Shielding Characteristics of Neutron-Shielding Materials in a Cask Structure

Many shielding experiments and analyses have been reported on the shielding effect of materials, and some benchmark or mock-up experiments have been carried out to examine the shielding effects of the specified materials. However, there is no systematic experiment or analysis on the shielding assessment of the materials. The systematic shielding assessment consists of evaluating not only the shielding effects of the material alone but also the effects of combination with other materials and constructing the optimum shielding arrangement with structural materials. In a spent-fuel shipping cask shielding materials are not used alone but are employed with constructional materials such as steel or stainless steel. Accordingly, it is important to investigate the shielding effects not only for the material but also for an arrangement with other materials. Furthermore, the construction of the shielding optimization bring the weight-mitigation of a fabric. Prior to the present work, Ueki and Nam.ito carried out the shielding experiments using iron and polyethylene shields with a 252Cf neutron source to fmd an optimum arrangement to minimize neutron and total dose-equivalent rates (Ueki and Nam.ito, 1987, 1989). The total dose-equivalent rate is composed of neutron and secondary gamma-rays. In this study, the three types of experiments are proposed as a systematic shielding effect of neutron shielding materials. Type 1 is for each shielding material alone, Type 2 is the combination of a neutron shielding material and a structural material, and Type 3 is to constructing the shielding optimization with the materials used in the Type 2 experiment. Especially, due to carry out the Type 2 experiment and analyze it by the Monte Carlo calculation, the acceleration effect of the structural materials, such as steel or stainless steel, which is located to the source side is cleared to the shielding materials located to the detector side.