GENFLO: A general thermal hydraulic solution for accident simulation

Thermal hydraulic simulation capability for accident conditions is needed as a part of several programs. Specific thermal hydraulic models are too heavy for simulation, because also the simulation of the rest of the system requires computer resources. The coupling between different physical models may be so complex that the fixed scope system codes are impossible to install for serving the special physical applications. Hence, the GENFLO (=GENeral FLOw) thermal hydraulic model has been developed at VTT for special applications. This report describes the generalised thermal hydraulic model, GENFLO, which at present has been used in three different applications. In RECRIT, the model is coupled the 2-D transient neutronics model TWODIN for calculating the recriticality accidents in the BWR plant. In FRAPTRAN application the model has been coupled with the transient fuel behaviour code FRAPTRAN for making the study of complex fuel transient possible by simulating the sub-channel thermal hydraulics as realistic as possible. In APROS-SA application the model calculates the core thermal hydraulics during the severe accident until the fuel material relocation and pool generation to the bottom of the reactor vessel is simulated.