Optimization studies for planning of substitution experiments in the ZED-2 critical facility with plutonium-thorium test fuel

Reactivity data from experiments in the Zero Energy Deuterium (ZED-2) critical facility enable advanced pressure-tube heavy water reactor (PT-HWR) fuel design concepts to be tested. Experiments on a limited quantity of test fuel show an increased relative uncertainty, due to the influence of the larger reference lattice, but new substitution analysis methods increase the flexibility of fuel substitution configurations. MCNP computer simulations are used to optimize the configurations for better sensitivity to the test fuel, which is found to enhance the precision substantially. Conceptual designs with thorium-based fuel cycles have been proposed to improve resource utilization. A plan has been developed for a substitution experiment to be conducted on plutonium-thorium test fuel in a smaller reference lattice of slightly enriched uranium fuel, and more of the test fuel in regions of higher importance. The findings suggest an opportunity to glean better data from optimization of new substitution measurements on other experimental fuel types that are already available to the ZED-2 critical facility.