Reactivity calculation in molten salt reactors with inverse kinetics model

Most molten salt reactor designs present a liquid fuel that, mixed with the coolant composed of molten salts, circulates through the reactor. This circulation introduces important phenomena in the study of reactor physics, thus requiring changes in the existing physical models applied in conventional reactors with solid fuel. One of the main influences of the fuel flow in the reactor is in the delayed neutron precursors’ concentration, which partially decay outside the core, not contributing to the fission chain reaction. In this paper, we investigate the physical models used for this type of reactor, especially the neutron point kinetics, in order to develop an inverse kinetics model, which has practical applications such as core reactivity monitoring. We develop a semi-analytical solution for the proposed model, which is used to solve two transients: a linear variation between power levels, and the determination of criticality regions during a decrease in flow velocity. •Circulation of a fluid fuel influences delayed neutrons precursors (DNP) distribution.•DNP heavily affect the system’s neutron kinetics.•Inverse Point Kinetics model developed for determining reactivity.•Numerical and semi-analytical solutions for obtained model were proposed.