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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