ML24304B031
| ML24304B031 | |
| Person / Time | |
|---|---|
| Site: | Electric Power Research Institute |
| Issue date: | 09/30/2024 |
| From: | Licensing Processes Branch |
| To: | |
| References | |
| EPID L-2022-TOP-0029, MRP-227, 3002020105 | |
| Download: ML24304B031 (76) | |
Text
OFFICIAL USE ONLYPROPRIETARY INFORMATION Enclosure OFFICIAL USE ONLYPROPRIETARY INFORMATION 9/30/2024 Safety Evaluation for a Topical Report Summary Information Topical Report No.:
Technical Report No. 3002020105 Topical Report
Title:
Materials Reliability Program (MRP): Pressurized Water Reactor Internals Inspection and Evaluation Guidelines (MRP-227, Revision 2)
Sponsor:
Electric Power Research Institute (EPRI)
Summary of Request:
EPRI requested the U.S. Nuclear Regulatory Commission review and issue a safety evaluation on MRP-227, Revision 2, for the purpose of supporting generic regulatory improvements related to the methodologies for verifying pressurized water reactor (PWR) internals integrity throughout the life of the plant, including the extended operating period authorized by license renewal in accordance with Part 54 of Title 10 of the Code of Federal Regulations Applicability:
PWRs during subsequent license renewal period Submittal:
May 9, 2022, Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML22129A138 Supplements:
April 4, 2023, ADAMS Accession No. ML23095A048 April 4, 2024, ADAMS Accession No. ML24095A274 May 28, 2024 ADAMS Accession No. ML24150A091 EPID No.:
L-2022-TOP-0029 Principal Contributors to Safety Evaluation:
Senior Mechanical Engineer, Vessels and Internals Branch, Division of New and Renewed Licenses, Office of Nuclear Reactor Regulations Senior Mechanical Engineer, Vessels and Internals Branch, Division of New and Renewed Licenses, Office of Nuclear Reactor Regulations Date:
September 30, 2024
ii OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Table of Contents Summary Information..................................................................................................................... i Table of Contents.......................................................................................................................... ii 1.0 Introduction........................................................................................................................ 1 1.1 Description of Request................................................................................................... 1 1.2 Background.................................................................................................................... 1 2.0 Evaluation Criteria.............................................................................................................. 1 2.1 Regulations..................................................................................................................... 1 2.2 Mandated Licensing Basis Document Information......................................................... 2 2.3 NRC-Approved Topical Reports..................................................................................... 2 2.4 Applicable Guidelines..................................................................................................... 2 3.0 Technical Evaluation.......................................................................................................... 2 3.1 Updated Criteria in MRP-227, Revision 2 - General Considerations............................. 5 3.1.1.
MRP-227, Revision 2, Section 5, Examination Acceptance Criteria and Expansion Criteria................................................................................................ 5 3.1.2.
MRP-227, Revision 2, Section 6, Evaluation Methodologies.............................. 7 3.1.3.
MRP-227, Revision 2, Section 7, Implementation Requirements....................... 9 3.1.4.
MRP-227, Revision 2, Appendix A, Reactor Internals Operational Experience 14 3.1.5.
MRP-227, Revision 2, Appendix B, Guidance on Plant-Specific Applicability Related to Fuel Design or Management......................................... 15 3.1.6.
MRP-227, Revision 2, Appendix C, Options for Alternate Aging Management Approaches for Westinghouse and CE Designs.......................... 15 3.1.7.
MRP-227, Revision 2, Appendix D, Guidance for Flexible Power Operation of Westinghouse and CE Designs..................................................................... 15 3.2 Component-Specific Evaluations.................................................................................. 16 3.2.1.
Component-Specific Evaluations of B&W-Design RVI Components................... 17 3.2.2.
Component-Specific Evaluation Topics for CE-Design Internals........................ 36 3.2.3.
Component-Specific Evaluation Topics for WEC-Design Internals..................... 47 4.0 Limitations and Conditions............................................................................................... 67 5.0 Conclusion....................................................................................................................... 67 6.0 References....................................................................................................................... 67 7.0 Abbreviations................................................................................................................... 73
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION
1.0 INTRODUCTION
1.1 Description of Request By letter dated May 9, 2022, the Electric Power Research Institute (EPRI) submitted technical report Materials Reliability Program: Pressurized Water Reactor Internals Inspection and Evaluation Guidelines (MRP-227, Revision 2) or Topical Report (TR) to the U.S. Nuclear Regulatory Commission (NRC) staff for review and approval (EPRI 2022).
Previously approved versions MRP-227-A (EPRI 2012) and MRP-227, Revision 1-A (EPRI 2020a), identify inspection and evaluation (I&E) guidelines for managing the long-term aging of reactor vessel internal (RVI) components of pressurized water reactors (PWRs),
specifically PWR internals through 60-year plant operating period. Nuclear power plants (NPPs) are initially licensed for a 40-year period of operation. Initial license renewal extends NPP licenses from 40 to 60-year period of operation. Therefore, MRP-227-A and MRP-227, Revision 1-A, applies to both initial and initial renewal periods of operation. MRP-227, Revision 2 (EPRI 2022) updates the aging management guidelines for relevant operating experience and to address subsequent license renewal operation (60-80 years period of operations) and adds two new appendices to expand the options available to implementing utilities.
The staff reviewed and accepted MRP-227, Revision 2, on June 17, 2022 (NRC 2022a).
1.2 Background
The NRC staff issued two rounds of requests for additional information (RAIs) containing 27 questions:
December 1, 2022, ADAMS Package Accession No. ML22335A488 (NRC 2022b)
December 18, 2023, ADAMS Package Accession No. ML23352A235 (NRC 2023a)
The NRC staff performed an audit to support its review:
NRC audit plan dated October 11, 2022, ADAMS Accession No. ML22264A107 (NRC 2022c)
NRC audit report dated February 7, 2023, ADAMS Accession No. ML23027A098 (NRC 2023b) 2.0 EVALUATION CRITERIA 2.1 Regulations Title 10 of the Code of Federal Regulations (10 CFR) Part 21, Reporting of defects and noncompliance (10 CFR 21 and hence forth known as Part 21) 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities (10 CFR 50) 10 CFR 50.55a, Codes and standards 10 CFR 50.59, Changes, tests and experiments
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 10 CFR Part 54, Requirements for Renewal of Operating Licenses for Nuclear Power Plants (10 CFR 54) 10 CFR 54.4, Scope 10 CFR 54.21, Contents of application--technical information 2.2 Mandated Licensing Basis Document Information License renewal provisions and commitments are listed in the updated final safety analysis report (FSAR). For licensed owners of PWR facilities, this includes implementation of the required PWR RVI aging management program (AMP) that are managed in accordance with the latest staff-approved version of the MRP-227 guideline report.
2.3 NRC-Approved Topical Reports MRP-227-A (EPRI 2012) and MRP-227, Revision 1-A (EPRI 2020a), address PWR RVI AMPs for initial license renewal.
2.4 Applicable Guidelines NUREG-1801, Generic Aging Lessons Learned (GALL) Report, December 2010 (NRC 2010a)
NUREG-1800, Standard Review Plan for Review of License Renewal Applications for Nuclear Power Plants, December 2010 (NRC 2010b)
NUREG-2191, Volumes 1 and 2, Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report, July 2017 (NRC 2017a)
NUREG-2192, Standard Review Plan for Review of Subsequent License Renewal Applications for Nuclear Power Plants, July 2017 (NRC 2017b)
NRC Subsequent License Renewal Interim Staff Guidance Document No.
SLR-ISG-2021-01-PWRVI, Updated Aging Management Criteria for Reactor Vessel Internal Components for Pressurized Water Reactors, January 2021 (NRC 2021a)
3.0 TECHNICAL EVALUATION
MRP-227, Revision 2, supplements and extends MRP-227, Revision 1-A, by including operations through 80-years, which would include the subsequent license renewal period of extended operation. The scope of the NRC staffs review of MRP-227, Revision 2, as documented in this SE is limited to:
(1) the general assessments of the contents of MRP-227, Revision 2, include:
Section 5, Examination Acceptance Criteria, Section 6, Evaluation Methodologies, Section 7, Implementation Requirements,
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Appendix A, Reactor Internals Operational Experience, Appendix B, Guidance on Plant-Specific Applicability Related to Fuel Design or Fuel Management, Appendix C, Options for Alternate Aging Management Approaches for Westinghouse and Combustion Engineering (CE) Designs, Appendix D, Guidance for Flexible Power Operation of Westinghouse and CE Designs, Appendix E, Incorporation of Interim Guidance from MRP 2018-022 into MRP-227, Revision 2, and Appendix F, Summary of Changes to Document.
(2) new, amended, or redefined screening result, inspection categorization, and I&E criteria bases for specified RVI component types in MRP-227, Revision 2, include:
Section 3, Component Categorization and Aging Management Strategy Development, Section 4, PWR Internals Management Requirements, or Section 5, Examination Acceptance Criteria.
The MRP-227, Revision 2, methodology, as shown in TR Figure 2-2, continues to use the sample selection and inspection categorization process as previously approved in MRP-227, Revision 1-A, for evaluating the inspection needs or alternate aging management strategies of PWR RVI components that are subject to an aging management review. The process results in the placement of the RVI components into one of the following aging management categories of the program:
(1) A set of Primary, or P, category RVI locations are defined for each of the three plant designs because they are expected to be leading locations for age-related degradation, as defined in one or more of the age-related aging effects and mechanism combinations defined above. EPRIs sampling process in TR Figure 2-2 places PWR RVI components into this inspection or aging management category based on: (1) either a moderate initial age-related susceptibility ranking of B or a high initial age-related susceptibility ranking of C for the component type in TR Tables 3-1, 3-2, or 3-3, and (2) an aging management screening of Primary as the highest identified screening result for the column entry of at least one of the eight aging mechanisms evaluated for the component type in TR Tables 3-1, 3-2, or 3-3.
(2) For some Primary category RVI components, a set of sample-expansion components (Expansion category, or E, RVI components) is defined to expand the inspection or alternate aging management strategy sample should the indications of degradation from inspected Primary components be more severe than anticipated. EPRIs sampling process in TR Figure 2-2 places PWR RVI components into this inspection or aging management category based on: (1) either a low initial age-related susceptibility ranking of A or a moderate initial age-related susceptibility ranking of B for the component type TR Tables 3-1, 3-2, or 3-3, with (2) an aging management screening of Expansion
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION as the highest identified screening result for the column entry of at least one of the eight aging mechanisms evaluated for the component type in Table 3-1, 3-2, or 3-3 of the TR.
(3) For Westinghouse Electric Company (WEC)-design or CE-design PWRs, potential degradation in a third set of RVI components is deemed to be adequately managed by Existing Programs, or X, such as the American Society of Mechanical Engineering (ASME) Boiler and Pressure Vessel Code,Section XI (ASME 2024) in-service inspection program, or for WEC-design flux thimble tubes, the Flux Thimble Tube Inspection Program defined by GALL-SLR AMP XI.M37. EPRI MRPs sampling process in TR Figure 2-2 places WEC-design or CE-design RVI components into this inspection or aging management category based on assignment of a screening ranking of X for at least one of the aging mechanisms evaluated for the component type in TR Tables 3-2 or 3-3.
(4) A fourth set of PWR RVI components (No Additional Measures, or N category components) are deemed to require no aging management activities because:
- a. the component type does not serve an intended function and potential failure of the component would not impact the integrity of the reactor pressure vessel or another RVI component serving a safety-related safe shutdown or accident mitigation function or
- b. EPRIs age-related degradation screening assessment for the component type did not screen the component type in (above a low-level screening ranking of A or N) for any of the age-related aging mechanisms evaluated for the component type in TR Tables 3-1, 3-2, or 3-3.
The NRC staff noted that the updated PWR RVI component-specific criteria defined in MRP-227, Revision 2, through 80 years of plant operations include some amended component-specific aging management criteria. MRP-227-A or MRP-227, Revision 1-A, reports covered a single operating period range 60 years. MRP-227, Revision 2, has three operating period ranges: 40 - 60, 60 - 80, or 40 - 80 years.
As previously stated, the NRC staffs review documented in this SE is limited to: (1) the general assessments of the contents of TR Sections 5, 6, and 7, and the TR appendices, and (2) new, amended, or redefined screening result, inspection categorization, and I&E criteria bases for specified RVI component types in MRP-227, Revision 2, Sections 3, 4, or 5. This SE is focused on evaluating the significant differences between the guidelines in MRP-227, Revision 2, and the guidelines in MRP-227, Revision 1-A, and documents the issues in the NRC staffs review that warranted a more detailed evaluation or were the subject of an RAI. For component-specific criteria in the TR not specifically evaluated in SE Section 3.2, the staff found the component-specific criteria to be acceptable because they satisfy one of the following aging management criteria cited below for demonstrating that the impacts of aging on the intended functions of the specified RVI component type(s) will be adequately managed through the end of a proposed subsequent period of extended operation, as required in accordance with 10 CFR 54.21(a)(3):
Confirmed acceptable placement of a specific PWR RVI component type in the No Additional Measures, or N, category based on confirmation that the component does not serve a license renewal function or there are no plausible aging effects or mechanisms requiring management based on aging mechanism susceptibility rankings
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION above a risk category of A or N for the eight aging mechanisms referenced and evaluated for the component type in either TR Tables 3-1, 3-2, or 3-3.
For Primary, Expansion, or Existing Program components whose 40 - 60 year I&E criteria for the component types carry over as the basis for managing the components during years 60 - 80, staff confirmation that there is no operating experience (OE) that would challenge the capability of the current I&E aging management strategies to manage the components for years 60 - 80 and that the current I&E criteria for managing the components during years 40 - 60 remain valid for managing the same components during years 60 - 80, or years 40 - 80.
Expansion or Existing Program components in MRP-227, Revision 1-A, that were conservatively upgraded to Primary category components in the TR, or N category components in MRP-227, Revision 1-A, that were conservatively upgraded to either Primary, Expansion, or Existing Program components in the TR, or new RVI components that are placed in Primary, Expansion, or Existing Program categories of the TR for newly identified aging mechanisms needing management. The staff generally accepted these types of changes in the TR because: (1) the proposed aging management strategy referenced in the TR resulted in the placement of a specified component type in a more conservative inspection/aging management category of the TR, and (2) the staff has confirmed that the proposed aging management strategy for the specified component type is sufficient to demonstrate that the impact of the applicable aging effects on the intended function(s) of the component type will be adequately managed during through the end of the subsequent period of extended operation, as required in accordance with 10 CFR 54.21(a)(3).
Changes in the TR that permit use of more stringent volumetric or surface non-destructive examination (NDE) methods in lieu of visual inspection techniques. For example, the options for specified PWR RVI welds in the TR that allow for use of ultrasonic test (UT) volumetric methods or eddy current test (ECT) inspection techniques in lieu of enhanced visual testing (EVT-1) visual methods for detection of evidence of cracking in welds.
3.1 Updated Criteria in MRP-227, Revision 2 - General Considerations 3.1.1.
MRP-227, Revision 2, Section 5, Examination Acceptance Criteria and Expansion Criteria MRP-227, Revision 2, Section 5, Examination Acceptance Criteria and Expansion Criteria, provides an updated set of general acceptance criteria bases for NDE methods that may be applied as inspection methods or condition monitoring methods, including the TR subsections that address general monitored flaw conditions and acceptance criteria bases for the specified NDE techniques referenced or discussed in MRP-227, Revision 2, Section 5.1 or 5.2.
In terms of the general flaw condition and acceptance criteria discussions provided for VT-1, EVT-1, ECT, UT, and physical measurement techniques, the staff found the general flaw condition and acceptance criteria discussion bases to be acceptable because: (1) the criteria are the same as those provided and previously accepted for the specified NDE techniques in MRP-227, Revision 1-A, and (2) there has been no industry OE to date that could potentially indicate that these NDE methods are incapable of detecting the type of flaw indications or non-
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION conforming design conditions specified for monitoring in MRP-227, Revision 2, Section 5, tables.
For the VT-3 visual methods discussed in Section 5.1.1 of MRP-227, Revision 2, the staff confirmed that the VT-3 visual inspection criteria remained the same as those previously provided for VT-3 methods in Section 5 of MRP-227, Revision 1-A, as modified by EPRIs response to RAI MRP-227-Gen-2 (EPRI 2023a). In RAI MRP-227-Gen-2 (NRC 2022b), the NRC staff asked whether conditions specified as being monitored by VT-3 techniques in MRP-227, Revision 2, Section 5.1.1, should include monitoring of potential foreign materials or corrosion products.
In its response to RAI MRP-227-Gen-2, EPRI clarified that treatment of foreign materials is within the scope of a licensees site-specific loose parts program or activities. EPRI also clarified that, in terms of corrosion product considerations, the EPRI materials degradation matrix does not conclude that corrosion products will be an issue for PWR RVI stainless steel or nickel-based alloy materials based on the PWR reactor coolant water chemistry environment. Given that licensees of PWRs address reactor coolant system (RCS) loose parts on a site-specific basis and that the PWR RCS water chemistry environment is normally in an alkaline pH environment (and may include corrosion inhibitors), the staff concludes that:
(1) foreign materials and corrosion products are already addressed through alternative aging management bases, including implementation of the licensees water chemistry control AMP and site-specific loose parts activities, and (2) VT-3 methods discussed in TR Section 5.1.1 do not need to be amended to include monitoring for foreign materials or corrosions products because there are alternate AMPs in place to check for these types of conditions in the RVI design.
Based on the discussed above, the NRC staff concludes that RAI MRP-227-Gen-2 is resolved and that EPRIs relevant condition and acceptance criteria bases for VT-3 methods in MRP-227, Revision 2, Section 5.1.1, are acceptable.
Sections 4.2.3 and 5.1.4 of MRP-227, Revision 2, initially included potential application of non-qualified visual inspections as a credited NDE technique in the TR. However, in EPRI MRPs response to RAI 9, dated April 4, 2024 (EPRI 2024ab), EPRI amended the TR to delete non-qualified visual inspection methods as a credited NDE technique. Refer to the NRC staffs evaluation of CE-design core shroud tie rods and nuts in Section 3.2.2.4 of this SE for additional details and further discussions regarding the use of non-qualified visual inspection techniques.
The staff also observed that MRP-227, Revision 2, Section 5, does not reference or discuss the specific NDE method that will be used for aging management of loss of material due to wear in WEC-design control rod drive mechanism (CRDM) penetration nozzle thermal sleeves, which are designated as Existing Program components for wear in Item W21a of MRP-227, Revision 2, Table 4-9. The NRC staff confirmed that the applicable NDE method is defined in the Pressurized Water Reactor Owners Group (PWROG) TR No. PWROG-16003-P, Revision 2, "Evaluation of Potential Thermal Sleeve Flange Wear" (PWROG 2024), as referenced in Item W21a of MRP-227, Revision 2, Table 4-9. Since MRP-227, Revision 2, application of this NDE method is limited to only a single Existing Program category component type, the NRC staff evaluates the ability of the specified NDE method in Section 3.2.3.8 of this SE that covers aging management of loss of material due to wear in WEC-design CRDM thermal sleeves.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.1.2.
MRP-227, Revision 2, Section 6, Evaluation Methodologies MRP-227, Revision 2, Section 6, Evaluation Methodologies, provides updated discussions on regulatory options that may be used to disposition component-specific inspection results that do not conform to the scope of acceptance criteria in MRP-227, Revision 2, Section 5. This includes options for dispositioning the specified Primary or Expansion category component(s) using a supplemental inspection or supplemental flaw analysis basis. Disposition of component-integrity by supplemental inspection does not require justification in this SE because supplemental inspections will be implemented in accordance with one of the NDE methods defined for the age-related condition of interest, as defined in either MRP-227, Revision 2, Section 5, or in MRP-228, Revision 4 (EPRI 2021a), the NDE inspection standard used for development of MRP-227, Revision 2; and the supplemental inspections are accepted for implementation in accordance with the staff evaluation discussed in Section 3.1.1 of this SE.
MRP-227, Revision 2, Section 6 bases for performing component-specific flaw evaluations (i.e., when triggered by inspection results) include lower bound fracture toughness values as part of the acceptance criteria. The staff noted that EPRI indicates that Technical Reports MRP-210 (EPRI 2009), MRP-211, Revision 1 (EPRI 2017a), or Boiling Water Reactor Vessels Internals Program (BWRVIP)-100, Revision 1-A (EPRI 2017b) may be used alternative methodology for establishing the component-specific lower bound fracture toughness values used in the flaw evaluations. In regard to MRP-227, Revision 2, reference of MRP-211, Revision 1, or BWRVIP-100, Revision 1-A, the staff emphasizes that EPRI has reported that the use of the fracture toughness determination methods and lower bound fracture toughness values as provided in BWRVIP-100, Revision 1-A (i.e., either directly or through referenced use in MRP-211, Revision 1), are subject to certain Part 21 notifications that were reported to the NRC in the EPRI letters to industry dated February 19, and March 19, 2021, as enclosed in Attachments 1 and 2 of EPRI Letter BWRVIP 2021-030 (EPRI 2021b). The NRC staff noted that this contrasts with MRP-227, Revision 2, disclaimer statement that MRP-227, Revision 2, is not subject to the requirements of 10 CFR 21.
The staff has already addressed the BWRVIP-100, Revision 1-A, Part 21 issue as part of the NRC staffs review (NRC 2023c) of the PWROGs WCAP-17096-NP, Revision 3, report (PWROG 2019a) for PWR RVI components. By e-mail dated July 24, 2023 (NRC 2023c), the staff-approved WCAP-17096-NP, Revision 3, and by letter dated September 5, 2023 (PWROG 2023), PWROG submitted WCAP-17096-NP-A, Revision 3. The NRC staffs July 24, 2023, SE includes an Open Item (OI-1) on resolution of the Part 21 impacts related to BWRVIP-100, Revision 1-A, reported fracture toughness data and values. Therefore, the staff recommends that any licensee using BWRVIP-100, Revision 1-A (i.e., either directly or indirectly through reference of BWRVIP-100, Revision 1-A in MRP-211, Revision 1) as an optional basis for lower bound fracture toughness values should track the status of the industrys efforts to resolve the 10 CFR Part 21 issue on BWRVIP-100, Revision 1-A, reported data and values (i.e., independent of whether that effort is performed by the EPRI or PWROG), and take appropriate actions under the corrective actions program element criteria of their PWR RVI AMPs. The NRC staff is not imposing this recommendation as a condition or A/LAI for the MRP-227, Revision 2, because the MRP-227, Revision 2, does not establish the use of BWRVIP-100, Revision 1-A, as the only means of determining the lower bound fracture toughness value that may be used as an acceptance criterion parameter in a component-specific flaw evaluation. Thus, the NRC staff finds that the referencing of BWRVIP-100, Revision 1-A in MRP-227, Revision 2, Section 6 to be acceptable because there is a sufficient
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION regulatory process in place under the licensees corrective actions program element part of its PWR RVI AMP to verify the validity and acceptability of reported lower bound fracture toughness values in BWRVIP-100, Revision 1-A. Open Item OI-1 issued in the staffs July 24, 2023, SE for WCAP-17096-NP-A, Revision 3, can be used as a corrective actions tool.
In its response to RAI MRP-227-Gen-4 (EPRI 2023a), EPRI revised Section 6 of MRP-227, Revision 2, to include discussions for incorporating conservative crack growth rates (CGRs) into component-specific flaw evaluations. Section 6 references the CGR modeling and bounding CGR bases in EPRI Report No. 3002003103 (EPRI 2014) as one method for establishing the CGRs to be used in a component-specific flaw evaluation. In RAI MRP-227-Gen-4, the NRC staff questioned the use of the CGR modeling and bases from EPRI Report No. 3002003103 (EPRI 2014) and noted that the same CGR bases were used to develop the alternate CGR bases in ASME Code Case N-889 (ASME 2017), and that the application of ASME Code Case N-889 is subject to several conditions, as defined and endorsed for use in Regulatory Guide (RG) 1.147, In-service Inspection Code Case Acceptability, ASME Section XI, Division 1, Revision 21 (NRC 2021b).
In addition, EPRI clarified that the conditions on use of Code Case N-889 would apply to any licensee using the CGR bases and modeling in the specified EPRI Report No. 3002003103 report as the basis for the bounding CGR used in a component-specific flaw evaluation. EPRI amended MRP-227, Revision 2, Section 6.1 to state: these CRG [control rod guide] control models can be used in PWR internals evaluations, if the conditions for the use of Code Case N-889 in RG 1.147 are met. Based on its review, the NRC staff finds the EPRIs revisions to TR Section 6 to be acceptable because: (1) updated Section 6 basis addresses that use of referenced EPRI CGR report and model in EPRI Report No. 3002003103 is subject to the NRC conditions on ASME Code Case N-889, as defined in RG 1.147, Revision 21, and (2) that licensees using EPRI Report No. 3002003103 as a CGR modeling basis must address the ASME Code Case N-889 conditions on use of this CGR modeling, as identified in RG 1.147, Revision 21. Therefore, RAI MRP-227-Gen-4 is resolved.
Based on its review, the staff finds that MRP-227, Revision 2, Section 6, as amended is acceptable for implementation because the general guidelines in Section 6 for performing component-specific flaw evaluations are consistent with applicable flaw evaluation engineering principles and include applicable guidelines for factoring lower bound fracture toughness values and upper bound CGRs into the flaw evaluations.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.1.3.
MRP-227, Revision 2, Section 7, Implementation Requirements MRP-227, Revision 2, Section 7, provides criteria for implementing the guidelines under the aging management protocols of the licensees PWR RVI AMP. The criteria are consistent with the program element criteria and protocols set for these types of programs in GALL/GALL-SLR AMP XI.M16A, as revised and established in Appendix D of the referenced SLR-ISG.
Conformance with the implementation criteria in MRP-227, Revision 2, Section 7, is a critical element of the RVI AMPs because this conformance helps ensure that the effects of aging in PWR RVI components will be adequately managed in accordance with the aging management requirements specified in 10 CFR 54.21(a)(3) and in conformance with the program element criteria guidance in GALL-SLR AMP XI.M16A. Conformance with the implementation criteria in MRP-227, Revision 2, Section 7, also includes the administrative controls and confirmation process program elements of GALL-SLR AMP XI.M16A that reference MRP-227-based PWR RVI AMPs as Nuclear Energy Institute (NEI) Report No. NEI 03-08, Revision 4, Guidelines for the Management of Materials Issues (NEI 2020), implemented programs. The NRC staffs evaluations of the subsections in MRP-227, Revision 2, Section 7, are contained in the following subsections.
3.1.3.1 MRP-227, Revision 2, Subsection 7.1 - NEI 03-08 Implementation Protocol MRP-227, Revision 2, Subsection 7.1, establishes criteria for implementing the guidelines of this TR (i.e., as applied to MRP-227-based PWR RVI AMPs) consistent with the guidelines of NEI 03-08 (NEI 2020), including:
(1) an NEI 03-08 mandatory implementation requirement (henceforth referred to as Mandatory Requirement) - EPRI requires the protocols to be implemented at all plants where applicable.
(2) an NEI 03-08 needed implementation requirement (henceforth referred to as Needed Requirement) - EPRI establishes that the protocols to be implemented whenever possible, but alternative approaches are acceptable.
(3) an NEI 03-08 good practice (henceforth referred to as Good Practice) - EPRI establishes that implementation of the protocol is expected to provide significant operational and reliability benefits, but the extent of use is at the discretion of the owner of the individual PWR facility.
In relation to these criteria, MRP-227, Revision 2, Section 7.1, includes the following statement:
A failure to meet a Needed or Mandatory requirement is a deviation from the guidelines; a written justification for the deviation must be prepared and approved as described in Appendix B of NEI 03-08.
The NRC staff finds these implementation criteria to be acceptable because: (1) MRP-227, Revision 2, basis for defining specific TR activities as either NEI 03-08 Mandatory Requirement, Needed Requirement, or Good Practice activities is consistent with the confirmation process and administrative controls program element criteria in GALL/GALL-SLR AMP XI.M16A, and (2) if MRP-227, Revision 2, is adopted as part of the current licensing basis (CLB), the basis for implementing the TRs specified NEI 03-08 mandatory requirements and needed requirements will be part of the PWR RVI AMPs basis
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION for managing aging in accordance with the requirements specified in 10 CFR 54.21(a)(3). The NRC staff also notes that EPRI defines NEI 03-08 Good Practice activities in MRP-227, Revision 2, as good asset management activities for specified PWR RVI component types.
Therefore, the NRC staff agrees that NEI 03-08 Good Practices applying to specified PWR RVI component types in MRP-227, Revision 2, should be evaluated for implementation by licensees that will be implementing the staff-approved version of this TR.
3.1.3.2 MRP-227, Revision 2, Subsection 7.2 - EPRI MRP Aging Management Requirement MRP-227, Revision 2, Subsection 7.2, establishes implementation of the guidelines as an NEI 03-08 Mandatory Requirement through the following statement:
Each commercial U.S. PWR unit shall develop, document, and maintain an engineering program for management of aging of reactor internal components.
EPRI states that, unless otherwise specified by the issuance letter of the approved version of this TR, updates of programs reflecting the requirements of the guidelines may be in accordance with plant-specific utility procedures.
In contrast to MRP-227, Revision 2, statement referenced in the previous sentence, the NRC staff notes that first renewed or subsequent renewed facility operating licenses typically include licensing clauses that permit the licensees to update or make changes to their AMPs (including the PWR RVI AMP) through implementation of the 10 CFR 50.59 process. Thus, the NRC staff finds these implementation criteria to be acceptable because: (1) the basis for developing a PWR RVI AMP utilizing the guidance of the TR is consistent with the criteria in GALL/GALL-SLR AMP XI.M16A that permits the AMP to be based on a version of MRP-227 that covers 80 years of plant operations, and (2) if MRP-227, Revision 2, is adopted as part of the CLB, the basis for incorporating this TRs criteria into the PWR RVI AMP and for implementing the criteria as part of the AMP will be required to be performed and reviewed in accordance with the licensees 10 CFR 50.59 design change review process, and will be part of the AMPs bases for complying with the aging management requirements specified in the 10 CFR 54.21(a)(3) rule.
3.1.3.3 MRP-227, Revision 2, Subsection 7.3 - EPRI MRP Reactor Internals Guidelines Implementation Requirement MRP-227, Revision 2, Subsection 7.3, includes the following statements that establish implementation of the I&E tables as Needed Requirements for MRP-227-based AMPs:
Each commercial U.S. PWR unit shall implement the requirements of Tables 4-1 through 4-9 and Tables 5-1 through 5-3 for the applicable design.
The examination requirements detailed in these tables may be replaced or modified without deviation by a plant implementing an alternate aging management strategy, that addresses the aging degradation mechanisms within these guidelines, supported by a plant-specific technical justification.
This may be necessary in cases such as bolt replacements or component modification. See Appendix C for additional details on performing such evaluations.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION In relation to this TR statement, the NRC staff noted that MRP-227, Revision 2, Section 7.3, includes the following statement regarding the date for converting the PWR RVI AMP from use of MRP-227, Revision 1-A over to use of a staff-approved version of MRP-227, Revision 2:
In accordance with Appendix C of NEI 03-08 [1], it was determined that NRC approval of MRP-227, Revision 2 via safety evaluation is needed prior to generic release for implementation. Therefore, implementation of Tables 4-1 through 4-9 and Tables 5-1 through 5-3 in MRP-227, Revision 2 is not required at this time. MRP-227 will be revised upon approval by the NRC (Revision 2-A), and an implementation timeline will be included at that time. If a site chooses to follow Tables 4-1 through 4-9 and Tables 5-1 through 5-3 in MRP-227, Revision 2, the site is responsible for reviewing its site-specific design bases, license renewal commitments and in-service relief requests per NEI-03-08 to ensure that there are no limitations that would preclude implementation.
Based on the staffs review and confirmation activities, the staff finds that the NEI 03-08 Needed Requirement in the TR for implementing TR Tables 4-1 through 4-9 and TR Tables 5-1 through 5-3 is acceptable because TR Table 4 inspections and TR Table 5 NDE inspection guidance provides for managing aging in accordance with the requirements in 10 CFR 54.21(a)(3).
3.1.3.4 MRP-227, Revision 2, Subsection 7.4 - EPRI Examination Procedure Requirement MRP-227, Revision 2, Subsection 7.4, includes the following statement that establishes implementation of the MRP-228 (EPRI 2021a) NDE inspection standard as a Needed Requirement for PWR RVI AMPs:
Examinations specified in these guidelines shall comply with the Needed Requirement in the MRP-228 Inspection Standard.
The staff acknowledges that this referenced NEI 03-08 Needed Requirement in MRP-227, Revision 2, Section 7.4, carries over from the same citation for implementation of MRP-228 in MRP-227, Revision 1-A, with the only change being the version of MRP-228 being referenced in this TR (which is cited in the TR as Revision 4 of the proprietary MRP-228 record). Thus, implementation of MRP-228, Revision 4, as a referenced record under MRP-227, Revision 2, Section 7.4, is not in question as an implementation criterion for the RVI AMP.
The staff has evaluated NDE methods in the TR from a generic perspective in Section 3.1.1 of this SE. The staff also evaluated EPRI MRPs basis for inspecting CE-design core shroud tie rods and nuts using non-qualified visual NDE methods in SE Section 3.2.2.3, and the basis for inspecting WEC-design CRDM thermal sleeves using laser monitoring methods in SE Section 3.2.3.8. The NRC staff finds the implementation criterion in MRP-227, Revision 2, Section 7.4, to be acceptable because: (1) EPRIs basis for performing NDE of PWR RVI components using staff-accepted NDE methods, referenced in approved versions of MRP-227, is established as part of the PWR RVI AMPs basis for managing aging in accordance with the requirements in 10 CFR 54.21(a)(3); and (2) the NRC staff has confirmed that the proprietary MRP-228, Revision 4, NDE standard includes appropriate criteria and standards for all NDE methods referenced for use in the TR, with the exception of the TRs component-specific NDE method that is being applied to the WEC-design CRDM thermal sleeves. For NDE methods applying to
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION WEC-design CRDM thermal sleeves using the NDE methods defined in the PWROG-16003-P, Revision 2, report (WEC 2024), refer to the NRC staffs evaluation of the WEC-design CRDM thermal sleeves in Section 3.2.3.8 of this SE.
3.1.3.5 MRP-227, Revision 2, Subsection 7.5 - EPRI Examination Results Requirement MRP-227, Revision 2, Subsection 7.5, includes the following Needed Requirement for dispositioning component-specific inspection results that are detected in a specified PWR RVI component type:
Examination results that do not meet the examination acceptance criteria defined in Section 5 of these guidelines shall be recorded and entered in the owners plant corrective action program and dispositioned. Engineering evaluations used to disposition an examination result that does not meet the examination acceptance criteria in Section 5, shall be conducted in accordance with NRC-approved evaluation methods (that is, ASME Code Section XI, PWR Owners Group topical report WCAP-17096-NP-A or equivalent method).
The NRC staff acknowledges that this EPRI-specified Needed Requirement carries over from MRP-227, Revision 1-A, and is consistent with the monitoring and trending, acceptance criteria, corrective actions, confirmation process, and administrative controls program element criteria for PWR RVI AMPs in the version of GALL/GALL-SLR AMP XI.M16A that is provided in the referenced SLR-ISG.
The NRC staff observed that, like MRP-227, Revision 2, Section 7.5, the criteria in MRP-227, Revision 2, Sections 5 and 6, may reference staff-approved versions of the WCAP-17096-NP report as an acceptable methodology for evaluating component-specific inspection results that fall outside of the examination acceptance criteria for specified Primary or Expansion category components in the applicable tables of MRP-227, Revision 2, Section 5. MRP-227, Revision 2, as amended in the response to RAI 2 (EPRI 2024a), references that the applicable, staff-approved version of WCAP-17096-NP is the version in WCAP-17096-NP-A, Revision 3.
However, the staff emphasizes that the acceptance criteria and data analysis criteria for specified Primary category and Expansion category components in staff-approved versions of WCAP-17096 only correlate to the categorization of those PWR RVI components that are defined as specific Babcock and Wilcox (B&W)-design, CE-design, and WEC-design Primary category and Expansion category components in a particular staff-approved version of MRP-227 report, as clarified below:
Primary and Expansion components evaluated in Appendices A, C, and E of WCAP-17096-NP-A, Revision 2 (PWROG 2016a) only correlate to the specific set of Primary and Expansion category components for B&W-, CE-, and WEC-designed PWRs in MRP-227-A Primary and Expansion components evaluated in Appendices A, C, and E of WCAP-17096-NP-A, Revision 3 (PWROG 2023), only correlate to the specific set of Primary and Expansion category components for B&W-, CE-, and WEC-designed PWRs in MRP-227, Revision 1-A
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION The PWROG has yet to develop or issue a version of WCAP-17096 that correlates to the set of Primary and Expansion category components for B&W-, CE-, and WEC-designed PWRs in the TR Thus, for Primary or Expansion category components that do not have component-specific acceptance criteria and data analysis criteria in the MRP-227, Revision 2, WCAP-17096-NP-A, Revision 2, or WCAP-17096-NP-A, Revision 3, any acceptance criteria and data analysis criteria needed to evaluate flaws or other age-related degradation conditions in a PWR RVI component type with detected degradation would need to be established on component-specific basis under the TRs specified Section 7.5 Needed Requirement. Given that MRP-227, Revision 2, Section 7.5, identifies that approved versions of WCAP-17096-NP-A are only one method of establishing the component-specific acceptance and data analysis criteria, the NRC staff finds the general referencing of WCAP-17096-NP-A in MRP-227, Revision 2, Sections 5, 6, and 7, to be acceptable for implementation.
Thus, with these explanations taken into consideration, the NRC staff finds the implementation criteria in MRP-227, Revision 2, Section 7.5, to be acceptable because: (1) the MRP-227, Revision 2, basis for treating inspection result evaluation and record retention activities as NEI 03-08 Needed Requirements is consistent with the monitoring and trending, acceptance criteria, corrective actions, confirmation process, and administrative controls program element criteria for PWR RVI AMPs in GALL/GALL-SLR AMP XI.M16A, and (2) if MRP-227, Revision 2, is adopted into the licensing basis, then the basis for recording and evaluating inspection results using a staff-approved version of the TR (e.g., a future Revision 2-A version of MRP-227) will form part of the PWR RVI AMPs basis for managing aging in accordance with the requirements in 10 CFR 54.21(a)(3). As is stated in MRP-227, Revision 2, Section 7.5, and has been explained and evaluated in the previous paragraphs, the NRC staff finds that component-specific engineering evaluations or flaw evaluations performed in accordance with the analysis methods defined in staff-approved versions of WCAP-17096-NP-A are one way (but not the only way) of dispositioning component-specific examinations results that do not meet the examination acceptance criteria defined for a specified component type in MRP-227, Revision 2, Section 5.
3.1.3.6 MRP-227, Revision 2, Subsection 7.6 - EPRI Examination Reporting Requirement MRP-227, Revision 2, Subsection 7.6, establishes the following NEI 03-08 Needed Requirement for reporting of PWR RVI component-specific inspection results:
Each commercial U.S. PWR unit shall provide a summary report of all inspections and monitoring (including coverage[s] achieved and inspection limitations), items requiring evaluation, and new repairs to the MRP Program Manager within six months of the completion of an outage during which PWR internals with NEI 03-08 inspection requirements and within the scope of MRP-227 are examined.
The NRC staff noted that this EPRI-specified Needed Requirement carries over from MRP-227, Revision 1-A, and is consistent with the corrective actions, confirmation process, and administrative controls program element criteria for PWR RVI AMPs in GALL/GALL-SLR AMP XI.M16A, which references use of the NEI 03-08 process for implementing those NEI 03-08 Mandatory Requirement or Needed Requirement activities referenced for implementation
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION in Chapter 7 of the TR. Other examples of these NEI 03-08 specified requirements are the Mandatory Requirement for developing a PWR RVI AMP that is based on MRP-227 technology and the Chapter 7 criteria for implementation of the specific TR Chapter 4 and 5 tables applying to the NSSS design as an NEI 03-08 Needed Requirement that is within the scope the PWR RVI AMP. The staff confirmed that the NEI 03-08 Needed Requirement on the reporting of inspection data is established to ensure that any reported age-related degradation detected on a site-specific and component-specific basis will be reported and disseminated to the remainder of the U.S PWR fleet for potential generic applicability to the other U.S. PWR units. The staff confirmed that EPRI MRP addresses generic OE through the issuance of biannual inspection data reports that summarize all inspection data reported to EPRI MRP in accordance with the referenced NEI 03-08 Needed Requirement. The staff has evaluated the TRs NEI 03-08 Needed Requirement regarding the site-specific inspection data reporting criterion and notes that it is consistent with the prior basis for implementing this NEI 03-08 Needed Requirement as defined in the MRP-227, Rev. 1-A report. Thus, the staff finds this implementation criterion to be acceptable because the criterion provides a sufficient basis for addressing generic OE and for managing aging in accordance with the requirements in 10 CFR 54.21(a)(3).
3.1.4.
MRP-227, Revision 2, Appendix A, Reactor Internals Operational Experience MRP-227, Revision 2, Appendix A, provides a compiled summary of relevant age-related OE that has occurred in B&W-designed, CE-designed and WEC-designed PWR RVI components.
The staff verified that the age-related aging effects or mechanisms for referenced component-specific OE summarized in MRP-227, Revision 2, Appendix A, have been accounted for in the applicable I&E criteria for managed component types in MRP-227, Revision 2, Tables 4-1, 4-2, 4-3, 4-4, 4-5, 4-6, 4-8, or 4-9. Additionally, the NRC staff has confirmed that EPRI has addressed recent OE outside of the scope of TR Appendix A through the following TR submittal processes: (1) OE involving cracking in WEC-design core barrel (CB) upper girth welds (UGWs) that was addressed in EPRIs responses to RAI 6, as submitted in the MRP letter 2024-006 of April 4, 2024 (EPRI 2024a) and (2) OE involving cracking in WEC-design clevis insert bolts, dowel pins, and Stellite wear surfaces that was addressed in EPRIs responses to RAI 1, as submitted in the April 4, 2024, letter. The NRC staff confirmed that the MRP-227, Revision 2, accounts for relevant OE on a component-specific basis, as confirmed appropriate for the updated RVI component-specific categorizations and I&E bases in this TR that are subject to:
(1) the general approval bases defined in Section 3.0 of this SE, (2) the NRC staffs assessment of relevant EPRI letter MRP 2018-022, Transmittal of MRP-191-SLR Screening, Ranking and Categorization Results and Interim Guidance in Support of Subsequent License Renewal at U.S. PWR Plants (EPRI 2018), OE-related information, as evaluated in Section 3.1.8 of this SE, or (3) when applicable, in the staffs component-specific evaluations for the specified B&W-design, CE-design, or WEC-design PWR RVI component types that are provided in the applicable subsections of Section 3.2.1, 3.2.2, or 3.2.3 of this SE. Given the staffs confirmation and the staffs evaluation of component-specific OE on a component-specific basis in Section 3.2 of this SE, the staff finds Appendix A of the TR to be acceptable for implementation.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.1.5.
MRP-227, Revision 2, Appendix B, Guidance on Plant-Specific Applicability Related to Fuel Design or Management MRP-227, Revision 2, Appendix B, provides the recommendations for continuing plant-specific fuel performance or fuel design confirmation activities as part of the confirmatory plant actions that were recommended for closure of the staffs prior A/LAI RAI1 on MRP-227-A topic, as defined and issued in the NRC staffs SE for MRP-227, Revision 0/Revision A (NRC 2011).
The staff confirmed that MRP-227, Revision 2, Appendix B includes bases for incorporating the fuel performance or fuel design confirmation activities previously recommended for WEC-design or CE-design plants in EPRI letter MRP 2013-025 (EPRI 2013) into the scope of MRP-227, Revision 2. This is in accordance with and consistent with EPRIs past efforts to use the previous guidance and confirmatory actions recommended in EPRI letter MRP 2013-025 as part of the EPRIs basis for closing the past A/LAI #1 topic in MRP-227, Revision 1-A. Given that MRP-227, Revision 2, Appendix B, has incorporated the EPRI letter MRP 2013-025 recommendations into the scope of this TR and continues to recommend implementation of these confirmatory fuel management and design activities as part of MRP-227, Revision 2, bases for WEC-design and CE-design plants, the NRC staff finds the criteria in MRP-227, Revision 2, Appendix B, to be acceptable for implementation, as applicable to WEC-design and CE-design PWRs and with the emphasis that B&W-design PWRs are not within the scope of the EPRI letter MRP 2013-025 guidelines.
3.1.6.
MRP-227, Revision 2, Appendix C, Options for Alternate Aging Management Approaches for Westinghouse and CE Designs MRP-227, Revision 2, Appendix C, was deleted in EPRIs response to RAI 8 (EPRI 2024a).
Based on deletion of MRP-227, Revision 2, Appendix C, no evaluation is necessary.
3.1.7.
MRP-227, Revision 2, Appendix D, Guidance for Flexible Power Operation of Westinghouse and CE Designs MRP-227, Revision 2, Appendix D, provides statements and evaluation regarding: (1) the applicability of the TR for licensees that have been approved to implement flexible (non-base load) power operations (FlexOps) of their PWR units, and (2) how FlexOps could potentially impact the inspection categorizations and I&E criteria for designated PWR RVI components.
The staff observed that EPRI initially addressed potential impacts of FlexOps on the I&E criteria for managed WEC-design and CE-design PWR RVI components in an EPRI letter Transmittal of MRP-227-A-Related Interim Inspection Guidance Regarding PWR Use of Flexible Operations," (EPRI 2019a).
In RAI MRP-227-Gen-1 (NRC 2022b), the NRC staff requested further clarifications on how FlexOps in TR Appendix D would impact the I&E criteria in TR Chapters 4 and 5. In its response to RAI MRP-227-Gen-1 (EPRI 2023a), EPRI made the following clarifications:
EPRI clarified that the FlexOps impact assessment and basis is limited only to 60-years of plant operations.
EPRI confirmed that the FlexOps impact assessment performed does not apply to designated B&W-design Primary and Expansion category components. EPRI stated that the impacts of FlexOps on the I&E criteria for defined B&W-design components are
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION outside of the scope of MRP-227, Revision 2, Appendix D, and are to be performed on a plant-specific or design-specific basis.
EPRI clarified that the FlexOps impact assessment in MRP-227, Revision 2, Appendix D, focused on potential impacts of WEC-design and CE-design Primary and Expansion category components that screen in for fatigue, as FlexOps could impact cumulative cyclical fatigue loads for fatigue design transients, especially the unit loading/unloading transient that is normally part of the plant-specific transients in the design basis. These transients involve a reduction in power to a lower level, followed by an increase back to full power (e.g., a drop to 15 percent of rated power where the rate of power change is bounded to a maximum 5 percent drop or increase in rated power per minute). For the WEC-design and CE-design components, EPRI clarified that generic stress reports were prepared for each general plant design, where a fatigue evaluation would include the unit loading/unloading transient, along with all other normal and upset condition transients that applied to the design basis.
For WEC-design internals, EPRI identified that the FlexOps focuses on impacts on the baffle-former bolts (BFBs), as these are WEC-design components that are most significantly impacted by fatigue loads. Specifically, EPRI stated that the FlexOps impact assessment focused on fatigue of WEC-design BFBs due to their location directly adjacent to the reactor core and the fact that the BFBs are sensitive to fatigue loads (because they were not qualified by analysis in the original design) and have been demonstrated to be susceptible to fatigue as the plant ages.
EPRI clarified that operating CE-design PWRs are differentiated from WEC-design PWRs due to the lack of bolted joints adjacent to the reactor core (that is, the only two CE-design PWRs with bolted core shroud design [equivalent term for a CE baffle assembly] have been decommissioned).
In light of the EPRI clarifications provided above, the NRC staff notes that the response to RAI MRP-227-Gen-1 establishes that licensees of PWR-designed units (including B&W-, CE-,
or WEC-designed PWR units) with license-amendment approved FlexOps of their units will need to perform plant-specific evaluations of the FlexOps impacts on the I&E criteria that are defined in MRP-227, Revision 2, for the Primary and Expansion category RVI components of their units. In this regard, the NRC staff considers the matters raised in RAI MRP-227-Gen-1 to be resolved and MRP-227, Revision 2, Appendix D, is acceptable for implementation based on the response to RAI MRP-227-Gen-1.
3.2 Component-Specific Evaluations The following subsections provide the staffs evaluations of B&W-design, CE-design, or WEC-design PWR RVI component types that were determined to need a more formal or detailed evaluation (i.e., for specified RVI component types that are not subject to and dispositioned by one or more of the staffs general component acceptance bases defined in Section 3.0 of this SE, or for RVI component types that were the subject of staff RAIs).
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.2.1.
Component-Specific Evaluations of B&W-Design RVI Components 3.2.1.1 Control Rod Guide Tube (CRGT) Spacer Castings and Vent Valve Bodies Primary Components and Items (Aging Effects or Mechanisms):
MRP-227, Revision 2, Table 4-1, Item B2 - CRGT spacer castings (cracking and thermal aging embrittlement)
Linked Expansion Components and Items in MRP-227, Revision 2:
None; however, the vent valve bodies were previously identified as the sole Expansion category components for CRGT spacer casting in Item B2.1 in Table 4-4 of MRP-227, Revision 1-A.
MRP-227, Revision 2, Matter Needing Further Assessment:
Removal of the vent valves bodies as sole Expansion category component for the Primary Item B2 CRGT spacer castings (40 year initial license renewal and 60 year subsequent license renewal periods of operation).
EPRIs basis for change:
EPRI uses its updated proprietary screening assessments for the vent valve bodies in MRP-189, Revision 3 (ERPI 2020b), as the basis for concluding the vent valve bodies are not susceptible to any aging mechanisms defined in MRP-227, Revision 2, and can be deleted as Expansion category components for the CRGT spacer castings. The resulting change leaves the B&W-design CRGT spacer castings (as made from CF8 cast austenitic stainless-steel materials) without any linked Expansion category components for the cracking mechanisms and thermal aging embrittlement mechanism that are managed by the VT-3 visual inspections.
Staff Evaluation:
The NRC staff finds that EPRIs basis for removing the vent valve bodies as an Expansion category component for the CRGT spacer castings to be acceptable for implementation during both 40 year initial license renewal and 60 year subsequent license renewal periods of operation. Based on its review of the updated aging mechanism screening assessments for the vent valves bodies in both MRP-189, Revision 3, and MRP-227, Revision 2, Table 3-1, and supporting information, the NRC staff determined that the screening basis for the vent valve assemblies support the staffs finding that the vent valve bodies are not susceptible to any of the eight aging mechanisms evaluated in MRP-227, Revision 2, and do not need to be designated as Expansion category components for the CRGT spacer castings. Additionally, the NRC staff has confirmed that the vent valve assemblies included in the RVI design of B&W-design PWRs are subject to 10 CFR 50.55a required ASME in-service testing activities and thus are managed by plant-specific performance-based management activities outside of the scope of PWR Vessel Internals Program.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.2.1.2 Upper Core Barrel (UCB), Lower Core Barrel (LCB), Flow Distributor (FD), Upper Thermal Shield (UTS), Lower Thermal Shield (LTS), and Surveillance Specimen Holder Tube (SSHT) Bolting Types and Associated Locking Devices Primary Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-1, Item B7 - UCB bolts, and supporting acceptance criteria and sample-expansion criteria in TR Table 5-1, Item B7 (for stress corrosion cracking (SCC), fatigue, ISR/IC, wear)
(2) MRP-227, Revision 2, Table 4-1, Item B8 - LCB bolts, and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B8 (for SCC, fatigue, ISR/IC, wear)
(3) MRP-227, Revision 2, Table 4-1, Item B12 - FD bolts, and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B12 (for SCC, fatigue)
NOTE: EPRI includes both 40 year initial license renewal and 60 year subsequent license renewal versions of these Primary Items in MRP-227, Revision 2, Table 4-1.
Linked Expansion Components and Items in MRP-227, Revision 2:
(1) MRP-227, Revision 2, Table 4-4, Item B7.1 - UTS bolts (for SCC)
(2) MRP-227, Revision 2, Table 4-4, Item B8.1 - LTS bolts or studs and nuts (for SCC)
(3) MRP-227, Revision 2, Table 4-4, Item B7.2 - SSHT bolts and bolt locking devices (for SCC, ISR/IC, and wear; Davis Besse (DB) only, and only for 40 year initial license renewal periods of operation)
Applicable RAI:
RAI MRP-227-B&W-1 (NRC 2022b) and response (EPRI 2023a)
TR Issue Needing Resolution:
Basis in MRP-227, Revision 2, Table 4-1, Note 10 (as related to I&E criteria in MRP-227, Revision 2, Items B7, B8, and B12) that states: Primary-Expansion relationship between the UCB, LCB, and FD bolts and the UTS and LTS bolts/studs is for SCC only.
EPRIs Response to the RAI:
In its response to RAI MRP-227-B&W-1, EPRI MRP clarified that UT inspections applied to the Primary UCB, LCB, or FD bolting types cannot distinguish between cracklike flaw indications induced by an SCC or IASCC mechanism from those induced by fatigue or component overload mechanism. Therefore, EPRI stated that sample-expansion to the UTS and LTS bolting types (and additionally to the SSHT bolts as an additional Expansion category component type for DB during the 40 year initial license renewal period)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION would be initiated regardless of the cracking mechanism that was found to be the cause of flaw indications detected in the Primary category UCB, LCB, or FD bolting types.
Staff Evaluation:
The staff finds EPRIs I&E in MRP-227, Revision 2, Items B7, B8, and B12 for managing aging in the Primary category UCB, LCB, and FD bolts, and in Items B7.1 and B8.1 for managing aging in the Expansion category UTS bolts and LTS bolts (or LTS studs and nuts) to be acceptable because EPRIs response to RAI MRP-227-B&W-1 clarifies that the basis for initiating UT sample-expansion inspections of the UTS and LTS bolting types (and additionally to the SSHT bolts as an additional Expansion category component type for DB during the 40 year initial license renewal period) is based strictly on the sample-expansion criteria defined in Items B7, B8, or B12 of MRP-227, Revision 2, Table 5-1.
Additionally, under these TR Table 5-1 items, EPRIs basis for sample-expansion to the specified Expansion category bolting types is initiated independent of the aging mechanism that may be the cause of cracking in the referenced Primary category bolting types. Under this basis, the NRC staff confirmed that, consistent with EPRIs response RAI MRP-227-B&W-1, Section 7.3 of the MRP-227, Revision 2, establishes implementation of the Items in TR Table 5-1 as NEI 03-08 Needed Requirements for the RVI management programs of B&W-design PWR facilities. Thus, based on the sample-expansion criteria defined in Items B7, B8, or B12 of TR Table 5-1 and EPRIs additional clarifications in its response to RAI MRP-227-B&W-1, potential sample-expansion to the UTS and LTS bolting types (and additionally to the SSHT bolts as an additional Expansion category component type for DB during the 40 year initial license renewal period) is to be initiated if unacceptable indications are detected and confirmed in more than 10 percent of the UCB, LCB, or FD bolting types (including previously failed or uninspectable Primary bolts). This is independent of the aging mechanism that is confirmed to be the cause of cracking in the Primary bolting type. Thus, consistent with EPRIs response to RAI MRP-227-B&W-1, Note 10 in MRP-227, Revision 2, Table 4-1, cannot be applied to the sample-expansion link basis for the specified Primary and Expansion category bolting types. The issue discussed in RAI MRP-227-B&W-1 is resolved.
3.2.1.3 B&W-Design CB Assemblies - Significant Changes to I&E Criteria for Managing Fatigue-Induced Cracking in the CB Assembly Welds and Components Primary Component and Item (Aging Effects or Mechanisms):
MRP-227, Revision 2, Table 4-1, Item B20 (new Item) - CB cylinder top flange circumferential weld regions, and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B20 (for fatigue)
NOTE: As amended inclusive of TR changes made in the attachment of the EPRI letter MRP 2024-013 (EPRI 2024b). Primary Item B20 allows for alternate aging management disposition of the Primary category component by supplemental analysis (for NRC approval as an EPRI established requirement) in lieu of inspection.
Linked Expansion Components and Items:
(1) MRP-227, Revision 2, Table 4-4, Item B20.1 - CB top and bottom cylinder center circumferential weld region
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (2) MRP-227, Revision 2, Table 4-4, Item B20.2 - CB bottom flange circumferential weld region (3) MRP-227, Revision 2, Table 4-4, Item B20.3 - CB cylinder vertical seam weld regions (4) MRP-227, Revision 2, Table 4-4, Item B20.4 - plenum cover (PC) weldment rib-to-rib welds (5) MRP-227, Revision 2, Table 4-4, Item B20.5 - core support shield (CSS) cylinder top flange (6) MRP-227, Revision 2, Table 4-4, Item B20.6 - CSS top and bottom flange circumferential weld regions NOTE: As amended inclusive of MRP-227, Revision 2, changes made in the attachment of the MRP 2024-013 letter (EPRI 2024b).
Applicable RAIs:
(1) RAI MRP-227-B&W-2 (NRC 2022b) and response (EPRI 2023a)
(2) RAI 3 (NRC 2023a) and response (EPRI 2024b)
MRP-227, Revision 2, Issue(s) Needing Resolution:
(1) Basis for why the scope of items in MRP-227, Revision 2, Table 4-1, for fatigue of Primary CB assembly base metal and weld components only included Primary Item B20 for the CB cylinder top flange circumferential weld regions and did not include Primary Items for all of the other CB assembly base metal and weld components that screened in as Primary for fatigue in TR Table 3-1. The response to RAI MRP-227-B&W-2 did not fully resolve this matter.
(2) How the need for sample-expansion to the Expansion category PC weldment rib-to-rib welds and CSS cylinder top flange would be determined and accomplished if aging management of cracking due to fatigue in the CB cylinder top flange circumferential weld regions is dispositioned using the component-specific fatigue analysis option.
In its response to RAI MRP-227-B&W-2, EPRI clarified that: (1) the objective of Note 5 in MRP-227, Revision 2, Table 3-1, is to indicate that, although the CB assembly and the associated CB assembly welds screen in as Primary for fatigue in MRP-227, Revision 2, Table 3-1, the CB top flange weld region is the most susceptible for fatigue. Therefore, the CB top flange weld region is designated as the Primary Item B20 weld that will be inspected for fatigue, and (2) Note 2 in MRP-227, Revision 2, Table 3-1, permits use of a fatigue analysis in lieu of inspection for the CB top and bottom flanges, top and bottom cylinder plates, and associated vertical and circumferential seam welds. EPRI responded that cumulative usage factor calculation would need to be performed that considers the entire CB assembly, including flanges, cylinders, and seam welds.
In its response to RAI 3, EPRI further supported its response to RAI MRP-227-B&W-2 by making additional clarifications and through the following revisions to the line-item entries for specified B&W-design CB assembly welds (and to linked Expansion category CSS and PC assembly welds) in MRP-227, Revision 2, Tables 3-1, 4-1, 4-4 or 5-1:
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION MRP-227, Revision 2, Table 3-1, is amended to designate that the following CB assembly and CSS assembly components screen in as Expansion category components for the fatigue screening mechanism: (1) CSS top flange and bottom flanges, and associated flange circumferential seam welds, (2) CSS cylinder, (3) CB top and bottom cylinders, and associated cylinder circumferential and vertical seam welds, and (4) CB bottom flange and associated flange circumferential seam weld. For the amending screening basis, Note 7 is added to TR Table 3-1 to identify that the Primary category CB top flange and associated top flange circumferential weld are the lead Primary components on fatigue for the referenced CSS and CB assembly Expansion category component types. Note 2 in TR Table 3-1 is maintained to identify that management of cracking by fatigue may be dispositioned by component-specific analysis in lieu of inspection.
MRP-227, Revision 2, Tables 4-1 and 4-4, are amended to identify that the following CB assembly components are the first tier Expansion category components (on fatigue) for the Primary Item B20 CB top flange and top flange circumferential weld regions:
(1) Item B20.1 CB top and bottom cylinder center circumferential weld region, (2) Item B20.2 CB cylinder vertical seam welds, and (3) Item B20.3 CB bottom flange and bottom flange circumferential weld region. MRP-227, Revision 2, Tables 4-1 and 4-4, are amended to identify that the following CSS and PC assembly components are secondary tier Expansion category components (on fatigue) for the first tier Expansion category CB top and bottom cylinder circumferential weld region, CB cylinder vertical seam weld, and CB bottom flange and bottom flange circumferential weld region components: (1) Item B20.4 PC weldment ribs to each other welds, (2) Item B20.5 CSS cylinder top flange, and (3) Item B20.6 CSS top and bottom flange circumferential weld regions. The amended items permit disposition of fatigue in the applicable Primary or Expansion category component types by either a NDE inspection method or component-specific analysis that is to be submitted to the NRC for staff approval. If aging management is accomplished by NDE inspection, NDE examination method and coverage criteria are to be included and submitted for NRC staff approval. For the option of aging management by component-specific analysis, the revised I&E criteria for Item B20 in TR Table 4-1 (as amended in Table 2-2 in the attachment of EPRI letter MRP 2024-013) includes specified criteria that the analysis must cover the entire CB assembly and the linked Expansion category CSS and PC assembly components, including the first tier Expansion category Item B20.1, B20.2, and B20.3 components and the second tier Expansion category B20.4, B20.5, and B20.6 components.
Item B20 in MRP-227, Revision 2, Table 5-1, is amended accordingly to redefine the flaw conditions and the Primary-to-Expansion category criteria for initiating sample-expansion to the first tier Expansion category Item B20.1, B20.2, and B20.3 components and the second tier Expansion category B20.4, B20.5, and B20.6 components if aging management is triggered by inspections performed on the referenced CB assembly Primary component type or one of the first tier Expansion category component Item B20.1, B20.2, or B20.3 component types. For this, the relevant condition is a detectable cracklike indication revealed by the EVT-1, visual, UT, or ECT inspection method, and sample-expansion (by inspection) is to be triggered by confirmed evidence of relevant indications in one or more of the specified Primary category or first tier Expansion category component locations (as defined for the sample-expansion basis).
The staff verified that the need for initiating sample-expansion to either the first tier or
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION secondary tier Expansion category component types using the component-specific analysis option is accounted for in EPRIs revision of MRP-227, Revision 2, Table 4-1, Item B20 in Table 2-2 of the attachment to EPRI letter MRP 2024-013.
Staff Evaluation:
The NRC staff finds the amended fatigue screening bases and I&E criteria for managing fatigue-induced cracking in the specified Primary and Expansion category CB assembly components and the linked secondary tier Expansion category PC weldment ribs to each other weld, CSS cylinder top flange, and CSS top and bottom flange circumferential weld region components to be acceptable for implementation, as supported by the additional technical bases and justifications provided in the following paragraphs.
The new component-specific aging mechanism screening bases and I&E criteria for the specified B&W-design component types are defined by EPRIs revisions to the fatigue screening bases for the specified component types in MRP-227, Revision 2, Table 3-1 (as made in Table 2-1 of EPRI letter MRP 2024-013) and revisions of MRP-227, Revision 2, Items B20 in MRP-227, Revision 2, Tables 4-1 and 5-1 and MRP-227, Revision 2, Items B20.1 - B20.6 in MRP-227, Revision 2, Table 4-4 (as made accordingly in Table 2-2, 2-3, or 2-4 of EPRI letter 2024-013). The staffs bases for issuing RAI MRP-227-B&W-3 and RAI 3 pertained to the staffs observations that TRs original screening basis in TR Table 3-1 identified that the specified B&W-design CB assembly component welds and linked CSS and PC assembly components would need to be age-managed for the fatigue mechanism (at least the Expansion category component level or at the Primary category level).
However, the NRC staff noticed that the TR did not always define the types of aging management options and details that would need to be implemented for the specified components types (including Primary-to-Expansion sample-expansion link details) in TR Sections 4 and 5, particularly if the aging management basis for the specified Primary component type (the CB top flange circumferential weld regions) was accomplished using a component-specific analysis option. The staff confirmed that the response to RAI 3 resolved this issue (in part) because the response established and redefined a new set of cascading aging management criteria for managing fatigue in the specified CB, CSS, and PC assembly components, where: (1) the CB top flange and top flange circumferential weld regions remain as the expected lead, Primary category components for fatigue, (2) the remaining CB assembly weld types are established as the first tier Expansion category welds types for the Primary CB top flange circumferential weld regions (as the next ranked components for fatigue), and (3) the PC weldment ribs to each other welds, CSS cylinder top flange, and CSS top and bottom flange circumferential weld regions are designated as the secondary tier Expansion category components for fatigue. The NRC staff found these amended MRP-227, Revision 2, screening and I&E criteria bases (including redefined Primary-to-first tier Expansion relationships and first tier Expansion-to-secondary tier Expansion relationships) to be acceptable because the amended I&E criteria for managing fatigue-induced cracking of these CB, CSS, and PC assembly weld components achieve the following aging management objectives for meeting the aging management requirements of 10 CFR 54.21(a)(3) (and for conforming to the aging management criteria for specified PWR RVI components in GALL-SLR AMP XI.M16A):
the aging management basis for the fatigue mechanism firmly categorizes which of the specified CB, CSS, and PC assembly components are expected to be the lead,
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION secondary, or tertiary ranked components for fatigue, as categorized into Primary, first tier Expansion, or secondary tier Expansion categories.
the staff has previously accepted cascading PWR RVI Primary and Expansion category aging management basis as part of the NRC staffs SE for the MRP-227, Revision 1-A (NRC 2019) (e.g., those for WEC-design Primary category BFBs, first tier Expansion category lower support column (LSC) bolts, and secondary tier core barrel-to-former (CBF) bolts, as defined in Item W6 of Table 5-3 in MRP-227, Revision 1-A).
if the component-specific analysis is selected as aging management option for the Primary category CB top flange and top flange circumferential weld region, the revised MRP-227, Revision 2, Item B20 will call for the component-specific fatigue assessment to include a fatigue assessment of all other remaining CB assembly cylinder and flange welds and any linked CSS and PC assembly Expansion category components, and for the fatigue analysis to be submitted for NRC review and approval under the NEI 03-08 Needed Requirement defined and specified in MRP-227, Revision 2, Section 7.3.
if inspection is selected as the aging management basis for managing fatigue in the Primary category CB top flange and top flange circumferential weld region, the revised criteria for Item B20 in MRP-227, Revision 2, Table 5-1 firmly establish detection of a relevant flaw condition in the inspected Primary Item B20 CB component types would trigger sample-expansion to the specified first tier Expansion category CB top and bottom cylinder circumferential weld region, CB cylinder vertical seam weld, and CB bottom flange and bottom flange circumferential weld region components by completion of the next refueling outage.
similarly, if inspection is selected as the aging management basis for managing fatigue in the first tier Expansion category components (as triggered by Item B20.1 for the CB top and bottom cylinder center circumferential weld region, Item B20.2 for the CB cylinder vertical seam welds, or Item B20.3 for the CB bottom flange and bottom flange circumferential weld region), the revised criteria for Item B20 in MRP-227, Revision 2, Table 5-1, firmly establish detection of a relevant flaw condition in Items B20.1, B20.2, or B20.3 component type would trigger sample-expansion to the specified secondary tier Expansion category PC weldment ribs to each other welds, CSS cylinder top flange, and CSS top and bottom flange circumferential weld regions components (as the secondary Expansion categories B20.4, B20.5, and B20.6 component type) by completion of the next refueling outage.
if sample-expansion to the first tier Expansion category CB top and bottom cylinder circumferential weld region, CB cylinder vertical seam weld region, and CB bottom flange and bottom flange circumferential weld region components, or the secondary tier Expansion category PC weldment ribs to each other welds, CSS cylinder top flange, and CSS top and bottom flange circumferential weld regions is triggered, the NDE method and frequency basis for managing the Expansion category component types using the inspection option of management or the component analysis for managing the Expansion category component types using the component-specific
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION analysis option of management is required to be submitted for NRC review and approval under the NEI 03-08 Needed Requirement defined in TR Section 7.3.
Based on the staffs acceptance of MRP-227, Revision 2, criteria changes to Items B20 and B20.1 - B20.6 (as identified and made in EPRI letter MRP 2024-013), the issues in RAI MRP-227-B&W-3 and RAI 3 are resolved.
3.2.1.4 B&W-Design CB Assemblies - Significant Changes to I&E Criteria for Managing SCC or IASCC, and Irradiation Embrittlement (IE), in the CB Assembly Welds and Components Primary Component(s) and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-1, Item B16 (new Item) - CB cylinder top flange circumferential weld regions (Oconee Nuclear Station, Unit 2 (ONS-2) and Arkansas Nuclear One, Unit 1 (ANO-1) units only), and supporting acceptance criteria and sample-expansion criteria in TR Table 5-1, Item B16 (for SCC and IE in the weld type)
(2) MRP-227, Revision 2, Table 4-1, Item B17 (new Item) - CB cylinder center circumferential weld regions, and supporting acceptance criteria and sample-expansion criteria in TR Table 5-1, Item B17 (for IASCC and IE in the weld type)
NOTE: The items listed above are amended per MRP-227, Revision 2, table items in the attachment of EPRI letter MRP 2023-003 (EPRI 2023a) or to the TR Table Notes in the attachment of EPRI letter MRP 2024-013 (EPRI 2024b). That is, the staff is referencing the amended versions of Items B16 and B17 of MRP-227, Revision 2, Tables 4-1 and 5-1, as identified respectively in Tables 2-1 and 2-3 of EPRI MRP letter MRP 2023-003 attachment.
The revised versions of Primary Items B16 and B17 allow for alternate aging management disposition of the Primary category component type by supplemental analysis (for NRC approval) in lieu of inspection.
Linked Expansion Components and Items:
(1) MRP-227, Revision 2, Table 4-4, Item B16.1 - CB cylinder top flange circumferential weld regions (ONS-1, ONS-3, and DB; first tier Expansion category weld for the Item B16 Primary weld type)
(2) MRP-227, Revision 2, Table 4-4, Item B16.2 - CB cylinder bottom flange circumferential weld regions (ONS-2 and ANO-1; first tier Expansion category weld for the Item B16 Primary weld type)
(3) MRP-227, Revision 2, Table 4-4, Item B16.3 - CB cylinder bottom flange circumferential weld regions (ONS-1, ONS-3, and DB - secondary Expansion components for the first tier Expansion weld components of Item B16.1)
(4) MRP-227, Revision 2, Table 4-4, Item B17.1 - CB cylinder center circumferential weld regions (ONS-1, ONS-3, and DB; first tier Expansion category weld for the Item B17 Primary weld type)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (5) MRP-227, Revision 2, Table 4-4, Item B17.2 - CB cylinder vertical seam weld regions (ONS-2 and ANO-1 first tier Expansion category weld for the Item B17 Primary weld type)
(6) MRP-227, Revision 2, Table 4-4, Item B17.3 - CB cylinder vertical seam weld regions (ONS-1, ONS-3, and DB - secondary Expansion components for the first tier Expansion weld components of Item B17.1)
NOTE: The items listed above are as amended inclusive of changes made to the MRP-227, Revision 2, table items the attachment of EPRI letter MRP 2023-003 (EPRI 2023a); that is, referencing the amended versions of Items B16.1, B16.2, B16.3, B17.1, B17.2, and B17.3 in MRP-227, Revision 2, Table 4-4, as identified respectively in Table 2-2 of the EPRI letter MRP 2023-003 attachment. The revised versions of referenced Expansion items allow for alternate aging management disposition of the Expansion category component type by supplemental analysis (for NRC approval as an EPRI established requirement) in lieu of inspection.
Applicable RAIs:
(1) RAIs MRP-227-B&W-3 and MRP-227-B&W-4 (NRC 2022b) and response (EPRI 2023a)
(2) RAI 4 (NRC 2023a) and response (EPRI 2024b)
MRP-227, Revision 2, Issues Needing Resolution:
(1) EPRIs basis and allowance in the MRP-227, Revision 2, that would permit a specified B&W-design CB assembly weld type to be placed in the No Additional Measures or N category of the program based on confirmation that the weld type had been subject to a post-weld heat treatment (PWHT) practice (e.g., residual stress relief practice) during the original fabrication of the weld (i.e. topic of the RAI MRP-227-B&W-3 RAI request).
(2) Definition and justification from the EPRI on the minimum weld coverage that would need to be achieved to take inspection credit of the EVT-1 visual, UT, or ECT NDE methods used for inspection of a given CB assembly weld type. In the prior MRP-227-A and MRP-227, Revision 1-A, report versions, all B&W-design CB assembly base metal and weld components were identified as being inaccessible to NDE inspection equipment, and the components were categorized and designated as inaccessible, Expansion category components for the Primary Item B10 baffle plates (i.e., topic of the RAI MRP-227-B&W-4 RAI request).
(3) After receiving EPRIs changes to the TR items for designated B&W-design CB assembly welds in Tables 4-1, 4-4, and 5-1 of the MRP-227, Revision 2 (as amended in the attachment of EPRI letter MRP2023-003 (EPRI 2023a)), the NRC staff requested EPRI to provide additional details on the TRs aging management basis for B&W-design CB assembly welds in the ONS-1, ONS-2, ONS-3, ANO-1, and DB nuclear facilities. As part of the applicable RAI, the NRC staff requested that EPRI provide any further data, research, publications, or details that could support EPRIs continued basis that use of original weld design PWHT activities would continue to be capable of providing residual stress relief for a specified CB assembly weld during a 60 year subsequent license renewal period of operation, and that implementation of PWHT (i.e., with confirmed absence of a weld repair after PWHT) could be maintained as a basis for placing a given
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION CB weld type in the Expansion category of the program (topic of the RAI 4, Part 1, request). The NRC staff also asked EPRI to further define how sample-expansion to the designated B&W-design Expansion category CB assembly welds would be triggered, particularly if: (1) the Primary category weld of interest and the linked Expansion category weld of interest were contained in different units owned by different licensees, or aging management SCC or IASCC in the Primary weld type of interest was dispositioned by a component-specific analysis (topic of the RAI 4, Part 2, request). The NRC staff also requested that EPRI MRP justify that no CB assembly weld at the DB facility would need to be designated as a Primary category weld during a 60 year subsequent license renewal period of operation (topic of the RAI 4, Part 3, request).
(1) In its response to RAI MRP-227-B&W-3 (EPRI 2023a), EPRI replied that the MRP-227, Revision 2, is being amended to disallow use of PWHT as a basis for placing a specific B&W-design CB assembly weld type in the N category of the program. Instead, EPRI clarified that use of original weld design PWHT (versus weld repair after original weld design PWHT) would only be used as a basis for determining whether a specified B&W-design CB assembly weld type for a given B&W-design PWR unit (i.e., ONS-1, ONS-2, ONS-3, ANO-1, or DB) should be defined as a Primary category or Expansion category weld for the version of the licensees PWR RVI AMP that is implemented during a 60 year subsequent license renewal period of operation. The revisions of the MRP-227, Revision 2, Section 4 and 5, line items for the specified B&W-design CB assembly weld types made in the attachment of EPRI letter MRP 2023-003 (in response to RAI MRP-227-B&W-4) confirm the validity of EPRIs change to MRP-227, Revision 2, inspection categorization bases for the specified B&W-design CB assembly weld types applying to the ONS-1, ONS-2, ONS-3, ANO-1, and DB reactor units.
(2) In its response to RAI MRP-227-B&W-4 (EPRI 2023a), EPRI explained why use of original weld design stress relief treatment could be used as a basis for managing SCC or IASCC mechanisms in the welds, so long as the basis for using weld stress relief activities as a preventative actions for weld residual stress levels is not used to place the CB welds in the No Additional Measures category of the AMP. Instead, as was previously conveyed and consistent with corresponding response to RAI MRP-227-B&W-3, EPRI stated that the use of original weld design stress relief treatment activities would only be used as a mitigation strategy for categorizing or placing the specified CB assembly welds in either the Primary or Expansion management categories. Therefore, as part of its response to RAI MRP-227-B&W-4, EPRI amended Item B16 for the Primary category CB top flange circumferential weld regions and Item B17 for the Primary category CB cylinder center circumferential weld regions in MRP-227, Revision 2, Table 4-1, and developed new Expansion category items in MRP-227, Revision 2, Table 4-4, for the remaining weld types in B&W-design CB assemblies (as defined on a unit-specific basis in the Linked Expansion Components and Items in the MRP-227, Revision 2, subsection of this SE section).
EPRI also defined a new minimum 50 percent coverage criterion for taking inspection credit of any NDE examinations used as an aging management basis for the designated weld types.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (3) (a) For the RAI 4, Part 1, topic on use of PWHT as a component-specific screening basis for SCC or IASCC mechanisms, EPRI responded and continued to support its prior RAI MRP-227-B&W-4 response basis that PWHT is used as the first-cut screening basis to place a specific B&W-design CB assembly weld in the Expansion category of the B&W-design units PWR RVI AMP, and that confirmation of weld repair practice after the performance of the PWHT activity during the original weld fabrication process is the screening process basis for elevating the CB assembly weld type to the Primary category for the version of the B&W-design PWR RVI AMP that will be implemented during a 60 year subsequent license renewal period of operation.
(b) For the RAI 4, Part 2, topic of how Primary-to-Expansion category information would be disseminated between different licensees owing different units, EPRI responded that MRP-227, Revision 2, Section 7.5, includes an NEI 03-08 Needed Requirement to report inspection results meeting the acceptance criteria of MRP-227, Revision 2, Table 5-1, to the EPRI program manager within six months of an refueling outage in which Primary inspections were performed. To address Primary CB assembly weld inspection results that exceed the acceptance criteria or standards in MRP-227, Revision 2, Table 5-1, and would need to be disseminated between different licensees, EPRI stated that the following new Note will be added to Items B16 and B17 in MRP-227, Revision 2, Table 5-1:
Confirmed evidence of relevant conditions shall be report reported to the MRP Program Manager and licensees with other B&W units within 30 days of the conclusion of the MRP-227 examination. This is necessary to initiate subsequent Expansion examinations and/or evaluations as detailed in Table 5-1. NRC-approved evaluations performed in lieu of examinations shall be communicated on the same timeline.
(c) For the RAI 4, Part 3, topic regarding why the DB units would not need to designate any CB assembly welds for Primary category inspections (or alternatively, an alternate Primary component analysis covering SCC or IASCC mechanisms), EPRI responded that there has been no evidence that any weld repairs have been performed on the CB assembly welds at DB. EPRI also explained that the new communications criterion note to Items B16 and B17 in MRP-227, Revision 2, Table 5-1, would allow for prompt implementation of the Expansion Items applying to DB under Items B16.1, B16.2, B16.3, B17.1, B17.2, or B17.3 criteria applying to DB for the 60 year subsequent license renewal period of operations (as identified in the MRP 2023-003 letter). EPRI clarified that the B16.X and B17.X Expansion items (as applying to DB and referenced above) would be triggered if the relevant criteria for initiation of sample-expansion to the first tier or secondary tier Expansion category CB weld types (as defined in the revision to MRP-227, Revision 2, Table 5-1, Items B16 and B17, in EPRI letter MRP 2023-003) are met. EPRI also clarified that sample-expansion would also be triggered if an approved evaluation is used in lieu of examination at a Primary unit, and that initiation of the applicable Expansion criteria would be addressed no later than two refueling outages after the initiating Primary peer criteria are met per the timeline requirements given by MRP-227, Revision 2, Table 5-1 (i.e., for the revised versions of MRP-227, Revision 2, Table 5-1, Items B16 and B17, in the attachment of EPRI letter MRP 2023-003).
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Staff Evaluation:
The NRC staff finds EPRIs amended screening bases and I&E criteria for managing SCC or IASCC-induced cracking in the Primary and Expansion category B&W-design CB assembly welds (as defined in the attachment of EPRI letter MRP 2023-003, and amended by the MRP-227, Revision 2, Table 5-1, note for disseminating inspection data between licensees, as provided in EPRI letter MRP 2024-013) to be acceptable for implementation, as supported by the additional technical bases and justifications provided in the following paragraphs. The NRC staffs evaluation applies to the following B&W-design CB assembly weld components and EPRIs newly defined set of cascading Primary-to-Expansion category sample-expansion relationships for the specified weld types:
MRP-227, Revision 2, Item B16 - CB cylinder top flange circumferential weld regions (Primary welds for the ONS-2 and ANO-1 units only)
MRP-227, Revision 2, Item B16.1 - CB cylinder top flange circumferential weld regions (Primary welds for the ONS-1, ONS-3, and DB units only as newly defined first tier, unit-specific Expansion category welds of MRP-227, Revision 2, Item B16, unit-specific Primary welds)
MRP-227, Revision 2, Item B16.2 - CB cylinder bottom flange circumferential weld regions (ONS-2 and ANO-1 units only as newly defined first tier, unit-specific Expansion category welds of MRP-227, Revision 2, Item B16, unit-specific Primary welds)
MRP-227, Revision 2, Item B16.3 - CB cylinder bottom flange circumferential weld regions (ONS-1, ONS-3, and DB units only as the newly defined secondary tier, unit-specific Expansion category welds of MRP-227, Revision 2, Item B16.1, unit-specific, first tier Expansion category welds)
MRP-227, Revision 2, Item B17 - CB cylinder center circumferential weld regions (Primary welds for the ONS-2 and ANO-1 units only)
MRP-227, Revision 2, Item B17.1 - CB cylinder center circumferential weld regions (ONS-1, ONS-3, and DB units only as the newly defined first tier, unit-specific Expansion category welds of the MRP-227, Revision 2, Item B17, unit-specific Primary welds)
MRP-227, Revision 2, Item B17.2 - CB cylinder vertical seam weld regions (ONS-2 and ANO-2 units only as newly defined first tier, unit-specific Expansion category welds of the MRP-227, Revision 2, Item B17, unit-specific Primary welds)
MRP-227, Revision 2, Item B17.3 - CB cylinder vertical seam weld regions (ONS-1, ONS-3, and DB units only as the newly defined secondary tier, unit-specific Expansion category welds for the MRP-227, Revision 2, Item B17.1, unit-specific, first tier Expansion category welds)
The NRC staffs basis for accepting the revised Primary and Expansion items on SCC or IASCC of the referenced CB assembly welds is based on a risk perspective that needed to consider whether the EPRIs sample-expansion basis for linking CB assembly welds in
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION different units would assure adequate management of cracking due to SCC or IASCC in the components. As part of this basis, the NRC staff considered: (1) whether the implementation basis in MRP-227, Revision 2, Section 7, defined adequate implementation activities for reporting CB inspection results or alternate analysis results not only to EPRI, but also between licensees, and (2) whether this type of aging management would be adequate for managing SCC or IASCC in the CB assembly welds at the DB unit, given that the MRP-227, Revision 2, items and sample-expansion bases for the weld types leave the DB without any Primary category CB assembly welds for inspection. Under these MRP-227, Revision 2, items, the NRC staff acknowledges EPRIs position is that aging management of the specified weld types is adequately accomplished by EVT-1 visual inspections, UT inspections, or ECT inspections applied to the Primary or Expansion category weld types, or alternatively by component-specific analysis that will be submitted to the NRC for approval.
In terms of the NDE coverage that is needed for taking inspection credit of NDE examinations used for aging management, the NRC staff confirmed that the responses to RAI MRP-227-B&W-4 and RAI 3 established a minimum 75 percent coverage criterion for taking inspection credit of NDE examinations on the B&W-design CB assembly welds with at least 75 percent accessibility considerations or 50 percent coverage for B&W-design CB assembly welds with less than 75 percent known weld accessibility. The NRC staff found that these NDE examination coverage criteria to be acceptable because they are consistent with the following minimum inspection coverage acceptance basis established for CB/core support barrel (CSB) welds of WEC-design or CE-design PWRs, as defined in Section 3.1.3.9 of the NRC staffs SE (NRC 2019) for the MRP-227, Revision 1-A, report:
.... the NRC staff understands that the minimum coverage specified in Note 8 to the 4-3 markup of 50 percent was chosen by EPRI to accommodate the plants with neutron panels, which are known to have coverage limitations of up to 50 percent. However, the table requires that 100 percent of the accessible weld length be examined, and the NRC staff expects that the Westinghouse plants with thermal shields will achieve much greater than 50 percent coverage, based on data reported in the MRP biannual reports on MRP-227-A RVI examinations, which show thermal shield plants have typically achieved between 75 percent and 90 percent coverage. For the CE core support barrel girth welds, the minimum required coverage of 75 percent is consistent with MRP-227-A and is therefore acceptable.
The NRC staff finds that the previous basis for acceptability is applicable and acceptable for MRP-227 Revision 2.
For the additional considerations, the NRC staff accepts EPRIs basis (in the response to RAI 4, Part 1) that MRP-227, Revision 2, Figure 2-2, risk-informed engineering screening process uses a CB weld repair after PWHT as the basis for placing a specific, unit-specific B&W-design CB weld in the Primary category of the AMP. Otherwise, all CB assembly welds are placed in the Expansion category of the program based on confirmed implementation of PWHT activities that were performed on the welds during original weld fabrication. Regarding this type of consideration, the NRC staff emphasizes that this type of Primary-to-Expansion sample-expansion basis is a precedent-setting basis in MRP-227, Revision 2, because until now, all sample-expansion criteria in the MRP-227 versions were based on linked Primary and Expansion category PWR RVI components in the same unit of
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION interest. For these CB assembly welds, the NRC staff observed that this is the first time that EPRI has established linked Primary and first tier Expansion sample-expansion criteria (or linked first tier Expansion and second tier Expansion sample-expansion criteria) for specified component types in different B&W-design PWR units, including units owned by different licensees. However, this acceptance basis is coupled with the staffs determination that the MRP-227, Revision 2, Table 5-1, note applying to the weld types was sufficient to resolve the NRC staffs inspection data dissemination issue because the linked sample-expansion criteria now establish a NEI 03-08 Needed Requirement that any inspection data exceeding the acceptance standards in Items B16 or B17 in Table 5-1 (or alternate analysis used as an aging management option) be disseminated between units (for evaluation) within a new 30-day time-period. The NRC staff considers this to be an adequate period for the reporting of data or analysis information between units, including units owned by different licensees. Thus, the NRC staff considers the RAI 4 (Parts 1 and 2) involving this matter have been adequately resolved in the MRP-227, Revision 2.
For the evaluation of EPRIs response to RAI 4, Part 3, the NRC staff assessed whether the newly defined I&E criteria of MRP-227, Revision 2, Items B16, B16.1, B16.2, and B16.3 (for the designated CB assembly welds susceptible to SCC as defined in EPRI letter MRP 2023-003) and MRP-227, Revision 2, Items B17, B17.1, B17.2, and B17.3 (for the designated CB welds susceptible IASCC as defined in EPRI letter MRP 2023-003) would be acceptable to leave the DB unit without any designated Primary CB assembly weld components. For its acceptance basis, the NRC staff considered the number of known times that the industry had reported incidents of cracking in a CB or CSB Expansion category weld (i.e., prior to any reports of cracking in the linked Primary category weld for the Expansion weld type), when compared to the number of PWRs that have been operating in the U.S. fleet to date. The NRC staff observed that EPRI has only reported the occurrence of two anomalous CB or CSB Expansion category weld cracking events to date: (1) reported cracking of CE-design Expansion category CSB axial welds that developed before cracking was detected in the Primary category CSB middle girth weld (as reported EPRI letter MRP 2019-023 (EPRI 2019b)), and (2) reported cracking n WEC-design Expansion category CB UGW cracking that developed before cracking was detected in the Primary category CB upper flange weld (as reported in EPRI letter MRP 2023-005 (EPRI 2023b)).
Thus, based on these observations, the NRC staff perceived that the probability of initiating an anomalous B&W-design CB Expansion category weld cracking event (i.e., without any inspections of the specified Expansion category welds to detect cracking) was very low when considering the number of B&W-design, CE-design, and WEC-design PWR units operating in the U.S. fleet. Additionally, the NRC staff notes that probability of cracking in PWR CB/CSB assemblies is low overall, and the staff has verified that no occurrences of CB weld cracking at DB or any other B&W-design PWR has been observed or reported by the industry to date.
Thus, based on its review, the NRC staff finds that the low likelihood of anomalous CB assembly cracking events supports EPRIs basis that all the B&W-design CB assembly welds at DB can be designated as first tier or secondary tier Expansion category components for the DB AMP. However, the NRC staff notes that this disposition does not relieve the licensee of the DB facility from performing the required VT-3 visual inspections of the CB assembly under the ASME Section XI, Table IWB-2500-1, Examination Category B-N-3 requirements applying to the facility. Thus, at least some inspections will be performed on the CB assembly of the applicable DB PWR unit (as implemented under the
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION GALL-SLR AMP XI.M1-based ASME Section XI In-Service Inspection (ISI) program for the facility). In this regard, the NRC staff considers that RAI 4 Part 3 involving this matter has been resolved in MRP-227, Revision 2.
Thus, for this evaluation basis, the NRC staff finds that MRP-227, Revision 2, proposed I&E criteria for managing SCC or IASCC in Primary, first tier Expansion, and second tier Expansion category B&W-design CB assembly welds to be acceptable for implementation because the NRC staff has confirmed that the I&E are adequate to manage in the impacts of SCC or IASCC-induced cracking on intended functions of the CB assembly during a proposed 60 year subsequent license renewal period of operation, as required by 10 CFR 54.21(a)(3).
3.2.1.5 B&W-Design Baffle-Former and Lower Internals Assemblies - Updated MRP-227, Revision 2, I&E for B&W-Design Baffle Plates, Former Plates, and Lower Grid Rib Sections Primary Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-1, Item B10 (for cracking and impacts of IE) - baffle plates, and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B10 (version of Item B10 covering the 40 year initial license renewal period)
(2) MRP-227, Revision 2, Table 4-1, Item B10 (for cracking and impacts of IE) - baffle plates, and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B10 (version of Item B10 covering the 60 year subsequent license renewal period)
Linked Expansion Components and Items:
(1) MRP-227, Revision 2, Table 4-4, Item B10.3 - lower grid rib sections (Item B10.3 applies to 40 year initial license renewal periods covering cracking and impacts of IE; revised, sole Expansion category component type for the 40 year initial license renewal period version of Primary Item B10 for the baffle plates)
(2) MRP-227, Revision 2, Table 4-4, Item B10.2 - formal plates (Item B10.2 applies to 60 year subsequent license renewal periods covering cracking and impacts of IE and void swelling (VS); revised, sole Expansion category component type for the 60 -
80-year subsequent license renewal period version of Primary Item B10 for the baffle plates)
MRP-227, Revision 2, Issue Needing Resolution:
Further clarifications on the following changes to the linked Expansion category components for the Primary Item B10 baffle plates, including:
Deletion of the Expansion Item B10.1, CB cylinder (including vertical and center seam welds), as a linked Expansion Category component type for both the 40 year initial license renewal and 60 year subsequent license renewal versions of Primary Item B10
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Deletion of the Expansion Item B10.2, former plates, as a linked Expansion Category component type for the 40 year initial license renewal version of Item B10 Deletion of the Expansion Item B10.3, lower grid rib sections, as a linked Expansion Category component type for the 60 year subsequent license renewal version of Item B10 Applicable RAI:
RAI MRP-227-B&W-5 (NRC 2022b) and response (EPRI 2023a)
EPRIs Response to the RAI:
In RAI MRP-227-B&W-5, the NRC staff addressed the basis for deleting the Item B10.2 former plates as a cited Expansion component type for the 40 year initial license renewal period version of Primary Item B10. In its response to this RAI, EPRI stated that the former plates were removed as an Expansion item due to the technical argument in response to MRP-227-A Applicant/Licensee Action Item 6. EPRI supported its position by clarifying that IASCC was screened as Category A in MRP-189, Revision 3 (ERPI 2020b),
due to the change in MRP-175 screening criteria for IASCC, after the MRP-175 report was revised from Revision 0 (NEI 2006) of the report to Revision 1 (EPRI 2017a) of the report.
Staff Evaluation:
The NRC staff finds EPRIs removal of the CB cylinder as a referenced Expansion category component type for both the 40 year initial license renewal and 60 year subsequent license renewal versions of Primary Item B10 to be an acceptable change for implementation. The NRC staff has confirmed that EPRI has placed the B&W-design CB assembly and associated CB flange, and the cylinder vertical and circumferential seams welds within the scope of their own aging management categories for both management of fatigue-induced cracking, and SCC-or IASCC-induced cracking, in the weld types. For CB assembly welds susceptible to SCC or IASCC, this includes evaluation strategies for addressing the potential impacts of IE on the TRs aging strategies for managing cracking induced by the mechanisms. Given that the NRC staff has evaluated EPRIs basis for managing fatigue-induced cracking of the B&W-design CB assembly welds in Section 3 of 2.1.3 of this SE and for managing SCC or IASCC of the welds in MRP-227, Revision 2, Section 3.2.1.4, B&W-design CB assembly (and the associated CB welds in the assembly) are within their own managed groupings in the MRP-227, Revision 2, and no longer need to be linked as an associated Expansion category component type for the Primary Item B10 baffle plates.
The NRC staff finds EPRIs removal of the Item B10.2 former plates as a referenced Expansion category component type for the 40 year initial license renewal period version of Primary Item B10 to be an acceptable change for implementation, as supported by EPRIs response to RAI MRP-227-B&W-5 (EPRI 2023a) and additional clarifications that follow in this paragraph. Specifically, the NRC staff confirmed that, in the 40 year aging mechanism screening ranking assessment for B&W-design former plates in Table 3-1 of MRP-227, Revision 1-A, the former plates only screened in as inaccessible Expansion category components because the former plates were identified as being moderately susceptible to the aging effect mechanism of IE. For this basis, if sample-expansion aging
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION management of the former plates was triggered by the results of Primary inspections performed on the baffle plates under the criteria in Table 5-1, B10 in MRP-227, Revision 1-A, management of cracking and the impacts of IE was to be accomplished by a component-specific analysis of the former plates (or of the entire baffle-former assembly), or else by replacement activities of the former plates. However, the NRC staff confirmed that EPRIs revised fluence analysis for the former plates in MRP-189, Revision 3 (EPRI 2020b)
(used as one of the supporting documents for B&W-design internals in MRP-227, Revision 2) did not screen the components in for the IE mechanism through 60 years of plant operations. Thus, based on this updated fluence assessments, the NRC staff confirmed that the former plates do not screen in for any aging mechanisms (including IE) above a susceptibility category or Category A (components for which the likelihood and severity of safety and economic consequences are insignificant) or N (components for which no additional measures are needed) in MRP-227, Revision 2, Table 3-1. As such, this supports the removal of the former plates as a linked Expansion category component for the baffle plates for the 40 year initial license renewal period of operation. The issue in RAI MRP-227-B&W-5 is resolved.
The NRC staff finds EPRIs removal of the Item B10.3 lower grid rib sections as a referenced Expansion category component type for the 60 year subsequent license renewal version of Primary Item B10 to be an acceptable change because the NRC staff confirmed that EPRI has elevated the lower grid rib sections to being Primary category components for B&W-designed PWRs during a 60 year subsequent license renewal period of operation, as established in new Item B18 of MRP-227, Revision 2, Table 4-1.
The NRC staff emphasizes that, under these collective set of MRP-227, Revision 2, items, the lower grid ribs sections remain as the sole Expansion category component type for the Item B10 former plates during a 40 year initial license renewal period of operation and that the former plates are the sole Expansion category component type for the Primary Item B10 baffle plates during a 60 year subsequent license renewal period of operation. If the need for sample-expansion of the former plates is triggered by the results of VT-3 visual inspections performed on the Primary category baffle plates (i.e., per the flaw condition acceptance standard established in Item B10 of MRP-227, Revision 2, Table 5-1),
Item B10.2 of MRP-227, Revision 2, Table 4-4, establishes that aging management of the former plates is to be accomplished by one of two aging management strategies:
(1) performance of a component-specific analysis of the former plates or baffle-former assembly that is performed in accordance with the MRP-227, Revision 2, Section 7.3, as an NEI 03-08 Needed Requirement process, or else by (2) implementation of licensee-implemented replacement activities performed on the former plates. The NRC staff finds these sample-expansion options to be acceptable because, as has been accepted by the staff in past versions in MRP-227-A or MRP-227, Revision 1-A, EPRI continues to define that the former plates are inaccessible for inspection in Item B10.2 of MRP-227, Revision 2, Table 4-4.
Based on these considerations, the NRC staff finds EPRIs 40 year and 60 year I&E criteria for baffle plates, former plates, and lower grid rib sections in the MRP-227, Revision 2, to be acceptable for implementation.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.2.1.6 B&W-Design Baffle-Former and CB Assemblies - Confirmation of Prior Component-Specific Bolt Inaccessibility or Inspection Capability Considerations Primary Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-1, Item B9, BFBs (covering IASCC, fatigue, IE, ISR/IC, wear and component overload mechanisms for both the 40 year initial license renewal period and 60 year subsequent license renewal period versions of Item B9 applying to the BFBs, and additionally VS as an added mechanism for the subsequent license renewal version of Item B9), and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B9.
(2) MRP-227, Revision 2, Table 4-1, Item B11, BFB locking devices and internal baffle-to-baffle (BB) bolt locking devices (covering fatigue and IE mechanisms during the 40 year period; includes locking welds), and supporting acceptance criteria and sample-expansion criteria in MRP-227, Revision 2, Table 5-1, Item B11.
Linked Expansion Components and Items:
(1) MRP-227, Revision 2, Table 4-4, Item B9.1, internal and external BB bolts and Item B.9.2, CBF bolts covering IASCC, fatigue, IE, ISR/IC, wear and component overload mechanisms for both the 40 year initial license renewal and 60 year subsequent license renewal versions of Items B9.1/B9.2 applying to the BB and CBF bolts. Additionally, VS as an added mechanism for subsequent license renewal versions of Items B9.1 and B9.2. If triggered, sample-expansion is to be accomplished by component analysis submitted to the NRC within one year of the sample-expansion necessity or replacement activities of the specified Expansion category bolting types).
(2) MRP-227, Revision 2, Table 4-4, Item B11.1, locking devices of the external BB bolts and locking devices of the CBF bolts covering fatigue and IE mechanisms of these Expansion locking devices during the 40 year period, including locking welds. If triggered, sample-expansion is to be accomplished by component analysis submitted to the NRC within one year of the sample-expansion necessity or replacement activities of the locking devices.
MRP-227, Revision 2, Issues Needing Resolution:
(1) In both MRP-227-A and MRP-227, Revision 1-A, the internal BB bolts (as one of the Expansion category bolting types linked to the Primary category BFBs) were previously claimed MRP-227, Revision 1-A, as not having a qualified, developed NDE method capable of inspecting the bolts. Therefore, the NRC staff sought confirmation whether the industry has had any opportunity to develop a qualified NDE method for inspection for the internal BB bolts since issuance of NRC staffs SE for MRP-227, Revision 1-A.
(2) The NRC staff sought confirmation that the external BB bolts and CBF bolts (as Expansion types for the BFBs), the locking devices (including locking welds) of the external BB bolts and locking devices (including locking welds) of the CBF bolts remain as Expansion category component types that are inaccessible to inspection.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Applicable RAI:
RAI MRP-227-B&W-6, Parts 1 and 2 (NRC 2022b) and response (EPRI 2023a)
EPRIs Responses to the RAI:
In relation to the aging management strategies for the internal and external BB bolts (as clarified in the responses to RAI MRP-227-B&W-6, Parts 1 and 2), EPRI clarified that the BB bolts do not serve any intended function other than the function of positioning of the baffle plate assemblies and adding general rigidity to the baffle-former assembly structure. EPRI also explained that B&W-design BB bolts are not credited for controlling potential gaps between the baffle plates and that it is not typical to justify structural integrity of BB bolts with detected flaw indications using an acceptable bolting pattern analysis. Therefore, EPRI established its position in the MRP-227, Revision 2, (as supplemented by the RAI response) that development of a qualified inspection program for B&W-design internal BB bolts was not a high priority for development of the I&E criteria applying to the B&W-design RVI components and that the aging management strategy applied to the internal BB bolts (as an Expansion category bolting type for the BFBs) would be akin to that and used for aging management of the analogous Expansion category external BB bolts and CBF bolts, which are managed by component-specific analysis or component-specific replacement activities if sample-expansion is triggered by the results of UT inspections performed on the BFBs.
In its response to RAI MRP-227-B&W-6, Part 2 (EPRI 2023a), EPRI reconfirmed that the external BB bolts, the bolt locking devices of the CBF bolts, and bolt locking devices of the external BB bolts remain in the I&E criteria bin of Expansion category components that are inaccessible to inspection.
Staff Evaluation:
The NRC staff finds EPRIs updated and revised I&E criteria for the Primary category BFBs, BFB bolt locking devices, internal BB bolt locking devices, the referenced Expansion category internal and external BB bolts, CBF bolts, CBF bolt locking devices, and external BB bolt locking devices to be acceptable for implementation. Given that the aging management provisions of 10 CFR 54.21(a)(3) would allow adequate aging management disposition of the internal BB bolts (i.e., as a specified Expansion category component type) to be accomplished by an aging management strategy other than inspection, the NRC staff finds the basis for dispositioning sample-expansion of the internal BB bolts by component-specific analysis or component replacement activities to be acceptable for implementation, and MRP-227, Revision 2, I&E criteria for the Expansion category internal BB bolts are acceptable for implementation.
Similarly, as was previously approved in the NRC staffs SE for MRP-227, Revision 1-A, the same aging management basis applies and remains the same for the Expansion category CBF bolts, external BB bolts, and the Expansion category bolt locking devices (including locking welds) of the CBF bolts and external BB bolts. This means aging management by component-specific analysis or component replacement activities, if sample-expansion is triggered by the results of Primary category inspections performed on the linked Primary component type. The NRC staff finds these alternate strategies for aging management by component-specific analysis or component replacement activities to be acceptable for implementation. In this case, the criteria in Items B9 and B11 of MRP-227, Revision 2,
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Table 5-1, clearly define that, if a component-specific analysis is applied as the aging management strategy for the Expansion bolting or bolt locking device type, the analysis is to be submitted to the NRC within one year of the date establishing the sample-expansion need activity (as defined as an NEI 03-08 Needed Requirement in MRP-227, Revision 2, Section 7.3). The issues in RAI MRP-227-B&W-6, Parts 1 and 2 are resolved.
3.2.2.
Component-Specific Evaluation Topics for CE-Design Internals 3.2.2.1 CE-Design Core Support Barrel Flexure Welds (CSBFWs), Upper Internals Assembly (UIA) Fuel Alignment Plates, and Lower Support Structure (LSS) Core Support Plates Primary Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-2, Item C7, CSBFW in the CSB assembly (for impacts of fatigue and IE during 40 year periods covering initial license renewal plus subsequent license renewal timeframes), and supporting component-specific acceptance criteria in MRP-227, Revision 2, Table 5-2, Item C7 (2) MRP-227, Revision 2, Table 4-2, Item C9, LSS core support plate (for impacts of fatigue and IE during 40 year periods covering initial license renewal plus subsequent license renewal timeframes), and supporting component-specific acceptance criteria in MRP-227, Revision 2, Table 5-2, Item C9 (3) MRP-227, Revision 2, Table 4-2, Item C10, UIA fuel alignment plate (for impacts of fatigue and IE during 40 year periods covering initial license renewal plus subsequent license renewal timeframes), and supporting component-specific acceptance criteria in MRP-227, Revision 2, Table 5-2, Item C9 Linked Expansion Components and Items:
There are no linked Expansion category Item components for the CE-design Primary category RVI component types applying to MRP-227, Revision 2, Primary Items C7, C9, or C10. However, MRP-227, Revision 2, does include:
(1) a second item (Expansion category item) for the CSBFW in MRP-227, Revision 2, Table 4-5, Item C5.5 (covering 40 year initial license renewal and 60 year subsequent license renewal periods of operation for management of cracking induced by SCC), as linked to the Primary Item for CE-design CSB UGWs in MRP-227, Revision 2, Table 4-2, Item C5.
(2) a second item (i.e., Expansion category item) for the UIA fuel alignment plate in MRP-227, Revision 2, Table 4-5, Item C6.4 (covering 60 year subsequent license renewal period of operation for management of cracking induced by fatigue, SCC, and IASCC mechanisms and impacted by IE) as linked to the Primary Item for CE-design CSB middle girth welds in MRP-227, Revision 2, Table 4-2, Item C6.
MRP-227, Revision 2, Issues Needing Resolution:
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (1) Needed clarification on whether the CSBFW would still be inspected as an Expansion category component under MRP-227, Revision 2, Item C5.5 (i.e., when triggered by the results of EVT-1, UT, or ECT inspections performed on the CSB UGW), if the CSBFW is inspected as a Primary component weld under MRP-227, Revision 2, Item C7.
(2) Requested clarification on why MRP-227, Revision 2, includes both a Primary category item (Item C9) and Expansion category item (Item C6.4) for the UIA fuel alignment plate.
Applicable RAI:
RAI MRP-227-CE-1 (NRC 2022b) and response (EPRI 2023a)
EPRIs Response to the RAI:
In the part of the response to RAI MRP-227-CE-1 pertaining to the CSBFWs, EPRI clarified that the two MRP-227, Revision 2, items for the CSBFW pertain to aging management of cracking in the CSBFW induced by two different aging mechanisms, where the weld type screens in as a Primary category component for the cracking mechanism of fatigue and as an Expansion category component for the cracking mechanism of SCC. EPRI explained that inspections of the CSB UGW (as a Primary category weld) would initiate sample-expansion to the CSBFW (i.e., as a defined Expansion component under MRP-227, Revision 2, Item C5.5) if the inspections of the UGW yielded flaw data that exceed the acceptance standards defined for the UGW in MRP-227, Revision 2, Table 5-2, Item C5. EPRI explained that this is regardless of the aging management strategy that is used to manage the CSBFW as a Primary category component for fatigue-induced cracking under MRP-227, Revision 2, Item C7 (i.e., independent of whether that is accomplished by component-specific analysis or periodic 10-year EVT-1 visual inspections of the weld type).
In its response to RAI MRP-227-CE-1 pertaining to the UIA fuel alignment plates, EPRI clarified that the two MRP-227, Revision 2, items for the fuel alignment plates pertained to two different CE-design PWR configurations, as defined in: (1) Primary Item C10 applying to UIA fuel alignment plates in CE-design PWRs that are designed with welded CS assemblies utilizing full height shroud plates, and (2) Expansion Item C6.4 for applying to UIA fuel alignment plates in CE-design PWRs that are designed with welded CS assemblies having two vertical sections. EPRI clarified that I&E criteria in MRP-227, Revision 2, Items C10 and C6.4, have no interconnected aging management relationships.
Staff Evaluation:
Based on EPRIs response to RAI MRP-227-CE-1, the NRC staff finds that the Primary I&E criteria for managing cracking of the CSBFW, LSS core support plate, and UIA fuel alignment plate component types in Items C7, C9, and C10 of TR Tables 4-2 and 5-2 to be acceptable for implementation. The NRC staff also finds the sample-expansion criteria for the CSBFW as an Expansion category component in MRP-227, Revision 2, Item C5.5, and for the UIA fuel alignment plate as an Expansion category component in MRP-227, Revision 2, Item C6.4, to be acceptable for implementation. The aging management strategy options (management by component-specific analysis or inspections) for managing fatigue-induced cracking of these component types (as designated Primary components) are analogous to those defined for the component types in MRP-227, Revision 1-A. The NRC staff has confirmed that there is no plant-specific OE with cracking of these component
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION types that could, otherwise, provide a challenge to EPRIs aging management strategies for the component types, as defined by the Primary I&E criteria for Items C7, C9, and C10 of MRP-227, Revision 2, Tables 4-2 and 5-2, or the Expansion I&E criteria of Items C5.5 and C6.4 in MRP-227, Revision 2, Table 4-5.
The NRC staff notes that the Primary criteria for the LSS core support plate in the C9 items of MRP-227, Revision 2, Tables 4-2 and 5-2, only apply to CE-design PWRs whose plant-specific designs include a LSS core support plate. Similarly, the Primary criteria for the UIA fuel alignment plate in the C10 items of MRP-227, Revision 2, Table 4-2 and 5-2, only apply to CE-design PWRs that are designed with welded CS assemblies utilizing full height shroud plates. Under these MRP-227, Revision 2, item bases, the I&E criteria for the CSBFW as a Primary category component (for fatigue) under Item C7 have no interconnection with the treatment of the CSBFW as a defined Expansion category weld type (for SCC) in MRP-227, Revision 2, Item C5.5. Similarly, the I&E criteria for the UIA fuel alignment plate as a Primary category component under Primary Item C10 has no interconnection with the treatment of the UIA fuel alignment plate as a defined Expansion category weld type in MRP-227, Revision 2, Item C6.4 (as MRP-227, Revision 2, Items C10 and C6.4, apply the UIA fuel alignment plate in CE-design PWRs with two different types of welded CS assembly configurations). Thus, the NRC staff finds that the MRP-227, Revision 2, Item C7, and MRP-227, Revision 2, Item C5.5, criteria for the CSBFW are acceptable because EPRI has clarified that the Items C7 and C5.5 I&E criteria apply to the management of two different aging mechanisms (i.e., fatigue versus SCC) in the CSBFWs and that implementation of MRP-227, Revision 2, Item C7, has no bearing on the implementation of MRP-227, Revision 2, Item C5.5 (or vice versa). Similarly, the NRC staff finds that MRP-227, Revision 2, Item C10 and MRP-227, Revision 2, Item C6.4, criteria for the fuel alignment plates are acceptable because they apply to the design of fuel alignment plates in two different CE PWR designs. The issues in RAI MRP-227-CE-1 are resolved.
3.2.2.2 CE-Design Control Element Assembly (CEA) Shroud Bolts Primary Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-2, Item C19, CEA shroud bolts (a new item in the MRP-227, Revision 2 (as amended in EPRI letter MRP 2023-003)), for management of cracking due to fatigue and IASCC, impacts of IE and ISR/IC, and supporting component-specific acceptance criteria in MRP-227, Revision 2, Table 5-2, Item C19 Linked Expansion Components and Items (1) None MRP-227, Revision 2, Issues Needing Resolution:
(1) For the original version of Item C19 in MRP-227, Revision 2, Table 4-2, needed clarification on: (1) the basis for including wear as a cited aging mechanism in Item C19, and (2) the basis why Item C19 in MRP-227, Revision 2, Table 4-2, did not cite ISR/IC as one of the applicable aging mechanisms for the CEA shroud bolts (as a Primary component type).
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (2) Given the needed aging mechanism clarifications summarized above, the adequacy of following aging management basis for the CEA shroud bolts, as specified in the Examination Method/Frequency column entry of the original version of Item C19, which states:
If screening for IASCC cannot be satisfied by plant-specific or generic evaluation, volumetric (UT) examination within two refueling outages of subsequent license renewal. The plant-specific or generic analysis must also demonstrate that wear and fatigue are either adequately managed or that the plant falls below screening thresholds.
Subsequent examinations are at a 10-year interval.
Applicable RAI:
RAI MRP-227-CE-2 (NRC 2022b) and response (EPRI 2023a)
EPRIs Response to the RAI:
In its response to RAI MRP-227-CE-2, EPRI clarified that the CEA shroud bolts screen in as Primary for the aging mechanisms of fatigue and IASCC as cracking mechanisms, IE as a loss of fracture toughness mechanism, and ISR/IC as a loss of preload mechanism, and that the bolting type does not screen in for wear. This includes EPRIs amendments of Effect (Mechanism) column entry of Item C19 to cite the applicable aging mechanisms as fatigue, IASCC, IE, and ISR/IC and to correct the Examination Method/Frequency column entry basis of MRP-227, Revision 2, Item C19, in the EPRI MRP-2023-003 letter as follows:
If screening for IASCC cannot be satisfied by plant-specific or generic evaluation, volumetric (UT) examination within two refueling outages of subsequent license renewal. The plant-specific or generic analysis must also demonstrate that wear and fatigue are either adequately managed or that the plant falls below the screening thresholds. Subsequent examinations are at a 10-year interval.
In relation to the revised Examination Method/Frequency column entry basis for Item C19, EPRI explained that the referenced component-specific analysis only needs to screen for the mechanisms of fatigue and IASCC based on the nature and treatment of the other two applicable mechanisms (i.e., IE and ISR/IC; as clarified by EPRI in the response to RAI MRP-227-CE-2 in the MRP 2023-003 letter and summarized below).
EPRI explained that the reference of a generic analysis in Item C19 would allow for a range of analyses, such as a subset of CE plants being considered together or some or all of the affected plants performing a more detailed evaluation that screens out this component, and that, independent of the approach, any evaluation or analysis used as an aging management strategy for the CEA shroud bolts would be supplemental to the current proprietary screening analysis for the CEA shroud bolts in MRP-232, Revision 2 report (EPRI 2021c).
Staff Evaluation:
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Based on the EPRIs response to RAI MRP-227-CE-2, the NRC staff finds the I&E criteria for the CEA shroud bolts in Items C19 of MRP-227, Revision 2, Tables 4-2 and 5-2 (inclusive of changes made to MRP-227, Revision 2, Table 4-2, Item C19, in the MRP 2023-003 letter) to be acceptable for implementation. EPRI amended MRP-227, Revision 2, Table 4-2, Item C19, criteria to: (1) include the appropriate mechanisms that the CEA shroud bolts screen in for management per the screening assessment for the component type in Table 3-2 of MRP-227, Revision 2 (which are the mechanisms of fatigue, IASCC, IE, and ISR/IC), and (2) appropriately define how a component-specific analysis of CEA shroud bolts would need to be implemented as an alternative aging management strategy for the bolting type (i.e., to demonstrate that CEA shroud bolts are not susceptible to cracking through a cumulative 80-year operational period, including analysis criteria to account for the impacts of IE and ISR/IC on cracking that may be detected in the component type).
The NRC staff confirmed that the net effect of the RAI response included EPRIs corrections and amendments of MRP-227, Revision 2, Table 4-2, Item C19, to fix the applicable aging mechanisms for the CEA shroud bolting type. Under this type of basis, EPRI includes wear as a subset of the ISR/IC mechanism since ISR/IC-induced loosening of the bolts could potentially induce wear of the bolts, which in turn might eventually lead to cracking of the bolts. Under this basis, if a supplemental component analysis is not applied as the aging management strategy for the CEA bolts or if the supplement analysis cannot demonstrate adequate protection against fatigue or IASCC-induced cracking, aging management of the CEA shroud bolts is to be accomplished by UT inspections performed on the shroud bolts within two refueling outages of entering the 60 year subsequent license renewal period, with subsequent UT inspections performed on a 10-year augmented ISI frequency.
Regarding the acceptance criteria established for the CEA shroud bolts in Item C19 of TR 5-2, the NRC staff emphasizes that there are no corresponding acceptance criteria that can be utilized from either WCAP-17096-NP-A, Revision 2, or WCAP-17096-NP-A, Revision 3, for evaluating flaw indications revealed by UT inspections performed on CEA shroud bolts.
These versions of the referenced WCAP-17096 report preceded the development of new I&E criteria for CEA shroud bolts in the TR and the referenced WCAP reports do not include CEA shroud bolts as an analyzed CE-design component type. The new acceptance criteria in Item C19 of MRP-227, Revision 2, Table 5-2, call for the development of the applicable acceptance criteria to be established as part of a site-specific or generically accepted technical justification for the CEA shroud bolts. The staff has confirmed that this is analogous to the technical justification criteria basis established for flaws detected by UT inspections of CE-design CS bolts per the version of Item C1 in Table 5-2 of the MRP-227, Rev. 1-A report. The staff has confirmed that EPRI MRP establishes that these necessary technical justifications are to be implemented as part of the Needed Requirement action for the implementing the TRs acceptance criterion table that applies to the CE-designed PWRs (i.e., TR Table 5-2 for CE-design PWRs), as defined in TR Section 7.3. The staff finds this to be a valid technical justification acceptance criterion basis for disposition of flaws detected in the CEA shroud bolts, given the staffs reference for implementation of MRP-227 defined NEI 08 Mandatory Requirements or Needed Requirements in the staffs update of the administrative controls and confirmation process program elements of GALL-SLR AMP XI.M16A, PWR Vessel Internals (as updated in SLR-ISG-2021-01-PWRVI).
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION The NRC staff finds that TRs basis and I&E criteria for managing cracking in the CEA shroud bolts (and impacts of IE and ISR/IC) to be acceptable because: (1) the criteria are analogous to those previously established for CE-design CS bolts in Item C1 of Table 4-2 in the MRP-227, Rev. 1-A report, as evaluated and accepted in the staffs April 25, 2019, SE for MRP-227, Rev. 1-A, (2) EPRI establishes the I&E criteria applying to CEA shroud bolts in the C-19 Items of TR Tables 4-2 and 5-2 are to be implemented as part of the NEI 03-08 Needed Requirement specified in TR Section 7.3, (3) the staff has referenced the importance of implementing these Needed Requirements in the administrative controls and confirmation process program elements of GALL-SLR AMP XI.M16A, PWR Vessel Internals, and (4) the staff has confirmed that implementation of the I&E criteria in accordance with the NEI 03-08 Needed Requirement will be capable of demonstrating that the effects of cracking (and the impacts of IE and ISR/IC) on the intended function(s) of the CEA shroud bolts will be adequately managed through the end of the subsequent period of extended operation, as required by 10 CFR 54.21(a)(3).The request in RAI MRP-227-CE-2 is resolved.
3.2.2.3 CE-Design CS Assemblies - Welded CS Designs that Include Tie Rod Assemblies Primary Component and Item (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-2, Item C18, CS tie rods and nuts (a new item for management of loss of material due to wear and loss of preload due to ISR/IC in the component type, as applicable to 40 year initial license renewal and 60 -80 year subsequent license renewal periods), and supporting component-specific acceptance criteria in TR Table 5-2, Item C18. The C18 items only apply to CE-design PWRs whose CS assemblies are secured by bolted tie rod assembly designs.
NOTE: The new I&E criteria defined in MRP-227, Revision 2, Table 4-2, Item C18, initially called for performance of a non-qualified visual inspection of the top ends of 100 percent of the CS tie rods (with inspections taken top-down and from the side of the tie rods) no later than two refueling outages from the beginning of the license renewal period, with reinspections of the components to be performed on a 10-year augmented ISI interval basis.
EPRI amended the specified NDE method from a non-qualified visual inspection to a VT-3 visual inspection technique in the MRP 2024-006 letter (EPRI 2024a). Item C18 in MRP-227, Revision 1, Table 5-2, identifies that the non-qualified NDE technique is performed to look for evidence of broken locking tabs, missing nuts, displaced tie rods, or evidence of wear that may occur in the tie rod assemblies. A diagram of the CS tie rod assemblies is given in MRP-227, Revision 2, Figure 4-24.
Linked Expansion Components and Items:
None MRP-227, Revision 2, Issue Needing Resolution:
Needed clarification on EPRIs basis and justification for specifying use of a non-qualified visual inspection technique as the applicable inspection-based aging management strategy for the component type. For this issue, the NRC staff confirmed that the EPRI NDE inspection standard (i.e., proprietary MRP-228, Revision 4 (EPRI 2021a)) used for development of the MRP-227, Revision 2, does not include any criteria or standards for
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION applying a non-qualified visual inspection technique as an inspection-based aging management strategy for defined aging effects or mechanisms in the MRP-227, Revision 2.
Applicable RAI:
RAI 9 (NRC 2023a) and response (EPRI 2024a)
EPRIs Response to the RAI:
In its response to RAI 9 (EPRI 2024a), EPRI amended the MRP-227, Revision 2, to delete Section 5.1.4 and use of non-qualified visual inspections as an accepted methodology for performing visual inspections of managed PWR RVI components. EPRI MRP also amended the visual examination technique cited for inspection of the CS tie rods and nuts in Items C18 of MRP-227, Revision 2, Tables 4-2 and 5-2, from citation of a non-qualified visual inspection method to use of VT-3 visual inspections as the visual condition monitoring technique for the CS tie rods and nuts (along with a number of associated administrative changes that were needed for the contents of the MRP-227, Revision 2).
Staff Evaluation:
The NRC staff finds the I&E criteria for the CS tie rods and nuts in Items C18 of MRP-227, Revision 2, Tables 4-2 and 5-2 (as amended inclusive of changes to the items in EPRI letter MRP 2024-006 (EPRI 2024a)) to be acceptable for implementation, as based on the following technical assessments.
For MRP-227, Revision 2, Item C18, the NRC staff confirmed that EPRI has amended the specified I&E criteria to credit a VT-3 method as the visual inspection technique that will be used to monitor and detect for evidence of wear or loss of preload that may be occurring in the upper portions (i.e., threaded connections) of the CS tie rod assemblies. The NRC staff confirmed that use of a non-qualified visual inspection method is no longer credited as the inspection technique for the component type. The NRC staff has also confirmed that the proprietary MRP-228, Revision 4 (EPRI 2021a), report provides the quality standards for performing the VT-3 inspections, which reinforce the ASME Section XI and GALL (NRC 2010a) AMP XI.M16A references that VT-3 methods are acceptable visual inspection techniques for detecting general component conditions (like loss of material or loosening
[loss of preload] of bolted connections). Given these confirmations, the NRC staff concludes that the I&E criteria for the CS tie rods and nuts in Items C18 of MRP-227, Revision 2, Tables 4-2 and 5-2, are acceptable for implementation because they satisfy the NRC regulations, requirements, and guidance for managing loss of material or loss of preload in accordance with 10 CFR 54.21(a)(3). The issues in RAI 9 are resolved.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.2.2.4 CE-Design LSS Deep Beams Primary Component and Item (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-2, Item C12, LSS deep beams (for management of cracking (fatigue, SCC and IASCC mechanisms) and impacts of IE during 40 year initial license renewal and 60 year subsequent license renewal periods) and supporting component-specific acceptance criteria in MRP-227, Revision 2, Table 5-2, Item C12.
NOTE: MRP-227, Revision 2, Item C12, only applies to CE-design PWRs with welded CS assembly configurations that utilize full height shroud plates. A 25 percent population of LSS deep beams (with EVT-1 visual inspections evenly distributed across the deep beam structure) is established as the Primary population set.
Linked Expansion Components and Items:
(1) No specified Expansion category item linked to the referenced Primary Item B12 component type in MRP-227, Revision 2, Table 4-5. However, the remaining 75 percent population of LSS deep beams is defined as the sample-expansion population in MRP-227, Revision 2, Item C12, if evidence of cracking is detected on the 25 percent Primary population set.
MRP-227, Revision 2, Issue Needing Resolution:
In the updated version of MRP-227, Revision 2, Table 4-2, Item C12, the Primary and Expansion populations of LSS deep beams are screened in for the cracking mechanisms of SCC and IASCC in addition to the cracking mechanism of fatigue (and the component material embrittlement mechanism of IE). In the corresponding item of MRP-227, Revision 2, Table 4-2, Item C12, in the NRC staff-approved MRP-227, Revision 1-A, the component type only screened in for the mechanisms of fatigue and IE. Given that the LSS deep beams now screen in for the cracking mechanisms of SCC and IASCC for the 60 year subsequent license renewal period basis, the NRC staff sought further justification for the following reinspection basis applying to the Primary population of LSS deep beams, as defined by the following Examination Method/Frequency column entry in MRP-227, Revision 2, Item C12: Subsequent examination at a 10-year interval if adequacy of remaining fatigue life cannot be demonstrated.
The NRC staff also sought clarifications on: (1) whether the updated I&E criteria for the Primary population of LSS deep beams in Item C12 of MRP-227, Revision 2, Table 4-2, were establishing another round of baseline inspections of the deep beams relative to the start date of the 60 year subsequent license renewal period applying to the specified PWR unit type, and (2) how the need for sample-expansion to the Expansion population of LSS deep beams (based on reinspections of the Primary population) could be determined if the reinspection necessity of the Primary population set of components could be permanently eliminated by a component-specific analysis.
Applicable RAI:
RAI 5 (NRC 2023a) and response (EPRI 2024a)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION EPRIs Response to the RAI:
In its response to RAI 5, EPRI clarified that MRP-227, Revision 2, Item C12, was not reestablishing a second round of baseline inspections for the Primary population of LSS deep beams. EPRI amended the Examination Method/Frequency column entry of MRP-227, Revision 2, Table 4-2, Item C12, to eliminate the option that previously allowed permanent deferral of the component-specific reinspection necessity if a component-specific analysis was performed that demonstrates fatigue is not an issue for the component type.
For this change, the reinspection basis of the Examination Method/Frequency column entry of MRP-227, Revision 2, Table 4-2, Item C12 is now defined and reads as:
Subsequent examination at a 10-year interval.
Staff Evaluation:
The NRC staff finds the I&E criteria for the LSS deep beams in Items C12 of MRP-227, Revision 2, Tables 4-2 and 5-2 (as amended inclusive of changes to the items in EPRI letter MRP 2024-006 (EPRI 2024a)) to be acceptable for implementation based on the following technical assessments.
The NRC staff confirmed that MRP-227, Revision 2, Table 4-2, Item C12, continues to establish the baseline EVT-1 visual inspection need of the 25 percent Primary population set (for the LSS deep beam component type) as based relative to baseline inspections performed during the 40 year initial license renewal period applying to the specified CE-design PWR unit type (i.e., units with weld CS assemblies utilizing full height shroud plates). Licensees owning these types of CE-design PWRs that have been approved for first renewed operating licenses should have completed the baseline inspections of the Primary population set for the component type during the 40 year initial license renewal period applying to the reactor unit, as defined in the first renewed operating license for the unit.
Thus, the NRC staff emphasizes that any further EVT-1 visual inspections of the Primary population set of components would be performed in accordance with the reinspection criteria of MRP-227, Revision 2, Item C12. The NRC staff finds it acceptable that EPRI amended the reinspection criteria for the Primary population of LSS deep beams to base the reinspection necessity only a specified time frame for performing the reinspections of components.
Based on EPRIs amendment to the Examination Method/Frequency column entry of MRP-227, Revision 2, Table 4-2, Item C12, the NRC staff has confirmed that: (1) the previous option that permitted permanent elimination of the reinspection necessity through performance of a component analysis is no longer part of the I&E criteria for the LSS deep beam component type in the revised version of Table 4-2, Item C12, and (2) when the reinspections of the Primary population set of components is performed, there should be sufficient reinspection data available to determine whether reinspection-based sample-expansion to the Expansion population of LSS deep beams is needed, as defined by the relevant conditions and acceptance criteria for the component type in MRP-227, Revision 2, Table 5-2, Item C12. The NRC staff has also confirmed that the 10-year reinspection frequency set for the Primary population of deep beams is similar to that specified for a number of other CE-design Primary category components as given in MRP-227, Revision 2, Table 4-2, or as approved for the Primary component types in the NRC staffs SE for MRP-227, Revision 1-A (NRC 2019) (e.g., those for the Primary category shroud plates
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION under Item C2 or C3 of MRP-227, Revision 2, Tables 4-2 and 5-2 or Item C2 or C3 of Tables 4-2 and 5-2 of MRP-227, Revision 1-A). Given the revisions to MRP-227, Revision 2, Table 4-2, Item C12 in the EPRI letter MRP 2024-006 (EPRI 2024a), the NRC staff concludes that the I&E criteria for the LSS deep beams in Items C12 of MRP-227, Revision 2, Tables 4-2 and 5-2 (inclusive of changes made in EPRI letter MRP 2024-006) are acceptable for implementation because they satisfy the NRC regulations, requirements and guidance for managing the impacts of cracking and IE on the specified component type in accordance with requirements of 10 CFR 54.21(a)(3). The issues in RAI 5 are resolved.
3.2.2.5 CE-Design In-core Instrument (ICI) Thimble Tubes (Top-Mounted ICI Designs Only)
Existing Program Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-8, Item C20, ICI thimble tubes - lower. This is a new item in the MRP-227, Revision 2, for managing changes in dimension by irradiation growth (or distortion) in the specified component type for both 40 year initial license renewal and 60 year subsequent license renewal periods. The item only applies to CE-design PWRs whose reactor design includes top-mounted ICIs.
NOTE: Item C20 in MRP-227, Revision 2, Table 4-8, defines that Existing Program examination method applied to the ICI thimble tubes is set by plant-specific programs, where the I&E criteria for the inspections may need to be updated for 60 year subsequent license renewal period operations. A figure of the component type is provided in MRP-227, Revision 2, Figure 4-29.
MRP-227, Revision 2, Issue Needing Resolution:
The staff noted that the supporting proprietary information for the top-mounted, ICI thimble tubes - lower in Section 4.1.7 of MRP-232, Revision 2 (EPRI 2021c) (which was used as supporting information for development of new Existing Program Item C20) did not provide sufficient supporting documentation as to the type of I&E protocols will be implemented as part of plant-specific Existing Program basis for the component type. Thus, the NRC staff sought additional clarifications of the types of plant-specific programs that apply to the ICI thimble tube - lower components and details on the types of aging management strategies that could be applied for managing potential changes in dimension of the specified ICI thimble tube - lower component type.
Applicable RAI:
RAI MRP-227-CE-3 (NRC 2022b) and response (EPRI 2023a)
EPRIs Response to the RAI:
In its response to RAI MRP-227-CE-3, EPRI explained that the plant-specific programs for these components were previously addressed in EPRIs resolution of A/LAI #3 in MRP-227, Revision 1-A, and that the aging management strategy utilized application of component-specific replacements of the thimble tubes (i.e., with shorter length tubes) as a mitigative, aging management strategy for preventing irradiation-induced growth from occurring in the tubes. Otherwise, if irradiation-induced growth were to occur in the tubes, the resulting distortion could potentially interfere with the licensees ability to insert the ICI thimble
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION monitoring equipment into the reactor core when needed for operational safety. However, EPRI clarified that the basis for the ICI thimble tubes in MRP-227, Revision 1-A, was for the 60-year considerations. For the 60 year subsequent license renewal period basis, EPRI explained that the objective of including Item C20 in MRP-227, Revision 2, Table 4-8, was to address the impacts of irradiation-induced material grain growth out to 80 years of operation. EPRI also explained that a licensee owing a CE-designed PWR unit with top-mounted ICI thimble tubes could address aging management of the component type on the plant-specific basis through selection of one of several aging management strategies, including: (1) performance of a supplemental evaluation that projects irradiation growth out to the end of plant operations, (2) additional monitoring of thimble tube length, or (3) similar to the 60-year basis specified in MRP-227, Revision 1-A, proactive replacements of the thimble tubes. Thus, based on these explanations, EPRI revised MRP-227, Revision 2, Table 4-8, Item C20, as shown in EPRI letter MRP 2023-003 letter (EPRI 2023a) in order to better define these aging management strategies as the aging management options that may be applied to the ICI thimble tubes in MRP-227, Revision 2, Item C20.
Staff Evaluation:
The NRC staff finds the I&E criteria for the ICI thimble tubes - lower component type in MRP-227, Revision 2, Table 4-8, Item C20 (as amended inclusive of changes to Item C20 in the EPRI letter MRP 2023-003 (EPRI 2023a)) to be acceptable for implementation based on the following technical assessments.
EPRI clarified that the aging management strategy selected for the component type through the end of a 60 year subsequent license renewal period would involve at least one of the specified aging management strategies accepted in GALL-SLR AMP XI.M16A for managing specific aging effects in the PWR RVI components. This includes aging management strategy options for implementing either of component-specific inspections of component type, performing a supplemental analysis of the ICI thimble tubes that accounts for potential changes in dimension induced by irradiation grain growth, or performing component-specific replacement activities of the thimble tubes.
For the inspection-based option, GALL-SLR AMP XI.M16A would allow visual inspections when coupled with a quantifiable measurement basis to be used as basis for determining whether changes in dimension was occurring in the ICI thimble tubes - lower component type. For EPRI, this is referenced as an NDE technique that is capable of monitoring changes in the thimble tube length. Since MRP-227, Revision 2, Item C20, has been revised to indicate that a licensee would need to take action to define the plant-specific aging management strategy option used for the component type, the NRC staff concludes that the revised version of MRP-227, Revision 2, Table 4-8, Item C20, is acceptable because: (1) the aging management strategy selected for the component type under MRP-227, Revision 2, Item C20, would be implemented as an NEI 03-08 Needed Requirement, as consistent with the provisions of TR Section 7.3, and (2) the specified TR Item C20 basis accounts for potential aging management strategy options that are within the scope of the GALL-SLR AMP XI.M16A program element provisions and are capable of satisfying the aging management requirements of 10 CFR 54.21(a)(3). The issues in RAI MRP-227-CE-3 are resolved.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.2.2.6 CE-Design Core Stabilizing Lugs, Shims, and Shim Bolts The NRC staff provides its assessment of EPRIs updated I&E criteria for CE-design core stabilizing lugs, shims, and shim bolts (as included in Item C17 of MRP-227, Revision 2, Table 4-8), as part of the NRC staffs evaluation for EPRIs updated I&E criteria that were included in W14 of MRP-227, Revision 2, Table 4-9, for WEC-design clevis insert components (including clevis insert bolts, dowel pins, and wear surfaces). Refer to the NRC staffs evaluation in Section 3.2.3.7 of this SE.
3.2.2.7 CE-Design CSB Assembly Welds Subject to OE Outside the Scope of the MRP-227, Revision 2 The NRC staff provides its assessment of EPRIs updated I&E criteria for CE-design CSB assembly welds impacted by new OE as part of the staffs evaluation for EPRIs updated I&E criteria that were made to the MRP-227, Revision 2, criteria for corresponding WEC-design CB assembly welds impacted by the OE, as evaluated and discussed in EPRI letter MRP 2024-006.
Refer to the NRC staffs evaluation in Section 3.2.3.4 of this SE.
3.2.3.
Component-Specific Evaluation Topics for WEC-Design Internals 3.2.3.1 WEC-Design Conduit Seal Assembly Bodies, Tubes, Tubesheets, and Tubesheet Welds No Additional Measures (N Category) Components:
(1) WEC-design conduit seal assembly bodies, tubes, tubesheets, and tubesheet welds NOTE: The basis for placing the conduit seal assembly bodies, tubes, tubesheets, and tubesheet welds in N category of the program is given in TR Table 3-3, as supported by the proprietary basis in Sections 4.2.8 and 5.2.8 of MRP-232, Revision 2.
MRP-227, Revision 2, Issues Needing Resolution:
(1) Needed clarifications and further justifications for EPRIs basis of placing the WEC-design conduit seal assembly bodies, tubes, tubesheets, and tubesheet welds in the N category based on aging management activities that would permit leakage to occur in the component types. The staff requested these clarifications because: (1) EPRI used MRP-232, Revision 2, to establish the referenced conduit seal assembly components that are managed using an alternate leakage-based AMP that is outside the scope of MRP-227, Revision 2, and (2) the NRC staffs position in Section A.1.2.3.4 of NUREG-2192 (NRC 2017b), Appendix A1 (i.e., NRC Branch Position RLSB-1) states that a program based solely on detecting structure and component failure should not be considered as an effective AMP for SLR.
Applicable RAI:
RAI MRP-227-WEC-1 (NRC 2022b) and response (EPRI 2023a)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION EPRIs Response to the RAI:
In response to RAI MRP-227-WEC-1, EPRI clarified that the conduit seal assembly body, tubesheet, tubesheet welds, and tubes provide a path for the thermocouples to enter the reactor pressure vessel (RPV) through the RPV closure head. EPRI explained that the portions of the conduit seal assemblies subject of the past OE are the Conoseal located above the RPV head and that the tube, tubesheets and tubesheet welds are located inside of the seal assembly body and are inaccessible to inspection. EPRI further explained that achieving access to these components would require the removal and replacement of the conduit seal assembly (which are activities outside the scope of MRP-227, Revision 2) and that the areas around the conduit seal assembly are inspected every refueling outage for evidence of primary pressure boundary leakage in accordance with licensees AMP that corresponds to AMP XI.M10, Boric Acid Corrosion, in the GALL, December 2010 (NRC 2010a) or GALL-SLR (NRC 2017a) reports.
Staff Evaluation:
The NRC staff finds the MRP-227, Revision 2, screening basis for placing conduit seal assembly bodies, tubes, tubesheets, and tubesheet welds into the N category (No Additional Measure category components for which no further action is needed) of the AMP is acceptable and appropriate, but only when taken into context with EPRIs position in the RAI response that the licensees Boric Acid Corrosion program should be the proper program credited with aging management of the component. The NRC staff acknowledges that boric acid corrosion programs are well established performance-based AMPs for managing cracking and potential leaks from primary pressure boundary components in PWRs. When this is taken into context with the use of the GALL-SLR AMP XI.M10 aging management strategy for managing cracking in the specified conduit seal assemblies (which is outside of MRP-227, Revision 2, aging management strategy), the NRC staff finds that EPRI has provided a valid basis for placing these conduit seal assembly components in the N category of the WEC-design PWR RVI AMP. The issue in RAI MRP-227-WEC-1 is resolved.
3.2.3.2 WEC-Design CB Outlet Nozzles and Safety Injection (SI) Nozzles No Additional Measures (N Category) Component:
(1) WEC-design CB outlet nozzles and SI nozzles NOTE: The basis for placing the CB outlet nozzles and SI nozzles in N category of the AMP is given in MRP-227, Revision 2, Table 3-3, as supported by the proprietary basis in Sections 4.2.2.6 and 5.1.2.2 of MRP-232, Revision 2.
MRP-227, Revision 2, Issue Needing Resolution:
(1) The NRC staff sought further clarifications on the N categorization basis for the CB outlet nozzles and SI nozzles in MRP-227, Revision 2, Table 3-3. The NRC staff perceived that MRP-232, Revision 2, may be subjecting these nozzles to specific types of NDE inspections, which could potentially conflict with EPRIs designation of the CB outlet nozzles and SI nozzles as N category, non-managed RVI component types in MRP-227, Revision 2, Table 3-3.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Applicable RAI:
RAI MRP-227-WEC-2 (NRC 2022b) and response (EPRI 2023a)
EPRIs Response to the RAI:
In response to RAI MRP-227-WEC-2, EPRI clarified that the reference of the ASME Section XI program requirements for the CB outlet nozzle and SI nozzles is in reference to ASME Section XI implemented VT-3 visual inspections of the CB assembly (including the CB outlet and SI nozzles attached to the assembly) as a core support structure that is subject to the ISI criteria of ASME Section XI, Table IWB-2500-1, Examination Category B-N-3 requirements. EPRI explained that, although wear of the nozzles needed to be considered, there were no special concerns for these components by the expert panel review even with wear being considered as the limiting aging mechanism for the nozzle types. Although wear screened in for the CB outlet and SI nozzle types due to its potential impact of the mechanism on the safety-related core flow bypass intended function of the CB assembly, EPRI explained that the potential impact on the core flow bypass function was low because the amount of wear that could potentially occur is limited by the tolerance of the interfacing components. EPRI stated that a large volume of material would need to be removed due to wear or abrasion for the aging effect to have a potential impact on the safety-related core flow bypass function of the CB assembly. EPRI also stated that the amount of movement needed to reach this level of wear would also impact other internals components being inspected under the TR or ASME Section XI (e.g., the CB flange, radial keys, and clevis inserts).
Staff Evaluation:
The NRC staff finds the MRP-227, Revision 2, basis for placing the CB outlet nozzles and SI nozzles in the N category of the WEC-design RVI programs to be acceptable for implementation, as discussed below.
From a historical perspective, the NRC staff confirmed that the WEC-design CB outlet nozzles and SI nozzles were originally only designated as Expansion category for the CB upper flange weld (UFW) in the MRP-227-A report, and that the NRC staff accepted the removal of CB outlet nozzles and SI nozzles as refenced Expansion category components for the CB UFW in the NRC staffs SE for MRP-227, Revision 1-A. Given that the portions of the CB outlet nozzles and SI nozzles adjoining to the CB assembly would be required to be inspected as part of the ASME Section XI, Examination Category B-N-3 components that are subject to the licensees GALL/GALL-SLR AMP XI.M1, ASME Section XI In-service Inspection, Subsections IWB, IWC, and IWD, the NRC staff concludes that the EPRI has provided an adequate basis for continued placement of the WEC-design CB outlet nozzles and SI nozzles in the N category of the MRP-227, Revision 2. Under this basis, the NRC staff emphasizes that the portions of the CB outlet nozzles and SI nozzles adjoined to the CB assembly are still required to be visually inspected (using VT-3 NDE methods) in accordance with the licensees ASME Section XI In-service Inspection, Subsections IWB, IWC, and IWD AMP for the facility, as required by 10 CFR 50.55a(g)(4) and implemented to perform the ISI item requirements specified for the CB assembly in ASME Section XI, Table IWB-2500-1, Examination Category B-N-3, Item B13.70. The issue in RAI MRP-227-WEC-2 is resolved.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 3.2.3.3 WEC-Design CRGT Assembly Components Existing Program Component and Item (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-9, Item W1, CRGT guide plates (guide cards), C-tubes, and sheaths (for loss of material due to wear during both 40 year initial license renewal and 60 year subsequent license renewal periods)
NOTE: Item W1 credits the Existing Program basis in PWROG Proprietary Report No. WCAP-17451-P, Revision 2 (PWROG 2019b), as the Existing Program basis for the component types.
MRP-227, Revision 2, Issue Needing Resolution:
(1) The NRC staff sought reconciliation of the differences between the version of proprietary report WCAP-17451-P being referenced for aging management of loss of material due to wear in the CRGT guide cards, C-tubes, and sheaths in MRP-227, Revision 2, Table 4-9, Item W1 (i.e., WCAP-17451-P, Revision 2) from the prior version of WCAP-17451-P being referenced for aging management of the component types in Table 4-3, Item W1, of the MRP-227, Revision 1-A, report (i.e., WCAP-17451-P, Revision 1 (PWROG 2015)).
Applicable RAI:
(1) RAI MRP-227-WEC-3 (NRC 2022b) and response (EPRI 2023a)
EPRIs Response to the RAI:
In its response to RAI MRP-227-WEC-3, EPRI clarified and confirmed that the updated basis in MRP-227, Revision 2, Table 4-9, Item W1, is crediting WCAP-17451-P, Revision 2, as the version that is used to manage loss of material due to wear in CRGT guide cards, C-tubes, and sheaths.
Staff Evaluation:
The NRC staff finds that MRP-227, Revision 2, Table 4-9, Item W1, for managing loss of material due to wear in the CRGT guide cards, C-tubes, and sheaths is acceptable for implementation (as discussed below) and that the version of WCAP-17451-P, Revision 2, may be applied as the updated version used for aging management of the specified Existing Program component types.
To accept MRP-227, Revision 2, Table 4-9, Item W1, for implementation, the NRC staff compared the aging management criteria for managing the CRGT guide cards, C-tubes, and sheaths in WCAP-17451-P, Revision 2, from those previously established for the specified component types in WCAP-17451-P, Revision 1. The NRC staff previously accepted WCAP-17451-P, Revision 1, as aging management methodology for these component types (as accepted in the NRC staffs SE for MRP-227, Revision 1-A) because the WCAP-17451-P, Revision 1, methodology provided an acceptable basis for: (1) selecting a meaningful population of CRGT guide cards for inspection, and (2) calculating and projecting CRGT guide card wear rates, and for using the calculated wear rates to
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION determine both the number of CRGT guide cards requiring subsequent reinspections and the specific schedule for performing the reinspections of the components. The NRC staff finds that the methodology served as the technical basis for implementing a conservative, component-specific minimum coverage criterion change for the specified the population of CRGT guide cards requiring inspection in WCAP-17451-P, Revision 1, from the prior 20 percent minimum population of CRGT guide cards requiring inspection in MRP-227-A.
The NRC staff noted that the PWROG updated the modeling criteria in WCAP-1741-P, Revision 2, through incorporation of revisions that PWROG made to the proprietary confidence limits used in the reports mathematical model for performing CRGT guide card wear rate calculations. In relation to this observation, the NRC staff confirmed that the changes made in WCAP-17451-P, Revision 2, were supported by the PWROGs updated position in its letter No. OG-18-76 (PWROG 2018a) and provided a more conservative basis for selecting the minimum population of CRGT guide cards needed for inspection (including a more conservative, proprietary confidence limit basis in WCAP-17451-P, Revision 2s mathematical modeling).
Given that the methods in WCAP-17451-P, Revision 2 (as referenced in Item W1 of MRP-227, Revision 2, Table 4-9) still include I&E criteria for inspecting a majority of the CRGT guide cards, the NRC staff finds Existing Program Item W1 in MRP-227, Revision 2, Table 4-9, and the probabilistic model for inspecting these components in WCAP-17451-P, Revision 2, to be an acceptable Existing Program aging management strategy basis for the specified CRGT guide card, C-tube, and sheath component types. The issue in RAI MRP-227-WEC-3 is resolved.
3.2.3.4 WEC-Design CB Assembly and CE-Design CSB Assembly Welds Impacted by New OE Requiring Evaluation Primary Component and Item (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-3, Item W2, WEC-design CB UFW (for management of cracking due to SCC; for both 40 year initial license renewal and 60 year subsequent license renewal periods), and supporting component-specific acceptance criteria and sample-expansion link criteria in MRP-227, Revision 2, Table 5-3, Item W2 (2) MRP-227, Revision 2, Table 4-2, Item C5, CE-design CSB UFW (for management of cracking due to SCC; for both 40 year initial license renewal and 60 year subsequent license renewal periods), and supporting component-specific acceptance criteria and sample-expansion link criteria in MRP-227, Revision 2, Table 5-2, Item C5 Linked WEC-Design Expansion Components and Items in the TR for the Primary Category WEC-Design CB UFW:
(1) MRP-227, Revision 2, Table 4-6, Item W3.1, CB UGW (2) MRP-227, Revision 2, Table 4-6, Item W3.2, CB lower flange weld (LFW)
(3) MRP-227, Revision 2, Table 4-6, Item W3.3, CB upper axial welds (UAWs, as the specified second tier Expansion category welds for the first tier, Expansion category Item W3.1, CB UGW or the Item W3.2 CB LFW)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (4) MRP-227, Revision 2, Table 4-6, Item W3.4, lower support casting or forging (as a specified second tier Expansion category component type for the first tier, Expansion category Item W3.2 CB LFW)
Linked CE-Design Expansion Components and Items in MRP-227, Revision 2, for the Primary Category CE-Design CSB UFW:
(1) MRP-227, Revision 2, Table 4-6, Item C5.1, CSB UGW (2) MRP-227, Revision 2, Table 4-6, Item C5.2, CSB lower girth/flange weld (LGW/LFW)
(3) MRP-227, Revision 2, Table 4-6, Item C5.3, CSB UAWs (4) MRP-227, Revision 2, Table 4-6, Item C5.4, LSS lower core support beams (5) MRP-227, Revision 2, Table 4-6, Item C5.5, CSBFW Relevant OE After Issuance of MRP-227, Revision 2 In Fall 2022, the owner of a domestic WEC-design PWR detected cracking in that units CB UGW. The NRC staff noted that the reported CB UGW OE is relevant to the review of this TR because the flaws in the CB UGW were detected as part of the licensees ASME Code Section XI VT-3 visual inspections that were performed on the CB assembly in accordance with the licensees GALL XI.M1-based ASME Section XI ISI, Subsections IWB, IWC, and IWD AMP during the initial license renewal period of the unit. The flaw indications were not detected through implementation of the licensees MRP-227-based PWR RVI AMP, as the Primary EVT-1 visual inspections applied to the linked Primary category CB UFW did not reveal the presence of any flaw indication results that would prompt a sample-expansion inspection of the Expansion category CB UGW. Under the risk-based assumptions and Primary/Expansion inspection hierarchy of MRP-227, Revision 1-A or Revision 2, the CB UFW (as the designated, lead Primary component type) would have been expected to exhibit significant evidence of cracking first prior to any significant cracking that might be detected in the Expansion category CB UGW. For this OE event, the reverse occurred where the significant cracking was detected in the units Expansion category CB UGW prior to detection of any significant cracking in the units Primary category CB UFW.
MRP-227, Revision 2, Issue Needing Resolution:
(1) Given recent reported cracking experience with WEC-design CB UGWs noted above (i.e., U.S. domestic OE not accounted for in the scope of OE assessed in the TR), the NRC staff needed clarifications from EPRI on whether the CB UGW needs to be elevated as an additional WEC-design Primary CB assembly weld inspection (i.e., in addition to the designations of the CB UFW and CB LGW as designated WEC-design Primary category CB welds for the TR).
Applicable RAI:
(1) RAI 6 (NRC 2023a) and response (EPRI 2024a)
EPRIs Response to the RAI:
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION EPRI provided a response to RAI 6, Parts (a) and (b) in its MRP 2024-006 letter. EPRI stated that when the NRC-approved version (-A version) of MRP-227, Revision 2, is published and transmitted to the NRC, the NRC staff-approved version of MRP-227, Revision 2, will include the revised I&E criteria for WEC-design Primary CB assembly and the analogous CE-design Primary CSB assembly welds, along with the associated changes to the Expansion category components. EPRI also clarified that the inspections will be performed in accordance with the I&E criteria defined in EPRI letter No. MRP 2023-005 (EPRI 2023b), as clarified in a revision of the guidance letter (i.e., MRP 2023-005, Revision 1). For continuity objectives, EPRI included the MRP 2023-005, Revision 1, letter as Enclosure 2 to the MRP 2024-006 letter (EPRI 2024a). EPRI also provided the ensuing I&E criteria changes for defined WEC-design and CE-design Primary category CB/CSB welds and linked Expansion category CB/CSB welds and lower internals assembly components (along with associated screening basis and administrative content changes identified on Page 21 of Attachment 1 to the MRP 2023-005 letter) as part of the response to RAI 6.
The net effect of actions performed by EPRI (i.e., in resolution the OE event) in the MRP 2024-006 letter induces the following changes to the I&E criteria for WEC-design CB assembly welds and lower internals assembly (LIA) components and corresponding changes for CE-design CSB assembly welds and LSS components in the MRP-227, Revision 2:
WEC-design CB UGW is revised to be a Primary category weld for the management of SCC per Item W3a in MRP-227, Revision 2, Table 4-3 (for WEC-design PWRs).
New relevant conditions, sample-expansion link criteria and acceptance criteria of the CB UGW are defined as a Primary category weld in new Item W3a of MRP-227, Revision 2, Table 5-3. This results in the following corresponding changes in the MRP-227, Revision 2: (1) deletion of WEC-design CB UGW as a referenced Expansion category weld for the Item W3 criteria applying to Primary category CB UFWs in MRP-227, Revision 2, Tables 4-3 and 5-3; (2) referencing of the CB UAWs, LFW, and lower support forging or casting as the referenced MRP-227, Revision 2, Table 4-6, Item W3.2, W3.3, and W3.4 Expansion category components for the CB UGW, as a newly designated Primary category weld in MRP-227, Revision 2; (3) revised designations of the CB UFW and the CB UGW as the applicable, linked Primary welds for the Expansion items (MRP-227, Revision 2 Items W3.2, W3.3, and W3.4) applying to the CB UAWs, CB LFW, and LIA lower support casting or forging (as referenced Expansion category components) in MRP-227, Revision 2, Table 4-6, and newly defined acceptance criteria for the component types in MRP-227, Revision 2, Table 5-3.
CE-design CSB UGW is revised to be a Primary category weld for the management of SCC and impacts of IE (in CE-design units with welded CS assemblies designed in two vertical sections or with full height shroud plates) per new Items C5a and C5b in MRP-227, Revision 2, Table 4-2, and new relevant conditions, sample-expansion link criteria and acceptance criteria for the CSB UGW are defined as a Primary category weld in new Items C5a and C5b of MRP-227, Revision 2, Table 5-2. This results in the following corresponding changes in the MRP-227, Revision 2:
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (1) deletion of CE-design CSB UGW as a referenced Expansion category weld type for the MRP-227, Revision 2, Table 4-2 and 5-2, C5 items applying to the Primary CSB UFW in MRP-227, Revision 2, (2) referencing of CSB LFW/LGW, UAWs, LSS lower core support beams, and CSBFW as the new referenced Expansion category components for the CSB UGW as a Primary category weld in the MRP-227, Revision 2, C5a and C5b items, and (3) revised designations of the CB UFW and the CSB UGW as the applicable, linked Primary welds for the Expansion category CSB LFW/LGW, CBS UAWs, LSS lower support beams, and CSBFW under Items C5.1, C5.3, C5.4, and C5.5 of MRP-227, Revision 2, Table 4-6, and new defined acceptance criteria for the component types in MRP-227, Revision 2, Table 5-2.
Corresponding changes to the examination method and frequency criteria and examination coverage criteria for CB/CSB UGW that are analogous to those established for the inspections of the CB/CSB UFW (or linked CB/CSB Expansion category welds) using either EVT-1, UT, or ECT inspection techniques, with baseline inspections to be completed within two refueling outages of the start of the license renewal period and reinspections performed on a 10-year augmented ISI interval basis. If UT is utilized as the inspection technique, the inspection may be performed from only one surface of the weld (either the inside diameter (ID) surface or outer diameter (OD) surface of the weld).
Corresponding changes to the screening entries for WEC-design CB UGWs in MRP-227, Revision 2 Table 3-3 and CE-design CSB UGWs in MRP-227, Revision 2, Table 3-2, to replace the E categorizations with P categorizations for the applicable cracking mechanism(s) (fatigue, SCC, or IASCC) that screened in for the CB/CSB UGW in MRP-227, Revision 2, Table 3-2 or Table 3-3, and associated administrative changes of the MRP-227, Revision 2, to reference the Interim Guidelines in MRP 2023-005, Revision 1 (EPRI 2023b), as an applicable supplemental guideline for the CB/CSB welds.
Staff Evaluation:
The NRC staff finds the revised inspection category and I&E criteria for WEC-design and CE-design CB/CSB UFWs and UGWs, and the remaining CB/CSB weld components and LIA/LSS components, that link as Expansion category components for the Primary category UFWs and UGWs, to be acceptable because the changes: (1) appropriately address the impacts of the site-specific WEC-design CB UGW cracking OE event reported in the fall 2022, and (2) elevate the WEC-design CB UGW and CE-design CSB UGW back to Primary category CB weld components consistent with the manner the UGWs were previously characterized as a Primary category welds in the MRP-227-A report.
The NRC staff addressed the potential impacts of this OE event with EPRI during the audit phase of the staffs review. Subsequently, EPRI submitted its new interim guidance letters for WEC-design and CE-design CB/CSB UGWs, as provided in EPRI letter
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION Nos. MRP 2023-005, Revision 1 (EPRI 2023b). The NRC staff confirmed that, in these interim guidelines, EPRI provided its basis for reestablishing a WEC-design units CB UGW or a CE-design units CSB UGW as a Primary category weld for inspection, even though the changes in the inspection category and new I&E criteria for WEC-design and CE-design CB/CSB UGWs (and corresponding Expansion category component changes) were not reflected in MRP-227, Revision 2, prior to the receipt of the response to RAI 6. However, the NRC staff noted and confirmed that the response to RAI 6 in the MRP 2024-006 letter addressed this OE-related matter and identified the changes that would need to be made to MRP-227, Revision 2, I&E criteria for WEC-design and CE-design Primary and Expansion category CB/CSB assembly weld components and linked LIA/LSS Expansion category base metal components that are additional Expansion category components for the CB/CBS UFWs and UGWs. Given the elevation of the CB/CSB CB UGWs to Primary category and the associated changes to the specified and linked Expansion category components for both the specified CB/CSB UFWs and UGWs as Primary welds, the NRC staff concludes that the change to the I&E criteria made in EPRI letter MRP 2024-006 for these component types is acceptable for implementation. The issues in RAI 6, Parts (a) and (b) and the impacts of the referenced September 2022 OE event on MRP-227, Revision 2, aging management strategies for WEC-design and CE-design CB/CSB assembly weld types are resolved.
3.2.3.5 WEC-Design BFBs, Core Barrel-Former (CBF) Bolts, and Lower Support Column (LSC) Bolts - Significant I&E Criteria Changes Based on Relevant OE Primary Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-2, Item W6a, WEC-design Primary Tier 1 Ranked BFBs (for the management of cracking due to fatigue and IASCC and impacts of IE and ISR/IC for both 40 year initial license renewal and 60 year subsequent license renewal periods), and supporting component-specific acceptance criteria and sample-expansion link criteria in MRP-227, Revision 2, Table 5-3, Item W6 (2) MRP-227, Revision 2, Table 4-2, Item W6b, WEC-design Primary Tier 2 Ranked BFBs (for the management of cracking due to fatigue and IASCC and impacts of IE and ISR/IC for both 40 year initial license renewal and 60 year subsequent license renewal periods), and supporting component-specific acceptance criteria and sample-expansion link criteria in MRP-227, Revision 2, Table 5-3, Item W6 (3) MRP-227, Revision 2, Table 4-2, Item W6c, WEC-design Primary Tier 3 or 4 Ranked BFBs (for the management of cracking due to fatigue and IASCC and impacts of IE and ISR/IC for both 40 year initial license renewal and 60 year subsequent periods), and supporting component-specific acceptance criteria and sample-expansion link criteria in MRP-227, Revision 2, Table 5-3, Item W6 NOTE: In MRP-227, Revision 2, Table 4-3, EPRI divided the previous Item W6 item for BFBs (as previously given in Item W6 of Table 4-3 in MRP-227, Revision 1-A) into three new tier-based items for the BFBs: (1) Item W6a for Tier 1 BFBs as the highest ranked BFB grouping for IASSC susceptibility; (2) Item W6b for Tier 2 BFBs as the second highest ranked BFB grouping for IASCC susceptibility; and (3) Item W6c for Tier 3 or Tier 4 BFBs as the two lowest ranked BFB groupings for IASCC susceptibility.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION The different tier categories of WEC-designed BFBs are defined in WEC Nuclear Safety Alert letter No. Nuclear Safety Advisory Letter (NSAL)-16-1 (PWROG 2016b) as follows:
(1) Tier 1 BFBs - includes Tier 1a BFBs in 4-loop WEC-design PWRs operating in a downflow configuration whose BFBs are made from Type 347 stainless steel materials and Tier 1b BFBs in 4-loop WEC-design PWRs operating in a downflow configuration whose BFBs are made from Type 316 stainless steel materials; (2) Tier 2 BFBs - includes Tier 2a BFBs in 2-loop WEC-design PWRs operating in a downflow configuration whose BFBs are made from Type 347 stainless steel materials, Tier 2b BFBs in 3-loop WEC-design PWRs operating in a downflow configuration whose BFBs are made from Type 347 stainless steel materials, and Tier 2c BFBs in 2-loop or 3-loop WEC-design PWRs operating in a downflow configuration whose BFBs are made from Type 316 stainless steel materials; (3) Tier 3 BFBs - BFBs in WEC-design PWRs with converted upflow configurations, including those with BFBs made from either Type 316 or Type 347 stainless steel materials; and (4) Tier 4 BFBs - BFBs in WEC-design PWRs that have continuously operated in an upflow configuration, where the bolts are made from a Type 316 stainless steel material.
NOTE: Note 3 in MRP-227, Revision 2, Table 5-3, provides the definition for large clustered groupings of Primary category BFBs with detected and noted flaw indications, where the definition is established as the basis for treating the CBF bolts as direct, first tier Expansion category components linked to the BFBs under I&E criteria of MRP-227, Revision 2, Table 4-3, Items W6a, W6b, and W6c criteria and MRP-227, Revision 2, Table 4-6, Item W6.1. For groupings of Primary category BFBs that do not fall into this large, clustered grouping definition, the CBF bolts are treated as secondary tier Expansion category bolts for MRP-227, Revision 2, Item W6.2, LSC bolts that are first tier Expansion category bolting type for the BFBs.
Linked Expansion Components and Items:
(1) MRP-227, Revision 2, Table 4-6, Item W6.1, CBF bolts (defined as first tier Expansion category bolts for the Primary Tier 1, 2, 3, or 4 ranked BFBs if evidence of large clusters of degraded BFBs is detected in the population of BFBs being inspected under the I&E criteria of Primary Items W6a, W6b, or W6c (for the appropriate tier category), or defined as secondary tier Expansion category bolts for the first tier Expansion category Item W6.2 LSC bolts if no evidence of large, clustered groupings of degraded BFBs is detected).
(2) MRP-227, Revision 2, Table 4-6, Item W6.2, LSC bolts (first tier Expansion category bolts for Primary Tier 1, 2, 3, or 4 ranked BFBs); a diagram of the LSC bolts is provided MRP-227, Revision 2, Figure 4-41.
MRP-227, Revision 2, Issues Needing Resolution:
(1) EPRIs revised bases criteria for performing and completing baseline inspections of the BFBs based on their tier rankings, and for performing reinspections of the BFBs (2) Revisions of NDE methods credited for aging management of cracking due to fatigue or IASSC (or impacts of IE or ISR/IC)
(3) Changes to the Primary-to-Expansion category sample-expansion relationships between the Primary category BFBs and the Expansion category CBF bolts and LSC bolts
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (4) EPRIs new definition for large clustered groupings of degraded BFBs, as defined in Note 3 of MRP-227, Revision 2, Table 5-3 (this topic was the subject of RAI 2, Parts 1 - 5). In relation to this topic, the NRC staff observed that Note 3 of MRP-227, Revision 2, Table 5-3, defines large clustered groupings of degraded BFBs as:
any group of adjacent baffle-former bolts at least 3 rows high by at least 10 columns wide, or at least 4 rows high by at least 6 columns wide where 80% or greater of the baffle-former-bolts have unacceptable UT indications or are visibly degraded.
However, the NRC staff also observed that EPRI has provided a different definition for clustered groupings BFBs (with flaw indications) in MRP 2017-009 (EPRI 2017c; with the definition as stated below), where the definition was previously accepted in Section 3.1.3.7 of the NRC staffs SE for MRP-227, Revision 1-A:
Clustering defined per NSAL-16-1 Rev.1: three or more adjacent defective BFBs or more than 40% defective BFBs on the same baffle plate.
Untestable bolts should be reviewed on a plant-specific basis consistent with WCAP-17096-NP-A for determination if these should be considered when evaluating clustering.
Applicable RAI:
RAI 2, Parts 1 - 5 (NRC 2023a) and response (EPRI 2024a)
EPRIs Response to the RAI:
EPRI provided the following clarifications in its collective set of responses to RAI 2, Parts 1 - 5, in EPRI letter MRP 2024-006) (EPRI 2024a):
EPRI clarified that the definition in Note 3 of MRP-227, Revision 2, Table 5-3, serves as an acceptance criterion and was needed as a new quantitative basis for initiating direct sample-example of the Expansion category CBF bolts when inspections of the BFBs reveal that clustered grouping of BFBs has unacceptable flaw indications.
EPRI further clarified that the quantitative definition for clustered groupings of BFBs in EPRI letter MRP 2017-009 is used for different AMP program element objectives (i.e., the detection of aging and monitoring and trending elements), which is to assist the licensee in establishing the reinspection interval (no longer than a 10-year reinspection interval) for the BFB bolts when the BFBs in a clustered grouping are determined to have with flaw indications that are found as being unacceptable by the licensee-technical justification referenced in MRP-227, Revision 2, Table 5-3, Item W6.
EPRI clarified that the definition of clustered groupings of BFBs in Note 3 of MRP-227, Revision 2, Table 5-3, references two different array groupings of BFBs (i.e., 3-by-10 and 4-by-6 arrays of adjacent BFBs bolts with unacceptable indications) because these were the lower bound configurational arrays of degraded, clustered grouping of BFBs that were determined by structural analysis to be a challenge to the structural integrity of the baffle plates containing the BFBs (or adjacent baffle plates if the clustered grouping of BFBs spans two or more plates). For this basis,
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION EPRI clarified that it selected an 80 percent population of BFBs in the defined clustered condition arrays to create a sufficient margin for initiating sample-expansion to the CBF bolts before the structural integrity of the impacted baffle plates and of the CB assembly and CBF bolts could be challenged by a large clustered grouping of BFBs with unacceptable conditions.
In the RAI 2 topic pertaining to the population of bolts associated with the adjacent BFB arrays, the NRC staff observed that the defined adjacent BFB arrays might be different for potential differences in size of baffle plates and number of BFBs in the baffle plates of baffle-former assemblies in 2-loop, 3-loop, and 4-loop WEC-designed PWRs. However, EPRI clarified that the 80 percent parameter placed on the 3-by-10 and 4-by-6 BFB arrays and used as the acceptance criterion for initiating sample-expansion to CBF bolts is independent of the size of the baffle plates or number of BFBs in the plates. Thus, EPRIs specified arrays and 80 percent safety margin parameter would be based on the largest size baffle plates among WEC-design 2-loop, 3-loop, and 4-loop PWRs that have the largest population of BFBs, and thus the actual population of BFBs bolts in the specified arrays is not needed for staff acceptance of the definition provided in Note 3 of MRP-227, Revision 2, Table 5-3.
However, as EPRI explained in its RAI response, this amounts to 24 or more degraded BFBs for the 80 percent parameter placed on the 3-by-10 adjacent BFB array and 20 or more degraded BFBs for the 80 percent parameter placed on the 4-by-6 adjacent BFB array.
EPRI clarified that the definition of clustered groupings of BFBs in Note 3 of MRP-227, Revision 2, Table 5-3 (used for the direct sample-expansion basis to the CBF bolts) does not replace the definition of clustered groupings of BFBs in EPRI letter MRP 2017-009 used as part of the basis for establishing the reinspection interval for the BFBs.
Staff Evaluation:
(1) Timing and schedule for performing and completing baseline inspections and reinspections of the BFBs: For the new tier-based Primary Items W6a, W6b, and W6c in TR Table 4-3, the NRC staff finds the updated baseline timing requirements for performing and completing the baseline UT inspections of the BFBs and the maximum periodicity for performing reinspections of the BFBs (using the UT NDE technique) to be acceptable for implementation as discussed below.
To accept the scheduling criteria for performing and completing baseline inspections of the BFBs, the NRC staff confirmed that MRP-227, Revision 2, sets the following updated schedule for performing and completing the baseline UT inspections of the BFBs: (1) for highest ranked Tier 1 BFBs, all baseline inspections of the bolts have been completed, (2) for second highest ranked Tier 2 BFBs, the MRP-227, Revision 2, specifies that the baseline UTs are to be performed no later than 30 effective full power years (EFPY) of licensed plant operations at critical power levels, and (3) for the lowest ranked Tier 3 and 4 categories of BFBs, the MRP-227, Revision 2, specifies that the baseline UTs are to be performed no later than 35 EFPY of licensed plant operations at critical power levels. The NRC staff also confirmed that subsequent UT inspections of the BFBs (regardless of Tier ranking for the Items W6a, W6b, or W6c) need to be established at a
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION reinspection frequency that is dependent on the plant design and the results of the baseline inspections performed on the BFBs, but with a maximum reinspection frequency of no more than a once every 10-year inspection schedule (as established in Note 9 of TR Table 4-3). The NRC staff confirmed that these changes are consistent with EPRIs supplemental augmented inspection criteria established for the BFBs in EPRI letter MRP 2017-009, as previously approved in Section 3.1.3.7 of the NRC staffs SE for the MRP-227, Revision 1-A, report. The NRC staff finds the updated inspection schedules to be acceptable because the staff has confirmed that inspection schedule are sufficient for identifying IASCC mechanism.
Given that the MRP-227, Revision 2, Items W6a, W6b, and W6c, criteria all set a maximum reinspection frequency for the BFBs to a 10-year frequency, the NRC staff finds that the newly defined I&E criteria in MRP-227, Revision 2, Items W6a, W6b, and W6c, serve as an adequate basis for closing the A/LAI #1 topic that was previously raised in Section 3.1.3.7 of NRC staffs SE for the MRP-227, Revision 1-A, report. The rationale for this decision is that A/LAI #1 topic issued in the NRC staffs SE pertained to the potential that the EPRIs technical justification used for establishment of the reinspection interval basis could be used to justify a reinspection frequency for the BFBs in excess of a 10-year basis. Given that MRP-227, Revision 2, Item W6a, W6b, and W6c, criteria now limit the reinspection basis to a maximum 10-year interval, this possibility is eliminated in the MRP-227, Revision 2, justifying closure of the prior A/LAI #1 topic.
(2) Specified NDE methods: The NRC staff finds EPRIs basis for inspecting the Primary category BFBs (independent of tier ranking) and the Expansion LSC bolts and CBF bolts (with the CBF bolts being a secondary tier Expansion category component for the first tier Expansion category LSC bolts under non-clustered conditions) using UT techniques to be acceptable for implementation. In support of this decision, the NRC staff confirmed that the use of UT methods for inspecting the BFBs, LSC bolts, and CBF bolts was previously accepted in NRC staffs SE for the MRP-227, Revision 1-A, report and that use of UT methods for detection of cracking in bolted connections is cited as an approved condition monitoring method in GALL-SLR AMP XI.M16A, PWR Vessel Internals.
(3) Linked Expansion Components, Sample-Expansion Criteria, and Acceptance Criteria (Including the New Criteria for Treating the CBF bolts as First Tier Expansion Category Components Based on Clustered Conditions): The NRC staff finds that the sample-expansion criteria set in the Primary I&E criteria of Items W6a, W6b, and W6c in MRP-227, Revision 2, Tables 4-3 and 5-3, and in the Expansion I&E criteria of Items W6.1 and W6.2 in MRP-227, Revision 2, Tables 4-6, are acceptable for implementation. This includes EPRIs new criteria for treating the CBF bolts as first tier Expansion category components when first-line sample-expansion is triggered by degradation that is detected and confirmed in large clustered groupings of BFBs.
In its review of the MRP-227, Revision 2, Items W6a, W6b, W6c. W6.1 and W6.2, the NRC staff confirmed that, in the new Item W6a for Tier 1 category BFBs, Item W6b for Tier 2 category BFBs, and Item W6c for Tier 3 or 4 category BFBs, EPRI continues to designate that the Item W6.1 CBF bolts and Item W6.2 LSC bolts are the defined Expansion category components for the Primary category BFBs. However, NRC the staff
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION noted that, in the new W6a, W6b, and W6c Primary Items, EPRI amends the sample-expansion criteria, where the need for implementing sample-expansion inspections of the Expansion category CBF bolts (per Item W6.1) and LSC bolts (per Item W6.2) is dependent not only on the percentage of BFBs with detected flaws, but also on the proximity of BFBs with flaws to one another (i.e., detected flaws in isolated BFBs away from each other versus detected flaws in a large clustered grouping of BFBs in close proximity to one another).
The NRC staff confirmed that, under the previous versions of Item W6 in Tables 4-3 and 5-3 of MRP-227, Revision 1-A, EPRI designated that the UT inspections of the BFBs would initiate sample-expansion based on the following type of cascading sample-expansion relationships: (1) first-line population-based sample-expansion UT inspections of the Item W6.2 LSC bolts (as the main Expansion category bolting type for UT), as initiated and completed within three fuel cycles of any BFB inspections that confirm unacceptable indications in more than 5 percent of the BFBs that are actually examined and located on the four baffle plates at the largest distance from the reactor core, and (2) secondary population-based sample-expansion UT inspections of the Item W6.1 CBF bolts (as the secondary Expansion category bolting type), as initiated for sample-expansion within three fuel cycles of any sample-expansion LSC bolt inspections that confirm unacceptable indications in more than 5 percent of the LSC bolts examined as a first-line sample-expansion population set.
The NRC staff confirmed that, in the updated version of Item W6 in MRP-227, Revision 2, Table 5-3, EPRI maintains the same staff-accepted cascading sample-expansion bases for UT inspection relationships between Primary category BFBs, the main Expansion category LSC bolts, and secondary Expansion category CBF bolts.
However, EPRI adds in a new, direct sample-expansion link between Primary Items W6a, W6b, or W6c tier category BFBs and the Expansion Item W6.1 CBF bolts based on UT indications that may be detected in clustered groupings of BFBs located in a single baffle plate or adjacent baffle plates. Under this new clustered-based sample-expansion criterion, EPRI identifies that UT inspections of Primary BFBs that result in confirmation of the presence of a large clustered grouping of degraded BFBs are to initiate visual VT-3 visual inspections (and not UT inspections) of the CBF bolts adjacent to the cluster of degraded BFBs within the following three refueling outages. The NRC staff noted that there were two aspects of this new sample-expansion basis that needed further staff assessment:
(1) the basis for using a VT-3 visual inspection method for the CBF bolts under the large clustered grouping sample-expansion basis and the adequacy of the three refueling outage timing allowance for completing the VT-3 visual inspections of the CBF bolts if a population of BFBs was detected with relevant flaws and the population of BFBs with detected flaws met MRP-227, Revision 2, definition for clustered groupings of degraded BFBs, and (2) a review of MRP-227, Revision 2, definition for clustered groupings of BFBs with detected flaw indications in Note 3 of MRP-227, Revision 2, Table 5-3, in order to determine whether the new definition is acceptable as an acceptance criterion for initiating direct Expansion category inspections of the CBF bolts based on detected clustered groupings of BFBs with noted conditions.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION In terms of using VT-3 visual methods in lieu of UT for sample-expansion inspections of the CBF bolts under clustered conditions, the NRC staff determined that the NDE method is acceptable because it meets the NRC staffs guidance criteria in the detection of aging effects program element of GALL-SLR AMP XI.M16A that specifies VT-3 visual inspection methods may be used to detect and manage cracking in a redundant set of components used for structural integrity objectives (i.e., as is applicable for the redundant set of CBF bolts used to secure the CB to the plants former plates, as is depicted in MRP-227, Revision 2, Figure 4-40). In terms of the timing for implementing VT-3 sample-expansion inspections of the CBF bolts under clustered conditions, the staff verified that the MRP-227, Revision 2, three refueling outage allowance for completing the sample-expansion CBF bolt inspections (when triggered by a clustered grouping of BFBs with unacceptable flaw indications) is identical to the three refueling outage criterion for initiating and completing secondary level sample-expansion UT inspections of CBF bolts based on Expansion category LSC bolt inspection results. That is, if first level UT sample-expansion inspections of the LSC bolts are triggered by the results of the BFB inspections, and sample-expansion to the CBF bolts (as secondary tier Expansion components [without clustered conditions considered]) is triggered upon completion of the first tier Expansion category LSC bolt inspections. As such, the NRC staff finds that the three refueling outage time frame for initiating and completing VT-3 sample-expansion inspections of the CBF bolts is acceptable because the NRC staff has approved the three refueling outage time frame for completing the sample-expansion inspections of the CBF bolts in the NRC staffs SE for MRP-227, Revision 1-A. The NRC staff also finds the three refueling outage time frame for the CBF bolts to be acceptable because the staff has verified that a three refueling outage periodicity for completion of the inspections is sufficiently short-enough period to check whether cracking is occurring CBF bolts without threatening the core support function of the CB assembly at the plant.
(4) New Definition for Large Clustered Groupings of BFBs in Note 3 of MRP-227, Revision 2, Table 5-3. Based on EPRIs additional clarifications that were made in response to RAI 2, Parts 1 - 5, the NRC staff determined that the definition for large clustered groupings of degraded BFBs in Note 3 of MRP-227, Revision 2, Table 5-3, was acceptable for implementation because the definition defines a sufficient safety margin for initiating direct, first-line sample-expansion VT-3 inspections of the CBF bolts prior to structural failure of the baffle plates. The NRC staff finds that the definition for clustered groupings of BFBs in EPRI letter MRP 2017-009 should be used to develop the reinspection interval of the BFBs when a clustered grouping of BFBs is determined to have flaw indications that are found as being unacceptable by the licensee-technical justification referenced in MRP-227, Revision 2, Table 5-3, Item W6. As is stated in EPRIs response to RAI 2, the reinspection interval for WEC-design BFBs is not to exceed an augmented reinspection interval of 10 years.
3.2.3.6 WEC-Design and CE-Design RPV Interior Attachments - Additional OE Impacts Existing Program Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-8, Item C17, CE-design core stabilizing lugs, shims, and shim bolts (for cracking due to SCC in the bolts)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (2) MRP-227, Revision 2, Table 4-9, Item W14, WEC-design clevis insert assembly wear surfaces and bolts (for cracking due to SCC and loss of material due to wear)
NOTE: MRP-227, Revision 2, Item C17 and W14, I&E criteria credit the ASME Section XI VT-3 visual inspections and UT inspections performed in accordance with the PWROG letter No. OG-21-160 as the basis for managing SCC or loss of material (wear) in the specified component types. WEC Non-Proprietary Class 3 Technical Bulleting No. TB-14-5 (WEC 2014) is referenced as a supplemental guideline for the WEC clevis insert assemblies and radial keys.
MRP-227, Revision 2, Issues Needing Resolution:
(1) Needed clarification on the details and technical basis in PWROG letter No. OG-21-160 for performing UT inspections of the specified CE-design lug/shim components and WEC clevis insert assembly components, as the PWROG letter is not a docketed record.
(2) Needed clarification on the basis for omitting the clevis insert dowels from the scope of the specified clevis assembly components in MRP-227, Revision 2, Table 4-9, Item W14. The criteria in EPRI letter MRP 2018-022 (EPRI 2018), Table 5-14, identifies that clevis insert bolts and clevis insert dowels should be managed for cracking due to SCC and loss of material due to wear and that clevis insert wear surfaces should be management for loss of material due to wear.
(3) Requested justifications of why the I&E criteria for managing bolt cracking in the bolting types of MRP-227, Revision 2, Items W14 and C17, are considered to still be capable of managing the specified WEC-design clevis insert assembly components prior to a loss of integrity or intended core support function of the specified clevis insert or core stabilizing lug assembly type.
Applicable RAI:
RAI 1, Parts 1, 2, and 3 (NRC 2023a) and response (EPRI 2024a)
EPRIs Response to the RAI:
On pages 4 - 11 of Attachment 1 in EPRI letter MRP 2024-006 (EPRI 2024a), EPRI provided a detailed response to the requests in RAI 1, Parts 1, 2, and 3. The NRC staff determined that the net effects of the detailed information provided in the RAI 1 responses resulted in the following changes to the I&E criteria in MRP-227, Revision 2, Table 4-8, Item C17, for the CE-design core stabilizing assembly components or in MRP-227, Revision 2, Table 4-9, Item W14, for the referenced WEC-design clevis insert assembly components:
(1) deletion of the UT inspection option and the citation of OG-21-160 as the UT inspection guideline references from the scope of Existing Program Item W14 for the clevis insert assembly components and Existing Program Item C17 for the CE-design core stabilizing lug and shim components,
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (2) the addition and inclusion of the clevis insert dowel pins as additional component type for MRP-227, Revision 2, Item W14 (i.e., in addition to reference of the clevis insert bolts and clevis insert wear surfaces in Item W14), and (3) inclusion of supporting details that VT-3 visual inspections performed on the referenced WEC-design or CE-design Existing Program RPV component types have been capable of detecting cracking or loss of material due to wear in the components prior to a loss of the core support function of this type of RPV core stabilizing lug or clevis insert assembly interior attachment assemblies.
Staff Evaluation:
The NRC staff finds that the I&E criteria for WEC-design Existing Program clevis insert assembly components in MRP-227, Revision 2, Table 4-9, Item W14, and for CE-design design Existing Program core stabilizing lug assembly components in MRP-227, Revision 2, Table 4-8, Item C17 (as amended inclusive of changes to the specified TR items in EPRI letter MRP 2024-006 (EPRI 2024a)) are acceptable for implementation. Under the amended MRP-227, Revision 2, Item C17 or W14 criteria, the items now credit only the existing ASME Section XI VT-3 visual examinations as the condition monitoring-based strategies for managing cracking in the CE-design core stabilizing lug assembly components (for the lugs, shim, and shim bolts) or cracking of the WEC-design clevis insert bolts and dowels and loss of material due to wear in the clevis insert wear surfaces.
Based on EPRIs response to RAI 1, the NRC staff finds the amended versions of MRP-227, Revision 2, Items C17 and W14,to be acceptable because the NRC staff verified that the MRP-227, Revision 2, Items C17 and W14, are consistent with the I&E criteria and aging management strategies recommended the specified CE-design core stabilizing lug assembly and WEC-design clevis insert assembly components in EPRI letter MRP 2018-022. Additionally, the NRC staff has confirmed that, in spite of the past OE, EPRI and licensees of CE-design or WEC-design PWRs have adequately demonstrated to the staff that cracking of these interior attachment components (and loss of material due to wear in the clevis insert assembly wear surfaces) can be adequately managed through a combination of the ASME Section XI VT-3 inspections and licensee-implemented correction actions prior to a loss of the intended core support function. Thus, based on these MRP-227, Revision 2, changes, the NRC staff finds the amended versions of Item W14 in MRP-227, Revision 2, Table 4-9, and Item C20 in MRP-227, Revision 2, Table 4-8, to be acceptable for implementation. The issues in RAI 1 are resolved.
3.2.3.7 WEC-Design Thermal Shield Flexures - Recent OE Impacts Primary Component and Item (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-3, Item W9, thermal shield flexures (for management of cracking due to SCC and fatigue in the flexures during both 40 year initial license renewal and 60 year subsequent license renewal periods)
NOTE: The I&E criteria of MRP-227, Revision 2, Item W9, specify that visual VT-3 inspections will be performed on 100 percent of the accessible surfaces in 100 percent of the thermal shield flexures no later than two refueling outages from the beginning of the
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION license renewal period, with subsequent inspections to be performed on a once every 10-year ISI interval basis. MRP-227, Revision 2, Item W9, criteria reference the guidelines in WEC Technical Bulletin TB-19-5 (WEC 2019) as a basis for performing the scheduled VT-3 visual inspections of the thermal shields.
Linked Expansion Components and Items:
(1) None MRP-227, Revision 2, Issue Needing Resolution:
(1) Needed confirmation that MRP-227, Revision 2, criteria for performing VT-3 visual inspections of the thermal shield flexures on a 10-year reinspection interval basis is still sufficient for detecting and managing cracking in the thermal shield flexures prior to a loss of intended function, when assessed considering the cracking-based industry OE reported for the WEC-design thermal shield flexure component type to date.
Staff Evaluation:
The NRC staff finds the I&E criteria for WEC-design Primary category thermal shield flexures in MRP-227, Revision 2, Table 4-3, Item W9, to be acceptable for implementation, even with the relevant OE considered as discussed below.
The NRC staff confirmed that the basis for inspecting and evaluating thermal shield flexures per the I&E criteria in Items W9 of MRP-227, Revision 2, Tables 4-3 and 5-3, are supported by the OE summary that was provided in MRP-227, Revision 2, Appendix A, and MRP-227, Revision 2, references that identify WEC Technical Bulletin TB-19-5 serves as the basis for resolving the generic OE associated with WEC-design thermal shield flexure cracking. The NRC staff determined that the guidance in TB-19-5 provided sufficient information to support the VT-3 visual inspections of the thermal shield flexures at the specified schedule and frequency. The NRC staff also noted that this is based on the staffs acceptance of WECs statement provided in TB-19-5 that thermal shield flexures are thermal shield supports that do not serve an active safety function. Thus, the NRC staff concludes that I&E criteria in Item W9 of MRP-227, Revision 2, Table 4-3, remain acceptable for implementation because:
(1) the I&E criteria still calls for visual VT-3 inspections of thermal shield flexures even though there is no referenced safety function for the thermal shield flexures in TB-19-5, and (2) any cracking that has been detected in a WEC-design units thermal shield flexures has been demonstrated as being sufficiently dispositioned through implementation of the licensees ASME Section XI ISI process and the licensees corrective actions program.
3.2.3.8 WEC-Design Control Rod Drive Mechanism (CRDM) Penetration Nozzle Thermal Sleeves - Recent OE Impacts Existing Program Components and Items (Aging Effects or Mechanisms):
(1) MRP-227, Revision 2, Table 4-9, Item W21a, CRDM penetration nozzle thermal sleeves for aging management of loss of material due to wear in thermal sleeves - applicable to all WEC-design PWRs identified with thermal sleeves per NSAL-18-1 guidelines (WEC 2018)
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION (2) MRP-227, Revision 2, Table 4-9, Item W21b, CRDM penetration nozzle thermal sleeves for aging management of cracking due to fatigue in the thermal sleeves - applicable only to WEC-design PWRs identified with thermal sleeves having a stepped collar configuration per NSAL-20-1 (WEC 2021) guidelines NOTE: MRP-227, Revision 2, Table Item W21a, credits the specified NDE inspection technique defined in PWROG-16003-P, Revision 2 (PWROG 2024), as the condition monitoring strategy for managing loss of material in the CRDM thermal sleeves. EPRI also cites additional background reports as supporting information for the PWROG-16003-P, Revision 2, Existing Program basis for the component type. This includes the EPRIs reference of the WEC NSAL guidance in NSAL-18-1 (WEC 2018) and the guidance in NRC Information Notice (IN) 2018-10 (NRC 2018). TR Figure 4-50 provides a diagram of the WEC-design CRDM adapter housing, nozzle and thermal sleeve configurations.
NOTE: MRP-227, Revision 2, Table 4-9, Item W21b, was deleted from the scope of the table in the EPRI letter MRP 2024-006 (EPRI 2024a), along with associated administrative edits of the MRP-227, Revision 2, needed for consistency with the deletion of Item W21b (as defined on pages 38 and 39 of Attachment 1 to EPRI letter MRP 2024-006).
MRP-227, Revision 2, Issue Needing Resolution:
(1) Needed clarifications and justifications regarding how the use of laser NDE technology invoked by the PWROG-16003-P, Revision 2, and NSAL-18-1 are deemed as a sufficient condition monitoring-based aging management strategy for detecting loss of material due to wear in the CRDM thermal sleeves. The PWROG-16003-P, Revision 2, and NSAL-18-1 guidelines are not yet staff-approved guidelines or methodologies; they were developed subsequent to the NRC staffs acceptance of MRP-227, Revision 1-A, and prior to the development of the MRP-227, Revision 2, guidelines.
Applicable RAI:
RAI 7, Parts a. and b (NRC 2023a) and response (EPRI 2024a)
EPRIs Response to the RAI:
In its response to RAI 7, Part a., EPRI clarified that the I&E criteria for managing CRDM thermal sleeves wear is provided in the non-proprietary Appendix A part of PWROG-16003-P, Revision 2, and the safety assessment of control rod functionality and loose parts in the proprietary part of PWROG-16003-P, Revision 2. EPRI also explained that the I&E guidance for managing loss of material due to wear in PWROG-16003-P, Revision 2, is basically the same as that for managing wear in of thermal sleeves using the NEI 03-08 Needed Requirements in EPRI letter MRP 2018-027, which was included as an appendix in PWROG-16003-P, Revision 2, along with the inclusion of Tables 1 and 2 from NSAL-18-1. EPRI explained that the criteria in PWROG-16003-P, Revision 2 (as an update of the prior methods in PWROG-16003-P, Revision 1 (PWROG 2018b)) and NSAL-18-1 do not limit laser scanning methods as the only method for performing the physical measurements of the component type, but specify and establish that the performance of the physical measurements performed on the CRDM thermal sleeves must be capable determining the relative distance between a known reference point on the closure head and the bottom surface of the CRDM thermal sleeve guide funnel.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION In its response to RAI 7, Part b, EPRI stated that the PWROG has submitted a docketed version of PWROG-16003-P, Revision 2, in conjunction with EPRIs response to RAI 7.
EPRI clarified that its review of the Existing Program protocols for WEC-design CRDM thermal sleeves has prompted one additional set of changes to the MRP-227, Revision 2, that were outside the scope of the staffs requests in RAI 7. These changes involved EPRIs deletion of TR Item W21b (applicable to CRDM thermal sleeves with stepped collar configurations) from the scope of MRP-227, Revision 2, Table 4-9. EPRI explained that the industry recently published EPRI letter MRP 2023-009 (included in EPRI 2024a)) to document its basis and conclusion that I&E criteria in MRP-227, Revision 2, Item W21b, as originally included in MRP-227, Revision 2, Table 4-9, for managing fatigue-induced cracking of the CRDM thermal sleeves with stepped collar configurations are not necessary for the set of aging management strategies defined in the TR. EPRI stated the removal of Item W21b from the scope of MRP-227, Revision 2, Table 4-9, was based on the technical evaluations provided in NSAL-20-1, Revision 1, in which the PWROG concluded that fatigue-induced cracking of the thermal sleeves will not impede movement of the control rods during normal operations of the reactor (including safe shutdown operations or operations during design basis transient conditions), or during postulated design basis accident or faulted conditions. To support these MRP-227, Revision 2, contents changes, EPRI included EPRI letter MRP 2023-009 as docketed guidance in Enclosure 1 of EPRI letter MRP 2024-006 (EPRI 2024a).
Staff Evaluation:
The NRC staff finds the new I&E criteria in MRP-227, Revision 2, Table 4-9, Item W21a, for managing loss of material due to wear in the CRDM thermals sleeves acceptable for implementation. The NRC staff also finds the deletion of MRP-227, Revision 2, Table 4-9, Item 21b (which previously applied to management of cracking in CRDM thermal sleeves with stepped collar configurations and was deleted in EPRI letter MRP 2024-006), to be acceptable for implementation.
In its review of MRP-227, Revision 2, Table 4-9, Item W21a, for implementation, the NRC staff confirmed that the PWROG-16003-P, Revision 2, criteria categorize WEC-design PWRs for CRDM thermal sleeve wear susceptibility according to those reactor units whose thermal sleeves are considered to be either highly susceptible to wear (i.e., as identified in Table A-1 of Appendix A of the report for units with T-cold operations) or less susceptible to wear (i.e., as identified in Table A-2 of Appendix A of the report for units with T-hot operations). The NRC staff also confirmed that Appendix A of PWROG-16003-P, Revision 2, provides sufficient discussions for performing physical measurements of the CRDM thermal sleeves to monitor for any change in the dimension associated with the bottom of sleeve funnel and RPV closure head reference distance. Under this basis, EPRIs response to RAI 7, Part a, clarifies that use of laser scanning techniques is only one option for performing the needed physical measurement activity of CRDM thermal sleeve seating position on the CRDM housing adapter flange. Given the NRC staffs confirmation that PWROG-16003-P, Revision 2, establishes the needed performance of the physical measurement, the NRC staff concludes that PWROG-16003-P, Revision 2, can be established as the Existing Program condition monitoring basis for the CRDM thermal sleeves.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION In relation to the NRC staffs decision to accept the deletion of MRP-227, Revision 2, Table 4-9, Item W21b, the NRC staff noted that the cracking mechanism identified in the TR Item W21b was not within the scope of aging mechanisms evaluated in NSAL-18-1, which focused on management of wear that could occur in the CRDM thermal sleeves at the CRDM housing adapter flange junction (see MRP-227, Revision 2, Figure 4-50). In this regard, the NRC staff confirmed that: (1) potential cracking of the thermal sleeves was considered as a secondary effect caused by vibrational loads and postulated wear occurring in the thermal sleeves, and (2) the inclusion of Item W21b in MRP-227, Revision 2, Table 4-9, was not needed for the aging management, given that Item W21a in MRP-227, Revision 2, Table 4-9, already accounted for loss of material due to wear in the CRDM thermal sleeves. The issues in RAI 7 are resolved.
4.0 LIMITATIONS AND CONDITIONS The staff did not identify the need to include or issue any limitations, conditions, or A/LAIs in relation to the contents of the MRP-227, Revision 2, as supplemented.
5.0 CONCLUSION
To meet 10 CFR 54.21(a)(3), an application must, for each structure and component identified as subject to an aging management review under 10 CFR 54.21(a)(1), demonstrate that the effects of aging will be adequately managed so that the intended function(s) will be maintained consistent with the current licensing basis for the period of extended operation. Based on its review, the NRC staff finds that MRP-227, Revision 2, provides an acceptable means of demonstrating that the impacts of the effects of aging on the structural integrity of PWR RVI components will be adequately managed during the 60 year subsequent license renewal period of extended operation.
The NRC staff verified that the time-dependent assessments of aging RVI components adequately address a minimum 80-year cumulative period of licensed operations for the PWR facilities.
For WEC-design PWR RVI AMPs, the NRC staff also finds that the updated I&E criteria for BFBs appropriately incorporates the tier-based I&E criteria for the WEC-design BFBs established in the EPRI letter MRP 2017-009, Transmittal of NEI-03-08 Needed Interim Guidance Regarding Baffle-Former Bolt Inspections for PWR Plants as Defined in Westinghouse NSAL 16-01, Revision 1, dated March 15, 2017 (EPRI 2017c). The NRC staff finds that MRP-227, Revision 2, provides an acceptable basis for the NRC staffs closure of the prior A/LAI #1 topic and action that was previously issued in Section 3.1.3.7 of the NRC staffs SE for MRP-227, Revision 1-A.
6.0 REFERENCES
10 CFR Part 21. Code of Federal Regulations, Title 10, Energy, Part 21, Reporting of defects and noncompliance.
10 CFR Part 50. Code of Federal Regulations, Title 10, Energy, Part 50, Domestic Licensing of Production and Utilization Facilities.
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION 10 CFR Part 54. Code of Federal Regulations, Title 10, "Energy," Part 54, Requirements for Renewal of Operating Licenses for Nuclear Power Plants.
[ASME] American Society of Mechanical Engineering, 2017, ASME Code Case N889, Reference Stress Corrosion Crack Growth Rate Curves for Irradiated Austenitic Stainless Steel in Light-Water Reactor Environments,Section XI, Division 1, 2017.
[ASME] American Society of Mechanical Engineers, 2024, American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, Division 1, Rules for Inservice Inspection of Nuclear Power Plant Components (Accepted Editions in 10CFR 50.55a last updated on July 29, 2024, in 89 Federal Register 60795).
[EPRI] Electric Power Research Institute, 2009, Letter from D. Weakland, First Energy/EPRI, to NRC, Re-Submittal of EPRI Commercial Documents; Materials Reliability Program.:
Fracture Toughness Evaluation of Highly Irradiated PWR Stainless Steel Internal Components (MRP 210), MRP 2009-052, August 4, 2009 (ADAMS Package Accession No. ML092230741).
[EPRI] Electric Power Research Institute, 2012, "Materials Reliability Program: Pressurized Water Reactor Internals Inspection and Evaluation Guidelines (MRP 227 A)," MRP 2011-036, January 9, 2012 (ADAMS Package Accession No. ML120170453).
[EPRI] Electric Power Research Institute, 2013, Letter from A. Demma, EPRI, and T. Wells, SNOC, to NRC, "MRP227A Applicability Template Guideline," MRP 2013-025, October 14, 2013 (ADAMS Accession No. ML13322A454).
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Disposition of Curves Development, October 24, 2014 (Proprietary, not publicly available).
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7.0 ABBREVIATIONS AMP aging management program ASME American Society of Mechanical Engineering B&W Babcock and Wilcox BB baffle-to-baffle BFB baffle-former bolts CB core barrel CBF core barrel-to-former CE Combustion Engineering CEA control element assembly CGR crack growth rates CLB current licensing basis CRDM control rod drive mechanism CRGT control rod guide tube CS core shroud CSB core support barrel CSBFW core support barrel flexure weld CSS core support shield DB Davis Besse ECT eddy current test EFPY effective full power years EPRI Electric Power Research Institute EVT enhanced visual testing FD Flow Distributor FSAR final safety analysis report GALL Generic Aging Lessons Learned GALL-SLR Generic Aging Lessons Learned-Subsequent License Renewal I&E inspection and evaluation IASCC irradiation-assisted stress corrosion cracking ICI in-core instrumentation ID inner diameter IE irradiation embrittlement ISI in-service inspection
OFFICIAL USE ONLYPROPRIETARY INFORMATION OFFICIAL USE ONLYPROPRIETARY INFORMATION LCB lower core barrel LIA lower internals assembly LSC lower support column LSS lower support structure LTS lower thermal shield MRP Materials Reliability Program NDE non-destructive examination NEI Nuclear Energy Institute NRC U.S. Nuclear Regulatory Commission NSAL nuclear safety advisory letter OD outer diameter OE operating experience PC plenum cover PWHT post-weld heat treatment PWR pressurized water reactor PWROG Pressurized Water Reactor Owners Group RAI request for additional information RCS reactor coolant system RPV reactor pressure vessel RVI reactor vessel internal SCC stress corrosion cracking SI safety injection SSHT surveillance specimen holder tube TR topical report UAW upper axial welds UCB upper core barrel UGW upper girth welds UFW upper flange weld UFSAR updated final safety analysis report UIA upper internals assembly UT ultrasonic test UTS upper thermal shield VS void swelling WEC Westinghouse Electric Company