Development of critical experiments to provide validation data for multiphysics coupling codes

Modern reactor simulation tools provide advanced prediction capabilities by coupling multiphysics models to simulate reactor behaviors, involving thermal, neutronic, and mechanical interactions. To assure high-fidelity predictions by these tools, experimental data are needed to validate coupled-physics models deployed by these tools. In order to provide data to benchmark the feedback between thermal-hydraulic and neutronic simulations, coupled-physics critical experiments are designed and performed at a Reactor Critical Facility (RCF). The facility houses a low power and open-pool type light water reactor operated at the atmospheric pressure. The reactor allows flexible reconfigurations for many unique critical experiments. Recently, a water loop system has been designed and installed in the facility with the heated water circulating through the center of the reactor core, which broadens the range of validation experiments available for neutronics/thermal-hydraulics couplings. Direct effects of the loop water thermal dynamic change on reactor power and derived reactivity are demonstrated through a series of different experiments, including reactivity change over different loop water temperatures and reactor power evolution under influence of flow transient conditions in the water loop. Changes as low as 1% in the reactor power/neutron flux caused by small water temperature perturbations are observable experimentally.