Impurity evaporation behavior of alkali elements from lead-bismuth eutectic

Yamada, Yuya*; Fujiwara, Takuma*; Miyahara, Shinya*  ; Arita, Yuji*; Sasa, Toshinobu   ; Takei, Hayanori   ; Maekawa, Fujio  ; Obayashi, Hironari  ; Nakano, Keita   

Lead-Bismuth Eutectic (LBE) is a candidate material as a neutron generation target and a coolant in an Accelerator Driven System (ADS) proposed by Japan Atomic Energy Agency (JAEA). In the LBE of ADS, a large amount of radioactive materials is produced as spallation product (SP) via spallation reactions between a proton beam and the LBE. As the results, the LBE is highly activated due to the radioactive SPs. It is important to evaluate the release and transport behavior of the SPs from the LBE coolant to the cover gas from the viewpoints of the radiological hazard both in the cases of normal operation and accident. In the present study, in order to understand the evaporation behavior of Cs and Rb, which are produced in large amounts among alkaline metal elements, from the LBE, the chemical species and vapor pressures were measured using a Knudsen effusion mass spectrometer (KEMS). As the results, Cs and Rb were found to be easily evaporated than LBE.