Improvement of alpha aerosol monitor for in-situ measurement of airborne radioactive concentration in decommissioning

Tsubota, Yoichi   ; Honda, Fumiya; Yoshida, Masato; Nakagawa, Takahiro ; Tamakuma, Yuki*; Tokonami, Shinji*; Ikeda, Atsushi  

A large amount of radioactive aerosols are expected to be dispersed fuel during debris cutting during large-scale retrieval of fuel debris at the Fukushima Daiichi Nuclear Power Plant (1F) and dismantling of nuclear fuel attachments during decommissioning of nuclear fuel facilities. Particulates containing -nuclides (-aerosols) in particular have very high effective dose coefficients upon inhalation, therefore appropriate control and measurements are required. Conventional dust monitors using SSBD have difficulties with moisture resistance, noise resistance, and clogging of filter paper. We have designed and prototyped an -aerosol monitor that directly measures -rays from aerosols using a scintillator and a multi-channel photomultiplier tube after drying the aerosols by heating the flat channel inlet without using a collecting filter paper in order to realize monitoring near the point where highly concentrated -aerosols are generated. In this presentation, we report on the results of basic performance evaluations, the change in particle size due to air drying, and the improvement of the power supply method of the detection unit for on-site implementation at 1F.