ML17331B413
| ML17331B413 | |
| Person / Time | |
|---|---|
| Issue date: | 01/31/2018 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Karagiannis H | |
| Shared Package | |
| ML17317A196 | List: |
| References | |
| DG-1285 RG-1.174, Rev. 3 | |
| Download: ML17331B413 (24) | |
Text
Response to Public Comments on Draft Regulatory Guide DG-1285, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis Proposed Revision 3 of Regulatory Guide 1.174 On April 7, 2017, the Nuclear Regulatory Commission (NRC) published a notice in the Federal Register (82 FR 17402) announcing that Draft Regulatory Guide 1285 (DG-1285, proposed Revision 3 of Regulatory Guide (RG) 1.174) was available for public comment. The published version of DG-1285 was made available in the NRCs Agencywide Document Access and Management System (ADAMS) under accession number ML16358A153. The public comment period ended on May 22, 2017. The NRC received comments from the organization listed below. The bracketed identifiers at the end of each comment relate to annotations the NRC applied to the received comment documents. Annotated versions of the received comment documents are available in ADAMS under the indicated accession numbers below. The following table documents the public comments and NRC staffs responses.
The NRC received comments from the following:
Ms. Pamela B. Cowan Mr. James A. Gresham Mr. Justin T. Wheat Mr. David P. Helker
< pbc@nei.org > < greshaja@westinghouse.com > < jtwheat@southernco.com > Exelon Generation Company, LLC Nuclear Generation Division Westinghouse Electric Company Southern Nuclear Operating Company 200 Exelon Way Nuclear Energy Institute 1000 Westinghouse Drive 40 Inverness Center Parkway Kennett Square, PA 19348 1201 F Street, NW., Suite 1100 Cranberry Township, PA 16066 P.O. Box 1295 Dated: May 23, 2017 Washington, DC 20004 Dated: May 23, 2017 Birmingham, AL 35242 Dated: May 22, 2017 Dated: June 1, 2017 ADAMS Accession No.: ADAMS Accession No.: ADAMS Accession No.: ADAMS Accession No.:
ML17193A299 ML17193A298 ML17193A297 ML17193A300
Commenter Specific Comments NRC Resolution Nuclear The industry is concerned that Revision 3 to RG 1.174 does not reflect The NRC agrees that changing the label of the seven defense-in-depth Energy the Commissions direction in the March 9, 2016 Staff Requirements evaluation items from the factors to considerations is appropriate Institute Memoranda in response to SECY-15-0168, Recommendations on and the guidance has been revised accordingly.
Issues Related to Implementation of a Risk Management Regulatory Framework, which highlighted that a formal agency-wide definition and criteria for determining the adequacy of defense in depth should not be developed. Specifically, the draft revision includes factors of defense in depth, which may be overly prescriptive. The industry believes describing these as considerations would be more consistent with Commission direction. [NEI1-1, NEI1-2]
2
Nuclear Regarding the replacement of the terms PRA quality and PRA The staff recognizes that changing these terms may cause confusion in Energy technical adequacy with the new phrase PRA acceptability. The the near term while the NRC makes the transition in all its documents.
Institute term PRA acceptability causes confusion as the term acceptability However, in several NRC guidance documents, the terms PRA is used in the PRA context as well as the Regulatory Guide (RG) quality and technical adequacy have been used interchangeably and, context in reference to the methods and solutions provided (see Purpose in some cases, incorrectly. The NRC intends to standardize the use of of Regulatory Guides (page 2), Background (page 4, last paragraph; these terms in its documents.
page 5, first paragraph; page 6, second paragraph), and Staff Regulatory The staffs decision is supported by the NRCs resolution of differing Guidance (page 7, second paragraph)). The term acceptable is also professional opinion (DPO) DPO-2016-001, Differing Professional used in its common English definition sense (e.g., when referring to Opinion on Probabilistic Risk Assessment Language in Regulatory QHOs in the context of an acceptable level of risk (Background, page Guides (see ADAMS accession No. ML17013A015) raised these 4), treatment of uncertainty (Staff Regulatory Guidance, page 9).
issues for consideration and resolution by NRC management. The Furthermore, in Section B (page 3), the RG states that PRA resolution of DPO-2016-001 directed the staff to adopt the term PRA acceptability is replacing the terms PRA quality and technical acceptability rather than PRA quality and technical adequacy in adequacy; implying that quality and technical adequacy are RG 1.174.
equivalent. The industry perspective is that quality is a state of goodness for which the industry expects all PRAs to be at a high level Consistent with that resolution, the NRC implemented the change in the of quality. Technical adequacy refers to the ability of the PRA to following manner. In cases where terms such as PRA adequacy, support a risk-informed application based on scope, level of detail, and PRA technical adequacy, or PRA quality refer to the acceptability plant-specificity. Replacing these terms with acceptability causes or adequacy of the four PRA aspects of scope, conformance with confusion that could negatively impact the ability of a licensee to technical elements, level of detail, and plant representation, the term successfully get a risk-informed application approved. The term PRA PRA acceptability is now used in place of those terms. In cases where acceptability and its variants suffer from the same issues as those terms such as technical adequacy or PRA quality refer to provided against the use of the term technical adequacy. RG 1.200 conformance with the technical elements in the ASME/ANS PRA uses the terms technical adequacy and technically acceptable PRA. standard, the phrasing conformance with the technical elements is As an alternative to PRA acceptability, one could refer to acceptable now used in place of those terms.
technical adequacy. This would allow continued use of the current Additionally, in response to this comment, the NRC revised the terminology and still provide for the ability to qualify whether a PRA following sentence on page 3 from, In addition, this revision adopts models technical adequacy is sufficient to support a specific the term PRA Acceptability, including related phrasing variants, in application. As an example of the confusion introduced by the new place of the terms PRA quality and technical adequacy to describe terminology, the statement on page 8, ...the staff expects the the appropriateness of the PRA used to support risk-informed licensing following:...The plant-specific PRA supporting the licensees proposals submittals, to:
has been demonstrated to be acceptable is not clear. However, using
...demonstrated to be of acceptable technical adequacy is more clear In addition, this revision adopts the term PRA Acceptability, as applicants understand how to achieve technical adequacy. [NEI1-3] including related phrasing variants, in place of terms such as PRA quality, PRA technical adequacy, and technical adequacy to describe the appropriateness of the PRA used to support risk-informed licensing submittals.
3
Commenter Specific Comments NRC Resolution The staff is planning to engage the public to explain the meanings of the terms PRA acceptability, technical adequacy, and PRA quality; that this is only a change in NRC usage of terms; and the change in terminology does not impact any regulatory processes. It should be noted that the NRCs change in terminology is intended to be reflected in other relevant guidance documents (e.g., RG 1.200, NUREG-0800, etc.) as they are updated and revised.
Westinghouse DG-1285 replaces the term PRA "technical adequacy" with "PRA See the staffs response to a similar NEI comment [NEI1-3] above.
Electric acceptability." This change may result in confusion. On DG-1285, page In addition, the NRC revised the following sentence from page 42 in Company 36, it notes that limited-scope applications may place a reduced burden response to this comment from, An independent peer review (as on the PRA stating that: "A limited-scope application would lead the described in RG 1.200) is important in ensuring PRA acceptability, to:
staff to conduct a more limited review of the risk results, therefore placing less emphasis on PRA acceptability than would be the case for An independent peer review (as described in RG 1.200) is an a broad-scope application." That is appropriate and places the burden of important consideration in risk-informed applications.
acceptability of the PRA for the application with the regulator.
However, DG-1285, page 42 notes that: "An independent peer review (as described In. RG 1.200) is important in ensuring PRA acceptability." Thus; the industry peer review team determines the acceptability of the various high level and supporting requirements based on compliance to RG 1.200 (arid the ASME Standard) regardless of the application. However, while the peer review can determine the adherence of the PRA to the various supporting requirements for the PRA in general, some applications will require greater detail in the modeling of specific systems, while other applications will require far less to support a specific application. The peer review at that level was intended to establish the technical adequacy of the supporting requirements, and as such, the term was chosen to focus on the PRA general capability. However, the term "PRA acceptability" now being used in DG-1285 implies: (1) the PRA is acceptable for an application, and (2) the PRA is acceptable based on compliance to RG 1.200. While these decisions will frequently be the same, it will not always be so and could result in confusion. Based on this reason, it is recommended that the term "technical adequacy" be retained when referring to the peer review process. [WEC1-1]
4
Commenter Specific Comments NRC Resolution Nuclear Regarding the phrase (with variety including both types of models Although this comment is outside the scope of changes considered for Energy used and the detail of modeling needed), without proper context, it is Revision 3 of RG 1.174, the NRC does not believe revising the Institute difficult for the reader to understand the two types of models being language would impact other parts of the RG, and therefore, would not referenced. The examples that follow provide some context; however, it require any additional consideration. The NRC agrees that the cited is not enough to fully appreciate the concepts being conveyed. Suggest phrase is confusing and considers the associated paragraph and the describing the history of the RPP in more detail for readers not familiar subsequent paragraph on page 4 of DG-1285 to be unnecessary for the with the program. [NEI1-4] narrative in Section B. As such, these two paragraphs were removed
from the guidance.
See page 4, 2nd paragraph Nuclear Regarding the phrase reassessing plants with relatively high CDFs for Although this comment is outside the scope of changes considered for Energy possible backfit, without proper context, it is difficult for the reader to Revision 3 of RG 1.174, the NRC does not believe revising the Institute understand the intent. Suggest adding the reactor regulation program for language would impact other parts of the RG, and therefore, would not which the activity applies. [NEI1-5] require any additional consideration. The NRC agrees that the cited
phrase is confusing and considers the associated paragraph and the See page 4, 3rd paragraph preceding paragraph on page 4 of DG-1285 to be unnecessary for the narrative in Section B. As such, these two paragraphs were removed from the guidance.
Nuclear Suggest changing the sentence The principal focus of this RG is on the The NRC agrees that the cited language needs clarification and, based Energy use of PRA findings and risk insights in decisions on proposed changes on the resolution of comments NEI1-4 and NEI1-5, the NRC removed Institute to a plants licensing basis. to read The principal focus of this RG is the second and third paragraphs on page 4 of DG-1285 from the to provide guidance to the licensee on an acceptable approach to using guidance.
PRA findings and risk insights in deciding proposed changes to a plants licensing basis. [NEI1-6]
See page 4, 3rd paragraph Nuclear Licensing basis was abbreviated as LB but the abbreviation is not The NRC agrees with the comment and replaced all instances of the Energy used much throughout the document. Consider using the term acronym LB with licensing basis.
Institute licensing basis or the LB abbreviation consistently throughout the document. [NEI1-7]
See page 5, 1st paragraph 5
Commenter Specific Comments NRC Resolution Nuclear Section C.2.2.4 is not a sub-section of DG-1285. Suggest using Section The NRC agrees with the comment and revised the cited language as Energy C.2.4. [NEI1-8] proposed.
Institute ----
See page 9, 2nd bullet Nuclear In left box on Figure 3 change Define Change to read Define The NRC agrees with the comment and revised the cited Figure as Energy Proposed Change [NEI1-9] proposed.
Institute ----
See page 9, Figure 3 Nuclear Regarding the phrase with this staff expectation in mind, it is not The NRC agrees with the comment and revised the guidance by Energy clear what the staff expectation actually represents. Suggest removing removing the cited language as proposed.
Institute the phrase or clarifying the staff expectation. [NEI1-10]
See page 10, Section C.1, 3rd paragraph Nuclear The phrase proposed increases in CFR and LERF are small The NRC agrees with the comment and revised the cited language as Energy should read proposed increases in CDF and LERF are small proposed.
Institute [NEI1-11]
See page 12, Section C.2, 3rd paragraph Nuclear Regarding sentence Sections C.2.1.1 and C.2.1.2 below provide The NRC agrees with the comment and revised the cited language as Energy guidance on assessing whether implementation of the proposed follows:
Institute licensing basis change maintains adequate safety margins and consistency with the defense-in-depth philosophy. The section Sections C.2.1.1 and C.2.1.2 below present guidance on assessing references and description are backwards (i.e., the defense-in-depth whether the proposed licensing basis change remains consistent with discussion is first, then safety margin.) [NEI1-12] the defense-in-depth philosophy and maintains adequate safety
margins.
See page 12, Section C.2.1, 2nd paragraph 6
Commenter Specific Comments NRC Resolution Nuclear Regarding the sentence System redundancy, independence, and The NRC agrees with the comment and revised the cited language as Energy diversity result in high availability and reliability of SSCs and also help follows:
Institute ensure that system safety functions are not reliant on any single feature System redundancy, independence, and diversity result in high of the design. System redundancy, independence and diversity help availability and reliability of the function and also help ensure that ensure that safety functions are maintained; however, they do not system functions are not reliant on any single feature of the design.
necessarily result in high availability and reliability of SSCs in and of themselves. Suggest focusing on safety functions and not SSCs.
[NEI1-13]
See page 15, Section C.2.1.1.2, 1st paragraph under item 3 Nuclear Regarding sentence Examples include interfacing-system loss-of- The NRC agrees with the comment and revised the cited language as Energy coolant accidents (LOCAs) should read Examples include suggested, but removed the acronym because the term interfacing-Institute interfacing-system loss-of-coolant accidents (ISLOCAs) [NEI1-14] system loss-of-coolant accident is not used more than once in the
document.
See page 16, Section C.2.1.1.2, 2nd paragraph under item 5 Nuclear Regarding the 7th factor Continue to meet the intent of the plants The NRC agrees with the comment to the extent that it identifies the Energy design criteria, the intent of each plant design criterion is not defined, very broad nature of the 7th consideration. However, the NRC Institute making the factor particularly subjective. Because current regulations disagrees that any related changes to the text are needed. The NRC include the plants design criteria, there is no need to also consider the position is that the licensee should consider whether the proposed plants design criteria as part of an assessment of the impact of the licensing basis change meets the intent of the plants design criteria in change on defense-in-depth. Suggest deleting the 7th factor. As an addition to determining whether the proposed changes is in compliance alternative, define and/or clarify the phrase intent of the plants design with regulations (i.e., Principle 1 of the risk-informed decisionmaking criteria. For example, allowing changes to how the design criteria are process). As such, the guidance in Section C.2.1.1.3 states that, the met such that it can be demonstrated there is no significant reduction in licensee should demonstrate a full understanding of any impacts that the the effectiveness of one or more layers of defense. [NEI1-15] proposed licensing basis change might have on the design criteria or
severe accident design features of the plant. Thus, proper application See page 17, Section C.2.1.1.2, Item 7 of the 7th consideration would not prohibit changes to how the intent of the plants design criteria are met. Rather, the 7th consideration asks that the licensee have a full understanding of the effects of a proposed change on the design criteria before deciding whether to pursue the change.
7
Commenter Specific Comments NRC Resolution Nuclear Regarding the following excerpt Although the guidance is presented The NRC agrees that cited language needs clarification. It is possible Energy separately for each factor, the evaluation of the proposed licensing basis that small impacts to several of the defense-in-depth evaluation factors Institute change should be performed in an integrated fashion. The proposed (now called considerations as per the resolution of comment NEI1-1) licensing basis change is considered to maintain consistency with the could be considered a significant impact on defense-in-depth overall defense-in-depth philosophy if the integrated assessment demonstrates and therefore could be considered not to maintain consistency with the no significant impact on a single factor (i.e., the intent of each defense- defense-in-depth philosophy. As such, the NRC revised the second in-depth evaluation factor is met). On one hand the guidance suggests cited sentence as follows:
an integrated assessment and on the other hand it seems to focus on a The proposed licensing basis change is considered to maintain significant impact to a single factor. Could small impacts to several of consistency with the defense-in-depth philosophy if the integrated the factors be considered a significant impact on defense-in-depth assessment does not demonstrate a significant impact on a single overall? If so, please clarify. [NEI1-16]
consideration (i.e., the intent of each defense-in-depth evaluation factor is met) or there is not a significant impact collectively across all seven See page 17, Section C.2.1.1.3, 1st paragraph considerations.
Additionally, the portion of the first paragraph in Section C.2.1.1.3 starting with Although the guidance... and ending with ...quantitative and/or qualitative has been moved to the end of the first paragraph in Section C.2.1.1.4 to consolidate the guidance related to the integrated evaluation of the defense-in-depth consideration.
Nuclear Regarding the sentence Such an evaluation of the proposed licensing The NRC agrees with the comment and revised the cited language as Energy basis change against the seven factors might be qualitative. Because follows:
Institute both quantitative and qualitative methods can be used to support each of the factors suggest changing the sentence to read Such an evaluation of Such an evaluation of the proposed licensing basis change against the the proposed licensing basis change against the seven factors might be seven considerations might be quantitative, qualitative, or both.
quantitative and/or qualitative. [NEI1-17]
Consistent with the with the NRCs resolution of comment NEI1-1, See page 17, Section C.2.1.1.3, 1st paragraph factors has been changed to considerations.
Nuclear Regarding the phrase whether any increase in frequency or decrease The NRC agrees with the comment and revised the cited sentence Energy in dependability it is not clear what is meant by the term fragment as follows:
Institute dependability. Suggest using commonly understood terms (e.g.,
whether any increase in frequency or decrease in availability or availability, reliability.) [NEI1-18]
reliability See page 20, Section C.2.1.1.3, 3rd paragraph under item 3 8
Commenter Specific Comments NRC Resolution Nuclear Regarding the sentence However, the licensee should also qualitatively The NRC agrees with the comment and revised the cited sentence as Energy evaluate whether the change has adversely impacted any of the three follows:
Institute areas above to judge whether this factor has been met. It is not clear However, to judge whether this consideration has been met, the what the three areas above are specifically; please clarify. [NEI1-19]
licensee should also qualitatively evaluate whether the change has resulted in any of the four impacts listed above.
See page 21, Section C.2.1.1.3, last paragraph of item 4 Nuclear Regarding the sentence A PRA used in risk-informed regulation The NRC agrees with the comment and revised the cited language as Energy should be performed correctly, in a manner that is consistent with follows:
Institute accepted practices. Suggest removing the text correctly, so the A PRA used in risk-informed regulation should be performed in a sentence reads A PRA used in risk-informed regulation should be manner consistent with accepted practices.
performed in a manner that is consistent with accepted practices. This language also appears twice in Section 2.3.2, first paragraph. [NEI1-20] Additionally, the following related sentence in Section C.2.3.2 was
revised from, In general, a PRA that is performed correctly is one See page 25, Section C.2.3, 1st paragraph where the methods are implemented correctly and the assumptions and approximations are reasonable, to:
In general, a PRA that is performed in accordance with accepted practices is one in which the methods are implemented correctly and the assumptions and approximations are reasonable.
Nuclear Regarding the sentence The PRA should realistically reflect the actual Although this comment is outside the scope of changes considered for Energy design, construction, operational practices, and operational experience Revision 3 of RG 1.174, the NRC agrees with the comment and does Institute of the plant and its owner. Although the term owner was used in not believe it would impact other parts of the RG, and therefore, would Rev2 of RG 1.174, suggest replacing the term owner with licensee. not require any additional consideration. Consequently, the NRC
[NEI1-21] revised the guidance as proposed.
See page 25, Section C.2.3, last paragraph Nuclear Regarding phrase discussed in Section 2.3.1 and 2.3.3, The NRC agrees with the comment and revised the cited language as Energy respectively the letter C should be added to precede the section proposed. Similarly, the reference to Section 2.3.4 of has been Institute numbers. [NEI1-22] revised to Section C.2.3.4.
See page 26, Section C.2.3.2, 1st paragraph 9
Commenter Specific Comments NRC Resolution Nuclear Regarding the sentence It should be noted that in the next edition of The NRC agrees with the comment and removed the cited sentence.
Energy the ASME/ANS PRA standard the supporting requirements will only Additionally, the NRC revised the last paragraph to provide a more Institute include Capability Categories I and II, and Capability Category III will generalized discussion of the Capability Categories that omits no longer be included. This sentence should be deleted because it is references to specific Capability Category numbers.
speculating the content of a future revision to the PRA Standard.
[NEI1-23]
See page 26, Section C.2.3.2, last paragraph Nuclear In Figure 5 Acceptance guidelines for large early release frequency The NRC agrees with the comment and revised the cited figure as Energy suggest changing the reference in Region III from CDF to LERF and proposed.
Institute removing the Track Cumulative Changes. [NEI1-24]
See page 28, Section C.2.4, Figure 5 Nuclear Regarding sentence In addition, if compensatory measures are The NRC agrees with the comment and revised the cited language Energy proposed to counter the impact of the major risk contributors, such from, In addition, if compensatory measures are proposed to counter Institute arguments are considered in the decision process quantitatively. It is the impact of the major risk contributors, such arguments are not clear if quantifying compensatory measures is required for all cases considered in the decision process quantitatively to:
or just in cases where it is appropriate. Suggest adding more guidance In addition, if compensatory measures are proposed to counter the to provide clarity. [NEI1-25]
impact of the major risk contributors that influence the ability to demonstrate that the acceptance guidelines are met, those compensatory See page 34, Section C.2.5.5, 3rd paragraph measures should be included in the PRA model that supports the application.
Nuclear Regarding sentence Section C.6 of NUREG-1855 provides acceptable The NRC agrees that the cited language needs to be revised, but Energy guidance on addressing the SOKC. Suggest using Appendix 6-A of changed the reference to Section C.6 of NUREG-1855 to Section 6, Institute NUREG-1855. [NEI1-26] rather than directly to Appendix 6-A. The intent of directing the
reader to the Section 6 instead of Appendix 6-A is to first expose the See page 34, Section C.2.5.5, 2nd paragraph reader to the higher-level guidance on the SOKC provided in Section 6 of NUREG-1855, which includes a reference to the related Electric Power Research Institute report that provides guidance on the SOKC, and then direct the reader to Appendix 6-A for more detailed guidance.
10
Commenter Specific Comments NRC Resolution Nuclear Regarding sentence In many applications, the potential risk can be The NRC agrees with the comment that a revision is needed, but Energy limited by defining specific measures and criteria that are be monitored revised the cited language as follows to make the sentence slightly Institute subsequent to approval. The word to should be added between are easier to read:
and be. [NEI1-27]
In many applications, defining specific measures and criteria to be See page 36, Section C.2.6, 5th paragraph monitored subsequent to approval can limit the potential risk.
Nuclear Replace the sentence Quantitative risk results from PRA calculations The NRC disagrees with the comment and believes that it is important Energy are typically the most useful and complete characterization of risk, but to retain the existing language on the basis that qualitative risk insights Institute they should be supplemented by qualitative risk insights and traditional and traditional engineering analysis provide supplemental information engineering analysis where appropriate. with The quantitative risk that may not be completely addressed by a PRA (e.g., the unknown results from PRA models, when supplemented by an identification of unknowns). However, the cited language was revised as follows to the contributors and the corresponding risk insights, provide the most provide additional clarity on the context of the statement.
useful and complete characterization of the risk implications of the For risk-informed licensing basis changes, quantitative risk results proposed licensing basis change. [NEI1-28]
from PRA calculations are typically the most useful and complete characterization of risk, but they should be supplemented by qualitative See page 36, Section C.2.6, 2nd paragraph risk insights and traditional engineering analysis where appropriate.
Nuclear Replace the sentence Qualitative risk insights include generic results The NRC disagrees with the proposed revision of the cited language as Energy that have been learned from previous PRAs and from operational it is considered to be complimentary to the proposed resolution of Institute experience. with In addition, qualitative risk insights, including comment NEI1-28. However, the cited language was revised as follows generic results that have been learned from previous PRAs and from to provide additional clarity.
operational experience, can be used to supplement plant specific Qualitative risk insights may include generic results that have been insights. [NEI1-29]
learned from previous PRAs and from operational experience.
See page 36, Section C.2.6, 2nd paragraph Nuclear The first bullet ends with a period; however, it should be a comma. The NRC agrees that the period is an error, but changed the period to a Energy [NEI1-30] semicolon, rather than the comma suggested by the comment. This Institute ---- comment relates to the list of bullets on page 37.
See page 37, Section C.2.6, 1st bullet of list 11
Commenter Specific Comments NRC Resolution Nuclear Regarding the sentence In developing the risk information set forth in The NRC agrees with the comment and revised the cited language to Energy this RG, licensees are likely to identify SSCs with high risk significance the following:
Institute that are not currently subject to regulatory requirements or are subject In developing the risk information in this RG, licensees may identify to a level of regulation that is not commensurate with their risk SSCs with high risk significance that are not currently subject to significance. This sentence is speculative, and as such, should be regulatory requirements or are subject to a level of regulation that is not deleted or clarified to communicate the intent. [NEI1-31]
commensurate with their risk significance.
See page 40, Section C.4, last paragraph Nuclear Regarding the sentence The licensees resolution of the findings of the Although this comment is outside the scope of changes considered for Energy peer review should also be submitted. The sentence should be clarified Revision 3 of RG 1.174, the NRC agrees with the comment and does Institute to state that F&O resolutions are only submitted if they have not been not believe it would impact other parts of the RG, and therefore, would Closed Out per the Peer Review Finding Closure Process (Appendix not require any additional consideration. Consequently, the NRC X of NEI peer review Guidelines). Suggest stating The licensees revised the cited sentence to the following:
resolution of open peer review findings should also be submitted.
The licensees resolution of the findings of the peer review that have
[NEI1-32]
not been closed by an NRC-accepted process should also be submitted (see Section C.4.2 of RG 1.200 for additional guidance).
See page 42, Section C.6.3, last paragraph Additionally, in the final Federal Register notice (FRN) announcing the publication of Revision 3 of RG 1.174, the NRC included a discussion of the NRCs acceptance via a letter issued on May 3, 2017, (See ADAMS Accession No. ML17079A427) of an industry process entitled Close-out of Facts and Observations (F&Os) (See ADAMS Accession No. ML17086A431) that allows a licensee to formally close F&Os that were generated during a peer review process. In particular, the FRN will note that, if a licensee meets the conditions of acceptance as described in the NRCs letter, a licensee does not need to submit the closed F&Os in any future applications. Further, it was also noted that the NRC position in its May 3rd letter is expected to be incorporated into the next revision of RG 1.200.
12
Commenter Specific Comments NRC Resolution Nuclear Regarding the bullet that states An assessment of the change to CDF The NRC agrees that the phrase an assessment of realism in the cited Energy and LERF, including a description of the significant contributors to the text is unclear. Because an assessment of realism is not considered by Institute change and an assessment of the realism with which those contributors the NRC to be necessary for the review of an application, the phrase, have been evaluated. The phrase an assessment of realism is vague. ...and an assessment of the realism with which those contributors have Suggest that the phrase is clarified to ensure consistent interpretation. been evaluated, was deleted from the text.
[NEI1-33]
See page 43, Section C.6.3.1, 2th bullet of second list Nuclear Regarding the paragraph As an option, the submittal could also list This comment is outside of the scope of changes considered for Energy (but not submit to the NRC) past changes to the plant that reduced the Revision 3 of RG 1.174 and addresses language that was not revised Institute plant risk, especially those changes that are related to the current and has not had a negative impact on applications. Moreover, the application. A discussion of whether these changes are already included comment may impact other parts of the RG and therefore may need in the base PRA model should also be included. This paragraph is additional consideration. Additionally, it is unclear how the cited vague and unclear. Suggest adding additional language to ensure that language should be expanded to address the concern. Although no the guidance is clear and can be consistently implemented. [NEI1-34] changes have been made in response to this comment, the NRC will
document this comment for consideration in a subsequent revision to See page 44, Section C.6.3.2, last paragraph RG 1.174.
13
Commenter Specific Comments NRC Resolution Nuclear Regarding the sentence The NRC staff does not expect any existing The NRC disagrees with this comment and did not make any related Energy licensee to use or commit to using the guidance in this RG, unless the changes to the text. The language in Section D is generic template text, Institute licensee makes a change to its licensing basis. Suggest changes the written in coordination by multiple NRC offices to describe the NRCs sentence to read The NRC staff does not expect any existing licensee general intent regarding how regulatory guides will be used by the NRC to use or commit to using the guidance in this RG, unless the licensee staff, and is used verbatim in most NRC regulatory guides. Although makes a risk-informed change to its licensing basis. [NEI1-35] the NRC staff considers this template texts applicability for each
regulatory guide, it is not expected to change except under unusual See page 45, Section D, 4th paragraph circumstances, which do not exist for this regulatory guide. As such, the revision proposed by the comment could have significant implications for how this text should be interpreted in other regulatory guides. The following text from Section D explains more specifically when this regulatory guide would be applied, which addresses the concern raised by this commenter:
If an existing licensee voluntarily seeks a license amendment or change and (1) the NRC staffs consideration of the request involves a regulatory issue directly relevant to this RG and (2) the specific subject matter of this RG is an essential consideration in the staffs determination of the acceptability of the licensees request, then the staff may request that the licensee either follow the guidance in this RG or otherwise demonstrate compliance with the underlying NRC regulatory requirements.
Westinghouse Once RG 1.174, Revision 3 is approved, NUREG-1855 should be The NRC agrees with this comment. The NRC will document this Electric revised to reference the appropriate revision number. [WEC1-2] comment for consideration in a subsequent revision of NUREG-1855.
Company 14
Commenter Specific Comments NRC Resolution Southern The last paragraph of this section only partially supports use of risk- The NRC disagrees with the proposed resolution and did not make any Nuclear informed methods to modify TS completion times. The problem has related changes to the text. The NRC does not believe that the level of Operating been technical branches not allowing changes in risk-informed detail of the proposed resolution is appropriate for this Regulatory Company completion times because they disagree with the redundancy available Guide and that including such detailed guidance may be considered by when in a TS Action. Also, the NRC should consider revising Branch the Commission to be too prescriptive. The NRC recognizes that there Technical Position (BTP) 8-8 to eliminate conflict with R.G. 1.17 4 and have been issues related to inconsistent interpretation and to ensure BTP 8-8 adequately considers risk model insights for one- implementation of the defense-in-depth philosophy, which is the basis time or permanent allowable outage time extensions. for the development of this revision of RG 1.174. However, the NRC believes that the new guidance provided in Section C.2.1 is sufficient to Proposed Resolution: Add this as the last sentence. "Therefore, if a address the commenters concern. Regarding the elimination of licensee submits a request for a change to a Technical Specification BTP 8-8, such actions fall outside the scope of effort for the Completion Time based on risk-informed methods, it is not necessary to development of RG 1.174, Revision 3. However, this comment will be show single failure criteria is preserved during the brief allowable documented for further consideration by the NRC.
outage time if the requested time meets risk-informed criteria.
[SNC1-1]
See page 20, Section C.2.1.1.3, Item 3 Southern This guidance assumes the failure cause or coupling factor is known. It The NRC disagrees with the proposed resolution and did not make any Nuclear also does not recognize that protective actions for the redundant (vs. related changes to the text. The NRC does not consider the action of Operating diverse) component can reduce total plant risk. lowering total plant risk as a means of defending against common-cause Company failures, nor does reducing the total plant risk by protecting diverse or Proposed Resolution: In the third paragraph of this section, add a third redundant equipment, reducing the initiating event frequency, etc.
approach as follows: (3) reduce total plant risk by other means. Add defend against common cause failures. The NRC recognizes that the this as the last sentence: For proposed changes that weaken an existing discussion in the RG implicitly assumes that the failure cause or defense against common cause an acceptable mitigating argument could coupling factor can be (or is) understood with some degree of be based on compensatory measures to reduce the risk such as: reducing confidence and thus, the appropriate defense can be implemented. In the total plant risk by protecting diverse or redundant equipment, situations where the failure cause or coupling factor is not understood, reducing the initiating event frequency, etc." [SNC1-2]
the CCF contributor(s) for the associated group of components is (are) typically adjusted to reflect the increased conditional probability that See pages 20 to 21, Section C.2.1.1.3, Item 4 the group of components is susceptible to the same cause or coupling factor. Since the discussion is related to defending against common cause failures and not related to how to model specific situations, the above explanation is not presented in the RG. The NRC revised the text of the related paragraph (i.e., the third paragraph of item 4 in Section C.2.1.1.3) to include consideration of CCF dependencies and to cite relevant reference documentation.
15
Commenter Specific Comments NRC Resolution Southern Section 2.1.1 lists seven factors to evaluate how the proposed licensing The NRC disagrees with the proposed resolution and did not made any Nuclear basis change impacts defense-in-depth. Section 2.1.1.3 says it is related changes to the text. The language in the first paragraph of Operating considered acceptable to use the seven DID evaluation factors described Section C.2.1.1.3 related to noncompliance issues is not intended to Company in Section 2.1.1.2 to evaluate the impact of a proposed licensing basis imply that, for any given risk-informed licensing basis change, a review change on DID. Section 2.1.1.3 then says that it is presumed that, prior of the licensing basis should be performed in order to identify where the to the implementation of the proposed licensing basis change, the as- licensing basis is inconsistent with the defense-in-depth philosophy.
built and as-operated plant is consistent with the DID philosophy. If the The language is only intended to apply in cases where the there is a as-built and as-operate plant is not consistent with DID philosophy, known noncompliance issue.
Section 2.1.1.3 says the licensee and the staff should ensure compliance with existing requirements and implement an appropriate action to address any non-compliances. Section 2.1.1.2 DID evaluation Factor 4 to preserve adequate defense against potential common cause failure maintains the use of diverse components to provide the same safety function to prevent common cause failure from using the same components.
Proposed Resolution: The seven DID evaluation factors may not be the ones which were used to determine a plants compliance in DID philosophy for issuing the operation license for the plant. The seven DID evaluation factors in RG 1.174 should be consistent with the existing DID philosophy, which was used for the licensing of the as-built as-operated plant. [SNC1-3]
See pages 13 to 23, Sections C.2.1.1 to C.2.1.1.3 16
Commenter Specific Comments NRC Resolution Exelon This comment relates to the following text, In addition, this revision See the staffs response to similar comments in [NEI1-3] and [WEC1-Generation adopts the term PRA Acceptability, including related phrasing 1].
Company variants, in place of the terms PRA quality and technical adequacy to describe the appropriateness of the PRA used to support risk-informed licensing submittals. It is not entirely clear why this change is being made. One possibility is that it is a reaction to the following circular sentence in Revision 2: The technical adequacy of a PRA analysis used to support an application is measured in terms of its appropriateness with respect to scope, level of detail, technical adequacy, and plant representation (emphasis added). When the NRC used the term PRA Quality in documents such as SECY-04-0118 (Phased Approach Plan), the intention was to describe what the NRC would find as an acceptable PRA for a licensee to use in an application.
To that extent, changing the high-level concept from PRA quality or PRA adequacy to acceptability is semantically equivalent and should cause no misunderstanding. The intent is to make sure that the PRA has the appropriate scope, level of detail, conformance with the technical elements, and plant representation. In RG 1.200, which is entitled An Approach for Determining The Technical Adequacy of Probabilistic Risk Assessment Results For Risk-Informed Activities, conformance with the technical elements is addressed by showing conformance with the requirements of the standard, which demonstrates that, at the technical level, the PRA or the parts that are used to support an application have been performed in a technically correct manner. In this context the term technical adequacy has come to mean conformance with the standard.
Proposed Resolution: Section 2.3.2 Probabilistic Risk Assessment Technical Elements to Support an Application. Suggest changing the title to Technical Adequacy of the Probabilistic Risk Assessment to Support an Application. This addresses the issue of whether the PRA is technically correct and defendable. The term PRA acceptability is retained for the higher level to replace the old term PRA Quality.
[EGC1-1]
See page 3, Section B - Reason for Revision 17
Commenter Specific Comments NRC Resolution Exelon This comment relates to the following text: The PRA analysis used to See the staffs response to similar comments in [NEI1-3] and [WEC1-Generation support an application is measured in terms of its appropriateness with 1].
Company respect to scope, level of detail, conformance with the technical elements, and plant representation. See above (i.e., comment EGC1-1).
The change at the lower level has the potential to be confusing, since the term technical adequacy has come to be understood as conformance with the Standard. [EGC1-2]
See page 24, Section C.2.3 Exelon These paragraphs do not seem to flow well - suggest Although this comment is outside the scope of changes considered for Generation rewording/rewriting the paragraphs to address NRC programs first, then Revision 3 of RG 1.174, the NRC does not believe revising the Company follow on to the purpose of this RG. language would impact other parts of the RG, and therefore, would not require any additional consideration. The NRC agrees that the second Proposed Resolution: In parallel with the publication of the policy and third paragraphs on page 4 are confusing and considers them to be statement, the staff developed an implementation plant to define and the unnecessary for the narrative in Section B. As such, these two PRA-related activities being undertaken. This implementation plan is paragraphs were removed from the guidance.
known as the Risk-Informed and Performance-Based Plan, which is abbreviated as RPP. These activities cover a wide range of PRA applications and involve the use of a variety of PRA methods (with variety including both types of models used and the detail of modeling needed). With respect to reactor regulation, activities include for example, developing guidance for NRC inspectors on focusing inspection resources on risk important equipment and reassessing plants with relatively high CDFs for possible backfit. Another example involves the use of PRA in the assessment of operational events in reactors. The characteristics of these assessments rely on model changes or simplifying assumptions to change the PRA models so that they reflect the conditions experienced during an operational event. In contrast, other applications require the use of detailed performance and design information to provide a more realistic model of the plant.
[EGC1-3]
See page 4, Section B, 2nd and 3rd paragraphs 18
Commenter Specific Comments NRC Resolution Exelon Second paragraph begins with the sentence "To defend against CCF, The NRC agrees that a revision is appropriate, but rather than adopt the Generation one should first identify potential coupling factors between equipment suggested revision, the staff replaced the discussion of coupling factors Company failures." Searching for the cause should logically precede the search with a more general discussion of defenses against CCFs. The basis for for a coupling factor. On Page 16, it is not clear why this is included as this replacement is that level of detail of the discussion for a coupling factor. It is a cause of dependency, but not a Common Cause Consideration 4 in Section C.2.1.1.2 was inconsistent with the level of Factor (CCF) as defined in the literature. Support system dependencies detail of discussions for the other considerations in Section C.2.1.1.2.
(e.g., common power supplies, ventilation, cooling water, etc.). The discussion of Consideration 4 in Section C.2.1.1.3 was expanded to include a reference to more detailed documentation relevant to CCF.
Proposed Resolution: To defend against CCF, one should first understand the cause and then identify potential coupling factors between equipment failures. This parallels the discussion of the demonstration of addressing the factor. Suggest deleting the fourth bullet. [EGC1-4]
See pages 15 and 16, Section C.2.1.1.2, Item 4 Exelon Human errors include the failure of operators to perform the action The NRC agrees with the comment that additional clarification is Generation necessary to operate the plant or respond to off-normal conditions and appropriate, but rather than adopt the suggested revision, the staff Company accidents, errors committed during test and maintenance, and other revised the cited language as follows:
plant staff performing an incorrect action. Even though errors of commission in PRAs are not modeled, there should be some Human errors include the failure of operators to correctly and consideration for the potential for creating the conditions under which promptly perform the actions necessary to operate the plant or respond an Extent of Condition (EOC) might be more likely. Is this what the last to off-normal conditions and accidents, errors committed during test phrase is referring to? and maintenance, and incorrect actions by other plant staff.
Proposed Resolution: Human errors include the failure of operators to perform the actions necessary to operate the plant or respond to off-normal conditions and accidents correctly and in a timely manner, errors committed during test and maintenance, and other plant staff performing an incorrect action. [EGC1-5]
See page 16, Section C.2.1.1.2, 1st paragraph under item 6 19
Commenter Specific Comments NRC Resolution Exelon The following sentences seem somewhat out of place. It appears that The NRC disagrees with the comment and did not make any related Generation this should be addressed under a different process. "However, there changes to the text. The NRC position is that the cited language is only Company might be situations where a plant is not in compliance with its design applicable in cases where there is a known noncompliance issue.
basis or licensing basis or new information might arise indicating that the design basis or licensing basis is deficient. In such cases, the as-built and as-operated plant might not be consistent with the defense-in-depth philosophy prior to the implementation of the proposed licensing basis change. When this occurs, the licensee and the staff should ensure compliance with existing requirements (e.g., regulations, license conditions, orders, etc.) and implement appropriate actions to address any non-compliances. When addressing these deficiencies or non-compliances, consideration should be given to the concepts in this document to help achieve consistency with the defense-in-depth philosophy."
Proposed Resolution: Suggest deleting these sentences. [EGC1-6]
See page 17, Section C.2.1.1.3, first paragraph 20
Commenter Specific Comments NRC Resolution Exelon This discussion essentially provides no new guidance on how to address The NRC agrees that the paragraph cited in the proposed resolution Generation this item other than to look at each of the four layers in turn. Since this could be expanded, but rather than adopt the suggested revision, the Company is a RG addressing the use of Probabilistic Risk Assessment (PRA), one NRC staff revised the text to insert the following sentence before the might expect some guidance on how to use the PRA to provide insights last sentence of the paragraph cited in the proposed resolution.
into how the balance is achieved both prior to and post change.
Understanding the drivers of the change in risk (i.e., at the level of Understanding the drivers of the change in risk (i.e., at the level of initiating events, accident sequences, cut sets, etc.) can focus attention initiating events, accident sequences, cut sets, etc.) can focus attention on which aspect of defense-in-depth is likely to be affected.
on which aspect of defense-in-depth is likely to be affected. For example, for very low frequency scenarios, such as Large LOCAs, for which the diversity of mitigation methods is reduced, it may be more important to focus on changes that might affect the likelihood of the initiator.
Proposed Resolution: An expansion of the following paragraph providing some examples of how the risk assessment can be used would be helpful: A comprehensive risk analysis can provide insights into whether the balance among the layers of defense remains appropriate to ensure protection of the public health and safety. Such a risk analysis would include the likelihood of challenges to the plant (i.e., initiating event frequencies) from various hazards as well as CDF, containment response, and dose to the public. In addition, qualitative and quantitative insights from the PRA might help justify that the balance across all the layers of defense is preserved. [EGC1-7]
See page 18, Section C.2.1.1.3, 4th paragraph under item 1 21
Commenter Specific Comments NRC Resolution Exelon There is relatively little concrete guidance on how to demonstrate that The NRC disagrees with the proposed resolution and did not make any Generation these factors are met. Furthermore, some of them are clearly related. related changes to the text. While the NRC recognizes that there are Company For example, the introduction of a compensatory measure is relevant to some PRA insights that can be used to inform the evaluation of whether the assessment of both Items 2 and 6. the licensing basis change maintains consistency with the defense-in-depth philosophy, the scope of this portion of the RG is relates to Proposed Resolution: Expanding the guidance to focus on using PRA performing that evaluation using the seven defense-in-depth insights to focus the attention on where defense-in-depth is weakest considerations (formerly known as factors). As stated in resolution to would help. While the PRA can only reflect what is in the model, and EGC1-7, the staff revised the guidance to include additional does not address the unknowns, the value comes in the presumption that information about how PRA insights may be used for the defense-in-we start with adequate defense-in-depth and what we're looking for is depth evaluation. Moreover, as stated in Section B, NUREG/KM-0009, changes. The scenarios that are driving the change will provide the Historical Review and Observations of Defense-in-Depth is a necessary focus. [EGC1-8]
recommended resource for gaining a more detailed understanding of defense-in-depth.
See pages 12 through 23, Section C.2.1 Exelon The discussion focuses on the introduction of new compensatory The NRC agrees with the comment and revised the following text in the Generation measures, but one possible change is to the way in which programmatic second paragraph of the second defense-in-depth consideration from, Company activities are conducted, which might lessen their effectiveness The evaluation of the proposed licensing basis change should compared to the base case. demonstrate that the change does not result in an excessive reliance on programmatic activities that are used to compensate for an intended Proposed Resolution: Consider a discussion of License Amendment reduction in the capability of engineered safety features, to:
Requests (LARs) that address changes to programmatic activities as opposed to design changes. [EGC1-9]
The evaluation of the proposed licensing basis change should demonstrate that the change does not result in an excessive reliance on See page 19, Section C.2.1.1.3, Item 2 programmatic activities that are used to compensate for an intended reduction in the capability of engineered safety features (or previously approved programmatic activities).
22
Commenter Specific Comments NRC Resolution Exelon This first sentence seems superfluous. "The proposed licensing basis The NRC agrees with the comment that additional clarification is Generation change should not significantly increase the potential for or create new appropriate, but rather than adopt the suggested revision, the staff Company human errors that might adversely impact one or more layers of revised the text by replacing the three list items under the sixth defense-defense. With respect to the bullets, creating new actions is not in in-depth consideration (formerly known as a factor) in Section C.2.1.1.3 itself a demonstration of a loss of defense-in-depth, and in fact could with the following:
be a compensatory measure. What is important, is whether the response can be performed reliably. Mental and physical demands are two (1) create new human actions that are important to preserving any of important PSFs but they are not the only ones. the layers of defense for which a high reliability cannot be demonstrated or (2) significantly increase the probability of existing Proposed Resolution: Suggest clarifying the intent. Consider the human errors by significantly affecting performance shaping factors, following: The evaluation of the proposed licensing basis change including mental and physical demands and level of training.
should demonstrate that the change does not adversely affect the ability of plant staff to perform necessary actions, nor introduce new required actions for which the likelihood of failure is not insignificant.
- Create new human actions that are important to preserving any of the layers of defense for which a high reliability cannot be demonstrated.
- Significantly increase the probability of existing human errors by virtue of significantly affecting PSFs including, for example, mental and physical demands, and level of training. [EGC1-10]
See page 22, Section C.2.1.1.3, Item 6 Exelon There appears to be a typographical discrepancy in the LERF The NRC agrees with the comment and revised the cited language in Generation figure (CDF instead of LERF in the Region III annotation) [EGC1-11] Figure 5 as proposed.
Company ----
See page 28, Section C.2.4, Figure 5 23
Commenter Specific Comments NRC Resolution Exelon It is becoming commonly accepted that the quantitative results are good The NRC agrees that the cited language on quantitative risk results and Generation indicators but that they must be augmented with an understanding of the the subsequent sentence need additional clarification; these sentences Company contributors. The following sentence is therefore a little misleading: were revised based on similar concerns expressed in comments "Quantitative risk results from PRA calculations are typically the most NEI1-28 and NEI1-29. Additionally, the NRC expanded the guidance useful and complete characterization of risk, but they should be under the first defense-in-depth consideration in Section C.2.1.1.3 in supplemented by qualitative risk insights and traditional engineering response to comment EGC1-7 to emphasize how PRA can be used in analysis where appropriate." evaluating whether the proposed licensing basis change is consistent with the defense-in-depth philosophy. This expansion of the guidance Proposed Resolution: The following is believed to be a more accurate provides similar language to that proposed by the commenter for the statement: "The quantitative risk results from PRA models when third paragraph of Section C.2.6. The NRC believes these changes supplemented by an identification of the contributors and the adequately address this comment and have not made any additional corresponding risk insights provide the most useful and complete related changes to the text.
characterization of the risk implications of the proposed licensing basis change. In the third paragraph, suggest adding the words as indicated to link to the use of the PRA. Traditional engineering analysis provides insight into available margins and defense-in-depth. With few exceptions, these assessments are performed without any quantification of risk. However, a PRA can provide insights regarding the strengths and weaknesses of the plant design and operation relative to defense-in-depth by identifying significant contributors (cut-sets) to the relevant metrics and assessing whether the proposed change affects scenarios where the defense-in-depth or safety margins are marginal. [EGC1-12]
See page 36, Section C.2.6, 2nd paragraph 24