EVALUATION OF NEUTRON SHIELDING MATERIALS, TN VYAL BTM AND KOBESH EPRTM RESIN FOR INTERIM STORAGE CASKS

Neutron shielding materials which used for interim storage casks are required to have an excellent neutron shielding performance and long-term stability such as heat and radiation resistances. The evaluations of stabilities against these conditions are necessary in order to reflect these characteristics into the designs of interim storage casks. Therefore, a series of tests of neutron shielding materials, TN Vyal BTM and Kobesh EPRTM resins are performed. TN Vyal BTM is vinylester based resin developed by TN International, and Kobesh EPRTM is EthylenePropylene-Rubber (EPR) based developed by Kobe Steel, Ltd. The long-term heating tests up to 10,000hours are performed to estimate weight losses of both TN Vyal BTM and Kobesh EPRTM after 60 years storage by using Larson-Miller Parameter and Arrhenius equation. The heating tests in sealed condition are performed to estimate pressures after 60 years storage in resin areas considering the case of safety valves which release gas pressure are not set. Gas analyses of emitted gas indicate that the main component is carbon dioxide. Ion chromatography of emitted gas also indicates that the amount of acids in emitted gases such as formic acid, acetic acid and sulphuric acid are negligible. It is also confirmed that gamma-irradiation have no or negligible influence on weight loss or appearance of heated resins. The figure of TG-DTA indicates that these resins are stable up to approximately 230°C in both TN Vyal BTM and Kobesh EPRTM in the short term. From the results of these tests, it is proved that these neutron shielding materials, TN Vyal BTM and Kobesh EPRTM resins have excellent thermal and anti-gamma-irradiation properties. These data are also used for the design and safety analysis of our casks to confirm the safety during long-term storage and transport.