Safety Analysis of the Homogeneous Slowpoke Reactor

Abstract

An opportunity is presented with the approaching end of some of the SLOWPOKE-2 research reactors’ design life, which consists of replacing the current heterogeneous core with a homogeneous assembly that would allow the extraction of radioisotopes (such as 99Mo) for nuclear medicine and other applications. Preliminary investigation has demonstrated the feasibility of this concept and produced an initial design of a Homogeneous SLOWPOKE reactor that demonstrates the potential for inherent safety based on calculations of a strong negative reactivity coefficient due to temperature. The present research aims at continuing the safety analysis of the proposed homogeneous assembly, most notably in assessing its inherent safety characteristics with respect to factors such as void fraction of the moderator and additional thermalhydraulic effects. Modelling of the reactor is accomplished using both the deterministic WIMS-AECL and the probabilistic MCNP 5 for the determination of the reactor’s reactivity and flux shape, while COMSOL Multiphysics is used for thermalhydraulics modelling. In pursuing the safety analysis, the design of the reactor is improved. One example of the improvements is the proposed substitution of the required additional reflector material in the initial design with graphite instead of beryllium. Another improvement is the replacement of the unique control rod in the core centre with a cluster of control rods within the radial reflector. This would not only simplify the construction of the reactor vessel, but increase the core volume for added radioisotope production capacity. The latest results of reactor simulations and the safety analysis will be presented.