Jeremy L. Dillon
RW Monitor
6/13/2014
The Nuclear Waste Technical Review Board is calling on the Department of Energy to increase the scope and analyses in its test plan for its upcoming study on high burnup spent nuclear fuel in dry cask storage. The Department’s study is aimed to better understand the effects of high burn-up fuel aging on dry storage cask systems and to support DOE’s ongoing research and development to advance understanding of the long-term aging of spent fuel, but the NWTRB feels the project could be doing more. “The Board supports DOE efforts to begin monitoring the condition of SNF and storage systems sooner rather than later,” NWTRB Chairman Rodney Ewing wrote in a June 5 letter to Assistant Energy Secretary for Nuclear Energy Pete Lyons.
One of the NWTRB’s recommendations called for an increase in test casks. The original plan calls for a single cask demonstration, but the Board argued that more casks would provide additional data. “The Board agrees and believes that using a statistically meaningful number of tests—as opposed to the single cask demonstration included in the CDP—would provide additional data and confidence in the results,” the Board’s letter says. The additional demonstrations would also enable different tests to be performed at different time frames in the storage period, the Board said, which could allow for more sophisticated technology to emerge to better test the results for some casks that would be scheduled to be opened later in the test program.
The Board also called for more extensive testing of the casks and fuel while it sits in storage. The original plan only calls for regular testing of cask temperature, inter-seal temperature, and external dose rates during storage, with gas pressure measurements and sampling only occurring during the two weeks after the cask had been de-watered and prepared for ISFSI storage. The Board, though, would like to see continuous monitoring of these measurements so a better understanding of the rate of change properties of the high burnup spent nuclear fuel could be reached. This can be accomplished, the Board said, by incorporating more instrumentation that measure “advanced parameters” into the cask/cask lid when the spent fuel is loaded. “In particular, the Board recommends the utilization or development of instrumentation that can be installed in or attached to the canister when the SNF is loaded,” the letter says. “This would allow the monitoring of the condition of the SNF and the storage system during extended storage and subsequent transportation.”
The test plan calls for the periodic temperature measurement of high burnup fuel from a dry cask storage container. A TN-32 bolted lid cask will be loaded with intact, high burnup SNF with three different kinds of cladding at Dominion Virginia Power’s North Anna Power Station and then transported to the Idaho National Laboratory. The TN-32 lid will be modified to allow insertion of temperature probes inside the cask at various axial and radial locations, and cask cavity gas samples will be obtained while in a monitored area controlled for potential radiological release, the plan said. Researchers will also examine two dozen spent fuel rods before they are placed in the cask to determine the changes that occur over long-term storage. After the casks have been dried correctly, the researchers will move it to the ISFSI pad, where it will be stored for a decade. The test plan calls for the project to put the spent fuel in the dry cask storage in 2017.
