Neutronic and thermal-hydraulic analysis of alternative ceramic fuels in the next-generation of light water reactors

The Burn-Up enlargement is one of the most important issues in the nuclear reactor core fuel management. In recent years some reactor design companies have focused on the reactor cycle length enlargement in next generation of pressurized water reactors. An increased cycle length results in an increased fuel burn-up which directly leads to low electricity costs and more efficiency. One of the promising issues is to change the chemical state of fuel that is on the agenda of the Mitsubishi Company as US-APWR nuclear power plant designer. In the present study, the neutronic as well as thermal-hydraulic analysis of some commercial ceramic fuels such as UN, UC, and UN15 instead of conventional UO2 have been studied. The sub-channel analysis approach has been selected for these investigations. In this regard, a US-APWR fuel assembly was modelled using MCNPX2.6 Monte Carlo code by considering the periodic boundary condition in X-Y directions. It was found that the use of UC and UN15 instead of UO2 has a deep effect on the reactor cycle length such that the power plant operational time was increased by a factor of 1.5. The COBRA-EN code with modified MATPRO subroutine has been used in thermal-hydraulic tasks. Since the thermal conductivity of these selected fuels is six times greater than UO2, the thermal-hydraulic analysis of candidate fuels was led to outstanding results. It was found that the fuel centerline temperature in UN15 and UC cases are about half of UO2 one, which is drastically beneficial. In summary the thermal power of next generation of pressurized water reactors could be increased considerably by using the candidate ceramic fuels instead of conventional UO2 one.