DEVELOPMENTS ON MSF CASK FOR TRANSPORT AND STORAGE OF SPENT NUCLEAR FUEL

Cask system for interim storage of spent nuclear fuel (SNF) should have sufficient integrity to comply with both transport and storage regulations. In recent years, cask for higher burnup and shorter cooling time SNFs are needed and economization of interim storage is an important issue as well as its safety. The following developments for the MSF cask fleet have targeted on improving its safety and reducing its manufacturing cost. SUBCRITICALITY AND HEAT DISSIPATION New boron containing aluminum alloys manufactured with powder metallurgy process have been developed for basket materials of the MSF cask. The aluminum alloys have high boron content, homogeneous boron distribution, higher toughness and sufficient strength for long-term service. One of the alloys has been registered as ASME Code Case N-673. The other added mechanical alloy process has higher strength at high basket temperature. The alloys can be formed into various shaped basket assembly parts by hot extrusion, such as square tubes and rectangular hollow plates. SHIELDING MHI has developed a new neutron shielding material ®, which has high-temperature stability for long-term service. The material is made of epoxy based resin and filler for refractory. The mixing and filling up facility for the material has also been developed to save manufacturing cost and to improve quality control. CONTAINMENT AND STRUCTURAL INTEGRITY The monolithic forging method that forms a cask body shell with its bottom plate in a single process has been developed under joint project with JCFC. This method allows reduction of the manufacturing steps and elimination of structural evaluation and inspections for a plate-to-cylinder weld line. MHI also improved forging low alloy steel based on ASTM A350 which has sufficient fracture toughness and strength under service conditions. Based on the IAEA regulations, MHI has performed various in-house drop tests to verify the structural integrity including sealing system performance and impact limiters performance. MHI has also collected a multitude of useful data from drop tests with scale model casks performed by MHI and drop tests with both full size and scale model casks performed by the Bundesanstalt fuer Materialforschung und -pruefung (BAM) in Germany.