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ATF Fuel Fragmentation, Relocation, and Dispersal Consequences Workshop 3
	ML25260A541
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Issue date:	09/19/2025
From:	Delosreyes J; Licensing Processes Branch
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ATF Fuel Fragmentation, Relocation, and Dispersal Consequences Workshop 3 September 18, 2025 September 19, 2025

Meeting visuals and audio are through MS Teams.

Participants are in listen-only mode until the discussion and public feedback period. During which, we will first allow in-person attendees to participate, then allow remote attendees to un-mute.

Remote attendees should utilize the hand raised feature in MS Teams, if possible.

This is an Observation Meeting. Public participation and comments are sought during specific points during the meeting.

NRC will consider the input received but will not prepare written responses.

No regulatory decisions will be made during this meeting.

This meeting is being recorded.

Meeting Logistics

Meeting Purpose

Discuss the NRCs and industrys positions on topics related to performance monitoring, inspections, and seismic risk.

Provide feedback on NEI and EPRIs proposed white paper on Materials Degradation Research and NEI 03-08 Materials Initiative.

Provide an opportunity for members of the public to ask questions of the NRC staff.

The NRC is not looking for feedback on the Increased Enrichment (IE)

Rulemaking.

Proposed Workshop Schedule Workshop 1 (May 20-21)

- Fuel Fragmentation, Relocation, and Dispersal

- Recriticality Workshop 2 (July 30-31)

- Exemptions

- Coolability

- Reporting Workshop 3 (Today)

- Materials

- Inspections Workshop 4

- Transition Break Size

- Graded Approach

Agenda - Day 1 Time Topic Speaker 9:00 am Welcome NRC 9:05 am Opening Remarks NRC, NEI 9:10 am Performance Monitoring Through Inspections and Demonstrating Acceptable Seismic Failure Risk NRC 10:00 am Discussion 10:30 am Break 10:40 am Demonstration of the Proven Effectiveness of Existing Materials Management and Inspection Programs NEI, EPRI 11:20 am NRC Efficiency Improvements NEI 11:30 am Discussion 12:00 pm Adjourn NRC Topic times are estimated based on the participation level and presentation length.

Agenda - Day 2 Time Topic Speaker 9:00 am Welcome NRC 9:05 am Discussion 10:30 am Break 10:40 am Discussion 11:45 am Public Comment Period 11:55 am Closing Remarks NRC, NEI 12:00 pm Adjourn NRC Topic times are estimated based on the participation level and presentation length.

Opening Remarks

Performance Monitoring Through Inspections and Demonstrating Acceptable Seismic Failure Risk Nuclear Regulatory Commission ATF Fuel Fragmentation, Relocation, and Dispersal Consequences Workshop #3 NRC Headquarters September 18 - 19, 2025

Performance Monitoring

Performance Monitoring (PM) is one of the 5 fundamental considerations in a risk-informed licensing change under 1.174

PM options are limited for reactor coolant pressure boundary (RCPB) passive components (i.e., piping)

Pressure/hydrostatic testing to evaluate structural integrity beyond leak-tightness is not required nor is it practical

Leakage monitoring not considered PM as it is inconsistent with GDC-14

Provides effective defense in depth (DID) in systems exhibiting leak-before-break (LBB)

Chemistry control provides assurance that global conditions exist to limit degradation but does not address localized variability or degradation within acceptable limits

Inspections are the most valuable PM tool that can provide both generic and plant-specific assurance that degradation rates are acceptable Integrated Decision Making Defense in depth Performance Monitoring Increase in risk is small Change meets current regulations Safety Margins ATF Public Workshop: September 18-19, 2025 2

RCPB Piping Weld Inspections: History

ASME Section XI (IWB-2500) specifies conventional in-service inspection (ISI) requirements for NPS > 4 B-J welds

Requires a 25% inspection sample

Terminal ends connected to vessels

Terminal ends connected to other components with high applied stress or cumulative usage factor (CUF) associated with operation and seismic

Non B-F dissimilar metal welds

Can include additional hot leg and cold leg welds to reach 25%

Plants have been implementing alternative risk-informed ISI (RI-ISI) for approximately the last 30 years

Approved plant-specific requests to use ASME CC N-560, N-578

Approved generic RI-ISI topicals: WCAP-14572, Rev 1; EPRI TR-112657

Approved ASME Section XI, Appendix R, Supplement 2 (EPRI TR-112657) in 10 CFR 50.55a

Approved ASME CC N-716-3 in RG 1.147, Revision 21

RI-ISI provides smaller, less prescriptive inspection sample ATF Public Workshop: September 18-19, 2025 3

RCPB Piping Weld Inspections:

Section XI, Appendix R, Supplement 2

Define risk categories from high consequence, high failure potential (1) to low consequence, low failure potential (7)

Inspection for segments (consequence + DM) susceptible to FAC, IGSCC, and PWSCC are defined through owners programs

Users can count these inspections as part of their sample

Sampling requirements

Risk categories 1 - 3: 25% inspection sample

Risk categories 4 - 5: 10% inspection sample

Risk categories 6 - 7: exempt from inspection requirements

If application scope only applies to B-J welds, excluding socket welds

Elements selected starting with high-risk group and working toward the low-risk group until 10% sample obtained

No more than 50% of owners program examinations credited toward the 10% inspection sample

When selecting welds, following shall be considered

Elements susceptible to DMs

Plant-specific cracking experience

Availability of previous examination results

Inspections for each DM and combination of DMs

Risk Category 4 inspections based on stress concentration, terminal ends, or geometric discontinuities

Accessibility

Minimization of worker exposure

Minimization of support services (e.g., scaffolding, insulation, and rigging)

Inspection reductions from existing program justified by change-in-risk evaluation ATF Public Workshop: September 18-19, 2025 4

RCPB Piping Weld Inspections: CC N-716-3

Owners programs for components susceptible to erosion-cavitation, IGSCC, PWSCC, and MIC

Other requirements based on degradation mechanism (DM) and safety significance

Inspections only required for high safety significance (HSS) components

LSS exempt from Section XI inspection requirements, except VT2

Global 10% sample of piping welds, prorated among butt and socket welds

Can credit IGSCC welds toward global requirement

Remaining welds selected as follows 1.

25% of welds susceptible to an identified DM 2.

10% of RCPB welds including at least 2/3rd of these between RPV and first isolation valve (or 25%

between RPV and first isolation valve) 3.

10% of RCPB welds outside containment 4.

10% of welds within break exclusion region

If more than 10%, prorate categories 1 - 4 to reach 10%

When selecting welds, following shall be considered

Plant-specific cracking experience

Weld repairs

Random selection

Minimization of worker exposure

Inspection reductions from existing program justified by change-in-risk evaluation ATF Public Workshop: September 18-19, 2025 5

RI break exclusion region (BER)

Piping passing through containment penetrations to first outside isolation valve

Branch Technical Position MEB 3-1: 100% volumetric inspection or postulate breaks/leaks

EPRI TR-1006937 (NRC approved in 2002)

Extended TR-112657 methodology to BER

More focus on direct and indirect failure consequence assessment, consistent with SRP 3.6.2

Sampling requirements: high risk (25%) and medium risk (10%) elements for the RI-ISI and BER-only populations

The number of BER inspections should not be significantly less than 10% of the BER scope unless plant design features justify otherwise.

BER requirements are included in CC N-716-3

High Energy Line Break (HELB)

Break postulation and mitigation for higher stress and cumulative usage factor locations

EPRI 3002028939 (NRC approved in 2025)

Extended TR-112657 methodology to HELB

Develops HELB response strategies instead of optimizing inspections

Categories 1, 3: Validate FAC program

Category 2: Reduce consequences and/or 10% inspections based on DM, or follow existing HELB requirements

Category 4: Modify plant to reduce consequences or follow existing HELB requirements

Category 5: Validate FAC, modify plant to reduce consequences, or 10% inspections based on DM Extension of RI-ISI Concepts ATF Public Workshop: September 18-19, 2025 6

ASME Section XI: inspections of 10 steam generator (SG) and 5 pressurizer (PZR) items every interval

No evidence of degradation found to date

Potentially high consequences of rupture at inspection locations

PFM analyses concluded that failure risk is less than 1x10-6/yr

EPRI 3002032184 submitted for NRC review in June 2025

Developed fleet-wide optimized inspection plan

Provides PM using 25% sampling criterion from binomial distribution model

Assumed 5% defect rate and 90% probability of detecting one occurrence

Sample population: Code-required PZR inspections over next 30 years

Plan recognizes units with existing PM commitments obtained through Request for Alternative submittals

Inspection plan provides continual generic data and will be updated on a regular basis Steam Generator and Pressurizer Inspections ATF Public Workshop: September 18-19, 2025 7

Performance monitoring required for potentially high failure consequence components to provide assurance that plant risk remains acceptable

Volumetric inspections can provide reliable generic and plant-specific performance monitoring

Inspection sample should include components with potentially high failure consequences

10% to 25% of subject population are common targets

Inspections should be risk-informed and focus scope on highest failure likelihood locations under both normal operational and upset/seismic loading

Current inspections can be credited toward achieving an appropriate inspection sample

Inspections should occur on a consistent basis and findings with potential generic implications should be widely shared in a timely manner

Fleet-wide inspection may be appropriate to satisfy these objectives but plant-specific performance monitoring should be performed consistent with RG 1.174 principles Performance Monitoring Considerations ATF Public Workshop: September 18-19, 2025 8

Seismic risk not explicitly considered when determining LOCA frequencies in NUREG-1829

Objective is to ensure that the seismic risk is less than the normal operational risk

Seismic risk is an inherently plant specific convolution of seismic hazard and component fragility

Site location

Site characteristics

Plant configuration

Direct and indirect seismic risk can be addressed by existing evaluations (e.g.,

seismic PRA, seismic margin assessment) as long as component fragilities appropriately address potential effects of plant aging

Demonstrate that seismic risk is less than failure risk due to normal operation

Demonstrate that risk of failure of large piping components is a minor risk contributor Seismic Risk Considerations ATF Public Workshop: September 18-19, 2025 9

Addressing potential effects of plant aging

Gross material loss through corrosion or flow accelerated corrosion not expected to be applicable in RCPB piping

Loss of material fracture toughness in combination with the existence of flaws is one possible scenario

Loss of fracture toughness due to thermal aging

No significant effects expected in carbon steel or nickel-based alloy material systems

Affects cast austenitic steel (CASS) materials with certain chemistries (i.e., high delta ferrite and high Mo)

Affects stainless steel welds, more so for flux welds (i.e., SAW and SMAW) than GTAWs

Potential cracking mechanisms in susceptible materials

Thermal or mechanical fatigue

SCC has only been experienced in U.S. plants in off-normal, or crevice-type conditions Direct Seismic Risk Considerations ATF Public Workshop: September 18-19, 2025 10

1.

Qualitatively identify systems and weld locations with the highest potential failure risk due to seismic events 2.

Evaluate materials at those locations to determine potential for loss of fracture toughness 3.

Leverage results of existing or planned inspections at those locations to demonstrate that no unacceptable flaws exist 4.

If either 2 or 3 can be demonstrated, no further evaluation is required 5.

If neither 2 or 3 can be demonstrated, further evaluation may be needed 6.

Utilize existing current seismic evaluations to demonstrate indirect seismic risk is acceptable

Leverage existing PRA requirements

Leverage existing plant walkdown and maintenance requirements to address non-piping failure potential (e.g. supports, snubbers) and associated risk Possible Screening Approach for Evaluating Seismic Risk Northeastern U.S. Seismotectonic Source Zones (from NUREG/KM-0017)

ATF Public Workshop: September 18-19, 2025 11

Discussion Period

Break

w w w. e p r i. c o m EPRI Nuclear Materials Materials and Inspection Workshop Rockville, MD September 18, 2025 Demonstration of the Proven Effectiveness of Existing Materials Management and Inspection Programs Date: 08/18/2025

2 o

Updated analyses using the Extremely Low Probability of Rupture (xLPR) probabilistic fracture mechanics tool confirm that the original LOCA frequency estimates remain applicable, even when accounting for extended plant lifetimes and new data.

Validation of NUREG-1829 o

The industry remains committed to maintaining robust inspection programs including the RI-ISI programs, which ensure that high-risk piping segments are inspected with appropriate frequency and rigor, including similar metal stainless steel welds.

Inspection Program Effectiveness o

The NEI 03-08 framework, supported by Industry Materials Programs, has enabled the industry to anticipate and address degradation mechanisms before they impact safety.

Proactive Industry Initiatives Executive Summary The industrys current materials management and inspection infrastructure is sufficient to ensure continued safe operation of nuclear power plants without the need for additional piping fabrication searches and weld inspection requirements.

The conclusions of NUREG-1829 remain valid and applicable to the operating fleet, supporting the use of TBS without the need for plant-specific justification.

3 Contents NEI 03-08 Materials Initiative & Industry Materials Programs Current Inspection Programs Validation of NUREG-1829 Summary and Conclusions

4 Overview of NEI 03-08 Materials Initiative & Industry Materials Programs

5 NEI 03-08, Guideline for the Management of Materials Issues Documents the Materials Initiative and defines the scope Establishes policy - Each licensee will endorse, support and meet the intent of NEI 03-08 Defines roles, and responsibilities

- Executive / Management oversight

- Issue Programs (IPs)

- Utilities Approved unanimously by NSIAC in May 2003 Initiative was effective January 2, 2004 Current version is Revision 4, effective October 2020

6 NEI 03-08 Materials Initiative Objective and Purpose The objective is to assure safe, reliable and efficient operation of the U.S. nuclear power plants in the management of materials issues.

The purpose of this Initiative is to:

- Provide a consistent management process

- Provide for prioritization of materials issues

- Provide for proactive approaches

- Provide for integrated and coordinated approaches to materials issues Utility actions required by this Initiative include:

- Commitment of executive leadership and technical personnel

- Commitment of funds for materials issues within the scope of this Initiative High priority, emergent, and long-term issues

- Commitment to implement applicable guidance documents

- Provide for oversight of implementation

7 NEI 03-08 Benefit to U.S. and International Members Assures the Materials Programs are well integrated Consistent technical quality and rigor built into the work and products of the IPs Confidence that senior management perspectives are included, and programs will be living programs NEI 03-08 programs have effectively resolved / manage generic issues and gained USNRC acceptance Documents are recognized world-wide as aging management tools

- Referenced in USNRC Generic Aging Lessons Learned (GALL)

- Also recognized IAEAs International Generic Aging Lessons Learned report (IGALL)

Shows the Materials Programs are an excellent platform from which to develop plant and country specific aging management programs

8 NEI 03-08 Materials Initiative Accomplishments Integrated industry strategic plan for materials Achieved a high level of industry integration, coordination, alignment, and communication on material issues Established a process for prioritizing projects, budgets, and planning Predictable funding for materials R&D Engaged INPO as an active participant Defined expectations and protocols for industry actions upon discovery of an emergent issue Established consistent process for deviations and communication with NRC Executive level interactions between industry and senior NRC management Successful at closing materials issues and gaps Fewer unexpected materials related transients

9 US NRC Feedback on the NEI 03-08 Materials Initiative NEI 03-08 Revision 3 was transmitted to US NRC in March 2017

- US NRC issued a thank you letter to NEI in April 2017 NRC quote: We find that the NEI 03-08 program is a valuable component in achieving safe operation of nuclear power plants. -John Lubinski In 2023, NRC evaluated two options for action in their LIC-504 Risk Informed Safety Assessment of the French stainless steel piping stress corrosion cracking issue:

- Option 1: Establish targeted inspections and revision of inspection requirements for these piping locations

- Option 2: Take No Action but continue to monitor industry action NRC chose Option 2 noting in a 2/21/2024 presentation:

- With the implementation of the [industry] NEI 03-08 needed recommendation, the locations most susceptible in the non-isolable piping will be inspected with a SCC qualified technique Safety margins and performance monitoring will be maintained

10 EPRI Materials Aging Management Cycle

6. Optimize Inspections Increased confidence in ageing management strategies leads to optimized inspection requirements with respect to scope and frequency.

5. Calibrate Models Improve accuracy and technical robustness of databases that provide inputs to materials models; calibrate conservatism applied to ageing management strategies.

4. Address High-Priority Gaps Conduct research on representative materials, perform simulations, develop new models to address high-priority assessment and degradation mechanism gaps.

1. Collect Operating Experience EPRI SMEs collect data from field reports and inspection results and assess the efficacy of corrective actions (mitigation, repair, replacement).

2. Review Research Results Updated research results from EPRI

programs, technical literature, and conferences are reviewed by EPRI SMEs.

3. Evaluate Technical Gaps Review gaps from previous IMT (close, keep open, re-rank); define new gaps based on OE; prioritize gaps with utility members.

Materials Degradation Matrix (MDM) Revision 5 (3002030559; Nov 2024)

BWR Issue Management Tables BWRVIP-167 Rev. 4 (3002018319; June 2020)

PWR Issue Management Tables MRP-205 Rev. 4 (3002018255; September 2020)

Both being revised based on MDM, Rev 5

11 Systematic Approach to Prioritizing Industry Issues MDM IMT Materials Degradation Matrix Issue Management Tables Every material, every potential degradation mechanism, and status of knowledge

- Mapped to 80 years of operation

- Covers BWR, PWR, CANDU, & VVER Every component/material, failure modes, mitigation, repair/

replacement, I&E Guidance Knowledge Gaps identified and prioritized

- Covers BWR, PWR, CANDU, & VVER Revision 5: 3002030559 PWR: 3002018255 (MRP-205, R4)

BWR: 3002018319 (BWRVIP-167, R4)

VVER: 3002021033 (MRP-471)

CANDU: 3002031002 (IMR-101)

12 MDM Revision 5: PWR Example - Primary Pressure Boundary Piping The status was conservatively set to yellow to reflect potential gaps in knowledge with respect to the identification of susceptible components based on the recent OE with SCC of non-isolable branch piping in the safety injection system of some plants.

Rev 4 Rev 5

Ohi-3 (2020), KEPCO Pressurizer spray line, weld HAZ 4.4 mm depth, circum. crack.

Suspected cause: high surface hardness.

Several EDF N4/P4 Plants (2021-2023)

Cold leg SI & RHR suction lines.

Shallow but long circum. cracks.

Suspected cause: high stress thermal stratification + weld residual.

Aux. Piping IGSCC

13 Overview of Existing Inspection Programs

14 Overview of Existing Inspection Programs Risk Informed Inservice Inspection

Focuses inspections on high-risk piping segments using probabilistic and deterministic methods

NRC-approved methodologies (Traditional & Streamlined) implemented across 100% of U.S. fleet

Enhances safety while reducing unnecessary inspections and regulatory burden Augmented Inspection Programs Performance Demonstration Initiative Targeted inspections for known degradation mechanisms (e.g., SCC, thermal fatigue)

Supports early detection and Industry-wide commitment to proactive materials management Standardized qualification of ultrasonic NDE systems (personnel, procedures, equipment)

Ensures high reliability in flaw detection and sizing, aligned with ASME and NRC standards

15 RI-ISI Overview and Methodologies Structured processes for identifying risk-significant components:

- Traditional (EPRI TR-112657): Uses consequence and failure potential evaluations to classify piping segments

- Streamlined (ASME Code Case N-716): Predefines high safety significant (HSS) piping and supplements with plant-specific outlier search Inspection Focus:

- High-risk segments: 25% inspection population.

- Medium-risk segments: 10% inspection population

- Low-risk segments: No periodic NDE required Similar Metal Welds:

- RI-ISI programs include similar metal welds in primary loop piping (PLP)

Surveyed plants confirm these welds are being sampled under RI-ISI protocols

16 RI-ISI Benefits and Implementation Safety Enhancement: Focuses inspections on components with highest failure potential and safety impact Efficiency Gains: Reduces unnecessary inspections, minimizing worker exposure and operational costs Regulatory Alignment: Supports NRC PRA Policy Statement and RG 1.174 for risk-informed decision-making NUREG-1829 Relevance: RI-ISI programs cover LOCA-sensitive piping, validating continued applicability of Transition Break Size (TBS)

Stainless Steel Weld Inclusion: Welds with elevated SCC risk are routinely examined RI-ISI Methodologies are NRC Approved RI-ISI implementation was available and in use during the development of NUREG-1829

17 Summary of Plant Survey Results 37 plants (25 PWRs and 12 BWRs) were surveyed to determine the number of PLP similar metal piping circumferential welds being examined under the RI-ISI program Reactor Type

of Units Surveyed NSSS Design

of PLP SMW Exams Description of PLP Locations Selected for RI-ISI Examination PWR 13 West 4-Loop and 2-Loop 48 Hot leg and cold leg SMW locations adjacent to RV nozzle-to-safe end DMWs 5

B&W Lowered Loop 36 Hot leg, cold leg and crossover leg SMW locations 7

CE 2-Loop 61 Hot leg, cold leg and crossover leg SMW locations BWR 12 GE BWR-1, 2, 3, 4, 5 and 6 194 SMW locations with a NPS greater than the largest diameter FW or RHR piping Totals 37 339

18 Industry Augmented Inspection Programs The Inspection Programs differ in their focus, scope, and methodologies, however they share common goals of inspecting critical welds (e.g., leading indicators), both dissimilar and similar metals MRP-139 MRP-146 MRP-192 BWRVIP-75-A BWRVIP-155 BWRVIP-196 Like RI-ISI, Augmented Inspection Programs enhance the safety and reliability of nuclear power plants by focusing inspection efforts on the most critical components while considering the likelihood of degradation and defense in depth

19 MRP-146 and MRP-192 Provide thermal fatigue monitoring and inspection guidelines for non-isolable branch lines in the RCS and mixing tees

- These lines often experience more severe stress and environmental conditions than the main reactor coolant loop, making them early indicators of potential degradation mechanisms in similar metal welds French SS SCC was discovered during similar thermal fatigue inspections

- The industry proactively applied MRP-146 using NEI 03-08 guidance to ensure that any potential SS SCC in the U.S.

fleet would be identified at an early stage, if present

20 MRP-139 and ASME Code Case N-770 Addresses Primary Water Stress Corrosion Cracking (PWSCC) in Alloy 600/82/182 materials used in PWR reactor pressure vessel nozzles and dissimilar metal welds

- Regulatory Alignment: Informed ASME Code Case N-770, mandated by 10 CFR 50.55a Analyses (MRP-480, xLPR) show Alloy 82/182 welds are more limiting than similar metal, which demonstrate high flaw tolerance Fleet-wide inspections per 10 CFR 50.55a ensure effective oversight of the most limiting PLP components

21 BWRVIP-75-A In conjunction with Generic Letter (GL) 88-01, provides a comprehensive inspection framework for BWR austenitic stainless steel piping welds susceptible to Intergranular Stress Corrosion Cracking (IGSCC).

Risk-Based Optimization: Revises inspection schedules from Generic Letter 88-01 to concentrate resources on welds with greater IGSCC risk, particularly non-resistant welds without stress improvement.

Industry Impact: Aligns with NRC requirements and enhances understanding of material degradation, supporting the development of future optimized aging management programs.

22 BWRVIP-155 AND BWRVIP-196 Provide thermal fatigue screening and inspection guidance for BWRs, analogous to MRP-146 and -192 for PWRs.

Proactive Screening: BWRVIP-155 defines methods to evaluate stagnant branch connections for thermal fatigue susceptibility, even without prior operating experience in BWRs.

Limited Susceptibility: BWRVIP-196 addresses mixing tee fatigue risks in two BWR systems, recommending inspections or operational checks despite minimal BWR operating experience.

23 EPRI PERFORMANCE DEMONSTRATION INITIATIVE (PDI)

Purpose of PDI: Provides a rigorous framework for qualifying ultrasonic examination systems used in nuclear piping inspections, including those within the scope of NUREG-1829.

Regulatory Compliance: Ensures inspections meet ASME and NRC standards, enhancing reliability and safety across nuclear power plants.

Industry Value: Participation in PDI supports continued safety, reliability, and efficiency for utilities, vendors, and regulators.

Since 1994, EPRI has led the PDI program, qualifying over 100 procedures, conducting hundreds of thousands of personnel tests, and supporting adoption in multiple countries.

24 NUREG-1829 Comparative Analyses Leak Detection Leak Before Break

25 NUREG-1829 Comparative Analyses MRP-480, Materials Reliability Program: xLPR Estimation of PWR Loss-of-Coolant Accident Frequencies, was used to evaluate PWR piping systems identified as LOCA-sensitive in NUREG-1829

- Investigated dissimilar metal welds and stainless steel welds EPRI has since investigated welds in carbon steel piping as well

26 NUREG-1829 Comparative Analyses Used xLPR, which is a state-of-the-art probabilistic fracture mechanics code jointly developed by the NRCs Office of Nuclear Regulatory Research and EPRI MRP-480 key outputs:

- Rupture frequency outputs (which were compared against LOCA frequency estimates given in NUREG-1829)

- Time between detectable leakage and LOCA

- Time between detectable leakage and rupture Investigated 20 additional years of service experience since NUREG-1829 was published

27 NUREG-1829 Comparative Analyses Alloy 82/182 dissimilar metal welds Most limiting in the PLP

- Most cases showed zero rupture occurrence when inspection and leak rate detection were credited Nonzero rupture cases were part of sensitivity analyses and do not reflect realistic operating conditions Evaluation of time between leakage and rupture showed that operators had sufficient time to identify leakage and shutdown reactor Results demonstrates that substantial margin between the target break frequency and the typical TBS used by Licensees sufficiently accounts for plant-to-plant variability, making plant-specific justification of NUREG-1829's applicability unnecessary Similar metal welds

Minimal flaw growth No leaks or ruptures Demonstrated high flaw tolerance, consistent with operating experience Carbon steel welds had similar performance to stainless steel welds

28 Leak Detection Capabilities Operating plant leakage action levels are grounded in a risk-informed approach, supported by PRA, operating experience, and engineering judgment, ensuring that the recommendations are both conservative and practical Enhanced safety through early detection is supported by xLPR demonstrating a significant window for intervention

29 Leak Detection Capabilities For example, WCAP-16465 provides standardized guidance for PWR licensees on establishing RCS leakage action levels and response guidelines

- RCS leakage is classified into distinct levels based on severity and potential impact:

Action Level 1: One seven (7) day rolling average of daily Unidentified RCS leak rates > 0.1 gpm Action Level 2: Two consecutive daily Unidentified RCS leak rates > 0.15 gpm Action Level 3: One daily Unidentified RCS leak rate >

0.3 gpm

30 Leak-Before-Break All operating PWRs in the US have received Leak-Before-Break (LBB) approval for the PLP

- One additional reactor that is restarting is pursuing LBB LBB approval demonstrates that leak detection systems are sufficient, making plant-specific leak detection evaluations redundant LBB evaluations are used to confirm that breaks larger than the TBS are extremely unlikely

- Supports the continued use of generic TBS values without requiring plant-specific justification, as long as LBB conditions are met

31 01 02 03 The fleet continues to implement a substantive ongoing inspection program for the reactor coolant pressure boundary inclusive of the PLP.

The likelihood of a break larger than the TBS continues to be extremely remote is applicable to the operating fleet without the need for plant-specific justification.

The substantial margin between the target break frequency and the typical TBS used by Licensees sufficiently accounts for plant-to-plant variability.

SUMMARY

Industry programs focused on leveraging operating experience, sound engineering principles, and advanced analytical tools to ensure that the reactor coolant pressure boundary is effectively managed

32 Conclusion The industrys current materials management and inspection infrastructure is sufficient to ensure the continued safe operation of nuclear power plants

- Existing inspection programs appropriately prioritize the highest safety and risk significance welds

- Decades of additional operating experience have not revealed new degradation mechanisms that would challenge the assumptions of NUREG-1829 The conclusions of NUREG-1829 remain valid and applicable to the operating fleet, supporting the continued use of TBS without the need for plant-specific justification

- The likelihood of a break larger than the TBS continues to be extremely remote

33

w w w. e p r i. c o m TOGETHERSHAPING THE FUTURE OF ENERGY

Remove 5 wt% U-235 limit

Increase to policy limit of 20 wt% U-235

Improved regulatory efficiency and durability:

ATF/LEU+/HBU and 24-month fuel cycle Advanced reactor fuels 50.46a: Risk-Informed LOCA

Proposed Final Rule Discontinued in 2016

Voluntary, risk-informed alternative to 50.46

Increased potential for larger power uprates

Improved realism for advanced fuel licensing

Allows enrichments to LEU+/HAELU

NUREG-2266 for up to 10 wt% U235 enrichments & 80 GWd/MTU burnup

Existing UF6 packages <10 wt% U235

Amended control room dose design criteria (5 to 25 Rem TEDE)

Improved AST models in RG 1.183R2

Reduced risk significance of LOCA/FFRD

ATF/LEU+/HBU and uprates do not reasonably increase piping degradation

Current programs addressing concerns

Address degradation issues in AMPs, ASME Code, etc. but not in the IE rule 50.46c: Acceptance Criteria for ECCS

Proposed Final Rule withdrawn in 2024

Accounts for fuel embrittlement mechanisms

Excessive burden for little to no safety benefit

Commission returned it to the staff and required combining 50.46a/c with the IE rulemaking

Questions

Discussion Period

Public Comment Period

Closing Remarks

Adjourn

ML25260A541

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