Analysis stabilization technique of nuclear power plant simulation system

The plant simulator is required to be capable of simulating accident events stably and accurately, particularly for applications to an operation support system for plant accident events. The simulation system has a three-dimensional neutron calculation, a two-phase flow calculation, a fuel rod temperature calculation, and a control-block calculation. The two-phase flow calculation uses a two-phase flow stabilized calculation model to cover a wide pressure range. The two-phase flow calculation includes the virtual mass term and an explicit diffusion term to remove numerical instability. And in particular for the low pressure and large diameter flow channel conditions, the interfacial shear model was developed using experimental data and it was applied in the two-phase flow calculation. We evaluated effect of the stabilization by the steady-state two-phase flow analysis in a vertical pipe and confirmed that the stability of the analysis was sufficiently good and the void fraction was predicted accurately in the pressure range from 0.5 MPa to 7.2 MPa by introducing the explicit diffusion term and the developed interfacial shear model for the low pressure and the large diameter flow channel. (author)