Current Progress in Standardization of Shielding Concrete Composition for Japanese Facility Design

The working group on shielding materials under the Standards Committee of the Atomic Energy Society of Japan has been studying the standard composition of shielding concrete that has a clear basis for use in the design of Japanese facilities. The policy for determining the composition, the procedure of study, the results obtained to date, and future tasks are described. Concrete is broadly classified into silicon type and calcium type depending on the aggregate. The reference mix design and composition were selected from the Japanese recommendation, and minor elements in the composition were replaced with silicon and calcium while preserving their weight in order to reduce regional differences. However, the penetration dose calculation for ²³⁵U thermal fission neutrons indicated that iron and carbon should be retained. The penetration dose calculations for photons from ²³⁵U prompt fission and radioisotopes showed that the attenuation ratios of silicon-type and calcium-type concretes differ in the energy region where electron pair production becomes dominant. The water content of concrete was found to vary with thickness as a result of moisture migration analysis over time. Finally, a draft composition of silicon-type concrete by thickness was determined using the residual water content at 60 years after placement. A method for correcting the elemental content under different mix conditions was also proposed.