Fabrication and characterization of (Th, Pu)O2 fuel at Canadian Nuclear Laboratories

Thorium and other advanced fuels are of interest to the nuclear industry because of their potential role in ensuring long-term sustainable nuclear energy. Thoria (ThO2)-based fuel cycles are options for both conventional water-cooled reactors (including light water and heavy water reactors) as well as various advanced reactor concepts. Plutonium-bearing thoria-based fuels are an attractive option for consuming stockpiles of Pu, while breeding fissile U-233 and extracting energy from thorium. Canadian Nuclear Laboratories (CNL; formerly Atomic Energy of Canada Limited, AECL) has been carrying out research and developing thoria-based fuels, including (Th, Pu)O2, for more than 55 years. The CNL irradiation test of (Th, Pu)O2 fuel assemblies (BDL-422) in the National Research Universal (NRU) research reactor at the Chalk River Laboratories culminated in the publication of post-irradiation examination results during 2008-2013. More recently, CNL has undertaken efforts to further characterize as-fabricated and irradiated (Th, Pu)O2 fuel by developing and implementing improved ceramographic techniques and conducting fabrication trials to better control and improve pellet microstructure. In addition, autoradiography techniques have been developed and applied to irradiated (Th, Pu)O2 fuel to better characterize fuel microstructural behaviour in combination with scanning electron microscope (SEM) characterization. This work has resulted in improvements in the microstructural characterization and fabrication of (Th, Pu)O2 fuels.