Simulation of condensation in the presence of noncondensible gases using the French Thermal Hydraulic computer code CATHARE

Abstract

The modeling of the complex thermal hydraulics of reactor systems involves the use of experimental test systems as well as numerical codes. A simulation of the phenomena of condensation in the presence of noncondensible gas was performed using the CATHARE thermal hydraulic code. The experiments were conducted at the University of California, Berkeley, and at the Energy Research Laboratory in Japan; supervised by Hitachi, Ltd.. The experiments involved the condensation of a steam/air mixture in downward flow through pipes. The test sections approximate the design of isolation condensers included in the passive containment cooling system in the new generation of nuclear reactors. Both the University of California at Berkeley and Hitachi test sections consisted of a stainless steel pipe connected to an upper and lower plenum. An annulus containing cooling water was present in both experiments. The steam/air mixture was introduced into the test section by means of mixers connected to the upper plenum. The transient runs were conducted on two separate platforms. The University of California at Berkeley simulation was conducted on a HP 9000/720 Workstation at Texas A&M University. The Hitachi simulation was performed on the "ventoux" branch of the HP network located at the Centre D'Etudes Nucleaires de Grenoble, located in Grenoble, France. The position in which condensation began to occur was overpredicted in the Berkeley simulation, but was accurate in the Hitachi simulation. The liquid heat flux was heavily underpredicted in both the Berkeley and Hitachi simulation. As a result of the underprediction in the heat flux profile, the condensing tube wall temperature and the local overall temperature coefficients were underpredicted in comparison to the experimental data. Secondary side cooling water temperature was also underpredicted as a result of the underprediction of the primary side heat flux. Overall, the CATHARE simulation were in reasonable agreement with both the low and high pressure cases.