Simulation of BWR shutdown followed by a forced coolant recirculation faulty using a RELAP5-MOD3.3 modeling

The RELAP5 code is widely used for thermal hydraulic studies of commercial nuclear power plants. Aiming to demonstrate the RELAP5 code capability of reproducing severe thermal hydraulic transients in nuclear reactors, a simulation of an accident, similar to that occurred in the Fukushima unit 1 in 2011, has been considered in this work. To perform the calculation, a RELAP5 model validated for a boiling water reactor (BWR) was used. In the RELAP5 simulation, the plant was shutdown when was operating in steady state at about 1350 MW of power. Just after, the coolant recirculation pumps were stopped; consequently, the heat produced in the core stopped to be removed causing excessive heating in the reactor. The time evolution of coolant, cladding and fuel temperatures following this extreme transient have been presented and analyzed from the safety view point. (author)