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Neutronic Study of UO2-BeO Fuel with Various Claddings

The neutronic properties of UO2-BeO fuel with various claddings are investigated through the Monte Carlo method and the Linear Reactivity Model. A second order polynomial function is suggested to describe the relationship between the difference of the reactivity at the End of Cycle and two factors, the uranium enrichment and the volume fraction of BeO in the UO2-BeO fuel. The uranium enrichment is determined to ensure the same cycle length for each BeO fraction with zircaloy, FeCrAl, and SiC claddings. Similar neutronic properties are observed between the zircaloy and SiC claddings for a given BeO fraction, including the infinite multiplication factor, the gas release, the power distribution, and the isotopic concentrations. An important feature of UO2-BeO fuel is the production of 4He, which is significant compared with current UO2 fuel. Lower production rates of xenon and krypton are found in the case of the UO2-BeO-FeCrAl fuel-cladding system, while those in the UO2-BeO-zircaloy and UO2-BeO-SiC systems are quite similar to the current UO2-zircaloy system. The power distribution in an assembly and in a fuel pellet is flatter for a higher BeO fraction with the same cladding. Higher peak power is found in fuel assemblies with FeCrAl compared to the other two claddings, while the radial power distribution is quite similar for the three claddings.