2017 Water Reactor Fuel Performance Meeting September 10 (Sun) 14 (Thu), 2017 Ramada Plaza Jeju Jeju Island, Korea

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Extended Storage Collaboration Program for Addressing Long-Term Dry Storage Issues Hatice Akkurt 1 1 Electric Power Research Institute (EPRI), 1300 W WT Harris Blvd, Charlotte, NC 28262, hakkurt@epri.

1 Extended Storage Collaboration Program for Addressing Long-Term Dry Storage Issues Hatice Akkurt 1 1 Electric Power Research Institute (EPRI), 1300 W WT Harris Blvd, Charlotte, NC 28262, hakkurt@epri.com ABSTRACT: With the prospect of spent nuclear fuel being stored at reactor sites for the foreseeable future, the Electric Power Research Institute (EPRI) established the Extended Storage Collaboration Program (ESCP) in 2009 to investigate aging effects and mitigation options for the extended storage and transportation of spent nuclear fuel. The mission of ESCP is to provide the technical bases to ensure continued safe, long-term used fuel storage and future transportability. Since its formation, with only one country and 39 members, ESCP has been growing and currently includes more than 550 members, representing 19 countries. A significant number of organizations and countries participate in ESCP to investigate aging effects and mitigation options for the extended storage and transportation of used nuclear fuel and high level waste (HLW). As ESCP has evolved, a number of subcommittees were established to focus collective resources into smaller groups. Currently, ESCP has six subcommittees: Fuel Assembly Subcommittee, Chlorine-Induced Stress Corrosion Cracking (CISCC) Subcommittee, Non Destructive Evaluation (NDE) Subcommittee, Mitigation and Repair Subcommittee, Thermal Modeling Subcommittee, and International Subcommittee. In this paper, the ESCP and its objectives and activities are presented. KEYWORDS: Used fuel storage; High level waste (HLW); Extended Storage Collaboration Program (ESCP) I. INTRODUCTION As nuclear power reactors were first being constructed in the United States, the initial plan for the nuclear fuel cycle included reprocessing. This led to the construction of relatively small spent fuel pools. When reprocessing was abandoned and the policy was changed to a once-through fuel cycle, utilities were faced with the need for additional storage capacity for spent fuel. Following demonstration of several technologies for increasing storage capacity, dry cask storage of spent fuel emerged as the primary technology. Currently, in the United States alone, used fuel is stored in more than 2500 casks. The initial license period for these casks was 20 years, with some having been extended an additional 40 years, for a total of 60 years in dry storage. However, with the cancellation of the final geological repository and no clear path for the ultimate disposition of spent fuel spent fuel will continue to be stored in dry casks for an extended period of time. As spent fuel remains in dry storage, a number of technical issues are being identified that will need to be addressed for extended storage of spent fuel in dry casks past the renewal period and beyond 60 years. In November 2009, the Electric Power Research Institute (EPRI) hosted a workshop to discuss potential issues associated with extended storage. Based on that workshop, the Extended Storage Collaboration Program (ESCP) was created. A significant number of organizations and countries participate in ESCP to investigate aging effects and mitigation options for the extended storage and transportation of used nuclear fuel and high level waste (HLW). In this paper, the ESCP program and its objectives and activities are presented. II. EXTENDED STORAGE COLLABORATION PROGRAM The ESCP mission is to provide the technical bases to ensure continued safe, long-term used fuel storage and future transportability. The objectives of the ESCP include the following: 1. Bring together U.S. and international organizations engaged with active or planned R&D in the used fuel area and identify the long-term aging issues for maintaining safe wet and dry storage and transportation. 2. Identify options for addressing aging issues such as data collection and analysis and determine potential areas for formal collaborations. 1

2 3. Develop a plan to address aging issues, with the eventual goal of establishing the technical bases for very-longterm storage, followed by plans for transportation and information sharing across organizations and countries. A significant number of organizations and countries participate in ESCP to investigate aging effects and mitigation options for the extended storage and transportation of used nuclear fuel and HLW. Participation in ESCP is voluntary; ESCP does not dictate, instead providing recommendations and guidance for the technical bases. Formal collaborations are performed outside of ESCP. Since its formation in 2009, ESCP has held more than 20 meetings and currently has over 550 members representing ~70 organizations in 19 countries. Participating organizations for each country include utilities, research and development organizations, regulators, national laboratories, and universities. Annually, ESCP conducts one spring meeting and a winter meeting in the United States. Depending on schedules, ESCP aims to conduct an international meeting in conjunction with other meetings and conferences. The data on the behavior of dry storage systems and the spent fuel inside them after some period of dry storage, particularly extended storage, are limited. Therefore, much of the initial work within ESCP was focused on reviewing current knowledge gaps (i.e., the understanding available through existing data on potential degradation mechanisms of dry storage system components). Several organizations, including the U.S. Department of Energy (DOE), Nuclear Regulatory Commission, and EPRI, have performed gap analyses [1-5] to identify areas where additional data and research may be needed to support the technical bases for extended storage of fuel in dry storage casks. Given limited resources and a desire to reach conclusions in a reasonable timeframe, it is necessary to prioritize the gaps. For this purpose, potential degradation mechanisms were identified for the various systems, structures, or components (SSCs), namely, the fuel (in particular, the cladding), cask, concrete overpack, and concrete storage pad. With this background, the various potential degradation mechanisms were evaluated. In order to focus on high priority items, subcommittees were established. In addition to the subcommittees, ESCP also has a steering committee that involves a very limited number of members. The ESCP steering committee evaluates the health and progress of the subcommittees, determining whether there is a need to form a new subcommittee in order to address technical gaps in a specific relevant area or if the objectives of a subcommittee are accomplished. When it is agreed that a subcommittee has completed its defined objectives, it is sunset. III. EXTENDED STORAGE COLLABORATION PROGRAM SUBCOMMITTEES As ESCP has evolved, a number of subcommittees were established to focus collective resources into smaller groups. Currently, ESCP has six subcommittees: 1. Fuel Assembly Subcommittee 2. Chlorine-Induced Stress Corrosion Cracking (CISCC) Subcommittee 3. Non Destructive Evaluation (NDE) Subcommittee 4. Mitigation and Repair Subcommittee 5. Thermal Modeling Subcommittee 6. International Subcommittee The objectives and activities of each subcommittee are described in the following sections. III.A Fuel Assembly Subcommittee The Fuel Assembly Subcommittee is focused on the margins related to the cladding integrity degradation mechanisms. This group focuses on identification of data gaps and recommendations into research programs to identify the higher priority experiments and to provide the type of data most important to a supporting basis for long-term storage of spent fuel in dry casks. The current priorities for this subcommittee include: End-of-life (EOL) PWR gas pressures in high-burnup (HBU) fuel rods Best-estimate cladding and plenum temperatures HBU cladding mechanical properties and failure limits Hydride distribution in as-irradiated cladding 2

3 Assembly materials degradation (e.g., lifting bar) This subcommittee also provides input to a HBU confirmatory data project [6] by reviewing test plans and providing feedback. III.B Chlorine-Induced Stress Corrosion Cracking (CISCC) Subcommittee The CISCC Subcommittee seeks to address the issue of potential stress corrosion cracking (SCC) of the welded stainless steel canisters exposed to salt air. Several studies have been performed on the effect of marine environments on dry storage canisters. These studies have determined it is possible that SCC can occur on the materials used for dry storage canisters; however, the experiments are performed under extreme conditions and will likely lead to overly conservative estimations. What is not well understood are the actual conditions of the canisters in service. SCC of the material is affected by a number of factors such as surface temperature, humidity, distance and elevation from the salt water, airflow, and the concentration of chlorides and other particulates in the air. Led by EPRI, a number of inspections for in-service canisters were performed. Inspections included: visual inspection for signs of corrosion, canister surface temperature distribution, and salt and dust deposition on the canister surfaces (amounts and composition). Other ESCP participants are collecting additional information on the conditions required to initiate general cracking and SCC under more representative conditions. This combined information can then be used to determine which, if any, dry storage canisters may be susceptible to SCC and when they may become susceptible. III.C Non-Destructive Examination (NDE) Subcommittee The NDE Subcommittee is working toward identifying NDE techniques and procedures to monitor the integrity of the cask or canister. The initial focus of this subcommittee was to provide support to the CISCC Subcommittee in developing ways to examine the canisters in marine atmospheres. The NDE Subcommittee has focused on coordinating efforts to develop inspection systems that could be field-deployed. To date, four inspections using robotics have been completed. These inspections were led by EPRI but involved many organizations. This subcommittee also coordinates development of mockups and sharing among members for testing purposes. The NDE Subcommittee is also working toward a collaborative report that is intended to be a snapshot in time of the ongoing efforts across much of the industry to organize collaborations, build representative mockups containing realistic flaws, and develop and deploy NDE equipment and delivery systems to ultimately solve the inspection challenges posed by dry cask storage systems. The report is clearly not all-inclusive of efforts industrywide, but best efforts were made to include as many organizations as possible in this report. Submissions were obtained from 21 different organizations/groups involved in NDE method development and inspection approaches. The report [7] is slated for publication by October III.D Mitigation and Repair Subcommittee The Mitigation and Repair Subcommittee was formed in December Although this subcommittee is tasked with addressing both mitigation and repair activities, the initial focus is on repair, especially given that NDE activities are ahead of schedule and several more inspections are scheduled. The subcommittee is taking a practical approach as opposed to an R&D approach to its work. This is facilitated by the fact that there are multiple current technologies that appear to be good candidates for repair and mitigation. Committee members are closely coordinating with other groups and organizations pursuing complimentary activities, especially to determine activities that can be leveraged to further the efforts of this committee. The committee is putting together a white paper for the identification of current and available candidate technologies for container mitigation and repair. At the moment, there appear to be several good current technologies available. A number of these technologies have already been evaluated and/or even used by committee members, including those from national laboratories and nuclear industry members for other areas (i.e., reactor components). The committee is also working toward establishment of a set of criteria for the screening and eventual selection of best candidate repair and mitigation technologies. Factors include the selection of technologies as well as the following: 1. Consideration of the application in terms of access, location, and configuration to the mitigation and repair area 2. Long-term effectiveness of the repair and mitigation technique 3

4 3. Maturity level of the technology including whether it is a qualified and commercial technology or requires additional work 4. Identification and characterization of potential unintended consequences of applying the technology or specific technique 5. Cost of the technology Based on the identified candidates, the committee will down-select the best technologies and identify actions leading to commercialization for application to demonstration and qualification activities. III.E Thermal Modeling Subcommittee The Thermal Modeling Subcommittee was officially formed in May Analysis for the HBU demonstration project identified that potentially the majority of modeling tools are estimating decay heat values [8]. This has also been confirmed by EPRI s Cask Loader software [9]. The goal of this subcommittee is to perform validation studies and blind tests in order to evaluate the accuracy of the current thermal modeling tools. For this purpose, temperature data will be collected during loading of the HBU confirmation project cask. Modeling will be performed based on specifications prior to data collection, with modeling results compared against measured data. At the conclusion, an EPRI report will be published, expected in Clear benefits of improved thermal models include the following: Support aging management programs Improve operational flexibility Facilitate transportation and ultimate spent fuel disposal III.F International Subcommittee Recognizing that there is a global interest in extended storage and transportation, the ESCP International Subcommittee was established in December 2010 to extend the reach of ESCP internationally in order to fully address extended storage and transportation issues as they apply to different systems, national policies, and regulations worldwide. This subcommittee serves to deepen the overall understanding of degradation mechanisms associated with storage and transportation systems, improve access to data and programs related to extended storage and transportation, and strengthen the overall technical basis for programmatic decisions. The International Subcommittee established three basic objectives: 1. Conduct a technical data gap survey 2. Assess opportunities to leverage specific research that will benefit the larger international group 3. Integrate ESCP work with relevant International Atomic Energy Agency (IAEA) committee work To serve these objectives, the International Subcommittee published a report in 2012 [5], with seven countries and multiple organizations from each country participating. In this report, the technical gaps and priorities that need to be addressed to support licensing activities within each country were identified. Varying types of storage and transportation system designs, national policies and regulations, identified commonalities, and differences emphasize the importance of this work on an international scale. Currently, the International Subcommittee is working on a revised version of this report to update the status of gaps, determine what has been done to date including remaining items with new prioritization, and include new countries. It is anticipated that the updated international data gap report will be published in III.G Previous Subcommittees An earlier subcommittee, the Concrete Subcommittee was focused on addressing the performance of the concrete from an aging management perspective. Concrete degradation was a low priority item from the gap analysis because it is well understood. The goal of this subcommittee was to simply recommend inspection, prevention, and repair methods that are already known and documented, with specific focus on spent fuel storage casks. The Concrete Subcommittee published its findings in an EPRI ESCP report [10]; this subcommittee was sunset in 2015 since its objectives were achieved. 4

5 IV. SUMMARY and CONCLUSIONS Utilities continue to safely store spent nuclear fuel in dry storage founded on a solid understanding of the conditions for the currently licensed period of 20 years, with additional efforts (i.e., aging management plans) to continue safe storage for independent spent fuel installation (ISFSI) license renewal periods of up to 60 years. While it is expected that continued dry storage of spent fuel will remain safe and no degradation mechanisms are anticipated to have a significant impact on safety, there is insufficient data to provide a sound technical basis for extended storage well beyond 60 years. The ESCP is intended to provide this technical basis to ensure safe management of spent fuel in dry storage systems until a permanent disposition path becomes available. ACKNOWLEDGMENTS The author would like to thank ESCP subcommittee chairs, co-chairs, and members for their contributions and efforts toward making ESCP a successful program. REFERENCES 1. Extended Storage Collaboration Program (ESCP) Progress Report and Review of Gap Analyses. EPRI, Palo Alto, CA: Evaluation of the technical basis for extended dry storage and transportation of used nuclear fuel, U.S. Nuclear Waste Technical Review Board (2011). 3. Materials aging issues and aging management for extended storage and transportation of spent nuclear fuel, U.S. Nuclear Regulatory Commission, Washington, D.C. (2011), NUREG/CR Review of Used Nuclear Fuel Storage and Transportation Technical Gap Analyses, FCRD-USED , PNNL Prepared for the U.S. Department of Energy Used Fuel Disposition Campaign, Washington, D.C. (2012). 5. Extended Storage Collaboration Program International Subcommittee Report: International Perspectives on Technical Data Gaps Associated With Extended Storage and Transportation of Used Nuclear Fuel. EPRI, Palo Alto, CA: EPRI High Burnup Dry Storage Cask Research and Development Project Final Test Plan. Electric Power Research Institute, Palo Alto, California. 7. Extended Storage Collaboration Program (ESCP): Nondestructive Evaluation (NDE) Subcommittee Industry Progress Report. EPRI, Palo Alto, CA: A. SCURLOCK, et al., Dry cask storage systems thermal analysis project, Proceedings of International High- Level Radioactive Waste Management (IHLRWM) 2017, Charlotte, NC, April 9 13, B. DISTLER, et al., Comparison of Cask Loader versus ORIGEN Decay Heat Calculation Results, Proceedings of IHLRWM 2017, Charlotte, NC, April 9 13, Degradation Mechanisms and Inspection Techniques for Concrete Structures in Dry Storage Systems for Spent Nuclear Fuel. EPRI, Palo Alto, CA:

INSPECTION AND MONITORING OF DRY CANISTER STORAGE SYSTEMS

INSPECTION AND MONITORING OF DRY CANISTER STORAGE SYSTEMS Jeremy B. Renshaw 1, Shannon Chu 1, John H. Kessler 1, and Keith Waldrop 1 1 Electric Power Research Institute, 1300 West W T Harris Blvd., Charlotte,