ML003740149

Regulatory Gudie 1.175 (Draft Was Issued as DG-1062), an Approach for Plant-Specific, Risk-Informed Decisionmaking: Inservice Testing

ML003740149
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Issue date:	08/31/1998
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RG-1.175
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U.S. NUCLEAR REGULATORY COMMISSION August 1998 REGULATORY GUIDE OFFICE OF NUCLEAR REGULATORY RESEARCH REGULATORY GUIDE 1.175 (Draft was Issued as DG-1 062)

AN APPROACH FOR PLANT-SPECIFIC, RISK-INFORMED DECISIONMAKING: INSERVICE TESTING A. INTRODUCTON are consistent with currently approved staff positions (e.g., regulatory guides, standard review plans, branch technical positions) are normally evaluated by the NRC

Background

staff using traditional engineering analyses. In such During the last several years both the U.S. Nuclear cases, the licensee would not be expected to submit risk Regulatory Commission (NRC) and the nuclear indus information in support of the proposed change.

try have recognized that probabilistic risk assessment Licensee-initiated IST program change requests that go (PRA) has evolved to be more useful in supplementing beyond current staff positions may be evaluated by the traditional engineering approaches in reactor regula staff using traditional engineering analyses as well as tion. After the publication of its policy statement (Ref. the risk-informed approach set forth in this regulatory

1) on the use of PRAin nuclear regulatory activities, the guide. A licensee may be requested to submit supple Commission directed the NRC staff to develop a regu mental risk information if such information is not pro latory framework that incorporated risk insights. That vided in the proposed risk-informed inservice testing framework was articulated in a November 27,1995, pa (RI-IST) program submitted by the licensee. If risk in per to the Commission (Ref. 2). This regulatory guide, formation on the proposed RI-IST program is not pro which addresses inservice testing (IST) of pumps and vided to the staff, the staff will review the information valves, and its companion regulatory documents (Refs. provided by the licensee to determine whether the ap 3-8) implement, in part, the Commission policy state plication can be approved based upon the information ment and the staff's framework for incorporating risk provided using traditional methods, and the staff will insights into the regulation of nuclear power plants. either approve or reject the application based upon the The NRC's policy statement on probabilistic risk review. For those licensee-initiated RI-IST program analysis encourages greater use of this analysis tech changes that a licensee chooses to support (or is re nique to improve safety decisionmaking and improve quested by the staff to support) with risk information, regulatory efficiency. One activity under way in re this regulatory guide describes an acceptable method sponse to the policy statement is the use of PRAin sup for assessing the nature and impact of proposed RI-IST port of decisions to modify an individual plant's IST program changes by considering engineering issues program. Licensee-initiated IST program changes that and applying risk insights. Licensees submitting risk USNRC REGULATORY GUIDES The guides ae Issued Inthe following ten broad divisions:

Regulatory Guides aweIssued to describe and make available to the public auch Wlorma ton as methods acceptable to he NRC staff for Implementing specific parts of the Com- 1. Power Reactors 6. Products mission's regulations, lechniques used by the staff inevaluating specific problemror pos- 2. Research and Test Reactors 7. Transportation tulated accidents, and data needed by the NRC staff in its review of applications for per- 3a Fuels and Materials Facilities & Occupational Health mits aid licenss. Regulatory guides are not substitutes for regulations, and comprmence 4. Environmental and Sting 9. Antitrust and Frnancial Review with them i not requlred. Methodsnd solutMonsdifferentfrom ho9 setoutIntheguides materials "n Plant Protection 10L General wil be acceptable Ithey provide a basis for the findings requisite to the Issuance or con Unuance of a permit or license by the Commission. Single copies of regulatory goides may be obtained free of charge by writing the Repro duction and Distribution Services Section, Office of the Chief Information Officer, U.S. Nu considerationhnofthesae guides racaived all times,Corn-from theatpublic- or by Regulatory dear Commission, Washington, DC 20555-0001; or by fax at (301)415-2289; This menitsgilds end suggestions lor iomments was Isued after improvements areencouraged on a-mail to GRWl@NRC.GOV.

to reflect new In deswilbe revised, as appropriate, to accommodate comments and ation or aipennc. Issued guides may also be purchased from the National Technical Information Service on Written commerts may be aubmitted lo the Rules Review and Directives Branch, ADM, a standing order basis. Details on this service may be obtained by writing NTIS, 5285 Port U.S. Nuclear Regula Commission, Washington, DC 20555-0001. Royal Road, Springfleld, VA 22161.

information should address each of the principles of ance on the technical aspects that are common to devel risk-informed regulation discussed in Regulatory oping acceptable risk-informed programs for all ap Guide 1.174, "An Approach for Using Probabilistic plications such as 1ST (this guide), inservice Risk Assessment in Risk-Informed Decisions on Plant inspection, graded quality assurance, and technical Specific Changes to the Licensing Basis" (Ref. 3) and specifications.

repeated in this guide. Licensees should identify how This regulatory guide provides application chosen approaches and methods (whether they are specific details of a method acceptable to the NRC staff quantitative or qualitative, traditional or probabilistic), for developing RI-IST programs and supplements the data, and criteria for considering risk are appropriate for information given in Regulatory Guide 1.174. This the decision to be made. guide provides guidance on acceptable methods for uti IST of snubbers was not addressed in this regula lizing PRA information with established traditional en tory guide, however, licensees interested in implement gineering information in the development of RI-IST ing a RI-IST program for snubbers may submit an alter programs that have improved effectiveness regarding native to the NRC for consideration. the utilization of plant resources while still maintaining acceptable levels of quality and safety.

Relationship to the Maintenance Rule In this regulatory guide, an attempt has been made 10 CFR 50.65 to strike a balance in defining an acceptable process for The Maintenance Rule, Section 50.65, "Require developing RI-IST programs without being overly pre ments for Monitoring the Effectiveness of Maintenance scriptive. Regulatory Guide 1.174 identifies a list of at Nuclear Power Plants," of 10 CFR Part 50, "Domes high-level safety principles that must be maintained tic licensing of Production and Utilization Facilities," during all risk-informed plant design or operational requires that licensees monitor the performance or con changes. Regulatory Guide 1.174 and this guide iden dition of structures, systems, or components (SSCs) tify acceptable approaches for addressing these basic against licensee-established goals in a manner suffi high-level safety principles; however, licensees may cient to provide reasonable assurance that such SSCs propose other approaches for consideration by the NRC are capable of fulfilling their intended function. Such staff. It is intended that the approaches presented in this goals are to be established, where practicable, com guide be regarded as examples of acceptable practice mensurate with safety, and they are.to take into account and that licensees should have some degree of flexibil industrywide operating experience. When the perfor ity in satisfying regulatory needs on the basis of their mance or condition of a component does not meet es accumulated plant experience and knowledge.

tablished goals, appropriate corrective actions are to be Organization taken.

This regulatory guide is structured to follow the ap Component monitoring that is performed as part of proach given in Regulatory Guide 1.174. The discus the Maintenance Rule implementation can be used to sion, Part B, gives a brief overview of a four-element satisfy monitoring needs for RI-IST, and for such cases, process described in Regulatory Guide 1.174 as applied the performance criteria chosen should be compatible to the development of an RI-IST program. This process with both the Maintenance Rule requirements and is iterative and generally not sequential. Part C, Regula guidance and the RI-IST guidance provided in this tory Position, provides a more detailed discussion of guide. the four elements including acceptance guidelines. In Part C, Regulatory Position 1 addresses the first ele Purpose and Scope ment in the process in which the proposed changes to Current IST programs are performed in com the IST program are described. This description is pliance with the requirements of 10 CFR 50.55a(f) and needed to determine what supporting information is with Section XI of the ASME Boiler and Pressure Ves needed and to define how subsequent reviews will be sel Code (Ref. 9), which are requirements for all plants. performed. Regulatory Position 2 contains guidance This regulatory guide describes an acceptable alterna for performing the engineering evaluation needed to tive approach applying risk insights from PRA to make support the proposed changes to the IST program (sec changes to a nuclear power plant's IST program. An ac ond process element). Regulatory Position 3 addresses companying Standard Review Plan (SRP) (Ref. 7) has program implementation, performance monitoring, been prepared for use by the NRC staff in reviewing RI and corrective action (third element). Regulatory Posi IST applications. Another guidance document, Regula tion 4 addresses documentation requirements (fourth tory Guide 1.174 (Ref. 3), is referenced throughout this element) for licensee submittals to the NRC and identi report. Regulatory Guide 1.174 provides overall guid- fies additional information that should be maintained in 1.175-2

the licensee's records in case later review or reference is ISI inservice inspection needed. The appendix contains additional guidance for IST inservice testing dealing with certain IST-related issues such as might LERF containment large early release frequency arise during the deliberations of the licensee in carrying out integrated decisionmaking. LSSC low safety-significant component MCS minimal cut set Relationship to Other Guidance Documents NEI Nuclear Energy Institute This regulatory guide provides detailed guidance NUMARC Nuclear Utilities Management Research on approaches to implement risk insights in IST pro Council grams that are acceptable to the NRC staff. This O&M Operations and Maintenance (ASME application-specific guide makes extensive reference committee) to Regulatory Guide 1.174 (Ref. 3) for general guid ance. PRA probabilistic risk assessment PSA probabilistic safety assessment Companion regulatory guides (Refs. 4 and 5) ad dress graded quality assurance and technical specifica RAW risk achievement worth risk importance tions, and contain guidance similar to that given in this measure RI-ISTguide. SRP chapters associated with the risk-in RI-IST risk-informed IST (e.g., RI-IST programs) formed regulatory guides are available (Refs. 6-8). The SRP standard review plan SRP chapters are intended for NRC use during the re SSCs structures, systems, and components view of industry requests for risk-informed program changes. SRP Chapter 3.9.7 (Ref. 7) addresses RI-IST THERP Technique for Human Error Rate Predic and is consistent with the guidance given in this regula tion tory guide. USAR Updated Safety Analysis Report In the 1995-1998 period, the industry developed a USNRC U.S. Nuclear Regulatory Commission number of documents addressing the increased use of The information collections contained in this regu PRAin nuclear plant regulation. The American Society latory guide are covered by the requirements of 10 CFR of Mechanical Engineers (ASME) developed guide Part 50, which were approved by the Office of Manage lines for risk-based IST (Ref. 10) and later initiated ment and Budget, approval number 3150-0011. The code cases addressing IST component importance NRC may not conduct or sponsor, and a person is not ranking and testing of certain plant components using required to respond to, a collection of information un risk insights. The Electric Power Research Institute less it displays a currently valid OMB control number.

(EPRI) published its "PSA Applications Guide" (Ref.

11) to provide utilities with guidance on the use of PRA information for both regulatory and nonregulatory ap B. DISCUSSION plications. The Nuclear Energy Institute (NEI) has also been developing guidelines on risk-based IST (Ref. Key Safety Principles 12). These documents have provided useful viewpoints Regulatory Guide 1.174 (Ref. 3) identifies five key and proposed approaches for the staff's consideration safety principles to be met for all risk-informed applica during the development of the NRC regulatory guid tions and to be explicitly addressed in risk-informed ance documents. plant program change applications. As indicated in Abbreviations Regulatory Guide 1.174, while these key principles are stated in traditional engineering terminology, efforts ASME American Society of Mechanical Engi should be made wherever feasible to utilize risk evalua neers tion techniques to help ensure and to show that these CCF common cause failure principles are met. These key principles and the loca CDF core damage frequency tion in this guide where each is addressed for RI-IST programs are as follows:

EPRI Electric Power Research Institute FV Fussell-Vesely risk importance measure 1. The proposed change meets the current regu lations unless it Is explicitly related to a requested GQA graded quality assurance exemption or rule change. (This principle is ad HEP human error probability dressed in Regulatory Positions 1.1 and 2.1 of this HSSC high safety-significant component guide.)

I1.1

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Figure 1 Principles of Risk-Informed Regulation

2. The proposed change is consistent with the tions made about the impact of the changes to the IST defense-in-depth philosophy. (Regulatory Position program are not invalidated. For example, if the test in 2.2.1) tervals are based on an allowable margin to failure, the monitoring is performed to make sure that these mar

3. The proposed change maintains sufficient gins are not eroded. An overview of this process specif safety margins. (Regulatory Position 2.2.2) ically related to RI-IST programs is given in this sec

4. When proposed changes result in an increase tion. The order in which the elements are performed in core damage frequency or risk, the increases may vary or occur in parallel, depending on the particu should be small and consistent with the intent of the lar application and the preference of the program devel Commission's Safety Goal Policy Statement. (Regu opers.

latory Positions 2.3, 2.4) Element 1: Define Proposed Changes to the

5. The impact of the proposed change should be Inservice Testing Program.

monitored using performance The purpose of this element is to identify (1) the measurement strategies. (Regulatory Position 3.3) particular components that would be affected by the Regulatory Guide 1.174 gives additional guidance proposed changes in testing practices, including those on the key safety principles applicable to all risk currently in the IST program and possibly some that are informed applications. Figure I of this guide, repeated not (if it is determined through new information and in from Regulatory Guide 1.174, illustrates the consider sights such as the PRA that these additional compo nents are important in terms of plant risk) and (2) spe ation of each of these principles in risk-informed deci sion making. cific revisions to testing schedules and methods for the chosen components. Plant systems and functions that A Four-Element Approach to Risk-Informed rely on the affected components should be identified.

Decisionmaking for Inservice Testing Programs Regulatory Position 1 gives a more detailed description of Element 1.

Regulatory Guide 1.174 (Ref. 3) describes a four element process for developing risk-informed regulato Element 2: Perform Engineering Analysis ry changes. The process is highly iterative. Thus, the fi In this element, both traditional engineering and nal description of the proposed change to the IST PRA methods are used to help define the scope of the program as defined in Element I depends on both the changes to the IST program and to evaluate the impact analysis performed in Element 2 and the definition of of the changes on the overall plant risk. Areas that are to the implementation of the IST program performed in be evaluated include the expected effect of the proposed Element 3. The Regulatory Position of this guide pro RI-IST program on the design basis and severe acci vides guidance on each element. dents, defense-in-depth attributes, and safety margins.

While IST is, by its nature, a monitoring program, In this evaluation, the results of traditional engineering it should be noted that the monitoring referred to in Ele and PRA methods are to be considered together in an ment 3 is associated with making sure that the assump- integrated decision process that will be carried over into 1.175-4

the implementation phase described below in Element NRC according to SRP Chapter 19 and Section 3.9.7

3. PRA results should be used to provide information (Refs. 6 and 7). Guidance on documentation require for the categorization of components into groupings of ments for RI-IST programs is given in Regulatory Posi low safety-significant components (LSSC) and high tion 4 of this regulatory guide.

safety-significant components (HSSQ. Components In carrying out this process, the licensee will make in the LSSC group would then be candidates for less rigorous testing when compared with those in the a number of decisions based on the best available infor HSSC group. When the revised IST plan has been de mation. Some of this information will be derived from veloped, the plant-specific PRA should be used to eval traditional engineering practice and some will be pro babilistic in nature resulting from PRA studies. It is the uate the effect of the planned program changes on the licensee's responsibility to ensure that its RI-IST pro overall plant risk as measured by core damage fre gram is developed using a well-reasoned and integrated quency (CDF) and containment large early release fre decision process that considers both forms of input in quency (LERF).

formation (traditional engineering and probabilistic) in During the integration of all the available informa a complementary manner. This important decisionma tion, it is expected that many issues will need to be re king process may at times require the participation of solved through the use of a well-reasoned judgment special combinations of licensee expertise (licensee process, often involving a combination of different en staff), depending on the technical and other issues in gineering skills. This activity has typically been re volved, and may at times also need outside consultants.

ferred to in industry documents as being performed by Industry documents have generally referred to the use an "expert panel." As discussed further at the end of this of an expert panel for such decisionmaking. The appen section and in the appendix, this important process is dix to this guide discusses a number of IST-specific is the licensee's responsibility and may be accomplished sues such as might arise in expert panel deliberations.

by means other than a formal panel. In any case, the key safety principles discussed in this guide must be ad C. REGULATORY POSITION dressed and shown to be satisfied regardless of the ap proach used for RI-IST program decisionmaking. 1. ELEMENT 1: DEFINE PROPOSED CHANGES TO INSERVICE TESTING Additional application-specific details concerning PROGRAM RI-IST programs and Element 2 are contained in Regu In this first element of the process, the proposed latory Positition 2 of this guide.

changes to the IST program are defined. This involves Element 3: Define Implementation and describing what IST components (e.g., pumps and Monitoring Program valves) will be involved and how their testing would be changed. Also included in this element is identification In this element, the implementation plan for the of supporting information and a proposed plan for the IST program is developed. This involves determining licensee's interactions with the NRC throughout the both the methods to be used and the frequency of test implementation of the RI-IST.

ing. The frequency and method of testing for each com ponent is commensurate with the component's safety 1.1 Description of Proposed Changes significance. To the extent practicable, the testing A full description of the proposed changes in the methods should address the relevant failure mecha IST program is prepared. This description would in nisms that could significantly affect component reli clude:

ability. In addition, a monitoring and corrective action program is established to ensure that the assumptions (1) Identification of the aspects of the plant's design, upon which the testing strategy has been based contin operations, and other activities that require NRC ue to be valid, and that no unexpected degradation in approval that would be changed by the proposed performance of the HSSCs and LSSCs occurs as a re RI-IST program. This will provide a basis from sult of the change to the IST program. Specific guid which the staff can evaluate the proposed changes.

ance for Element 3 is given in Regulatory Position 3. (2) Identification of the specific revisions to existing testing schedules and methods that would result Element 4: Submit Proposed Change from implementation of the proposed program.

The final element involves preparing the documen (3) Identification of the components in the plant that tation to be included in the submittal and the documen are directly and indirectly involved with the pro tation to be maintained by the licensee for later refer posed testing changes. Any components that are ence, if needed. The submittal will be reviewed by the not presently covered in the plant's IST program 1.175-5

but are determined to be important to safety (e.g., staff (i.e., as defined in the approved RI-IST program through PRA insights) should also be identified. description). Prior to implementation, a process or pro In addition, the particular systems that are affected cedures should be in place to ensure that any such by the proposed changes should be identified changes to the previously approved RI-IST program since this information is an aid in planning the meet the acceptance guidelines of this section.

supporting engineering analyses. The cumulative impact of all RI-IST program (4) Identification of the information that will be used changes (initial approval plus later changes) should in support of the changes. This will include perfor comply with the acceptance guidelines given in Regu mance data, traditional engineering analyses, and latory Position 2.3.3 below.

PRA information.

Examples of changes to RI-IST programs that (5) A brief statement describing the way how the pro would require NRC's review and approval include, but posed changes meet the objectives of the Commis are not limited to, the following:

sion's PRA Policy Statement (Ref. 1).

" Changes to the RI-IST program that involve pro 1.2 Inservice Testing Program Scope grammatic changes (e.g., changes in the accep tance guidelines used for the licensee's integrated IST requirements for certain safety-related pumps decisionmaking process),

and valves are specified in 10 CFR 50.55a. These com ponents are to be tested according to the requirements " Component test method changes that involve devi of Section XI of the American Society of Mechanical ation from the NRC-endorsed Code requirements, Engineers (ASME) Boiler and Pressure Vessel Code NRC-endorsed Code Case, or published NRC (the Code) (Ref. 9) or the applicable ASME Operations guidance.

and Maintenance (O&M) Code (Ref. 13). Examples of changes to RI-IST programs that For acceptance guidelines, the licensee's RI-IST would not require NRC's review and approval include, program would include all components in the current but are not limited to, the following:

Code-prescribed IST program. In addition, the pro " Changes to component groupings, test intervals, gram should include those non-Code components that and test methods that do not involve a change to the the licensee's integrated decisionmaking process cate overall RI-IST approach that was reviewed and ap gorized as HSSC.

proved by the NRC, 1.3 RI-IST Program Changes After Initial " Component test method changes that involve the Approval implementation of an NRC-endorsed ASME Code This section provides guidance on reporting ofpro or an NRC-endorsed Code Case, gram activities. The NRC will formally review the " Recategorization of components because of expe changes proposed to RI-IST programs that have al rience, PRA insights, or design changes, but not ready received NRC approval. programmatic changes when the process used to The licensee should implement a process for deter recategorize the components is consistent with the mining when proposed RI-IST program changes re RI-IST process and results that were reviewed and quire formal NRC review and approval. Changes made approved by the NRC.

to the NRC-approved RI-IST program that could affect the process and results that were reviewed and ap 2. ELEMENT 2: PERFORM ENGINEERING proved by the NRC staff should be evaluated to ensure ANALYSIS that the basis for the NRC staff's prior approval has not As part of defining the proposed change to the li been compromised. All changes should be evaluated censee's IST program, the licensee should conduct an against the change mechanisms described in the regula engineering evaluation of the proposed change using a tions (e.g., 10 CFR 50.55a, 10 CFR 50.59) to determine combination of traditional engineering methods and whether NRC review and approval is required prior to PRA. The major objective of this evaluation is to con implementation. If there is a question regarding this is firm that the proposed program change will not com sue, the licensee should seek NRC review and approval promise defense in depth and other key safety prin prior to implementation. ciples described in this guide. Regulatory Guide 1.174 For acceptance guidelines, licensees can change (Ref. 3) provides general guidance for the performance their RI-IST programs consistent with the process and of this evaluation, to be supplemented by the RI-IST results that were reviewed and approved by the NRC specific guidance in this guide.

1.175-6

2.1 Licensing Considerations For acceptance guidelines, the licensee should re view applicable documents to identify proposed 2.1.1 Evaluating the Proposed Changes changes to the IST program that would alter the design, On a component-specific basis, the licensee should operations, and other activities of the plant. On a com determine whether there are instances in which the pro ponent-specific basis, the licensee should (1) identify posed IST program change would affect the design, op instances in which the proposed RI-IST program erations, and other activities at the plant, and the li change would affect the design, operations, and other censee should document the basis for the acceptability activities of the plant, (2) identify the source and nature of the proposed change by addressing the key prin of the requirements (or commitments), and (3) docu ciples. In evaluating proposed changes to the plant, the ment the basis for the acceptability of the proposed re licensee should consider other licensing basis docu qulrement changes, e.g., by addressing the key prin ments (e.g., technical specifications, Final Safety Anal ciples.

ysis Report (FSAR), responses to NRC generic letters) The licensee must comply with 10 CFR 50.59, in addition to the IST program documentation. 50.90, and 50.109 as applicable. The staff recognizes The principal focus should be on the use of PRA that there are certain docketed commitments that are findings and risk insights in support of proposed not related to regulatory requirements that can be changes to a plant's design, operation, and other activi changed by licensees via processes other than described ties that require NRC approval. Such changes include in NRC regulations (e.g., consistent with Reference (but are not limited to) license amendments under 14).

10 CFR 50.90, requests for use of alternatives under 2.1.2 Relief Requests and Technical Specification 10 CFR 50.55a, and exemptions under 10 CFR Part 12. Changes However, the reviewer should note that there are certain docketed commitments that are not related to regula The licensee should have included in the RI-IST tory requirements (e.g., commitments made by the li program submittal the necessary exemption requests, censee in response to NRC Generic Letter 89-10 or technical specification amendment requests, and relief 96-05) that may be changed by licensees via processes requests necessary to implement their RI-IST program.

other than as described in NRC regulations (e.g., con Individual component relief requests are not re sistent with Reference 14). quired for adjusting the test interval of individual com ponents that are categorized as having low safety sig A broad review of the plant's design, operations, nificance (because the licensee's implementation plans and other activities may be necessary because proposed for extending specific component test intervals should IST program changes could affect requirements or have been reviewed and approved by the NRC staff as commitments that are not explicitly stated in the licens part of the licensee's RI-IST program submittal). Simi ee's FSAR or IST program documentation. Further larly, if the proposed alternative includes improved test more, staff approval of the design, operation, and main strategies to enhance the test effectiveness of compo tenance of components at the facility have likely been nents, additional relief to implement these improved granted in terms other than probability, consequences, test strategies is not required.

or margin of safety (i.e., the 10 CFR 50.59 criteria).

Therefore, it may also be appropriate to evaluate pro For acceptance guidelines, the following are to be posed IST program changes against other criteria (e.g., approved by the NRC before implementing the RI-IST criteria used in either the licensing process or to deter program:

mine the acceptability of component design, operation " A relief request for any component, or group of and maintenance). components, that is not tested in accordance with The Director of the Office of Nuclear Reactor Reg the licensee's ASME Code of record or NRC ulation is allowed by 10 CFR 50.55a to authorize alter approved ASME code case.

natives to the specific requirements of this regulation " A technical specification amendment request for provided that the proposed alternative will ensure an any component, or group of components, if there acceptable level of quality and safety. Thus, alterna are changes from technical specification require tives to the acceptable RI-IST approaches presented in ments.

this guide may be proposed by licensees so long as sup porting information is provided that demonstrates that 2.2 Traditional Engineering Evaluation the key principles discussed in Chapter 2 of this guide This part of the evaluation is based on traditional are maintained. engineering methods (not probabilistic). Areas to be 1.175-7

evaluated from this viewpoint include the potential ef ing from the RI-IST program will maintain a balance fect of the proposed RI-IST program on defense-in between prevention of core damage, prevention of con depth attributes and safety margins. In addition, de tainment failure, and consequence mitigation. Redun fense in depth and safety margin should also be dancy, diversity, and independence of safety systems evaluated, as feasible, using risk techniques (PRA). should be considered after the initial choice is made in the categorization of components to ensure that these 2.2.1 Defense-in-Depth Evaluation qualities are not degraded by the categorization. Inde pendence of barriers and defense against common Because of its importance, both historically during cause failures should also be considered in the review the evolution of reactor safety practice and for the con of the categorization. The improved understanding of tinuation of public health and safety, the concept of de the relative importance of plant components to risk re fense in depth has been included in Regulatory Guide sulting from the development of the RI-IST program 1.174 (Ref. 3) as one of the five key principles. In refer should promote an improved overall understanding of ring to a proposed risk-informed program change, Sec how the components in the IST program contribute to a tion 2 of Regulatory Guide 1.174 states that the pro plant's defense in depth, and this should be discussed in posed change should be consistent with the the application.

defense-in-depth philosophy. Furthermore, as stated in Section 2.2.1.1, 2.2.2 Safety Margin Evaluation Consistency with the defense-in-depth philos The maintenance of safety margins is also a very ophy is maintained if: important part of ensuring continued reactor safety and is included as one of the key safety principles in Section

" A reasonable balance is preserved among 2 of Regulatory Guide 1.174 (Ref. 3). This principle prevention of core damage, prevention of states that the proposed change maintains sufficient containment failure, and consequence miti safety margins.

gation.

In addition, in Section 2.2.1.2, it is stated that with

" Over-reliance on programmatic activities sufficient safety margins:

to compensate for weaknesses in plant de

"* Codes and standards or alternatives ap sign is avoided.

proved for use by the NRC are met.

" System redundancy, independence, and di

" Safety analysis acceptance criteria in the li versity are preserved commensurate with censing basis (e.g., FSAR, supporting anal the expected frequency, consequences of yses) are met, or proposed revisions pro challenges to the system, and uncertainties vide sufficient margin to account for (e.g., no risk outliers). analysis and data uncertainty.

" Defenses against potential common cause failures are preserved, and the potential for It is possible that the categorization process will the introduction of new common cause fail identify components that are currently not included in ure mechanisms is assessed. the IST program, and their addition as HSSCs will clearly improve safety margin in terms of CDF and

"* Independence of barriers is not degraded.

LERF. It is also important that the performance moni

"* Defenses against human errors are pre toring program be capable of quickly identifying sig served. nificant degradation in performance so that, if neces

"* The intent of the General Design Criteria in sary, corrective measures can be implemented before the margin to failure is significantly reduced. The im 10 CFR Part 50, Appendix A is maintained. proved understanding of the relative importance of These defense-in-depth objectives apply to all risk plant components to risk resulting from the develop ment of the RI-IST program should promote an im informed applications, and for some of the issues in volved (e.g., no over-reliance on programmatic activi proved understanding of how the components in the IST program contribute to a plant's margin of safety, ties and defense against human errors), it is fairly straightforward to apply them to the RI-IST program and this should be discussed in the application.

evaluation. Some specific examples of how certain oth 2.3 Probabilistic Risk Assessment er of these objectives may be met for RI-IST applica Issues specific to the IST risk-informed process are tions are as follows. The use of the multiple risk metrics discussed in this section. Regulatory Guide 1.174 (Ref.

of CDF and LERF and controlling their change result-1.175-8

3) contains much of the general guidance that is apl ,li- test intervals or strategies. The PRA model should be cable for this topic. developed to the component level for the systems im In RI-IST, information obtained from a PIRA portant to safety.

should be used in two ways: First, to provide input to If less than a full-scope PRA is used to support the the categorization of SSCs into HSSC and LS'SC proposed RI-IST program, supplemental information groupings; and second, to assess the impact of the piro- (deterministic and qualitative) must be considered dur posed change on CDF and LERF. Regulatory Positi .on ing the integrated decisionmaking process.

2.3.1 discusses, in general terms, issues related to Ithe Acceptance guidelines for the required PRA quali quality, scope, and level of detail of a PRA that is usied ty and scope are further defined in Regulatory Guide for IST applications. More specific considerations ire 1.174.

given in Regulatory Positions 2.3.2, and 2.3.3, whiich address the use of PRA in categorization and in the s 2.3.2 Categorization of Components sessment of the impact on risk metrics respectively The categorization of components is important in the implementation of the RI-IST program since it is an 2.3.1 Scope, Level of Detail, and Quality of efficient and risk-informed way ofproviding insights in Probabilistic Risk Assessments for Inservik,e the areas in which safety margin can be relaxed without Testing Applications unacceptable safety consequences. Thus, categoriza For the quantitative results of the PRA to pla3y a dion of components, in addition to the traditional engi major and direct role in decision making, there is a ne ed neering evaluation described in Regulatory Position to ensure that they are derived from "quality" analysies, 2.2 and the calculation of change in overall plant risk and that the extent to which the results apply is well t in- described in Regulatory Position 2.3.3, will provide derstood. Section 2.2.3 of Regulatory Guide 1.174 significant input to the determination of whether the (Ref. 3) addresses in general terms the issues related to IST program is acceptable or not.

scope, level of detail, and quality of the PRA applied to The determination of safety significance of com risk-informed applications. ponents by the use of PRA-determined importance While a full scope PRA that covers all modes of c1p. measures is important for several reasons.

eration and initiating events is preferred, a lesser scope

• When performed with a series of sensitivity evalu PRA can be used to provide useful risk informatic)n. ations, it can identify potential risk outliers by However, it must then be supplemented by additioraal identifying IST components that could dominate considerations as discussed below. risk for various plant configurations and operation For the PRA to be useful in the development olf a al modes, PRA model assumptions, and data and RI-IST program, it is necessary that the PRA model be model uncertainties.

developed to the component level for the systems, iin- Importance measure evaluations can provide a use cluding non-safety systems, considered important Ifor ful means to identify improvements to current IST prevention of core damage and release of radioactiviity. practices during the risk-informed application pro A PRA used in RI-IST should be performed c()r cess.

rectly and in a manner that is consistent with accept ed System- or functional-level importance results can practices. The PRA should reflect the actual desiEPIP provide a high level verification of component-lev construction, operating practices, and operating expe:ri- el results and can provide insights into the potential ence of the plant. The quality required of the PRA is risk significance of IST components that are not commensurate with the role it plays in the determin a- modeled in the PRA.

tion of test intervals or test methods and with the rc le General guidelines for risk categorization of com the integrated decisionmaking panel plays in compe n- ponents using importance measures and other informa sating for limitations in PRA quality. Regulatory Gui de tion are provided in Regulatory Guide 1.174 (Ref. 3).

1.174 and SRP Chapter 19 (Refs. 3 and 6) further diis- These general guidelines address acceptable methods cuss the requirements of PRA quality. for carring out categorization and some of the limita To be acceptable for application to RI-IST, PRA dions of this process. Guidelines that are specific to the models must reflect the as-built, as-operated plant, aiWd IST application are given in this section. As used here, they must have been performed in a manner that is co)n- risk categorization refers to the process for grouping sistent with accepted practices. The quality of the PRA IST components into LSSC and HSSC categories.

has to be shown to be adequate, commensurate with t]he Components are initially categorized into HSSC role the PRA results play in justifying changes to t]he and LSSC groupings based on threshold values for the 1.175-9

importance measures. Depending on whether the PRA In classifying a component not modeled in the is performed using the fault tree linking or event tree PRA as LSSC, the expert panel should have determined linking approach, importance measures can most easily that:

be provided at the component or train level. In either "* The component does not perform a safety case, the importance measures are applicable to the function, or does not perform a support items taken one at a time, and therefore, as discussed in function to a safety function, or does not Regulatory Guide 1.174, while a licensee is free to complement a safety function.

choose the threshold values of importance measures, it "* The component does not support operator will be necessary to demonstrate that the integrated im actions credited in the PRA for either proce pact of the change is such that Principle 4 is met. One dural or recovery actions.

acceptable approach is discussed in the next section.

"* The failure of the component will not result in the eventual occurrence of a PRA initiat PRA systematically takes credit for non-Code ing event.

components as providing support, acting as alterna tives, and acting as backups to those components that "* The component is not a part of a system that are within the current Code. Accordingly, to ensure that acts as a barrier to fission product release the proposed RI-IST program will provide an accept during severe accidents.

able level of quality and safety, these additional risk "* The failure of the component will not result important components should be included in licensees' in unintentional releases of radioactive ma RI-IST proposals. Specifically, the licensee's RI-IST terial even in the absence of severe accident program should include those ASME Code Class 1, 2, conditions.

and 3 and non-Code components that the licensee's in For acceptance guidelines, when using risk impor tegrated decisionmaking process categorized as HSSC tance measures to identify components that are low risk and thus determined these components to be appropri contributors, the potential limitations of these mea ate additional candidates for the RI-IST program. sures have to be addressed. Therefore, information to be provided to the licensee's integrated decisionmaking Although PRAs model many of the SSCs involved process (e.g., expert panel) must include evaluations in the performance of plant safety functions, other that demonstrate the sensitivity of the risk importance SSCs are not modeled for various reasons. However, results to the important PRA modeling techniques, as this should not imply that unmodeled components are sumptions, and data. Issues that the licensee should not important in terms of contributions to plant risk. consider and address when determining low risk con For example, some components are not modeled be tributors include truncation limit used, different risk cause, certain initiating events may not be modeled metrics (i.e., CDF and LERF), different component (e.g., low power and shutdown events, or some external failure modes, different maintenance states and plant events); in other cases, components may not be directly configurations, multiple component considerations, modeled because they are grouped together with events defense in depth, and analysis of uncertainties (includ that are modeled (e.g., initiating events, operator recov ing sensitivity studies to component data uncertainties, ery events, or within other system or function bound common-cause failures, and recovery actions).

aries); and in some cases, components are screened out While the categorization process can be used to from the analysis because of their assumed inherent highlight areas in which testing strategy can be im reliability; or failure modes are screened out because of proved and areas in which sufficient safety margins ex their insignificant contribution to risk (e.g., spurious ist to the point that testing strategy can be relaxed, it is closure of a valve). When feasible, adding missing the determination of the change in risk from the overall components or missing initiators or plant operating changes in the IST program that is of concern in demon states to the PRA should be considered by the licensee.

strating that Principle 4 has been met. Therefore, no ge When this is not feasible, information based on tradi nerically applicable acceptance guidelines for the tional engineering analyses and judgment is used to de threshold values of importance measures used to cate termine whether a component should be treated as an gorize components as HSSC or LSSC are given here.

LSSC or HSSC. One approach to combining these dif Instead, the licensee should demonstrate that the over ferent pieces of information is to use what has been re all impact of the change on plant risk is small as dis ferred to as an expert panel. Appendices B and C of cussed in Regulatory Position 2.3.3.

Standard Review Plan Chapter 19 (Ref. 6) contain staff expectations on the use of expert panels in integrated As part of the categorization process, licensees decisionmaking and SSC categorization respectively. must also address the initiating events and plant operat-1.175-10

ing modes missing from the PRA evaluation. The li operate when demanded, even though for some pur censee can do this either by providing qualitative argu poses it would have been considered "good" before be ments that the proposed change to the IST program ing subjected to the stress of the demand itself. This does not result in an increase on risk, or by demonstrat would have the effect of adding a constant to the test-in ing that the components significant to risk in these mis terval-dependent contribution to the component un sing contributors are maintained as HSSC. availability on demand. The assumption that the total unavailability scales linearly with the test interval (i.e.,

2.3.3 Use of a PRA To Evaluate the Risk Increase doubles when test interval doubles) is conservative in from Changes in the IST Program the sense that it scales the test-interval-independent One of the important uses of the PRAis to evaluate contribution along with the test-interval-dependent the impact of the IST change with respect to the accep contribution, and in that respect tends to overstate the tance guidelines on changes in CDF and LERF as dis effect of test interval extension. This approximation is cussed in Section 2.2.2 of Regulatory Guide 1.174 therefore considered acceptable; however, it should be (Ref. 3). In addition, the PRA can provide a baseline noted that guidance aimed at improving the capability risk profile of the plant, and the extent of analysis of the of tests to identify loss of performance margin is aimed baseline CDF and LERF depends on the proposed partly at reducing the "demand" contribution as well, so change in CDF and LERF. As discussed in Regulatory that improved modeling in this area would appear to Guide 1.174, if the PRA is not full scope, the impact of have the potential to support further improvements in the change must be considered by supplementing the allocation of safety resources.

PRA evaluation by qualitative arguments or by bound ing analyses. This model essentially assumes that failures are random occurrences and that the frequency of these oc 2.3.3.1 Modeling the Impact of Changes in the currences does not increase as the test interval is in IST Program. In order for the PRA to support the deci creased. However, as test intervals are extended, there sion appropriately, there should be a good functional is some concern that the failure rate, X,may increase.

mapping between the components associated with IST This failure rate, generally assumed constant, is based and the PRA basic event probability quantification. on data from current IST test intervals and therefore Part of the basis for the acceptability of the RI-IST pro does not include effects that may arise from extended gram is a quantitative demonstration by use of a PRA test intervals. It is possible that insidious effects such as that established risk measures are not significantly in corrosion or erosion, intrusion of foreign material into creased by the proposed changes to the IST for selected working parts, adverse environmental exposure, or components. To establish this demonstration, the PRA breakdown of lubrication, which have not been encoun includes models that appropriately account for the tered with the current shorter test intervals, could sig change in reliability of the components as a function of nificantly degrade the component if test intervals be the IST program changes. In general, this will include come excessively long. Therefore, unless it can be not only changes to the test interval but also the effects demonstrated that either degradation is not expected to of an enhanced testing method. Enhanced testing might be significant or that the test would identify degrada be shown to improve or maintain component availabil tion before failures are likely to occur, use of the ity, even if the interval is extended. That is, a better test constant failure rate model could be nonconservative.

might compensate for a longer interval between tests.

Licensees who apply for substantial increases in test in One way to address this uncertainty is to use the terval are expected to address this area, i.e., as appropri PRA insights to help design an appropriate imple ate, consider improvements in testing that would com mentation and monitoring program, for example, to ap pensate for the increased intervals under consideration. proach the interval increase in a stepwise fashion rather than going to the theoretically allowable maximum in a One model for the relationship between the com single step, or to stagger the testing of redundant com ponent unavailability on demand and the test interval is ponents (test different trains on alternating schedules) given in NUREG/CR-6141 (Ref. 16), which assumes a so that the population of components is being sampled constant rate (k) of transition to the failed state. Refer relatively frequently, even though individual members ence 16 also describes how to account for various test of the population are not. By using such approaches, the strategies.

existence of the above effects can be detected and.com In addition to transitions to a failed state that occur pensatory measures taken to correct the testing of the between component demands or tests, there is also a remaining population members. However, it is impor demand-related contribution to unavailability, corre tant that the monitoring includes enough tests to be sponding to the probability that a component will fail to relevant, and that the tests are capable of detecting the 1.175-11

time-related degradation (performance monitoring is be consistent with the guidelines provided in Section discussed in Regulatory Position 3.3). 2.2.4 of Regulatory Guide 1.174. In comparing the cal culated risk to the guidelines, the licensee should ad A check should also be performed to determine dress the model and completeness uncertainty as dis whether non-IST manipulation has been credited either cussed in Regulatory Guide 1.174 (Ref. 3). In addition, in IST basic events or in compensating-component ba the licensee should address parameter uncertainty ei sic events. If a component is stroked or challenged be ther by propagating the uncertainty during sequence tween instances of IST, and if these activities are capa quantification or by demonstrating that the "state-of ble of revealing component failure, the effective fault knowledge correlation" effect is not significant, espe exposure time can be less than the RI-IST interval. It cially in cutsets in which the RI-IST changes affect can be appropriate to take credit for this shortening of multiple components that are similar.

fault exposure time in the PRA quantification, pro vided that there is assurance that the important failure In evaluating the change in plant risk from pro modes are identified by the stroking or the system chal posed changes in the IST program, the licensee should lenges. This is not always trivial: If a functional success perform the following.

can be achieved by any one of n components in parallel, "* Evaluate the risk significance of extending the test so that the function succeeds even if n-1 of the compo interval on affected components. This requires that nents fail, then merely monitoring successful function the licensee address the change in component al response does not show whether all components are availability as a function of test interval. The analy operable unless verification of each component's state sis should include either a quantitative considera is undertaken. In addition, some instances of revealing tion of the degradation of the component failure a component fault through challenge have adverse con rate as a function of time, supported by appropriate sequences, including functional failure, and if credit is data and analysis, or arguments that support the taken for shortening fault exposure time through func conclusion that no significant degradation will oc tional challenges, it is necessary to account for this cur.

downside in the quantification of accident frequency.

"* Consider the effects of enhanced testing to the ex 2.3.3.2 Evaluating the Change in CDF and tent needed to substantiate the change.

LERF. Once the impact on the individual basic event Other issues that should be addressed in the quanti probabilities has been determined, the change in CDF fication of the change in risk include the following.

and LERF can be evaluated. There are some issues that must be carefully considered, which become more im "* The impact of the IST change on the frequency of portant the larger the change in basic event probabili event initiators (those already included in the PRA ties. When using a fault tree linking approach to PRA, it and those screened out because of low frequency) is preferable that the model be re-solved rather than should be determined. For applications in RI-IST, simply requantifying the CDF and LERF cutset solu potentially significant initiators include valve fail tions. In addition, it is important to pay attention to the ure that could lead to interfacing system loss-of parametric uncertainty analysis, especially if the coolant accidents (LOCAs) or to other sequences change is dominated by cutsets that have multiple that fail the containment isolation function.

LSSCs. .The "state of knowledge" correlation effect "* The effect of common cause failures (CCFs)

(Ref. 16) could be significant if there are a significant should be addressed either by the use of sensitivity number of cutsets with similar SSCs contributing to the studies or by the use of qualitative assessments that change in risk. Regulatory Guide 1.174 (Ref. 3) dis show that the CCF contribution would not become cusses the parametric uncertainty analysis in more significant under the proposed IST program (e.g.,

detail. by use of phased implementation, staggered test In addition, model and completeness uncertainties ing, and monitoring for common cause effects).

should be addressed as discussed in Regulatory Guide "* Justification of lST relaxations should not be based 1.174. In particular, initiating events and modes of on credit for post-accident recovery of failed com plant operations whose risk impact are not included in ponents (repair or ad hoc manual actions, such as the PRA need additional analyses or justification that manually forcing stuck valves to open). However, the proposed changes do not significantly increase the credit may be taken for proceduralized imple risk from those unmodeled contributors. mentation of alternative success strategies. For 23.3.3 Acceptance Guidelines. The change in each human action that compensates for a basic risk from proposed changes to the IST program should event probability increasing as a result of IST re-1.175-12

laxation, there should be a licensee commitment to safety principles. Because of the importance of these ensure performance of the function at the level expectations, they will be repeated here.

credited in the quantification. Excessively low hu

• All safety impacts of the proposed change man failure probabilities Qess than 10-3) cannot be are evaluated in an integrated manner as accepted unless there is adequate justification and part of an overall risk management ap there are adequate training programs, personnel proach in which the licensee is using risk practices, plant policies, etc., to ensure continued analysis to improve operational and engi licensee performance at that level. neering decisions broadly by identifying and taking advantage of opportunities for

"* The failure rates and probabilities used for compo reducing risk, and not just to eliminate re nents affected by the proposed change in IST quirements the licensee sees as undesirable.

should appropriately consider both plant-specific For those cases when risk increases are pro and generic data. The licensee should determine posed, the benefits should be described and whether individual components affected by the should be commensurate with the proposed change are performing more poorly than the aver risk increases. The approach used to iden age associated with their class; the licensee should tify changes in requirements should be used avoid relaxing IST for those components to the to identify areas where requirements should point that the unavailability of the poor performers be increased, 1 as well as where they could would be appreciably worse than that assumed in be reduced.

the risk analysis. In addition, components that have "* The scope and quality of the engineering experienced repeated failures should be reviewed analyses (including traditional and proba to see whether the testing scheme (interval and bilistic analyses) conducted to justify the methods) would be considered adequate to support proposed licensing basis change should be the performance credited to them in the risk appropriate for the nature and scope of the analysis.

change, should be based on the as-built and as-operated and maintained plant, and

" The evaluation should be performed so that the should reflect operating experience at the truncation of LSSCs is considered. It is preferred plant.

that solutions be obtained from a re-solution of the model, rather than a requantification of CDF and "* The plant-specific PRA supporting li LERF cutsets. censee proposals has been subjected to quality controls such as an independent 2

" The cumulative impact of all RI-IST program peer review or certification.

changes (initial approval plus later changes) "* Appropriate consideration of uncertainty is should comply with the acceptance guidelines given in analyses and interpretation of find given in this section. ings, including using a program of monitor-2.4 Integrated Decisionmaking This section discusses the integration of all the t technical considerations involved in reviewing submit Tbe NRC staff is aware of but does not endorse guide lines that have been developed (e.g., by NEI/NU tals from licensees proposing to implement RI-IST pro MARC) to assist in identifying potentially beneficial grams. General guidance for risk-informed applica changes to requirements.

tions is given Regulatory Guide 1.174 (Ref. 3) and in 2As discussed in Section 2.2.3.3 of Regulatory Guide 1.174 (Ref. 3) in its discussion of PRA quality, such a the new SRP sections, Chapter 19 (Ref. 6) for general peer review or certification is not a replacement for guidance, and Section 3.9.7 (Ref. 7) for IST programs. NRC review. Certification is defined as a mechanism for assuring that a PRA, and the process ofdeveloping These documents discuss a set of regulatory findings and maintainingthat PRA, meet aset Oftechnicalstan that form the basis for the staff to prepare an acceptable dards established byadiverse groupofpersonnel expe rienced in developing PRA models, performing PRAs, safety evaluation report (SER) for a licensee's risk and performing quality reviews of PRAs. Such a pro informed application. Specifically, Section 2 of Regu cess has been developed and integrated with a peer re latory Guide 1.174 identifies a set of "expectations" viewprocess by, forexample, the BWR Owners Group and implemented for the purpose of enhancing quality that licensees should follow in addressing the key of PRAs at several BWR facilities.

1.175-13

ing, feedback, and corrective action to ad are appropriately reflected in the licensee's component dress significant uncertainties. grouping. This should include components required to maintain adequate defense in depth as well as compo The use of core damage frequency (CDF) nents that might be operated as a result of contingency and large early release frequency (LERF) 3 plans developed to support the outage. K as bases for probabilistic risk assessment acceptance guidelines is an acceptable ap Licensees are also expected to review licensing ba proach to addressing Principle 4. Use of the sis documentation to ensure that the traditional engi Commission's Safety Goal qualitative neering related factors mentioned above are adequately health objectives (QHOs) in lieu of LERF is modeled or otherwise addressed in the PRA analysis.

acceptable in principle and licensees may propose their use. However, in practice, im When making final programmatic decisions, plementing such an approach would require choices must be made based on all the available infor an extension to a Level 3 PRA, in which mation. There may be cases when information is in case the methods and assumptions used in complete or when conflicts appear to exist between the the Level 3 analysis, and associated uncer traditional engineering data and the PRA-generated in tainties, would require additional attention. formation. It is the responsibility of the licensee in such cases to ensure that well-reasoned judgment is used to

• Increases in estimated CDF and LERF re resolve the issues in the best manner possible, includ sulting from proposed changes will be lim ing due consideration to the safety of the plant. This ited to small increments. The cumulative process of integrated decisionmaking has been dis effect of such changes should be tracked cussed in various industry documents (Refs. 10 and considered in the decision process. through 12) with reference to the use of an expert panel.

• The acceptability of proposed changes The appendix to this regulatory guide includes some should be evaluated by the licensee in an in detailed guidance on certain aspects of integrated deci tegrated fashion that ensures that all prin sionmaking specific to RI-IST programs. As discussed 4

ciples are met. in the appendix, it is not intended that an administrative body such as an expert panel must always be formed by

• Data, methods, and assessment criteria the licensee to fulfill this function. Some general accep used to support regulatory decisionmaking tance guidelines for this important activity follow, with must be well documented and available for more specific details given in the appendix.

public review.

These expectations apply to both probabilistic and In summary, acceptability of the proposed change traditional engineering considerations, which are ad should be determined by using an integrated decision dressed in more detail in this chapter and in Regulatory making process that addresses three major areas: (1) an Guide 1.174 (Ref. 3). evaluation of the proposed change in light of the plant's licensing basis, (2) an evaluation of the proposed Licensees are expected to review commitments re change relative to the key principles and the acceptance lated to outage planning and control to verify that they criteria, and (3) the proposed plans for implementation, 3In this context, LERF is being used as a surrogate for performance monitoring, and corrective action. As the early fatality quantitative health objective (QHO). stated in the Commission's Policy Statement on the in It isdefined as the frequency of those accidentsleading to significant, unmitigated releases from containment creased use of PRA in regulatory matters (Ref. 1), the in a time frame prior to effective evacuation of the PRA information used to support the RI-IST program close-in population such that there is a potential for early health effects. Such accidents generally include should be as realistic as possible, with reduced unnec unscrubbedreleasesassociatedwithearlycontainment essary conservatisms, yet include a consideration of failure at or shortly after vessel breach, containment uncertainties. These factors are very important when bypass events, and loss of containment isolation. This definition is consistent with accident analyses used in considering the cumulative plant risk and accounting the safetygoal screening criteria discussed in the Com for possible risk increases as well as risk benefits. The mission's regulatory analysis guidelines. An NRC con tractor's report (Ref. 15) describes a simple screening licensee should carefully document all of these kinds of approach for calculating LERF. considerations in the RI-IST program description, in 4

One important element of integrated decisionmaking cluding those areas that have been quantified through can be the use of an'"expert panel." Such a panel is not a necessary component of risk-informed decisionmak the use of PRA, as well as qualitative arguments for ing; butwhen it is used, the key principles and associat those areas that cannot readily be quantified.

ed decision criteria presented in this regulatory guide still apply and must be shown to have been met or tobe irrelevant to the issue at hand. The following are acceptance guidelines.

1.175-14

• The licensee's proposed RI-ISTprogram should be duct the existing approved Code IST test at an extended supported by both a traditional engineering analy interval.

sis and a PRA analysis. An acceptable strategy for testing components The licensee's RI-IST program submittal should be categorized HSSC and LSSC may be defined in NRC consistent with the acceptance guidelines con approved ASME risk-informed Code Cases. Licensees tained throughout this regulatory guide, specifi who choose to pursue RI-IST programs should consid cally with the expectations listed in this section, or er adopting test strategies developed by ASME and en the submittal should justify why an alternative ap dorsed by the NRC. Deviations from endorsed Code Cases must be reviewed and approved by the NRC staff proach is acceptable.

as part of the RI-IST program review.

If the licensee's proposed RI-IST program is ac In establishing the test strategy for components, ceptable based on both the deterministic and pro the licensee should consider component design, service babilistic analyses, it may be concluded that the condition, and performance, as well as risk insights.

proposed RI-IST program provides "an acceptable The proposed test strategy should be supported by data level of quality and safety" [see 10 CFR that are appropriate for the component. The omission of 50.55a(a)(3)(i)]. either generic or plant-specific data should be justified.

The proposed test interval should be significantly less

3. ELEMENT 3: DEFINE IMPLEMENTATION than the expected time to failure assumed in the PRAof AND MONITORING PROGRAM the components in question (e.g., an order ofmagnitude Upon approval of an RI-IST program, the licensee less).5 In addition, the licensee should demonstrate that should have in place an implementation schedule for adequate component capability (margin) exists, above testing all HSSCs and LSSCs identified in their pro that required during design-basis conditions, such that gram. This schedule should include test strategies and component operating characteristics over time do not testing frequencies for HSSCs and LSSCs that are with result in reaching a point of insufficient margin before in the scope of the licensee's IST program and compo the next scheduled test activity.

nents identified as HSSCs that are not currently in the The IST interval should generally not be extended IST program. beyond once every 6 years or 3 refueling outages (whichever is longer) without specific compelling doc 3.1 Inservice Testing Program Changes umented justification available on site for review. Ex This section discusses the test strategy changes tensions beyond 6 years or 3 refueling outages (which (i.e., component test frequency and methods changes) ever is longer) will be considered as component that licensees should make as part of a RI-IST program. performance data at extended intervals is acquired.

This is not meant to restrict a licensee from fully imple For acceptance guidelines, the RI-IST program menting NRC-approved component Code Cases.

should identify components for which the test strategy Components categorized HSSc that are not in the (i.e., frequency, methods or both) should be more fo licensee's current IST program should (where practi cused as well as components for which the test strategy cal) be tested in accordance with the NRC-approved might be relaxed. The information contained in, and de ASME risk-informed Code Cases, including com rived from, the PRA should be used to help construct pliance with all administrative requirements. When the testing strategy for components. To the extent prac ASME Section XI or O&M Code testing is not practi ticable, components with high safety significance cal, alternative test methods should be developed by the should be tested in ways that are effective at detecting licensee to ensure operational readiness and to detect their risk-important failure modes and causes (e.g., component degradation (i.e., degradation associated ability to detect failure, to detect conditions that are pre with failure modes identified as being important in the cursors to failure, and predict end of service life). Com licensee's PRA). As a minimum, a summary of these ponents categorized LSSC may be tested less rigor components and their proposed testing should be inclu ously than components categorized as HSSC (e.g., less ded in the RI-IST program.

frequent or informative tests).

For components categorized as HSSC that were the In some situations, an acceptable test strategy for subject of a previous NRC-approved relief request (or components categorized HSSC may be to conduct the an NRC-authorized alternative test), the licensee existing approved Code IST test at the Code-prescribed 5 Forexample, the MOVexercise requirement (which is comparable to frequency. In some situations, an acceptable test strat the current stroke time test) should be performed at intervals consid egy for components categorized LSSC may be to con- erably smaller than the expected time to failure.

1.175-15

. I

should discuss the appropriateness of the relief in light referenced in the IST program and in the implementing of the safety significance of the component in their RI and test procedures to ensure that testing failures are re IST submittal. evaluated for possible adjustment to the component's grouping and test strategy.

If practical, IST components (with the exception of certain check valves and relief valves) should, as a It is acceptable to implement RM-IST programs on a minimum, be exercised or operated at least once every phased approach. Subsequent to the approval of a RI refueling cycle. More frequent exercising should be IST program, implementation of interval extension for considered for components in any of the following cate LSSC may begin at the discretion of the licensee and gories, if practical: may take place on a component-, train-, or system level. However, it is not acceptable to immediately ad-,

"* Components with high risk significance, just the test intervals of LSSC to the maximum pro-'

"* Components in adverse or harsh environmental posed test interval. Normally, test interval increases conditions, or will be done step-wise, with gradual extensions being permitted consistent with cumulative performance data

"* Components with any abnormal characteristics for operation at the extended intervals. The actual test (operational, design, or maintenance conditions). ing intervals for each component in the RI-IST program The testing strategy for each component (or group should be available at the plant site for inspection.

of components) in the licensee's RI-IST program It should be noted that the test described in the cur should be described in the RI-IST program description. rent ASME Code may not be particularly effective in The RI-IST program description should summarize all detecting the important failure modes and causes of a testing to be performed on a group of components (e.g., component or group of components. A more effective MOV testing in response to NRC Generic Letter 96-05, test strategy may be to conduct an enhanced test at an Ref. 18). The specific testing to be done on each com extended test interval.

ponent (or group of components) should be delineated in the licensee's IST program plan and is subject to HSSCs that are not in the current IST program NRC inspection. should be tested, where practical, in accordance with the ASME Code, including compliance with all admin 3.2 Program Implementation istrative requirements. When ASME Section XI or The applicable ASME Code generally requires that O&M testing is not practical, alternative test methods safety-related components within the program scope as should be developed by the licensee to ensure opera defined in the current ASME Code be tested on a quar tional readiness and to detect component degradation terly frequency regardless of safety significance. The (i.e., degradation associated with failure modes identi authorization of a risk-informed inservice testing pro fied as being important in the licensee's PRA). As a gram will allow the extension of certain component minimum, a summary of these components and their testing intervals and modification of certain component proposed testing should be provided to the NRC as part testing methods based on the determination of individ of this review and prior to implementation of the risk ual component importance. The implementation of an informed IST program at the plant.

authorized program will involve scheduling test inter An acceptable method to extend the test interval for vals based on the results of probabilistic analysis and LSSC is to group like components and stagger their deterministic evaluation ofeach individual component. testing equally over the interval identified for a specific The R1-1ST program should distinguish between component based on the probabilistic analysis and de high and low safety-significant components for testing terministic evaluation of each individual component.

intervals. Components that are being tested using spe Initially, it would be desirable to test at least one com cific ASME Codes, NRC-endorsed Code Cases for RI ponent in each group every refueling outage. For exam IST programs, or other applicable guidance should be ple, component grouping should consider valve actua individually identified in the RI-IST program. The test tor type for power operated valves and pump driver intervals of the HSSC should be included in the R1-IST type, as applicable. With this method, generic age program for verification of compliance with the ASME related failures could be identified while allowing im Code requirements and applicable NRC-endorsed mediate implementation for some components. For ASME Code Cases. Any component test interval or component groups that are insufficient in size to test method that is not in conformance with the above one component every refueling outage, the imple should have specific NRC approval. Plant corrective mentation of the interval should be accomplished in a action and feedback programs should be appropriately more gradual step-wise manner, The selected test fre-1.175-16

quency for LSSC that are to be tested on a staggered ba itoring when testing under design basis conditions is sis should be justified in the RI-IST program. impracticable. In most cases, component-level moni toring will be expected.

The following implementation activities are ac ceptable: Two important aspects of performance monitoring are whether the test frequency is sufficient to provide

• For components that will be tested in accordance meaningful data and whether the testing methods, pro with the current NRC-approved Code test frequen cedures, and analysis are adequately developed to en cy and method requirements, no specific imple sure that performance degradation is detected. Compo mentation schedule is required. The test frequency nent failure rates cannot be allowed to rise to and method should be documented in the licensee's unacceptable levels (e.g., significantly higher than the RI-IST program. failure rates used to support the change) before detec

• For components that will employ NRC-endorsed tion and corrective action take place.

ASME Codes or Code Case methods, implementa The NRC staff expects that licensees will integrate, tion of the revised test strategies (i.e., interval ex or at least coordinate, their monitoring for RI-IST pro tension plan) should be documented in the licens gram with existing programs for monitoring equipment ee's RI-IST program. performance and other operating experience on their

• For any alternative test strategies proposed by the sites and, when appropriate, throughout the industry. In licensee (i.e., for components within the scope of particular, monitoring that is performed as part of the the current ASME code), the licensee should have Maintenance Rule (10 CFR 50.65) implementation can specific NRC approval. be used in the RI-IST program when the monitoring performed under the Maintenance Rule is sufficient for The licensee should increase the test interval for the SSCs in the RI-IST program. As stated in Regulato components in a step-wise manner (i.e., equal or suc ry Guide 1.174, if an application requires monitoring of cessively smaller steps, not to exceed one refueling SSCs not included in the Maintenance Rule, or in cycle per step). If no significant time-dependent fail volves SSCs that need a greater resolution of monitor ures occur, the interval can be gradually extended until ing than the Maintenance Rule (e.g., component-level the component is tested at the maximum proposed ex vs. train- or plant-level monitoring), it may be advanta tended test interval. An acceptable approach is to group geous for a licensee to adjust the Maintenance Rule similar components and test them on a staggered basis. monitoring program rather than to develop additional Guidance on grouping components is contained in monitoring programs for RI-IST purposes. Therefore, Position 2 of NRC Generic Letter 89-04 (Ref. 19) for it may be advantageous to adjust the Maintenance Rule check valves; Supplement 6 to NRC Generic Letter performance criteria to meet the acceptance guidelines 89-10 (Ref. 20), and Section 3.5 of ASME Code Case below.

OMN-1 (Ref. 21) for motor-operated valves, or other For acceptance guidelines, monitoring programs documents endorsed by the NRC.

should be proposed that are capable of adequately 3.3 Performance Monitoring tracking the performance of equipment that, when de Performance monitoring in RI-IST programs re graded, could alter the conclusions that were key to fers to the monitoring of inservice test data for compo supporting the acceptance of the RI-IST program.

nents within the scope of the RI-IST program (i.e., in Monitoring programs should be structured such that cluding both HSSC and LSS). The purpose of SSCs are monitored commensurate with their safety performance monitoring in a RI-IST program is two significance. This allows for a reduced level of moni fold. First, performance monitoring should help con toring of components categorized as having low safety firm that no insidious failure mechanisms that are re significance provided the guidance below is still met.

lated to the revised test strategies become important The licensee's performance monitoring process enough to alter the failure rates assumed in the justifica should have the following attributes:

tion of program changes. Second, performance moni

• Enough tests are included to provide meaningful toring should, to the extent practicable, ensure that ade data, quate component capability (i.e., margin) exists, above

"* The test is devised such that incipient degradation that required during design-basis conditions, so that can reasonably be expected to be detected, and component operating characteristics over time do not result in reaching a point of insufficient margin before "* The licensee trends appropriate parameters as re the next scheduled test activity. Regulatory Guide quired by the ASME Code or ASME Code Case 1.174 (Ref. 3) provides guidance on performance mon- and as necessary to provide reasonable assurance 1.175-17 fr

that the component will remain operable over the determined for all components categorized as hav test interval. ing high safety significance, as well as for compo Assurance must be established that degradation is nents categorized as having low safety signifi cance when the apparent cause of failure may not significant for components that are placed on an ex contribute to common cause failure.

tended test interval, and that failure rate assumptions for these components are not compromised by test data. (4) Assesses the applicability ofthe failure ornoncon It must be clearly established that those test procedures forming condition to other components in the RI and evaluation methods are implemented that reason IST program (including any test sample expansion ably ensure that degradation will be detected and cor that may be required for grouped components such rective action will be taken. as relief valves).

3A Feedback and Corrective Action (5) Corrects other susceptible RI-IST components as necessary.

The licensee's corrective action program for this application should contain a performance-based feed (6) Considers the effectiveness of the component's back mechanism to ensure that if a particular compo test strategy in detecting the failure or nonconfor nent's test strategy is adjusted in a way that is ineffec ming condition. Adjust the test interval and/or test tive in detecting component degradation and failure, methods, as appropriate, when the component (or particularly potential common cause failure mecha group of components) experiences repeated or nisms, the RI-IST program weakness is promptly de age-related failures or nonconforming conditions.

tected and corrected. Performance monitoring should The corrective action evaluations should periodi be provided for systems, structures, and components cally be provided to the licensee's PRA group so that with feedback to the RI-IST program for appropriate any necessary model changes and re-grouping are done adjustments when needed. as might be appropriate. The effect of the failures on If component failures or degradation occur at a overall plant risk should be evaluated as well as a con higher rate than assumed in the basis for the RI-IST pro firmation that the corrective actions taken will restore gram, the following basic steps should be followed to the plant risk to an acceptable level.

implement corrective action. The RI-IST program documents should be revised

"* The causes of the failures or degradation should be to document any RI-IST program changes resulting determined and corrective action implemented. from corrective actions taken.

" The component's test effectiveness should be re 3.5 Periodic Reassessment evaluated, and the RI-IST program should be mo dified accordingly. RI-IST programs should contain provisions whereby component performance data periodically The following are acceptance guidelines.

gets fed back into both the component categorization The licensee's corrective action program evaluates and component test strategy determination (i.e., test in RI-IST components that either fail to meet the test ac terval and methods) process. These assessments should ceptance criteria or are otherwise determined to be in a also take into consideration corrective actions that have nonconforming condition (e.g., a failure or degraded been taken on past IST program components. (This pe condition discovered during normal plant operation). riodic reassessment should not be confused with the The evaluation: 120-month program updates required by 10 CFR 50.55a(f)(5)(i), whereby the licensee's IST program (1) Complies with Criterion XVI, "Corrective Ac must comply with later versions of the ASME Code tion," of Appendix B to 10 CFR Part 50. that have been endorsed by the NRC.)

(2) Promptly determines the impact of the failure or The assessment should:

nonconforming condition on system/train oper ability and follows the appropriate technical spec " Review and revise as necessary the models and ification when component capability cannot be data used to categorize components to determine demonstrated. whether component groupings have changed.

(3) Determines and corrects the apparent or root cause " Reevaluate equipment performance to determine of the failure or nonconforming condition (e.g., whether the RI-IST program should be adjusted improve testing practices, repair or replace the (based on both plant-specific and generic informa component). The root cause of failure should be tion).

1.175-18

The licensee should have procedures in place to

• A description of the PRA used for the catego identify the need for more emergent RI-IST program rization process and for the determination of updates (e.g., following a major plant modification or risk impact, in terms of the process to ensure following a significant equipment performance prob quality and the scope of the PRA, and how lim lem). itations in quality, scope, and level of detail are compensated for in the integrated decision Licensees may wish to coordinate these reviews making process (see Regulatory Position 2.3.1 with other related activities such as periodic PRA up above),

dates, industry operating experience programs, the Maintenance Rule program, and other risk-informed

• A description of how the impact of the change program initiatives. is modeled in the IST components (including a quantitative or qualitative treatment of compo The acceptance guideline is that the test strategy nent degradation) and a description the impact for RI-IST components should be periodically assessed of the change on plant risk in terms of CDF and to reflect changes in plant configuration, component LERF and how this impact compares with the performance, test results, and industry experience. decision guidelines (see Regulatory Position 2.3.3),

4. ELEMENT 4: DOCUMENTATION

• A description of how the key principles were The recommended content of an RP-IST submittal (and will continue to be) maintained (see Reg is presented in this Regulatory Postion. The guidance ulatory Positions 2.2, 2.3, and 2.4),

provided below is intended to help ensure the com

• A description ofthe integrated decisionmaking pleteness of the information provided and should aid in shortening the time needed for the review process. The process used to help define the RI-IST pro licensee should refer to the appropriate section of this gram, including any decision criteria used (see regulatory guide to ascertain the level of detail of the Regulatory Position 2.4),

documentation that should either be submitted to the

• A general implementation approach or plan NRC staff for review or retained onsite for inspection. (see Regulatory Positions 3.1 and 3.2),

To the extent practical the applicable sections of the re a A description of the testing and monitoring gulatory guide have been identified on each list of proposed for each component group (see Reg documents.

ulatory Position 3.2),

4.1 Documentation That Should Be in The

• A description of the RI-IST corrective action Licensee's RI-IST Submittal plan (see Regulatory Position 3.4),

• A request to implement a RI-IST program as an au 0 A description of the RI-IST program periodic thorized alternative to the current NRC-endorsed reassessment plan (see Regulatory Position 3.5 ASME Code pursuant to 10 CFR 50.55a(a)(3)(i). above).

0 A description of the change associated with the " A summary of any previously approved relief re proposed RI-IST program (see Regulatory Posi quests for components categorized as HSSC along tion 1.1 above). with any exemption requests, technical specifica tion changes, and relief requests needed to imple 0 Identification of any changes to the plant's design, ment the proposed RI-IST Program (see Regula operations, and other activities associated with the tory Position 2.1.2).

proposed RI-IST program and the basis for the ac

" An assessment of the appropriateness of pre ceptability of these changes (see Regulatory Posi viously approved relief requests.

tion 2.1.1).

• A summary of key technical and administrative as 4.2 Documentation That Should Be Available pects of the overall RI-IST program that includes: Onsite For Inspection A description of the process used to identify "* The overall IST Program Plan candidates for reduced and enhanced IST re "* Administrative procedures related to RI-IST quirements, including a description ofthe cate

"* Component or system design basis documentation gorization of components using the PRA and the associated sensitivity studies (see Regula "* Piping and instrument diagrams for systems that tory Position 2.3.2 above), contain components in the RI-IST program 1.175-19 I I I  ; I I

" PRA and supporting documentation (see Regula " Completed test procedures and any supplemental tory Position 2.3) test data related to RI-IST (see Regulatory Position 3.3)

" Categorization results, including the RI-IST pro cess summary sheet for each component or group " Corrective action procedures (see Regulatory Posi of components (see Regulatory Position 2.3.2) tion 3.4)

" Plant-specific performance data (e.g., machinery

" Integrated decisionmakingprocess procedures, ex history) for components in the RI-IST program pert panel meeting minutes (if applicable) (see (see Regulatory Positions 2.3.3 and 3.1)

Regulatory Position 2.4)

" A description of individual changes made to the

" Detailed implementation plans and schedules (see RI-IST program after implementation (see Regula Regulatory Position 3.2) tory Position 1.3) 1.175-20

REFERENCES

1. USNRC, "Use of Probabilistic Risk Assessment 10. American Society of Mechanical Engineers, Methods in Nuclear Regulatory Activities: Final "Risk-Based Inservice Testing-Development of Policy Statement," FederalRegister, Vol. 60, p Guidelines," Research Report (CRDT-Vol. 40-2, 42622, August 16, 1995. Volume 2), 1996.0

2. USNRC, "Framework for Applying Probabilistic 11. Electric Power Research Institute, "PSAApplica Risk Analysis in Reactor Regulation," tions Guide," EPRI TR-105396, August 1995.1 SECY-95-280, November 27, 1995.1 12. Nuclear Energy Institute Draft (Revision B), "In

3. USNRC, "An Approach for Using Probabilistic dustry Guidelines for Risk-Based Inservice Test Risk Assessment in Risk-Informed Decisions on ing," March 19, 1996.1 Plant-Specific Changes to the Licensing Basis," 13. American Society of Mechanical Engineers Regulatory Guide 1.174, July 1998.2 (ASME) Code for Operations and Maintenance of 3

Nuclear Power Plants, OM Code-1995.

4. USNRC "An Approach for Plant-Specific, Risk Informed Decisionmaking: Graded Quality As 14. Nuclear Energy Institute, "Guidelines for Manag surance," Regulatory Guide 1.176, August 1998.2 ing NRC Commitments," Revision 2, Decem ber 19, 1995.1

5. USNRC, "An Approach for Plant-Specific, Risk

15. W.T. Pratt et al., "An Approach for Estimating the Informed Decisionmaking: Technical Specifica Frequencies of Various Containment Failure tions," Regulatory Guide 1.177, August 1998.2 Modes and Bypass Events," Draft NUREG/

6. USNRC, "Standard Review Plan for Risk CR-6595, December 1997.2 Informed Decision Making," Standard Review 16. P.K. Samanta et al., "Handbook of Methods for Plan, NUREG-0800, Chapter 19, July 1998.2 Risk-Based Analyses of Technical Specifica

7. USNRC, "Standard Review Plan for Risk tions," NUREG/CR-6141, December 1994.4 Informed Decision Making: Inservice Testing," 17. G.E. Apostolakis and S. Kaplan, "Pitfalls in Risk Standard Review Plan, NUREG-0800, Chapter Calculations," Reliability Engineering, Vol. 2, 3.9.7, August 1998.2 pages 135-145, 1981.

8. USNRC, "Standard Review Plan for Risk 18. USNRC, "Periodic Verification of Design-Basis Informed Decision Making: Technical Specifica Capability of Safety-Related Power-Operated tions," Standard Review Plan, NUREG-0800, Valves," Generic Letter 96-05, September 18, Chapter 16.1, August 1998.2 1996.1

9. American Society of Mechanical Engineers 19. USNRC, "Guidance on Developing Acceptable (ASME) Boiler and Pressure Vessel Code, Section Inservice Testing Programs," Generic Letter XI, ASME. 3 89-04, April 3, 1989.1

20. USNRC, "Safety-Related (1) Motor-Operated Valve Testing and Surveillance," Generic Letter 1

Copies are available for inspection or copying for afee from the NRC 89-10, June 28, 1989.1 Public Document Room at 2120 L Street NW, Washington, DC; the 21. American Society of Mechanical Engineers PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax (202)634-3343. (ASME) Alternative Rules for Preservice and In 2

Single copies of regulatory guides, both active and draft, and draft service Testing of Certain Electric Motor Oper NUREG documents may be obtained free of charge by writing the ated Valve Assemblies in LWR Power Plants, Reproduction and Distribution Services Section, OCIO, USNRC, Code Case OMN-1, OM Code-1995; Subsection Washington, DC 20555-0001, or by fax to (301)415-2289, or by email to GRWI@NRC.GOV. Active guides may also be purchased from ISTC. 3 the National Technical Information Serviceonastandingorderbasis.

Details on this service may be obtained by writing NTIS, 5285 Port 4 Royal Road, Springfield, VA22161. Copiesofactive and draftguides Copiesare available atcurrent ratesfrom the U.S.GovernmentPrint are available for inspection or copying for a fee from the NRC Public ing Office, P.o. Box 37082, Washington, DC 20402-9328 (telephone Document Room at 2120 L Street NW, Washington, DC; the PDR's (202)512-2249); or from the National Tbchnical Information Service mailingaddressisMailStopLL-6,WashingtonDC20555;telephone by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161.

(202)634-3273; fax (202)634-3343. Copies are available forinspection orcopyingforafee from the NRC Public Document Room at 2120 L Street NW, Washington, DC; the 3

Copiesmaybe obtained fromASME,345 East 47thStreet, NewYork, PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; NY 10017.) telephone (202)634-3273; fax (202)634-3343.

1.175-21

APPENDIX A DETAILED GUIDANCE FOR INTEGRATED DECISIONMAKING A.1 Introduction (e.g., defense in depth, common cause, and the single failure criterion), which may be more constraining than The increased use of probabilistic risk assessment the risk-based criteria in some cases. Consideration (PRA) in nuclear plant activities such as in risk-in must be given to these issues and component perfor formed inservice testing (IST) programs will require a mance experience before the IST requirements for the balanced use of the probabilistic information with the various components are determined.

more traditional engineering (sometimes referred to as "deterministic") information. Some structured process IST experience should contribute an understanding for considering both types of information and making of the important technical bases underlying the existing decisions will be needed that will allow improvements testing program before it is changed. The critical safety to be made in plant effectiveness while maintaining ad aspects of these bases should not be violated inadver equate safety levels in the plant. This will be particular tently in changing over to a RI-IST, and important plant ly important during initial program implementation experience gained through the traditional IST should be and also for the subsequent early phases of the program. considered during the change.

In some instances, the physical data from the PRA and The plant-specific PRA information should in from the deterministic evaluations may be insufficient clude important perspectives With respect to the limita to make a clearcut decision. At times, these two forms tions of PRA modeling and analysis of systems, some of information may even seem to conflict. In such of which may not be explicitly addressed within the cases, it is the responsibility of the licensee to assemble PRA analysis. An understanding should also be pro the appropriate skilled utility staff (and in some cases vided as to how the proposed changes in pump and consultants) to consider all the available information in valve testing could affect PRA estimates of plant risk.

its various forms and to supplement this information with engineeringjudgment to determine the best course Plant safety experience should provide insights as of action. The participants involved in this important sociated with the traditional analyses (Chapter 15 ofthe role have generally been referred to in various industry plant Final Safety Analysis Report) and any effect that documents as an "expert panel." In this appendix, this proposed changes in testing might have on the tradi function will be described as being an engineering eval tional perspective of overall plant safety.

uation without specifying how the evaluation is to be Plant operational input should supplement the in performed administratively. It is not the intention of sights of plant safety with additional information re this guidance to indicate that a special administrative garding the operational importance of components un body needs to be formed within the utility to satisfy this der normal, abnormal, and emergency conditions.

role. It is the function that is important and that must be There should also be input on operating history, system performed in some well-organized, repeatable, and interfaces, and industry operating experience to supple scrutable manner by the licensee. This function is all ment information from the IST.

pervasive in the implementation phase of such activi Maintenance considerations should provide per ties as inservice inspection (ISI) and IST, and accord spectives on equipment operating history, work prac ingly, the licensee has the responsibility to see that this tices, and the implementation of the maintenance rule.

function is done well.

Systems design considerations should include the A.2 Basic Categories of Information To Be potential effect of different design configurations (e.g.,

Considered piping, valves, and pumps) on planning for a risk informed IST, particularly if future plant modifications Risk-importance measures may be used together are contemplated or if systems are temporarily taken with other available information to determine the rela out of service for maintenance or replacement or repair.

tive risk ranking (and thus categorization) of the com ponents included in the evaluation. Results from all A.3 Specific Areas To Be Evaluated these sources are then reviewed prior to making final This section addresses some technical and admin decisions about where to focus IST resources. istrative issues that are currently believed to be particu Although the risk ranking of components can be larly important for RI-IST applications. Additional is used primarily as the basis for prioritizing IST at a sues of a more general nature that may arise in expert plant, additional considerations need to be addressed panel deliberations are given in SRP Chapter 19.

1.175-22

It should be confirmed that proper attention has " Attention should be given to the fact that compo been given to component classifications in systems nent performance can be degraded from the effects identified in emergency operating procedures (and of aging or harsh environments, and this issue will other systems) depended upon for operator recov need to be addressed and documented.

ery actions, primary fission product barriers ex " The engineering evaluation should include the cluded from the PRA due to their inherent reliabil choice of new test frequencies, the identification of ity (such as the RPV), passive items not modeled in compensatory measures for potentially important the PRA (such as piping, cable, supports, building components, and the choice of test strategies for or compartment structures such as the spent fuel both HSSCs and LSSCs.

pool), and systems relied upon to mitigate the ef fects of external events in cases where the PRA " Until the ASME recommendations for improved considered only internal events. test methods are available, the existing IST test methods should be evaluated prior to choosing the Failure modes modeled by the PRA may not be all test methods tobe used for the HSSCs and LSSCs, inclusive. Consideration should be given to the depending on their expected failure modes, service failure modes modeled and the potential for the conditions, etc.

introduction of new failure modes related to the

"* Because of the importance of maintaining defense IST application. For example, if valve misposi in depth, particular attention should be given to tioning has been assumed to be a low-probability identifying any containment systems involving event because of independent verification and IST components.

therefore is not included in the PRA assumptions, any changes to such independent verifications "* Step-wise program implementation, as discussed should be evaluated for potential impact on the in Regulatory Position 3.2, should be included as PRA results. part of the licensee's integrated decisionmaking process.

Other qualitative or quantitative analyses that shed light on the relative safety importance of compo "* The licensee's performance monitoring approach, nents, such as FMEA, shutdown risk, seismic risk, as discussed in Regulatory Position 3.3, should be and fire protection should be included in the re included as part of the licensee's decisionmaking source information base. process.

Value/Impact Statement A draft value/impact statement was published with the draft of this guide (DG- 1062) when it was issued for public comment in June 1997. No significant changes were necessary from the original draft, so a separate value/impact statement for this final guide has not been prepared. A copy of the draft value/impact statement is available for inspection or copying for a fee in the Commission's Public Document Room at 2120 L Street NW, Washington, DC.

1.175-23 I I

UNITED STATES FIRST CLASS MAIL NUCLEAR REGULATORY COMMISSION POSTAGE AND FEES PAID USNRC WASHINGTON, DC 20555-0001 PERMIT NO. G-67 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE, $300