Fuel neutronic performance of LiF-BeF₂-ThF₄-UF₄ on a small mobile molten salt reactor

The analysis of neutronic performance has been carried out for the molten salt fuel LiF-BeF₂-ThF₄-UF₄ on a Small Mobile-Molten Salt Reactor (SM-SMR). The core configurations and operating temperature should be adjusted in using the new fuel in order to get the calculated k_eff and CR (conversion ratio) are > 1 in the fraction of 0.5% ²³³U, 20% ²³²Th, 28% Li, 51.5% Be. After obtained that k_eff and CR close to 1, then the analysis of changes in the Th to Be and Be to Li are carried out, it indicates the changes of k_eff and CR. Then the ²³³U fraction is varied between 0.5–0.46% to obtain the condition k_eff >1 and CR>1. To determine the temperature coefficient of reactivity (T),the temperature of core is changed about 25 K dan 50 K. To determine the void reactivity coefficient (V), fuel density is reduced to 90%. The result shows that the reduction of Th causes the decrease of CR and increase of k_eff due to the number fertile material is less. The addition of Be to Li will make the k_eff is increase and the CR is decrease, because the macroscopic absorption cross section of Li is greater than Be. From the five ²³³U composition in the ranges 0.5–0.46%, the calculated k_eff and CR varies in the range of 1.00001 – 1.00327 and 1.00016 – 1.00731, respectively. For power peaking factor (PPF), the calculation results give the value in the range of 2.4311 -2.4714. However, for the safety parameters, the negative temperature reactivity coefficient (T) and negative void reactivity CR (V) in the range of 4.972×10^-5 – 5.909×10^-5 and 2.596×10^-2 - 2,8287×10^-2 k/k/K, respectively. It can be concluded that the SM-MSR core has negative value for those reactivity for all fractions, so the core fulfill the safety criteria and inherent safety. (author)