Researchers have developed high-fidelity modeling capabilities for predicting radiation interactions outside of the reactor core—a tool that could help keep nuclear reactors running longer. The Consortium for Advanced Simulation of Light Water Reactors, headquartered at Oak Ridge National Laboratory, has integrated the new capability into its code suite VERA, or Virtual Environment for Reactor Applications. Working with the Tennessee Valley Authority, CASL simulated the refueling of the Watts Bar Unit 1 nuclear power plant. When comparing VERA’s results to the detector measurements in the ex-core—the region outside a reactor’s pressure vessel—the simulation of detector response closely tracked the measured data. “Not only is this advancement more accurate than other tools, it also significantly improves the computing efficiency needed to perform these high-fidelity simulations,” said ORNL’s Eva Davidson. The technique will provide industry and regulators better predictions for ex-core issues of current reactors, including material degradation that could affect performance and license renewals.