A benchmarked dynamic model of xenon behavior in a molten salt reactor

Abstract

Molten salt reactors are a type of nuclear reactor that are being considered for deployment in the fourth generation nuclear power technology. Molten salt reactors use molten a alkali / actinide halide salt melt at temperatures far in excess of temperatures found in a typical pressurized water reactor. This thesis focuses on graphite moderated reactors with fluoride as the halide. The salt melt, called the fuel salt, is circulated between a moderator and a heat exchanger. While within the moderator, the dissolved actinides undergo fission and generate heat. Among products of nuclear fission is gaseous xenon, and in particular the isotope xenon-135 that acts as a neutron absorber. In solid fueled reactors, the xenon is effectively static and trapped within the fuel matrix. In a molten salt reactor, conversely, the fuel matrix is the mobile, circulating fuel salt that transports the xenon along with the rest of the fuel. This thesis focuses on modeling the behavior of xenon in a molten salt reactor. Existing literature in the field is reviewed and compiled. A model of xenon behavior in a molten salt reactor (the Molten Salt Reactor Experiment in particular) has been developed and the model is presented in this thesis. The model is benchmarked against experimental data using best available data, then minimal necessary justifiable adjustment is made to model parameters in order to fit the model to the experimental data. As a result this model is able to fit two transients, something that no xenon model of the molten salt reactor experiment has been able to do previously.