Distribution and behaviour of 233 Pa in 2LiF-BeF 2 molten salt.

Distribution and behavior of 233 Pa, essential in the thorium-uranium nuclear fuel cycle, were studied in 2LiF-BeF 2 (66 : 34 mole%, FLiBe) molten salt by γ-ray spectrometry. The experiments showed that 233 Pa deposited slightly on the surface of graphite crucible. The addition of Hastelloy and metallic lithium decreased the 233 Pa specific activity in the salt by 1 to 2 orders of magnitude rapidly. Analysis indicated that reductive deposition of 233 Pa was responsible for the rapid decrease of 233 Pa specific activity in the salt. Additional experiments strongly supported the mechanism of reductive deposition of 233 Pa induced by Hastelloy and metallic lithium. In view of the large deposition of 233 Pa on Hastelloy, the possible influence of fissile nuclide 233 U produced from 233 Pa decay on the operation of thorium-based molten salt reactor was discussed.