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.