RATEG: A PROGRAM FOR NUMERICAL SIMULATION OF NON-STATIONARY THERMOHYDRAULICS OF NETS WITH TWO-PHASE COOLANT. CALCULATIONAL MODEL AND NUMERICAL SOLUTION METHOD

O.A. Voronova, R.Ya. Gatilova, T.G. Ivchenko, M.S. Samigulin
VANT. Ser.: Mat. Mod. Fiz. Proc 1994. Вып.4. С. 23-32.

      RATEG program is intended for numerical simulation of nonstationary thermohydraulic processes in branching nets with two-phase coolant. The description of the models used in the program is presented: net elements (pumps, branchings, local resistences); flow models for vapor-fluid coolant and heat transfer in heat elements and numerical solution methods. Two- velocity, two-temperature model (2V2T) of coolant flow allows to take into account velocity and temperature nonequilibrium of flow structure, the mode of heat exchange with channel walls and so on. The difference equation system for coolant flow is approximated by linear semi-implicit one-step difference scheme, in which the time-step is not restricted by resistence conditions. Heat transfer in heat elements is calculated in 1-D heat, conduction approximation. The program capabilities allow to use it for simulation of loss-of-coolant accidents in nuclear power systems.

      The test results are presented for RATEG program intended for numerical simulation of nonstationary flows in branching thernriohydraulic nets, particularly in circulation circuits of nuclear power systems. The simulation is performed for phenomena characteristic of loss-of-coolant, accidents: outflow of boiling fluid at depressurization, chocking and turning over of a flow in the vertical channel; flows with heat exchange crisis in the heated channel. The comparison of calculational and experimental data proves acceptability of program accuracy for some applications in describing of such flows. The calculation of stationary mode of WWER-440 reactor circuit is performed in simulating of real systems for demonstration of program capabilities.