Distribution and behaviour of 233Pa in 2LiF–BeF2 molten salt

Abstract

Distribution and behavior of ²³³Pa, essential in the thorium–uranium nuclear fuel cycle, were studied in 2LiF–BeF₂ (66 : 34 mole%, FLiBe) molten salt by γ-ray spectrometry. The experiments showed that ²³³Pa deposited slightly on the surface of graphite crucible. The addition of Hastelloy and metallic lithium decreased the ²³³Pa specific activity in the salt by 1 to 2 orders of magnitude rapidly. Analysis indicated that reductive deposition of ²³³Pa was responsible for the rapid decrease of ²³³Pa specific activity in the salt. Additional experiments strongly supported the mechanism of reductive deposition of ²³³Pa induced by Hastelloy and metallic lithium. In view of the large deposition of ²³³Pa on Hastelloy, the possible influence of fissile nuclide ²³³U produced from ²³³Pa decay on the operation of thorium-based molten salt reactor was discussed.