ML25107A057
| ML25107A057 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 04/24/2025 |
| From: | Tony Nakanishi NRC/NRR/DORL/LPL4 |
| To: | Entergy Operations |
| References | |
| EPID L-2024-LLR-0065, ANO2-RR-24-001 | |
| Download: ML25107A057 (12) | |
Text
April 24, 2025 ARKANSAS NUCLEAR ONE, UNIT 2 - AUTHORIZATION AND SAFETY EVALUATION FOR ALTERNATIVE REQUEST NO. ANO2-RR-24-001 (EPID L-2024-LLR-0065)
LICENSEE INFORMATION Licensee:
Entergy Operations, Inc.
Licensee Address:
ANO Site Vice President Arkansas Nuclear One Entergy Operations, Inc.
N-ADM-8 1448 S.R. 333 Russellville, AR 72802 Plant Name and Unit:
Arkansas Nuclear One, Unit 2 (ANO-2)
Docket No.:
50-368 APPLICATION INFORMATION Submittal Date: October 21, 2024 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML24295A119 (Package)
Supplement Date: November 11, 2024 Supplement ADAMS Accession No.: ML24316A002 (Package)
Licensee Proposed Alternative No. or Identifier: Alternative ANO2-RR-24-001 Applicable Provision: Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1),
Acceptable level of quality and safety Applicable Code Edition and Addenda: 2007 Edition through 2008 Addenda of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code),
Section XI; 1992 Edition of ASME Code,Section III, subsection NB; ASME Code,Section XI, Code Case N-729-6, as amended in 10 CFR 50.55a(g)(6)(ii)(D) Augmented ISI [Inservice Inspection] requirements: Reactor vessel head inspections; ASME Code,Section III, 1968 Edition through Summer 1970 Addenda (Original Construction Code)
Applicable Code Requirements:
ASME Code,Section XI, 2007 Edition through 2008 Addenda IWB-3420, states Each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaws. These dimensions shall be used in conjunction with the acceptance standards of IWB-3500.
IWB-3132.3, states A component whose volumetric or surface examination detects flaws that exceed the acceptance standards of Table IWB-3410-1 is acceptable for continued service without a repair/replacement activity if an analytical evaluation, as described in IWB-3600, meets the acceptance criteria of IWB-3600. The area containing the flaw shall be subsequently reexamined in accordance with IWB-2420(b) and (c).
ASME Code,Section III, 1992 Edition NB-5245, Partial Penetration Welded Joints, specifies progressive surface examination of partial penetration welds.
NB-5330(b), states:
Indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.
ASME Code Case N-638-11, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique ASME Code Case N-638-11 provides requirements for automatic or machine gas tungsten arc welding (GTAW) of Class 1 components without the use of preheat or post-weld heat treatment (PWHT). Code Case N-638-11 is listed as an acceptable Section XI code case in table 1 of Regulatory Guide 1.147, Revision 21, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, March 2024 (ML23291A003). The Framatome Inc. temper bead welding procedures were established in accordance with Code Case N-638-4. Code Case N-638-11, section 2, Welding Qualifications, paragraph (b) permits use of existing welding procedures qualified in accordance with previous revisions of the Code Case. When the existing welding procedure was qualified in accordance with Code Case N-638-4, the test coupon base material was post-weld heat treated to comply with paragraph 2.1(a) of the Code Case (N-638-4), which states: The base material for the welding procedure qualification shall be of the same P-Number and Group Number as the materials to be welded. The materials shall be post-weld heat treated to at least the time and temperature that was applied to the materials being welded.
Brief Description of the Proposed Alternative and Basis:
By letter dated October 21, 2024 (ML24295A120), Entergy Operations, Inc. (the licensee) submitted proposed Alternative ANO2-RR-24-001 for ANO-2. In proposed Alternative ANO2-RR-24-001, the licensee stated that a flaw located in reactor vessel closure head (RVCH) penetration nozzle No. 71 was determined to be unacceptable based on requirements of the ASME Code. In order to address the flaw, the licensee stated it will perform a half-nozzle repair of penetration nozzle No. 71. The licensee made this request in accordance with (10 CFR 50.55a(z)(1), to ensure structural integrity of penetration nozzle No. 71 for one cycle (18-months) of operation at ANO-2.
REGULATORY EVALUATION Regulatory Basis: 10 CFR 50.55a(z)(1)
The NRC regulations in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, state that, Alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation.
The licensee must demonstrate that its request meets one of two criteria: (1) the proposed alternative would provide an acceptable level of quality and safety in accordance with paragraph (z)(1); or (2) compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety in accordance with paragraph (z)(2).
The licensee submitted the request on the basis that the proposed alternative would provide an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1). Based on the above regulations, the NRC staff finds that regulatory authority exists to authorize an alternative to ASME Code,Section III and Section XI, as requested by the licensee.
TECHNICAL EVALUATION During the ANO-2 fall 2024 refueling outage 2R30, the licensee performed ultrasonic testing (UT) examinations on RVCH penetration nozzles in accordance with Item No. B4.20 in ASME Code Case N-729-6, Alternative Examination Requirements for PWR [Pressurized-Water Reactor] Reactor Vessel Upper Heads with Nozzles Having Pressure-Retaining Partial Penetration Welds,Section XI, Division 1. An axial, planar indication was identified in control element drive mechanism (CEDM) penetration nozzle No. 71, which is an ASME Code Class 1 component. The indication was located along the outside diameter of the nozzle at the toe of J-groove weld and downhill side of the nozzle.
The licensee proposed to perform a half-nozzle repair of the subject penetration nozzle. By letter dated October 21, 2024, the licensee requested approval of the proposed alternative to the ASME Code repair and replacement requirements. On October 21, 2024 (ML24296A065),
the NRC staff verbally authorized the use of the proposed alternative for Operating Cycle 31, which is currently expected to conclude in spring 2026.
The licensee submitted the final one cycle flaw analytical evaluation, evaluation of repair, and the corrosion evaluation by letter dated November 11, 2024. This section documents the NRC staffs technical evaluation of the previously verbally-approved proposed alternative and the associated one cycle justification analysis for the use of the repair weld for one 18-month operating cycle (i.e., Cycle 31).
Welding Requirements The licensee indicated that paragraph 2(b) of ASME Code Case N-638-11 permits the use of welding procedures qualified in accordance with previous revisions of the code case.
Accordingly, the licensee proposed to use the welding procedure that was qualified in accordance with Code Case N-638-4, which is an earlier version of N-638-11.
The licensee explained that the proposed alternative involves a deviation from the weld qualification provisions of ASME Code Case N-638-4. Specifically, Code Case N-638-4, paragraph 2.1(a) states that, The base material for the welding procedure qualification shall be of the same P-Number and Group Number as the materials to be welded. The materials shall be post-weld heat treated to at least the time and temperature that was applied to the materials being welded. However, the welding procedure qualification test plate used by the licensee underwent 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> of simulated PWHT, whereas the RVCH material at ANO-2 received at least 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> of PWHT. This condition does not comply with Code Case N-638-4, paragraph 2.1(a), which requires the simulated PWHT time for the qualification test plate to be equivalent to or exceed the total aggregate time applied to the component to be welded.
The licensee justified the deviation by referencing the changes made in ASME Code Case N-638-11, paragraph 2.1(a), which states that, test assembly is neither required nor prohibited.
However, if used, the simulated PWHT shall not exceed the time or temperature already applied to the base material to be welded. This revision acknowledges that excessive simulated PWHT on the qualification test plate can artificially enhance the contrast between the impact properties of the base material and the temper bead heat-affected zone, making passing the impact testing requirements less difficult. This effect is documented in Electric Power Research Institute (EPRI) report 1025169, Welding and Repair Technology Center: Welding and Repair Technical Issues in ASME Section XI, section 3.0, which discusses the impact of simulated PWHT on the welding qualification process.
As discussed above, the NRC staff finds that the licensees use of the welding qualification process in ASME Code Case N-638-4, with an exception for the simulated PWHT time, is acceptable because: (1) Code Case N-638-11 allows the use of the temper bead weld process that was qualified in accordance with a previous version of the code case; (2) the licensee uses the weld process qualified in accordance with Code Case N-638-4 with one deviation; (3) the deviation (i.e., the simulated PWHT time and temperature not exceeding those applied to the base material) aligns with the provisions in Code Case N-638-11; and (4) Code Case N-638-11 is approved for use in regulatory guidance without a condition regarding the simulated PWHT time and temperature in the welding qualification.
Therefore, the proposed welding procedure for the half-nozzle repair on CEDM penetration nozzle No. 71 complies with the updated, simulated PWHT requirements of ASME Code Case N-638-11, with reasonable assurance of structural integrity and safety of the repair.
Acceptance Examination of Inside Diameter Temper Bead Weld Repair The licensee stated that the acceptance examination of the inside diameter temper bead (IDTB) weld repair follows the requirements outlined in ASME Code,Section III, 1992 Edition.
Specifically, NB-5245 prescribes a progressive surface examination for partial penetration welds, which is considered more practical than volumetric examination due to the conventional geometry of these weld configurations.
However, given the repair weld's suitability for UT and accessibility from both the top and bottom surfaces, as illustrated in figures 4 through 8 of the proposed alternative, the licensee proposed using both penetrant testing (PT) and UT for examination.
For the acceptance of the modified configuration of the repaired nozzle, the licensee proposed volumetric examination using UT in accordance with ASME Code Case N-638-11, paragraphs 4(a)(2) and 4(a)(6). Since these provisions are included in the approved code case, the NRC staff determined that the licensees approach to volumetric examination using UT is acceptable. The UT examination system is designed to scan cylindrical surfaces with inside diameters of approximately 2.82 inches. The scanning process utilizes:
A 0° longitudinal-wave (L-wave) transducer, 45° L-wave transducers in two opposed axial directions, 70° L-wave transducers in two opposed axial directions, 45° L-wave transducers in two opposed circumferential directions.
The repair weld undergoes 100 percent volumetric examination. Additionally, the low-alloy steel extending 0.25 inches beneath the weld into the base material as shown in figure 3 of the licensees submittal is examined using a 0° L-wave transducer to detect potential under bead cracking and lack of fusion in the heat-affected zone. The acceptance criteria for UT examination are specified in ASME Code,Section III, NB-5330. Furthermore, the UT examination volume extends 1 inch into the Alloy 600 nozzle material above and below the weld.
In addition to UT, the licensee proposed a surface PT examination of the entire weld. This final examination of the new weld and the immediate surrounding region ensures that no defects have been introduced into the ferritic low-alloy steel RVCH base material due to welding. The acceptance criteria for the PT examination align with NB-5350 of ASME Code,Section III, 1992 Edition.
The NRC staff concluded that the licensees proposal to use UT and PT examinations is acceptable because; (1) the proposed UT and PT examinations comply with ASME Code Case N-638-11 provisions; (2) the examination volume is sufficient to verify the structural integrity and acceptability of the weld repair modification; and (3) the acceptance criteria are consistent with ASME Code,Section III, construction code requirements.
The licensees proposed approach effectively ensures the reliability of the repaired nozzle, maintains compliance with industry standards, and has been previously approved for similar repair activities by the NRC.
Preservice and Inservice Inspections The proposed alternative describes the preservice and inservice inspections for CEDM penetration nozzle No. 71, including the repair weld. The inspections will be conducted in accordance with ASME Code Case N-729-6, as approved by the NRC in 10 CFR 50.55a, Codes and standards. Specifically, the preservice and inservice inspections will involve performing volumetric examination as outlined in Code Case N-729-6, table 1, Item No. B4.20.
ASME Code Case N-729-6 specifies that the examination region must extend 1.5 inches above and below the J-groove weld. However, an alternative examination region is proposed, which extends up to the outer surface of the head (greater than 1.5 inches above the repair weld),
including the roll transition region, and 1 inch below the structural weld, as depicted in figure 9 of the licensees submittal. The lower extent of the new pressure boundary (structural weld) jurisdiction is located at the transition point between the inside diameter and taper of the lower replacement nozzle. The portion of the repair weld above the jurisdictional boundary is classified as a pressure-retaining structural weld, while the portion below the jurisdictional boundary is classified as a permanent, non-structural attachment weld.
The NRC staff finds that the proposed examination volume extended above the repair weld is acceptable because: (1) the examination volume of the repair weld extends up to the outer surface of the RVCH, which exceeds the requirements of ASME Code Case N-729-6; (2) the extended examination volume can effectively identify relevant indications in the Alloy 600 nozzle and assess potential leakage paths; and (3) the extended examination volume fully encompasses the roll transition region, which may have increased primary water stress corrosion cracking (PWSCC) susceptibility due to roll expansion and associated cold-work.
Examination coverage below the repair weld will be less than the 1.5-inch requirement in ASME Code Case N-729-6 due to geometric limitations of the repaired nozzle. However, examination coverage will extend at least 1 inch below the structural weld, ensuring the maximum practical examination volume. Justification for the sufficiency of this coverage includes: (1) the repair weld material (Alloy 52M) is highly resistant to PWSCC; (2) the replacement nozzle material (Alloy 690) is also resistant to PWSCC; and (3) the replacement nozzle is non-pressure-retaining.
If the licensee operates ANO-2 for more than the next 18-month refueling cycle with the current RVCH, then successive examinations required by ASME Code Case N-729-6 will be performed on CEDM penetration nozzle No. 71 during each refueling outage. All other ANO-2 RVCH CEDM and nozzles will continue to be examined in accordance with Code Case N-729-6, as modified by 10 CFR 50.55a(g)(6)(ii)(D) and other NRC-approved alternatives. Future inservice inspection examinations will therefore comply with these requirements as outlined in figure 9 of the submittal.
The reexamination interval of one fuel cycle (18 months) for the repaired configuration of CEDM penetration nozzle No. 71 will ensure structural integrity and leak-tightness of the remnant Alloy 600 material above the IDTB weld.
Triple Point Anomaly ASME Code,Section III, NB-5330(b) specifies that indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length. With respect to this requirement, the proposed alternative addresses the material anomaly associated with the welding process. The licensee explained that the anomaly is a result of the welding technique used in the repair process. As depicted in figure 2 of the licensees submittal, the anomaly appears at specific points where different materials intersect in the weld. These points include the interface between the original base material and the repair weld, as well as areas where different alloys meet. The licensee further described the anomaly as a minor irregularity within the weld structure, consisting of a very small void. Mockup testing confirmed that such anomalies are typical and do not exceed 0.10 inches in through-wall extent. For analysis purposes, the licensee assumed that these anomalies could be present along the entire circumference at both triple point weld location.
In the submittal dated November 11, 2024, the licensee provided a comparative assessment of the anomaly, comparing the repair and operating conditions of ANO-2 CEDM penetration nozzle No.71 with that of a previously approved repair. This comparative analysis demonstrated that the existing precedent is applicable to the current case and ensures acceptability for at least one operational cycle. The previously approved analysis was based on a flaw growth assessment over a 20-year period, while the current repair only requires justification for an 18-month operating cycle. The licensee confirmed that the previously established analysis is conservative and adequately bounds the current case in terms of operational duration.
Additionally, the licensee verified that the pressure and temperature conditions affecting crack growth in the current case are comparable to those in the previously approved analysis. The transient loading cycles were reviewed, confirming that the number of cycles considered in the prior analysis remains conservative when applied to the current case. The licensee also confirmed that the stress conditions in the RVCH from the previous analysis are bounding for this repair case, considering factors such as component dimensions and operating pressures.
Furthermore, a comparison of nozzle geometry, including thickness and diameter, demonstrated that these parameters do not significantly alter the analysis results.
Regarding fracture toughness, the licensee evaluated the reference nil-ductility transition temperature (RTNDT) of the reactor vessel material in both cases. The comparison confirmed that the previously approved analysis involved a more limiting RTNDT than the current case, ensuring a conservative assessment.
The NRC staff review confirms that the licensees analysis meets the ASME Code, acceptance criteria, including:
Section XI, IWB-3612 - Ensuring that the applied stress intensity factor remains below the fracture toughness with appropriate safety margins.
Section XI, IWB-3642 - Verifying sufficient loading capacity under a fully circumferential flaw assumption.
Section III, NB 3227.1 - Shear stress criteria for a cylindrical flaw, ensuring that the flaw does not exceed allowable shear stress limits.
Section XI, IWB-3643 - Ensuring that flaws deeper than 75percent of the wall thickness remain unacceptable.
The NRC staff finds that the licensees one cycle justification for the triple point anomaly is acceptable because: (1) the triple point anomaly analyses of half-nozzle repairs that previously have been approved by the NRC staff involve a significantly longer analysis period (greater than 20 years) compared to the analysis period of the ANO-2 weld repair (18 months); (2) the previous triple point anomaly analyses confirmed the structural integrity of the repaired nozzle and adjacent RVCH in accordance with the acceptance criteria of ASME Code; and (3) the licensees comparative analysis confirms that the analysis parameters of the previously approved case is representative of or bounding for the ANO-2 triple point anomaly analysis (e.g., RVCH and nozzle dimensions, stress levels, transient loading, and transient cycle numbers) and, therefore, the ANO-2 weld repair is acceptable in terms of the triple point anomaly analysis As-left J-Groove Weld Flaw Evaluation The licensee addressed the evaluation of the as-left J-groove weld flaw in accordance with the provisions outlined in IWB-3600 of ASME Code,Section XI. These provisions for analytical flaw evaluation assume that cracks are fully characterized in compliance with IWB-3420. The licensee clarified that no qualified UT examination techniques are currently available to assess the original nozzle-to-RVCH J-groove welds. Given the impracticality of characterizing the flaw geometry in the J-groove weld, the licensee conservatively assumed that the as-left condition involved a flaw extending through the entire Alloy 82/182 J-groove weld, including the weld buttering.
The licensee further explained that the primary direction for crack propagation would be radial due to the dominance of hoop stresses in the J-groove weld. A radial crack in the J-groove weld would propagate into the low-alloy steel by fatigue crack growth, as the low-alloy steel is resistant to PWSCC. This scenario is consistent with the assumed flaw growth mechanism and the material properties of the low-alloy steel RVCH.
The NRC staff finds the licensees approach and assumptions for the as-left J-groove weld flaw evaluation to be acceptable. First, since no UT examination technique is available to characterize the flaw size in the J-groove weld, the assumption that the flaw extends throughout the entire weld is conservative. Second, the postulation of axial-radial crack growth direction is justified, as hoop stress is dominant near the nozzle, and the radial crack orientation is in line with the licensees nondestructive examination results. Third, since the low-alloy steel RVCH material is resistant to PWSCC, fatigue crack growth is the primary crack growth mechanism for the RVCH, confirming the flaw evaluation's validity.
As part of the proposed alternative, the licensee performed a comparative analysis of the as-left J-groove weld flaw for the ANO-2 repair, comparing it with a previously approved weld repair analysis. The licensee also confirmed that the RTNDT of the previous analysis is greater than that of the ANO-2 RVCH steel and, therefore, demonstrated that the RVCH steel fracture toughness of the previous analysis is more limiting than that of the ANO-2 RVCH steel.
The NRC staff noted that the previously approved analysis for the J-groove weld flaw meets the acceptance criteria of ASME Code,Section XI, IWB-3612, which states that a flaw is acceptable if the applied stress intensity factor at the final flaw size is less than the fracture toughness at the crack tip temperature of the material with appropriate safety factors.
The NRC staff finds that the licensees one cycle justification for the J-groove welds flaw evaluation is acceptable because of the following: (1) the previous flaw growth analyses of similar half-nozzle repair, which have been approved by the NRC staff, involve a significantly longer analysis period that the analysis period of the ANO-2 weld repair; (2) the previous flaw analyses confirmed the structural integrity of the RVCH in accordance with the acceptance criteria of ASME Code; and (3) the licensees comparative analysis confirms that the analysis parameters of the previous analysis is representative of or bounding for the ANO-2 flaw analysis (e.g., RVCH and penetration dimensions, stress levels, transient loading, and transient cycle numbers) and, therefore, demonstrates that the ANO-2 weld repair is acceptable in terms of the as-left J-groove weld flaw analysis for 18-month operation.
PWSCC Evaluation Following the repair, a PWSCC crack growth analysis was conducted to assess the integrity of the remaining Alloy 600 material within the repaired nozzle. This evaluation considered the degradation of the Alloy 600 nozzle material without the application of surface stress remediation.
The analysis utilized the crack growth rate model from MRP-420, Materials Reliability Program:
Crack Growth Rates for Evaluation Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Materials and Alloy 82, 182, and 132 Welds, Revision 1, incorporating conservative assumptions regarding flaw initiation and propagation. Key conclusions from this evaluation include:
The estimated time for a postulated flaw to reach the 75 percent through-wall acceptance limit exceeds the nominal operating cycle length of 18 months.
The remaining Alloy 600 material in the repaired nozzle is unlikely to contain preexisting PWSCC flaws due to the absence of historical conditions conducive to PWSCC initiation, as well as the flaw detection and material removal processes implemented during the repair.
The analysis conservatively applied a K-independent crack growth rate to model crack growth, ensuring a bounding assessment that does not rely on stress intensity factor variations.
The evaluation satisfies preservice volumetric inspection requirements per ASME Section XI, Division 1, Code Case N-729-6.
These findings confirm that the repaired CEDM penetration nozzle No. 71 will maintain structural integrity throughout the planned 18-month operating cycle. To further validate this conclusion, the licensee provided bounding crack growth analysis for postulated flaws to confirm that the time required for a postulated flaw in the remnant Alloy 600 material to grow to the 75 percent through-wall acceptance limit exceeds the nominal cycle length of 18 months.
Corrosion Evaluation The licensee explained that the IDTB nozzle modification leaves an annular crevice between the RVCH and the replacement lower nozzle, exposing a small portion of the low-alloy steel in the RVCH to reactor coolant. The licensee further discussed that an evaluation was performed for similar prior repairs to assess potential corrosion concerns for the wetted surface of the low-alloy steel. This evaluation, based on previous operating experience, confirmed that common corrosion mechanisms, such as galvanic corrosion, hydrogen embrittlement, stress corrosion cracking (SCC), and crevice corrosion, are not expected to pose a threat to the exposed low-alloy steel in the RVCH.
The licensee indicated that general corrosion of the exposed low-alloy steel is anticipated within the crevice formed between the IDTB weld and the original J-groove weld. However, this corrosion will likely be limited to an initial phase, as corrosion products will accumulate and pack the crevice, gradually restricting reactor coolant system flow and slowing the corrosion rate.
After this phase, the corrosion rate is expected to significantly decrease. A conservative sustained corrosion rate has been applied in the ASME Code,Section III, analysis for the one fuel cycle justification, and the increase in bore diameter due to corrosion will be considered in the reinforcement calculations as required by NB-3330.
Further, the licensee pointed out that the lack of oxygen in the crevice, combined with the tight geometry and low flow conditions, will inhibit the continued progression of general corrosion over time. Additionally, as the surface of the low-alloy steel passivates, the long-term corrosion rate is expected to be negligible.
The licensees evaluation also concluded that, based on prior operating experience and studies documented in reports, galvanic corrosion, hydrogen embrittlement, and SCC are not expected to be concerns for the exposed low-alloy steel. These studies have shown that the galvanic difference between materials in the reactor environment does not lead to significant corrosion.
Moreover, hydrogen embrittlement and SCC have not been observed in similar materials in PWRs under normal operating conditions.
Finally, the licensee emphasized that, over time, the corrosion products filling the crevice would further isolate the exposed steel from the primary coolant, leading to a reduced oxygen supply and, consequently, a decrease in corrosion activity. This, coupled with the passivation of the steel surface, provides reasonable assurance that corrosion will not compromise the structural integrity of the RVCH over the life of the repair.
The NRC staff finds that the licensees corrosion evaluation offers reasonable assurance that the effect of general corrosion is negligible, as the corrosion rate in the tight gap between the nozzle and RVCH is expected to decrease significantly with time.
CONCLUSION As set forth above, the NRC staff determines that proposed alternative, as described in the licensees letter dated October 21, 2024, as supplemented by letter dated November 11, 2024, for the use of the temper bead welding repair on ANO-2 RVCH penetration nozzle No. 71 is acceptable on the basis that the proposed alternative provides an acceptable level of quality and safety. The NRC staff finds that the proposed alternative will provide reasonable assurance of the structural integrity and leak-tightness of the repaired nozzle for one cycle of operation.
Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes the use of the proposed alternative for one operating cycle (Cycle 31), which is scheduled to end in spring 2026 at ANO-2.
All other requirements in ASME Code,Section III and Section XI, for which relief or an alternative was not specifically requested and approved as part of this subject request, remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: O. Khan Date: April 24, 2025 Tony Nakanishi, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv TONY NAKANISHI Digitally signed by TONY NAKANISHI Date: 2025.04.24 15:58:18 -04'00'
- concurrence via email OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA NRR/DNRL/NPHP/BC*
NAME DGalvin PBlechman MMitchell DATE 4/17/2025 4/22/2025 3/28/2025 OFFICE NRR/DORL/LPL4/BC NAME TNakanishi DATE 4/24/2025