Innovative alpha radioactivity monitor for clearance level inspection based on ionized air transport technology; CFD-simulated and experimental ion transport efficiencies for uranium-attached pipes

Hirata, Yosuke*; Nakahara, Katsuhiko*; Sano, Akira*; Sato, Mitsuyoshi*; Aoyama, Yoshio ; Miyamoto, Yasuaki ; Yamaguchi, Hiromi ; Nambu, Kenichi*; Takahashi, Hiroyuki*; Oda, Akinori*

An innovative alpha radioactivity monitor for clearance level inspection has been developed. This apparatus measures an ion current resulting from air ionization by alpha particles. Ions generated in a measurement chamber of about 1 m in volume are transported by airflow to a sensor and measured. This paper presents computational estimation of the ion transport efficiencies for two pipes with different lengths, the inner surfaces of which were covered with a thin layer of uranium. These ion transport efficiencies were compared with those experimentally obtained for the purpose of validating our model. Good agreement was observed between transport efficiencies from simulations and those experimentally estimated. Dependence of the transport efficiencies on the region of uranium coverage was also examined, based on which such characteristics of ion currents as anticipated errors arising from unknown contaminated positions are also discussed to clarify the effective operation conditions of this monitor.