Recent measurements on plutonium-thorium fuel by substitution experiments in the ZED-2 critical facility

Abstract

This paper summarizes the results of experimental measurements recently made on heavy water moderated plutonium-thorium (Pu-Th) mixed-oxide fuel bundles in the ZED-2 critical facility of Canadian Nuclear Laboratories. Pu-Th fuel in pressure-tube Heavy water reactors can help extend nuclear energy resources by utilizing plutonium from spent fuel, and extracting the energy potential of thorium. The ZED-2 experiment was a series of substitution measurements, with (Pu,Th)O2 test fuel placed into vertical channels filled with air or heavy water in a reference lattice of very low-enriched uranium (LEU) fuel. Sensitivity to the test fuel was optimized by placement into positions of higher power. MCNP5 simulations of the fuel substitution series are within uncertainty of critical moderator height measurements. The precision of the substitution measurements can help support the validation of reactor physics codes for evaluation of reactivity coefficients in PT-HWRs with fuel that contains a mixture of thorium and plutonium oxides.