ML18317A374

Completion of Review of Power Reactor Licensee Responses to Generic Letter 2016-01, Monitoring of Neutron-Absorbing Materials in Spent Fuel Pools

ML18317A374
Person / Time
Issue date:	11/27/2018
From:	Robert Lukes NRC/NRR/DSS/SNPB
To:	Mirela Gavrilas NRC/NRR/DSS
Krepel, S., NRR/DSS, 301-302-0399
References
GL-2016-01
Download: ML18317A374 (13)

Text

November 27, 2018 MEMORANDUM TO: Mirela Gavrilas, Director Division of Safety Systems Office of Nuclear Reactor Regulation FROM: Robert G. Lukes, Chief /RA/

Nuclear Performance and Code Review Branch Division of Safety Systems Office of Nuclear Reactor Regulation

SUBJECT:

COMPLETION OF REVIEW OF POWER REACTOR LICENSEE RESPONSES TO GENERIC LETTER 2016-01, MONITORING OF NEUTRON-ABSORBING MATERIALS IN SPENT FUEL POOLS On April 7, 2016, the U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2016-01, Monitoring of Neutron-Absorbing Materials in Spent Fuel Pools (Agencywide Documents Access and Management System Accession No. ML16097A169) to all nuclear power reactors with a license issued under Title 10 of the Code of Federal Regulations Part 50, Domestic Licensing of Production and Utilization Facilities, except those that have permanently ceased operations with all reactor fuel removed from onsite spent fuel pool (SFP) storage. The stated purpose of GL 2016-01 for power reactors was (1) to request that addressees submit information or provide references to previously docketed information that demonstrate that credited neutron-absorbing materials in the SFP are in compliance with the licensing and design basis and with applicable regulatory requirements and that measures are in place to maintain this compliance and (2) to collect the requested information and determine whether additional regulatory action is required.

The staff of the NRC Nuclear Performance and Code Review Branch in the Division of Safety Systems and the staff of the Chemical, Corrosion, and Steam Generator Branch in the Division of Materials and License Renewal have completed the detailed review of licensees responses to GL 2016-01. The review assesses the information provided by the licensees to support a conclusion that their monitoring programs will be effective in identifying any degradation or deformation of neutron-absorbing materials credited for compliance with the NRCs subcriticality requirements and that any degradation of the neutron-absorbing materials in the SFPs for nuclear power plants is being managed to maintain reasonable assurance that the materials are capable of performing their safety function. The staff has issued individual plant closure letters CONTACT: Scott T. Krepel, NRR/DSS 301-302-0399

M. Gavrilas and plans to take appropriate follow up actions to confirm that the licensees are properly managing the degradation of their neutron-absorbing materials.

The enclosed report summarizes the NRC staffs evaluations of the responses to GL 2016-01, any relevant technical conclusions, and actions taken (or to be taken) to help ensure that the issues discussed in GL 2016-01 do not recur.

Enclosure:

As stated

M. Gavrilas

SUBJECT:

COMPLETION OF REVIEW OF POWER REACTOR LICENSEE RESPONSES TO GENERIC LETTER 2016-01, MONITORING OF NEUTRON-ABSORBING MATERIALS IN SPENT FUEL POOLS DATED:

DISTRIBUTION:

DSS R/F DMLR R/F BBenney ADAMS Accession Number: ML18317A374 *via-e-mail NRR-106 OFFICE NRR/DSS/SNPB NRR/DSS/SNPB* NRR/DSS/SNPB* NRR/DMLR/MCCB*

NAME SKrepel KWood APatel AChereskin DATE 11/20/2018 11/20/2018 11/20/2018 11/20/2018 OFFICE NRR/DMLR/MCCB* TECH ED* NRR/DMLR/MCCB* NRR/DSS/SNPB NAME MYoder JDougherty SBloom RLukes DATE 11/20/2018 11/19/2018 11/20/2018 11/27/2018 OFFICIAL RECORD COPY

CLOSURE OF REVIEW OF POWER REACTOR LICENSEE RESPONSES TO GENERIC LETTER 2016-01, MONITORING OF NEUTRON-ABSORBING MATERIALS IN SPENT FUEL POOLS

SUMMARY

AND CONCLUSIONS The staff of the Nuclear Performance and Code Review Branch in the U.S. Nuclear Regulatory Commissions (NRCs) Division of Safety Systems and the staff of the Chemical, Corrosion, and Steam Generator Branch in the Division of Materials and License Renewal have completed the detailed review of power reactor licensees responses to Generic Letter (GL) 2016-01, Monitoring of Neutron-Absorbing Materials in Spent Fuel Pools, dated April 7, 2016 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16097A169). The review assesses the information provided by the licensees to support a conclusion that their monitoring programs will be effective in identifying any degradation or deformation of neutron-absorbing materials credited for compliance with the NRCs subcriticality requirements and that any degradation of the neutron-absorbing materials in the spent fuel pools (SFPs) associated with nuclear power plants is being managed to maintain reasonable assurance that the materials are capable of performing their safety function. The staff has issued individual plant closure letters and is supporting the regions in performing follow up inspections as part of the baseline reactor oversight process to ensure that specific licensees are properly managing degradation of their neutron-absorbing materials through corrective actions.

GL 2016-01 has brought attention to the potential safety significance associated with unidentified and unmitigated degradation of neutron-absorbing materials in SFPs. Based on licensees responses to GL 2016-01, the NRC staff was able to verify that most licensees are adequately monitoring neutron-absorbing materials in their SFPs or that they do not credit any neutron-absorbing materials for compliance with the NRCs subcriticality requirements. Some licensees did not have effective monitoring programs in place and voluntarily initiated an industrywide operating experience database collection effort through the Electric Power Research Institute (EPRI). A small number of licensees were found to have open corrective action items associated with resolving Boraflex degradation issues, and the staff is partnering with the regions through follow up inspections to confirm that the corrective actions are adequate to manage the degradation of Boraflex.

Based on the review of licensees responses, the NRC staff has determined that no additional regulatory guidance is needed. The Nuclear Energy Institute (NEI) submitted NEI 2016-03, Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, Revision 0, issued August 2016 and approved by the NRC on March 3, 2017 (ADAMS Accession No. ML16354A486). NEI 2016-03 provides adequate guidance on what constitutes an effective monitoring program.

GL 2016-01 states that unidentified, unmitigated, and unmonitored degradation or deformation of the credited neutron-absorbing materials may reduce the safety margin and potentially challenge the subcriticality requirement. The NRC staff has been able to verify that in the majority of cases, reasonable assurance exists that degradation or deformation has not occurred to the extent necessary to result in a significant reduction in the safety margin. In some cases, the NRC staff identified that licensees are taking corrective actions to manage the Enclosure

degraded condition of Boraflex neutron-absorbing materials. Through inspections or licensing actions, the NRC will confirm that the corrective actions are adequate to ensure that licensees are maintaining appropriate safety margins to criticality.

LESSONS LEARNED GL 2016-01 was generally effective in enabling the NRC staff to verify the current known state of all neutron-absorbing materials used in SFPs associated with commercial nuclear power plants and any associated monitoring programs. The GL 2016-01 process also provided a vehicle through which the NRC staff could identify the most efficient approach necessary to address the remaining open issues. In addition, the NRC identified concrete continuing actions as part of the existing oversight and licensing activities as an appropriate way to help ensure that these issues are not likely to recur.

However, the process of development, issuance, and closeout of GL 2016-01 took more time and required more resources than originally anticipated. The most significant challenge was associated with management turnover. GL 2016-01 required alignment among Branch Chiefs and division management in multiple divisions; therefore, any change in supervisory or management personnel would frequently delay any ongoing activities that may require their approval. In addition, significant staff time and resources would be required to bring the new Branch Chiefs or division management up to speed and, on several occasions, to reestablish alignment between the divisions because of differences in opinion. This challenge was frequently exacerbated by the lack of a well-defined outcome or path forward that had clear management support within all divisions.

Some secondary challenges added further delays to the process, such as the relatively low prioritization of issues related to GL 2016-01 compared to other more immediate concerns or an unforeseen change in the Office of Management and Budgets policy related to clearance requests for information collections. These delays were not under the control of the NRC staff working on GL 2016-01 and did not, by themselves, lead to an increase in staff resources expended on the GL. However, they did increase the probability that more management or staff turnover would happen, which had a more tangible effect on staff resources and triggered further delays.

For similarly broad cross-cutting issues that involve multiple divisions in the future, the staff recommends an early engagement of all cognizant Branch Chiefs and division management to develop better defined expectations for possible outcomes. An appropriate document should capture any consensus positions to help support continuity, especially those positions that the technical staff will use to ensure that its decision making process is consistent with management expectations. If emergent issues raise new questions or challenge the previous consensus positions, reengagement may be warranted. This recommendation is not intended to solve all potential schedule delays; however, it would provide a stronger framework to support staff decisions and encourage efficient decision making.

BACKGROUND GL 2016-01 focuses on the following three principal concerns:

(1) Neutron-Absorbing Material Characterization. The susceptibility of neutron-absorbing materials is not only a function of the material properties, but it may also depend on the materials manufacturer, vintage, installation configuration, and degree of exposure to

the SFP environment and on any deformation or degradation of the materials that has already occurred. Consequently, this information was necessary to allow the NRC staff to determine whether the actions being taken by the licensee are adequate to identify and manage degradation or deformation of the neutron-absorbing material.

(2) Monitoring Programs. Criterion XI, Test Control, of Appendix B, Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants, to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities, requires licensees to establish a test program to assure that all testing required to demonstrate that structures, systems, and components will perform satisfactorily in service. Inspections and reviews of proposed licensing actions identified several licensees that had ineffective test programs to confirm that the neutron-absorbing materials would continue to perform their safety function.

(3) Licensing Basis. The safety function of neutron-absorbing materials is to ensure that licensees maintain compliance with the NRCs subcriticality requirements (e.g., 10 CFR 50.68, Criticality Accident Requirements). Typically, licensees maintain compliance by confirming that the SFP conditions and operations are consistent with the nuclear criticality safety (NCS) analysis of record (AOR). During inspections or reviews, the NRC identified multiple cases of proposed licensing actions in which licensees did not adequately account for known degradation or deformation of neutron-absorbing materials in their NCS AORs.

To minimize unnecessary burden on licensees, the NRC offered two sets of guidance in GL 2016-01. The first set of guidance provided specific screen-out criteria that licensees could use to determine whether the NRC needed a detailed response from them. The criteria considered the fact that some licensees do not have any useful information to provide or that the NRC has already received and reviewed the necessary information as part of previous licensing actions. The second set of guidance clarified the level of detail expected in licensees responses to the information request, with a graded approach based on the known susceptibility of each neutron-absorbing material type to degradation or deformation.

GL 2016-01 gives more details on the relevant issues, the information being requested, the aforementioned guidance provided by the NRC staff, and the regulatory bases.

The NRC issued GL 2016-01 on April 7, 2016. Under 10 CFR 50.54(f), the NRC required addressees to submit a written response within 210 days of the date of GL 2016-01. The NRC received responses from all licensees by early November. Some licensees subsequently found it necessary to supplement their initial response to correct errors, and the staff reviewed the information in these supplements as part of its evaluation. After reviewing the initial responses to GL 2016-01 from licensees that applied the screen-out criteria to determine whether a detailed response to the GL was required, the staff determined that it needed more detailed responses from four licensees. Subsequently, the NRC issued a request for the missing information to these licensees by letter dated March 7, 2017. Upon completion of its evaluation of all the detailed responses, the staff determined that it needed some additional information to clarify the licensees initial responses. The NRC sent requests for additional information (RAIs) to the appropriate licensees through a series of letters in October through December 2017; all licensees have provided acceptable responses, with no further need for additional information.

DISCUSSION The staff reviewed responses from 65 nuclear power plant sites that included 106 reactor units.

These numbers reflect licensees that have produced spent fuel from an operating reactor that may currently be stored in an SFP. As such, the licensee responses include a number of decommissioned units that continue to store fuel on site. The staff evaluated the licensee responses in three stages. First, in winter 2016 and 2017, the staff reviewed all the responses to GL 2016-01 from licensees that self-identified as belonging to Category 1 through Category 3 as defined in GL 2016-01 and, therefore, screened out from the requirement to provide a detailed response to the GL. Secondly, during spring and summer 2017, the staff reviewed the initial detailed responses for Category 4 licensees to determine whether they provided sufficient information to allow the staff to determine whether the degradation of the neutron-absorbing materials in the SFP is being managed to maintain reasonable assurance that the materials are capable of performing their safety function and to verify that the licensees are in compliance with the regulations. Some follow up RAIs were necessary for clarification or elaboration on some of the licensees initial responses. Finally, during summer 2018, the staff reviewed the information submitted in response to the RAIs and confirmed that no further information was needed. The sections below discuss each stage of the evaluation in more detail.

Screen-Out Evaluation GL 2016-01 defines four categories of licensees based on the following screen-out criteria:

(1) power reactor addressees that do not credit neutron-absorbing materials other than soluble boron in the AOR, (2) power reactor addressees that have an approved license amendment to remove credit for existing neutron-absorbing materials and that intend to complete full implementation no later than 24 months after the issuance of GL 2016-01, (3) power reactor addressees that have incorporated their neutron-absorbing material monitoring programs into their licensing basis through an NRC-approved technical specification change or license condition, and (4) all other power reactor addressees.

The staff reviewed all licensees that self-identified as belonging to Category 1 through Category 3 to confirm that the screen-out criteria were applied correctly and that the responses were of the expected scope. In most cases, both questions were answered in the affirmative.

Because of the nature of the specific situations represented by these licensees, no further evaluation was necessary because there was either nothing to evaluate or the NRC had previously evaluated the relevant information as part of a formal licensing review.

The NRC staff found that 12 responses incorrectly applied the screen-out criteria for Category 3 by interpreting that incorporated their neutron-absorbing material monitoring programs into their licensing basis through an NRC-approved TS [technical specification] change or license condition applied to the standard license condition for approved license renewals. This license condition requires licensees to incorporate appropriate information on the aging management programs into their final safety analysis report, as updated, before the beginning of the period of extended operation. This was not the intent of the NRC staff because this license condition did

not explicitly capture the neutron-absorbing material monitoring program into the operating license for the plant. However, the responses referenced the license renewal application documentation and affirmed that no changes had been made to the programs described therein.

Therefore, the NRC staff reviewed the previously docketed information referenced in the responses to determine whether it contained the information consistent with an acceptable Category 4 response.

In 8 out of the 12 cases, the staff determined that the license renewal application documentation contained sufficient information to meet the intent of GL 2016-01. In particular, the license renewal application included the key features for the licensees neutron-absorbing material monitoring program, consistent with existing NRC guidance (NEI 2016-03, Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, (ADAMS Accession No. ML16354A486) and NUREG-1802, Generic Aging Lessons Learned (GALL) Report, Revision 2, issued December 2010 (ADAMS Accession No. ML103490041)). In addition, based on the licensees statements in their responses to GL 2016-01, the NRC staff found that the licensees intend to continue their monitoring programs. Therefore, the NRC closed out GL 2016-01 for these licensees with no further regulatory action needed. The appropriate NRC oversight process would address any failure by licensees to continue monitoring of their neutron-absorbing materials in the future. The Summary of Licensee Responses to GL 2016-01 below provides further detail on the technical basis for closing out GL 2016-01 for these licensees, with no further regulatory action.

In four cases, the license renewal application did not contain sufficient information to meet the intent of responding to GL 2016-01. Consequently, the NRC staff sent a targeted request asking these licensees to provide the needed information from the detailed list in GL 2016-01, Appendix A, Guidance for Category 4 Responders to Generic Letter 2016-01, which the staff was unable to locate in the license renewal application. The staff evaluated these four GL 2016-01 responses, along with the supplements resulting from the NRC staffs request for information, with the remainder of the responses from licensees that self-identified as Category 4.

Initial Evaluation of Detailed Responses The remainder of the responses to GL 2016-01 generally followed the guidance in Appendix A to the GL. Appendix A established a detailed list of information that the staff believed to be necessary to address the issues discussed in GL 2016-01. The amount of information varied based on the neutron-absorbing material being credited and the current state of knowledge regarding the materials susceptibility to degradation or deformation. In the case of borated stainless steel and mixed metallic composites, operating experience that indicates changes in material properties beyond the development of small pits does not currently exist. Therefore, the information request focused on characterization of the material and the monitoring program.

Boral is known to experience bulging or blistering resulting from a gas buildup; therefore, in addition to the material characterization and monitoring questions, the NRC staff also requested information on the criticality impact of any applicable material deformation. Finally, because Boraflex and phenolic resins are known to suffer from substantial loss of neutron-absorbing material, more information is necessary to address all of the technical issues.

The NRC staff performed an initial review of the detailed responses and separated the individual responses into bins based on how the monitoring and degradation management questions were addressed. The Summary of Licensee Responses to GL 2016-01 below further discusses the

bins. In many cases, the staff found that it needed additional information to complete its evaluation. The NRC staff issued RAIs to the appropriate licensees in fall and winter 2017.

Approximately half of the RAIs were plant-specific requests for clarification on key details of the licensees GL 2016-01 responses. The remaining RAIs were, in essence, similar RAIs directed to multiple licensees that indicated that (1) they were monitoring industry operating experience in lieu of maintaining a site-specific monitoring program for their Boral material or (2) the criticality impact of deformation issues known to affect Boral is insignificant. In these RAIs, the NRC staff asked the licensee to further justify these statements. The NRC staff received all the responses to the RAI letters in winter and spring 2018; the two sections below discuss the staffs evaluations of the RAI responses.

Evaluation of Responses to Plant-Specific Requests for Additional Information The intent of the plant-specific RAIs was to request any necessary clarification of individual licensees responses to GL 2016-01. In general, these plant-specific RAIs fell into one of the following categories:

• RAIs to confirm that an appropriate acceptance criterion with regard to the boron-10 areal density exists for the monitoring program

• RAIs to confirm the applicability of the monitoring program results to all of the neutron-absorbing materials currently credited for criticality control in the licensees SFPs

• RAIs to confirm that licensees are taking appropriate actions to manage any identified degradation In all but one case, each licensee provided sufficient information to allow the NRC staff to confirm the appropriate binning for its responses, as discussed in the Summary of Licensee Responses to GL 2016-01, below. In the response from Southern Nuclear Operating Company, Inc., on Edwin I. Hatch Nuclear Plant, Units 1 and 2, the licensee provided information that showed an approximately 7-year gap between installation of the Boral panels in the SFP racks and the installation of the Boral coupons. However, the licensee also stated that the Boral coupons were located near freshly discharged fuel at each refueling outage. During a telephone call on August 9, 2018, the licensee clarified that it is a procedural requirement to place freshly discharged fuel adjacent to the coupons at every outage and that this requirement has been in place since the coupons were installed. Therefore, the NRC staff has reasonable assurance that the Boral coupons will be representative of the inservice Boral panels because the procedural requirement has sufficiently accelerated the radiation dose accumulation of the coupons relative to the inservice Boral panels to allow the NRC staff to reasonably expect that the coupons have caught up to the operating history of the inservice Boral panels.

Evaluation of Generic Responses to Requests for Additional Information Most licensees that received the similar RAIs opted to participate in an effort coordinated through NEI and EPRI to develop and provide information that would generically address the technical issues. The NRC staff actively engaged with NEI, EPRI, and the industry during the process of developing this information to enable it to provide feedback on whether the information would be sufficient to address the RAIs. The result was that all licensees except for

one provided the same responses to the RAIs. Licensees that were asked to justify their statement that the criticality impact caused by deformation issues known to affect Boral is insignificant responded by referencing a generic study performed by EPRI (EPRI Technical Report No. 3002013119, Evaluation of the Impact of Neutron Absorber Material Blistering and Pitting on Spent Fuel Pool Reactivity, issued May 2018 (ADAMS Accession No. ML18226A292)). The one exception was Susquehanna Nuclear, LLC, on behalf of Susquehanna Steam Electric Station (Susquehanna). The licensee provided information on a site-specific evaluation that addressed the criticality impact of known deformation issues in the Susquehanna SFP. Licensees that were asked to justify the use of industry operating experience in lieu of maintaining a site-specific monitoring program for their Boral material stated that they will continue to monitor industry operating experience related to Boral and will continue to participate in the EPRI Neutron Absorber Users Group and its related programs (EPRI Technical Update Report No. 3002013122, Roadmap for the Industrywide Learning Aging Management Program (i-LAMP) for Neutron Absorber Materials in Spent Fuel Pools, issued May 2018 (ADAMS Accession No. ML18226A291)). The licensees also stated that currently there are no known plant-specific conditions or rack attributes that would indicate that their SFP racks or environment are not bounded by industrywide operating experience.

EPRI Technical Update Report No. 3002013122 describes an industrywide effort, coordinated by EPRI, to gather water chemistry and Boral coupon data for SFPs. The report describes how EPRI collects and analyzes these data and how it plans to use the analysis to eventually define sister pool criteria. The purpose of the sister pool criteria is to inform the condition of the Boral at a plant with no coupon, or in situ, testing of its Boral with the coupon test results from other plants that have similar water chemistry, service environment, service life, and Boral material. EPRI Technical Report No. 3002013119 documents a series of sensitivity studies performed on representative SFP rack configurations to demonstrate that the amount of observed pitting and blistering would not be expected to have a significant reactivity impact.

Preliminary conclusions are obtained based on the estimated reactivity impact from EPRI Technical Report No. 3002013119 for the maximum observed pitting and blistering dimensions to date, as collected by the program documented in EPRI Technical Update Report No. 3002013122. The longer term data collection and analysis efforts described in EPRI Technical Update Report No. 3002013122 is intended to reinforce these preliminary conclusions.

The sensitivity studies performed in EPRI Technical Report No. 3002013119 contain several limitations, including the following, which preclude their use for broader licensing purposes:

• The specific fuel and SFP rack configurations used do not necessarily represent, or bound, all fuel and SFP rack configurations for [plant name].

• The calculations were not performed in accordance with a quality program that meets the requirements of 10 CFR Part 50, Appendix B.

• Some of the assumptions inherent in the sensitivity studies may not be conservative under all situations.

To perform confirmatory calculations, the NRC staff used independent models that showed similar results. The preliminary conclusions based on the operating experience reported in EPRI Technical Report No. Report 3002013119 show that the maximum reactivity impact, with conservative assumptions, would be expected to be within the range of a few dozen percent

milli-rho, which the NRC staff agrees is not safety significant. However, the inherent limitations in the studies preclude them from being used to justify the reactivity impact resulting from degradation or deformation that goes significantly beyond that summarized in EPRI Technical Report No. 3002013119. Therefore, the NRC staff does not agree with the following statement in Section 7.3 of EPRI Technical Report No. 3002013119:

allows the report to be used as the technical basis for quantifying the reactivity impact of future operating experience even if it significantly exceeds current operating experience.

The NRC would expect licensees to address the criticality impact of any operating experience applicable to their SFPs that significantly exceeds that discussed in EPRI Technical Report No. 3002013119.

During its review of EPRI Technical Update Report No. 3002013122, the staff noted that the Boral coupon database, water chemistry database, and sister pool definitions are not yet complete. The EPRI report states that, Based on the initial proposed schedule, it is anticipated by the end of 2019, data collection and analysis will be completed. It goes on to state that this data and analysis will be used to develop guidelines for sister pool criteria and potentially for water chemistry and coupon analysis. The EPRI report proposes a schedule that shows the development of guidelines for sister pool criteria and documentation that will occur in 2020.

During this time, the EPRI program may change, based on interactions with stakeholders and the further analysis described in the report. However, the report provides the staff with the information required to satisfy, in part, the request in GL 2016-01 at this time by providing data to show that there is currently no gross degradation of Boral that would pose an immediate safety concern. Additionally, because of the margins determined by the sensitivity studies in EPRI Technical Report No. 3002013119 for the maximum blister and pit dimensions collected to date through the program described in EPRI Technical Update Report No. 3002013122, the staff does not believe there is an immediate safety concern based on previously observed degradation. The calculations performed show that criticality impacts from known degradation mechanisms will be relatively small. These results were a significant factor in the staffs determination that no additional information or regulatory actions are required as part of GL 2016-01. However, the development and application of appropriate sister pool criteria or implementation of a coupon/in situ monitoring program are important in ensuring that licensees monitor and manage Boral material degradation in the future.

EPRI Technical Update Report No. 3002013122 and EPRI Technical Report No. 3002013119 neither constitute nor should be considered as a technical basis for a license amendment request (LAR) because the reports have not received a quality assurance review commensurate with the expectations for an LAR. Nevertheless, the NRC staffs evaluation concludes that the EPRI reports adequately address the information needs requested in GL 2016-01 and demonstrate that no immediate safety concern exists at this time. Therefore, the staff determined that no additional regulatory action is required at this time.

The EPRI reports were fleet wide evaluations, not plant specific. The uncertainties, conservatisms, models, or assumptions used in the evaluations do not apply equally to all plants in the fleet. Therefore, the results of the analyses or any part of those analyses may be inappropriate for site-specific justification of equipment operability, design-basis changes, or licensing changes outside of a formal LAR under 10 CFR 50.90, Application for Amendment of License, Construction Permit, or Early Site Permit, subject to a separate review by the NRC.

As previously discussed, Susquehanna Nuclear, LLC, provided information on a site-specific criticality evaluation performed to conservatively address the operating experience identified at Susquehanna. In particular, Scenario 2 demonstrates that, even under a very conservative scenario in which all moderator is removed from the poison can/fuel channel gap in the model used in the Susquehanna NCS AOR, the maximum k-effective would still be maintained below NRC subcriticality limits. The NRC found that this response adequately addressed the issues discussed in GL 2016-01; therefore, no further regulatory action is required at this time.

SUMMARY

OF LICENSEE RESPONSES TO GL 2016-01 Based on the licensees responses to GL 2016-01, the NRC staff determined that all neutron-absorbing materials could be sorted into four bins based on how the issues in GL 2016-01 were dispositioned, as follows:

• The abbreviated response was acceptable based on the licensee having correctly screening out as Category 1, 2, or 3.

GL 2016-01 provided screening criteria that licensees could use to determine whether they needed to provide a detailed response. The NRC staff developed these screening criteria to identify specific situations in which the burden of providing the information requested in the GL would not be commensurate with its contribution to resolving the long-term issues documented in the GL. Category 1 addresses the obvious situation in which a licensee does not credit neutron-absorbing materials to meet NRC subcriticality requirements; therefore, no monitoring is necessary. Category 2 addresses the special situation in which a licensee intends to implement an approved license amendment in the near future, which would remove credit for an existing neutron-absorbing material.

The NRC staff sees limited value to requesting information related to a neutron-absorbing material that will soon have no relevance to regulatory compliance.

Finally, Category 3 addresses cases in which licensees obtained approval for a license amendment related to SFP criticality and explicitly captured the neutron-absorbing material monitoring program in their license through a license condition or technical specification change. In these cases, the licensee would have submitted consistent information with that being requested in GL 2016-01 to justify the proposed license amendment. Furthermore, the TS program or license condition would mean that the licensee would not be able to make a significant revision to its monitoring program without submitting it to the NRC for explicit review and approval. Therefore, the NRC staff has confidence that the technical basis for the monitoring program would remain the same as that previously reviewed and approved by the NRC.

• The evaluation of the information in the GL 2016-01 response or license renewal application led to a conclusion that the licensees monitoring program is effective for neutron-absorbing material and that the licensee is adequately managing any known degradation or deformation.

In all but one case, for licensees in this bin, the NRC staff found that the information provided by the licensees demonstrated that they have the following key elements for an effective monitoring program and that they are adequately managing any identified deformation or degradation of their neutron-absorbing materials:

- neutron attenuation testing of in situ material or representative coupons

- established processes to ensure that the licensees will take the appropriate corrective actions if any potentially nonconforming material is discovered

- a testing frequency consistent with NRC guidance such as NEI 2016-03 and NUREG-1802 (the GALL Report)

- acceptance criteria to ensure maintenance of the 5-percent subcriticality margin for the SFP, which is typically based on confirming the continuing validity of specific assumptions in the NCS AOR such as a minimum boron-10 areal density or an assumed maximum degradation In one case, at Millstone Power Station (Millstone), Unit 2, the licensee stated that it only performs visual inspections (i.e., no neutron attenuation testing). This case is special because the neutron-absorbing material credited for criticality safety is borated stainless steel rodlets that are inserted into specific guide tubes of the fuel assemblies stored in the SFP. The stainless steel is very similar to materials that withstand the much higher neutron flux near the operating reactor core with no significant material degradation or loss.

The license amendment dated June 23, 2016 (ADAMS Accession No. ML16003A008),

notes that intergranular corrosion resistance of borated stainless steel exposed to acidic conditions decreases with increased boron content and that long-term tests with borated stainless steel indicate that no measurable corrosion effects take place in the SFP environment. Therefore, any meaningful corrosion degradation of poison rodlets will not likely occur during their service life. However, to assure that, at all times, there is enough poison material for reactivity control, the licensee maintains a program for surveillance and inspection of the rodlets. This surveillance program, at 5-year intervals, will have 1 percent of the rodlets visually inspected for any material degradation.

Currently, 27 rodlets, which have been in continuous use at Millstone Unit 2 since their installation in 1994, are designated as surveillance rodlets. These rodlets are reinspected during subsequent periods to permit trending.

• The evaluation of the information in the responses to GL 2016-01, along with supporting references to the EPRI reports, led to a conclusion that licensees did not have an effective site-specific monitoring program; however, the information was sufficient to find reasonable assurance that there is no significant safety concern.

The Evaluation of Generic Responses to Requests for Addition Information above documents the staffs considerations in reviewing the EPRI reports. The use of operating experience from surrogate SFPs, as described in the EPRI documentation, does not meet the minimum standards described in NRC guidance (e.g., NEI 2016-03, NUREG-1802 (the GALL Report)). In addition, the criticality studies performed by EPRI have limitations in their applicability to specific SFPs. However, the information provided shows that, for all identified operating experience with Boral deformation, the criticality impact would be expected to be very small. Additional operating experience will be collected by EPRI and considered for applicability to SFPs that do not have site-specific monitoring programs. For this reason, the NRC staff finds that reasonable assurance exists that the known material deformation issues for Boral do not have a significant criticality impact and that existing site-specific monitoring programs would most likely identify any new, widespread issues. Long-term concerns exist with regard to applicability of the EPRI studies if the Boral material deformation continues to become

worse and with regard to the robustness of the surrogate SFP approach to ensure that adequate data exist to verify the condition of the Boral in an SFP with no site-specific monitoring program. The NRC staff expects that these concerns will be addressed as part of future licensing actions (i.e., subsequent license renewals or license amendments).

• The evaluation of the information in the GL 2016-01 responses indicates that the neutron-absorbing material is currently nonconforming and that the licensee has implemented short-term corrective actions to address immediate safety concerns and plans to implement additional corrective actions to resolve the long-term safety concerns.

At the time that they submitted their responses to GL 2016-01, seven licensees were still crediting Boraflex in their SFPs, which is known to be degrading and, in most cases, has degraded beyond the assumptions of their NCS AORs. The GL 2016-01 responses, license renewal applications, or other available documents for these licensees confirm that the licensees corrective action programs have open corrective actions to address the inconsistency between the plant licensing basis and the actual state of affairs. Three of these licensees have already submitted LARs that will update the licensing basis for their sites (Indian Point Nuclear Generating Station, Shearon Harris Nuclear Power Plant, and Nine Mile Point Nuclear Station) to remove credit for Boraflex. Two more licensees have had presubmittal meetings with the NRC staff and plan to submit an LAR for their sites (Fermi and River Bend Station) in the near future to remove credit for Boraflex. The NRC staff has conducted inspections at the two remaining sites (Oyster Creek Nuclear Generating Station and Pilgrim Nuclear Power Station) to verify that the interim corrective actions are adequate and will continue oversight activities to ensure that they are implementing long-term corrective actions. The NRC staff will continue to use inspection and oversight activities, as needed, to ensure that the licensees are continuing to implement a long-term resolution of the Boraflex degradation issues.

Based on the results of the review and the various interactions with different industry groups, the NRC has determined that the licensees have made significant improvement on issues involving the monitoring of neutron-absorbing material in SFPs and the management of any identified degradation or deformation. In light of this improvement, the NRC concludes that reasonable assurance exists that SFPs can continue to operate safely while the NRC and industry continue to address the remaining long-term issues.

FOLLOWUP ACTIONS As discussed above, significant progress has been achieved in clarifying and addressing the issues identified in GL 2016-01. The NRC staff has received and evaluated the required responses and has completed its review of GL 2016-01. Based on its review of the responses to GL 2016-01, the NRC staff determined that some additional regulatory action is required, as stated in list item 2 under Purpose in GL 2016-01. The NRC will do the following to ensure that licensees continue to adequately monitor and manage neutron-absorbing materials credited for criticality control in SFPs:

• Support the regions in conducting inspections, as needed, to confirm that the corrective actions being taken to manage Boraflex degradation are adequate.

• Address the long-term acceptability of licensee monitoring programs, as needed, as part of future aging management program reviews and oversight.

• Continue to engage with industry through the EPRI Neutron Absorber Users Group to stay abreast of industry operating experience and research involving the condition of neutron-absorbing materials installed in SFPs, including the continued development and use of the EPRI program established to monitor industrywide operating experience.