RS-15-071, Response to NRC Request for Additional Information, Set 45, Dated January 22, 2015, Related to License Renewal Application

Response to NRC Request for Additional Information, Set 45, Dated January 22, 2015, Related to License Renewal Application

ML15054A030
Person / Time
Site:	Byron, Braidwood
Issue date:	02/23/2015
From:	Gallagher M Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-15-071, TAC MF1879, TAC MF1880, TAC MF1881, TAC MF1882
Download: ML15054A030 (34)

Text

Michael P. Gallagher Vice President. License Renewal Exelon Generation Exelon Nuclear 200 Exelon Way Kennett Square. PA 19348 610 765 5958 Office 610 765 5956 Fax www.exeloncorp.com michaelp.gallagher@exeloncorp.com 10 CFR 50 10CFR51 10 CFR 54 RS-15-071 February 23, 2015 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455

Subject:

Response to NRC Request for Additional Information, Set 45, dated January 22, 2015, related to the Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2, License Renewal Application

References:

1. Letter from Michael P. Gallagher, Exelon Generation Company LLC (Exelon) to NRC Document Control Desk, dated May 29, 2013, "Application for Renewed Operating Licenses"

2. Letter from Lindsay R. Robinson, US NRC to Michael P. Gallagher, Exelon, dated May 19, 2014 "Request for Additional Information forthe Review of the Byron Station, Units 1 and 2, and Braidwood Station, Units 1 and 2, License Renewal Application -Aging Management, Set 24 (TAC NOS. MF1879, MF1880, MF1881, AND MF1882)"

3. Letter from Michael P. Gallagher, Exelon Generation Company LLC (Exelon) to NRC Document Control Desk, dated June 9, 2014, "Responses to NRC Requests for Additional Information, Set 24, dated May 19, 2014, related to the Byron Station, Units 1 and 2, and Braidwood Station, Units 1 and 2 License Renewal Application"

4. Letter from Lindsay R. Robinson, US NRC to Michael P. Gallagher, Exelon, dated October 10, 2014, "Request for Additional Information for the Review of the Byron Station, Units 1 and 2, and Braidwood Station, Units 1 and 2, License

February 23, 2015 U.S. Nuclear Regulatory Commission Page2 Renewal Application, Set 42 (TAC NOS. MF1879, MF1880, MF1881, and MF1882)"

5. Letter from Michael P. Gallagher, Exelon to NRC Document Control Desk, dated October 31, 2014, "Response to NRC Request for Additional Information, Set 42, dated October 10, 2014, related to the Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2, License Renewal Application"

6. Letter from Michael P. Gallagher, Exelon, to NRC Document Control Desk, dated November 22, 2014, "Supplemental Commitment related to the October 31, 2014 Response to NRC Request for Additional Information, Set 42, dated October 10, 2014, related to the Braidwood Station, Units 1 and 2, and Byron Station, Units 1 and 2, License Renewal Application"

7. Letter from Lindsay R. Robinson, US NRC to Michael P. Gallagher, Exelon, dated January 22, 2015, "Request for Additional Information for the Review of the Byron Station, Units 1 and 2, and Braidwood Station, Units 1 and 2, License Renewal Application, Set 45 (TAC NOS. MF1879, MF1880, MF1881, and MF1882)"

In Reference 1, Exelon Generation Company, LLC (Exelon) submitted the License Renewal Application (LRA) for the Byron Station, Units 1 and 2, and Braidwood Station, Units 1 and 2 (BBS). In References 2 through 6, the NRC Staff and Exelon exchanged information supporting the Staff's review of the adequacy of the Flux Thimble Tube Inspection aging management program for BBS for license renewal.

In Reference 7, the Staff requested additional detailed information associated with the Flux Thimble Tube Inspection aging management program, specifically related to the program at Braidwood Station, Units 1 and 2.

Enclosure A to this letter provides the response to this request for additional information.

Enclosure B contains updates to sections of the LRA (except for the License Renewal Commitment List) affected by the response.

Enclosure C provides an update to the License Renewal Commitment List (LRA Appendix A, Section A.5) associated with the response.

There are no other new or revised regulatory commitments contained in this letter.

February 23, 2015 U.S. Nuclear Regulatory Commission Page 3 If you have any questions, please contact Mr. Al Fulvio, Manager, Exelon License Renewal, at 610-765-5936.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on Respectfully,

~

Vice President - License Renewal Projects s

Exelon Generation Company, LLC

Enclosures:

A Response to Request for Additional Information RAI B.2.1.24-1 b B. Byron and Braidwood Stations (BBS), Units 1 and 2, License Renewal Application Updates Associated with RAI B.2.1.24-1 b C. Byron and Braidwood Stations (BBS}, Units 1 and 2, License Renewal Commitment List Update cc: Regional Administrator- NRC Region Ill NRC Project Manager (Safety Review), NRR-DLR NRC Project Manager (Environmental Review}, NRR-DLR NRC Senior Resident Inspector, Braidwood Station NRC Senior Resident Inspector, Byron Station NRC Project Manager, NRR-DORL-Braidwood and Byron Stations Illinois Emergency Management Agency - Division of Nuclear Safety

RS-15-071 Enclosure A Page 1 of 23 Enclosure A Byron and Braidwood Stations (BBS), Units 1 and 2 License Renewal Application Response to Request for Additional Information RAI B.2.1.24-1b

RS-15-071 Enclosure A Page 2 of 23 RAI B.2.1.24-1b Applicability:

Braidwood Station (Braidwood), Units 1 and 2

Background:

By letter dated October 31, 2014, the applicant provided a response to the staffs request for additional information (RAI) B.2.1.24-1a (ADAMS Accession No. ML14304A345). In the response, the applicant described problems encountered during the latest flux thimble tube inspections. Specifically, the applicant failed to obtain any useful data for most of the tubes it attempted to inspect. The response failed to provide an adequate root cause for the issues encountered during the last outages for Braidwood, Units 1 and 2. In addition, the response failed to provide a technical basis for the adequacy of the program.

By letter dated November 22, 2014, the applicant supplemented its response to RAI B.2.1.24-1a (ADAMS Accession No. ML14330A480). The supplemental response, in part, provided a license renewal commitment to replace flux thimble tubes every three refueling cycles if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection Program.

Issue:

In the license renewal application (LRA), the applicant stated that the existing Flux Thimble Tube Inspection Program is consistent with Generic Aging Lessons Learned (GALL) Report aging management program (AMP) XI.M37, Flux Thimble Tube Inspection. However, based on the available information, it is apparent that the applicant is currently not able to perform inspections of or obtain usable data from the thimble tubes. Therefore, the applicants program does not meet the guidance provided in GALL Report AMP XI.M37.

Specifically, in Element 3, parameters monitored or inspected, the applicants program does not provide adequate parameters monitored or inspected; in Element 4, detection of aging effects, the applicants program does not provide adequate detection of aging effect (wear); in Element 5, monitoring and trending, the applicants program does not provide adequate monitoring and trending; and in Element 7, corrective actions, the applicants corrective actions have not identified the causal factors of its inspection problems, and the implemented corrective measures have not mitigated the inspection problems. Therefore, the staff is not certain why the applicant has not identified these as exceptions to the GALL Report AMP XI.M37.

In addition, the staff noted in the applicants RAI response dated June 9, 2014, that one tube installed in spring of 2009 experienced 37 percent wear per cycle during the fall 2010 outage at Unit 1. The tube was removed from service in 2012 after only two cycles of service. The staff also noted in the same response that a tube experienced 35 percent wear per cycle at Unit 2 in spring of 2011 outage. Based on plant-specific operating experience at Braidwood provided by the applicant, it appears that most tubes will last for more than three cycles and still meet the acceptance criteria of 80 percent tube wear. However, the staff is concerned that the outliers, for example, locations that can experience higher wear of 35 percent or 37 percent per cycle, may not last for three cycles. In addition, there have been instances when a location that had historically experienced low wear for many cycles had unusually higher wear rates in a subsequent cycle. In addition, replacement tubes can

RS-15-071 Enclosure A Page 3 of 23 have different wear rates than those that they replaced. Therefore, the staff is concerned that in these instances, degraded tubes would not be identified without successful inspections and that acceptance criteria may not be met at all times for all locations.

Furthermore, the staff noted that the applicant had prior issues related to obtaining wear data or completing scheduled inspections, which were entered in the applicants corrective action program to prevent recurrence. The applicant speculated possible causal factors in its response dated October 31, 2014, and stated that it may consider several additional corrective actions. However, based on the latest information, it appears the problems associated with successful completion of eddy current examinations (i.e., getting usable wear data) have worsened.

Finally, the staff noted that if movable detector(s) get stuck, the isolation valves would not be able to isolate the affected flux thimble tube(s) in the event of leakage due to wear.

Request:

1) Review the current Flux Thimble Tube Inspection Program for Braidwood, and identify all exceptions to GALL Report AMP XI.M37, Flux Thimble Tube Inspection. If necessary, provide a plant-specific AMP, which addresses the higher than usual wear rates, and justify the programs long-term viability based on the possibility of not obtaining any inspection data on wear. Describe the technical basis that tube wear acceptance criteria are met and that the program is adequate.

2) Identify all cases of higher wear (27 percent per cycle or more). Justify the adequacy of the program if tube replacement is performed every three cycles with consideration of the operating experience of high wear rates as discussed above. Provide information on all instances when a tube was removed from service after three or less cycles of service.

3) Justify why the historical wear rates would be applicable during the period of extended operation if additional examinations are not performed or did not provide usable data, taking into consideration that wear rates can change.

4) Provide a root cause analysis which adequately identifies all the problems encountered during the recent inspections; discuss corrective measures which will be implemented to address these problems.

5) Provide information in regards to instances when detectors became stuck at Braidwood, Units 1 and 2. Explain how leakage would be isolated if detectors are stuck when a flux thimble tube develops a leak.

RS-15-071 Enclosure A Page 4 of 23 Exelon Response:

Introduction:

The intent of the Braidwood Station Flux Thimble Tube Inspection Program is to implement the recommendations made in GALL Report AMP XI.M37 fully, without exception. The recent difficulties obtaining eddy current testing data that have been experienced at the Braidwood Station have been entered into the 10 CFR Part 50 Appendix B corrective action program. There is an action plan to address this issue as described in the response to Request 4. There is high confidence that the action plan will resolve the issue and eddy current testing will be successful in upcoming refueling outages. Although there is confidence that the current issues will be resolved in a timely manner, the program is enhanced as shown in Enclosure B and Enclosure C to proactively replace flux thimble tubes to ensure the integrity of the reactor coolant pressure boundary is maintained until the corrective actions to address the current difficulties in obtaining eddy current testing data are successfully completed. This enhancement does not replace or supersede the requirement to perform periodic eddy current testing of the flux thimble tubes at Braidwood Station.

As described in the response to Request 5, the combined factors of low leak rate, leak detection capability, and the ability to isolate the leakage, allow a flux thimble tube leak to be classified as a maintenance issue and not a reactor safety issue. The Braidwood Flux Thimble Tube Inspection Program, as enhanced, is considered sufficiently robust to manage flow induced wear of flux thimble tubes.

RS-15-071 Enclosure A Page 5 of 23

1) Exceptions to the GALL Report recommendations, as defined in Section 3.0.1 of NUREG-1800, Standard Review Plan for Review of License Renewal Applications for Nuclear Power Plants, are portions of the GALL Report AMP that the applicant does not intend to implement. As described in Sections A.2.1.24 and B.2.1.24 of the LRA, the intent of the Braidwood Flux Thimble Tube Inspection program is to implement the recommendations made in GALL Report AMP XI.M37 without exception. However, the existing Braidwood program has been unsuccessful at obtaining eddy current testing data during recent refueling outages. Therefore, commitments are made to enhance the program as shown in Enclosure B and Enclosure C to ensure that the Braidwood program will be consistent with the recommendations made in GALL Report AMP XI.M37 during the period of extended operation. A summary of the element-by-element evaluation of the Braidwood Flux Thimble Tube Inspection AMP against the recommendations made in GALL Report AMP XI.M37 is provided below.

Element 1, Scope of Program: The Braidwood Flux Thimble Tube Inspection AMP manages aging of the flux thimble tubes which establish part of the reactor coolant pressure boundary, as described in LRA Sections A.2.1.24 and B.2.1.24. The aging management program credits the existing Flux Thimble Tube Inspection program which implements the commitments made in the Braidwood response to IE Bulletin 88-09, which has been accepted by the NRC. Any changes to these commitments would require amendment of the response to IE Bulletin 88-09 and approval by the NRC. The Braidwood Flux Thimble Tube Inspection program is consistent with the recommendations made in Element 1 of GALL Report AMP XI.M37 without exception.

Element 2, Preventive Actions: The Braidwood Flux Thimble Tube Inspection AMP is a condition monitoring AMP that does not include any preventive actions. The Braidwood Flux Thimble Tube Inspection program is consistent with the recommendations made in Element 2 of GALL Report AMP XI.M37 without exception.

Element 3, Parameters Monitored/Inspected: The Braidwood Flux Thimble Tube Inspection AMP requires periodic eddy current testing of all flux thimble tubes, as described in LRA Sections A.2.1.24 and B.2.1.24. The existing implementing procedures for this program require performance of eddy current testing, and require evaluation when full length eddy current testing of a flux thimble tube is not completed. However, the existing program has been unsuccessful in performing eddy current testing of flux thimble tubes during recent refueling outages. Therefore, the program will be enhanced as shown in Enclosure B and Enclosure C such that the Braidwood program will be consistent with the recommendations made in Element 3 of GALL Report AMP XI.M37 during the period of extended operation.

Corrective actions are in progress to ensure that these issues are resolved, as described in the response to Request 4.

As described in the Element 1 discussion above, the Braidwood program implements commitments made in response to IE Bulletin 88-09. Performance of periodic eddy current testing is required by the commitments made in the Braidwood response to IE Bulletin 88-09. In the unlikely event that corrective actions to obtain eddy current data are unsuccessful and an alternate method is necessary to ensure the intended function of the flux thimble tubes is maintained, then an amended response to IE

RS-15-071 Enclosure A Page 6 of 23 Bulletin 88-09 describing the alternate method of ensuring flux thimble tube integrity would be submitted to the NRC for approval.

The Braidwood Flux Thimble Tube Inspection program will be enhanced to be consistent with the recommendations made in Element 3 of GALL Report AMP XI.M37 without exception.

Element 4, Detection of Aging Effects: The Braidwood Flux Thimble Tube Inspection AMP requires periodic eddy current testing of all flux thimble tubes, as described in LRA Sections A.2.1.24 and B.2.1.24. Eddy current testing has been demonstrated effective at detecting wear of flux thimble tubes and has been accepted by the NRC.

However, the existing program has been unsuccessful in performing eddy current testing of flux thimble tubes during recent refueling outages. Therefore, the program will be enhanced as shown in Enclosure B and Enclosure C such that the Braidwood program will be consistent with the recommendations made in Element 4 of GALL Report AMP XI.M37 during the period of extended operation. Corrective actions are in progress to resolve these issues, as described in the response to Request 4.

As described in the Element 1 discussion above, the Braidwood program implements commitments made in response to IE Bulletin 88-09. Performance of periodic eddy current testing is required by the commitments made in the Braidwood response to IE Bulletin 88-09. In the unlikely event that corrective actions to obtain eddy current data are unsuccessful and an alternate inspection technique is determined appropriate, then an amended response to IE Bulletin 88-09 would be submitted to the NRC for approval.

The frequency of eddy current testing is determined based on plant-specific wear data and utilizes conservative wear predictions. Eddy current testing results are evaluated and trended to determine if the eddy current testing frequency should be modified. Eddy current testing is currently scheduled on a one (1) cycle frequency at Braidwood due to the recent data collection issues.

The Braidwood Flux Thimble Tube Inspection program will be enhanced to be consistent with the recommendations made in Element 4 of GALL Report AMP XI.M37 without exception.

Element 5, Monitoring and Trending: The Braidwood Flux Thimble Tube Inspection AMP requires trending of eddy current testing data, as specified in LRA Sections A.2.1.24 and B.2.1.24. Trending of eddy current testing data is performed to establish plant-specific wear rates and is used to develop conservative projections of future wear to ensure that wall thickness acceptance criteria continue to be met during plant operation between scheduled inspections. Although the existing program has been unsuccessful in performing eddy current testing of flux thimble tubes during recent refueling outages, there is sufficient historic eddy current testing data for currently installed flux thimble tubes such that conservative projections can be made to ensure that wall thickness acceptance criteria continue to be met through the next scheduled refueling outage (Spring 2015 for Unit 1 and Fall 2015 for Unit 2) when eddy current testing will next be performed. In the unlikely event that eddy current testing is again unsuccessful, despite the corrective actions described in the response to Request 4, conservative replacement of flux thimble tubes will be

RS-15-071 Enclosure A Page 7 of 23 performed as described in Enhancement 2 for Braidwood Unit 1 and Enhancement 3 for Braidwood Unit 2 until periodic eddy current testing of the flux thimble tubes is re-established.

The trending activities recommended in Element 5 of GALL Report AMP XI.M37 require periodic eddy current data be obtained. Therefore, the program will be enhanced as shown in Enclosure B and Enclosure C such that the Braidwood Flux Thimble Tube Inspection program will be consistent with the recommendations made in Element 5 of GALL Report AMP XI.M37 without exception.

Element 6, Acceptance Criteria: The Braidwood Flux Thimble Tube Inspection AMP specifies conservative acceptance criteria for flux thimble tube wear, as described in LRA Section B.2.1.24. Measured wear exceeding 60% or projected wear exceeding 80% prior to the next scheduled inspection require corrective actions. These acceptance criteria are technically justified and supported by industry guidance provided in WCAP-12866, Bottom Mounted Instrumentation Flux Thimble Wear.

The Braidwood Flux Thimble Tube Inspection program is consistent with the recommendations made in Element 6 of GALL Report AMP XI.M37 without exception.

Element 7, Corrective Actions: The Braidwood Flux Thimble Tube Inspection AMP requires corrective actions for flux thimble tubes that do not meet acceptance criteria, as specified in LRA Sections A.2.1.24 and B.2.1.24. This program relies on the 10 CFR Part 50, Appendix B corrective action program. Corrective actions include repositioning, isolation, or flux thimble tube replacement. The Braidwood program includes corrective actions for when eddy current testing cannot be performed, consistent with the recommendations made in GALL Report AMP XI.M37. If eddy current testing cannot be performed, an evaluation is performed utilizing historical wear for that tube to establish conservative projections for wear until the next inspection opportunity. If the tube cannot be analytically shown to be satisfactory for continued service, then the tube is removed from service or replaced to ensure the integrity of the reactor coolant pressure boundary. During recent refueling outages, difficulties obtaining eddy current testing data have been experienced. To address these issues the program will be enhanced as shown in Enclosure B and Enclosure C to ensure that the intended function of the flux thimble tubes is maintained while issues obtaining eddy current testing data are being resolved. The enhanced Braidwood Flux Thimble Tube Inspection program will be consistent with the recommendations made in Element 7 of GALL Report AMP XI.M37 without exception.

Element 8, Confirmation Process: The Braidwood Flux Thimble Tube Inspection AMP relies on the requirements of 10 CFR Part 50, Appendix B. The Braidwood Flux Thimble Tube Inspection program is consistent with the recommendations made in Element 8 of GALL Report AMP XI.M37 without exception.

Element 9, Administrative Controls: The Braidwood Flux Thimble Tube Inspection AMP relies on the requirements of 10 CFR Part 50, Appendix B. The Braidwood Flux Thimble Tube Inspection program is consistent with the recommendations made in Element 9 of GALL Report AMP XI.M37 without exception.

RS-15-071 Enclosure A Page 8 of 23 Element 10, Operating Experience: GALL Report AMP XI.M37 is based on the requirements established in NRC IE Bulletin 88-09 which was developed in response to industry operating experience of flux thimble tube thinning in Westinghouse reactors due to flow-induced wear. This industry operating experience was summarized in NRC Information Notice 87-44. In response to these documents, the Westinghouse Owners Group developed WCAP-12866. WCAP-12866 analyzed industry operating experience and developed a model to predict wear growth as well as guidance for an effective program to manage flow-induced wear of flux thimble tubes. Industry operating experience described in Information Notice 87-44 and WCAP-12866 includes examples of single cycle wear in excess of 27%. For example, Supplement 1 of Information Notice 87-44 identifies a nuclear station where indications approaching 40% through-wall loss had developed over a single cycle of operation. Furthermore, Braidwood plant-specific operating experience shows that flux thimble tube wear growth aligns with the wear trends predicted in WCAP-12866, as described in the response to Request 2.

As described in Element 10 of GALL Report AMP XI.M37, the inspection programs developed in accordance with IE Bulletin 88-09 have shown excellent results in managing wear of flux thimble tubes throughout the industry. Although Element 10 of GALL Report AMP XI.M37 references several instances of leaks in the industry, no flux thimble tube leaks have occurred at Braidwood, which demonstrates that the existing program has been effective. As described in the response to Request 2, the worst instances of wear occurred during the first cycle of operation and were reported to the NRC in the Braidwood response to IE Bulletin 88-09. The NRC accepted the existing program with knowledge of the high wear experienced in the first cycle of operation, as documented in NRC letter dated February 26, 1991 (ADAMS Accession No. 9103040392). Recent operating experience of higher than usual wear rates is bounded by the wear rates considered by the NRC when the existing program was accepted by the NRC.

The higher than usual wear rates experienced at Braidwood and the overall history of flux thimble tube wear at Braidwood is bounded by the industry operating experience for which GALL Report AMP XI.M37 was evaluated and bounded by the plant-specific operating experience for which the existing program was evaluated.

The Braidwood Flux Thimble Tube Inspection program is consistent with Element 10 of GALL Report AMP XI.M37 without exception.

The enhanced Braidwood Flux Thimble Tube Inspection AMP will be consistent with the recommendations made in GALL Report AMP XI.M37 without exception. As described in the Element 10 review, the historical wear experienced at Braidwood, including the higher than usual wear rates, is bounded by the industry operating experience for which the GALL Report AMP was evaluated. The plant-specific conditions (e.g.,

materials of construction, service environments, configuration) are also bounded by the conditions for which the GALL Report AMP was evaluated. A plant-specific AMP is not necessary because the plant-specific conditions and age-related operating experience is bounded by the conditions and age-related operating experience for which GALL Report AMP XI.M37 was evaluated.

Existing Braidwood commitments require the performance of periodic eddy current testing. Because there have been recent difficulties in obtaining eddy current testing

RS-15-071 Enclosure A Page 9 of 23 data, the program will be enhanced as shown in Enclosure B and Enclosure C to address these issues. In the unlikely event that corrective actions to obtain eddy current data are unsuccessful and an alternate inspection technique is required, then an amended response to IE Bulletin 88-09 would be submitted to the NRC for approval.

Furthermore, as discussed in the response to Request 3, the presumption that inspection data on wear will never be obtained is not reasonable.

Technical Basis for Adequacy of the Program:

As described above, the program requires periodic eddy current testing to monitor flux thimble tube wear and uses the data from the periodic eddy current testing to project future wear using conservative models. This ensures that the flux thimble tubes remain satisfactory for continued service until the next opportunity to perform eddy current testing. Although there have been recent difficulties in obtaining eddy current testing data, the program will be enhanced as shown in Enclosure B and Enclosure C such that the program will be consistent with the recommendations made in GALL Report AMP XI.M37. As discussed in the response to Request 2, the plant-specific operating experience confirms that flow induced wear of the flux thimble tubes at Braidwood aligns with the wear trends predicted by WCAP-12866. Since, based on historic eddy current data, plant-specific wear is consistent with predicted trends; there is reasonable assurance that the conservative projections utilized by the program are adequate to ensure that the intended function of the flux thimble tubes will be maintained between inspections.

The recent difficulties in obtaining eddy current testing data have been entered into the corrective action program for resolution. To address these issues, the program is enhanced as shown in Enclosure B and Enclosure C. As described in the response to Request 4, corrective actions are planned or in-progress to ensure that future eddy current testing is successful. The program includes a corrective action for when eddy current testing data cannot be obtained in which analytical methods are used to demonstrate that a flux thimble tube is acceptable for continued service. The program has been enhanced to ensure the intended function of the flux thimble tubes is maintained until the corrective actions to address the current difficulties in obtaining eddy current testing data are successfully completed. The enhancement requires the replacement of affected flux thimble tubes every three (3) cycles if eddy current data is not obtained in accordance with the program. The three (3) cycle replacement frequency is conservative based on plant-specific operating experience, as described in the response to Request 2.

Despite the recent difficulties in obtaining eddy current testing data, Braidwood is committed to periodic eddy current testing of the flux thimble tubes as described in LRA Section A.2.1.24 and the Braidwood response to IE Bulletin 88-09. The intent is to fully implement the program consistent with the recommendations made in GALL Report AMP XI.M37 without exception, as described in LRA Sections A.2.1.24 and B.2.1.24.

The corrective actions described in the response to Request 4 will be completed by Spring 2015 for Unit 1 and Fall 2015 for Unit 2 and provide confidence that the recent difficulties in obtaining eddy current testing data will be resolved. In order to discontinue the performance of periodic full-length eddy current testing of the flux thimble tubes in the unlikely event that corrective actions are unsuccessful, an amended response to IE Bulletin 88-09, submitted to the NRC for approval, would be required.

RS-15-071 Enclosure A Page 10 of 23 Based on the above, there is reasonable assurance that wear of the flux thimble tubes will be adequately managed such that intended functions are maintained consistent with the current licensing basis through the period of extended operation.

RS-15-071 Enclosure A Page 11 of 23

2) A review of instances in which the maximum wear depth of a flux thimble tube increased by 27% of nominal wall thickness or more over a single cycle is provided in Table 1 -

Summary of High Wear Occurrences.

Table 1 - Summary of High Wear Occurrences Description of cases of Background Information higher wear (>27% within one cycle)

Originally Installed Flux Thimble Three (3) flux thimble tubes were replaced after the initial cycle of plant operation due to Tubes (1st Cycle): indications of wear. On Unit 1, one (1) flux thimble tube had 43% wear after one (1) cycle and another had 62% wear after one (1) cycle. On Unit 2, one (1) flux thimble tube had Eleven occurrences of higher 60% wear after one (1) cycle. The three (3) replacement flux thimble tubes remained in wear were detected after the initial service for at least 15 cycles, therefore the high initial wear was considered to be cycle of reactor operation, associated with startup activities and event driven rather than aging.

Braidwood Unit 1 (Fall 1989) and Braidwood Unit 2 (Fall 1990). One (1) flux thimble tube was replaced after the initial cycle of plant operation to support a plant modification. This Unit 2 flux thimble tube had 27% wear after one (1) cycle. The Results submitted to NRC in Unit replacement flux thimble tube remained in service for 15 cycles.

1 letter dated January 8, 1990 (ADAMS Accession No. One (1) flux thimble tube remained in service for four (4) cycles. This Unit 2 flux thimble 9001190169) and Unit 2 letter tube had 30% wear after one (1) cycle. The indicated wall loss at time of replacement was dated August 2, 1990 (ADAMS 55%. Eddy current testing performed after the first cycle testing confirmed the wear rate Accession No. 9008060402). for this tube had significantly decreased, as predicted by WCAP-12866. The replacement Accepted by NRC as documented flux thimble tube remains in service.

in NRC letter dated February 26, 1991 (ADAMS Accession No. Six (6) flux thimble tubes remained in service for at least nine (9) cycles of operation. All 9103040392) six (6) were on Unit 2 with wear ranging from 27% to 33% after one (1) cycle. Eddy current testing performed after the first cycle testing confirmed the wear rate for each of these tubes had significantly decreased, as predicted by WCAP-12866.

Originally Installed Flux Thimble One (1) flux thimble tube experienced the higher wear during the second cycle of Tubes (Mid Service Life): operation. This Unit 2 flux thimble tube had no measured wear after the first cycle and 32% wear after the second cycle. The flux thimble tube remained in service for a total of Four (4) occurrences of higher four (4) cycles. The indicated wall loss at the time of replacement was 61%.

wear were detected after a flux thimble tube had been in service Three (3) flux thimble tubes experienced the higher wear during the fourth cycle of for at least one (1) cycle. operation. One (1) Unit 1 flux thimble tube had no measured wear after the third cycle and 33% wear after the fourth cycle. This flux thimble tube was replaced after being in service for nine (9) cycles. One (1) Unit 2 flux thimble tube had no measured wear after the third cycle and 45% wear after the fourth cycle. This flux thimble tube was replaced after being in service for nine (9) cycles. One (1) Unit 2 flux thimble tube had no measured wear after the third cycle and 28% wear after the fourth cycle. This flux thimble remains in service with no change in wear. Wear was last measured after the 16th cycle of service and no increase in wear had occurred since the fourth cycle. This flux thimble tube will be replaced in the Fall 2015 refueling outage if eddy current data is not obtained, per Enhancement 3.a.

RS-15-071 Enclosure A Page 12 of 23 Table 1 - Summary of High Wear Occurrences (continued)

Description of cases of Background Information higher wear (>27% within one cycle)

Replacement Flux Thimble Tubes One (1) Unit 1 replacement flux thimble tube had a wear indication of 27% after one (1)

(1st Cycle): cycle of operation. This flux thimble tube was eddy current tested after the second cycle of operation and there was no change in the measured wear. Since the wear for this flux Three (3) occurrences of higher thimble tube stabilized, the flux thimble tube could remain in service for at least three (3) wear were detected after the first cycles. However, this flux thimble tube will be replaced in the Spring 2015 refueling cycle subsequent to the flux outage if eddy current data is not collected, per Enhancement 2.a.

thimble tube being replaced. Two (2) after the Braidwood Unit 1 One (1) Unit 1 replacement flux thimble tube had a wear indication of 37% after one (1) fifteenth cycle (Fall 2010) and one cycle of operation. Eddy current testing after the second cycle of operation could not be (1) after the Braidwood Unit 2 performed due to a neutron detector being stuck. Since subsequent eddy current data fifteenth cycle (Spring 2011). was not obtained, the projected wear after the third cycle of operation can be determined using the bounding exponent specified in WCAP-12866. The projected wear after the third These three (3) occurrences were cycle of operation would be 77% indicating the flux thimble tube could remain in service for discussed in the response to RAI at least three (3) cycles. However, this flux thimble tube is currently removed from service B.2.1.24-1 provided in Exelon (i.e., capped) and will be replaced in the Spring 2015 refueling outage, per letter RS-14-165.

Enhancement 2.a.

One (1) Unit 2 replacement flux thimble tube had a wear indication of 35% after one (1) cycle of operation. This flux thimble tube was eddy current tested after the second cycle of operation and the measured wear was 41% (6% increase). Since more than one (1) eddy current data point was obtained a tube specific exponent can be determined using the WCAP-12866 methodology. Using a tube specific exponent the projected wear after the third cycle of operation would be 45% indicating the flux thimble tube could remain in service for at least three (3) cycles. However, this flux thimble tube will be replaced in the Fall 2015 refueling outage if eddy current data is not collected, per Enhancement 3.a.

This review shows that instances of single cycle wear exceeding 27% are rare and have never recurred over consecutive cycles. Braidwood Unit 1 and Unit 2 are each in the 18th cycle of operation and sufficient flux thimble tube eddy current data is available to support operation during the current cycle. Prior to the occurrence of the current issues with obtaining eddy current testing data for the flux thimble tubes, Braidwood Unit 1 had operated for 16 cycles and Braidwood Unit 2 had operated for 15 cycles. This equates to over 1700 tube cycles of operation. Out of the greater than 1700 tube cycles there have been only 18 instances where single cycle wear was 27% or greater.

The justification that the enhanced Braidwood Flux Thimble Tube Inspection program is adequate is based on several aspects. Periodic flux thimble tube eddy current testing will continue to be performed during the period of extended operation and the continued absence of eddy current testing data is not considered plausible as discussed in the response to Request 3 and 4 below. As stated in the supplemental response to RAI B.2.1.24-1a provided in Exelon letter RS-14-336, dated November 22, 2014, a review of the Braidwood Units 1 and 2 operating experience, which includes instances of high wear defined as outliers in the Issue, demonstrates that a three (3) refueling outage replacement frequency is appropriate since none of the 116 flux thimble tubes were required to be replaced due to age-related degradation in less than four (4) refueling cycles. There have been only three (3) instances in which a flux thimble tube had to be replaced due to age-related degradation after being in installed for four (4) cycles. The indicated wear for these three (3) flux thimble tubes ranged from 55% to 72%. Based on

RS-15-071 Enclosure A Page 13 of 23 this, it was concluded that conditional replacement of flux thimble tubes on a three (3) refueling cycle frequency if eddy current testing data is not obtained in accordance with the Flux Thimble Tube Inspection program requirements is conservative. However, as stated in the Issue, there have been isolated instances in which wear exceeding 27%

has been experienced over a single cycle. It should be noted that industry operating experience has shown that flux thimble tube wear due to flow induced vibration decreases exponentially over the flux thimble tube service life. Using the methodology provided in WCAP-12866 for predicting flux thimble tube wear and the conservative exponent defined in WCAP-12866, 56.3% wear is predicted after three (3) cycles when 27% wear is experienced in the first cycle.

A review of the instances in which a flux thimble tube was removed from service or replaced in three (3) or less cycles is summarized in Table 2 - Units 1 and 2 Flux Thimble Tubes Replaced or Capped in < 3 Cycles.

Table 2 - Units 1 and 2 Flux Thimble Tubes Replaced or Capped in < 3 Cycles Reason for Replacement Number of Tubes Cycles in Service Pressurizer water level 2 1 modification 2 2 Wear incurred during plant initial 3 1 operating cycle Blockage during flux mapping or 4 3 restriction preventing eddy 1 2 current testing (replacement was 2 1 conservative)

Damage (unable to retract) 2 1 Stuck neutron detector 1 2 Total 17 As presented in Table 2, a total of 17 flux thimble tubes for both units have been replaced in three (3) cycles or less. Four (4) flux thimble tubes were replaced in two (2) or less cycles of service to support a modification to the pressurizer water level system.

This modification required the removal/replacement of the flux thimble tubes to allow the water level indicators used during refueling to be connected to the flux thimble guide tubes. As described in Table 1, three (3) flux thimble tubes were replaced after one (1) cycle due to indications of high wear after the initial cycle of plant operation. The three (3) replacement flux thimble tubes for these flux thimble tubes remained in service for at least 15 cycles, therefore the high initial wear was considered to be associated with startup activities and is event driven rather than aging. Seven (7) flux thimble tubes were replaced in three (3) or less cycles due to blockages preventing the neutron detector traversing the flux thimble tube during flux mapping or the collection of eddy current data. Two (2) flux thimble tubes were replaced after one (1) cycle of service due to not being able to be retracted (i.e., withdrawn to support refueling). These were replacement flux thimble tubes from the Zion Station that had a larger diameter. One (1) flux thimble tube was replaced after two (2) cycles due to a stuck neutron detector. The results of this review support the three (3)-cycle replacement requirement if eddy current data is not collected since the flux thimble tubes replaced in three (3) cycles or less were replaced due to issues other than flow induced wear.

RS-15-071 Enclosure A Page 14 of 23 In summary, the justification for the adequacy of the enhanced Flux Thimble Tube Inspection aging management program is based on the plant-specific operating experience, as discussed above, that shows; the program requires periodic eddy current testing to be performed during the period of extended operation and the compensatory action to replace a flux thimble tube after three (3) cycles of operation only applies if useful eddy current data cannot be obtained for a flux thimble tube, no flux thimble tube has been replaced due to age-related degradation in less than four (4) cycles and there have been only three (3) instances of replacement at four (4) cycles due to age-related wear, flux thimble tubes replaced in three (3) cycles or less were replaced due to issues other than flow induced wear, single cycle wear of 27% or greater is rare, consecutive cycles with wear of 27% or greater does not occur, and overall wear of the Braidwood flux thimble tubes does not follow a linear trend but rather follows the exponentially decreasing trend predicted in WCAP-12866.

RS-15-071 Enclosure A Page 15 of 23

3) The historical flux thimble tube wear rates experienced at Braidwood are applicable during the period of extended operation based on a review of plant-specific operating experience over the past 25 plus years of operation (per unit) which demonstrates that the flow-induced flux thimble tube wear trend is not changing. The observed flux thimble tube wear at Braidwood Station has behaved as predicted in WCAP-12866. A review of the flux thimble tube replacement history for both units indicates that flux thimble tube replacements due to wear have not increased as the plant ages. As discussed in WCAP-12866, plant parameters that may potentially impact flux thimble tube wear due to flow induced vibration include; reactor geometry, fuel assembly design, reactor coolant system flow conditions, and flux thimble tube design. Changes such as different fuel product lines have been made, however flux thimble tube eddy current test results showed no impact on wear rates. No significant changes to any of these plant parameters have been made since the recent issues associated with flux thimble tube eddy current testing began. Any changes to these plant parameters would be made using the engineering change process which require an evaluation for any impact on interfacing plant systems/components and testing/replacement requirements. In addition, a review of the wear behavior of 43 Unit 1 and 33 Unit 2 originally installed flux thimble tubes (i.e., tubes that have never been replaced) did not identify any abnormal or unexpected change in wear rate for these originally installed flux thimble tubes. If a change in a plant parameter had occurred that impacted flow-induced wear of the flux thimble tubes, then it is expected that it would have affected all 116 installed flux thimble tubes. Since no abnormal or unexpected change in wear rate for the 76 flux thimble tubes (approximately 65% of the 116 total tubes) that have been installed over the entire operating life of the station has occurred, then it can be concluded that wear is not changing as the plant ages.

The historical wear rates were used to determine a conservative replacement frequency in the highly unlikely event useful flux thimble tube eddy current data is never collected from the present to the end of the period of extended operation. As discussed in the response to Request 2 above, none of the 116 flux thimble tubes were required to be replaced due to age-related degradation in less than four (4) refueling cycles and no flux thimble tube leaks have occurred in over 25 years of operation per unit. Since 1) no flux thimble tubes were required to be replaced due to age-related degradation in less than four (4) refueling cycles, and 2) a review of the plant-specific operating experience demonstrates that wear is not changing, there is objective evidence that no flux thimble tube will be required to be replaced due to age-related wear in less than four (4) cycles through the period of extended operation.

Therefore, a conservative replacement frequency of three (3)-cycles was selected to ensure that the intended function of the flux thimble tubes is maintained. Although there have been isolated instances of higher wear in flux thimble tubes that had historically experienced low wear, these instances have been limited to one (1) or two (2) flux thimbles tubes during a testing interval and have not repeated over multiple test intervals. The three (3)-cycle replacement if eddy current data is not collected will minimize the possibility a flux thimble tube will experience a postulated mid-service life jump in wear by limiting the time a flux thimble tube will remain in service if eddy current data is not collected. Any wear prior to or after a postulated mid-service life jump in wear would also be minimized by limiting the time a flux thimble tube can be installed if eddy current data is not collected.

RS-15-071 Enclosure A Page 16 of 23 The concern that the periodic flux thimble tube eddy current testing required by the Flux Thimble Tube Inspection aging management program will not provide usable data from the present to the end of the period of extended operation is not a credible situation. This concern appears to be based on one (1) Unit 1 (Fall 2013) and two (2)

Unit 2 (Fall 2012 and Spring 2014) flux thimble tube eddy current testing attempts that failed to obtain usable data on most flux thimble tubes tested and the ineffectiveness of the corrective actions taken to date. A thorough evaluation of the potential causes of these issues has been performed and corrective actions are planned or are in-progress to address each of these potential causes, as described in the response to Request 4 below. This action plan will be completed well before the start of the period of extended operation, which begins in 2026 for Unit 1, over 10 years from now. This 10-year period (>6 operating cycles on each unit) provides ample time to resolve the issues associated with flux thimble tube eddy current testing prior to entering the period of extended operation. A conditional periodic replacement or removal from service of flux thimble tubes on a frequency of three (3)-cycles, if eddy current data is not obtained provides assurance that flux thimble tube integrity will be maintained until the issues with eddy current testing have been resolved.

==

Conclusion:==

The justification that historical wear rates would remain applicable and that the enhanced Braidwood Flux Thimble Tube Inspection program provides reasonable assurance that the intended function of the flux thimble tubes will be maintained consistent with the current licensing basis is based on the following:

observed flux thimble tube wear is consistent with WCAP-12866, there is no increase in flux thimble tube replacement indicating wear rates are changing, no abnormal or unexpected change in wear rate has been observed in 76 originally installed flux thimble tubes, historical wear rates plus additional conservatism was used to select the three (3)-cycle conditional replacement frequency, operating experience provides objective evidence that no flux thimble tube will be required to be replaced due to age-related wear in less than four (4) cycles through the period of extended operation, instances of higher wear in flux thimble tubes that had historically experienced low wear are rare and have not repeated over multiple test intervals, and the three (3)-cycle replacement frequency if eddy current data is not obtained will minimize the consequence of any potential changes in wear rate by limiting the amount of time a flux thimble tube remains in service.

RS-15-071 Enclosure A Page 17 of 23

4) As discussed in the response to RAI B.2.1.24-1a submitted in Exelon letter RS-14-313 dated October 31, 2014, problems were encountered during recent attempts to perform eddy current testing of the Braidwood flux thimble tubes. The problems were limited to the inability to fully insert the eddy current probe into the flux thimble tubes.

The inability to obtain flux thimble tube eddy current test data at Braidwood has been entered into the corrective action program. Flux thimble tube eddy current testing can only be performed with the unit shut down and depressurized and, therefore, the opportunity for investigation is limited. The timeliness of the actions being taken is commensurate with the risk and safety significance of the missing eddy current data, since adequate historical and recent eddy current data is available to support current operation based on conservative wear projections.

The potential causes for the inability to fully insert the eddy current probes into the flux thimble tube are as follows: internal obstruction within the flux thimble tubes (i.e.,

moisture, lubricant, and debris), deformation of the flux thimble tubes, or improper eddy current testing equipment/process. Each of these potential causes is evaluated below. The corrective actions that are planned or in progress to address each of these potential causes are identified after the potential causes are listed.

Internal Obstruction An internal obstruction within the flux thimble tubes could prevent the eddy current probe from being fully inserted. The potential sources of an internal obstruction are moisture, build-up of lubricant (i.e., NeolubeTM), or debris from insertion of the neutron detector and eddy current probe. Each of these potential sources is addressed below:

Moisture: Moisture in the flux thimble tubes was cited by the eddy current technician during the initial failed attempts to collect eddy current data. The source of the moisture was initially believed to be inadequate drying of the flux thimble tubes after cleaning and subsequently believed to be condensation that had accumulated between the time when the flux thimble tube was dried and when eddy current testing was attempted. A summary of the timeline of events is provided below:

Fall 2010: Unit 1 - Usable eddy current data was collected on all 58 flux thimble tubes.

Spring 2011: Unit 2 - Usable eddy current data was collected on 57 of the 58 flux thimble tubes, 1 flux thimble tube was restricted.

Spring 2012: Unit 1 - Eddy current testing was abbreviated due to outage time restraints. The scope of testing was limited to all flux thimble tubes that had greater than 20% wear when tested in Fall 2010 (16 tubes). Fifteen of the 16 tubes that had prior wear greater than 20% were successfully tested. One (1) of the 16 tubes could not be tested due to a stuck neutron detector. However, this tube was replaced and the replacement tube was eddy current tested.

Fall 2012: Unit 2 - Usable eddy current data was collected on 28 of the 58 flux thimble tubes. The difficulties in obtaining eddy current testing data were attributed to moisture in the flux thimble tubes by the eddy current technician.

RS-15-071 Enclosure A Page 18 of 23 The cause of moisture was attributed to inadequate drying after cleaning. An inadequate drying process could affect every flux thimble tube and is, therefore, consistent with the recent widespread inability to obtain eddy current testing data.

Fall 2013: Unit 1 - To address the issues experienced at Unit 2, additional time was allotted to the drying process during the Unit 1 Fall 2013 refueling outage to ensure the flux thimble tubes were fully dry prior to eddy current testing.

However, no usable eddy current data was obtained. The reported cause was again moisture in the flux thimble tubes preventing insertion of the eddy current probe. Since the flux thimble tubes were verified dry after cleaning, the source of the moisture was attributed to condensation. During this outage, cleaning and drying had been performed at the beginning of the outage and eddy current testing had been performed at the end of the outage potentially allowing the accumulation of moisture in the flux thimble tubes.

Spring 2014: Unit 2 - Due to the issues encountered during the previous two eddy current tests only half the flux thimble tubes were cleaned and the performance of eddy current testing was moved to the beginning of the outage immediately after drying of the flux thimble tubes that were cleaned. Usable eddy current data was only collected on 8 out of 39 flux thimble tubes attempted.

Similar widespread difficulties in obtaining eddy current testing data were experienced for both the cleaned and the un-cleaned flux thimble tubes.

Since changes to the cleaning/drying process and timing of the eddy current testing did not significantly affect the ability to obtain eddy current testing data it is unlikely that moisture within the flux thimble tubes, alone, is the cause of the current difficulties.

Lubricant: Historically, sporadic internal blockage of individual flux thimble tubes has occurred due to the build-up of the lubricant applied to the neutron detector and cable. These historic instances of internal blockage of flux thimble tubes due to the build-up of lubricant had caused difficulties in performing in-core flux mapping.

However, cleaning of the flux thimble tubes has historically been successful at preventing the build-up of lubricant and has minimized difficulties in performing in-core flux mapping.

Unlike moisture, internal obstruction of a flux thimble tube due to the build-up of lubricant would not be eliminated by evaporation as the tubes heat up. Therefore, it is expected that an internal obstruction caused by the build-up of lubricant would adversely affect the performance of in-core flux mapping as well as eddy current testing. Since the recent widespread difficulties in performing eddy current testing of the flux thimble tubes have not been accompanied by similar difficulties performing in-core flux mapping, it is unlikely that internal obstruction due to the build-up of lubricant is the cause of the current difficulties. Furthermore, due to the historical issues related to excessive lubrication of the neutron detector and cable, the use of lubricant is limited to minimize the potential for internal blockage. In summary, it is unlikely that the current difficulties in obtaining eddy current data are due to internal blockage of the flux thimble tubes due to the following: historic issues with lubricants affected individual tubes and was not widespread, performance of flux mapping has not been affected, cleaning or the lack of cleaning did not significantly affect the

RS-15-071 Enclosure A Page 19 of 23 ability to obtain eddy current testing data, and lubrication of the neutron detector and cable is limited.

Debris: It is possible that debris could be left in the flux thimble tubes due to the insertion of the neutron detector and cable. The debris could potentially build up within the flux thimble tube and accumulate such that the eddy current probe cannot be fully inserted. However, it is unlikely that, if this were to occur, it would happen simultaneously across all 58 flux thimble tubes at both units. In addition, the recent difficulties have not affected the ability to perform flux mapping. It is likely that a build-up of debris on the internal surface of the flux thimble tubes would prevent the full insertion of the neutron detectors as well as the eddy current probe.

Furthermore, since cleaning of the flux thimble tubes does not appear to improve the ability to perform eddy current testing, it is unlikely that internal debris is the cause.

As described above, it is unlikely that internal blockage of the flux thimble tubes, alone, is the cause of the inability to fully insert the eddy current probe. Corrective actions that have been performed to address this potential cause to date are improvements to the drying process, changes to the scheduling of eddy current testing, and evaluation of the need for cleaning. Corrective actions to address the recent difficulties in obtaining eddy current testing data are discussed below. Corrective Actions 1, 2, 3, 4, 5, and 7 address the potential for internal obstructions within the flux thimble tubes.

Deformation of the Flux Thimble Tubes Deformation of the flux thimble tubes such that the internal dimension of the tubes is affected could prevent the eddy current probe from being fully inserted. Deformation could occur due to improper handling or installation of the flux thimble tubes. However, it is unlikely that deformation of all 58 flux thimble tubes at both units would occur simultaneously. A review of operating experience indicates that when physical deformation of the flux thimble tubes occurs it is isolated rather than widespread across all 58 flux thimble tubes. In addition, a physical deformation capable of preventing eddy current testing would likely cause difficulties in performing flux mapping which have not been experienced. Based on the above it is unlikely that physical deformation of the flux thimble tubes is the cause of the current difficulties in obtaining eddy current testing data.

Corrective actions to address the recent difficulties in obtaining eddy current testing data are discussed below. Corrective Actions 1, 3, 4, 5, and 7 address the potential for deformation of the flux thimble tubes.

Improper Eddy Current Testing Equipment/Process If there is not an internal obstruction within the flux thimble tubes or physical deformation of the flux thimble tubes, then the difficulties in obtaining eddy current testing data are likely due to eddy current test equipment or process issues. Flawed equipment or eddy current testing process would cause widespread difficulties in obtaining eddy current testing data for all 58 flux thimble tubes at both units simultaneously, as experienced at Braidwood. In addition, an equipment or process issue for performing eddy current testing would not affect the ability to perform in-core flux mapping. Since difficulties in performing flux mapping have not been experienced and since widespread issues in

RS-15-071 Enclosure A Page 20 of 23 obtaining eddy current testing data occurred simultaneously for all 58 flux thimble tubes at both units, it is concluded that issues related to the eddy current testing equipment or testing process are the likely cause of the recent issues related to obtaining eddy current testing data.

Corrective actions to address the recent difficulties in obtaining eddy current testing data are discussed below. Corrective Actions 1, 3, 4, and 6 address the potential for improper eddy current testing equipment/process.

Corrective Actions:

The following corrective actions are planned or in-progress to address the potential causes of the recent difficulties in obtaining eddy current testing data at Braidwood:

1. Mock-up testing of a new flux thimble tube is currently in-progress. Attempts will be made to fully insert the existing eddy current probe into a new flux thimble tube that is free of internal obstructions and physical deformations. If the eddy current probe passes freely through the new test flux thimble tube, then the cause of the current issues is likely related to either an internal obstruction or physical deformation of the tube. However, if similar difficulties are experienced when attempting to insert the eddy current probe into the new test flux thimble tube, which is free of internal obstructions and physical deformations, then the cause of the current difficulties is likely related to an equipment or testing process issue. To address potential equipment issues, the use of improved eddy current testing equipment will be evaluated by attempting to fully insert an eddy current probe with a smaller diameter and an eddy current probe with a stiffer drive cable into the new test flux thimble tube. The mock-up testing will provide further information to determine the cause of the current issues in obtaining eddy current testing data and ensure that appropriate corrective actions are taken to resolve this issue.

2. The performance of routine wet cleaning of the flux thimble tubes will be eliminated to align with industry practice and remove a source of moisture. During the next refueling outage, wet cleaning will not be performed prior to eddy current testing.

3. An eddy current probe with a stiffer drive cable similar to the neutron detector cable will be available for use in the upcoming refueling outage. The use of a stiffer eddy current probe drive cable could allow insertion of the eddy current probe beyond the blockage point (i.e., internal obstruction or physical deformation). Prior to the upcoming refueling outage, an eddy current probe with a stiffer drive cable will be tested using a mock-up flux thimble tube (see corrective action 1) to determine if the stiffer drive cable facilitates the performance of eddy current testing of a new test flux thimble tube that is free of internal obstructions and physical deformations.

4. An eddy current probe with a smaller diameter will be available for use in the upcoming refueling outage. A smaller eddy current probe would provide additional clearance such that the probe can be inserted beyond the blockage point (i.e.,

internal obstruction or physical deformation). Prior to the upcoming refueling outage, a smaller eddy current probe will be tested using a mock-up flux thimble tube (see corrective action 1) to determine if the smaller eddy current probe facilitates the

RS-15-071 Enclosure A Page 21 of 23 performance of eddy current testing of a new test flux thimble tube that is free of internal obstructions and physical deformations.

5. The use of a larger diameter flux thimble tube is being evaluated. A larger diameter flux thimble tube would provide additional clearance for the insertion of an eddy current probe and mitigate the effects of future potential internal obstructions and/or physical deformation.

6. Eddy current testing will be performed with flux thimble tubes retracted to allow more time during refueling outages for eddy current testing, if initial attempts to perform eddy current testing with the flux thimble tubes inserted are unsuccessful. Allotting additional time for the testing process will allow for troubleshooting to be performed and increase the probability of success.

7. A plan is being developed to perform a controlled extraction and analysis of a flux thimble tube, if eddy current testing is unsuccessful in the upcoming refueling outage. The controlled extraction and analysis will be performed to determine if an internal obstruction or physical deformation exists at the location where the eddy current probe becomes stuck.

==

Conclusion:==

As described above, corrective actions are planned or in-progress to address each of the potential causes for the recent difficulties in obtaining eddy current testing data for the flux thimble tubes at Braidwood. Completion of these corrective actions provides high confidence that future eddy current testing of the flux thimble tubes at Braidwood is successful. The corrective actions described above are planned to be completed by Spring 2015 for Unit 1 and Fall 2015 for Unit 2.

RS-15-071 Enclosure A Page 22 of 23

5) There has been only one (1) instance when a detector became stuck and could not be retracted. This instance occurred on Unit 1 in 2010. The detector could not be retracted and remained in the core until the next outage. The flux thimble tube and detector cable were cut using bolt cutters and the flux thimble tube and detector were replaced.

In the event that a flux thimble tube develops a leak at Braidwood, regardless of whether a neutron detector is currently inserted, coolant would first fill the damaged flux thimble tube and then flow out of the open end of the thimble and into the flux detector transfer box located above the seal table. The transfer box is connected to several flux thimble tubes. The coolant leaking from the failed flux thimble tube may enter some or all of the adjacent thimbles connected to the common detector transfer device. The transfer unit is equipped with a drain line to a sump. The drain line is normally closed off by a solenoid operated valve. As the leaking coolant fills the drain line, it activates the float switch which opens the valve and activates an alarm in the main control room. The fluid then drains to the sump. Any leakage would be contained within the Primary Containment.

In addition to the alarmed float activated switch, Braidwood Station, Units 1 and 2 seal table rooms are equipped with area radiation monitors. In the event of a flux thimble tube leak, the area radiation monitors will detect the increased radioactivity and activate an alarm. These two (2) diverse mechanisms ensure that, in the event that a flux thimble tube leak was to occur, it is promptly detected.

The expected leakage from a guillotine break of a flux thimble tube with an inside diameter of 0.210 inches was determined to be approximately five (5) gallon per minute in WCAP-12866, Bottom Mounted Instrumentation Flux Thimble Wear. The flux thimble tubes currently used at Braidwood Station have an inside diameter of 0.201 inches, therefore the maximum possible leakage from a guillotine break is expected to be less than five (5) gallons per minute. The five (5) gallon per minute leak value is a conservative upper limit since the typical flux thimble tube failure is wear resulting in a localized hole on the side of the flux thimble tube as opposed to a guillotine break. A five (5) gallon per minute leak is well within the units non-emergency normal make-up capacity of 127 gallons per minute. Since flux thimble tubes wear at different rates, the failure of multiple flux thimble tubes at the same time is highly improbable. Industry operating experience indicates that actual observed leakage rates have been on the order of one (1) gallon per minute. If a flux thimble tube leak occurs and the neutron detector/drive cable cannot be retracted, the resulting leakage would be significantly reduced due to the drive cable partially filling the flux thimble tube and restricting the flow of coolant. Industry operating experience of a flux thimble tube leak with a stuck neutron detector occurred in 1988 at a domestic plant and is documented in WCAP-12866. The observed leakage was on the order of 0.02 gallon per minute.

Once a flux thimble tube leak is detected, the plant operator must determine which flux thimble tube is causing the leak. This determination can be made visually, via thermography, or by comparing the temperature of the flux thimble tubes to detect which one is noticeably hotter than the others. Since Braidwood Station, Units 1 and 2 are equipped with manual isolation valves directly above the seal table, a flux thimble

RS-15-071 Enclosure A Page 23 of 23 tube leak may be isolated by simply closing the isolation valve if a neutron detector/drive cable is not stuck in the flux thimble tube.

To isolate a leaking flux thimble tube with a stuck detector/drive cable, the reactor is shutdown and the reactor coolant system is depressurized. A section of flux thimble tubing and drive cable between the seal table and the detector transfer device is then cut and the flux thimble tube is capped. The tubing from the detector transfer device will also be capped to eliminate a potential alternate drain path. The flux thimble tube would then be replaced during the next refueling outage.

As stated in WCAP-12866, the combined factors of low leakage rate, leak detection capability, and the ability to isolate the leakage, allow the flux thimble wear issue to be classified as a maintenance concern, not a reactor safety issue. The Braidwood Flux Thimble Tube Inspection Program, as enhanced, is considered sufficiently robust to manage flow induced wear of flux thimble tubes.

RS-15-071 Enclosure B Page 1 of 5 Enclosure B Byron and Braidwood Stations, Units 1 and 2 License Renewal Application Updates Associated with:

RAI B.2.1.24-1b Note: To facilitate understanding, portions of the original LRA have been repeated in this Enclosure, with revisions indicated. Existing LRA text is shown in normal font. Changes are highlighted with bolded italics for inserted text and strikethroughs for deleted text.

RS-15-071 Enclosure B Page 2 of 5 As a result of the response provided in Enclosure A of this letter, LRA Appendix A, Section A.2.1.24, page A-28, is revised as shown below. In addition, an editorial correction is made in enhancements 2.b and 3.b. Additions are indicated with bolded italics and deletions indicated by strikethroughs.

A.2.1.24 Flux Thimble Tube Inspection The Flux Thimble Tube Inspection aging management program is an existing condition monitoring program that manages the loss of material in flux thimble tubes due to wear (i.e., wall thinning). Flux thimble tubes, which provide a path for the in-core neutron flux monitoring system detectors, establish part of the reactor coolant pressure boundary and are subject to flow-induced fretting which causes wear. The program uses the non-destructive examination methodology of eddy current testing to periodically inspect the full length of all flux thimble tubes, which encompasses the path from the reactor vessel instrument nozzle to the fuel assembly instrument guide.

The results of the periodic eddy current testing are evaluated and trended to determine if corrective actions are required or if the inspection frequency needs to be changed to ensure reactor coolant pressure boundary integrity is maintained. Corrective actions include flux thimble tube limited repositioning (one-time), replacement, or isolation (removal from service).

The Flux Thimble Tube Inspection program implements the recommendations of NRC IE Bulletin 88-09, Thimble Tube Thinning in Westinghouse Reactors. This existing aging management program will continue to be implemented during the period of extended operation.

The Flux Thimble Tube Inspection aging management program will be enhanced as follows:

1. For Braidwood Units 1 and 2: Perform corrective actions to re-establish periodic eddy current testing of the flux thimble tubes prior to the period of extended operation to ensure that wall thickness is monitored to detect loss of material from the flux thimble tubes. Once periodic eddy current testing is re-established, eddy current testing will be performed for each flux thimble tube every refueling outage until sufficient data has been accumulated to establish a plant-specific eddy current testing frequency to ensure that no flux thimble tube is predicted to incur wear that exceeds 80% before the next inspection. Flux thimble tube wall thickness measurements will be trended and wear rates will be calculated based on plant-specific data. Wall thickness will be projected using plant-specific data in accordance with the WCAP-12866, Bottom Mounted Instrumentation Flux Thimble Wear, methodology.

2 1. For Braidwood Unit 1:

a. The 17 Braidwood Station, Unit 1 flux thimble tubes that exhibited indications of wear during eddy current testing performed during A1R15 Refueling Outage (Fall 2010), will be replaced or removed from service during A1R18 Refueling Outage (Spring 2015), unless eddy current data is

RS-15-071 Enclosure B Page 3 of 5 obtained as required by the Flux Thimble Tube Inspection program. (Flux thimble tubes 1 (J-8), 8 (K-6), 9 (H-11), 12 (E-9), 14 (H-4), 18 (L-11), 19 (L-5), 21 (E-11), 23 (D-10), 36 (J-14), 37 (P-9), 41 (N-4), 44 (R-8), 45 (N-13),

48 (P-4), 54 (A-11), 55 (N-14))

b. The remaining Braidwood Station, Unit 1 flux thimble tubes, not replaced during A1R18, will be replaced or removed from service during A1R19 Refueling Outage (Fall 2016), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection Tube program.

c. Following A1R19, any Braidwood Station, Unit 1 flux thimble tube will be replaced every three (3) refueling outages or removed from service if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection program.

3 2. For Braidwood Unit 2:

a. The 29 Braidwood Station, Unit 2 flux thimble tubes that exhibited indications of wear during eddy current testing performed during A2R15 Refueling Outage (Spring 2011) and not replaced during A2R17 Refueling Outage (Spring 2014), will be replaced or removed from service during A2R18 Refueling Outage (Fall 2015), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection program. (Flux thimble tubes 1 (J-8), 4 (H-6), 5 (F-8), 6 (J-10), 7 (F-7), 9 (H-11), 10 (L-8), 11 (G-5),

18 (L-11), 22 (K-12), 23 (D-10), 24 (H-13), 25 (N-8), 26 (H-3), 27 (C-8), 29 (N-6), 32 (L-13), 33 (C-5), 34 (H-2), 36 (J-14), 37 (P-9), 40 (F-14), 41 (N-4),

42 (D-3), 45 (N-13), 46 (J-1), 50 (R-6), 52 (L-15), 56 (N-2))

b. The remaining Braidwood Station, Unit 2 flux thimble tubes, not replaced during A2R17 or A2R18, will be replaced or removed from service during A2R19 Refueling Outage (Spring 2017), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection Tube program.

c. Following A2R19, any Braidwood Station, Unit 2 flux thimble tube will be replaced every three (3) refueling outages or removed from service if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection program.

These enhancements will be implemented in accordance with the schedule specified in the enhancement.

RS-15-071 Enclosure B Page 4 of 5 As a result of the response provided in Enclosure A of this letter, the Enhancements section of LRA Appendix B, Section B.2.1.24, page B-153, is revised as shown below. In addition, an editorial correction is made in 2.b and 3.b. Additions are indicated with bolded italics; deletions are shown with strikethroughs.

B.2.1.24 Flux Thimble Tube Inspection Enhancements The following enhancements will be implemented in the following program elements:

1. For Braidwood Units 1 and 2: Perform corrective actions to re-establish periodic eddy current testing of the flux thimble tubes prior to the period of extended operation to ensure that wall thickness is monitored to detect loss of material from the flux thimble tubes. Once periodic eddy current testing is re-established, eddy current testing will be performed for each flux thimble tube every refueling outage until sufficient data has been accumulated to establish a plant-specific eddy current testing frequency to ensure that no flux thimble tube is predicted to incur wear that exceeds 80% before the next inspection. Flux thimble tube wall thickness measurements will be trended and wear rates will be calculated based on plant-specific data. Wall thickness will be projected using plant-specific data in accordance with the WCAP-12866, Bottom Mounted Instrumentation Flux Thimble Wear, methodology.

Program Element Affected: Parameters Monitored/Inspected (Element 3),

Detection of Aging Effects (Element 4), Monitoring and Trending (Element 5), and Corrective Actions (Element 7) 2 1. For Braidwood Unit 1:

a. The 17 Braidwood Station, Unit 1 flux thimble tubes that exhibited indications of wear during eddy current testing performed during A1R15 Refueling Outage (Fall 2010), will be replaced or removed from service during A1R18 Refueling Outage (Spring 2015), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection program. (Flux thimble tubes 1 (J-8), 8 (K-6), 9 (H-11), 12 (E-9), 14 (H-4), 18 (L-11), 19 (L-5), 21 (E-11), 23 (D-10), 36 (J-14), 37 (P-9), 41 (N-4), 44 (R-8), 45 (N-13), 48 (P-4), 54 (A-11), 55 (N-14))

b. The remaining Braidwood Station, Unit 1 flux thimble tubes, not replaced during A1R18, will be replaced or removed from service during A1R19 Refueling Outage (Fall 2016), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection Tube program.

c. Following A1R19, any Braidwood Station, Unit 1 flux thimble tube will be replaced every three (3) refueling outages or removed from service if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection program.

Program Element Affected: Corrective Actions (Element 7)

RS-15-071 Enclosure B Page 5 of 5 3 2. For Braidwood Unit 2:

a. The 29 Braidwood Station, Unit 2 flux thimble tubes that exhibited indications of wear during eddy current testing performed during A2R15 Refueling Outage (Spring 2011) and not replaced during A2R17 Refueling Outage (Spring 2014), will be replaced or removed from service during A2R18 Refueling Outage (Fall 2015), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection program. (Flux thimble tubes 1 (J-8), 4 (H-6), 5 (F-8), 6 (J-10), 7 (F-7), 9 (H-11), 10 (L-8), 11 (G-5),

18 (L-11), 22 (K-12), 23 (D-10), 24 (H-13), 25 (N-8), 26 (H-3), 27 (C-8), 29 (N-6), 32 (L-13), 33 (C-5), 34 (H-2), 36 (J-14), 37 (P-9), 40 (F-14), 41 (N-4),

42 (D-3), 45 (N-13), 46 (J-1), 50 (R-6), 52 (L-15), 56 (N-2))

b. The remaining Braidwood Station, Unit 2 flux thimble tubes, not replaced during A2R17 or A2R18, will be replaced or removed from service during A2R19 Refueling Outage (Spring 2017), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection Tube program.

c. Following A2R19, any Braidwood Station, Unit 2 flux thimble tube will be replaced every three (3) refueling outages or removed from service if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection program.

Program Element Affected: Corrective Actions (Element 7)

RS-15-071 Enclosure C Page 1 of 3 Enclosure C Byron and Braidwood Stations (BBS) Units 1 and 2 License Renewal Commitment List Update This Enclosure identifies commitments made in this document and is an update to the Byron and Braidwood Station (BBS) LRA Appendix A, Table A.5, License Renewal Commitment List.

Any other actions discussed in the submittal represent intended or planned actions and are described to the NRC for the NRCs information and are not regulatory commitments. Changes to the BBS LRA Appendix A, Table A.5 License Renewal Commitment List are as a result of this submittal.

Notes:

To facilitate understanding, portions of the original License Renewal Commitment List have been repeated in this Enclosure, with revisions indicated.

Existing LRA text is shown in normal font. Changes are highlighted with bold italics for inserted text and strikethroughs for deleted text.

RS-15-071 Enclosure C Page 2 of 3 As a result of the response provided in Enclosure A of this letter, LRA Appendix A, Table A.5 License Renewal Commitment List, Item 24 on page A-80, is revised as shown below. In addition, an editorial correction is made in enhancements 2.b and 3.b. The correspondence that led to this commitment modification is listed in the SOURCE column. Any other actions described in this submittal represent intended or planned actions. They are described for the NRCs information and are not regulatory commitments.

Additions are indicated with bolded italics; deletions are shown with strikethroughs.

NO. PROGRAM OR IMPLEMENTATION COMMITMENT SOURCE TOPIC SCHEDULE*

24 Flux Thimble Tube Section A.2.1.24 Inspection Flux Thimble Tube Inspection is an existing program that will be Byron: Ongoing enhanced as follows: Exelon letter (Note 3)

Braidwood: Schedule for flux RS-14-336

1. For Braidwood Units 1 and 2  : Perform corrective thimble tube replacement 11/22/2014 actions to re-establish periodic eddy current testing of the activities identified in flux thimble tubes prior to the period of extended operation commitment. Exelon letter to ensure that wall thickness is monitored to detect loss of RS-15-071 material from the flux thimble tubes. Once periodic eddy Corrective actions to re- 02/23/15 current testing is re-established, eddy current testing will be establish periodic eddy performed for each flux thimble tube every refueling outage current testing at Braidwood until sufficient data has been accumulated to establish a will be completed either no plant-specific eddy current testing frequency to ensure that later than six months prior no flux thimble tube is predicted to incur wear that exceeds to the PEO, or before the 80% before the next inspection. Flux thimble tube wall end of the last refueling thickness measurements will be trended and wear rates will outage prior to the PEO, be calculated based on plant-specific data. Wall thickness whichever occurs later.

will be projected using plant-specific data in accordance with the WCAP-12866, Bottom Mounted Instrumentation Flux Thimble Wear, methodology.

2 1. For Braidwood Unit 1 (Note 3):

a. The 17 Braidwood Station, Unit 1 flux thimble tubes that exhibited indications of wear during eddy current testing performed during A1R15 Refueling Outage (Fall 2010), will be replaced or removed from service during A1R18 Refueling Outage (Spring 2015), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection program. (Flux thimble tubes 1 (J-8), 8 (K-6), 9 (H-11), 12 (E-9), 14 (H-4), 18 (L-11), 19 (L-5), 21 (E-11), 23 (D-10), 36 (J-14), 37 (P-9), 41 (N-4), 44 (R-8), 45 (N-13), 48 (P-4), 54 (A-11), 55 (N-14))

RS-15-071 Enclosure C Page 3 of 3 NO. PROGRAM OR IMPLEMENTATION COMMITMENT SOURCE TOPIC SCHEDULE*

b. The remaining Braidwood Station, Unit 1 flux thimble tubes, not replaced during A1R18, will be replaced or removed from service during A1R19 Refueling Outage (Fall 2016),

unless eddy current data is obtained as required by the Flux Thimble Tube Inspection Tube program.

c. Following A1R19, any Braidwood Station, Unit 1 flux thimble tube will be replaced every three (3) refueling outages or removed from service if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection program.

3 2. For Braidwood Unit 2 (Note 3):

a. The 29 Braidwood Station, Unit 2 flux thimble tubes that exhibited indications of wear during eddy current testing performed during A2R15 Refueling Outage (Spring 2011) and not replaced during A2R17 Refueling Outage (Spring 2014), will be replaced or removed from service during A2R18 Refueling Outage (Fall 2015), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection program. (Flux thimble tubes 1 (J-8), 4 (H-6), 5 (F-8), 6 (J-10), 7 (F-7), 9 (H-11), 10 (L-8), 11 (G-5), 18 (L-11), 22 (K-12), 23 (D-10), 24 (H-13), 25 (N-8), 26 (H-3), 27 (C-8), 29 (N-6), 32 (L-13), 33 (C-5), 34 (H-2), 36 (J-14), 37 (P-9), 40 (F-14), 41 (N-4), 42 (D-3), 45 (N-13), 46 (J-1), 50 (R-6), 52 (L-15), 56 (N-2))

b. The remaining Braidwood Station, Unit 2 flux thimble tubes, not replaced during A2R17 or A2R18, will be replaced or removed from service during A2R19 Refueling Outage (Spring 2017), unless eddy current data is obtained as required by the Flux Thimble Tube Inspection Tube program.

c. Following A2R19, any Braidwood Station, Unit 2 flux thimble tube will be replaced every three (3) refueling outages or removed from service if eddy current data is not obtained in accordance with the Flux Thimble Tube Inspection program.