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Low-activation multilayer shielding structure of light water reactor has been designed using various types (1/10, 1/100, 1/1,000 and 1/10,000) of low-activation concrete composed of low-activation raw materials. The term "1/10 of low-activation concrete" denotes that the activity reduction rate to ordinary concrete is designed to be 1/10. As an example, iterative calculations of induced activities and Di/Ci (Di: concentration of radionuclide i, Ci: clearance level of radionuclide i) values of multilayer model for the Japan Power Demonstration Reactor (JPDR) have been performed by using a discrete ordinate code. It is concluded that most of the shielding concrete of JPDR would be classified below clearance level on decommissioning by adopting such low-activation multilayer shielding structures.

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In order to solve the situation laying contaminated soils beside children on a daily basis, two types of shielding concrete pods and two levels of the contaminated soil with radioactive cesium were prepared. First concrete pod was made by special heavy concrete with the density of 4.57 g/cm 3 , which were developed by using special iron balls and developed mixture tables. Second pod was made by recycled concrete consisted of aggregate from collapsed building in Miyagi with density of 2.13 g/cm 3 . Two pods were cylindrical shapes with diameters of 0.5 m and 0.7 m, and with heights of 0.6 m and 0.8 m, respectively. These pods can contained 28 liters of contaminated soils (diameter of 0.25 m and height of 0.4 m) and designed same shielding effect in the beginning stage. Dose rates were measured from two sorts of contaminated soil samples with heavy concrete pod, recycled concrete pod, and themselves (without shielding) in Fukushima by the survey meter, which was calibrated by 137 Cs standard source. On the other hand, Monte Carlo simulations by MCNP4C2 were carried out for two sorts of contained soils and two types of manufactured concrete pods. The simulations gave good agreements with measured results and therefore the accuracy of the simulation was confirmed. So, some investigational optimization calculations were performed.