time volumetric examination of a weld pad, or subsequent examinations, there is an indication of crack growth or new cracking, Duke Energy will evaluate the condition of the weld pad in accordance with Section XI of the ASME Code and take action (e.g., repair, subsequent re-examination, etc.)
in accordance with ASME Code requirements.
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 7 of 12 5.4 The Basis for the Proposed Alternative Acceptance Criteria is as Follows:
CC N-853 requires a UT volumetric examination to be demonstrated in accordance with Section V of the ASME Code. This procedure is then used to volumetrically examine the newly deposited pad material and HAZ in accordance with the Construction Code or Section III, with NB-5330 as the acceptance criteria.
The IWB-3514 acceptance criteria are based on UT examination methods. In using the rules in IWB-3514 for evaluation of flaws in the weld pad, the thickness of only the weld pad is used. However, the examination volume specified in Figure 6, Surface and Volumetric Acceptance Examination for BCWMB Prior to Nozzle Welding, of CC N-853 for Alloy 52M weld-pad and HAZ is scanned by UT during fabrication inspection.
The use of IWB-3514 rules was previously approved by the NRC in the 5th Interval ONS Relief Request (Reference 8.15). The proposed inspection criteria detects flaws in the weld overlays such as inter-bead lack of fusion, inclusions, or cracks, and meets the standards of IWB-3514 for acceptability. The N-853 weld pad is also preemptively applied and uses the same Alloy 690 weld material and welding process as past Full Structural Welds Overlays (FSWOs) made at ONS and are subjected to these same potential welding defects (Reference 8.16). Applying the proposed alternative inspection criteria better matches the sensitivity of the UT inspection technique that is used for the weld pad, as discussed in NRC safety evaluation (Reference 8.16), and repeated here:
ASME Code,Section III, flaw acceptance standards are derived from the capability of radiography to detect and size flaws originating from the fabrication process used during new facility construction. The ASME Code,Section III acceptance criteria do not allow for the presence of any cracks or crack-like indications, regardless of their size, and are geared more towards volumetric flaws. The capability of radiography is a function of density differences such as 2 percent or greater changes in density. The density changes normally associated with cracks, depending on orientation, are much less than the detection capability of radiography. There is an inherent, unknown tolerance in the ASME Code,Section III acceptance criteria for radiography which encompasses tight cracks and densities below the detection capabilities of radiography. Flaws detected using radiography are not precise enough for applying ASME Code,Section XI crack growth analyses, as flaw depth cannot be measured with radiography. ASME Code,Section III radiography is not applicable for evaluating flaws for continued plant operations because of the difficulty associated with depth-sizing flaws.
The inspection and examination criteria of the underlying base metal material for lamellar tearing per CC N-853(3)(d)(3) remains unchanged.
The UT utilized for the fabrication inspection of Alloy 52M weld-pad and HAZ is not demonstrated and qualified in accordance with ASME Code,Section XI, Appendix VIII, Supplement 11. Demonstration and qualification meets the requirements of CC N-853 paragraph (a) for demonstration and paragraph (b) for personnel qualification.
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 8 of 12 A Manual Phased Array UT Procedure is used that meets the demonstration requirements of ASME Code,Section V. This procedure employs technical elements of Performance Demonstration Initiative (PDI) qualified Supplement 11 procedures, which is implemented by PDI-qualified Supplement 11 weld overlay examiners. In addition, the Electric Power Research Institute (EPRI) does not currently have any sample flaw sets available (based on weld pad thickness and branch connection configuration) to perform qualified Manual PDI UT on the proposed branch connection weld repair pad. Meeting the CC N-853 requirements for nondestructive examination (NDE) provides an acceptable level of quality and safety.
The weld pads planned for installation at ONS are thick (approximately 1.3 thick) and wide (about 14 inches square). Their deposition by welding produces a complex residual stress field that is used to evaluate the fatigue crack growth per CC N-853 requirements. Current rules in Section III would not allow for any crack like defects, regardless of size, orientation, depth, cause, or significance to the overall structural integrity of the pad and its protection of the underlying pressure boundary material.
Section III criteria would require removal of a portion of the pad, that would then have to be rewelded and re-inspected. The primary benefit to using the IWB-3514 acceptance criteria is that small, structurally insignificant defects, i.e., those that meet the IWB acceptance criteria, if found, would be allowed to remain without repair. This would result in a structurally acceptable, unrepaired weld pad producing an intact residual stress field that would protect the RCS pressure boundary components from PWSCC. The proposed alternative does not alter the required examination coverage, or the specific UT method used for the inspection. In addition, the manual pad repairs are dose and time intensive processes; therefore, not repairing a weld pad enhances outage personnel safety by reducing potential injuries during grinder usage and the accumulation of less radiation exposure.
Section XI, IWB-3514 is the general acceptance criteria used for fabricated components and welds. IWB-3514-2 was originally incorporated into the ASME Code during the 1980s and has been utilized for accepting planar flaws for IWB-2500 inspected components with a good service history. It should be noted that ID connected defects in SCC susceptible material cannot use the IWB-3500 acceptance criteria. Since the welded pad deposit is applied with SCC resistant material (Alloy 52M), this concern does not exist.
In summary, Duke Energy is requesting relief under 10 CFR 50.55a(z)(1) from the ASME Code,Section XI CC N-853 inspection requirements. The repair/replacement activity will follow the requirements stated in CC N-853 and modified herein. The requested relief is based on the use of CC N-853 (with the noted deviations/exceptions) that provides an alternative with an acceptable level of quality and safety. The subject welds will be preemptively mitigated or repaired by application of a PWSCC resistant reinforcing pad and attachment of a PWSCC resistant nozzle. The use of CC N-853 as guidance for the repair/replacement activity, as modified herein, provides an acceptable level of quality and safety.
6.0 PRECEDENTS The proposed CC N-853 deviations for the 6th ISI interval of ONS Units 1, 2, and 3 were previously approved for the 5th ISI interval of ONS Units 1, 2, and 3 under safety
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 9 of 12 evaluations dated February 26, 2020 (Reference 8.14) and February 7, 2022 (Reference 8.15).
In addition, weld metal buildups with a replacement nozzle have been performed to repair leaking nozzles on reactor pressure vessels and pressurizers. These instances formed the basis of Code Case N-853. Listed below are examples with the submitted request for alternative (RR) and safety evaluation (SE).
- b. Limerick Generation Station (RR Reference 8.12; SE Reference 8.13) 7.0 DURATION OF PROPOSED ALTERNATIVE The alternative is requested to be implemented for the 6th ISI Interval for ONS 1, 2, and 3, which is scheduled to start on July 15, 2024 and end on July 14, 2034. The duration of each physical repair is requested for the remainder of the current licensed operating life of each ONS unit. The repairs are designed to meet the requirements of CC N-853 (with deviations described herein), ASME Code,Section III (Reference 8.9), and ASME Code,Section XI (Reference 8.3). The design considers operation until the end of the current renewed operating licenses for each unit as follows:
Docket Number License Expires Unit 1 05000269 02/06/2033 Unit 2 05000270 10/06/2033 Unit 3 05000287 07/19/2034
8.0 REFERENCES
8.1 American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, 2007 Edition with the 2008 Addenda.
8.2 Federal Register (Vol. 87, No. 207, October 27, 2022) - American Society of Mechanical Engineers 2019-2020 Code Editions.
8.3 American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, 2019 Edition.
8.4 ASME Code Case N-722-1, Additional Examinations for PWR Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 Materials,Section XI, Division 1, Approval Date: January 26, 2009.
8.5 ASME Code Case N-853, PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking,Section XI, Division 1, Approval Date: June 27, 2016.
8.6 Federal Register (Vol. 85, No. 42, March 3, 2022) - Approval of American Society of Mechanical Engineers Code Cases.
8.7 Regulatory Guide RG 1.147, Revision 20; December 2021 (ADAMS Accession No. ML21181A222).
8.8 Waskey, D., McCracken, S., (2016); Technical Basis for Code Case N-853 - A600
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Page 10 of 12 Branch Connection Weld Repair for SCC Mitigation; Proceedings of the ASME 2016 Pressure Vessels and Piping Conference; PVP2016; July 17-21, 2016, Vancouver, British Columbia, Canada; PVP2016-63902.
8.9 ASME Code Section III, 2013 Edition.
8.10 Arizona Public Service Company letter, American Society of Mechanical Engineers (ASME) Code,Section XI, Request for Approval of an Alternative to Flaw Removal and Characterization - Relief Request 51, dated November 8, 2013 (ADAMS Accession No. ML13317A071).
8.11 NRC letter, Palo Verde Nuclear Generating Station, Unit 3 - Request for Relief from ASME Code,Section XI Requirements Regarding Half-Nozzle Repair and Flaw Evaluation as an Alternative to Flaw Removal and Flaw Characterization for Flaw in Bottom-Mounted Instrument Nozzle Penetration No.3 (TAC No. MF3051), dated April 10, 2014 (ADAMS Accession No. ML14093A407).
8.12 Exelon Generation letter, Proposed Relief Request Associated with Reactor Pressure Vessel Nozzle Repairs, dated May 15, 2017 (ADAMS Accession No. ML17135A423).
8.13 NRC letter, Limerick Generating Station, Unit 2 - Relief Request I4R-17, Associated with the Alternate Repair of a 2-Inch Instrument Line Nozzle at Penetration N-16D on the Reactor Pressure Vessel (CAC No. MF9702), dated August 14, 2017 (ADAMS Accession No. ML17208A090).
8.14 NRC Safety Evaluation, Safety Evaluation by the Office of Nuclear Reactor Regulation Proposed Alternative Request 19-ON-001 to use Modified American Society of Mechanical Engineers Boiler and Pressure Vessel Code Case N-853, Duke Energy Carolinas, LLC, Oconee Nuclear Station, Units 1, 2, and 3, Docket Numbers 50-269, 50-270, and 50-287, dated February 26, 2020 (ADAMS Accession No. ML20055F571).
8.15 NRC Safety Evaluation, Oconee Nuclear Station, Units 1, 2, and 3 - Authorization and Safety Evaluation for Relief Request RA-20-0334 for Use of Alternative Acceptance Criteria in Code Case N-853 (EPID L-2021-LLR-0032), dated February 7, 2022 (ADAMS Accession No. ML22028A365).
8.16 NRC Safety Evaluation, Safety Evaluation by The Office of Nuclear Reactor Regulation Inservice Inspection Program Relief Request Nos. 06-ON-004 and 07-ON-001 Oconee Nuclear Station, Units 1, 2, and 3 Duke Power Company LLC Docket NOS. 50-269, -270, -287, dated August 6, 2007 (ADAMS Accession Number ML071280781).
Enclosure Proposed Alternative RA-23-0018 in Accordance with 10 CFR 50.55a(z)(1)
Page 11 of 12 Figure 1a: Sketch of Example Existing Nozzle Configuration Figure 1b: Sketch of Example Fast RTE Nozzle Connection
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Page 12 of 12 Figure 2: Sketch of Example Repaired Nozzle Configuration with Code Case N-853 J-Groove Weld Figure 3: Sketch of Example Repaired Nozzle Configuration with Proposed Alternative Full Penetration Corner Weld