Development of a point-kinetics simulator for molten-salt reactors

Abstract

Molten-salt-fueled reactors (MSRs) are nuclear fission reactors that use a mixture of fissile material and molten fluoride salts as both fuel and primary coolant. Such reactors, which can operate at low pressure and high temperature, have been initially proposed in the 1950s and have been the subject of renewed interest and investigations in the last decade. In contrast to regular, fixed-fuel reactors, the dynamic behavior of MSRs is determined by both the fuel properties and by the fact that fuel is constantly flowing in and out of the core, which causes some of the delayed-neutrons to be produced outside the core, thus not contributing to the fission chain. Most of the kinetics codes in current use for power reactors do not have the capability to account for fuel convection (flow). The objective of this work was to develop a point-kinetics code for simulating MSR transient behavior while accounting for fuel convection, with intended applications in education and preliminary studies of MSR conceptual designs. The code was developed in the FORTRAN programming language and uses finite differences to discretize the coupled differential equations. Several MSR-specific transient scenarios are analyzed using the developed code to demonstrate its capabilities, to illustrate how the dynamic behavior of the reactor is influenced by changes in the fuel flow rate, and to study the effect of different precursor-mixing approximations.