A review on emerging mixed-spectrum nuclear reactors for safety and sustainability of nuclear energy systems

The goals of achieving net-zero CO2 emissions and bolstering energy security have increased the interest in nuclear power in recent years. Existing nuclear reactors are typically designed based on a thermal or fast neutron spectrum. The thermal neutron spectrum is advantageous for enhancing fission reaction, whereas the fast neutron spectrum is beneficial for fissile breeding and radioactive waste incineration. However, the thermal-spectrum reactor has problems such as limited fuel utilization and long-lived nuclear waste production, while the fast-spectrum reactor faces issues such as a small void feedback coefficient and the potential of proliferation. A mixed-spectrum nuclear reactor is a design that combines thermal spectrum and fast spectrum within a single nuclear reactor, hence combining the benefits of thermal spectrum and fast spectrum for versatile application reasons. In order to provide a full understanding of this revolutionary reactor concept, this study offers a review of global reports on emerging mixed-spectrum reactor techniques. The mixed-spectrum design has been examined in a variety of reactor types, including supercritical water-cooled reactors, fusion-fission hybrid reactors, test reactors, liquid-metal-cooled reactors, gas-cooled reactors, and accelerator driven systems, etc. These activities and ideas have revealed the potential of mixed-spectrum nuclear reactors for enhancing fuel utilization, nuclear waste transmutation, non-proliferation, nuclear material testing, etc. It is envisaged that in the future the mixed-spectrum nuclear reactor may serve as a multi-purpose reactor type enhancing the safety and sustainability of nuclear energy systems.