DEMONSTRATION OF THE SAFETY OF SPENT FUEL TRANSPORT CASKS UNDER REGULATORY TESTS AND REALISTICALLY SEVERE ACCIDENT

ABSTRACT The objective of this paper is to demonstrate that casks (NFT type) transporting high burn-up spent fuel not only meet the regulatory requirements, but also keep their integrity in an event of realistically severe accident. A regulatory 9-m drop test using a full-scale model of NFT-14P cask had been carried out. On the other hand, a drop test of a full-scale model of NFT-32B cask was carried out simulating a realistic drop accident during unloading work at a harbor. The cask with skid was dropped from a height of 7.8-m onto a concrete floor. This would be the most realistically severe accident during transport of spent fuel in Japan. In both cases, it was ascertained that these two casks were found sound according to the results of tests and analyses on the stresses generated in these tests. In addition, it was recognized by measurements and analyses that the stresses generated under the regulatory drop test of NFT-14P cask gave larger values compared with those generated under the accidental drop. A regulatory fire test (800 degrees in Celsius for 30 minutes) using a full-scale model of NFT-14P cask had been carried out after the 9-m drop test. On the other hand, an analysis was conducted for the NFT-14P cask subjected to a realistic fire accident due to a collision with a tank truck, which was selected as a realistically severe accident during the transport. It was ascertained that in both cases the cask was found sound according to the results of the test and analysis on the temperatures developed in the cask. It was also recognized that the maximum temperature of a sealed boundary at the cask lid reached a more stringent temperature under the regulatory fire test than that under the realistic fire accident. It was ascertained that the high burn-up spent fuel cask NFT-14P was found sound under the regulatory drop and fire tests and realistically severe accident in Japan. Furthermore, it was recognized that the regulatory drop and fire test dominate realistically severe accidents in Japan.