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NEI - Spent Fuel Management: Safety and Efficiency Improvements Through Technology and Performance Margins - NRC PIRTs Public Meeting Rev. 8.15.2024 Final
	ML24229A001
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Site:	Nuclear Energy Institute
Issue date:	08/19/2024
From:	Richter M; Nuclear Energy Institute
To:	; Office of Nuclear Material Safety and Safeguards
	Daneira Melendez
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Spent Fuel Management:

Safety and Efficiency Improvements Through Technology and Performance Margins NEI-NRC Public Meeting Mark Richter Technical Advisor Nuclear Energy Institute August 19, 2024

Congress sent a clear signal that nuclear is essential to the transition to a clean energy economy Backbone of stable electric grid Meeting growing demand for more clean energy ADVANCE Act Maintains U.S. global leadership Enables testing, demonstration and deployment of accident tolerant fuels and advanced nuclear reactor fuel concepts Supports modernization of licensing and oversight of operating reactors Nuclear Energy: National Importance

Embodies NRC Principles of Good Regulation PIRT Implementation is a Key Opportunity to Modernize

©2024 Nuclear Energy Institute 4 Advanced fuels may increase source term and decay heat Load canisters more efficiently with shielding while reducing dose, handling and improving spent fuel pool management Ultra conservative assumptions reduce safety and efficiency Actionable definitions of gross rupture, performance-based peak clad temperature and thermal margin enable efficiencies and flexibility in analysis and operations-enhance safety and efficiency Use of performance-based results provides a good example of how NRC can use risk insights and allow us to live up to our collective safety imperative The Opportunity

w w w. e p r i. c o m Keith Waldrop Senior Technical Leader August 19, 2024 Spent Fuel PIRTs -

Pathway to Implementation NRC Public Meeting

6 Background

Recommendations IV-1-5 Goals: Update thermal modeling methods for improved focus on safety including a revised thermal modeling metric and a graded approach for thermal modeling to expand margins and operational flexibilities with increased safety and cost savings Most efficient regulatory implementation vehicle pending further discussions:

EPRI Topical Report and/or NRC Standard Review Plan update DEFINING SPENT FUEL PERFORMANCE MARGINS by NEI Spent Fuel Margins White Paper Development Task Force November 8, 2019

7 Background

Fuel Performance PIRT

- The onset of fuel failure is not abrupt, but rather a continuum no cliff-edge effect is associated with the current NRC recommended 400 °C limit (ISG-11 Rev. 3)

Decay Heat PIRT

- Regulatory guidance (RG. 3.54 Rev. 1) significantly overestimates decay heat over wide range of fuel burnups.

Thermal PIRT

- Excess conservatism in thermal calculations leads to negative impact on worker dose and fuel performance

8 Background

Gross Rupture PIRT

- RCS chemistry records from operation may be used to establish if fuel cladding gross rupture failure occurred to determine storage requirements Alternate Fuel Performance Metrics PIRT

- Increasing PCT limit to 450oC or 500oC are potentially acceptable metrics to pursue Other metrics considered but not recommended: hoop stress, average cladding temperature Excessive Layers of Conservatisms More dose to the workers Less regulatory efficiency

9 Objectives of PIRTs Implementation Define pathways to leverage the benefits of all the PIRTs for Gross Rupture PCT and Graded Approach

10 Gross Rupture

11 Gross Rupture Topical Report - Background Unclear guidance in NUREG-2215

- p xxviii: Gross Breach. A breach in the spent fuel cladding that is larger than either a pinhole leak or a hairline crack and allows the release of particulate matter from the spent fuel rod.

- p8-35 SFAs with any of the following characteristics are expected to be classified as damaged:

Reactor operating records or fuel classification records indicate that the SFA contains fuel rods with gross breaches.

- p8-36: gross breaches should be considered to be any cladding breach greater than 1 mm (0.04 in.).

And in NUREG-2216

- p7-49: The staff considers that adequate reactor operating records that identify only gaseous or volatile decay products (no heavy metals) in the reactor coolant system are acceptable evidence that cladding breaches are no larger than a pinhole leak or hairline crack.

Current definition of gross rupture non-actionable due to:

Lack of criteria regarding use of reactor operating records

Demonstration that 1mm criteria is met difficult to achieve

12 Gross Rupture Topical Report Scope

- Implement new definition to use chemistry records in lieu of fuel inspections (e.g. sipping) to demonstrate cladding integrity Safety benefits of New Gross Rupture Definition

- Better comply with ALARA principles Reduce dose to the workers

- Reduce risk Avoid unnecessary handling by minimizing need for sipping campaigns and pool-side exams New definition of gross rupture to clarify NRC guidance and allow stakeholders to use consistent and actionable metrics Clarity Efficiency Reliability FSARs and CoC do not preclude the use of the new gross rupture definition

13 Topical report

- Technical basis for new definition of gross rupture based Input from Gross Rupture PIRT Guidance regarding:

- Applicability criteria (e.g., quality of chemistry records)

- Key parameters to survey (e.g., increase in fuel products concentration during cycle and vs.

previous cycle)

Impacts on SRP and other NRC guidance documents

- Generic Directly referenceable by licensees Gross Rupture Topical Report CoC amendments may not needed Most CoCs already have wording that allows using the new definition Underlying documents for fuel qualification may need to be changed + criteria used in site procedures Review / approve TR (SER)

Revise guidance (SRP storage and transportation) industry does not need to wait to start implementing once SER is issued Revise inspection criteria Expected Industry Actions Expected NRC Actions

14 Benefits for the NRC Clarification of NRC guidance inconsistencies

- Definition of gross rupture currently non-actionable by industry

- Inconsistency between storage and transport SRPs

- Comply with principles of good regulation Generic implementation of criteria change for broad adoption

- Reduce regulatory burden and review Recommendations to update guidance

- RCS chemistry applicability criteria

- Technical justification of key parameters Reduce risk

- Eliminate unnecessary fuel moves Better compliance with ALARA principles

- Eliminate unnecessary dose-consuming activities Reduce undue burdens

- Reduce number of damage fuel containers

15 PCT and Graded Approach

16 PCT and Graded Approach Topical Report Scope

- Implement increased PCT limit of 450oC Include a graded approach for storage and transportation safety analyses Safety benefits

- Shorter loading times

- Fewer canisters loaded

- Regulation efficiency increased

- Risk-informed analyses leveraged Operational Flexibility

- More time for certain operations,

- Eliminate supplemental cooling system,

- Add shielding Compliance with ALARA principles, such as:

Public: Less transportation events (precursor)

Workers: Increased shielding, Fewer/shorter loadings

17 Performance Margin - Fuel rod has additional capacity to go to higher temperature without failure Methods Margin - Conservatisms in the modeling Graded approach would require increased analytical rigor to tighten uncertainties as you approach 450°C limit Peak Cladding Temperature - Graded Approach Analytical Rigor PCT (°C) 400 425 450 Uncertainties reduction through analytical rigor Objective: Develop a risk-informed and graded approach and avoid making licensing more complicated with additional analyses where more margin exists

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©2019 Nuclear Energy Institute 18 NAC-STC High-Burnup Fuel Amendment Excessive analytical level of detail (academic exercise) required for a licensed system resulting in no impact to the safety of the design NAC initially provided thermal analysis, based on the existing NRC approved thermal methods/models for the NAC-STC to support reasonable assurance the cask would perform as required No basket design changes Change in individual fuel thermal loads and loading pattern NRCs thermal reviewers suggested that NAC needed to develop and qualify new, best estimate models for assessing HBU fuel performance, and included directions to use NUREG-2152 (authored by the thermal reviewers) for the development and qualification of thermal models

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©2019 Nuclear Energy Institute 19 Why the industry believes the PIRT work and applying Risk Informed criteria is Valuable In 2019-20, NAC submitted an amendment for a content change using the license basis MOE.

Ultimately, regulatory direction, via RAI, was for NAC to develop 3 brand new discrete thermal models to support a methodical discretization allowing performance of a Grid Convergence Index (GCI).

Why? Because NACs reported PCT was within 25C of the 400C limit If the PCT limit is really a safety limit and Risk Informed Regulation determines that reporting temperatures within some percent triggers the need to address uncertainties (i.e. GCI performance) then this should be clear to the licensee through regulation and not invoked through the RAI process.

After a long RAI process ultimately involving the GCI methodology, the associated costs to the project and delays in licensing resulted in a little over one degree F lower PCT for the three additional models.

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NAC was had no choice but to develop 3 brand new discrete thermal models (utilizing 900K, 3000K, 7200K elements including mesh refinement in axial direction) to support a methodical discretization allowing development of a Grid Convergence Index (GCI)

Performance of this work required over 2000 additional man-hours, demonstrated no significant change in PCT and resulted in no changes to the design or loading configuration(s)

Proximity (~25F) of our calculated PCT, with no credit given for conservatisms in the model, to the PCT limit was used as the basis for requiring the GCI be performed Model ID Number of Hexahedral Elements PCT (F)

T (F)

Model No. 1 7,168,000 633 151 Model No. 2 3,024,000 632 151 Model No. 3 896,000 629 151 Base Model 95,672 638 153

21 Benefits for the NRC Improved clarity, efficiency, and reliability

- Graded approach to apply resources more efficiently and effectively Generic implementation of criteria change for broad adoption

- Reduce regulatory burden and review Recommendations to implement updated metrics into future NRC guidance

- Clarify limits and uncertainties

- Reflect better understanding of thermal margins into NRC guidance Risk-informed application of operational margin to be leveraged to:

- Decrease dose to the workers

- Decrease operational risks by eliminating unnecessary actions

22 Implementation

23 Potential Pathway SRP / Guidance Updates Gross Rupture TR Gross Rupture TR NRC Review SER Plant Procedure Updates Fee waiver request PCT TR PCT TR NRC Review Gap Data SER Vendor CoC Amendment Plant document updates NRC Review Amendments Fee waiver request Case Study Next:

Future:

24 Timeline September 2024: Fee Waiver Request Letter for Gross Rupture TR Q1 2025: Gross Rupture TR TBD: Fee Waiver Request Letter for PCT and Graded Approach TR TBD: PCT and Graded Approach TR Duration NRC review?

If fee waiver for GR approved If fee waiver for PCT approved

25 Summary

- The 5 PIRTs provide strong basis to improve regulatory efficiency, clarity and reliability for all stakeholders.

- Objective is to improve safety and efficiency:

Decrease dose to the workers Reduce accident precursor events (transportation)

Improve realism to optimize safety and efficiency

- Near term: Gross Rupture TR Fee waiver request Directly applicable recommendations to improve regulatory guidance

- Longer term: PCT and Graded Approach TR Increased PCT limit Graded approach Operational impacts

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

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