MONSTR/RELAP5: code system for comprehensive modeling of transients and accidents in pressurized water-cooled nuclear reactors

The structure, methods and assumptions of the MONSTR/RELAP5 code system are described in the paper. The system was developed for calculation of 3D LWR core neutron kinetics, thermal hydraulics and thermal mechanics of fuel rods with account for reactivity feedbacks due to change in temperature and nuclear densities of core materials as well as feedbacks between fuel rod deformation and cladding-to-coolant heat transfer. In particular, reactivity-initiated accidents and loss-of-coolant accidents in VVER reactors are supposed to be modeled with the MONSTR/RELAP5 system. As a step of verification procedure, the system was used for calculation of AER-4 benchmark problem, which is a 3D dynamic benchmark for the VVER-440 reactor, simulating a cooler de-borated water slug entry in the core. The results of the developed system are compared in the paper with the results obtained by the codes, widely used for LWR analysis. (author)