Distribution and behavior of fission product ⁹⁵Nb in FLiBe salt

Abstract

The 235,238UF4 was irradiated by photo-neutrons, distribution and behavior of the fission product 95Nb from irradiated 235,238UF4 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 95Nb 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 95Nb maintained in molten salt. Addition of lithium metal made 95Nb 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 95Nb 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.

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

“…In our previous work, 9 it was found that the specic activities of the ssion products 131 I, 140 Ba, 140 La, 141 Ce and 143 Ce remained well a constant during a four-day experimental period. As indicated by ORNL, these nuclides belonged to the salt-seeking ssion products, which dissolved quantitatively and existed steadily in molten salt.…”

“…Differently from Pa, the deposition of Nb could reach 16% in a similar condition, as reported in our previous work. 9 It was more or less surprising that the specic activity of 233 Pa underwent greater variation compared with those of actinides mentioned above. As shown in Fig.…”

“…The materials, equipment and methods employed in this work have been described in our previous work. 9 Briey, UF 4 and ThF 4 powders loaded separately in sealed acrylic (polymethyl methacrylate) boxes were irradiated for about 3 days with neutrons source driven by a 15 MeV electron linear accelerator. 10 Aer cooling for about 20 hours, about 0.2 g UF 4 /ThF 4 powder was weighted precisely and mounted on a counting plate for g-spectrum measurement separately to obtain the original inventory of radionuclides.…”

Transient release of radioactive iodine from the fission of UF4 in 2LiF–BeF2 salt

“…A self-designed reaction apparatus placed in a glove box in Ar atmosphere was used to investigate the behavior of iodine, and the detailed description has been reported in our previous works. 10,13,14 A graphite crucible with an inner diameter of 25 mm and a height of 60 mm was used as the reaction crucible.…”

“…Thus, their behavior and dependence on the redox potential, especially for 95 Nb, has become one of the key research objects. 9,10 Iodine isotopes are signicant ssion products because of their high yield and wide mass numbers involved in mass distribution. Moreover, they are also the precursor nuclei both for delayed neutron emitters and neutron poison 135 Xe.…”