Comparative study of two models simulate a large break LOCA on the pressurized envelope of a typical irradiation test loop using Relap5/SCDAP3.2 system code

The work presented in this summary is a simulation of a large break loss of coolant accident on the inner pressure tube active section containing the test fuel bundle of the CALLISTO test loop facility (CApabiLity for Light water Irradiation in Steady state and Transient Operation ) using RELAP5/SCDAP3.2 thermal hydraulic system code. The scenario under consideration in this study is the rupture of large size in the inner pressure tube of in pile section of this loop with an initial mass flow rate at the break location of 5 kg/s. Two manners considered to model the accident of LOCA. First, the pressure tubes is simply modelled with a single volume connected to the broken tube with a trip valve, without taking into account the second tube. The second model takes into account the actual geometry of both pressure tubes separated by the space of helium formed in all the pressurized envelope. The latter is modelled in several annulus of different diameters. The break is modelled by a valve between two annulus containing the pressurized water and the Helium. The behaviour of the loop main parameters following this accident in both models is represented graphically and discussed.