Radioactivation analysis of a concrete wall in a high-energy electron accelerator facility

The high-energy electron accelerator facilities for free-electron laser (FEL) generators at Osaka University have been in operation since 1994. The main operations of the accelerators almost ended in 2001. Therefore, decommissioning of the facility has been considered, although there is a problem with radioactive materials. In addition to the activation of the accelerator body, activation of the building is a serious problem. In this study, the radioactivation of a concrete wall in an accelerator room was investigated. Core samples of the concrete wall were collected at certain positions, and their radionuclides were determined using gamma-ray spectrometry. Gamma-ray spectrometry revealed that the major radionuclides were 22Na, 60Co, and 152Eu. The amount of 55Fe was analyzed using liquid scintillation counting. The radioactivity estimated using the nuclear particle transport simulation code was approximately consistent with the results of the radioactivity measurements for 22Na, 55Fe, 60Co, and 152Eu. The amount of 3H was measured by 3H sampling and liquid scintillation counting. The 3H amount was found to be considerably smaller than the amount estimated using the simulation code probability, owing to diffusion in concrete. These results reveal the radioactivity issues in the facility and are expected to aid in its decommissioning.