ML042930591
| ML042930591 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  (NPF-010, NPF-015) |
| Issue date: | 10/15/2004 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ISI-3-1 WCAP-1 5882-NP, Rev 4 | |
| Download: ML042930591 (32) | |
Text
,I -.
1 VSOUTHERN CALIFORNIA i -
EDISON An EDISON INTERNP TIONAL Company A. Edward Scherer Manager of Nuclear Regulatory Affairs October 15, 2004 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Docket Nos. 50-361 and 50-362 Additional Information Supporting Third Ten-Year Inservice Inspection (ISI) Interval Relief Request ISI-3-1 Request to Use Risk-Informed Inservice Inspection (RI ISI)
San Onofre Nuclear Generating Station Units 2 and 3
References:
1)
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC) dated July 2, 2003;
Subject:
Docket Nos. 50-361 and 50-362, Notification of Updating the Inservice Inspection Program and Submittal of Relief Requests for the Third 10-Year Inspection Interval, San Onofre Nuclear Generating Station Units 2 and 3
- 2)
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC) dated September 15, 2004;
Subject:
Additional Information Supporting Third Ten-Year Inservice Inspection (ISI) Interval Relief Request ISI-3-1 Request to Use Risk-informed Inservice Inspection (RI ISI) San Onofre Nuclear Generating Station Units 2 and 3
Dear Sir or Madam,
As requested, this letter provides WCAP-1 5882-NP, Revision 4, 'San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 Risk-Informed Inservice Inspection Program Evaluation" to support the Southern California Edison (SCE) Relief Request ISI-3-1, Request to Use Risk-Informed Inservice Inspection. Relief Request ISI-3-1 was submitted on July 2, 3003, by reference 1 and supplemented by reference 2 on September 15, 2004.
P.O. Box 128 San Clemente, CA 92674-0128 949-368-7501 Fax 949-368-7575
Document Control Desk October 15, 2004 Should you have any questions, please contact Mr. Jack Rainsberry, Manager, Plant Licensing at (949) 368-7420.
Sincerely, cc:
B. S. Mallett, Regional Administrator, NRC Region IV B. M. Pham, NRC Project Manager, San Onofre Units 2 and 3 C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 and 3
Westinghouse Non-Proprietary Class 3 WCAP-1 5882-NP Revision 04 July 2004 San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 Risk-Informed Inservice Inspection Program Evaluation Westinghouse
L E GA L LEGALNOTICE This report was prepared as an account of work sponsored by Southern California Edison and Westinghouse Electric Company LLC. Neither Southern California Edison nor Westinghouse Electric Company LLC, nor any person acting on their behalf:
A.
Makes any warranty or representation, express or implied including the warranties of fitness for a particular purpose or merchantability, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B.
Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this report.
Westinghouse Electric Company P.O. Box 500 Windsor, Connecticut 06095-0500
Westinghouse Non-Proprietary Class 3 WCAP-15882-NP, Rev. 04 San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 Risk-Informed Inservice Inspection Program Evaluation July 2004 Author:
Rupert A. Weston Reliability & Risk Assessment Reviewer:
1*
Robed Jaquith Reliability Risk Assessment Appr<
Reliability sk Assessment
© 2004 Westinghouse Electric Company P.O. Box 500 Windsor, Connecticut 06095-0500 All Rights Reserved
COPYRIGHT NOTICE This report has been prepared by Westinghouse Electric Company, LLC for Southern California Edison. Information in this report is the property of and contains copyright information owned by Westinghouse Electric Company LLC and /or its subcontractors and suppliers. It is transmitted to you in confidence and trust, and you agree to treat this document and the information contained therein in strict accordance with the terms and conditions of the agreement under which it was provided to you.
As the recipient, you are permitted to make the number of copies of the information contained in this report which are necessary for your internal use in connection with your implementation of the report results for your plant(s) in your normal conduct of business.
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The NRC is permitted to make the number of copies beyond those necessary for its internal use that are necessary in order to have one copy available for public viewing in the appropriate docket files in the NRC public document room in Washington, DC if the number of copies submitted is insufficient for this purpose. Copies made by the NRC must include the copyright notice in all instances.
© 2004 Westinghouse Electric Company P.O. Box 500 Windsor, Connecticut 06095-0500 All Rights Reserved
TABLE OF CONTENTS
1.0 INTRODUCTION
1 1.1 RELATION TO NRC REGULATORY GUIDE 1.174..........................................................
1 1.2 PROBABILISTIC RISK ANALYSIS (PRA) QUALITY..........................................................
1 2.0 PROPOSED ALTERNATIVE TO ASME SECTION XI IST PROGRAM................................................
2 2.1 ASME SECTION XI..........................................................
2 2.2 AUGMENTED PROGRAMS..........................................................
2 3.0 RISK-INFORMED ISI PROCESSES..........................................................
3 3.1 SCOPE OF PROGRAM.........................
3 3.2 CONSEQUENCE EVALUATION.........................
3 3.3 FAILURE ASSESSMENT.........................
4 3.4 RISK EVALUATION.........................
4 3.5 ELEMENT SELECTION.........................
4 3.6 ADDITIONAL EXAMINATIONS.........................
7 3.7 PROGRAM RELIEF REQUESTS.........................
7 3.8 RISK IMPACT ASSESSMENT.........................
8 4.0 IMPLEMENTATION AND MONITORING PRO GRAM.10 5.0 PROPOSED ISI PROGRAM CHANGE.
in
6.0 REFERENCES
/DOCUMENTATION, 10 WCAP-15882-NP, Rev. 04 July 2004 Page i of ii
1.2-1 3.1-1A 3.1-lB 3.3-1 3.4-1 3.4-2A 3.4-2B 3.5-1A 3.5-1B 3.8-1A 3.8-1B List of Tables Main Contributors to CDF at SONGS Units 2 and 3....................................................... 11 System Selection and Element Scope for SONGS Unit 2................................................ 12 System Selection and Element Scope for SONGS Unit 3................................................ 13 Degradation Mechanism Assessment Summary for SONGS Units 2 and 3.................... 14 Number of Segments by Risk Category for SONGS Units 2 and 3................................. 15 Number of Welds by Risk Category for SONGS Unit 2.................................................. 16 Number of Welds by Risk Category for SONGS Unit 3.................................................. 17 Number of Locations/Inspections by Risk Category for SONGS Unit 2......................... 18 Number of Locations/Inspections by Risk Category for SONGS Unit 3......................... 19 Summary of Proposed RI-ISI and ASME Section XI Programs for SONGS Unit 2....... 20 Summary of Proposed RI-ISI and ASME Section XI Programs for SONGS Unit 3....... 22 WCAP-15882-NP, Rev. 04 July 2004 Page ii of ii
1.0 INTRODUCTION
1.1 RELATION TO NRC REGULATORY GUIDE 1.174 Inservice inspections (ISI) are currently performed on piping to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section XI, 1989 Edition as required by 10CFR50.55a. San Onofre Nuclear Generating Station (SONGS) Units 2
& 3 are currently in the second inspection interval as defined by the Code for Program B.
The objective of this evaluation is to support a change to the inservice inspection (ISI) program plan for SONGS Units 2 and 3 ASME Section XI Examination Category B-J and B-F welds in accordance with the risk-informed process described in EPRI TR 112657, Revision B-A, "Risk-Informed Inservice Inspection (RI-ISI) Evaluation Procedure" (Reference 6.1).
SONGS Units 2 & 3 plan to incorporate the RI-ISI program during the first period of the third inspection interval. The third 10-year inspection interval is scheduled to begin on August 18, 2003.
As a risk-informed application, this evaluation meets the intent and principles of Regulatory Guide 1.174. Further information is provided in Section 3.8 relative to defense-in-depth.
1.2 PROBABILISTIC RISK ANALYSIS (PRA) QUALITY The consequences of pipe ruptures were evaluated by using the SONGS Units 2 & 3 Living Probabilistic Risk Assessment (PRA). A summary of the PRA results and conclusions and how they are used in the evaluation is presented below.
The base core damage frequency from the PRA is 4.1E-5 per year and the base large early release frequency from this version is 1.4E-6 per year. The main contributors to core damage frequency (CDF) are summarized in Table 1.2-1.
Several measures have been implemented in the development of the SONGS Units 2 & 3 PRA to ensure quality. Changes in the model that impact assumptions, success criteria, basic event probabilities, system, and plant models formally undergo several levels of review, and, depending on the complexity of the change, may also include peer and/or technical expert panel review. A comprehensive independent peer review of the SONGS Units 2 & 3 Level I and Level 2 internal events living PRA for full power and shutdown operations was conducted between August 1996 and April 1997. During this review, documents, procedures, and supporting calculations and analyses were available. The review was based primarily on the guidance provided in the PRA procedure guides such as NUREG/CR-2300 and NUREG/CR-4550, as well as PRA application documents such as EPRI TR-105396 and NUREG-1489.
The results of all independent review activities performed by internal and external reviewers were documented in the SCE PRA Change Package process and tracked in the PRA Punch List Database. More recently (February 2002), Westinghouse performed a pre-certification WCAP-15882-NP, Rev. 04 Page 1 of 23 July 2004
evaluation of the SONGS Units 2 & 3 PRA. In addition to reviewing against the CEOG Peer Certification Guidance (which mirrors NEI peer review guidance NEI-002), Westinghouse reviewed the SONGS Units 2 & 3 PRA against the high level requirements of Revision 14a of the ASME standard. Based on both reviews, SCE concludes that the SONGS Units 2 & 3 PRA was adequate to support risk-informed in-service inspection.
In addition to extensive review, these refined full-scope models were used to support the approved SONGS Units 2 & 3 Diesel Generator (DG), Low Pressure Safety Injection (LPSI), and Safety Injection Tank (SIT) allowed outage extension submittals to the NRC as well as the SONGS Units 2 & 3 approved risk-informed in-service test (IST) program. In addition to detailed model review of the SONGS Units 2 & 3 Individual Plant Examination (IPE) by the NRC, the SONGS PRA received application-specific regulatory reviews as a pilot plant for risk-informed Technical Specifications. This review was in many ways similar to the review performed for the Comanche Peak risk-informed IST pilot project. The safety evaluation report (SER) for the DG was granted on September 9, 1998. The SER for the SIT and LPSI submittals was granted on June 19, 1998.
In summary, the SONGS Units 2 & 3 PRA has been subjected to extensive peer and regulatory reviews. The PRA model, assumptions, database changes and improvements, and computer code are controlled and documented by administrative procedure. The model and database reflect the as-built plant and the most recent historical data. Therefore, the SONGS Units 2 & 3 PRA is of a quality consistent with that required to perform accurate, thorough, and comprehensive evaluations for a risk-informed ISI application.
2.0 PROPOSED ALTERNATIVE TO ASME SECTION XI ISI PROGRAM 2.1 ASME SECTION XI Subsection IWB of ASME Section XI specifies the inservice inspection requirements for Class I components in light-water cooled plants. The specific examination and inspection requirements for pressure retaining welds in Class I piping are contained in Subarticle IWB-2500 and Table IWB-2500-1 Examination Category B-J and B-F.
As an alternative, a RI-ISI program will be implemented in accordance with guidance and process procedures described in EPRI TR-I 12657 Revision B-A. The RI-ISI program will be substituted for the current examination program on piping in accordance with 10 CFR 50.55a(a)(3)(i) by alternatively providing an acceptable level of quality and safety. Other non-related portions of the ASME Section XI Code will be unaffected. EPRI TR-I 12657 Revision B-A provides the requirements defining the relationship between the risk-informed examination program and the remaining unaffected portions of ASME Section XI.
2.2 AUGMENTED PROGRAMS None of the augmented inspections at SONGS Units 2 & 3 changed as a result of these RI-ISI selections.
WCAP-15882-NP, Rev. 04 Page 2 of 23 July 2004
3.0 RISK-INFORMED ISI PROCESSES The processes used to develop the RI-ISI program are consistent with the methodology described in EPRI TR 112657 Revision B-A. The process that is being applied, involves the following steps:
Scope Definition
- Consequence Evaluation
- Failure Assessment
- Risk Evaluation
- Element Selection
- Program Implementation
- Feedback Loop 3.1 SCOPE OF PROGRAM The scope of the R1-1SI evaluation included all ASME Section XI Examination Category B-J and Category B-F welds. The systems included in the risk-informed ISI program are identified in Tables 3.1-1A and 3.1-lB for SONGS Units 2 & 3, respectively. The piping and instrumentation diagrams and additional plant information were used to define system boundaries.
3.2 CONSEQUENCE EVALUATION The consequences of pressure boundary failures were evaluated and ranked based on their impact on core damage and containment performance (isolation, bypass and large early release). The impact on these measures due to both direct and indirect effects was considered using the guidance provided in EPRI TR-1 12657 Revision B-A.
The consequences of pressure boundary failures were evaluated and ranked based on their impact on conditional core damage probability (CCDP) and conditional large early release probability (CLERP). The impact on these measures due to both direct and indirect effects associated with pipe ruptures was determined using the PRA model described in Section 1. Consequence categories (High, Medium or Low) were assigned according to Table 3-1 of EPRI TR-I 12657 Revision B-A. One of the enhancements incorporated into this application of the EPRI RI-ISI methodology was the direct use of the PRA models to support the estimation of CCDP and CLERP values for each pipe element in the scope of the RISI evaluation, in lieu of the consequence tables in EPRI TR-I 12657 Revision B-A. This step was taken to support a more complete and realistic quantification of the risk impacts of the RI-ISI program in comparison with previous applications of this methodology.
All Class 1 piping at SONGS Units 2 & 3 is located inside containment. Direct effects associated with pipe ruptures inside the containment cause a loss of reactor coolant initiating event.
Indirect/spatial effects associated with pipe ruptures inside containment were based on pipe whip, jet impingement, pressurization, and temperature effect analyses documented in Reference 6.2.
All safety equipment inside containment has been qualified to function under accident/post-WCAP-15882-NP, Rev. 04 Page 3 of 23 July 2004
accident environmental conditions. There are no indirect/spatial effects associated with flooding caused by pipe ruptures inside containment.
3.3 FAILURE ASSESSMENT Failure potential estimates were generated utilizing industry failure history, plant specific failure history and other relevant information. These failure estimates were determined using the guidance provided in EPRI TR-1 12657 Revision B-A.
Table 3.3-1 summarizes the failure potential assessment by system for each degradation mechanism that was identified as potentially operative.
3.4 RISK EVALUATION In the preceding steps, each run of piping within the scope of the program was evaluated to determine its impact on core damage and containment performance (isolation, bypass, and large, early release) as well as its potential for failure. Given the results of these steps, piping segments are then defined as continuous runs of piping potentially susceptible to the same type(s) of degradation and whose failure will result in similar consequence(s). Segments are then ranked based upon their risk significance (i.e., risk categories) as defined in EPRI TR-1 12657 Revision B-A.
The results of these calculations are presented in Tables 3.4-1, 3.4-2A, and 3.4-2B.
3.5 ELEMENT SELECTION In general, EPRI TR-1 12657 Revision B-A requires that 25% of the locations in the high risk regions (i.e., risk categories 1, 2, and 3) and 10% of the locations in the medium risk regions (i.e.,
risk categories 4 and 5) be selected for inspection. The results of the selection are presented in Tables 3.5-1A and 3.5-lB for SONGS Units 2 & 3, respectively. Once the risk-informed inspection scope is defined, non-destructive examination (NDE) methods tailored to the applicable degradation mechanism were then defined for each weld. Section 4 of EPRI TR-112657 Revision B-A was used to determine the examination requirements for these locations.
SONGS Unit 2 At SONGS Unit 2, 679 examination Category B-J and Category B-F welds, excluding socket welds, were evaluated. A total of 83 welds (-12%) were subsequently selected for inclusion in the RI-ISI program inspection population. These welds are distributed among risk categories 2, 4, and 5 as described below for the various systems.
Thermal transients (TT), thermal stratification, cycling and striping (TASCS), and primary water stress corrosion cracking (PWSCC) degradation mechanisms were identified in the thirty-six risk category 2 segments for the Reactor Coolant System (RCS). Thirty risk category 2 welds were selected from these segments. The bimetallic welds in the RCS are considered especially vulnerable to PWSCC. All such welds are included in risk category 2 segments for the RCS.
Twelve bimetallic welds were selected for inspection. Six of the twelve bimetallic welds were WCAP-15882-NP, Rev. 04 Page 4 of 23 July 2004
selected to monitor for PWSCC, and the remaining six welds were selected to monitor for PWSCC and TT. Eighteen non-bimetallic category 2 welds were selected to monitor for either TT or TASCS. Eight risk category 4 welds were selected from the twenty-four risk category 4 segments for the RCS. One risk category 5 weld was selected from the four risk category 5 segments that were identified for this system.
Four risk category 2 segments were identified for the Chemical and Volume Control System (CVCS). The degradation mechanism evaluation for this system identified the welds in two of the risk category 2 segments as being susceptible to TT. The welds in the remaining two risk category 2 segments were identified as being susceptible to both TT and PWSCC. Three risk category 2 welds were selected from these segments. Two welds were selected to monitor for TT, and one weld was selected to monitor for TT and PWSCC. One risk category 4 weld was selected from the one risk category 4 segment that was identified for this system.
Four risk category 2 segments were identified for the Main Spray System (MSS). The degradation mechanism evaluation for this system identified the welds in two of the risk category 2 segments as being susceptible to PSWCC. The welds in another risk category 2 segment were susceptible to TASCS, and the welds in the remaining segment were susceptible to both TASCS and PWSCC. Six risk category 2 welds were selected from these segments. Four welds were selected to monitor for TASCS, one weld was selected to monitor for PWSCC, and one weld was selected to monitor for both PWSCC and TASCS. Nine risk category 4 welds were selected from the four risk category 4 segments that were identified for this system.
Both TT and TASCS were the degradation mechanisms identified in the one risk category 2 segment for the Auxiliary Spray System. Two risk category 2 welds were selected from the segment. No other selections were made for this system.
Eight risk category 2 segments were identified for the Safety Injection System (SIS). The degradation mechanism evaluation for this system identified the welds in four of the risk category 2 segments as being susceptible to either TT or TASCS. The welds in the remaining four risk category 2 segments were identified as being susceptible to both TASCS and PWSCC.
Nine risks category 2 welds were selected from these segments. Seven welds were selected to monitor for TASCS, and two welds were selected to monitor for both PWSCC and TASCS.
Two risk category 4 welds were selected from the two risk category 4 segments. TASCS was also the only degradation mechanism identified in the four risk category 5 segments for the SIS.
Five risk category 5 welds were selected from the four risk category 5 segments for this system.
Three risk category 2 segments were identified for the Shutdown Cooling System (SDCS). The degradation mechanism evaluation for this system identified the welds in two of the risk category 2 segments as being susceptible to either TT or TASCS. The weld in the remaining risk category 2 segment was identified as being susceptible to both PWSCC and TT. Two risk category 2 welds were selected to monitor for TT, one weld was selected to monitor for TASCS, and one weld was selected to monitor for PWSCC and TT. One risk category 4 weld was also selected from the two risk category 4 segments that were identified for this system. TT was also identified as the degradation mechanism for the welds in the risk category 5 segment for this system. One risk category 5 weld was selected for this system.
WCAP-15882-NP, Rev. 04 Page 5 of 23 July 2004
SONGS Unit 3 At SONGS Unit 3, 660 examination Category B-J and Category B-F welds, excluding socket welds, were evaluated. A total of 80 welds (-12%) were subsequently selected for inclusion in the RI-ISI program inspection population. These welds are distributed among risk categories 2, 4, and 5 as described below for the various systems.
TT, TASCS, and PWSCC degradation mechanisms were identified in the thirty-six risk category 2 segments for the RCS. Twenty-seven risk category 2 welds were selected from these segments.
The bimetallic welds in the RCS are considered especially vulnerable to PWSCC. All such welds are included in risk category 2 segments for the RCS. Twelve bimetallic welds were selected for inspection. Six of the twelve bimetallic welds were selected to monitor for PWSCC, and the remaining six welds were selected to monitor for PWSCC and TT. Fifteen non-bimetallic category 2 welds were selected to monitor for either TT or TASCS. Nine risk category 4 welds were selected from the twenty-four risk category 4 segments for the RCS. One risk category 5 weld was selected from the four risk category 5 segments that were identified for this system.
Four risk category 2 segments were identified for the CVCS. The degradation mechanism evaluation for this system identified the welds in two of the risk category 2 segments as being susceptible to TT. The welds in the remaining two risk category 2 segments were identified as being susceptible to both TT and PWSCC. Four risk category 2 welds were selected from these segments. Three welds were selected to monitor for TT, and one weld was selected to monitor for TT and PWSCC. One risk category 4 weld was selected from the one risk category 4 segment that was identified for this system.
Four risk category 2 segments were identified for the MSS. The degradation mechanism evaluation for this system identified the welds in two of the risk category 2 segments as being susceptible to PSWCC. The welds in another risk category 2 segment were susceptible to TASCS, and the welds in the remaining segment were susceptible to both TASCS and PWSCC.
Four risk category 2 welds were selected from these segments. Two welds were selected to monitor for TASCS, one weld was selected to monitor for PWSCC, and one weld was selected to monitor for both PWSCC and TASCS. Nine risk category 4 welds were selected from the four risk category 4 segments that were identified for this system.
Both TT and TASCS were the degradation mechanisms identified in the one risk category 2 segment for the Auxiliary Spray System. Two risk category 2 welds were selected from these segments. No other selections were made for this system.
Eight risk category 2 segments were identified for the SIS. The degradation mechanism evaluation for this system identified the welds in four of the risk category 2 segments as being susceptible to either TT or TASCS. The welds in the remaining four risk category 2 segments were identified as being susceptible to both TASCS and PWSCC. Ten risks category 2 welds were selected from these segments. Eight welds were selected to monitor for TASCS, and two welds were selected to monitor for both PWSCC and TASCS. One risk category 4 weld was selected from the two risk category 4 segments. TASCS was also the only degradation WCAP-I 5882-NP, Rev. 04 Page 6 of 23 July 2004
mechanism identified in the four risk category 5 segments for the SIS. Four risk category 5 welds were selected from the four risk category 5 segments for this system.
Three risk category 2 segments were identified for the SDCS. The degradation mechanism evaluation for this system identified the welds in two of the risk category 2 segments as being susceptible to either TT or TASCS. The weld in the remaining risk category 2 segment was identified as being susceptible to both PWSCC and TT. Two risk category 2 welds were selected to monitor for TT, one weld was selected to monitor for TASCS, and one weld was selected to monitor for PWSCC and TT. Two risk category 4 welds were also selected from the two risk category 4 segments that were identified for this system. TT was also identified as the degradation mechanism for the welds in the risk category 5 segment for this system. One risk category 5 weld was selected for this system.
3.6 ADDITIONAL EXAMINATIONS Since the risk-informed inspection program may require examinations of a number of elements constructed to lesser pre-service inspection requirements, the program in all cases will determine through an engineering evaluation the root cause of any unacceptable flaw determined to be service related or relevant condition found during examination. The evaluation will include the applicable service conditions and degradation mechanisms to establish that the element(s) will still perform their intended safety function during subsequent operation. Elements not meeting this requirement will be repaired or replaced.
The evaluation will include whether other elements of the segment or segments are subject to the same root cause and degradation mechanism. Additional examinations will be performed on these elements up to a number equivalent to the number of elements initially required to be inspected on the segment or segments. If unacceptable flaws determined to be service related or relevant conditions are again found similar to the initial problem, the remaining elements identified as susceptible will be examined. No additional examinations will be performed if there are no additional elements identified as being susceptible to the same service related root cause conditions or degradation mechanism.
3.7 PROGRAM RELIEF REQUESTS Alternate methods are specified to ensure structural integrity in cases where examination methods cannot be applied due to limitations such as inaccessibility or radiation exposure hazard.
A minimum of > 90% volume coverage (per Code Case N460) will be provided, when possible, when performing the risk-informed examinations. However, some limitations will not be known until the examination is performed, since some locations may be examined for the first time by the specified techniques.
At this time, all the risk-informed examination locations that have been selected are estimated to exceed > 90% volume coverage. In instances where a location may be found at the time of the examination that does not meet > 90% coverage, the process outlined in EPRI TR 112657 Revision B-A will be followed.
WCAP-15882-NP, Rev. 04 Page 7 of 23 July 2004
3.8 RISK IMPACT ASSESSMENT Change in Risk The risk-informed ISI program has been developed in accordance with Regulatory Guide 1.174, and the risk from implementation of this program is expected to remain neutral or increase negligibly compared to that estimated from current requirements.
This evaluation identified the allocation of segments into High, Medium, and Low risk regions of the EPRI TR-1 12657 risk ranking matrix, and then determined for each of these risk classes what inspection changes are proposed for each of the locations in each segment. The changes include changing the number and location of inspections within the segment and in many cases improving the effectiveness of the inspection to account for the findings of the RI-ISI degradation mechanism assessment. For example, for locations subject to thermal fatigue, inspection locations have an expanded volume and the examination is focused to enhance the probability of detection during the inspection process. A comparison of the current Section XI and proposed RI-ISI inspection programs is summarized in Tables 3.8-1A and 3.8-1B for SONGS Units 2 & 3, respectively.
A comprehensive risk impact evaluation was performed in accordance with Section 3.7 of EPRI TR-1 12657 Revision B-A (Reference 6.1). The risk impact evaluation followed the decision process and evaluation criteria in EPRI TR-1 12657 Revision B-A Figure 3-6 and included the following elements:
- 1. A qualitative evaluation - The potential risk impacts was assessed for each pipe segment due to increases and decreases in the number of examinations; and for expected enhancements to the inspection detection probability due to the implementation of expanded weld inspection volumes prescribed in Section 4.0 of EPRI TR-1 12657 Revision B-A.
- 2. Bounding and simplified quantitative evaluations - The rupture frequencies from Table A-8 in EPRI TR-1 11880 (Reference 6.3) were used to assess the risk impacts for all piping segments. The bounding quantitative evaluations conservatively took no credit for the inspection effectiveness (e.g., probability of detection - POD) associated with either the RI-ISI or Section XI based inspection programs. Inspection effectiveness was credited in the simplified quantitative evaluation.
As shown in Tables 3.8-1A and 3.8-1B, risk category 2, as defined in EPRI TR-1 12657 Revision B-A, is the only high-risk category identified for SONGS Units 2 & 3. Risk category 2 occurs in all systems, which include RCS, CVCS, MSS, SIS, SDCS, and Auxiliary Spray System. For the majority of systems, there is a decrease in the number of inspections required by the proposed RI-ISI program over the current ASME Section XI program for SONGS Units 2 & 3, except for the Auxiliary Spray System and SDCS risk category 2 inspections at Unit 2 and the Auxiliary Spray System, MSS, and SDCS risk category 2 inspections at Unit 3. The risk category 2 inspections for the Auxiliary Spray System remained unchanged and the inspections for the SDCS were increased at SONGS Unit 2. The risk category 2 inspections for the Auxiliary Spray System and MSS were increased and the inspections for SDCS remained unchanged at SONGS Unit 3.
WCAP-15882-NP, Rev. 04 Page 8 of 23 July 2004
Based on the overall population of risk category 2 welds, the number of inspections decreased under the proposed RI-ISI program.
The medium risk region consists of risk categories 4 and 5. Risk category 4 occurs in all of the systems for SONGS Units 2 and 3, except the Auxiliary Spray System. In each of the applicable systems, the number of risk category 4 inspections decreased under the proposed RI-ISI program over the current ASME Section XI program. Risk category 5 occurs in three systems (RCS, SIS, and SDC) for SONGS Units 2 and 3. For SONGS Unit 2, the number of risk category 5 inspections decreased for SIS and the number of category 5 inspections increased for RCS and SDCS under the proposed RI-ISI program. For SONGS Unit 3, the number of category 5 inspections decreased for RCS and SIS and the number of risk category 5 inspections for SDCS increased under the proposed RI-ISI program.
As discussed in EPRI TR-l 12657 Revision B-A, the contribution to risk from risk category 6 and 7 locations is negligible. Risk category 6 occurs in four systems (CVCS, AS, SIS, and SDC).
No risk category 7 locations were identified.
Tables 3.8-1 A and 3.8-1 B present a summary of the proposed RI-ISI program versus the current Section XI program. These results of the quantitative risk impact evaluation show that the total change in core damage frequency (CDF) and large early release frequency (LERF) associated with the proposed RI-ISI program satisfy the acceptance guidelines specified in EPRI TR-112657 Revision B-A.
Defense-In-Depth The intent of the inspections mandated by ASME Section XI for piping welds is to identify conditions such as flaws or indications that may be precursors to leaks or ruptures in a system's pressure boundary. Currently, the process for picking inspection locations is based upon structural discontinuity and stress analysis results. As depicted in ASME White Paper 92-01-01 Revision 1, "Evaluation of Inservice Inspection Requirements for Class 1, Category B-J Pressure Retaining Welds," this method has been ineffective in identifying leaks or failures. EPRI TR-112657 Revision B-A and ASME Code Case N-578 provide a more robust selection process founded on actual service experience with nuclear plant piping failure data.
This process has two key independent ingredients: (1) a determination of each location's susceptibility to degradation and (2) an independent assessment of the consequence of the piping failure. These two ingredients assure defense-in-depth is maintained. First, by evaluating a location's susceptibility to degradation, the likelihood of finding flaws or indications that may be precursors to leak or ruptures is increased. Secondly, the consequence assessment effort has a single failure criterion. As such, no matter how unlikely a failure scenario is, it is ranked High in the consequence assessment, and no lower than Medium in the risk assessment (i.e., Risk Category 4), if, as a result of the failure, there is no mitigative equipment available to respond to the event. In addition, the consequence assessment takes into account equipment reliability, with less credit given to less reliable equipment.
WCAP-15882-NP, Rev. 04 Page 9 of 23 July 2004
All locations within the reactor coolant pressure boundary will continue to receive a system pressure test and visual VT-2 examination as currently required by the Code regardless of its risk classification.
4.0 IMPLEMENTATION AND MONITORING PROGRAM Upon approval of the RI-ISI program, SONGS Units 2 & 3 procedures that comply with the guidelines described in EPRI TR-1 12657 Revision B-A will be prepared to implement and monitor the program. The new program will be integrated into the third ASME Section XI interval. No changes to the Updated Final Safety Analysis Report are necessary for program implementation.
The applicable aspects of the Code not affected by this change would be retained, such as inspection methods, acceptance guidelines, pressure testing, corrective measures, documentation requirements, and quality control requirements. Existing ASME Section XI program implementing procedures would be retained and would be modified to address the RI-ISI process, as appropriate.
The RI-ISI program is a living program requiring feedback of new relevant information to ensure the appropriate identification of high safety significant piping locations. As a minimum, risk ranking of piping segments will be reviewed and adjusted on an ASME period basis. In addition, significant changes may require more frequent adjustment as directed by NRC Bulletin or Generic Letter requirements, or by industry and plant specific feedback.
5.0 PROPOSED ISI PROGRAM CHANGE The initial program will be started in the first period of the third interval scheduled to start on August 18, 2003. The current second interval, which ends on August 17, 2003, will not be impacted.
6.0 REFERENCES
/DOCUMENTATION 6.1 EPRI TR 112657, Rev. B-A, "Revised Risk-Informed Inservice Inspection Evaluation Procedure," Final Report, December 1999.
6.2 SONGS Units 2 and 3 UFSAR Section 3.6, Revision 13.
6.3 EPRI TR-111880, "Piping System Failure Rates and Rupture Frequencies for Use In Risk Informed In-service Inspection Applications," Final Report, September 1999.
6.4 A-SG2-ST-0001, Rev. 1, "Implementation of the EPRI Risk-Informed Inservice Inspection Evaluation Procedure for Class I Piping at SONGS Unit 2," July 2004.
6.5 A-SG3-ST-0001, Rev. 2, "Implementation of the EPRI Risk-Informed Inservice Inspection Evaluation Procedure for Class 1 Piping at SONGS Unit 3," July 2004.
WCAP-15882-NP, Rev. 04 Page 10 of 23 July 2004
- Initiating Event Turbine Trip with PC' Loss of Power Conver Loss of Offsite Power Main Steam Line/Fee(
Small-Small LOCA (S Steam Generator Tubc Interfacing System LC Reactor Pressure Vess Loss of Component C0 Loss of DC Power 12' Loss of DC Power 12<
Loss of Control Room Fire Internal Flooding Seismic Table 1.2-1 Main Contributors to CDF at SONGS Units 2 and 3 IE Frequency (Per CDF Year)
S Initially Available (TT) 1.3E+00 1
sion System (PCS) 4.2E-01 2
(LOP) 5.4E-02 7
dwater Line Break (SLB) 5.413-04 2
6.513-05 4
7.1E-05 3
2.9E-03 9
- SL) 1.11E-04 4
Rupture (SGR) 3.9E-03 4
)CA (VL) 3.5E-08 3
el Rupture 2.7E-07 2
Doling Water (CCW)
Initiator Fault Tree 9
5 VDC Bus DI (LDCI) 8.OE-04 4
5 VDC Bus D2 (LDC2) 8.OE-04 4
HVAC Initiator Fault tree 1
Area dependent 1
Screened during Scree IPE Seismic level dependent (Per Year)
Percent
.lE-06 2.4E-06
.8E-07
.6E-07
.813-07
.6E-07
.6E-06
.513-09
.9E-08
.513-08
.7E-07
.11E-07
.5E-08
.5E-08
.41E-06 1.4E-05 ened during IPE
.5E-06 2.7%
5.8%
1.9%
0.6%
1.2%
0.9%
23.3%
0.0%
0.1%
0.1%
0.7%
2.2%
0.1%
0.1%
3.4%
33.9%
0.0%
23.0%
Total 4.1E-05 WCAP-15882-NP, Rev. 04 July 2004 Page 11 of 23
Table 3.1-1A System Selection and Element Scope for SONGS Unit 2
System Description
Number of Segments Number of Elements Reactor Coolant System (RCS) 64 167 Chemical and Volume Control System 10 54 (CVCS)
Main Spray (MS) 8 101 Auxiliary Spray (AS) 3 37 Safety Injection System (SIS) 32 282 Shutdown Cooling System (SDC) 7 38 Total 124 679 WCAP-15882-NP, Rev. 04 July 2004 Page 12 of 23
Table 3.1-IB System Selection and Element Scope for SONGS Unit 3
System Description
f Number of Segments i Number of Elements Reactor Coolant System (RCS) 64 162 Chemical and Volume Control System 10 51 (CVCS)
Main Spray (MS) 8 88 Auxiliary Spray (AS) 3 44 Safety Injection System (SIS) 32 277 Shutdown Cooling System (SDC) 7 38 Total 124 660 WCAP-1 5882-NP, Rev. 04 July 2004 Page 13 of 23
Table 3.3-1 Degradation Mechanism Assessment Summary for SONGS Units 2 and 3 Thermal Fatigue Stress Corrosion Cracking Local Corrosion Flow Sensitive SYSTEM 1
TT TASCS IGSCC TGSCC ECSCC PWSCC MIC Pitting CC E-Cav FAC RCS X
X XX CVCS X
MS X
X AS X
X X
SIS X
X X
SDC X
X X
Nomenclature:
RCS - Reactor Coolant System, CVCS - Chemical and Volume Control System, MS - Main Spray, AS - Auxiliary Spray, SIS - Safety Injection System, SDC -
Shutdown Cooling, TT - Thermal Transient, TASCS - Thermal Stripping, Cycling and Stratification, IGSCC - Intergranular Stress Corrosion Cracking, TGSCC - Transgranular Stress Corrosion Cracking, ECSCC - External Chloride Stress Corrosion Cracking, PWSCC - Primary Water Stress Corrosion Cracking, MIC - Microbiologically Influenced Corrosion, Pitting - Pitting, CC - Crevice Corrosion Cracking, E-Cav -Cavitation, FAC - Flow Accelerated Corrosion.
WCAP-15882-NP, Rev. 04 July 2004 Page 14 of 23
Table 3.4-1 Number of Segments by Risk Category "I for SONGS Units 2 and 3 System Risk Category 1 iRisk Category 2 Risk Category 3 Risk egory 4Risk Category 5 Risk Category 6 Risk Category 7 RCS 0
36 0
24 4
0 0
CVCS 0
4 0
1 0
5 0
MS 0
4 0
4 0
0 0
AS 0
1 0
0 0
2 0
SIS 0
8 0
2 4
1 8 0
SDC 0
3 0
2 1
1 0
TOTAL 0
56 0
33 9
26 0
Note I - As defined in EPRI TR-1 12657 Revision B-A, Reference 6.1.
WCAP-15882-NP, Rev. 04 July 2004 Page 15 of 23
Table 3.4-2A Number of Welds by Risk Category (1) for SONGS Unit 2 System Risk Category 1 Risk Category 2 Risk Category 3 Risk Category 4 Risk Category 5 1 Risk Category 6 Risk Category 7 RCS 0
84 0
75 8
0 0
CVCS 0
8 0
12 0
34 0
MS 0
18 0
83 0
0 0
AS 0
10 0
0 0
27 0
SIS 0
35 0
8 45 194 0
SDC 0
11 0
19 6
2 0
TOTAL T 0
166 l
0 197
]
59 257 0
Note 1 - As defined in EPRI TR-I 12657 Revision B-A, Reference 6.1.
WCAP-15882-NP, Rev. 04 July 2004 Page 16 of 23
Table 3.4-2B Number of Welds by Risk Category "I for SONGS Unit 3 System Risk Category 1 Risk Category 2 Risk Category 3 Risk Category 4 Risk Category 5 Risk Category 6 Risk Category 7 RCS 0
78 0
76 8
0.
0 CVCS 0
1 0 0
12 0
29 L 0 MS 0
12 0
76 0
0 0
AS 0
10 0
0 0
34 0
SIS 0
40 0
8 38 191 0
SDC 0
11 0
19 6
2 0
TOTAL 0
161 0
191 52 256 0
Note 1 - As defined in EPRI TR-l 12657 Revision B-A, Reference 6.1.
WCAP-15882-NP, Rev. 04 July 2004 Page 17 of 23
Table 3.5-1A Number of Locations/Inspections by Risk Category (') for SONGS Unit 2 Risk ategory 2 Risk Category 4 Risk Category 5 Risk Category 6 SystemInp Pop l-Insp.
Pop Insp.
Pop Insp.
Pop Insp.
RCS 84 30 75 8
8 1
0 0
CVCS 8
3 12 1
0 0
34 0
MS 18 6
83 9
0 0
0 0
AS 10 3
0 0
0 0
27 0
SIS 35 9
8 2
45 5
194 0
SDC 11 4
19 1
6 1
2 0
TOTAL 166 55 197 21 59 7
l 257 0
Pop.
Population, the number of welds in each risk category Insp.
Inspected, the number of welds in each category selected for inclusion in the RI-ISI program Note 1 - As defined in EPRI TR-l 12657 Revision B-A, Reference 6.1.
WCAP-15882-NP, Rev. 04 July 2004 Page 18 of 23
Table 3.5-lB Number of Locations/Inspections by Risk Category (') for SONGS Unit 3 Risk Category 2 Risk Category 4 Risk Category 5 Risk Category 6 S
Pop Insp.
Pop Insp.
Pop Insp.
Pop
]
Insp.
RCS 78 27 76 9
8 1
0 0
CVCS 10 4
12 1
0 0
29 0
MS 12 4
76 9
0 0
0 0
I__
AS 10 3
0 0
0 0
34 0
SIS 40 10 8
1 38 4
191 0
SDC 11 4
19 2
6 1
2 0
TOTAL 161 52 191 22 52 6
256 0
Pop.
Population, the number of welds in each risk category Insp.
Inspected, the number of welds in each category selected for inclusion in the RI-ISI program Note I - As defined in EPRI TR-l 12657 Revision B-A, Reference 6.1.
WCAP-15882-NP, Rev. 04 July 2004 Page 19 of 23
Table 3.8-1A Summary of Proposed RI-ISI and ASME Section XI Programs for SONGS Unit 2 Risk Consequence Damage Section XI RI-ISI Delta Augmented Qualitative Risk Quantitative Risk Impact System Category Rank Mechanism Exams Exams Inspections Programs Impact (2)
P POD w/POD
__lACDF I ALER lCDF l ALERF RCS 2
HIGH TT, TASCS, 33 30
-3 INCREASE (
6.67E-07 2.97E-09 -1.33E-08 -2.09E-09 4
HIGH NONE 52 8
-44 INCREASE (I) 7.22E-08 2.73E-10 3.61E-08 1.37E-10 5
MEDIUM TT 0
1 1
DECREASE(3')
8.27E-12 -1.51 E-13 -7.45E-12 -1.36E-13 CVCS 2
HIGH TT, PWSCC 5
3
-2 INCREASE (
2.62E-08 4.77E-10 -1.36E-08 -2.48E-10 4
HIGH NONE 4
1
-3 INCREASE (')
5.58E-09 1.02E-10 2.79E-09 5.08E-I I 6
MEDIUM NONE 14 0
-14 NEGLIGIBLE 2.60E-08 4.74E-10 1.30E-08 2.37E-10 MS 2
HIGH TASCS 8
6
-2 INCREASE (
5.97E-08 2.71 E-I 0 -3.79E-08 -1.72E-10 4
HIGH NONE 36 9
-27 INCREASE 4.13E-08 1.88E-10 2.07E-08 9.38E-11 AS 2
HIGH TT,TASCS, 3
3 0
NO CHANGE 0.00E+00 0.00E+00 -1.72E-08 -3.14E-10 PWSCC 6
MEDIUM NONE 7
0
-7 NEGLIGIBLE 1.30E-11 2.37E-13 6.51E-12 I.19E-13 SIS 2
HIGH PWSCC 13 9
-4 INCREASE 2.69E-08 1.01E-10 -1.27E-08 -4.77E-11 4
HIGH NONE 6
2
-4 INCREASE (1) 1.84E-09 8.36E-12 9.22E-10 4.18E-12 5
MEDIUM TASCS 18 5
-13 INCREASE(1) 2.38E-10 7.56E-11 1.65E-11 5.23E-12 6
MEDIUM NONE 49 0
-49 NEGLIGIBLE 3.28E-10 l 1.02E-10 1.64E-10 5.12E-I1 WCAP-15882-NP, Rev. 04 July 2004 Page 20 of 23
Table 3.8-1A (Continued)
Summary of Proposed RI-ISI and ASME Section XI Programs for SONGS Unit 2 TQuantitative Risk Impact Risk Consequence Damage Section XI RI-ISI Delta Augmented Qualitative Risk System Category Rank Mechanism Exams Exams Inspections Programs Impact (2)
W/O POD w/POD l ACDF I ALERF I ACDF ]ALERF SDC 2
HIGH
- TTTASCS, 3
4 1
DECREASE(3 ) -1.55E-09 -5.81E-12 -1.04E-08 -3.90E-l1 4
HIGH NONE 5
1
-4 INCREASE 2.68E-09 1.01E-11 1.34E-09 5.04E-12 5
MEDIUM TT 0
1 1
DECREASE(3 ) -1.55E-09 -5.81E-12 -1.39E-09 -5.23E-12 6
MEDIUM NONE 0
0 0
NO CHANGE O.00E+00 0.00E+00 0.00E+00 0.00E+00 Total 256 83
-173 9.27E-07 5.04E-09 -3.15E-08 -2.33E-09 (1) Increase due to reduced inspections.
(2)
Per EPRI TR-112657 Revision B-A, the contribution to risk from Risk Category 6 locations is negligible.
(3)
Decrease due to increased inspections.
WCAP-15882-NP, Rev. 04 July 2004 Page 21 of 23
Table 3.8-1B Summary of Proposed RI-ISI and ASME Section XI Programs for SONGS Unit 3 Quantitative Risk Impact Risk Consequence Damage Section XI RI-ISI Delta Augmented Qualitative Risk I
Category Rank Mechanism Exams Exams Inspections Programs Impact (2) w/o POD w/POD l ACDF [ALERF I ACDF 1ALERF RCS 2
HIGH TT,TASCS, 35 27
-8 INCREASE '
6.77E-07 3.87E-09 1.40E-08 -1.59E-09
______PWSCC 4
HIGH NONE 55 9
-46 INCREASE (1) 7.61E-08 3.01E-10 3.80E-08 1.51E-10 5
MEDIUM TT 3
1
-2 INCREASE (1) 1.65E-I 3.02E-13 0.00E+00 0.00E+00 CVCS 2
HIGH TT, PWSCC 8
4
-4 INCREASE (1) 4.53E-08 8.25E-10 -1.36E-08 -2.48E-10 4
HIGH NONE 3
1
-2 INCREASE 3.72E-09 6.78E-11 1.86E-09 3.39E-1 1 6
MEDIUM NONE 13 0
-13 NEGLIGIBLE 2.42E-08 4.40E-10 1.21E-08 2.20E-10 MS 2
HIGH TASCS 3
4 1
DECREASE (3) -1.26E-08 -5.73E-11 -5.39E-08 -2.44E-10 4
HIGH NONE 25 9
-16 INCREASE (')
3.50E-08 1.59E-10 1.75E-08 7.93E-11 AS 2
HIGH TT, TASCS, 2
3 1
DECREASE (3) -9.56E-09 -1.74E-10 -2.01E-08 -3.66E-10 PWSCC 6
MEDIUM NONE 2
0
-2 NEGLIGIBLE 3.72E-12 6.78E-14 1.86E-12 3.39E-14 TA CS SIS 2
HIGH
- TASCS, 13 10
-3 INCREASE (')
2.53E-08 9.50E-11 -1.41E-08 -5.29E-11 4
HIGH NONE 4
1
-3 INCREASE (1) 1.38E-09 6.27E-12 6.91E-10 3.14E-12 5
MEDIUM TASCS 23 4
-19 INCREASE 3.47E-10 1.10E-10 6.03E-11 1.92E-1 I 6
MEDIUM NONE 37 0
-37 NEGLIGIBLE 2.63E-10 8.14E-11 1.32E-10 4.07E-11 WCAP-15882-NP, Rev. 04 July 2004 Page 22 of 23
Table 3.8-1B (Continued)
Summary of Proposed RI-ISI and ASME Section XI Programs for SONGS Unit 3 Quantitative Risk Impact Syt Risk Consequence Damage Section XI RI-ISI Delta Augmented Qualitative Risk R
Ipac ystem Category Rank Mechanism Exams Exams Inspections Programs Impact (2) w/o POD I
W/POD
=
TACDF I ALERF I ACDF I ALERF SDC 2
HIGH
- TTTASCS, 4
4 0
NO CHANGE 0.00E+00 0.00E+00 -9.92E-09 -3.72E-1 I 4
HIGH NONE 7
2
-5 INCREASE I')
3.35E-09 1.26E-11 1.68E-09 6.29E-12 5
MEDIUM TT 0
1 1
DECREASE)3 ) -1.55E-09
-5.81E-12 -1.39E-09 -5.23E-12 6
MEDIUM NONE 2
0
-2 NEGLIGIBLE 1.34E-09 5.04E-12 6.71E-10 2.52E-12 Total 239 80
-159 8.69E-07 5.73E-09 -2.63E-08 -1.99E-09 (1) Increase due to reduced inspections.
(2)
Per EPRI TR-112657 Revision B-A, the contribution to risk from Risk Category 6 locations is negligible.
(3)
Decrease due to increased inspections.
WCAP-15882-NP, Rev. 04 July 2004 Page 23 of 23
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