THYC, a 3D thermal-hydraulic code for steam generators, heat exchangers and condensers: recent developments and validation tests

PWR steam generators, tubular heat exchangers and condensers, are basic components of nuclear power plants involving two-phase flows in tube bundles. The operation of these components lead to vibration and corrosion inside the tube bundle, and to deposits and thermal shocks on the tube sheet of steam generators. A deep knowledge of the detailed flow patterns on the shell side is necessary to predict, quantify and prevent these risks. Moreover it is also useful to assess the efficiency of new designs, such as the economizer of the N4 nuclear plant steam generator. For these purposes, Electricite de France has developed, since 1986, a general purpose code named THYC (Thermal HYdraulic Code) designed to study three-dimensional single and two-phase flows in tube bundle (pressurized water reactor cores, steam generators, condensers, heat exchangers). Two types of components in the 3D domain are taken into account: fluid and solids (i.e. porous media approach). The THYC model is obtained by space-time averaging of the instantaneous equations (mass, momentum and energy) of each fluid phase over control volumes including fluid and solids. The THYC-EXCHANGER version solves three to five conservation equations of the fluid outside the tubes, plus the energy equation of the fluid inside the tubes. That makes the code able to model all types of heat exchangers, from single phase heat exchangers, to components involving boiling or condensation. First of all, this paper describes the physical model and the numerical method used in THYC-EXCHANGER. Secondly, validation tests (comparison with experiments) and applications are presented. We present successively : (a) the single-phase heat exchanger mock-up VACARM; (b) the PALUEL steam generator with temperature measurement; (c) the steam generator mock-up CLOTAIRE with void fraction and gas velocity measurements. They emphasize the latest developments, the new capabilities and the adaptability of the code to compute the local thermal-hydraulics of various kinds of heat exchangers. (authors). 17 refs., 6 figs., 3 tabs