VVER-1200 Reactor Core Pin Cell Steady-State Thermal Hydraulics Analyses and Cross-Validation

A nuclear fuel element is designed with materials that are not only capable of withstanding extreme thermal stresses, but also effectively participating in heat transfer from the fuel to the coolant. Despite the poor thermal conductivity of gases relative to solids, it is necessary to include a gas gap in the fuel element to create room for accumulation of fission products. In this case, we have to consider an inert gas that is capable of transferring heat. Therefore, thermal hydraulics analysis becomes a prerequisite procedure for testing the possible violation of the established critical and maximum permissible parameters associated with the materials of the fuel element. To verify the safety of the VVER-1200 reactor core pin cell, the behavior of heat transfer from the fuel to the primary coolant was studied by solving the steady-state form of the heat conduction equation by analytical and numerical techniques. In the calculation schemes, the pin cell temperature distribution was established by solving for the temperature drop along the radial profile. The results revealed a VVER-1200 reactor core pin cell design exhibiting operations that do not violate the established permissible parameters associated with the adopted materials.