Design Outline of MSF Transportable Storage Casks for Spent Fuels and The First “Type Approval” Experience in Japan

Japanese “Type Approval” license system for a storage cask was institutionalized in 2012 in Japan, which can make a part of storage license certification for a storage cask in advance.MHI applied two types of MSF (MITSUBISHI Spent Fuel) cask in 2015-2016, one of which is type MSF-52B for BWR spent fuel assemblies, the other of which is type MSF-21P for PWR spent fuel assemblies. The MSF cask is a transportable storage cask developed for interim storage of spent fuel assemblies in Japan. It has double lids with metallic gaskets which could have long term containment integrity during storage period. A tertiary lid with elastomer O-rings which could follow up a displacement between lid and body flange will be attached during transport for more safety. MSF-52B/MSF-21P can accommodate 52 BWR/21 PWR spent fuel assemblies with maximum burn-up of 50/48 GWd/t and with cooling period of 12/15 years or more, respectively. Under the new licensing guideline relating to type approval, mainly sub-criticality, shielding, heat removal, containment, structure and long term integrity of materials had been examined and the first type certification was issued for MSF-52B by the Japanese competent authority, Nuclear Regulation Authority (hereinafter called “NRA”).