SUBJECTS Light water reactor fuel I High-level radioactive waste management TOPICS Spent-fuel storage Thermal hydraulics models AUDIENCE Fuels engineers I R&D scientists Heat transfer Shielding Testing and Analyses of the TN-24P PWR Spent-Fuel Dry Storage Cask Loaded With Consolidated Fuel Full-scale testing has confirmed that the TN-24P storage cask offers a technically sound and practical method for storing consolidated spent fuel. COBRA-SFS code predictions of cask performance at conditions near its design limits agreed very well with actual test data. BACKGROUND As at-reactor storage basins attain maximum capacity, many utilities are expected to implement dry spent-fuel storage systems. To demonstrate the storage of dry spent fuel in large metal casks, EPRI and DOE have sponsored tests of metal casks loaded with unconsolidated fuel at the Idaho National Engineering Laboratory (INEL). This most recent study was initiated to investigate a TN-24P cask containing consolidated fuel. OBJECTIVES To demonstrate the thermal, shielding, and operational performance of the TN-24P cask loaded with consolidated spent nuclear fuel; to assess the ability of the COBRA-SFS heat transfer code (developed by Pacific Northwest Laboratory) to model the cask system and predict thermal performance. APPROACH Prior to the testing, the TN-24P cask contained 24 unconsolidated PWR assemblies from Virginia Power's Surry nuclear power station. The project team replaced the assemblies with 24 canisters of spent fuel, consolidated at a ratio of two assemblies per canister. INEL's rod consolidation project provided the filled test canisters. Researchers used the COBRA-SFS computer code to predict cask thermal performance. The team then instrumented and tested the cask in horizontal and vertical positions with three internal storage environments (nitrogen, helium, and vacuum). They compared the COBRA-SFS predictions with actual test data, refined the code to reflect test results, and performed posttest predictions. Transnuclear, Inc., the cask manufacturer, sponsored an additional test to simulate the insulating influence of impact limiters. RESULTS The TN-24P cask is well suited to store consolidated spent fuel. Its heat transfer performance was exceptionally good, as peak cladding temperatures for a cask heat load of 23.3 kW were well under 300°C with helium, ORDERING INFORMATION Requests for copies of this report should be directed to Research Reports Center (ARC), Box 50490, Palo Alto, CA 94303, (415) 965-4081. There is no charge for reports requested by EPRI member utilities and affiliates, U.S. utility associations, U.S. government agencies (federal, state, and local), media, and foreign organizations with which EPRI has an information exchange agreement. On request, ARC will send a catalog of EPRI reports.

No abstract

No abstract

Initially, casks for dry storage of spent fuel were licensed for assembly-average burnup of about 35 GWd/MTU. Over the last two decades, the discharge burnup of fuel has increased steadily and now exceeds 45 GWd/MTU. With spent fuel burnups approaching the licensing limits (peak rod burnup of 62 GWd/MTU for pressurized water reactor fuel) and some lead test assemblies being burned beyond this limit, the need was identified for a confirmatory dry storage demonstration program after the U.S. Nuclear Regulatory Commission (NRC) published their Interim Staff Guidance 11 (ISG-11) in May 1999. With the publication of the second revision of ISG-11 in July 2002, the desirability for such a program further increased to obtain confirmatory data about the potential changes in cladding mechanical properties induced by dry storage, which would have implications to the transportation, handling, and disposal of high-burnup spent fuel. While dry storage licenses have kept pace with reactor discharge burnups, transportation licenses have not-and are considered on a case by case basis. Therefore, this feasibility study was performed to examine the options available for conducting a confirmatory experimental program supporting the dry storage, transportation, and disposal of spent nuclear fuel with burnups well in excess of 45 GWd/MTU. Summary x has a policy, because of an agreement with the State of Idaho, that prohibits spent fuel being brought into and residing in the state for >5 years, which is not commensurate with the needs of the demonstration program. Estimated costs and schedule for the three options are provided in Table S-1. The options are estimated to run from 5 to 12 years with destructive post-irradiation examinations (PIEs)

Research studies by the Electric Power Research Institute (EPRI) established the technical and operational requirements necessary to enable the onsite cask-to-cask dry transfer of spent nuclear fuel. Use of the dry transfer system has the potential to permit shutdown reactor sites to decommission pools and provide the capability of transferring assemblies from storage casks or small transportation casks to sealed transportable canisters. Following an evaluation by the Department of Energy (DOE) and the National Academy of Sciences, a cooperative program was established between DOE and EPRI, which led to the cost-shared design of a dry transfer system (DTS). EPRI used Transnuclear, Inc., of Hawthorne, New York, to design the DTS in accordance with the technical and quality assurance requirements of the code of Federal Regulations, Title 10, Part 72 (10CFR72). EPRI delivered the final design report to DOE in 1995 and the DTS topical safety analysis report (TSAR) in 1996. DOE submitted the TSAR to the United States Nuclear Regulatory Commission (NRC) for review under 10CFR72 and requested that the NRC staff evaluate the TSAR and issue a Safety Evaluation Report (SER) that could be used and referenced by an applicant seeking a site-specific license for the construction and operation of a DTS. DOE also initiated a cold demonstration of major subsystem prototypes in 1996. After careful assessment, the NRC agreed that the DTS concept has merit. However, because the TSAR was not site-specific and was lacking some detailed information required for a complete review, the NRC decided to issue an Assessment Report (AR) rather than a SER. This was issued in November 2000. Additional information that must be included in a future site-specific Safety Analysis Report for the DTS is identified in the AR. The DTS consists of three major sections: a Preparation Area, a Lower Access Area, and a Transfer Confinement Area. The Preparation Area is a sheet metal building where casks are prepared for loading, unloading, or shipment. The Preparation Area adjoins the Lower Access Area and is separated from the Lower Access Area by a large shielded door. The Lower Access Area and Transfer Confinement Area are contained within concrete walls approximately three feet thick. These are the areas where the casks are located and where the fuel is moved during transfer operations. A floor containing two portals separates the Lower Access Area and the Transfer Confinement Area. The casks are located below the floor, and the fuel transfer operation occurs above the floor. The cold demonstration of the DTS was successfully conducted at the Idaho National Engineering and Environmental Laboratory (INEEL) as a cooperative effort between the DOE and EPRI. The cold demonstration was limited to the fuel handling equipment, the cask lid handling equipment, and the cask interface system. The demonstration included recovery operations associated with loss of power or off-normal events. The demonstration did not include cask receiving and lid handling; cask transport and lifting; vacuum/inerting/leak test; canister welding; decontamination; heating, ventilation, and air conditioning; and radiation monitoring. The demonstration test was designed to deliberately challenge the system and determine whether any specific system operation could adversely impact or jeopardize the operation or safety of any other function or system. All known interlocks were challenged. As in all new systems, there were lessons learned during the operation of the system and a few minor modifications made to ease operations. System modifications were subsequently demonstrated. The demonstration showed that the system operated as expected and provided times for normal fuel transfer operations. The demonstration also showed that recovery could be made from off-normal events.