ML21067A002

ACRS Version Response to Public Comments on DG-4026 Rev 0, Volcanic Hazards Assessment for Nuclear Power Reactor Sites - Proposed RG 4.26

ML21067A002
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Issue date:	03/05/2021
From:	Jacqueline Thompson NRC/NRR/DEX/EXHB
To:
O'Donnell E
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ML20272A070	List: ML20272A168 ML20272A169 ML20272A170 ML21064A403 ML21067A002
References
RG 4.26 DG- 4028, DG-4026
Download: ML21067A002 (13)

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Response to Public Comments on Draft Regulatory Guide (DG)-4026 Volcanic Hazards Assessment for Nuclear Power Reactor Sites Proposed Regulatory Guide (RG) 4.26 On March 19, 2020 the NRC published a notice in the Federal Register (85 FR 16147) that Draft Regulatory Guide, DG-4026, a proposed new Regulatory Guide was available for public comment. The Public Comment period ended on May 19, 2020. The NRC received comments from the individuals or organizations listed below. The NRC has combined the comments and NRC staff responses in the following table.

Comments were received from the following:

Kevin Coppersmith Anonymous Coppersmith Consulting, Inc. ADAMS Accession No. ML20086H877 2121 N. California Blvd, #290 Walnut Creek, CA, 94596 kevin@coppersmithconsulting.com ADAMS Accession No. ML20106F061 Marcus R. Nichol Nuclear Energy Institute (NEI) 1201 F Street, NW, Suite 1100 Washington, DC 20004 mrn@nei.org ADAMS Accession No. ML20213A749 Commenter Section Specific Comments NRC Resolution of DG-4028 Kevin Section In the discussion of the selection of the SSHAC Level, it is The NRC agrees that NUREG-2213 is clear about the equivalency of regulatory Coppersmith B, Senior stated on page 9 that there is a distinction between assurance between Levels 3 and 4 (NUREG 2213 Section 2.5 and others), and Seismic the attributes that would require a Level 3 study versus a Level clarified the language in the RG for consistency. The staff clarified on page 12 Hazard 4 study. In particular, the criteria for a Level 4 study are more that higher regulatory assurance occurs at the higher levels (i.e., Levels 3 and Analysis challenging than those for a Level 3 study. This position implies 4) and added a reference to the discussion in NUREG-2213 about study level Committe that a Level 4 study would provide a higher level of regulatory selection (Section 2.5). RG 4.26 also includes a citation on page 12 to include e Study assurance than a Level 3 study because it can handle that NUREG-2213 Section 3.2.1 provides discussion of the factors for choosing a Guideline additional challenges. However, this position is in direct SSHAC study. RG 4.26 also replaces the final two bullets as suggested in the s contrast to the position in NUREG-2213 and NUREG-2117. comment (i.e.; Applicable for a facility with potentially large sourceterms or design

As stated at multiple locations in NUREG-2213, the NRC fragilities,a significant number of available alternative or potentially contradictory makes no distinction in terms of regulatory assurance between hazard models,low confidence in the completeness and accuracy of the geologic SSHAC Levels 3 and 4. record,and/ornumerous complex, multi-hazard scenarios that can be considered.

For example, on page 3-14: "As noted in NUREG-2117, the .. The staff also updated the final bullet on Page 12 with the following additional NRC makes no distinction between SSHAC Level 3 and 4 text: A Level 3 or Level 4 study may be chosen depending on the organization of studies in terms of the regulatory assurance afforded by either the study (i.e., whether a single or multiple logic trees will need to be developed, level. As a result, in order to achieve the high levels of the complexity of the study, the methods for characterizing uncertainty, and other regulatory assurance needed for nuclear facilities (see Section factors). The NRC staff should be consulted for determination of which study level 2.5) and to avoid some of the additional burdens associated is appropriate (NUREG-2213 Section 2.6.16)..

with Level 4 studies (see Section 3.1), "

Because of this lack of a distinction on the part of the NRC, the Level 3 approach has gained significant favor for nuclear facilities in the US and worldwide because it involves fewer people, costs less, and takes less time. To artificially create a distinction in this Reg Guide will lead to confusion not only in the application to future volcanic hazard analyses, but also to decisions made previously by nuclear utilities regarding SSHAC Levels based on their understanding of regulatory guidance documents, including NUREG-2213. As discussed in detail in NUREG-2213, the distinction in regulatory assurance between Level 2 and Level 3 studies is much larger than the distinction between Levels 3 and 4. I therefore suggest that the third bullet on page 9 be deleted and the fourth bullet be reworded slightly to the following:

Level 3 or 4: facility with potentially large source terms or design fragilities; significant number of alternative or potentially contradictory hazard models available; low confidence in the completeness and accuracy of the geologic record; and numerous complex, multi-hazard scenarios considered.

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This revised wording and concept is consistent with other regulatory guidance issued by the NRC.

Anonymous General I recommend we not build any more nuclear plants until we The comment is beyond the scope of the proposed guide.

Comment figure out how to use fusion instead of fission and we can safely store or reuse spent nuclear waste.

NEI #1 General The regulatory guide is not sufficiently risk-informed because RG 4.26 allows the use of appropriate risk-insight information throughout the Comment it does not consider the potential radiological consequences. volcanic hazards assessment process. Although radiological consequences are It is noted that the NRC is exploring development of an not explicitly used as risk-significance metrics, the applicant may use such enhanced technology-inclusive (TI) and risk-informed and consequences, as well as other risk-insight information, to evaluate the performance based (RIPB) conceptual seismic design significance of potential volcanic hazards.

approach to achieve desired seismic safety for advanced To enhance the clarity of potential risk-significance determinations, the staff non-light-water reactors that would align with the NEI 18-04, revised RG 4.26 to include guidance based on NEI 18-04 and RG 1.233 for the Risk-Informed Performance-Based Technology Inclusive identification of volcanic hazards as a contribution to potential initiating events for Guidance for Non-Light Water Reactor Licensing Basis design basis event (DBE), and beyond design basis event (BDBE) sequences.

Development, approach endorsed in RG 1.233. This approach would align more closely with the approach used to evaluate other natural hazards at a site.

NEI Recommendation: The regulatory guide should provide a more clearly risk-informed process that considers For sites with potential volcanic hazards based on the evaluation of site potentialradiological consequences and the ability to design characterization information, the guidance now allows potential mitigating actions, for, or mitigate, those potential radiological consequences which prevent the occurrence of potential DBE and BDBE sequences, early in the due to volcanic hazards. The example that follows this table volcanic hazards assessment process. This flexibility of the process is shown in illustrates the need to address options for both design and Figure 1.

mitigation against volcanic hazards in order to provide guidance for various application scenarios. Additionally, as the NRC approach to apply RG-1.233 to seismic safety moves forward, the NRC should consider how it could also be applied to other external events, like volcanic hazards.

NEI #2 General As cited by the Staffs October 21, 2019 presentation, The NRC staff agrees that technical criteria can be developed to consider Comment applicants must assess, Geological, seismological, and potential hazards from distant volcanoes early in the screening process. RG 4.26 engineering characteristics. The geological, seismological, and has been revised to better leverage the information developed from the Part 100 engineering characteristics of a site and its environs must be site characterization program to determine if additional consideration is warranted investigated in sufficient scope and detail to permit an for hazards from volcanoes >320 km (200 mi) of a proposed site. Figure 1 was 3

adequate evaluation of the proposed site...permit adequate also updated to reflect the evaluation of the Part 100 geologic site engineering solutions to actual or potential geologic and characterization information as an initial screening criteria.

seismic effects at the proposed site. The size of the region to be investigated and the type of data pertinent to the The applicant typically conducts a geological characterization of the region investigations must be determined based on the nature of the extending 320 km (200 mi) from a proposed site. Quaternary volcanoes within this region surrounding the proposed site. ...each applicant shall region indicate the need to consider potential hazards from future eruptions of investigate all geologic and seismic factors (for example, these volcanoes or volcanic systems.

volcanic activity) that may affect the design and operation of the proposed nuclear power plant... [excerpted from 10 CFR Nevertheless, some large Quaternary volcanoes might be located >320 km from 100.23(c)]. the proposed site, and might have the potential to produce hazards. To evaluate these hazards, RG 4.26 has been revised to rely on the more detailed geological The US Geologic Survey (USGS) regularly updates their information collected as part of site characterization within the 40 km vicinity of publication, National Volcanic Threat Assessment, including the site.

the most recent update in 2018

[1]. The USGS A volcanic hazards assessment is warranted for a Quaternary volcano located systematically evaluates the potential hazards posed by 165 >320 km from the propsed site if there are Quaternary deposits from the volcano individual volcanic features across the US, including territories. located within 40 km (25 mi) of the proposed site.

Of those 165 features, 48 are locatedin ten western states; ranging from 1 each in Colorado, Nevada, and Wyoming, to 14 Thus, a volcanic hazards assessment is warranted if the site characterization in Oregon. Using the aviation planning tool Great Circle determined that either i) a Quaternary volcano is located within 320 km of a Mapper (gcmap.com) and the 2018 report Appendix longitude proposed site, and/or ii) deposits from a Quaternary volcano more than 320 km data of each feature, the eastern edge of a 400 mile (644 km) away from the proposed site occur within 40 km of the proposed site.

radius from the three easternmost features depicted in Figure 6 of the 2018 update was generated. This effort found that no sites in the continental US east of 98 degrees 30 minutes W longitude (roughly the longitude of Wichita Falls, TX) were included within the above parameters. This result corresponds with the academic literature regarding volcanism in the central and eastern US; the consensus being that volcanic activity ceased long before the 2.6 million years ago (2.6 Ma) interval discussed by the Staff. Even recent literature regarding the youngest volcanic features in the CEUS [Mazza, et. al. DOI:

10.1130/G35407.1] found that these features date to at least 47 Ma. The relevant Title 10 regulations apply uniformly to all sites within the jurisdiction of the NRC. As the proposed Regulatory Guide is an appropriate tool to provide guidance to 4

potential applicants on this topic, it would be in the interest of the public, NRC, and applicants to, with sound scientific basis, specifically delineate the region of the continental United States in which this particular hazard does not apply and thus, applicants are not expected to prepare, nor Staff review, any application content regarding volcanic hazards.

NEI Recommendation: Use the USGS National Volcanic Threat Assessment, as a technical basis to state in the Regulatory Guide that applications for sites located in the continental US east of 98 degrees 30 minutes W longitude do not have to prepare application content regarding volcanic hazards. Referencing the USGS National Volcanic Threat Assessment, in defining the region of interest is in keeping with the NRC Principles of Good Regulation of regulatory clarity and efficiency. Applications for proposed sites west of 98 degrees 30 minutes W longitude and all US territories would be expected to use the USGS National Volcanic Threat Assessment, to characterize the volcanic threat, if any, and then address volcanic hazards in their application with the contents of the proposed Regulatory Guide offering one acceptable process to prepare such application content.

NEI #3 General The DG states that the NRC staff relied heavily on detailed Although DG-4028 relied, in part, on information in both IAEA SSG-21 and information in IAEA-TECDOC-1795 and SSG-21. While this TECDOC-1795, use of selected technical information from these documents does may provide useful insights, there are a number of technical not constitute endorsement by NRC of non-cited information. The NRC staff areas that are not aligned with the NRC approach to regulate clarified the text in RG 4.26 on this point.

other external events and/or are not consistent with a risk-informed approach. For example, the IAEA-TECDOC-1795 Some text in RG 4.26 section on Consideration of International Standards has look at 10 million years to identify hazards does not align with also been revised to further clarify important distinctions between the methods NRCs use of 2.6 million years in DG-4028. Application of the proposed in IAEA SSG-21 and RG 4.26.

IAEA guidance in its entirety would result in excessive conservatism and could preclude the ability to site advanced reactors in much of the western United States.

NEI Recommendation: The NRC should avoid referencing IAEA-TECDOC-1795 and SSG-21, since there are portions of 5

those guidance documents that are inconsistent with the NRC approach to regulating other external events. If the NRC references IAEA-TECDOC-1795 or SSG-21, it should be limited to areas where they are consistent with the NRC regulation of other external events.

NEI #4 General In several areas, the draft guide uses subjective criteria, for 1) The NRC staff did not make any changes based on this comment since example: this is a statement of what IAEA recommends, not what the NRC is proposing in its RG.

(1)Pg. 9, 2nd paragraph under Harmonization...: the stepwise 2) RG 4.26 includes revised text and a new Figure 1 that provide further approach uses available information to conduct a screening clarification of what would be considered acceptable to complete the evaluation analysis at step 3, or proceed to step 4, 6 or 7.

(2)Pg. 11, Figure 1, which simply ends if risk insights are 3) As with the previous comment, there a significant revisions to Step 3 to developed and plant performance is acceptable. provide additional clarification.

(3)Pg. 13, under Step 3: evaluated to determine whether the 4) The NRC staff did not make changes to this particular sentence but the total system performance would be acceptable for volcanically overall changes to the text provide additional clarification.

induced failures. Similar statement on pg. 17, 2nd paragraph.

(4)Pg. 14, 1st full sentence: shows that the potential volcanic hazards did not significantly affect safety, then additional analyses would not be warranted.

While subjective criteria is not as straightforward for an applicant or reviewer, as weve learned with the defense in depth assessment for emergency planning zones (EPZ), a subjective approach may be the best option in some cases.

NEI Recommendation: Provide some guidance for what would be acceptable to meet these criteria:(1) The use of available information could eliminate the need to develop a model (conceptual model of tectono-magmatic processes).(2) and (3)

Should allow for complete SSC failure if response of other SSCs or plant is acceptable. (4) Significantly affect safety could be judged by comparison to meeting the safety goals.

NEI #5 Section Hydrothermal proximal hazards is only mentioned once in this The NRC staff determined that some volcanic hazards, such as hydrothermal B, document without any guidance on acceptable modeling of this volcanic hazards, are expected to be restricted to within 40 km (25 mi) of a Overview volcanic phenomenon. The DG states that the NRC staff relied volcanic vent. Consequently, if a proposed site is greater than 40 km (25 mi) from of heavily on detailed information in IAEA-TECDOC-1795, but this a Quaternary volcano or potential volcanic vent, the volcanic hazards assessment 6

Volcanic document identifies hydrothermal activity as the one would not need to consider hazards from avalanche/landslide/slope failure, Hazards, phenomenon without a practicable model (see Conclusion, missiles, gases and aerosols, atmospheric phenomena (e.g. lightning), ground Other page 189, 2ndparagraph). The DG needs to provide specific deformation, hydrothermal systems and groundwater effects.

Proximal modeling guidance on hydrothermal hazard evaluation.

Hazards, If a proposed site is located less than 40 km (25 mi) from a Quaternary volcano, Page 6 NEI Recommendation: Specify one or more acceptable or potential volcanic vent, then pre-licensing interactions would be needed to methodologies for an applicant to evaluate hydrothermal determine the appropriate scope of the VHA for proximal hazards.

volcanic hazards.

The Section B, Discussion, of the revised guide includes a new subsection that addresses the consideration of proximal hazards.

NEI #6 Section The section titled Risk Informed Regulation ends with the RG 4.26 clarifies that items a through e are from concept #5, Risk Informed B, Risk following statement: The significance of the volcanic hazards Approach in SECY 98-144.

Informed assessment could then be determined using the suite of Regulatio information available to support risk-informed decision-making n, Page 8 (i.e., items a-e in SECY-98-144). The items in SECY-98-144 are denoted with numbers, so it is not clear which items are being referenced here.

NEI Recommendation: Revise the reference for clarity. Also, given the discussion of risk significance supporting risk-informed performance-based licensing basis development in RG 1.233, there is an opportunity to include recognition of the potential use of this reference as well.

NEI #7 Section NRC staff guidance for SSHAC study level uses qualitative The NRC staff note that the SSHAC guidance was purposefully written with B, Senior adjectives low-level, modest, high confidence, qualitative adjectives to maximize flexibility for application to a variety of hazard Seismic straightforward, intermediate, modest, moderate assessments and types of facilities, and to be applied both domestically and Hazards confidence, potentially large, potentially significant, internationally. The context referred to in the suggestion pertains to the choice of Analysis moderate-to-low confidence, etc. appropriate SSHAC study levels and, although mentioned as an example on RG Committe Page 12, source term is not the only factor to be considered in selection of a e Study NEI Recommendation: To the extent that this guidance may be study level (see NUREG-2213 Section 3.2.1 for discussion of the various factors Guideline modelled on the SSHAC process, clarify by specific for choosing a SSHAC study). Providing a specific quantification and detailed s, Page 9 quantification and detailed definition the adjective descriptors definition needlessly restricts the flexibility of SSHAC study level application and used in staff guidance for SSHAC study level. For example, a consideration of other determination factors.

low-level source term is one which would not exceed the 1 rem Total Effective Dose Equivalent (TEDE) Protective Action The staff provided brief clarifying text in the RG that i) explains the flexibility of the Guide (PAG) at the EPZ plume exposure distance. SSHAC guidelines and that they can be beneficially applied for various types and 7

completeness of information available, tailored to a facility and location; ii) reminds that the SSHAC guidelines are a practical, approved method but are not legally binding or regulations; and iii) encourages pre-application interactions with NRC for choosing the level of study, if a SSHAC process is used (NUREG-2213 Section 2.6.16, The regulator should have input into the choice of the SSHAC study level). Specifically, RG 4.26 refers to NUREG 2213 Sections 2.5, 3.1, and 3.2; note that the factors are meant to be subjective and are dependent on qualitative factors. Staff also added a brief explanation of the purpose and potential outcomes that can be expected of a SSHAC used to assess volcanic hazards.

NEI #8 Section The Level 1 SSHAC is defined as having a high confidence in The response to this comment is similar to the previous response to Comment #7.

B, Senior the completeness and accuracy of the geologic record. It is Qualifiers are used to allow flexibility; however, SSHAC Level 1 studies are to be Seismic not clear what high confidence is when the recommended used in situations where there is high confidence that the driving factors for Hazards volcanic assessment covers the Quaternary Period, defined as hazard are well understood and uncertainty is low (i.e., there are not significantly Analysis the geologic timeframe ranging from 2.6 million years ago. conflicting models or interpretations, or sites may be data rich.) In other Committe words, the center of the center, body, and range of technically defensible e Study NEI Recommendation: Define per Comment No. 7,above, and interpretations is easily defined and well understood. Higher levels of SSHAC are Guideline consider changing to moderate confidence. required when uncertainties are larger in order to fully capture the body and s, Page 9 range. In addition, NUREG-2213 specifies that higher levels of SSHAC are needed when additional stability of the hazard is needed (i.e., the numerical results of the hazard analysis should be expected to remain stable for a reasonable period of time after the completion of the hazard study; for example, to support a licensing basis). As with the resonse to Comment #7, the staff added clarifying text to refer to NUREG-2213 Sections 2.5, 3.1, and 3.2 and Figure 2-1 (center, body and range diagram) in RG 4.26. Additionally, the staff emphasizes the need for pre-application meetings with NRC if use of SSHAC is an option. The text in RG 4.26 was updated accordingly.

NEI #9 Section This section does not endorse IAEA requirements for The intent was that individual licensees do not need to monitor volcanoes B, monitoring volcanoes in the U.S. for nuclear reactors, stating themselves, as required by IAEA SSG-21, because volcano monitoring is the Harmoniz that it does not appear applicable for nuclear reactors in the statutory authority of the USGS. NRC staff revised the text to clarify that ation with United States. It goes on to point to the USGS statutory prospective applicants should work with the USGS to fill any identified gap in Internatio authority and what actions would be taken if there is a volcano monitoring for a proposed site.

nal perceived gap in monitoring at a proposed nuclear reactor site.

Standard These statements are contradictory and confusing. If the 8

s, item USGS has statutory volcanic activity monitoring authority and (3), Page IAEA requirements are not applicable, how would there be a 10 perceived gap in monitoring that would be filled in by the USGS? Perhaps the intent was that individual nuclear reactors are not required to monitor volcanoes themselves because the USGS performs this role nationally. The USGS fulfilling this role (including regular publication of their, National Volcanic Threat Assessment) meets NRC requirements for volcano monitoring.

NEI Recommendation: Revise the statements in item (3) on page 10 to explain the role, authority, requirements, and acceptability of USGS volcanic monitoring as applied to U.S.

commercial nuclear reactor sites being proposed. Delete If there is a perceived gap in monitoring activities at a proposed commercial nuclear reactor, the U.S. Geological Survey will fill that gap.

NEI #10 Figure 1, Step 1 should be consistent with Step 1 in the text. Step 1 has been revised in both the text and Figure 1 and is now titled, Evaluate Page 11 Site Characterization Information.

NEI Recommendation: Please refer to Step 1 in the Figure as Perform Initial Characterization.

NEI #11 SectionC, The draft guidance states: For the purpose of the initial The response to this comment is incorporated in the response to NEI comment Page 12, evaluation of potential hazards from volcanic ash falls, the #2. Potential hazards from a Quaternary volcano >320 km (200 mi) from a Step 1, region of interest for the volcanic hazards assessment should proposed site only need to be considered if Quaternary volcanic deposits from Paragrap extend a sufficient distance beyond 320 km (200 mi) to this volcano occur within 40 km (25 mi) of the proposed site. This is also reflected h2 encompass those Quaternary volcanic systems that have the in Figure 1.

potential to affect the design or operation of the proposed reactor. This leaves a lot of ambiguity surrounding the sufficient distance to consider ash fall a potential hazard.

NEI Recommendation: Suggest the guidance characterize volcanic hazard regions of effects to determine the areas where they need to be considered, e.g., using the USGS National Volcanic Threat Assessment, rather than the current draft guidance to search for hazards based on distance from the site selected.

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NEI #12 Section In performing initial characterization, when there is evidence of The text in RG 4.26 was enhanced to further explain that a conceptual model C, Page Quaternary volcanism in the regions of interest, a conceptual provides a series of technical rationale to determine if all Quaternary volcanoes in 12, Step model of tectono-magmatic processes is recommended to be the site region warrant analysis in the volcanic hazards assessment. This model 1, developed to determine how past patterns of volcanism should provides a framework to determine if the large-scale tectonic and magmatic Paragrap be projected to estimate future activity. It is unclear whether a processes that controlled volcanism during the Quaternary Period can be h3 2D or 3D model is required, or if applicants need to use reasonably extrapolated to evaluate the likelihood of future volcanic activity. A LaMEM, FDSTAG, or other software to prepare the model. numerical model is not required to develop this conceptual understanding.

NEI Recommendation: Provide reference(s) of acceptable Examples of tectono-magmatic conceptual models are cited in RG 4.26.

models and examples of use and applicability.

NEI #13 Section The draft guidance states: The hazard analysis can screen out The revised guidance clarifies that a geologic analysis, engineering analysis, and C, Page volcanic systems that are not consistent with the tectono- operational considerations may all contribute to the screening of volcanic hazards 12, Step magmatic model. This screening, however, is dependent on at the site. The flexibility of the approach to perform a volcanic hazards 1, establishing sufficient confidence in the underlying technical assessment, engineering analysis or consider site operations to screen volcanic Paragrap basis showing that future volcanism is not a credible event. hazards is also shown in revised Figure 1 and the accompanying text.

h4 This suggests that future reactors will need an increased burden of proof over the existing fleet (excluding Columbia) to The revised guide also clarifies that proximal hazards would only need to be screen volcanic hazards. considered for sites located in distributed volcanic fields with the expectation that proximal hazards from volcanoes would not need to be considered since the NRC Additionally, the term, sufficient confidence, though followed does not anticipate proposed reactor sites within 40 km (25 mi) of the central vent by one example, is ambiguous and subject to a wide range of of a Quaternary volcano. This is described in a new section on the consideration interpretation by applicants and NRC reviewers. of proximal hazards.

NEI Recommendation: The guidance should provide more flexibility to screen volcanic hazards without this model in places where: 1. nuclear facilities already exist, 2. entire regions (e.g. the eastern United States) where consideration of volcanic hazards is excluded based on the USGS, National Volcanic Threat Assessment, and 3. locations where there are no significant proximal volcanic hazards. Suggesting that a tectono-magmatic model is required for those areas is counter to a risk-informed performance-based approach.

Clarify with a specific quantifiable definition what is meant by sufficient confidence.

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NEI #14 Section ...volcanoes in the region of interest are consistent with the Response to this comment is the same as to NEI comment #12.

C, Page tectono-magmatic model... lacks the same clarity addressed in 13, Step Comment No. 12on Step 1.

2, Paragrap NEI Recommendation: Once the acceptable type(s) of models h1 have been provided in Step 1, provide a reference here back to that section.

NEI #15 Section Quantify what credible means. ...credible distance...credible The term credible in DG-4028 is used in its common English context, that is:

C, Page phenomena... offering reasonable grounds for being believed (Oxford-Merriman Dictionary). Its 13, Step usage does not imply any metric of frequency. Additional discussion of DBE and 2, NEI Recommendation: Credible is defined as an annual BDBE sequences for volcanic hazards were added to RG 4.26 to provide Paragrap frequency of occurrence of 1 x 10-5 per year in Section 6-2.3 additional clarity on the credibility of a future volcanic event.

h1 of the ASME/ANS PRA Standard.

NEI #16 Section The draft guidance states: ...the screening analysis should The revised guide includes numerous clarifications on what a suitable screening C, Page evaluate... analysis would entail such that an example analysis is not necessary.

13, Step Additionally, the NRC does not typically provide example analyses in regulatory 2, NEI Recommendation: An example of a representative guidance and so has not included one here.

Paragrap screening analysis should be provided as a go-by reference.

h4 NEI #17 Section The term beyond-design-basis event is used with no As discussed in response to NEI Comment #1, the NRC staff revised the guide to C, Page definition. better incorporate the concepts and definitions in RG 1.233. These revisions in 14, Step the Risk Insights discussions in RG 4.26 make a clear distinction between DBE 3 NEI Recommendation: Recommend including a metric for and BDBE for event sequences initiated by potential volcanic hazards.

beyond-design-basis event based on probability of occurrence; for example, RG 1.233 and NEI 18-04, define beyond-design-basis event as event sequences with mean frequencies of 5x10-7/plant-year to 1x10-4/plant-year.

NEI #18 Section Typo: IAEA-TECCOC-1795 Staff revised RG 4.26 to correct this typo.

C, Page 18, first NEI Recommendation: Revise to IAEA-TECDOC-1795 sentence NEI #19 Section This section requires a robust technical basis for the amount of The staff replaces robust with practicable in the discussion of mitigative actions C, Page time available for mitigative actions, but in the same paragraph, and expanded the discussion on potential mitigative actions to clarify the need for 18, Step acknowledges that considerable uncertainties exist in any such an applicant to demonstrate that the proposed mitigative actions are practicable.

7, predictions based on historical data. There is no specification The text in RG 4.26 was enhanced to better explain the concept of practicability, of how a reviewer or applicant can provide a robust technical such as the development of action levels based on volcano monitoring 11

Paragrap basis. This section identifies appropriate monitoring information, rationale for accomplishing mitigative actions in allotted time, and h2 resources to accommodate these uncertainties without inclusion of actions in appropriate operation plans.

defining what is appropriate. USGS monitoring is sufficient and no additional monitoring from the site is needed.

NEI Recommendation: Considering the effort to be risk-informed, specify acceptable methodologies and appropriate monitoring resources for providing a robust technical basis to estimate the amount of time available for mitigative actions.

NRC should work with stakeholders to determine an appropriate process for receiving timely information from the USGS on volcanic activity from sources that could impact a plant.

NEI #20 Section The first bulleted item in Step 7 indicates monitoring resources The general process for notifications of an impending volcanic event or hazard is C, Page are established to provide early indication of potential eruption, that the local civil protection would be responsible for notifying the affected areas 18, Step yet item (3) on page 10 states, if there is a perceived gap in once the USGS issues a notification. The USGS Volcano Hazards Monitoring 7, first monitoring activities at a proposed commercial nuclear reactor, Program also has a notification system bullet the U.S. Geological Survey will fill that gap. See Comment (https://volcanoes.usgs.gov/vhp/notifications.html) that can be used by applicants No. 9. Here it is implied the plant is responsible, at least in or licensees for additional information on volcanic events. The staff revised the part, for its own monitoring activities; however, USGS guide to reflect this information.

monitoring is sufficient and no additional monitoring from the site is needed.

NEI Recommendation: NRC should work with stakeholders to determine an appropriate process for receiving timely information from the USGS on volcanic activity from sources that could impact a plant.

NEI #21 Consider This section states that if the outcome of the volcanic hazards The section on consideration of alternative sites has been deleted and Figure 1 ation of assessment indicates that volcanic hazards are beyond the revised accordingly.

Alternativ facilitys design basis and cannot be mitigated effectively, then e Sites, alternative sites should be investigated. This does not appear Page 20 to accurately reflect the general approach for addressing external events. We would expect that an applicant would use an assessment to understand hazards and ensure the design protects against those hazards. An applicant always has the option to select a more suitable site. This section is 12

unnecessary; if the plant is unable to achieve acceptable results, then the applicant will not pursue a site that would not be approved in the NRC safety review.

NEI Recommendation: Delete the section on Consideration of Alternative Sites. If the staff wish to retain this section, work with stakeholders to clarify that this is not related to the alternatives analysis required per §51.50(b) or (c). The focus of this guidance is volcanic hazards assessment as an input to the safety review.

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