Development and Verification of a Spatial Dynamics Code RESTA-3D for Light Water Reactors

A neutronics/thermal-hydraulics (TH) coupled spatial dynamics code, reactor system transient analysis-three dimensional (RESTA-3D), has been developed for both static and transient analysis of large advanced light water reactors (LWRs), with a focus on control rod (CR) ejection accidents. The code is based on a neutron diffusion model, employing the widely used “two-step” strategy in 3D Cartesian coordinates. A polynomial nodal expansion method (NEM) is used to handle spatial variables, while the neutron kinetics solver applies the exponential transformation technique. Additionally, the code integrates a single-channel TH module and a steam table set at 15.5 MPa. The accuracy of the code has been validated against three transient benchmarks: the 3D-LRA benchmark for boiling water reactors (BWRs), the NEACRP 3D benchmark, and the mixed oxide (MOX)/UO2 core benchmark for pressurized water reactors (PWRs). These benchmarks address both static and transient behaviors, and the results have been thoroughly analyzed. The close agreement between the RESTA-3D results and reference data, as well as other codes, confirms its reliability, making it a promising tool for future dynamic analyses of large-scale advanced PWRs.