ML013460265
| ML013460265 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 01/30/2002 |
| From: | Stephen Dembek NRC/NRR/DLPM/LPD4 |
| To: | Randolph G Union Electric Co |
| Donohew J N, NRR/DLPM,415-1307 | |
| References | |
| TAC MB1205, TR-112657 | |
| Download: ML013460265 (13) | |
Text
January 30, 2002 Mr. Garry L. Randolph Vice President and Chief Nuclear Officer Union Electric Company Post Office Box 620 Fulton, MO 65251
SUBJECT:
APPROVAL OF RELIEF REQUEST FOR APPLICATION OF RISK-INFORMED INSERVICE INSPECTION PROGRAM FOR AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE CLASS 1 AND 2 PIPING FOR CALLAWAY PLANT, UNIT 1 (CALLAWAY)
Dear Mr. Randolph:
By letter dated February 16, 2001 (ULNRC-4392), you requested approval of an alternative risk-informed inservice inspection (RI-ISI) program for American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code) Class 1 and 2 piping welds for Callaway. The letter included an enclosure describing the proposed program. Additional information was provided in your letter dated October 25, 2001 (ULNRC-4544), which was in response to our request for additional information dated October 3, 2001.
The RI-ISI program for Callaway was developed in accordance with Electric Power Research Institute Topical Report TR-112657, Revision B-A, using the Nuclear Energy Institute template methodology. Based on the enclosed safety evaluation, we conclude that the proposed RI-ISI program is an acceptable alternative to the requirements of Section XI of the ASME Code for ISI. Therefore, your request for relief is authorized pursuant to 10 CFR 50.55a(a)(3)(i) on the basis that the alternative provides an acceptable level of quality and safety. The relief is authorized for the second 10-year ISI interval for Callaway.
Sincerely,
/RA/
Stephen Dembek, Chief, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-483
Enclosure:
Safety Evaluation cc w/encl: See next page
January 30, 2002 Mr. Garry L. Randolph Vice President and Chief Nuclear Officer Union Electric Company Post Office Box 620 Fulton, MO 65251
SUBJECT:
APPROVAL OF RELIEF REQUEST FOR APPLICATION OF RISK-INFORMED INSERVICE INSPECTION PROGRAM FOR AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE CLASS 1 AND 2 PIPING FOR CALLAWAY PLANT, UNIT 1 (CALLAWAY)
Dear Mr. Randolph:
By letter dated February 16, 2001 (ULNRC-4392), you requested approval of an alternative risk-informed inservice inspection (RI-ISI) program for American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code) Class 1 and 2 piping welds forCallaway. The letter included an enclosure describing the proposed program. Additional information was provided in your letter dated October 25, 2001 (ULNRC-4544), which was in response to our request for additional information dated October 3, 2001.
The RI-ISI program for Callaway was developed in accordance with Electric Power Research Institute Topical Report TR-112657, Revision B-A, using the Nuclear Energy Institute template methodology. Based on the enclosed safety evaluation, we conclude that the proposed RI-ISI program is an acceptable alternative to the requirements of Section XI of the ASME Code for ISI. Therefore, your request for relief is authorized pursuant to 10 CFR 50.55a(a)(3)(i) on the basis that the alternative provides an acceptable level of quality and safety. The relief is authorized for the second 10-year ISI interval for Callaway.
Sincerely,
/RA/
Stephen Dembek, Chief, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-483 DISTRIBUTION:
PUBLIC SAli
Enclosure:
Safety Evaluation PDIV-2 Reading SDinsmore RidsNrrDlpmPdiv (SRichards) DBujol, RIV cc w/encl: See next page RidsNrrPMJDonohew SMorris, EDO RidsNrrLaEPeyton WJohnson, RIV RidsOgcRp GHill (2)
RidsACRSACNWMailCenter SDembek RidsRgn4MailCenter(KBrockman) MRubin RidsNrrDssaSpsb(RBarrett) TChan RidsNrrDeEmcb(WBateman)
- EMCB and PSAB Memo dated January 7, 2002 ACCESSION NO.: ML013460265 OFFICE PDIV-2/PM PDIV-2/LA EMCB/SC SPSB/SC OGC PDIV-2/SC NAME JDonohew EPeyton TChan* MRubin* RHoefling SDembek DATE 1/18/2002 1/29/02 01/07/2002 01/07/2002 1/23/02 1/30/2002 DOCUMENT NAME: C:\Program Files\Adobe\Acrobat 4.0\PDF Output\ReliefRequest-RI-ISI.cw.wpd
OFFICIAL RECORD COPY Callaway Plant, Unit 1 cc:
Professional Nuclear Mr. Otto L. Maynard Consulting, Inc. President and Chief Executive Officer 19041 Raines Drive Wolf Creek Nuclear Operating Corporation Derwood, MD 20855 Post Office Box 411 Burlington, KA 66839 John ONeill, Esq.
Shaw, Pittman, Potts & Trowbridge Mr. Dan I. Bolef, President 2300 N. Street, N.W. Kay Drey, Representative Washington, D.C. 20037 Board of Directors Coalition for the Environment Mr. Mark A. Reidmeyer, Regional 6267 Delmar Boulevard Regulatory Affairs Supervisor University City, MO 63130 Regulatory Affairs AmerenUE Mr. Lee Fritz Post Office Box 620 Presiding Commissioner Fulton, MO 65251 Callaway County Court House 10 East Fifth Street U.S. Nuclear Regulatory Commission Fulton, MO 65151 Resident Inspector Office 8201 NRC Road Mr. David E. Shafer Steedman, MO 65077-1302 Superintendent Licensing Regulatory Affairs Mr. J. V. Laux, Manager AmerenUE Quality Assurance Post Office Box 66149, MC 470 AmerenUE St. Louis, MO 63166-6149 Post Office Box 620 Fulton, MO 65251 Mr. John D. Blosser, Manager Regulatory Affairs Manager - Electric Department AmerenUE Missouri Public Service Commission P.O. Box 620 301 W. High Fulton, MO 65251 Post Office Box 360 Jefferson City, MO 65102 Mr. Gary McNutt, Director Section for Environmental Public Health Regional Administrator, Region IV P. O. Box 570 U.S. Nuclear Regulatory Commission Jefferson City, Missouri 65102-0570 Harris Tower & Pavilion 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 Mr. Ronald A. Kucera, Deputy Director for Public Policy Department of Natural Resources 205 Jefferson Street Jefferson City, MO 65101
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RISK-INFORMED INSERVICE INSPECTION PROGRAM UNION ELECTRIC COMPANY CALLAWAY PLANT, UNIT 1 DOCKET NO. 50-483
1.0 INTRODUCTION
By application dated February 16, 2001 (Reference 1), Union Electric Company (the licensee) proposed a risk-informed inservice inspection (RI-ISI) program as an alternative to a portion of their current inservice inspection (ISI) program for Callaway Plant, Unit 1 (Callaway). The scope of the RI-ISI program is limited to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (the ASME Code) Class 1 and 2 piping (Categories B-F, B-J, C-F-1, and C-F-2 welds) only. Additional information was provided in a letter from the licensee dated October 25, 2001 (Reference 2). The licensees letter dated October 25, 2001, was in response to the Nuclear Regulatory Commission (NRC) staffs request for additional information dated October 3, 2001. There was also a conference call on December 5, 2001, with the licensee to clarify one of the licensees responses in its letter of October 25, 2001 (ADAMS Accession No. ML013520472).
The licensees RI-ISI program was developed in accordance with the methodology contained in the Electric Power Research Institute (EPRI) Topical Report (TR) EPRI TR-112657, Revision B-A (Reference 3), which was previously reviewed and approved by the NRC staff.
Reference 3 contains the letter issued by the staff on October 28, 1999, that approved the TR.
The RI-ISI program proposed by the licensee is an alternative pursuant to 10 CFR 50.55a(a)(3)(i).
2.0 BACKGROUND
2.1 Applicable Requirements Pursuant to 10 CFR 50.55a(g), the ISI of the ASME Code Class 1, 2, and 3 components must be performed in accordance with Section XI of the ASME Code, "Rules for Inservice Inspection of Nuclear Power Plant Components," and applicable addenda, except where specific written relief has been granted by the NRC pursuant to 10 CFR 50.55a(g)(6)(i). The regulation, 10 CFR 50.55a(a)(3), states in part that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if the proposed alternatives would provide an acceptable level of quality and safety, or if the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements set forth in the ASME Code, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that ISI of components conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
Callaway is in its second 10-year interval, and the applicable edition of the ASME Code,Section XI is the 1989 edition, no addenda.
2.2 Summary of Proposed Approach The licensee has proposed to use a RI-ISI program for ASME Code Class 1 and 2 piping (Examination Categories B-F, B-J, C-F-1, and C-F-2 welds), as an alternative to the ASME Code,Section XI requirements. The ASME Code requires in part that for each successive 10-year ISI interval, 100 percent of Category B-F welds and 25 percent of Category B-J welds for the ASME Code Class 1 non-exempt piping be selected for volumetric and/or surface examination, based on existing stress analyses and cumulative usage factors. For Category C-F welds, 7.5 percent of non-exempt welds are selected for volumetric and/or surface examination. The application follows the staff-approved RI-ISI process and methodology delineated in Reference 3.
The number of inspection locations is significantly reduced by assessing piping failure potential and piping failure consequences, and performing probabilistic risk assessment (PRA) and safety significance ranking of piping segments. However, the RI-ISI program retains the fundamental requirements of the ASME Code, such as inspection methods, acceptance guidelines, pressure testing, corrective measures, documentation requirements, and quality control requirements. Thus, ISI program requirements of other non-related portions of the ASME Code,Section XI are unaffected.
The licensee stated that the augmented ISI program for flow accelerated corrosion (FAC) implemented in response to NRC Bulletin 89-08, "Erosion/Corrosion - Induced Pipe Wall Thinning," is not changed by the RI-ISI program. The licensee also indicated that the augmented inspection program for high energy "No Break Zone" piping is not affected by this RI-ISI program. The licensee further stated that the augmented examinations to address the thermal fatigue issues documented in NRC Bulletin 88-08, "Thermal Stresses in Piping Connected to Reactor Coolant System," and NRC Information Notice 93-20, "Thermal Fatigue Cracking of Feedwater Piping to Steam Generators," have been subsumed into the RI-ISI program, as allowed by Reference 3. Other remaining augmented ISI programs are either unaffected or modified in accordance with the guidance of Reference 3.
According to the information provided in Reference 1, Callaway is currently in the middle of the second period of its second 10-year interval. The licensee stated that 37.7 percent of the examinations required by ASME Code Section XI have been completed. The licensee further stated that 62.3 percent of the RI-ISI examinations will be performed during the remaining second and third periods so that 100 percent of the selected examinations are performed during the interval. In response to a staff question (Reference 2), the licensee stated that
although only 62.3 percent of the existing ISI program examinations remain to be performed, it will perform 67 percent RI-ISI program examinations during the remainder of the second interval. The licensee also stated that the remaining RI-ISI examinations will be based on risk categorization and that the more risk significant welds will be inspected first.
The implementation of an RI-ISI program for piping should be initiated at the start of a plants 10-year ISI interval consistent with the requirements of the ASME Code and Addenda committed to by the licensee in accordance with 10 CFR 50.55a. However, the implementation may begin at any point in an existing interval, as long as the examinations are scheduled and distributed consistent with the ASME Code requirements (e.g., the minimum examinations completed at the end of the three inspection periods under ASME Code Program B should be 16 percent, 50 percent, and 100 percent, respectively, and the maximum examinations credited at the end of the respective periods should be 34 percent, 67 percent, and 100 percent, respectively).
It is also the staffs view that the inspections for the RI-ISI program and for the balance of the ISI program should be on the same interval start and end dates. This can be accomplished by either implementing the RI-ISI program at the beginning of the interval, or merging the RI-ISI program into the ISI program for the balance of the inspections if the RI-ISI program is to begin during an existing ISI interval. One reason for this view is that it eliminates the problem of having different ASME Codes of record for the RI-ISI program and for the balance of the ISI program. A potential problem, with using two different interval start dates, and hence two different ASME Codes of record, would be having two sets of repair/replacement rules depending upon which program identified the need for repair (e.g., a weld inspection versus a pressure test). According to the information provided in Reference 1, the licensee will merge the RI-ISI program into the existing ISI program so that the 10-year interval start and end dates will not be impacted.
3.0 EVALUATION Pursuant to 10 CFR 50.55a(a)(3)(i), the staff has reviewed and evaluated the licensees proposed RI-ISI program, including those portions related to the applicable methodology and processes contained in Reference 3, based on guidance and acceptance criteria provided in Regulatory Guides (RGs) 1.174 (Reference 4) and 1.178 (Reference 5), and in Standard Review Plan Chapter 3.9.8 (Reference 6).
3.1 Proposed Changes to the ISI Program The scope of the licensees proposed RI-ISI program is limited to ASME Code Class 1 and Class 2 piping welds for the following examination categories: B-F for pressure retaining dissimilar metal welds, B-J for pressure retaining welds in piping, C-F-1 for pressure retaining welds in austenitic stainless steel or high alloy piping, and C-F-2 for pressure retaining welds in carbon or low alloy steel piping. The RI-ISI program is proposed as an alternative to the existing ISI requirements of the ASME Code,Section XI. A general description of the proposed changes to the ISI program is provided in Sections 3 and 5 of Attachment 1 to Reference 1.
During the course of its review, the staff verified that the proposed RI-ISI program is consistent with the guidelines contained in Reference 3, which states that industry and plant-specific piping failure information, if any, is to be utilized to identify piping degradation mechanisms and failure modes, and consequence evaluations are to be performed using PRAs to establish piping segment safety ranking for determining new inspection locations. Thus, the staff concludes that the licensees application of the Reference 3 approach is an acceptable alternative to the current Callaway piping ISI requirements with regards to the number, locations, and methods of inspections, and provides an acceptable level of quality and safety pursuant to 10 CFR 50.55a(a)(3)(i).
3.2 Engineering Analysis In accordance with the guidance provided in References 4 and 5, an engineering analysis of the proposed changes is required using a combination of traditional engineering analyses and supporting insights from the PRA. The licensee elaborated as to how the engineering analyses conducted for the Callaway RI-ISI program ensure that the proposed changes are consistent with the principles of defense-in-depth. This is accomplished by evaluating a locations susceptibility to a particular degradation mechanism and then performing an independent assessment of the consequence of a failure at that location. No changes to the evaluation of design basis accidents in the final safety analysis report are being made in the RI-ISI process.
Therefore, sufficient safety margins will be maintained.
The licensees RI-ISI program at Callaway is limited to ASME Code Class 1 and 2 piping welds.
The licensee stated in Reference 1 that other non-related portions of the ASME Code will be unaffected by this program. Piping systems defined by the scope of the RI-ISI program were divided into piping segments. Pipe segments are defined as lengths of pipe whose failure leads to similar consequences and are exposed to the same degradation mechanisms. That is, some lengths of pipe whose failure would lead to the same consequences may be split into two or more segments when two or more regions are exposed to different degradation mechanisms.
In Reference 1, the licensee stated that failure potential categories were generated utilizing industry failure history, plant-specific failure history, and other relevant information using the guidance provided in Reference 3. The degradation mechanisms identified in the submittal include thermal fatigue, including thermal stratification, cycling and striping (TASCS), and thermal transients; intergrannular stress corrosion cracking (IGSCC); localized corrosion; and FAC. The licensee stated in Section 2.2 of Attachment 1 to Reference 1, that the augmented inspection program for FAC is relied upon to manage this mechanism, and is not changed by the RI-ISI program.
In Section 3 of Attachment 1 to Reference 1, the licensee described a deviation to the EPRI RI-ISI methodology for assessing the potential for TASCS that was implemented by the licensee. In Reference 2, the licensee stated that the methodology for assessing TASCS in the Callaway RI-ISI submittal is identical to the Materials Reliability Project (MRP) methodology in EPRI TR-1000701, "Interim Thermal Fatigue Management Guideline (MRP-24)," January 2001.
The staff has reviewed the guidance for evaluating TASCS in EPRI TR-1000701 and finds it to be acceptable. The licensee further stated that it will update the RI-ISI program based on the final EPRI MRP guidance if warranted.
Additionally, the licensee stated that the consequences of pressure boundary failure were evaluated and ranked based on their impact on core damage and containment performance (isolation, bypass and large early release), and that the impact due to both direct and indirect effects was considered using guidance provided in Reference 3. The licensee reported no deviations from the consequence evaluation methodology in Reference 3. The licensee further stated that shutdown operation and external events are included in the analysis. Based on above discussion, the staff finds that the consequence evaluation performed for this application to be acceptable.
3.3 Probabilistic Risk Assessment The licensee used the first update of the individual plant examination (IPE) model for Callaway (dated February 1999) as the plant-specific PRA to evaluate the consequences of pipe rupture for the RI-ISI assessment. Based on the IPE model, the licensee reported a core damage frequency (CDF) of 3.96E-5/year and a large early release frequency (LERF) of 4.22E-7/year.
The IPE for Callaway was submitted in September 29, 1992. The staff evaluation report (SER),
dated May 26, 1996, concluded that the Callaway IPE satisfied the intent of Generic Letter 88-20, "Individual Plant Examination for Severe Accident Vulnerabilities." No deficiencies or weakness were identified; however, the staff noted there were five procedural and design enhancements implemented by the licensee that, if modeled in the PRA, would decrease CDF.
In Reference 2, the licensee described the current status of the implementation of these enhancements in the PRA. Two of these enhancements have been modeled in the current PRA. Three of the enhancements have not yet been modeled in the PRA. In the conference call of December 5, 2001 (see ADAMS Accession No. ML013520472), the licensee clarified that, when modeled in the PRA, each of the three enhancements would decrease the conditional core damage probability (CCDP) and conditional large early release probability (CLERP) for all pipe segment ruptures included in the scope of the analysis. The EPRI method categorizes each segment independently based on the magnitude of the CCDP and CLERP.
Therefore, the categorization in the RI-ISI submittal is, if affected at all, conservative, and the analysis is adequate to support the RI-ISI submittal.
A Westinghouse Owners Group Probabilistic Risk Analysis peer review was performed in November 2000 on the second update of the Callaway IPE. Both the PRA update and the review occurred after the RI-ISI project was complete. However, the licensee stated that updated loss-of-coolant initiating event frequency and other important modeling changes were taken into account during the RI-ISI project. Callaway has established a procedure that requires an update of the plant-specific PRA on a 36-month frequency at a minimum or more frequently if conditions warrant.
The staff did not review the IPE analysis to assess the accuracy of the quantitative estimates.
The staff recognizes that the quantitative results of the IPE are used as order of magnitude estimates for several risk and reliability parameters used to support the assignment of segments into three broad consequence categories. Inaccuracies in the models or in assumptions large enough to invalidate the broad categorizations developed to support RI-ISI should have been identified during the staffs review of the IPE and by the licensees model update control program. Minor errors or inappropriate assumptions will affect only the consequence categorization of a few segments and will not invalidate the general results or
conclusions. The staff finds the quality of the licensees PRA sufficient to support the proposed RI-ISI program.
The degradation category and the consequence category were combined according to the approved methodology described in Reference 3 to categorize the risk significance of each segment. The risk significance of each segment is used to determine the number of weld inspections required in each segment.
As required by Section 3.7 of Reference 3, the licensee evaluated the change in risk expected from replacing the current ISI program with the RI-ISI program. The calculations estimated the change in risk due to removing locations and adding locations to the inspection program. The expected change in risk was quantitatively evaluated using the "Simplified Risk Quantification Method" described in Section 3.7.2 of Reference 3. For high consequence category segments, the licensee used the CCDP and CLERP based on the highest estimated CCDP and CLERP.
For medium consequence category segments, bounding estimates of CCDP and CLERP were used.
The licensee performed their bounding analysis with and without taking credit for an increased probability of detection (POD). In Reference 1, the licensee estimated for Callaway the aggregate change in CDF to be about -4.13E-9/year and the aggregate change in LERF to be about -5.480E-10/year excluding credit for any increased POD due to the use of improved inspection techniques. Including the expected increased POD results in an aggregate estimated change in CDF of -1.29E-8/year and an aggregate estimated change in LERF of
-1.71E-9/year.
The staff finds that the licensees process to evaluate and bound the potential change in risk is reasonable because it accounts for the change in the number and location of elements inspected, recognizes the difference in degradation mechanism related to failure likelihood, and considers the effects of enhanced inspection. System level and aggregate estimates of the changes in CDF and LERF are less than the corresponding guideline values in Reference 3.
The staff finds that re-distributing the welds to be inspected with consideration of the safety-significance of the segments, provides assurance that segments whose failures have a significant impact on plant risk receive an acceptable and often improved level of inspection.
Therefore, the staff concludes that the implementation of the RI-ISI program as described in the licensees application will have a small impact on risk consistent with the guidelines of Reference 4.
3.4 Integrated Decisionmaking As described in Reference 1, an integrated approach is utilized in defining the proposed RI-ISI program by considering, in concert, the traditional engineering analysis, risk evaluation, and the implementation and performance monitoring of piping under the program. This is consistent with the guidelines of Reference 5.
The selection of pipe segments to be inspected using the results of the risk category rankings and other operational considerations is described in Section 3.5 of Attachment 1 of Reference 1. Table 3.5-1 provides the number of locations and inspections by risk category for the various systems in Callaway. Tables 5-1 and 5-2 in Attachment 1 to Reference 1 compares
the number of inspections required under the existing ASME Code,Section XI ISI program with the alternative RI-ISI program for Callaway. The risk impact analysis results for each system are provided in Table 3.6-1. The licensee used the methodology described in Reference 3 to guide the selection of examination elements within high and medium risk-ranked piping segments. The methodology described in Reference 3 requires that existing augmented programs, other than thermal fatigue and IGSCC Category A piping welds, which the RI-ISI program subsumes, be maintained. Reference 3 describes targeted examination volumes (typically associated with welds) and methods of examination based on the type(s) of degradation expected. The staff has reviewed these guidelines and has determined that, if implemented as described, the RI-ISI examinations should result in improved detection of service-related degradations over those currently required by ASME Code,Section XI.
The staff finds that the location selection process is acceptable since it is consistent with the process approved for Reference 3, takes into account defense-in-depth, and includes coverage of systems subjected to degradation mechanisms in addition to those covered by augmented inspection programs.
The objective of the ISI required by ASME Code,Section XI is to identify conditions (i.e., flaw indications) that are precursors to leaks and ruptures in the pressure boundary that may impact plant safety. Therefore, the RI-ISI program should meet this objective if found to be acceptable for use. Further, since the risk-informed program is based on inspection for cause, element selection should target specific degradation mechanisms. The inspection for cause approach involves identification of specific damage mechanisms that are likely to be operative, the location where they may be operative, and appropriate examination methods and volumes specific to address the damage mechanisms.
Chapter 4 of Reference 3 provides guidelines for the areas and/or volumes to be inspected, as well as the examination method, acceptance standard, and evaluation standard for each degradation mechanism. Based on review of the cited portion of Reference 3, the staff concludes that the examination methods for the proposed RI-ISI program are appropriate since they are selected based on specific degradation mechanisms, pipe sizes, and materials of concern.
3.5 Implementation and Monitoring Implementation and performance monitoring strategies require careful consideration by the licensee and are addressed in Element 3 of References 5 and 6. The objective of Element 3 is to assess the performance of the affected piping systems under the proposed RI-ISI program by implementing monitoring strategies that confirm the assumptions and analyses used in the development of the RI-ISI program. To approve an alternative pursuant to 10 CFR 50.55a(a)(3)(i), the staff must conclude that implementation of the RI-ISI program, including inspection scope, examination methods, and methods of evaluation of examination results, must provide an adequate level of quality and safety.
The licensee stated that, upon approval of the RI-ISI program, procedures that comply with the guidelines in Reference 3 will be prepared to implement and monitor the RI-ISI program. The licensee confirmed that the applicable portions of the ASME Code, such as inspection methods,
acceptance guidelines, pressure testing, corrective measures, documentation requirements, and quality control requirements would be retained.
The licensee stated in Section 4 of Attachment 4 to Reference 1 that the RI-ISI program is a living program and its implementation will require feedback of new, relevant information to ensure the appropriate identification of safety significant piping locations. The submittal also states that, as a minimum, risk ranking of piping segments will be reviewed and adjusted on an ASME Code period basis, and that significant changes may require more frequent adjustment as directed by NRC bulletin or generic letter requirements, or by industry and plant-specific feedback.
In response to the staffs request for further clarification, the licensee stated in Reference 2 that the ISI program will be updated and submitted to the NRC consistent with regulatory requirements in effect at the time such update is required (currently every 10 years). The licensee stated that this may again take the form of a relief request to implement an updated RI-ISI program depending on future regulatory requirements. Reference 2 also stated that the RI-ISI program will be resubmitted to the NRC prior to the end of any 10-year ISI interval if there is some deviation from the RI-ISI methodology described in Reference 1, or if industry experience determines that there is a need for significant revision to the program as described in Reference 1.
The licensee presented the criteria, in Reference 1, for engineering evaluation and additional examinations if unacceptable flaws or relevant conditions are found during examinations. The licensee further stated in Reference 1 that the evaluation will include whether other elements in the segment or segments are subject to the same root cause conditions. In Reference 2, the licensee clarified that additional examinations will be performed on these elements up to a number equivalent to the number of elements required to be inspected on the segment or segments scheduled for the current outage. Reference 2 also stated that elements selected for additional examinations will be selected based on the root cause or damage mechanism and will include high risk-significant, as well as medium risk-significant elements (if needed), to reach the required number of additional elements.
The proposed periodic reporting requirements meet existing ASME Code requirements and applicable regulations and, therefore, are acceptable. The staff finds that the proposed process for RI-ISI program updates meets the guidelines of Reference 4 which provide that risk-informed applications should include performance monitoring and feedback provisions; therefore, the licensees proposed process for program updates is acceptable.
4.0 CONCLUSION
S In accordance with 10 CFR 50.55a(a)(3)(i), proposed alternatives to regulatory requirements may be used when authorized by the NRC when the applicant demonstrates that the alternative provides an acceptable level of quality and safety. In this case, the licensee's proposed alternative is to use the risk-informed process described in the NRC-approved Reference 3.
The staff finds that the results of the different elements of the engineering analysis are considered in an integrated decision-making process. The impact of the proposed change in
the ISI program is founded on the adequacy of the engineering analysis and acceptable change in plant risk in accordance with the guidelines in References 4 and 5.
The Callaway methodology also considers implementation and performance monitoring strategies. Inspection strategies ensure that failure mechanisms of concern have been addressed and there is adequate assurance of detecting damage before structural integrity is affected. The risk significance of piping segments is taken into account in defining the inspection scope for the RI-ISI program.
System pressure tests and visual examination of piping structural elements will continue to be performed on all Class 1, 2, and 3 systems in accordance with the ASME Code,Section XI program. The RI-ISI program applies the same performance measurement strategies as existing ASME Code requirements and, in addition, increases the inspection volumes at weld locations that are exposed to thermal fatigue.
The Callaway methodology provides for conducting an engineering analysis of the proposed changes using a combination of engineering analysis with supporting insights from a PRA.
Defense-in-depth and quality are not degraded in that the methodology provides reasonable confidence that any reduction in existing inspections will not lead to degraded piping performance when compared to existing performance levels. Inspections are focused on locations with active degradation mechanisms, as well as selected locations that monitor the performance of system piping. As discussed in Section 3.2 above, the licensee will address any staff concern, if applicable, as a result of a separate, ongoing review on the generic report MRP-24 regarding alternative TASCS screening criteria.
The staffs review of the licensees proposed RI-ISI program concludes that the program is an acceptable alternative to the current ISI program, which is based on ASME Code,Section XI, requirements for Class 1 and Class 2 welds. In Section 3.1 above, the staff concluded that the licensees proposed RI-ISI program, as described in its application and supplemental responses to the staff, will provide an acceptable level of quality and safety pursuant to 10 CFR 50.55a(a)(3)(i) with regard to the number of inspections, locations of inspections, and methods of inspections. Therefore, the licensees request for relief is authorized pursuant to 10 CFR 50.55a(a)(3)(i) on the basis that the request provides an acceptable level of quality and safety. This safety evaluation authorizes application of the proposed RI-ISI program during the second 10-year ISI interval for Callaway.
5.0 REFERENCES
- 1. Letter, dated February 16, 2001 (ULNRC-4392), Alan C. Passwater to U. S. Nuclear Regulatory Commission, containing Relief Request for Application of an Alternative to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section XI Examination Requirements for Class 1 and 2 Piping Welds, Callaway Plant.
- 2. Letter, dated October 25, 2001 (ULNRC-4544), J.D. Blosser to U. S. Nuclear Regulatory Commission, containing Relief Request for Application of an Alternative to the ASME Boiler and Pressure Vessel Code Section XI Examination Requirements for Class 1 and 2 Piping Welds, Callaway Plant.
- 3. EPRI TR-112657, Revision B-A, Revised Risk-Informed Inservice Inspection Evaluation Procedure, January 2000.
- 4. NRC Regulatory Guide 1.174, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, July 1998.
- 5. NRC Regulatory Guide 1.178, An Approach for Plant-Specific Risk-Informed Decisionmaking Inservice Inspection of Piping, September 1998.
- 6. NRC NUREG-0800, Chapter 3.9.8, Standard Review Plan for Trial Use for the Review of Risk-Informed Inservice Inspection of Piping, September 1998.
Principal Contributors: Syed Ali Stephen Dinsmore Date: January 30, 2002