Distribution and behavior of fission product 95Nb in FLiBe salt

Abstract The 235,238 UF 4 was irradiated by photo-neutrons, distribution and behavior of the fission product 95 Nb from irradiated 235,238 UF 4 in FLiBe salt were investigated by the measurement of its activity in the salt with the γ-ray spectroscopy. The experiments indicated that a part of 95 Nb deposited on the surfaces of graphite and Hastelloy, as the moderator and the structural materials of molten salt reactor (MSR), respectively, and the majority of 95 Nb maintained in molten salt. Addition of lithium metal made 95 Nb in salt to be reduced and settled, leading to the decrease in its activity. Degree of the decrease was found to be correlated with niobium concentration. The experimental results supported the statement proposed early by ORNL, that 95 Nb might be used as a redox indicator for MSR. Finally, the problem met with on-site monitoring for redox potential in MSR was pointed, and a possible protocol to resolve the problem was proposed.