Feasibility Study of Variable Spectrum Molten Salt Reactor by Adjusting Fuel Salt Compositions for the LiF-BeF2-ZrF4-UF4 System

Abstract The Variable Spectrum Molten Salt Reactor (VSMSR) is proposed to produce a variable neutron energy spectrum field in the core. The feasibility of the VSMSR is investigated by adjusting the fuel salt composition for the LiF-BeF2-ZrF4-UF4 quaternary system. The available fuel salt compositions are reviewed on the basis of past thermophysical studies, and the candidate fuel salt compositions are determined. The neutronics analyses are performed to examine the feasibility of VSMSR from the aspects of criticality and neutron energy spectrum. The criticality analyses show that more than 5 mol% UF4 and more than 15 wt% 235U enrichment are necessary to satisfy the criticality criterion, and the fractions of (LiF+ BeF2), as well as the UF4 fraction, have a significant influence on the infinite neutron multiplication factor kinf. Also, the neutron energy spectrum is strongly affected by the fractions of UF4, LiF, and BeF2. The calculated thermal neutron flux below 1.1 eV has a difference of about 104 order among the candidate compositions, and the present study concludes that the adjustment of the fuel salt composition is very applicable to change the neutron energy spectrum of an MSR.