Neutronic and thermal analysis of heat pipe cooled graphite moderated micro reactor

Abstract

Heat pipe micro reactors are drawing a lot of interest lately due to their distinct features, including the elimination of moving parts required for transferring the heat, as they do so passively through heat pipes, combined with the ability of such reactors to provide energy to remote locations. This present study introduces a proposed design for heat pipe cooled graphite moderated micro reactor suitable for remote locations and space applications. The main requirements of the design include long core lifetime, two shutdown mechanisms, uniform power distribution, and strong negative temperature coefficient. Neutronic calculations were performed using MCNP 6.2 code. Criticality analysis demonstrated the ability of both control devices incorporated in the design to independently control and shutdown the reactor. Calculations of the flux and power distribution showed that, for a thermal power of 0.25 MW, the maximum flux at mid-plane of the reactor is in the order of 1012n/(cm2·s), while radial and axial power peaking factors were found to be 1.2 and 1.13, respectively. The results also showed that the reactor has an overall negative temperature coefficient. Additionally, burnup calculations were carried out to calculate the core lifetime which was estimated to be more than 70 years. A preliminary steady-state thermal analysis was conducted for the reactor using ANSYS FLUENT, assuming 1/12th symmetry. The obtained temperature distribution of the reactor showed that the operating temperatures are within the accepted limits where the highest temperature reached in the fuel was 1074 K. Furthermore, soft coupling of MCNP and ANSYS FLUENT was conducted through an iterative process of performing neutronic and thermal simulation using updated results for the temperatures and power distributions in each iteration.