Measurements on (233U, Th)O2 fuel by substitution experiments in the ZED-2 critical facility

Abstract This paper summarizes the results of experimental measurements on mixed-oxide (233U,Th)O2 fuel bundles in the ZED-2 heavy water critical facility of Canadian Nuclear Laboratories (CNL) in Chalk River, Canada. Pressure-tube heavy water reactors can use such fuel to extract the energy potential of thorium, which helps extend nuclear energy resources and reduces waste. Measurements were made in a series of substitution ZED-2 experiments, with (233U,Th)O2 test fuel placed into vertical channels filled with air or heavy water in a reference lattice of very low-enriched uranium fuel. Fuel was arranged to maximize the importance of the test fuel. Each fuel and coolant configuration in the substitution series was simulated in MCNP5 to verify the measurement of critical moderator height. The precision of the substitution measurements can help support the validation of reactor physics codes for evaluation of reactivity coefficients in reactors with fuel that contains oxides of thorium and thorium-derived uranium.