Distribution And Behaviour Of Pa-233 In 2lif-Bef2 Molten Salt

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