Activation dose-reduced structures

Purpose: To reduce the activation dose and increase the mechanical strength of shieldings. Constitution: A nuclear reactor is surrounded with a cylindrical first shielding and a plurality of activation dose-reduced structures are secured with no gaps to the inside of the first shielding to constitute the second shielding. The second shielding is formed with activation dose-reduced structures using aggregates composed of lime stones, white cements and fine silica powders. Since the structures contain less mineral ingredients such as Fe, Co, Eu, Mn, etc. forming radioisotope elements upon nuclear reaction with neutrons, the activation dose is extremely low. Accordingly, the exposure dose is reduced upon maintenance and operation of the nuclear reactor thereby enabling safety operation. Further, since fine silica powder is mixed together, the mechanical strength can be improved as well. (Yoshino, Y.)