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

Modem 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 temperature and neutronic simulations, coupled-physics critical experiments have been designed and performed at a Reactor Critical Facility (RCF). The facility's low power and open-pool atmospheric pressure configuration allows 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 core, which broadens the range of validation experiments available. Direct effects of the temperature on reactor state and excess reactivity are demonstrated, through a series of different measurements, including reactor change of state through moderator temperature change, influence of heated water in the center of the core on the reactivity, and transient temperature influence on reactor power evolution. Changes as low as of 1% in the reactor power caused by small water temperature perturbations arc observable experimentally.