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.