A modern light water reactor (LWR) of 1 GWe capacity will typically discharge about 20-25 tonnes of irradiated fuel (spent fuel) per year of operation. Despite the low content of about 0.1-0.2% of minor actinides in spent fuel, these actinides can nonetheless contribute significantly to decay heat loading and neutron output, as well as to the overall radiotoxic hazard of spent fuel. For this reason, there has long been an interest in transmuting minor actinides to reduce their impact on the back end of the fuel cycle. Fast reactors are needed to effectively transmute transuranics (TRUs), including minor actinides. However, recent studies have demonstrated that TRU transmutation rates can also be achieved in thermal reactors, although with certain limitations due to the accumulation of transuranics through recycling and their impact on the safety of power plants. The transmutation of TRUs could potentially be implemented in a substantial number of thermal reactors operating today, while waiting for a similar programme in fast reactors to allow for commercial-scale operations in 20 to 30 years or more.

This publication provides an introduction to minor actinide nuclear properties and discusses some of the arguments in favour of minor actinide recycling, as well as the potential role of thermal reactors in this regard. Various technical issues and challenges are examined from the fuel cycle, operations, fuel designs, core management and safety/dynamics responses to safety and economics. The focus of this report is on the general conclusions of recent research that could be applied to thermal reactors. Further research and development needs are also considered, with summaries of findings and recommendations for the direction of future R&D efforts.