A Study On Neutronics Characteristics For The Core Of Thorium Molten Salt Reactor

As the only liquid fuelled reactor of Gen-IV, molten salt reactor not only has the advantages which the solid fuelled reactors lack, but also may lead the way to modularization and miniaturization. Nowadays, the research of the molten salt reactor in our country stays at the phase of preliminary core design, which the neutronic characteristics and the thermal-hydraulics of a specific core should be the primacy to figure out. A core protype of the molten salt reactor which had been raised by L. Mathieu et al. and its neutronics characteristics will be discussed and optimized in this paper.Neutronics characteristics of a reactor mainly depend on the distribution of neutron fluxes. For instance, the reaction rate in certain cell equals the multiple integration of the product of flux density and micro fission cross section in phase space. To calculate this integration, the Deterministic Methods and Monte Carlo Method are generally used. However, for the Deterministic Methods, multiple dimensions integration makes the solving process too complex, but the Monte Carlo Method can make the solving process simpler.Therefore, in this paper, the Monte Carlo Method is settled down the neutronics characteristics of the molten salt reactor which burns 233U. The results show that the graphite matrix which the channels distribute homogenously results in awful neutronics characteristics, thus the inhomogeneous ditribution would be prefered. Based on an overall consideration of various factors, the optimized inhomogeneous ditribution plan should be:On condition that keeping the total salt volume of the core constant, enlarging the size of the radius of the most interior channels while reducing that of the most external channels. By this way, better neutronics characteristics would be acquired.Besides, we build a dynamic model to observe the impact of the thermal neutrons capture of 233Pa on 232Th-233U conversion. This model displays the change of the content of 233Pa in salt over time on condition that the power density and the neutron flux distribution are constant and no 232Th supplyment. The results show that the existence of 233Pa affects very little on 232Th-233U conversion during an acceptable operating time (at least 900 days).