ML20154S746
| ML20154S746 | |
| Person / Time | |
|---|---|
| Issue date: | 09/30/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| References | |
| NUREG-0800, NUREG-0800-03.9.8, NUREG-800, NUREG-800-3.9.8, SRP-03.09.08, SRP-3.09.08, NUDOCS 9810280076 | |
| Download: ML20154S746 (30) | |
Text
_
/
iM.
UNITED STATES NUCLEAR REGULATORY COMMISSION I STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION Standard Review Plan for Trial Use For the Review of Risk-Informed inservice inspection of Piping SRP Chapter 3.9.8 i
September 1998 Contacts:
S. A. Ali (301) 415-2776 (NRR)
J. Guttmann (301) 415-6561 (RES)
S. Dinsmore (301) 415-8482 (NRR)
/
D. Jackson (301) 415-5887 (RES) lh0 Standard review plans are prepared for the guidance of the Office of Nuclear Regulation staff responsible for the review of applications to construct and operate nuclear power plants. These documents are made available to the public as part of the Commission's policy to inform the nuclear industry and the general public of the regulatory procedures and policies.
Standard review plans are not substitutes for regulatory guides or the Commission's regulations, and compliance with them is not required. The standard review plan sections are keyed to the Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants. Not all sections of the Standard Format have a corresponding review plan.
Published standard review plans will be revised periodically, as appropriate, to accommodate comments and to D
refloct new information and experience.
Comments and suggestions for improvement will be considered and should be sent to the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Washington, DC 20555.
9810280076 980936"
~
1 l
D i
1 Standard Review Plan for Trial Use For the Review of Risk-Informed Inservice inspection of Piping FOREWORD The U.S. Nuclear Regulatory Commission's (NRC) Policy Statement on the use of probabilistic risk assessment (PRA) in nuclear regulatory activities encourages greater use of this analysis technique to improve safety decision making, reduce unnecessary burden and improve regulatory efficiency. A number of NRC staff and industry activities are in progress to consider approaches for expanding the scope of PRA applications in regulatory activities.
Several activities are ongoing which consider appropriate uses of PRA in support of the modification of individual plant's design, operation or other activities that reauire NRC D
license amendments under 10 CFR 50.90.inis could include items such as exemption reque aooroval.
This Standard Review Plan (SRP) chapter describes review procedures and acceptance guidelines for NRC staff reviews of proposed plant-specific, risk-informed changes to a licensee's inservice inspection (ISI) arogram for piping. The review procedures contained in this SRP are consistent with the acceptable methods for implementing a risk-informed ISI (RI-ISI) program described in RG 1.178 (Reference 2). Licensees may propose RI-ISI programs consistent with the guidance provided in RG 1.178, propose an alternative approach for implementing a RI-ISI program (which must be demonstrated to be consistent with the fundamental principles identified in this standard review plan), or maintain their ISl programs in accordance with the American Society of Mechanical Engineers (ASME) Code as referenced in 10 CFR 50.55s.
It is the NRC staff's intention to initiate rulemaking as necessary to permit licensees to implement Rl-ISI programs, consistent with this SRP chapter, without having to get NRC approval of an alternative to the ASME Code requirements pursuant to 10 CFR SO.55afal/3). Until the completion of such rulemaking, the staff anticipates reviewing and approving each licensee's RI-ISI program as an alternative to the current Code required ISI program. As such, the licensee's RI-ISI program will be enforceable under 10 CFR 50.55a.
The current ASME Code inservice inspection requirements, as endorsed in 10 CFR 50.55a, have been determined to provide reasonable assurance that public health and safety will be maintained. The individual ASME Code committees concerned with inservice inspection continually review these inspection strategies to develop improvements to the existing i
Code requirements. Changes to the ASME Code, either as new Code editions or Code Cases, are subject to review and approval by the NRC to ensure that the new inspection requirements maintain an adequate level public health and safety. A risk-informed inservice inspection program, if properly constructed, will also provide an acceptable level of quality and safety by evaluating and possibly improving the inspection effectiveness for the high-safety significant pirk J (as identified by the licensee's integrated decision making process) in conjunction with 1,.s relaxation of inspection requirements for the low-safety significant piping.
l l
I j
I O
ii
)
Standard Review Plan for Trial Use For the Review of Risk-informed Inservice inspection Applications TABLE OF CONTENTS 3.9.8 RISK-INFORMED INSERVICE INSPECTION OF PIPING Paae R EVIEW RES PONSIBILITIES....................................... 1 1.
A R EA O F R EVI EW.......................................... 1 1.1 Element 1: Define the Proposed Changes to ISI Program.............. 2 1.2 Element 2: Engineering Analysis............................... 3
)
1.2.1 Traditional Analysis................................. 3 1.2.2 Probabilistic Risk Assessment.......................... 4 1.2.2.1 Scope of Piping Systems................... 4 1.2.2.2 Piping Segments......................... 4 1.2.2.3 Evaluating Pipe Failures with PRA............. 4 1.2.2.4 Piping Failure Potential..................... 5 1.2.2.5 Consequences of Failure................... 6 1.2.2.6 Risk impact of ISI Changes.................. 6 1.2.3 Integrated Decisionmaking
............................6 1.3 Element 3: Implementation and Monitoring Programs................ 7 11.
AC CEPTAN CE CRITERIA.................................... 8 11.1 Element 1: Define the Proposed Changes to ISI Program.............. 8 11.2 Element 2: Engineering Analysis............................... 9
- 11. 2. 1 Tradition al Analysis................................. 9
- 11. 2. 2 Probabilistic Risk Assessment......................... 10 iii
l 81
- 11. 2. 2. 1 Scope of Piping Systems.................. 10
!!.2.2.2 Piping Segments........................ 10
- 11. 2. 2. 3 Evaluating Pipe Failures with PRA........... 11
- 11. 2. 2. 4 Piping Failure Potential.................... 11
- 11. 2. 2. 5 Consequences of Failure................... 12
- 11. 2. 2. 6 Risk Impact of ISI Changes................. 13
- 11. 2. 3 Integrated Decisionmaking
...........................14 11.3 Element 3: Implementation and Monitoring Programs............... 15 lli.
REVIEW PRO C EDU R ES..................................... 16 111.1 Element 1: Define the Proposed Changes to ISI Program............. 17 Ill.2 Element 2: Engineering Analysis.............................. 18 111. 2. 1 Traditional Analysis................................ 18 lll.2.2 Probabilistic Risk Assessment......................... 18 Ill.2.2.1 Scope of Piping Systems.................. 19
{
lll.2.2.2 Piping Segments
........................19 Ill.2.2.3 Evaluating Pipe Failures with PRA............ 19 111. 2. 2. 4 Piping Failure Potential.................... 19 111.2.2.5 Consequences of Failure................... 20 111. 2. 2. 6 Risk Impact of ISI Changes................. 20 lll.2.3 Integrated Decisionmaking
...........................20 111.3 Element 3: Implementation and Monitoring Programs............... 21 IV.
ELEMENT 4: D O CU MENTATION............................ 21 V.
EVALUATION FINDINGS
...................................22 VI.
IM PLE M ENTATIO N........................................ 24 Vll.
R EF E R E N C E S............................................. 2 4 l
iv
l l
Standard Review Plan for Trial Use For the Review of Risk-informed Inservice inspection Applications 3.9.8 RISK-INFORMED INSERVICE INSPECTION REVIEW RESPONSIBILITIES Primary - Civil Engineering and Geosciences Branch (ECGB)
Secondary - Probabilistic Safety Assessment Branch (SPSB) for PRA, Materials and Chemical Engineering Branch (EMCB) for Fracture Mechanics I.
AREAS OF REVIEW
)
The purpose of this standard review plan is to describe the procedure that the NRC staff will utilize to review the application of risk-informed methods to develop inservice inspection (ISI) programs for piping that are different from the current ISI programs at a nuclear power facility, in implementing risk-informed decision making, the licensee must ensure that any proposed change to the ISI program or the regulation meets ths following key principles:
1 The proposed change meets the current regulations unless it is explicitly re'ated to the request for alternatives under 10 CFR 50.55a/al/3) or a requested exemption or rule change (i.e., a 50.12 " specific exemption" or a 2.802 " petition for rulemaking").
2.
The proposed change is consistent with the defense-in-depth philosophy.
3.
The proposed change maintains sufficient safety margins.
4.
Proposed increases in core damage frequency and risk are small and are consistent with the intent of the Commission's Safety Goal Policy Statement.
5.
The impact of the proposed change should be monitored using performance measurement strategies.
Each of these principles should be considered in the risk-informed, integrated D
decisionmaking process. Given these principles of risk-informed decision making, the staff has identified a four-element approaches that form the basis for evaluating proposed l
3.9.8-1
changes to a plant's ISI program based on risk-informed methods. This approach is not sequential in nature; rather, it is iterative.
The first element involves the characterization of the proposed change. The licensee should identify those aspects of the plant's licensing bases that may De affected by the proposed change in ISI requirements, including, but not limited to, rules and regulations, final safety analysis report (FSAR), technical specifications, licensing conditions, and e
licensing commitments. The licensee should also identify all aspects and elements of the ISI program that it intends to modify in future evaluations without prior NRC approval of the change. Piping systems, segments, and welds that are affected by the chsnge in ISI program should be identified. Plant systems and functions that rely on the affected piping should also be identified. Industry and plant specific information applicable to the piping degradation mechanisms that characterizes the relative effectiveness of past inspections should be documented.
As part of the second element, the licensee should evaluate the proposed change witn regard to the principles that the proposed change is consistent with the defense-in-depth philosophy, that sufficient margins are maintained, and that proposed increases in core damage frequency and risk are small and are consistent with the intent of the Commission's Safety Goal Policy Statement as discussed in RG 1.174. This element consists of engineering evaluations, including traditional engineering analyses as well as PRAs. The PRA-based assessment of the proposed change should explicitly consider the affected I
piping segments and assess the impact on the core damage frequency (CDF) and large early release frequency (LERF) caused by changing the licensee's current ISI program. The results of the complementary traditional and PRA methods should be used in an integrated decisionmaking process.
The third element involves developing implementation and monitoring programs. The primary goal for this element is to assess the performance of piping under the proposed change by establishing performance-monitoring strategies to confirm the assumptions and analyses that were conducted to justify the change. Inspection scope, intervals, and techniques should be clearly defined. The inspection scope and techniques shouid address all relevant failure mechanisms that could significantly impact the reliability and integrity of i
the piping.
The fourth element involves documenting the analyses and submitting the request for NRC review and approval. The submittalis reviewed by NRC in accordance with this standard review plan.
The following areas related to the use of RI-ISI program for Inservice inspection (ISI) of piping are reviewed.
L1 Element 1: Define the Prooosed Chanae to ISI Proaram The licensee's RI ISI submittal is reviewed to verify that the proposed changes to the ISI program have been defined in general terms. Those aspects of the plant's licensing uues that may be affected by the proposed change, including, but not limited to, rules and 3.9.8-2
I regulations, FSAR, technical specifications, and licensing conditions are reviewed, in addition, licensing commitments are reviewed. Particular piping systems and welds that are affected by the change in inspection practices are reviewed. Specific revisions to inspection scope, schedules, locations, and techniques are reviewed. The licensee's program and procedures guiding the evaluations leading to future changes to the ISI program without prior NRC approval are reviewed.
Plant systems and functions that rely on the affected piping are also reviewed. The staff reviews available engineering studies, methods, codes, applicable plant-specific and industry data and operational experience, PRA findings, and research and analysis results relevant to the proposed change. Plant-specific experience with inspection program results is reviewed and characterization relative to the effectiveness of past inspections of the piping and the flaws that have been observed is reviewed.
L2 Element 2: Enaineerina Analvsis As part of the second element, the staff will review the licensee's engineering analysis of the proposed changes. The purpose of the review is to determine whether defense-in-depth is maintained, sufficient safety margins are maintained, and that proposed increases in risk, and their cumulative effect, are small and do not cause the NRC Safety Goals to be exceeded. Regulatory Guides (RG) 1.174 and RG 1.178 provide guidance for the performance of this evaluation.
I L2J, Traditional Analvsis The engineering analyses are reviewed to determine whether the impact of the proposed ISI changes is consistent with the principles that defense-in-depth and adequate safety margins are maintained.
The primary regulations governing ISI of piping are 10 CFR 50.55a and Appendix A to 10 CFR Part 50. The regulations reference other codes and requirements that define the elements of defense-in-depth and safety margins to ensure that structuralintegrity of piping is maintained. The staff reviews the licensee's assessment of whether the proposed changes meet the regulations.
10 CFR 50.55a references ASME Boiler and Pressure Vessel Code (BPVC)Section XI for the detailed requirements regrrding piping ISI. Inspections required by ASME BPVC Section XI are performed on a sample basis with additionalinspections, in terms of locations as well as frequency, mandated in response to detection of flaws. The objective of the ISI has been to identify conditions, such as flaw indications, that are precursors to leaks and ruptures in pressure boundaries that may impact plant safety. The staff reviews the licensee's bases for the assessment that the proposed change meets the intent of the ASME Code requirements.
Additional augmented inspection programs to address generic piping degradation problems have been recommended by the NRC to preclude piping failure and implemented by the D
industry. Notable examples of augmented programs for piping inspections are to address l
3.9.8-3 g
m
intergrannular stress corrosion cracking (IGSCC) of stainless steel piping at boiling water reactors (BWR) (Generic Letter 88-01, Reference 11) and erosion corrosion (EC) in the balance of plant for both pressurized water reactors (PWR) and BWRs (Generic Letter 89-08, Reference 12). The manner in which the augmented inspection programs for piping are addressed is reviewed.
L21 Probabilistic Risk Assessment The scope, level of detail, and quality required of the PRA is commensurate with the emphasis that is put on the risk insights and on the role the PRA results play in the integrated decision making process, if the justification for the change is based on well l
I founded traditional arguments supported by PRA insights, a limited PRA review may be warranted. However, if the justification for change is based on complex PRA arguments, then the breadth and depth of the PRA review will be substantially greater. Only those parts of the PRA which are used to support the ISI change application need to be reviewed.
12d Scone of Pioina Svstems The scope of piping included in the proposed RI-ISI program is reviewed. The current ISI requirements for nuclear power plant piping are specified in 10 CFR 50.55a which incorporates, by reference, the requirements of ASME BPVC Section XI. The extent to which the RI lSI program scope incorporates ASME Class 1,2 and 3 piping systems currently included in ASME BPVC Section XI program and any balance of plant piping is reviewed. The process to select the scope of piping, justification for the scope, and the specific choice of piping selected is reviewed.
l.2.2.2 Pioina Seaments The procedure for defining piping segments within the piping systems for the purpose of modeling a run of a pipe in a PRA or to define its ISI requirements is reviewed. The methods by which the failure consequences such as an initiating event, loss of a train, loss of a system, or a combination thereof, is incorporated in the definition of segments are reviewed, in addition to the failure consequences, the procedure and criteria used to identify and document the degradation mechanisms that can be present in piping within the selected systems boundaries is reviewed.
The procedure by which the location of the piping in the plant, and whether inside or outside the containment, is taken into account in defining piping segments is reviewed.
The selection of piping segments within the piping system boundaries is an iterative process affected by degradation as well as consequence evaluation which is not completed at the time of initial selection of piping segnients within the selected piping systerns. The procedure by which degradation mechanisms and consequences of piping segment failures are incorporated in the iterative process is reviewed.
1.2.2.3 Evaluatina Pioe Failures with PRA Pipe ruptures are traditionally modeled as initiators and the failure of individual pipe 3.9.8-4
segments or structural elements are not modeled in PRAs. The manner in which PRA, or the PRA results, is modified so that a more detailed treatment of tne potential (or probability) of pipe failures and the influence of such failures on other systems is incorporated in the PRA is reviewed.
L ?d Pioino Failure Potential Set aent failure potential may be a quantitative estimate for each segment, or segments may be categorized into groups based on similar degradation mechanism, environment, and failure modes. There are three failure modes:
1.
Initiating event failures where the failure directly causes a transient and may or may not also fail one or more plant trains or systems. Initiating event failures are characterized by failure frequency.
2.
Standby failures are those failures that cause the loss of a train or system but which do not directly cause a transient. Standby failures are character..:ed by train or system unavailability which may require shutdown due to technical specifications or limiting conditions for operation. Unavailability is a combination of failure frequency and exposure time.
3.
Demand failures are failures accompanying a demand for a train or system and D
usually caused by the transient induced loads on the segment during system startup.
Demand failures are characterized by a probability per demand.
The approach used for the determination of failure potential of piping segments is reviewed.
The manner in which past failure data, expert opinion and probabilistic fracture mechanics is considered in determining the piping failure potentialis reviewed. The determination of exposure time appropriate to standby failures is reviewed, it is expected that inspections w ll be performed in accordance with the schedule of Inspection Program A or Program B as specified in ASME XI. When data analysis is utilized, appropriateness and completeness of data and whether data is taken over time is evaluated.
Probabilistic structural analysis techniques may be used to estimate a numerical frequency or probability of piping segment failure. This method utilizes conventional structural analysis techniques, such as fracture mechanics analysis, in combination with probabilistic j
methods, such as Monte-Carlo simulation. These techniques are implemented by computer l
codes to estimats failure probabilities as a function of time. The probabilistic structural analysis methodology for the determination of piping failure probabilities is reviewed to determine the appropriate application of fracture mechanics analysis and Monte-Carlo simulation techniques. Benchmarking of computer codes based on comparison with industry standard codes as well as operating experience is also reviewed. The applicant l
should demonstrate that the methodology is able to identify significant differences in failure frequencies or probabilities arising from differences in material properties and environmental influences such as the presence of known degradation mechanisms.
Alternatively, expert opinion or categorization based on degradation mechanisms may be 1
3.9.8-5
used in conjunction with, or in lieu of fracture mechanics analysis to assign each element into a small number of failure potential categories; high, medium, or low for example. In such cases, the process and basis of failure potential determination is reviewed.
For both quantitative estimates and classification into similar groups, the manner in which failure modes, applicable industry experience, piping material, degradation mechanisms, and various other parameters are identified and considered is evaluated. There are numerous uncertainties involved in performing an assessment of segment failure potential. The procedures for addressing these uncertainties when predicting failure potential are reviewed.
1.2.2.5 Consecuences of Failure Direct effects of piping f ailures include loss of coolant accidents (LOCA) or other flow diversions resulting in an initiator, or a consequential loss of systems because of the inability to deliver sufficient flow because of the failed piping. Indirect effects include consequential failures of additional equipment, including equipment in other systems, because of effects such as pipe whip, jet impingement, flooding, or temperature. The procedure by which direct and indirect effects are characterized and documented is reviewed to verify that appropriate f ailure mechanisms and dependencies will be evaluated in the risk analysis.
1.2.2.6 Risk imoact of ISI Chances The methodology used to characterize the change in risk due to the proposed change in the ISI program is reviewed. Part of the basis for the acceptability of any RI-ISI program is a demonstration that established risk measures are not significantly increased by the proposed reduction in the number of inspections for selected piping. To demonstrate this, the process and methodology used to appropriately account for the change in the number of elements inspected, and when feasible, the effects of an enhanced inspection method are reviewed, 7
i 1.2.3 Intearated Decisionmakina Acceptability of the impact of the proposed change in the ISI program is determined based on the review of the adequacy of the licensees fulfillment of the five key principles as listed in Section I and discussed in detailin RG 1.174. The licensee's processes, procedures, and decision criteria to integrate, and to iterate on the integration as necessary, the different elements of the engineering analysis discussed in Sections 1.2.1 and 1.2.2 and the key principles are reviewed.
The assignment of pipe elements into safety-significant categories is an integral part of the risk-informed ISI process. Consequently, the categorization process and all qualitative and quantitative guidelines used to support the categorization are also reviewed.
Risk measures utilized to characterize and differentiate the risk contributions from the individual piping segments are reviewed. The techniques, criteria, and the documentation 3.9.8-6
used to develop and describe the risk measures are reviewed. The criteria for utilizing these risk measures to categorize each pipe segment into groups of high-and low-safety-significant are reviewed. Consideration of absolute and relative figures of merit is reviewed. Review is focused on the criteria for risk significance determination for ISI at the pipe segment and structural element levels that are used to prioritize inspection locations.
The procedure used to perform review of piping segments and piping structural elements to ensure that no segments are inappropriately ranked as low-safety-significant is reviewed.
The criteria and procedure used to define the number and location of structural elements within the piping segments that will be subject to ISI is reviewed. The comparison between the ISI program for piping under ASME XI and the requested RI-ISI program is reviewed.
Q Element 3: Imolementation and Monitorina Proarams The adequacy of the implementation and monitoring plans is reviewed, inspection strategies are reviewed to ensure that failure mechanisms of concern have been addressed and there is a sufficiently high probability of detecting damage before structuralintegrity is impacted. Inspection strategies for selected segments are reviewed to determine if leak / break risks from pressure boundary piping failures are maintained below appropriate threshold values. The crocess by which the safety significance of piping segments is taken into account in defining the scope of the inspection program is reviewed, inspection scope, examination methods, and methods of evaluation of examination results are reviewed with the objective of establishing whether the RI-lSI inspection program provides an acceptable level of quality and safety.
The criteria for selecting areas and volumes of high-safety-significant as well as low-safety-significant piping structural elements for inspection are reviewed to ensure that the applicable degradation mechanisms are addressed. The methods by which the degradation mechanisms, postulated failure modes, and configuration of piping structural elements are incorporated in the inspection scope and inspection locations are reviewed. The manner in which significant stress concentration, geometric discontinuities, and generic as well as plant-specific pipe cracking experience is considered in selecting inspection locations is reviewed. Alternate methods to ensure structural integrity in cases where examination methods cannot be applied due to limitations, such as inaccessibility or radiation exposure hazard are reviewed, in the context of the RI ISI program, the sampling strategy is defined by the selection of structural elements that are proposed by the licensee for inclusion in the inspection. The reviewer will determine if expansion of the sample size is in accordance with the ASME Section IX criteria, e.g., through sequential sampling based on ISI findings and other evidence of structural degradation.
inspection methods and acceptance standards utilized in the implementation of the RI ISI 1
program are reviewed. Inspection methods selected by the licensee should address the degradation mechanisms, pipe sizes, and materials of concern. The manner in which the degradation mechanism is taken into consideration in determining the suitability of D
examination methods such as visual, surface, and volumetric examination is reviewed. The 3.9.8-7
=
extent to which the RI-ISI program incorporates inspection intervals, examination methods and acceptance standards currently specified in the ASME BPVC Section XI program is reviewed.
The reliability of any NDE method is dependent on the qualification of the inspection personnel. RI ISI program is reviewed to verify that inspection teams will meet industry codes and standards, and use accepted methods and procedures.
Implementation plan for the RI-ISI program is reviewed to ensure that appropriate modifications of the ISI plan are developed if new or unexpected degradation mechanisms occur. The manner in which the adequacy of the reliability of the implemented NDE methods is monitored is reviewed, ll.
ACCEPTANCE CRITERIA The acceptance criteria for the areas of review described in subsection I of this SRP are given below. Other approaches that can be justified to be equivalent to the stated acceptance criteria may be used. The staff accepts the risk-informed development of an inspection plan if the relevant requirements of 10 CFR 50.55a concerning ISI are complied with. The relevant requirements of 10 CFR 50.55a are:
1.
Proposed alternatives to the ISI requirements of paragraphs of 10 CFR 50.55a, which requires compliance with ASME XI for ASME Code Class 1,2, and 3 components, may be used when authorized by the Director of the Office of Nuclear Reactor Regulation.
2.
The applicant shall demonstrate that the proposed alternatives would provide an acceptable level of quality and safety.
General guidelines on judging the acceptability of the engineering evaluations and PRA used to support risk informed applications are provided in RG 1.174 and SRP Chapter 19. A summary of acceptance guidelines for engineering evaluations and selected PRA issues specific to ISI is provided in RG 1.178.
lla Elernent 1: Define the Procosed Chanae to ISI Proaram The licensee's RI ISI submittal should have defined the proposed changes to the ISI
~
program in general terms. The licensee should have confirmed that the plant is designed and operated in accordance with the currently approved requirements and that the PRA used in support of their RI-ISI program submittal reflects the actual plant. The licensee should identify those aspects of the plant's licensing bases that may be affected by the proposed change, including, but not limited to, rules and regulations, FSAR, technical specifications, and licensing conditions. In addition, the licensee should identify any changes to commitments. The programs and procedures in place guiding future changes to the ISI program without prior NRC approval should provide for engineering analyses, internal reviews, and degree of traceability consistent with the magnitude of the changes the licensee intends to make.
1 3.9.8-8 b _ _ __
I The particular piping systems, segments, and welds that are affected by the change in ISI program should be identified. Specific revisions to inspection scope, schedules, locations, and techniquas should also be identified. In addition, plant systems and functions that rely on the affected piping should be identified. Industry and plant-specific experience with inspection program results should be obtained and characterization relative to the effectiveness of past inspections of the piping and the flaws that have been observed should be described.
IL2 Element 2: Enaineerina Analvsis After the proposed changes to the licensee's ISI program have been defined, the licensee should conduct an engineering analysis of the proposed changes using a combination of traditional engineering analysis with supporting insights from a PRA. Regulatory Guides 1.174 and 1.178 provide guidance for the performance of this evaluation.
- 11. 2. 1 Iraditional Analvsis The traditional engineering analyses conducted should assess whether the impact of the proposed ISI changes (individually and cumulatively) is consistent with the principles that defense-in-depth and edeouate safety margins are maintained.
10 CFR 50.55a and Appendix A to 10 CFR Part 50 are the primary regulations governing ISI of piping. The intent of these documents is to maintain the structural integrity of piping I
in a nuclear power plant. The regulations reference other codes and requirements that define the elements of a defense-in-depth philosophy to ensure structuralintegrity of piping. For each of the regulations and licensing bases relevant to the ISI of piping, the licensee should ensure that the proposed changes to the ISl program do not deviate from the regulations and licensing bases.
10 CFR 50.55a references ASME BPVC Section XI for the detailed requirements regarding piping ISI for safety significant systems. The objective of the ISI requirements of the ASME Code has been to identify conditions, such as flaw indications, that are procursors to leaks and ruptures in pressure boundaries that may impact plant safety. The licensee should verify that the proposed changes to the ISI program meet or exceed the intent of the ASME BPVC Section XI to identify conditions that are precursors to leaks and ruptures and to provide plans for additional and more frequent inspections in response to detection of flaws and degradation mechanisms.
The nuclear industry has implemented augmented inspection programs to address generic industry wide piping degradation problems such as lGSCC and EC. The licensee should identify whether the proposed changes in the ISI program affect previous licensee commitments for augmented inspection programs for piping degradation problems such as lGSCC and EC.
D 3.9.8-9
\\
11.2.2 Probabilistic Risk Assessment The quality of the PRA should be compatible with the safety implications of the ISI change being requested and the degree that the justification of the change request depends on the PRA analysis Guidance relating the acceptable scope, level of detail, and quality of the PRA analysis based on the anticipated change in risk can be found in RG 1.174, Section 2.4.2, " Evaluation of Risk Impact, including Treatment of Uncertainties," and SRP Chapter 19.0, Section lll.2.2.4, " Quality of a PRA for Use in Risk-Informed Regulation."
The PRA performed should realistically reflect the actual design, construction, and operational practices and reflect the impact of previous changes made to the approved requirements. All calculations using the PRA model should be performed correctly, and in a manner that is consistent with accepted practices. Limitations and approximations in the PRA and the PRA techniques which can influence the interpretation of the results required to support the ISI application should be clearly described and appropriately addressed.
Parameter uncertainty, model uncertainty, and completeness uncertainty should be addressed in accordance with the guidelines of RG 1.174.
The programs and procedures regarding the long term maintenance, update, and use of the PRA should be sufficient to ensure that any anticipated changes in the ISI program which f
do not require NRC notification or approval will always be based on an appropriately generated set of risk insights.
ll12.2.1 Scone of Pioina Svstems The piping systems included in the RI-ISI program for the purpose of evaluating the impact of the proposed changes in the ISI program on total plant risk and for the purpose of screening to classify piping systems as high-safety-significant and low-safety-significant should be such that any proposed increases in core damage frequency and risk are small and are consistent with the intent of the Commission's Safety Goal Policy Statement.
- 11. 2. 2. 2 Pioina Seaments An acceptable method for modeling a run of a pipe in a PRA or to define its ISI requirements is to divide the pipe run into segments. Portions of piping within the piping l
systems having the same consequences of failure should be systematically identified.
Consequences of f ailure include an initiating event, loss of a particular train, loss of a system, or a combination thereof. The location of the piping in the plant, and whether inside or outside the containment, should be taken into account in defining piping segments.
Piping sections subjected to the same degradation mechanism should be systematically ioentified. Most of the degradation mechanisms present in nuclear power plant piping are dependent on a combination of design characteristics, fabrication processes and practices, opsrating conditions, and service experience. The degradation mechanisms to be considered include, but may not be limited to, vibration fatigue, thermal fatigue, corrosion cracking, primary water stress corrosion cracking (PWSCC), IGSCC, microbiologically 3.9.8-10
I induced corrosion (MIC), erosion, cavitation, and EC.
Piping segments should be defined taking into account potential degradation mechanism and consequence of failure at any point in the segment. Segments with the same consequences but a different degradation mechanism may be combined for consequence characterization, but the development of the inspection program should explicitly address the different degradation mechanisms within such segments, in addition, consideration should be given to identifying distinct segment boundaries at branching points such as flow splits or flow joining points, locations of size changes, isolation valve, MOV and AOV locations. Distinct segment boundaries should be defined if the break potentialis expected to be significantly different for various portions of piping.
II. 2. 2. 3 Evaluatina Pioe Failures with PRA The licensee's methodology should systematically utilize risk insights from the PRA and PRA results to characterize the impact of each segment's failure on the plant's risk. The characterization should allow for the determination of the relative safety-significance of the different pipe segments, and should also support the final determination regarding the impact of implementing the program on plant risk.
Generally, three or four primary system LOCA sizes and two steam line rupture locations representing the spectrum of demands on the mitigating systems are modeled in PRAs. An internal events flooding analysis is also included in most PRAs performed in response to I
Generic Letter 88-20. Much of this analysis will be used as a basis for determining the consequence of pipe failures. The review should focus on the robustness of the above models and methods in the baseline PRA, and appropriate use of this information to investigate the impact of the change in risk due to ISI implementation.
One acceptable approach is to investicate the change in risk due to an ISl program change is based on developing the pipe elements' failure potentials into probabilities, and integrating these probabilities into the existing quantitative PRA framework. The contribution to risk from each piping elements may be ranked and the safety significance of the element determined.
An alternative acceptable approach is based on categorizing each segment's failure potential and the consequences of each segment's failures. These two elements of risk, failure potential and consequences, are then systematically combined to determine the safety significance of each element.
- 11. 2. 2. 4 Pioina Failure Potential The determination of the degradation mechanisms present at each weld within all pipe runs included in the scope of the submittal is central to the success of the ISI application. The process used to identify the degradation mechanism at each weld should be well defined, systematic and applied to all welds within the scope. The documentation and engineering evaluations upon which the process is based should be capable of supporting the identification of all applicable degradation mechanisms.
l l
3.9.8-11
The determination of failure potential of piping segments, either as a quantitative estimate or a categorization into groups, should be based on appropriate design, operational, and inspection parameters in conjunction with the identified degradation mechanisms. The evaluation should include a determination of whether the potential f ailure of each segment is best characterized as a demand f ailure while responding to a plant transient or an operational failure which causes a plant transient i
When data analysis is utilized to develop a quantitative estimate, the data should be appropriate and complete. When elicitation of expert opinion is used in conjunction with, or in lieu of probabilistic fracture mechanics analysis, to develop a quantitative estimate, a systematic procedure should be developed for conducting such elicitation and a suitable team of experts should be selected and trained. When categorization based on degradation mechanism is used, the justification for the relationship between the degradation mechanism and the assigned category should be appropriate and complete.
l l
The assessment of piping failure potential should take into account uncertainties. These uncertainties include, but are not limited to, design versus f abrication differences; variation in material properties and strength; effect of various degradation and aging mechanisms; variation in steady-state and transient loads; availability and accuracy of plant operating history; availability of inspection and maintenance program data; and capabilities of analytical methods and models to predict realistic results.
The methodology, process, and rationale used to determine the failure potential of piping segments should be reviewed and approved by the plant expert panel as part of its deliberations during the final classification of the safety significance of each segment. This process should be justified, documented, and included in the submittal. When computer codes are used to develop quantitative estimates, the techniques should be verified and validated against established industry codes.
Inspections performed in accordance with the schedule of Inspection Program A or Program B as specified in ASME XI are acceptable.
- 11. 2. 2. 5 Conseauences of Failure The impact on risk due to piping pressare boundary failure should consider both direct and indirect effects. Consideration of direct effects should include failures that cause initiating events, disable single or multiple components, trains or systems, or a combination of these effects. Indirect effects of pressure boundary failures affecting other systems, components and/or piping segments, also referred to as spatial effects such as pipe whip, jet impingement, flooding, or consequentialinitiation of fire protection systems should also be considered.
The direct and indirect effects of pipe
' lures should be characterized to incorporate appropriate failure mechanisms and d encies into the PRA model. The possibility of different leak sizes ranging from minor leaks to full ruptuce should be considered, in general, the leak size resulting in the most severe consequence should be selected to characterize the consequence for each segment.
3.9.8-12
I An acceptable method of incorporating pipe failures is to classify pipe failures as leaks, disabling leaks, and breaks. Each of these failure modes may be characterized with a different failure probability or potential and a corresponding potential for degrading system performance through direct and/or indirect effects. The time available for operator actions also depends on the break size, and this timing dependence should be recognized and incorporated into the analysis as appropriate.
The consideration of indirect effects given a barrier rupture, should include the potential for, and consequence of, leakage through other barriers relied upon to mitigate the resulting transient including pipes, penetrations, bellows, etc. The potential benefit of including bservice examination of such barriers should be evaluated. Leaks can result in moisture intrusion through jet impingement, flooding, and sprays. Disabling leaks (larger break area than for leaks) can result in initiating events and loss of system function in addition to indirect effects. Breaks can result in damage due to pipe whip in addition to all of the above-mentioned damages. The corresponding failure probability or potential decreases as the break area increases.
- 11. 2. 2. 6 Hisk imoact of ISI Chanaes The guidelines discussed in RG 1.174, Section 2.4.2, " Evaluation of Risk Impact, including Treetment of Uncertainties" are applicable to ISI change requests. General guidance for reviewing the risk impact from changes to the current licensing basis can be found in SRP Chapter 19.0, Section 11.3.2.5 " Risk impact including Treatment of Uncertainty."
The licensee should demonstrate that principle four in RG 1.174 c.nd Section I in the Regulatory Guide 1.178 is met. Principle four states that proposed increases in core damage frequency and risk are small and are consistent with the intent of the Commission's Safety Goal Policy Statement. Increase in risk caused by changes in ISI program could arise from a decrease in the number of welds inspected, reduced efficiency from simplified weld inspections, or both. Decreases in risk could arise from inspecting welds not currently being inspected in the program, improved weld inspections, or both.
The greater the potential risk increase due to the proposed change in the ISI program (e.g.,
the larger the reduction in the number of welds to be inspected and of replacements of detailed inspections with simplified inspections) the more rigorous and detailed the risk analyses needed.
A direct evaluation of the fulfillment of principle four may be based on risk importance measures or bounding estimates capable of characterizing plant a
specific pipe element failure potential and consequences categories, a systematic process to combine failure potential and consequence to determine e
pipe element safety-significance, pipe segmentation and element inspection selection process which provides for e
changes in the ISI program based on the safety-significance of the pipe element, and I
3.9.8-13 l
a discussion and evaluation of the aggregate risk impact of the set of changes requested in the ISI program including an evaluation of uncertainty indicating that the uncertainties do not invalidate the conclusions.
Alternatively, principle four may be shown to be met by calculating the expected change in CDF and LERF. The expected change can be calculated using the baseline PRA and before change versus after change piping f ailure potential expressed as failure probabilities, i
An evaluation of the uncertainty in the results should be performed indicating that the uncertainties do not invalidate the conclusions.
II.2.3 Intearated Decisionmaking The integrated decision making must address all five key safety principles presented in Section I, " Areas of Review," in this SRP and should address each of the expectations discussed in Section 2.1, " Risk-informed Philosophy" of RG 1.174. The integrated decision making should also ensure that the proposed ISI program is consistent with the intent of each of the elements related to defense-in-depth and safety margins discussed in 2.4.1.1,
" Defense-in-Depth," and 2.4.1.2, " Safety Margins" of RG 1.174. The results of the different elements of the engineering analysis discussed in Sections 1.2.1 and 1.2.2 must be considered in an integrated decisionmaking process.
For ISI application, traditional requirements are outlined in 10 CFA 50.55a and the General Design Criteria in Appendix A to 10 CFR Part 50. To be acceptable, the traditional engineering analysis should address all of the relevant regulations and the licensing bases of L
the plant. Acceptability of impact of the proposed change in the ISI program is based on the adequacy of the traditional engineering analysis, acceptable change in plant risk relative to the criteria, and the adequacy of the proposed implementation and performance monitoring plan. The intent of the ASME BPVC to maintain integrity of reactor coolant system boundary by ISI should be preserved under the RI-ISI program.
An acceptable approach for the risk ranking of piping segments and elements is the use of risk reduction worth (RRW), risk achievement worth (RAW), conditional core damage probability (CCDP), conditional large early release probability (CLERP), or other importance measures. RRW is a measure of the maximum possible reduction in total CDF or LERF due to pressure boundary f ailures in plant piping systems that can result from making a component perfectly reliable. RAW, CLERP, and CCDP characterize the increase in risk associated with the pressure boundary f ailure The risk ranking methodology must be able to systematically identify all high-safety-significant pipe segment,. Within the scope of the RI-ISI program. Guidelines for using risk importance measuies to ceaorize SSCs with respect to safety significance can be found in RG 1.174.
The classification of piping segments should be evaluated to determine if any piping segment is inappropriately classified. Considerations should be given to the limitations resulting from the PRA structure, PRA scope, and risk importance measures. Operational insights from previous inspection results, industry data on pipe f ailures, and Maintenance Rule impacts should also be taken into account. Piping that are subject to ISI under ASME XI requirements but have no segments exceeding the piping segment screening criteria 3.9.8-14
should be further reviewed. Each ASME Class coded system should have some segments inspected for defense in-depth considerations.
The criteria for determining how many structural elements should be selected for inspection shoulu be based on the safety significance of the segment and the failure potential within that ugment. The potential for pipe failure directly drives the need for selecting elements for inspection and the location within a segment to be inspected. The sampling program for the s slection of number of elements to be inspected should be fully justified. Guidelines for an acceptable methodology for selection of structural elements for inspection within pipe segments are provided in the RG 1.178.
The intent of the ASME BPVC to maintain integdty of reactor coolant system boundary by ISI should be preserved under the RI-ISI program. Appropriate consideration should be given to implementation and performance monitoring strategies so that piping performance can be assessed under the proposed ISI program change to confirm the assumptions and analyses that were conducted to justify the ISI program change.
IL3 Element 3: Imolementation and Monitorina Proarams Careful consideration should be given to implementation and performance-monitoring strategies. The primary goal of this element is to assess pipin0 performance under the proposed RI-ISI program by establishing performance monitoring strategies to confirm the assumptions and analyses that were conducted to justify the changes in the ISI program.
As discussed in RG 1.178 (Reference 2), performance monitoring encompasses feedback and modification of the Rl-ISI program resulting frnm changes in plant design features, plant procedures, equipment performance, examination results, and individual plant and industry f ailure information.
Inspection scope and examination methods for the RI-ISI program should provide an acceptable level of quality and safety as stipulated in 10 CFR 50.55a/al/31//). Inspection strategies should ensure that failure mechanisms of concern have been addressed and there is a sufficiently high probability of detecting damage before structuralintegrity is impacted, Safety significance of piping segments should be taken into account in defining the inspection scope for the RI-ISI program. The RI-ISI program is reviewed to ensure that the inspection strategies for selected segments will maintain leak / break risks from pressure boundary piping failures below failure rates experienced by the industry in the past.
Degradation mechanisms, postulated failure modes, and configuration of piping structural elements should be incorporated in the definition of the inspection scope and inspection locations. For piping segments that are included in the existing plant EC or IGSCC inspection programs, the inspection locations should be the same as in the existing EC or IGSCC programs. For segments not in these programs, inspection locations should be mainly based on specific degradation mechanism and industry as well as plant-specific cracking experience. Determination of inspection locations for segments with no known degradation mechanism but high failure consequence should be based on sensitized weld locations, stress concentration, geometric discontinuities, and terminal ends. Plant-specific D
pipe cracking experience should be considered in selecting inspection locations. To be 3.9.8-15 e
acceptable, alternate examination methods should be specified to ensure structural integrity in cases where examination methods cannot be applied due to limitations, such as inaccessibility or radiation exposure hazard. System pressure tests and visual examination of ASME piping structural elements should continue to be performed regardless of whether the segments contain locations that have been classified as high or low-safety-significant.
The qualifications of NDE personnel, processes, and equipment should be demonstrated to be in compliance with ASME BPVC Section XI. The acceptance criteria for flaw evaluation i
should meet the requirements of ASME BPVC Section XI. For inspections outside the scope of Section XI (e.g., EC, IGSCC) the acceptance criteria should meet existing regulatory guidance applicable to those programs.
The risk-informed inspection program should specify appropriate inspection intervals consistent with the relevant degradation rate if the data on the degradation mechanism suggests that an inspection interval shcrter than that stated in the ASME Section XI is required. In such cases, inspection intervals should be sufficiently short so that degradation too small to be detected during one inspection does not grow to an unacceptable size before the next inspection is performed.
Updates to the RI ISI program should be performed at least on a 10-year periodic basis to coincide with the ISI requirements in ASME Section XI. Significant changes to the PRA model, plant design feature changes, plant procedure changes, and equipment performance changes should be included for review in the RI-ISI program update if needed to support the i
update. Leakage, flaws, or indications identified during scheduled RLISI program NDE examinations and system pressure tests should be evaluated as part of the RI-ISI program update. Periodic updates of RI-ISI programs should include individual plant as well as industry f ailure information.
Appropriate modifications of the ISI plan should be developed if new or unexpected degradation mechanisms occur. The adequacy of the reliability of the implemented NDE methods should be monitored. The adequacy of NDE performance levels and inspection intervals along with the appropriateness of the selected ISI locations should be considered valid only if the ISI program is successful in detecting degradation before it leads to leakage I
or rupture of piping.
Ill.
REVIEW PROCEDURES The staff reviews the licensees proposed RI-ISI program to determine if it appropriately describes the types of changes that the licensen can make without prior NRC approval and the types of changes that require NRC approval before implementation The reviewer ensures that all changes are evaluated using the change mechanisms described in existing applicable regulations (e.g.,10 CFR 50.55a,10 CFR 50.59,10 CFR 50, Appendix B for safety related SSC) to determine if NRC review and approvalis required prior to implementation. Licensees may request a variety of ISI programs supported by various levels of analyses and evaluations. In general, the degree of freedom the licensee receives to make future changes to the ISI program without prior NRC approval depends on the level of sophistication of the plant practices and procedures supporting the change to RI ISI.
3.9.8
- 6
I l
1 I
Some general guidance on determining which future changes are appropriate is given below.
Changes to segment groupings, inspection intervals, and inspection methods that do not involve a change to the overall RI-ISI approach where the overall RI-ISI approach was reviewed and approved by the NRC do not require specific review and approval prior to implementation provided that the effect of the changes on plant risk increase is insignificant. The overall ISI submittal should specify what types of changes without prior NRC approval are anticipated and describe how such changes will be developed, reviewed by plant personnel, documented, and implemented.
Segment inspection method changes which involve the implementation of an NRC endorsed ASME Code, NRC-endorsed Code Case, or published NRC guidance approved as part of the RI ISI program do not require prior NRC approval.
Inspection method changes that involve deviation from the NRC-endorsed Code requirements require NRC approval prior to implementation.
Changes to the RI-ISI program that involve programmatic changes (e.g., changes to the categorization criteria or figure of merit used to categorize components, and changes in the Acceptance Guidelines used for the licensee's integrated decision-making process) require NRC approval prior to implementation.
I Piping inspection method changes will typically involve the implementation of an applicable ASME Code, Code Case, or other requirements approved by the NRC Changes to the piping inspection methods for these situations do not require NRC approval. However, inspection method changes that involve deviation from the NRC approved Code requirements require NRC approval prior to implementation.
For each area of review, the following review procedure is foll owed to ensure consistency in review so as to satisfy the requirements of acceptance criteria stated in subsection ll.
IlL1 Element 1: Define the Prooosed Chanae to ISI Procram The staff reviewer verifies that the licensee's RI-ISI submittal defines the proposed changes to the ISI program in general terms. The reviewer ensures that the licensee has confirmed that the plant is designed and operated in accordance with the approved requirements and that the PRA used in support of their RI-ISI program submittal reflects the actual plant. The reviewer verifies that the licensee has identified regulations and licensing commitments that impact the current ISI requirements. This includes, but is not limited to, rules and regulations, FSAR, technical specifications, licensing conditions, and licensing commitments. The reviewer alsu verifies that the piping systems, segments, and welds that are affected by the change in 15; nroaram are identified, in addition, description of the proposed change is reviewed to verify mat plant systems and functions that rely on the affected piping have been identified. The characterization of the proposed change in the ISI program is reviewed to verify that detailed description of the industry and plant specific information applicable to the piping degradation mechanisms has been provided. The 3.9.8-17 i
description of the proposed change is also reviewed to verify that information that characterizes the relative effectiveness of past inspections and the types of flaws that have been identified has been provided. In addition, the reviewer verifies that specific revisions to existing inspection schedules, locatiors, and techniques have been described.
I 11L2 Element 2: Enaineerina Analvsis in the second element, the staff reviewer verifies that the licensee's engineering analysis of the proposed changes uses a combination of traditional engineering analysis with I
supporting insights from a PRA. To be acceptable, the licensee should have verified that defense-in-depth is maintained, sufficient safety margins are maintained, and that proposed j
increases in risk, and their cumulative effect, are small and do not cause the NRC Safety Goals to be exceeded. RGs 1.174 and 1.178 provide guidance for the performance of this l
evaluati)n.
lll.2.1 Traditional Analvsis The engineering analyses are reviewed to ensure that the impact of the proposed ISI changes is consistent with the principles that defense-in-depth and adequate safety margins are maintained in accordance with the acceptance criteria in subsection 11.2.1.
The reviewer verifies that the proposed changes to the ISI program meet or exceed the intent of the ASME BPVC Section XI to identify conditions that are precursors to leaks and i
ruptures and that the ISI program provides plans for additional and more frequent inspections in response to detection of flaws and degradation mechanisms. The reviewer ensures that the licent.ee has demonstrated that there is no adverse impact of the proposed changes in the ISI program on the augmented inspection programs such as (GSCC and EC.
IlLL2 Probabilistic Risk Assessment The PRA performed is reviewed in accordance with the acceptance criteria in subsection 11.2.2 to confirm that it realistically reflects the actual design, construction, and operational practices and reflects the impact of previous changes made to the approved requirements.
The reviewer should identify those parts of the PRA model which support the change application. All previous staff and utility reviews (such as the IPE and IPEEE staff evaluation reports, the maintenance rule inspection report, industry peer or certification reviews) should be obtained. The reviewer should ensure that any prior review findings which may influence those parts of the PRA model or results supporting the ISI change request have been adequately addressed, if necessary to support the change request, a focused scope or a more detailed PRA review should be undertaken. The assessed change in risk due to ISI implementation should be evaluated in accordance with the guidelines in Section 2.4.2 of RG 1.174. General guidance for focused scope and more detailed PRA quality reviews is presented in SRP Chapter 19.
ll1. 2.2.1 Scoce of Pioina Svstems Scope of piping systems included in the RI-ISI program is reviewed in accordance with the 1
3.9.8-18
1 I
acceptance criteria in subsection 11.2.2.1.
111. 2. 2. 2 Pinino Seaments Criteria and procedures used to establish piping segments within the piping systems are reviewed to determine whether consequences of failure, degradation mechanisms, and segment boundaries are properly considered for defining piping segments in accordance with the acceptance criteria given in subsection 11.2.2.3 of this SRP section, llL2.2.3 Evaluatino Pine Failures with PRA Acceptable approaches for evaluating pipe failures with PRA are provided in subsection l1.2.2.3. The approach used is reviewed to verify whether the sequence of events from new initiators is appropriately developed if piping segment failure introduce new initiating events if the pipe segment failure yields the same consequences as some other initiator already included in the PRA, the reviewer verifies that the risk from the original initiating event is appropriately represented in the ISI analysis, if pipe failures are characterized by a set of PRA basic events used as surrogates representing the equivalent impact of the pipe failure, the basic events are reviewed to insure that the surrogate is an adequate representation of the pipe segment failure, and that the resulting risk insights are reflected in the ISI analysis, if surrogate basic events cannot be found, the analysis used to characterize the new failure eventa using the PRA models or I
results and extract representative risk insights is reviewed.
Ill.2.2.4 Pioino Failure Potential The processes and documentation used to identify the degradation mechanisms is reviewed to verify that they are sufficient and were systematically applied. The identified degradation mechanisms are reviewed to determine that the results are an appropriate characterization and were developed at a level of detail consistent with the use of the information to support the change request. These detailed results are also compared to the reported inspection locations to determine the relationship between the inspection location, strategies, and degradation mechanisms. The procedures used to determine the failure potential of piping segments are reviewed in accordance with the acceptance criteria in subsection ll.2.2.4 to verify that the appropriate failure frequency, demand failure, or unavailability mode was used to characterize the impact of failure, and that the determination of the quantitative estimate or group classification is appropriate to the failure mode. The licensee's treatment of uncertainties in failure potential determination and all conclusions are reviewed. The incorporation of the findings of the uncertainty analyses into the final decision making process is reviewed.
When a computer code is used to develop a quantitative estimate, verification and validation of the computer code that implements the probabilistic fracture mechanics techniques is reviewed. When expert elicitation is used, the selection and training of the experts and the elicitation process is reviewed. When the failure potentialis determined by
}
classifying the failures into groups, the applicability of the classification scheme is 3.9.8 19
reviewed.
111. 2. 2. 5 Conseauences of Failure The reviewer verifies that the licensee has considered both direct and indirect effects of each segment f ailure The guidelines for determining the direct and, in particular, the indirect effects of pipe failure on plant equipment should be reviewed. The reviewer should verify that these guidelines have been consistently applied and that the results of the analysis are well documented. Guidelines for evaluating the consequence of different leak sizes and selecting the most severe consequence should also be reviewed if applicable.
lll. 2. 2.6 Risk imoact of ISI Chanaes l
The risk impact of the proposed change in the ISI program is reviewed for compliance with the acceptance criteria in subsection ll.2.2 of this SRP section. The licensee's risk assessment is reviewed to verify that any proposed increases in core damage frequency and risk are small and are consistent with the intent of the Commission's Safety Goal Policy Statement. Selection of piping segments is reviewed to ensure that assumption guiding the spatial effects of pipe f ailures are applied consistently. It should reflect the current plant ISI program, and risk insights developed should arise from comparing the baseline with the proposed RI-ISI program implementation plant risk. Risk insights are reviewed to ensure that they appropriately account for the change in the number of elements inspected, and when feasible, the effects of an enhanced inspection method. The emphasis put on the risk insights and on the PRA results in the decisionmaking process is determined. The PRA is reviewed to verify that the scope, level of detail, and the quality of the PRA is commensurate with the role the risk and the change in risk results play in determining the acceptability of the requested ISI program.
ll1.2.3 Intearated Dec;sionmakina Acceptance criteria for integrated decisionmaking process is given in subsection 11.2.3. The process by which the traditional engineering analysis addresses the relevant regulations and j
the currently approved requirements of the plant is reviewed to confirm that the regulation I
is met and the intent of the ASME BPVC to maintain integrity of reactor coolant system boundary by ISI is preserved under the RI-ISI program. The documentation providing input to the integrated decision making process is reviewed to ensure that all applicable risk insights, key principles, and supporting elements were addressed and communicated to the final decision making par.el. The documentation of the panel deliberations, recommendations, and finding should be review to ensure that all relevant risk informed insights were incorporated into the final program description. After the RI-ISI program is approved and initiated, plant performance should be supported by inspection and analysis and maintained by programmatic activities goals by comparison against specific performance goals.
Acceptability of selection of locations to be inspected is reviewed for compliance with the acceptance criteria in subsection 11.2.3.1 of this SRP. Risk measures used are reviewed to determine that appropriate thresholds are used to rank the piping into high-safety-3.9.8-20
l l
significant and low-safety-significant. The risk ranking process is reviewed to ensure that it i
is capable of systematically identifying all high-safety-significant pipe segments, including those that are not included under ASME Section XI.
The procedure used to further review piping segments and piping structural elements that may be inappropriately ranked as low-safety-significant is reviewed to verify that PRA limitations, operational insights, industry pipe f ailure data, and Maintenance Rule insights are taken into consideration. In addition, the procedure used to determine the ISI program for piping that are subject to ISI under ASME XI requirements but have no segments or piping structural elements exceeding the screening criteria is reviewed to ensure that it is in accordance with the acceptance criteria of subsection ll.2.3.1 of this SRP.
IlL3 Element 3: imolementation and Monitorina Proarams The reviewer verifies that the inspection strategies address failure mechanisms of concern and there is a sufficiently high probability of detecting damage before structural integrity is compromised. The reviewer verifies that the degradation mechanisms, postulated failure modes, and configuration of piping structural elements are incorporated in the defin! tion of the inspection scope and inspection locations. Selected inspection locations are reviewed to confirm that stress concentration, geometric discontinuities, and terminal ends are considered in establishing the inspection locations, in addition, the reviewer verifies that plant specific pipe cracking experience has been considered in selecting inspection locations. The reviewer also determines if alternate examination methods are specified to
)
ensure structuralintegrity in cases where examination methods cannot be applied due to limitations, such as inaccessibility or radiation exposure hazard. RI-ISI program is reviewed to ensure that system pressure tests and visual examination of piping structural elements is to be performed on all Class 1,2, and 3 systems in accordance with ASME BPVC Section XI Program regardless of whether the segments contain locations that have been classified as high or low-safety-significant.
Sample selection process is examined to verify that expansion of the sample size is consistent with ASME Section XI criteria, inspection methods selected by the licensee are examined to verify that they address the degradation mechanisms, pipe sizes, and materials of concern. The Rl-ISI inspection program is reviewed to confirm that appropriate examination methods and intervals are used and acceptance standards meet the requirements of ASME BPVC Section XI or existing regulatory guidance applicable to the piping system.
IV ELEMENT 4: DOCUMENTATION The reviewer will review the licensee's submittal to ensure that it contains the documentation necessary to conduct the review described in this SRP (i.e., the documentation described in RG 1.178). The RI-ISI program and its updates should be maintained on site and available for NRC inspection consistent with the requirements of 10 CFR 50, Appendix B.
3.9.8-21
l The reviewer should also ensure that the cover letter that transmits to the licensee the staff's safety evaluation approving the proposed RI Isl program (i.e., alternative ISI program to that prescribed by the ASME Code) contains a statement to the effect that " Failure to comply with the RI-ISI program as reviewed and approved by the NRC staff and authorized pursuant to 10 CFR 50.55a/ alls) le.g., including scope, inspection strategy, documentation, and other programmatic requirements] constitutes noncompliance with 10 CFR 50.55a and is enforceable."
V EVA'.UATION FINDINGS The reviewer verifies that sufficient i1 formation nas been provided and that the et aluation is sufficiently complete and adequate to support conclusions of the following type, to be included in the staff's safety ava.Wation r ! port.
The staff concludes that the proposed RI-ISI program, which provides an alternative to the IS! requirements of paragraphs of 10 CFR 50.55a, provides an acceptable level of quality and safety. This conclusion is based on the following findings.
The licensee's RI-ISI submittal defines the proposed changes to the ISI program in general terms. The licensee has confirmed that the plant is designed and operated in accordance with the currently approved requirements and that the PRA used in support of the RI-ISI program submittal mflects the actual plant. The licensee has identified those aspects of f
the. plant's licensing bases that may be affected by the proposed change, including rules and regulations, FSAR, technical specifications, and licensing conditions, in addition, the l
licensee has identified all changes to commitments that may be affected. The particular piping systems, segments, an 1 welds that are affected by the change in ISI program have I
bee identified. Specific revisions to inspection scope, schedules, locations, and tec iniques are also identified. In addition, plant systems and functions that rely on the affected piping have been identified, industry and plant-specific experience with inspection program results was obtMned and characterization relative to the effectiveness of past inspections of the piping and the flaws that have been observed is described.
l The licensee demonstrated that the plant's currently approved requirements and practices are properly reflected in the risk insights derived using the plant specific PRA model and that these insights reflect the impact of previous changes made to :ha approved requirements. The PRA quality, level of detail, and scope are approprla'e hr the ar,alysis and the integrated decision process compensated for potential limitationa in this quality, level of detail, or scope.
The licensee has conducted an engineering analysis of the proposed changes using a combination of traditional engineering analysis with supprting insights from a PRA. The licensee has demonstrated that the proposed change is consistent with the defense-in-depth philosophy and that it me.ruains suffi:ient safety margins as described in RG 1.174.
The scoae of the piping systems included in the Hi ISI program for the purpose of screening 1
to classify piping systems as high-safety-significant and low-safety-significant is adequate and the proposed increases in core damage frequency and risk a.e small and are consistent with the intent of the Commission's Safety Goal Policy Statement.
3.9.8-22 i.
l The procedure utilized to subdivide piping systems into segments is acceptable since portions of piping having the same consequences oi failure and degradation mechanisms have been placed into the sama piping segments, in addition, consideration is given to identifying distinct segment boundaries at branching points, locations of size changes, isolation valve, MOV and AOV locations, and pipe break probability.
Each segment's potential for failure is appropriately represented as failure on d. land, unavailability, or frequency of failure. The procedure utilhed is acceptable since the potential for failure is based on systematic consideration of d gradation mechanisms, segment and weld material cheracteristics, and environmental and operating stresses. The assessment of component fai!ure potential due to aging and degradation takes into account uncertainties. Any computer codes used to generate quantitative failure estimates have been verified and validated against established industry codes.
The impact on risk due to piping pressure boundary failure considers both direct and indirect effects. Consideration of direct effects includes failures that cause initiating events, disable single or multiple components, trains or systems, or a combination of these effects. Indirect effects of pressure boundary failures affecting other systems, components and/or piping segments, also referred to as spatial effects such as pipe whip, jet impingement, flooding or failure of fire protection systems have also been cons;dered.
The results of the different elements of the engineering analysis are considered in an integrated decisionmaking process. The impact of the proposed change in the ISI program
)
is acceptable since it is based on the adequacy of the traditional engineering anal-is, acceptable change in plant risk relative to the criteria, and the adequacy of the proposed implementation and performance monitoring plan.
Careful consideration has been given to implementation and performance-monitoring strategies. Inspection strategies ensure that failure mechanisms of concern have been addressed and there is a sufficiently high probability of detecting damage before structural integrity is impacted. Safety significance of piping segments is taken into account in defining the inspection scope for the RI-ISI program. Inspection scope and examination methods for the RI-ISI program provide an acceptable level of quality and safety as stipulated in 10 CFR 50.55ala)(3)(i).
Systam pressure tests and visual examination of piping structural elements will continue to be f.s. formed on all Class 1,2, and 3 systems in accordance with ASME BPVC Section XI program regardless of whether the segments contain locations that have been classified as high or low-safety-significant.
VI IMPLEMENTATION l
The following is intended to provide guidance to applicants and licensees regarding the NRC staff's plans for using this SRP section.
Except in those cases in which the applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method 3.9.8-23
l described herein will be used by the staff in its evaluation of conformance with Commission regulations.
Vll.
REFERENCES 1.
Draft Regulatory Guide RG 1.174, "An Approach for Plant Specific Risk-Informed Decision Making: General Guidance," February 28,1997.
I 2.
Draft Regulatory Guide 1.178, "An Approach for Plant-Specific, Risk-Informed Decisionmaking: Inservice Inspection of Piping," May 16,1997.
I 3.
Draft Stendard heview Plan Chapter 19, "Use of PRA in Regulatory Activities,"
dated Much 3,1997.
4.
Nuclear Energy Institute Draft (Draft A) " Industry Guideline for Risk-Based inservice inspection" dated April 12,1996.
5.
ASME Research Report (CRDT-Vol. 20-2, Volume 2 - Part 1), " Risk-Based Inspection
- Development of Guidelines" dated 1992.
6.
Westinghouse Owners Group Topical Report WCAP-14572, Rev5 ion 1, " Application of Risk-Informed Methods to Piping inservice Inspection," October 1997.
7.
EPRI Repcrt Ta-106706, " Risk-informed Inservice Inspection Evaluation Procedure,"
dated June 1996.
8.
ASME Code Case N 560, " Alternate Examination Requirements for Class 1, Category B-J Piping Welds,Section XI, Division 1," dated August 1996.
9.
Proposed ASME Code Case N-577, " Risk-informed Requirements for Class 1,2, and 3 Piping (Method A),Section XI, Division 1," dateri March 1997.
10.
Proposed ASME Code Case N-578, " Risk-Informed Requirements for Class 1,2, and 3 Piping (Method B),Section XI, Division 1," datec' March 1997.
11.
Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping," U.S. Nuclear Regulatory Commission, January 1988.
12.
Generic Letter 89-08, " Erosion / Corrosion-Induced Pipe Wall Thinning," U.S. Nuclear Regulatory Commission, May 1989.
l 0
3.9.8-24
1 lll l
lllll' D
IA ILP 7
AS 6
ME G.
E SFC A DR O S
LNN N
CA ST I
RA E
F T P
S O
.P N
O IS 1
S 0 0
IM 0 0
0 3
M-5 O5 E
S SS L5 E
0 SU TY2 EN E AR I
DA,
B R LP N
A EL I R NUO CO N G T FF I
E G F Y U R I OT N
L R H A
A S N
E E A P
LW CUN
[
llt