A study on induced activity in the low-activationized concrete for J-PARC

In high power proton accelerator facilities, concrete shield can be highly activated, which makes maintenance work of accelerators quite difficult. So, a low-activationized concrete is planned to be partially adopted as a concrete shield at the accelerator facilities of Japan Proton Accelerator Research Complex (J-PARC) aiming at reducing γ-ray exposure dose during maintenance period. The low-activationized concrete is the one using limestone as an aggregate. A new quantity, ²⁴Na-equivalent, was introduced as a criterion to assure effectiveness of the low-activationized concrete. In order to verify its effectiveness, test samples of both the low-activationized concrete and the ordinary concrete were irradiated using FNS at JAERI. The measurements were analyzed by using a shielding design calculation code system being used for J-PARC, showing that the measurements and the calculations of induced activity are in good agreement within a factor of two. Furthermore, by using the same code system, γ-ray exposure dose was calculated for modeled configuration of J-PARC to find out that γ-ray exposure dose due to the low-activationized concrete was about 10 times lower than that due to the ordinary concrete in a period of less than a few days after operation. (author)