Some Thoughts on Safety Goals
George Apostolakis
Former Commissioner, NRC
Former Member, ACRS
Director, Nuclear Risk Research Center
apostola@mit.edu
http://criepi.denken.or.jp/en/nrrc/index.html
Presented at theACRS Subcommittee Meeting on
Perspectives on Safety Goal Policy
August 24, 2023
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Changes over the years“safety goals are intended to be applied genericallyand are not for plant specific applications.“(Commission’s Policy Statement, 1995)•Individual plant CDF and LERF are compared to thegoals routinely.

Informal upper limits are implemented.
CDFs greater than 10-3 per ry prompt immediate action.

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Multi-Unit and Adjacent Sites• U.S.A.

 Currently at most 3 units Plant Vogtle will have 4
 Geographically adjacent sites: Salem 1&2 (PWRs) and HopeCreek (BWRs 3 total, PSEG); Nine Mile Point 1&2 (BWRsConstellation Energy) and FitzPatrick (BWRs Entergy 3total)• Canada Bruce Power: 8 units• Japan Kashiwazaki-Kariwa: 7 units

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Whole-Site Risk: Early Consideration• In the early 1980s, the NRC staff proposedthat Safety Goals be applied on a per-sitebasis• Commission decided not to impose a“bias” against multi-unit sites• Quantitative Health Objectives (NRC) are
now interpreted on a per-reactor basis

4How stable should the QHOs be?
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The QHOs are a commitment to society.
As such, they should be revised only when there iscompelling evidence that they should be.
One could argue that the Fukushima accident did
not violate the NRC’s QHOs.
Is this a valid comparison?
A Level 3 PRA prior to the accident would probably
have shown that the goals were not met.
There had been serious warnings that the tsunami
height had been underestimated.

5Some Proposals• “Our results suggest that the number of people
relocated is a good proxy for societal disruption, andrelatively straightforward to calculate. “ (Bier et al,PSAM 12, 2014)• “There should be no significant likelihood that alargescale, long-term evacuation will be needed as aresult of a nuclear power plant accident.” (Mubayi
Youngblood, Nuclear Technology, 2021)

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CNSC Technical Safety Objectives forNew Plants• Likelihood of accidents with serious radiologicalconsequences should be extremely low.
• Potential radiological consequences from severe
accidents limited to as far as practicable.

Greg Rzentkowski, Presentation at 34th Annual Conference ofCanadian Nuclear Society, Toronto, June 9-12, 2013

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CNSC Proposed Quantitative Safety
Metrics for New Plants• Frequency of severe core degradation (SCDF) < 10-5
per reactor year
• Frequency of release of 1015 Bq of I-131 triggering
evacuation < 10-5 per reactor year
• Frequency of release of 1014 Bq of Cs-137 triggering
long-term relocation < 10-6 per reactor year
SCDF “… the effects of adjacent units at multi-unit stations are considered
and accounted for when calculating the Safety Goals for internal events
sequences at the representative unit (generally, the lead unit).”LRF “The assessment is done per reactor year with due account of theeffects of adjacent units at multi-unit stations”
G. Rzentkowski, Y. Akl, and S. Yalaoui, Application of Probabilistic Safety Goals
to Regulation of Nuclear Power Plants in Canada.
8ACRS Letter, April 2004 (1)• The Quantitative Health Objectives (QHOs) apply tothe site as a whole. The sum of the contributions
from each reactor on the site to acute and latent
fatalities should be bounded by the QHOs.
• The Committee has not reached consensus on theapproach that should be taken to determine the coredamage frequency (CDF) goal. Two views arepresented in the discussion below.

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ACRS Letter, April 2004 (2)• Option 1

 The site goal (e.g., 10-4 per ry) is divided by the number ofunits at the site.
 The risk from and the likelihood of a core damage accidentat all sites cannot be precisely equal. However, there is theexpectation that they be comparable.

• Option 2

 CDF is an accident prevention goal and its value should be
the same for each reactor at every site.
 Requiring each module to have a CDF value given by theoverall CDF goal divided by the number of modules
introduces a new Safety Goal concept, a site CDF. Such a
concept was never intended to be part of the Safety Goals.

10Part 53 Metrics• The total frequency of exceeding a site boundary
dose of 100 millirem (mrem) from all LBEs shall not
exceed 1/plant-year.
• The average individual risk of early fatality within 1
mile of the exclusion area boundary from all LBEs
shall not exceed 5×10-7/plant-year.
• The average individual risk of latent cancer fatalities
within 10 miles of the exclusion area boundary fromall LBEs shall not exceed 2×10-6/plant-year.

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NEI (Nov. 5, 2021)•••

it is unclear why the NRC believes the QHOs must
be in the rule at all, rather than relying on the longstanding implementation of QHOs through theNRC’s Safety Goal Policy.
If the QHOs are in the rule, they must be met for
legal compliance, and since the PRA is the basis formeeting the QHOs, more, if not all, of the PRA willneed to be submitted on the docket and would be
subject to contention.
It is recognized that regardless of whether theQHOs are in the Safety Goal Policy or Rule
Language, the design, analysis, and licensing
approach that would be taken by an applicant, andthe NRC scope of review would be the same.
12NEI (Nov. 5, 2021)• There is at least one member of industry thatbelieves QHOs must be in the rule to provide
regulatory predictability by avoiding the need todevelop surrogate metrics for the QHOs.
• Therefore, more discussion on the benefits anddisadvantages of the options of how to address
QHOs in a way that achieves both predictability andflexibility would be beneficial.

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PRA
• If applicable, the PRA should include event
sequences involving two or more reactor modules aswell as two or more sources of radioactive material,
which could include waste processing and storage
systems. (NRC staff)• A standard exists: ASME/ANS RA-S-1.4-2021,
Probabilistic Risk Assessment Standard for
Advanced Non-Light Water Reactor Nuclear PowerPlants

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NRC Staff (1)• Risk-informed performance standards, including theQHOs, provide a fixed cumulative risk standard forlicensing events ranging from anticipated event
sequences to very unlikely event sequences.
• Without these cumulative risk standards in
Framework A, including the QHOs, there would be noequivalent to the collective effects of the prescriptive
requirements in Parts 50 and 52 that provide
reasonable assurance of adequate protection of
public health and safety.
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NRC Staff (2)• compliance with the existing totality of NRC(prescriptive) regulations provides reasonableassurance that adequate protection is maintained.
• Framework A proposes to support the adequate
protection finding with a collective set of functionoriented and performance-based requirements.
These requirements are intended to ensure that theproposed new regulations provide a level of safetycomparable to that required by the existing
regulations in Parts 50 and 52.

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NEI 21-07, Rev. 1, February 2022
•The PRA information included in Chapter 2 of theSAR should be at a summary level only asdescribed below. It should address the requirementin 10 CFR Part 52 that the SAR includes adescription of the PRA and its results.

•The applicant maintains complete PRA
documentation in its plant records.

•The supporting methods, data, and detailed
information used in the PRA will not be included in
the SAR but will be available for NRC audit.
17Conclusions
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The issue of major societal disruption should beinvestigated further for possible inclusion in thesafety goals. Comparisons with Fukushima should
be reevaluated.
The QHOs should be included in Part 53.
Doing a credible PRA for all sources of radioactivity
at the site will be challenging, even with theexistence of the JCNRM Standard.
The NRC staff should provide additional help
perhaps using insights from the PRA Level 3project.
The license application should include a PRA
summary and insights only. PRA details should beavailable to the NRC staff,18

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