Thermal-hydraulics and neutronic code coupling for RELAP/SCDAPSIM/MOD4.0

•Coupling thermal hydraulics with neutron kinetic models is shown.•Nodal kinetics and coupling methods are discussed.•A BWR transient with unexpected subcooled water injection is simulated for validation.•Results are benchmarked by using an OECD Benchmark. The design and analysis of energy systems requires robust and reliable computer codes that produce realistic results. The governing equations and closure models must represent the physical behaviors of the energy systems. Nuclear power plants, as the quintessential example of complex energy systems, must be modeled with such high-fidelity and accurate nuclear system codes in which thermal-hydraulics, neutronics and fuel performance models must be coupled for in order to produce high-fidelity predictions. Most commonly, the interplay between the various subsystems of a nuclear power plant (nuclear fuel, fluids, neutronics, control rods, power conversion, etc.) is modeled through a combination of different codes that are externally coupled. The objective of this paper is to present work that couples the RELAP/SCDAP SIM/MOD4.0 code with the NESTLE neutronic code within the 3DKIN package, thus providing the latter with updated neutron kinetic capabilites. The version of the RELAP/SCDAPSIM/MOD4.0 code used in this work has been developed by Innovate System Software (ISS) and is the latest in the series of such code versions developed as part of the international SCDAP Development and Training Program (SDTP) for best-estimate analysis to model reactor transients including severe accident phenomena. The new feature of 3DKIN enhances the simulation of the Nuclear Power Plants (NPP) response under accidental and operational scenarios in which high reliability of neutronic feedback is needed. The RELAP/SCDAPSIM code is described and the improvements implemented in it are presented, including nodal kinetics library as well the coupling method that is applied. Finally, a BWR transient with unexpected injection of subcooled water as specified in an OECD Benchmark has been simulated in order to assess the reliability of the package and the performance of the coupling. Results are compared to those of the other OECD benchmark participants. The comparison of fuel temperature, effective multiplication factor (keff) and power distribution results display good agreement with values within the range of those of other participants.