Thermal-mechanical safety analysis of heat pipe micro reactor

Heat pipe micro reactors are compact, innovative nuclear reactors that utilize heat pipe technology to manage heat transfer efficiently. The advantage of heat pipe micro reactors lies in their reduced complexity, high efficiency, and ability to provide stable power in various scenarios where traditional, larger reactors are not feasible or practical. This study presents a steady-state thermal-mechanical analysis of a 0.5 MWth heat pipe cooled graphite moderated micro reactor. The analysis was conducted through developing a thermal conduction model and a heat pipe model using Ansys Fluent, as well as a mechanical model using Ansys Mechanical. Thermalmechanical calculations were performed for steady-state normal operating conditions, and selected heat pipe failure scenarios. Parameters including temperature, heat pipe power load, stress, strain, and geometrical deformation were all obtained from the analysis. Results showed that temperatures and heat pipe loads calculated for the reactor are well below the safety limits, even for extreme cases that include the failure of six heat pipes in the central region of the core. However, structural analysis of the graphite monolith showed that the maximum stress found in the graphite might approach or even exceed the allowable stress limit in some failure scenarios. Two design modifications were considered for stress reduction; first, the use of a highly conductive thermal paste as a gap material, and second, employing non-uniform heat sink conditions. Both options lead to a significant decrease in the maximum stress value for the graphite monolith.