Although uranium dioxide (UO2) is currently the most important nuclear fuel, thorium dioxide or thoria (ThO2) is gaining more and more interest. Resource and long-lived waste concerns are some of the driving forces to consider thorium as an alternative nuclear fuel. Thorium is a valuable resource due to its high abundance in the earth crust and in addition, the thorium fuel cycle generates less transuranium elements than its uranium analogue. However, natural thorium is quasi-monoisotopic (232Th) which is fertile (233U breeding occurs in a thermal or epithermal spectrum), but not fissile and can thus not directly be used in a nuclear reactor: initial “enrichment” with a fissile isotope is needed (239Pu, 241Pu 233U or 235U). Besides the above mentioned pros and cons for the thorium fuel cycle, another reason for the growing interest in the use of thorium as nuclear fuel is the existence of large stockpiles of thorium, generated in the past mainly via monazite ore processing (monazite is an important commercial source of rare earth elements, thorium and uranium). Without valorisation in nuclear fuel, these thorium stocks will have to be considered as radioactive waste, a much more costly alternative.
Already since more than 10 years, SCK•CEN performs research on thorium-plutonium fuels including design, neutronic and safety studies, manufacturing, behaviour under irradiation, post-irradiation examinations, behaviour of spent nuclear fuel etc. Until now, all manufacturing processes were following routes that only work well on lab-scale but cannot be applied on a larger scale. The lack of data on production methods that can potentially be scaled up was identified as the biggest challenge to achieve a breakthrough in this alternative fuel cycle.