ML23107A230
| ML23107A230 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute |
| Issue date: | 03/31/2023 |
| From: | Uhle J Nuclear Energy Institute |
| To: | Andrea Veil Office of Nuclear Reactor Regulation |
| References | |
| Download: ML23107A230 (1) | |
Text
JENNIFER UHLE, Ph.D.
Vice President Technical and Regulatory Services 1201 F Street, NW, Suite 1100 Washington, DC 20004 P: 202.247.5717 jlu@nei.org March 31, 2023 Ms. Andrea Veil Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Project Number: 689
Subject:
Industry Recommendations for a 10 CFR 50.46a/c Combined Rulemaking
Dear Ms. Veil,
The Nuclear Energy Institute (NEI) 1, on behalf of its members, is writing to provide additional insights following the January 24, 2023, Commission meeting on accident tolerant fuel (ATF).
As discussed in the Commission meeting, much has changed since the NRC staff proposed the final rule language to the Commission in SECY-16-0033, Performance-Based Emergency Core Cooling System Requirements and Related Fuel Cladding Acceptance Criteria. In particular, advancements have been made in analytical methods, fuels technologies, and manufacturing techniques that warrant reconsideration of the proposed requirements. In addition, the recently passed Inflation Reduction Act (IRA) incentivizes utilities to provide more carbon-free energy to the grid and utilities are seeking power uprates, as summarized in the NEI report entitled, The Future of Nuclear Power - 2023 Baseline Survey.
As a result, we recommend that the NRC consider initiating an expedited rulemaking that would revisit the requirements proposed in SECY-16-0033, the so-called 10 CFR 50.46c draft final rule, while also incorporating draft final rule language that the staff submitted to the Commission in SECY-10-0161, Risk-informed Changes to Loss-of-Coolant Accident (LOCA)
Technical Requirements, the so-called 10 CFR 50.46a rulemaking. Completion of the combined rulemaking on a timeline that is consistent with the rulemaking effort summarized in SECY-21-0109, Rulemaking Plan on Use of Increased Enrichment of Conventional and Accident Tolerant Fuel Designs for Light-Water Reactors, would yield a modernized and risk-1 The Nuclear Energy Institute (NEI) is responsible for establishing unified policy on behalf of its members relating to matters affecting the nuclear energy industry, including the regulatory aspects of generic operational and technical issues. NEIs members include entities licensed to operate commercial nuclear power plants in the United States, nuclear plant designers, major architect and engineering firms, fuel cycle facilities, nuclear materials licensees, and other organizations involved in the nuclear energy industry.
Ms. Andrea Veil March 31, 2023 Page 2 informed Emergency Core Cooling System (ECCS) rule that would efficiently enable the deployment of advanced fuel designs, including ATF, higher enrichment and higher burnup.
We believe the NRC can take the extra time needed to achieve this outcome since the NRC staff affirmed the safety of the operating plants under the current regulatory requirements with its latest 2021-2022 ECCS performance safety assessment 2:
This assessment found that, due to measured cladding performance under loss-of coolant accident (LOCA) conditions, realistic fuel rod power history, and current analytical conservatisms, sufficient safety margin exists for operating reactors.
NRC senior management further acknowledged this fact during the January 24, 2023, Commission 3 meeting stating that the 10 CFR 50.46c proposed final rule would provide a negligible benefit to plant safety:
The statement that there is negligible safety provided when you look at the current fleet, that's true.
Given the negligible safety implications, taking the extra time would permit the NRC staff and the public to reconsider some of the unnecessary burden in the draft 10 CFR 50.46c final rule.
Such an approach could reduce the industrys backfitting concerns expressed in our letter dated November 17, 2016 4. In addition, implementation of the current draft final rule language would unnecessarily divert NRC resources to an issue of negligible safety significance since it would require that all holders of an operating license submit a license amendment application to reanalyze their ECCS performance within no later than 60 months and be in compliance with the rule no later than 84 months after the rule is finalized. These are the same industry and NRC staff resources currently working on the licensing of the safety-enhancing ATF technologies. They would need to be diverted to complete the fleet-wide compliance demonstration of a rule which the NRC has stated has negligible safety benefit, delaying the industrys ATF program significantly.
In summary, NEI believes revisiting the draft final rule language of 10 CFR 50.46c in a rulemaking that also permits a risk-informed treatment of LOCA on a timeline consistent with the current rulemaking effort summarized in SECY-21-0109 would more efficiently and effectively enable deployment of advanced fuel designs, including ATF, higher enrichment, and higher burnup. The industry adoption of advanced fuels will enable safer operation, provide 2
NRC ECCS Performance Safety Assessment and Audit Report, January 31, 2023; ML23032A196.
3 NRC Commission Meeting - Overview of Accident Tolerant Fuel Activities January 24, 2023, page 88, ML23026A288.
4 ML16323A432, NEI Letter, Supplemental Comments on SECY-16-033 Draft Final Rule - Performance-Based Emergency Core Cooling Systems Cladding Requirements and Related Fuel Cladding Acceptance Criteria (Docket ID NRC-2008-0332) (RIN 3150-AH42), November 17, 2016.
Ms. Andrea Veil March 31, 2023 Page 3 improved operational margins, more efficient fuel cycle utilization, reduced used fuel generation, and permit power uprates to generate more carbon-free electricity.
Specific industry recommendations associated with the rulemaking are attached.
If you have any questions, please contact me or Dr. Aladar Csontos at aac@nei.org or (202) 557-9727.
Sincerely, Jennifer Uhle
Ms. Andrea Veil March 31, 2023 Page 4 Attachment 1: Industry Technical Recommendations The industry offers the following comments pertaining to a combined SECY-10-0161 and SECY-16-0033 ECCS rulemaking. These comments are not considered to be comprehensive, but rather identify key areas for modernization and improvement.
SECY-10-0161:
The SECY-10-0161 draft final rule focused on risk-informed changes to align the assumptions for LOCA analysis to the initiating event. It created different standards for break ranges below and above a transition break size (TBS), based upon the lower event probability of occurrence and risk above the TBS. That regulatory effort is consistent with the Commissions continued direction and drive towards more modern and risk-informed regulation. For example, the Commission directed the staff in SRM-SECY-21-0109 5 to take a risk-informed approach when developing the regulatory basis and guidance to address and analyze fuel fragmentation, relocation, and dispersal (FFRD) issues relevant to fuels of higher enrichment and burnup levels. However, like SECY-16-0033, much time has passed since the NRC staff began developing a risk-informed approach to ECCS requirements over fifteen years ago. Since 2010, considerable advancements in Probabilistic Risk Assessment (PRA) and Probabilistic Fracture Mechanics (PFM) technologies have been made along with widespread industry adoption of risk-informed programs and peer review of PRAs using RG 1.200 PRA methods. The following recommendations are not comprehensive but are intended to illustrate some areas of SECY-10-0161 that should be modernized to account for current practices:
- 1. Industry recommends removing the requirement for the unnecessary Low Power and Shutdown Modes PRA in light of the industry advances in shutdown risk management (e.g., continuing improvements to NUMARC 91-06 defense-in-depth practices) and the negligible risk impact of 10 CFR 50.46a implementation during these modes of operation. The industry agrees that PRA quality must be adequate to calculate the risk impact from adoption of the rule. However, the risk impact of LOCAs greater than the TBS in low power shutdown modes is negligible and therefore this requirement is unnecessary.
- 2. Given more recent experience and knowledge, industry recommends removing the requirement for plant specific seismic analyses to demonstrate applicability of the TBS in the draft final rule, and to instead focus industry and NRC resources on demonstration of validity of PRA success criteria. NUREG-1903, Seismic Considerations for Transition Break Size, provided a technical analysis that dispositioned the need to 5
SRM-SECY-21-0109, Rulemaking Plan on Use of Increased Enrichment of Conventional and Accident Tolerant Fuel Designs for Light-Water Reactors
Ms. Andrea Veil March 31, 2023 Page 5 consider the impact of seismic events on the TBS given the very small contribution to potential failure modes. The rule, however, still calls for plant-specific seismic analysis to support application of the TBS. Per NEIs March 6, 2006, letter on the topic (Attachment 4 of ML060660036), The change in risk (delta risk) relative to seismic events is estimated to be negligible based on the fact that the TBS threshold does not directly impact either the seismic hazard (the seismic hazard is the same whether the SECY-10-0161 draft final rule was established or not) or the plant SSC seismic fragilities (the fragilities are a function of the structures/equipment construction, their design, their load path, their anchorage, etc. Establishing a TBS does not alter these from a seismic fragility perspective). More recent experience, analyses, and knowledge allow for more efficient ways of confirming that the conclusions of NUREG-1903 remain valid, with an emphasis on confirmation that the existing PRA success criteria remain valid following implementation.
- 3. The industry recommends that the evaluation model and compliance metric be established with a level of probability commensurate with risk. In the early stages of the 50.46a risk-informed rulemaking 6, a lower level of assurance commensurate with the likelihood of occurrence was proposed for piping breaks beyond the TBS. Hence, lower probability, larger piping breaks beyond the TBS would be allowed to demonstrate compliance in a more realistic manner. By the final draft rule (2010), the level of assurance reverted back to a high level of probability for both the more probable smaller piping breaks and breaks beyond the TBS. The final draft rule does not align with the intent of the risk-informed rulemaking.
- 4. The industry recommends the rulemaking extend the use of leak-before-break (LBB) for fuel licensing. This approach would provide additional realism for the greater than TBS break sizes and help resolve the LOCA induced fuel fragmentation, relocation and dispersal (FFRD) issue for high burnup fuel. Some safety benefits include but are not limited to the generation of less used fuel, reduced public and worker doses associated with the storage and transportation of this reduced inventory of used fuel, less worker dose due to elimination of outages for PWRs, and the lower risk of fuel handling, dry cask loading and transportation accidents with less used fuel. A revision to the current policy should be considered for its application to LOCA-induced FFRD.
6 Risk-Informed Changes to Loss-of-Coolant Accident Technical Requirements, FRN 70 FR 67597, November 7, 2005.
Ms. Andrea Veil March 31, 2023 Page 6 As stated in the NRC Policy Statement on Additional Applications of Leak-Before-Break Technology 54 Federal Register 18649 dated May 2, 1989:
Nonetheless, the Commission has decided to keep open an avenue for future consideration of rulemaking which would permit the application of LBB to ECCS and EQ. The Commission encourages industry to develop quantitative information that could justify the diversion of resources to the rulemaking efforts. Primary attention should be given to establishing an appropriate substitute or replacement for the double-ended pipe rupture used in ECCS and EQ evaluations. The Commission will consider modifying the current ECCS and EQ regulations when adequate technical justification supports the feasibility and benefits of the proposed modifications.
Deterministic fracture mechanics and PFM technologies have advanced substantially since this policy statement was issued, and LBB applications were approved for specific piping systems. LBB has been evaluated for a number of conditions and degradation mechanisms that could lead to pipe rupture. Some of these degradation mechanisms are not applicable to piping system above the proposed TBS. Piping systems that have been evaluated using the NRCs fracture mechanics analysis procedures support a determination that detectable leaks will occur before pipe rupture and support a determination that the probability of piping rupture is extremely low (<10E-6 per reactor-year).
SECY-16-0033:
The SECY-16-0033 draft final rule would update the regulations to capture the state-of-knowledge from research conducted in the 2000s on degradation mechanisms to fuel technologies. This rule rapidly became out-of-date as the industry moved to more modern fuel systems and improved manufacturing processes. While the industry recognizes that the degradation mechanisms identified in the SECY-16-0033 rule are relevant, the industry has made significant gains in understanding, predicting, and addressing these mechanisms. As an example, U.S. fuel vendors have implemented improved manufacturing processes that mitigate the identified degradation mechanisms in SECY-16-0033 and demonstrated that manufacturing processes are such that U.S. fuel is not susceptible to breakaway oxidation under postulated LOCA conditions. Furthermore, the SECY-16-0033 rulemaking was completed prior to the initiation of the industrys ATF program and does not consider the additional mitigative effects of ATF on those degradation mechanisms. The following recommendations are not
Ms. Andrea Veil March 31, 2023 Page 7 comprehensive but are intended to illustrate some areas of SECY-16-0033 that should be modernized to account for current practices:
- 1. The industry recommends that the implementation of the SECY-16-0033 requirements in a combined rulemaking be flexible and commensurate with required licensing changes consistent with plant specific licensing obligations. Certain future plant changes, such as power uprates, adoption of advanced fuel cladding materials, and/or high energy fuels, will result in both licensees and the regulator evaluating the need to adopt the new combined rule based on its safety benefit. This ensures that critical industry resources are not diverted from the licensing efforts associated with safety-enhancing ATF fuel systems.
- 2. Industry recommends improving the regulatory stability and durability of the combined rule by including a streamlined technology-neutral and regulatorily efficient approach that incorporates the beneficial safety impacts of ATF technologies. Substantial progress has been made on near-term ATF technologies that demonstrate mitigative effects to the identified degradation mechanisms in SECY-16-0033. The draft final rule does not consider these positive effects of ATF on those degradation mechanisms. The near-term commercial licensing and deployment of these ATF technologies should be addressed in a technology-neutral generic manner in the rulemaking.
At the ATF Commission Meeting on January 24, 2023, the staff identified a benefit of the elimination of exemption requests by approving the SECY-16-0033 rule. However, the SECY-16-0033 rule was fundamentally based on the failure mechanisms of the historically used zirconium-based claddings. As written, the rule may result in even more exemptions. For example, paragraph (g) provides a means to demonstrate compliance to the high-level criteria for uranium oxide or mixed uranium-plutonium oxide pellets within cylindrical zirconium-alloy cladding. Even the near-term ATF designs could be considered to challenge these rigid definitions, and based on the rule language proposed, would limit the incorporation of the safety benefits they offer. Coated-zirconium cladding ATF design concepts lead to differences in high-temperature oxidation kinetics and degradation mechanisms of the coating. As such, the SECY 0033 rule would produce fewer exemptions for the claddings already licensed (e.g.,
AXIOM, M5, and Ziron), but progressive technologies would require more exemptions to reflect their safety value.
Ms. Andrea Veil March 31, 2023 Page 8
- 3. Industry recommends an update to the SECY-16-0033 rule language in paragraph (g)(1)(iii) with regard to the periodic breakaway oxidation testing requirement. The draft regulation states:
The breakaway oxidation behavior must be periodically confirmed using an NRC-approved experimental technique capable of determining the effect of composition changes or manufacturing changes on the breakaway oxidation behavior. The frequency of confirmatory testing must provide reasonable assurance that fuel is being manufactured consistent with the specified analytical limit.
The draft final rule requires periodic testing for breakaway oxidation behavior, and the statement regarding the frequency can be interpreted in different ways. NRC approved fuel vendors use high levels of quality assurance and manufacturing standards for adequate control of the delivered fuel product. Factors affecting the onset of breakaway oxidation in zirconium tubing are alloy chemistry, final surface condition, the method of zirconium reduction as well as ingot fabrication, etc. These aspects are part of the vendors controlled manufacturing processes. NEI recommends that the issue be handled as a vendor-specific licensing action and a breakaway oxidation testing requirement be added to the change control process defined in the material specification to ensure that no process or equipment changes significantly reduce the breakaway oxidation resistance. This would allow the requirement for breakaway oxidation testing frequency to be removed from the regulation.