مجید حسینلو

Caramel UO2 fuel is a new type of fuel that is suitable for use in high power density research reactors with reduced fuel enrichment. Reducing the thickness and flatness of caramel fuels increases heat transfer and reduces the fuel temperature. The purpose of this study is to investigate the neutronic and thermal-hydraulics properties of caramel fuel. The MCNP nuclear code have been used to analysis the neutronic parameters of caramel fuel and compare it with the neutron parameters of Tehran research reactor. Also, ANSYS engineering software using finite element method (FEM), thermal-hydraulics and mechanical efficiency of caramel fuel has been evaluated. In this research, the important and measurable quantity of neutrons is the study of reactivity and effective multiplication factor of the core of the redesigned open reactor, and in the mechanical analysis of fuel, stress and strain phenomena are obtained. The results obtained from the open reactor designed with caramel fuel have been investigated with the results of Tehran reactor with U3O8-Al fuel. According to the results, it can be said that caramel fuels in terms of heat increase heat transfer and lower fuel temperature, and also in terms of neutrons with a lower percentage of enrichment than the fuel loaded in the core of the Tehran reactor to the desired and to arrives at the beginning of the cycle.

In recent years SMRs have received a lot of attention due to their small size and portability, as well as some nuclear propulsion. In this research, VVER-1000 fuel assembly has been used as a basis and has been compacted and reduced by special methods and arguments. In this paper, a hexagonal fuel assembly without soluble boron and rely on suitable burnable absorbers has been designed and proposed for use in the SMRs. The objectives of this research are elimination of boric acid from the coolant, determine the number of fuel rods and guide channels inside the fuel assembly, determine the optimal arrangement of fuel rods and guide channels inside the fuel assembly, keeping the fuel to moderator ratio and determine the appropriate dimensions Boron-free hexagonal fuel assembly for use in SMR reactors. Also, one of the challenges of this design was to keeping the ratio of fuel volume to moderator of the VVER-1000 reactor fuel assemblies for SMR reactor, which was solved with neutronics and safety considerations. Due to the maintenance of the fuel volume to moderator ratio, pitch of fuel rods of the VVER-1000 reactor is also intended for the boron-free fuel assembly. Also the desired cycle length for the designed fuel assembly is about 40 month, for which the fuel enrichment has been set at 6.6%. According to increase in fuel enrichment in the SMR cores, the reactivity at the beginning of the cycle is very high, therefore, this reactivity needs to be compensated. One of the most important challenges and concerns in this research is the control of reactivity at the beginning of the cycle, during the cycle and the reduction of the radial power distribution In the absence of boric acid, the burnable absorber of gadolinium was solved problem with proper design. The designed boron-free fuel assembly has 156 fuel rods, 12 guide channels and 1 central tube. It should be noted that MCNP and WIMS codes have been used to simulate fuel assembly and also to ensure the correct design process.

One of the most important issues in reactor design is the neutron energy or neutron energy spectrum at the reactor core. nuclear reactors have different fuel enrichment depending on the application. Propulsion reactors are among the reactors that must have lower xenon after shutdown to be able to turn on the reactor for a long time shortly after shutdown. Therefore, determining the correct enrichment of fuel is required to study the effect of increasing enrichment on the energy of neutrons and absorption cross sections.In this paper, while validating WIMS code libraries for use in fuels with a enrichment of more than 10%, the effect of using fuels with a enrichment of more than 10% on the neutron energy spectrum and absorption cross sections, especially the thermal absorption cross section of xenon Has been investigated. The results showed that the increase in enrichment leads to a decrease in the cross-section of ​​Xenon absorption and as a result, a decrease in Xenon peak after shutdown.