Thoria Irradiation and Post-Irradiation Examination Experience at AECL

Abstract

Thorium is a prominent advanced fuel in the global nuclear fuel cycle vision. Thoria (ThO₂) based fuels are under consideration for deployment in the Canadian-designed pressurized heavy water reactor and super-critical water reactor. AECL's experience in developing thoria fuels is a key enabler to the Canadian nuclear industry availing itself of thorium as a sustainable source of nuclear energy. This paper describes 50 years of AECL experience with thoria irradiation tests and performance assessments from ~1962 to the present. The paper reviews irradiation tests conducted in three experimental reactors, and the Nuclear Power Demonstration pressurized heavy water reactor. Various thoria-based fuels have been studied by AECL including natural thoria (ThO₂), (Th,U)O₂, and (Th,Pu)O₂. Fuel burnups up to 1130 MWh/kgHE (47 MWd/kgHE) have been achieved, with linear heat ratings up to 77 kW/m. This experience will be overviewed in this paper. Tests that studied fission-product release from intentionally-defected thoria fuels will be summarized. In addition, experience with thoria fuels that experienced failure during irradiation will be reviewed. Defect causes and behaviour will be summarized and contrasted with that of UO₂ fuel. Key findings and lessons learned from irradiation tests and post-irradiation examinations will be summarized. Irradiation tests that are in progress (targeting burnups up to 1500 MWh/kgHE) will be described, as well as future envisioned initiatives that will provide additional thoria fuel science and technology to the Canadian nuclear industry.