With the rapid pace of industrialisation, humanity faces two key energy challenges: energy consumption is dangerously outpacing energy production, and the reliance on fossil fuels continues to grow with a harmful environmental impact.

The world’s ever-growing demand for clean energy requires an urgent response through the design and implementation of sustainable energy sources. There is an undisputable need for optimal energy sources that will generate clean energy to meet this demand worldwide. An example of such an optimal energy source is a compact, energy dense microreactor that can be utilised in energy intensive industries, such as data centres, mines, and manufacturing industries or can be transported to disaster stricken regions where the electrical infrastructure has been compromised. Microreactors are capable of generating 1 to 10 megawatts (MW) of electricity.

Recent research conducted at the Clean Energy Research Group within the Department of Mechanical and Aeronautical Engineering has focused on a novel method to maximize the heat transfer in fuel assemblies of a 10 MW_th Advanced Micro-Reactor (AMR). This novel method proposes a fuel assembly in which coated fuel particles are contained within a silicon carbide (SiC) tube, with a lead-bismuth eutectic (LBE) alloy serving as a filler material to enhance thermal conductivity between the particles and the inner SiC wall. LBE has a low melting point and a significantly high boiling point, which means that during high temperature operations, the LBE remains stable in its liquid state.

Particles immersed in molten LBE for enhanced Heat Transfer

A thermal-hydraulic system computational fluid dynamics (CFD) model was also developed to simulate the reactor’s operation and to investigate the temperature profiles within the reactor’s core. The simulation validated that this novel concept of using a fuel assembly with a higher effective thermal conductivity yields peak temperatures that are safely less than the melting point of SiC on the coated particles and of the cladding tube.

A Novel Fuel Assembly Configuration

Safety remains a top priority in the design of any nuclear reactor, regardless of the size. Reactor safety can mean different things to different people, in this study, the reactor’s fuel assemblies were designed to retain fission products within a safe containment structure. More than 99% of the radioactivity in a reactor is contained within the fuel assemblies of the reactor.  The cladding material around the fissile material in the core serves as the primary barrier against the release of this activity. The second barrier is the steel pressure boundary and finally a reinforced concrete structure serving as a reactor containment designed to stop any radioactive contamination from being released into the environment around the reactor plant.

An Advanced Microreactor Assembly (STL Nuclear)

SiC, which is used as the cladding tube and coating of the fuel particles, has a melting point of 2 700^oC. The findings from the study depicted a peak fuel temperature of less than 1108 ºC, which is safely below the melting points of the reactor’s key components. Findings further depicted an axial shift of the maximum temperature due to this new configuration of fuel assemblies. Collectively, these findings highlight the importance of incorporating LBE into the design and assessment of fuel assemblies.