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M211209: Slides - Briefing on 10 CFR Part 53 Licensing and Regulation of Advanced Nuclear Reactors - E Lyman Slides
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UCS Perspectives on Part 53 Dr. Edwin Lyman Director of Nuclear Power Safety Climate and Energy Program Union of Concerned Scientists December 9, 2021

The foundation of a new reactor licensing rule

A new reactor licensing rule should

- Clearly provide for levels of safety, security, and environmental protection at least equivalent to the operating fleet

Or preferably, greater levels than the operating fleet

- Employ risk-informed provisions only to the extent that state-of-the-art risk assessment methods allow

- Maintain robust defense-in-depth

- Contain clear requirements for prototype testing

- Reject provisions that could result in disproportionate outcomes to disadvantaged communities 2

The Part 53 process is broken

Although UCS appreciates the greater degree of public engagement for developing the draft rule language required in SRM-SECY-0020-0032, the intermittent and iterative process has been ineffective and inefficient, and the high degree of industry involvement threatens to compromise the NRCs regulatory independence

- What was intended to be a flexible, technology-inclusive approach has split into at least three alternatives

Following the next release of draft language, UCS recommends that a more conventional notice-and-comment rulemaking process be restored, and that the NRC consider developing a regulatory basis document 3

Part 53 should be scrapped

Development of a technology-inclusive rule does not require starting from scratch and rewriting the entire rule book

The population of new reactor designs that the NRC is likely to receive for review for many years to come is not actually that diverse

- Coolants: liquid-metal, gas, molten salt

- Fuels: metal, TRISO, molten salt

- Size: very small (<20 MWe), small (<300 MWe); medium (<600 MWe)

The accident spectrum is fairly well-characterized for many of these design categories 4

Alternative approach Rather than a new part, NEIMAs intent can be addressed through a series of appendices to Parts 50/52

- Coolant-specific, size-specific, and fuel specific Each appendix specifies

- All regulations in Parts 50/52 that are not applicable

- Design-specific alternatives for inapplicable requirements that correspond to a safety or security function (e.g. 50.46)

Anticipated operational occurrences, design-basis accidents, and severe accidents determined through a structured process such as the Licensing Modernization Project, with sufficient error bars on frequency estimates to adequately encompass uncertainties Should be complemented with a requirement to conduct systematic searches for hazards, initiating events, and accident scenarios, as recommended by ACRS 5

Core safety approach

To ensure a clear correspondence with requirements for the operating fleet, fundamental defense-in-depth principles for AOOs and DBAs should be maintained on an equivalent level, including safety-related SSCs and the single-failure criterion

Severe accident risks should not be greater than those for the operating fleet (more on this later) 6

Alternative approach Part 53 will duplicateor may even be inconsistent withother rulemakings taking place for new reactors

- Limited-scope security

- EP requirements The risk-informed licensing approach should focus first and foremost on the design and construction of the plant

- Requirements covered by other parts of the regulations should remain where they are

- risk-informed voluntary alternatives should be available once designs have been approved (or demonstrated)

A structured approach is needed for application of analytical safety margins to operating flexibilities to ensure sufficient layers of defense-in-depth are maintained 7

Severe accidents and the use of PRA

There is no credible way to risk-inform licensing without a PRA other than providing defense-in-depth measures with unquantified risk benefitsi.e. a deterministic approach

There is no plausible way to define a maximum credible accident without a PRA (maximum credible implies a likelihood threshold) 8

Role of Quantitative Health Objectives in licensing

The QHOs are not adequate metrics for incorporation as regulatory requirements

- Magnitude is too high

latent fatality QHO corresponds to CDFs from 5x10-4 for an open containment (NUREG-1860) to 4x10-2 for a frequency-weighted average risk (2018 EPRI Margins study), compared to an average of 5x10-5 for the operating fleet

- Do not include societal risks (land contamination)

- Are based on population-averaged radiological risks that are insensitive to the disproportionate effects of ionizing radiation on disadvantaged populations such as Black people 9

Conclusion