Multiphysical Unsteady Simulations of Ballooning Pt and Ct Contact in the Benchmark Model of IAEA/ISCP

Abstract

LOCA(loss of coolant accident) is one of the representative severe accident in the operation of nuclear reactors. One of the possible cases is the ballooning of pressure tube and the contact with the Calandria tube for the outer coolant to boil abruptly to saturate. For the moderator system of CANDU-6 reactor, the benchmark model of IAEA/ISCP has been setup to conduct a test and comparison with numerical models on the multi-physics of ballooning PT(pressure tube) and its contact with CT(Calandria tube). The graphite heater is modeled as a volumetric heat source for the given unsteady power of 150 kW, and the PT and CT are installed eccentrically in a given interval. In the first stage, the radiation heat transfer between Zircalloy surfaces of tubes is considered with the same structural deformation model as CATHENA code for the zero-gradient temperature outer boundary condition. A commercial code, COMSOL Multiphysics is used for simulations, and the Gaussian quadrature is applied for the integration of gradient for temperature. The two-dimensional result shows a good agreement for high-order numerical integration in the model with CATHENA one.