Validation of CATHARE Code for Gas-Cooled Reactors: Comparison with E.V.O Experimental Data on Oberhausen II Facility

Extensively validated and qualified for light-water reactor safety studies, the thermal-hydraulics code CATHARE has been adapted to deal also with Gas-Cooled Reactor applications. In order to validate the code for these new applications, CEA (Commissariat a l'Energie Atomique) has initiated an ambitious long-term experimental program. The foreseen experimental facilities range from small-scale loops for physical correlations, to component technology and system demonstration loops. In the short-term perspective, CATHARE is being validated against existing experimental data, in particular from the German power plant Oberhausen II. Oberhausen II, operated by the German utility E.V.O (Energie Versorgung Oberhausen AG), is a 50 electrical Megawatts (MW(e)) direct-cycle Helium turbine plant. The power source is a gas burner instead of a nuclear reactor core, but the power conversion system resembles those of the GFR (Gas-cooled Fast Reactor) and other high-temperature reactor concepts. Oberhausen II was operated for more than 25 000 hours between 1974 and 1988. Design specifications, drawings and experimental data have been obtained through the European HTR-E project, offering a unique opportunity to validate CATHARE on a large-scale Brayton cycle. Available measurements of temperature, pressure and mass flow rate throughout the circuit have allowed a very comprehensive thermal-hydraulic description of the plant, in steady-state conditions for design data and operating data as well as during transients. First, the paper presents the modeling of the Oberhausen II plant with the CATHARE code, with a complete description of the modeling of each component: the recuperator, a complex gas to gas counter flow heat exchanger, the pre-cooler and inter-cooler, two complex gas to water cross flow heat exchanger, the heater, which is a gas burner, and the two turbines and two compressors. A particular attention is given to the modeling of leakages all along the circuit and to the modeling of cooling of the first stages of the high pressure turbine. The modeling of the helium storage tanks used for injection or removing of helium during load following is also described. Then, the results of the CATHARE calculations for four steady-state conditions are compared with E.V.O data. It concerns the design nominal point (50 MW(e)), the operating nominal point (30 MW(e)) and two operating partial loads (20 MW(e) and 13 MW(e)). The major differences between the expected design power (50 MW(e)) and the maximum operating power observed in the facility (30 MW(e)) are discussed. First conclusion is that results of calculation are in a good agreement with experimental data for these four nominal states. Finally, the results of a load following transient calculation performed with CATHARE are shown in comparison with experimental data. The scenario of this load following is a decrease of the electrical power from 10.6 MW to 7.6 MW due to a decrease of the mass flow rate and pressure levels caused by a removing of helium towards storage tanks. Calculation agrees well with measured data. (authors)