Verification of the Mathematical Model and Numerical Investigationinto the Thermal–Hydraulic Parameters of Fuel Assemblies Containing Microspherical Fuel Elements
The article presents the results from numerical investigations into the hydrodynamics and temperature field in the KLT-40S reactor’s fuel assembly (FA) in the case of using microspherical fuel elements as nuclear fuel. The simulated FA has the same overall dimensions as the existing FA containing fuel rods, due to which it can be accommodated in the reactor core without the need of modifying the reactor design. The specific feature of an FA with micro fuel elements (MF FA) is the need to set up radial flow of coolant through the bed of micro fuel elements, which is achieved by using distribution and collection headers. The numerical simulation was carried out using the ANSYS Fluent computer code. The mathematical model implemented in the code has been refined and verified against the experimental data obtained by the authors on a model experimental setup whose design is similar to that of the considered FA containing micro fuel elements. Radial flow of coolant through the pebble bed is arranged in the model installation. The numerical and experimental data on pressure loss and temperature distribution in the bed estimated at different values of coolant mass velocity mass are compared with each other. The design of an FA containing micro fuel elements for the KLT-40S reactor is proposed. It has been found that almost purely radial flow of coolant can be set up with the perforation parameters (cross-section coefficients) higher than those mentioned in the literature. The serviceability of such a fuel assembly is demonstrated. The distributions of temperature, excess pressure, and coolant velocity and current lines are obtained. The perforation parameters of jackets confining the bed of micro fuel elements are presented.Keywords: numerical simulation, pebble bed, micro fuel elements, radial flow, internal heat release, fuel assembly