Analytical Study of Thermo-Hydrodynamic Behaviour of the Reflood-Phase During a LOCA

摘要

The objectives of this study are: the check of the quench model proposed by the author and T. Sudoh, the establishment of the thermo-hydrodynamics downstream from the quench front, and the stabilization of the numerical calculations. In order to study these therms, the new version of the reflood analysis code 'REFLA-1D' was developed. The quench modes were classified into the following three types: 1) liquid column type (rewetting by subcooled water), 2) dryout type (annular flow type, rewetting by saturated water), and 3) rewetting type (entire surface temperature higher than rewetting temperature). For the thermo-hydrodynamic model downstream from the quench front, the flow pattern was divided into the five regimes: 1) subcooled film boiling regime, 2) transition flow regime, 3) dispersed flow regime, 4) superheated steam flow regime, and 5) rewetted regime. To stabilze the numerical calculation and shorten the computing time, the Lagrangian form of the energy equation of gase phase and dispersed flow region was used instead of the Eulerian form. Considerably close agreement between three PWR-FLECHT tests and the calculated results for the critical Weber number Wec=1.0 was obtained for fuel clad surface temperature and quench time except in earlier stage before turnaround, but poor agreement for the heat transfer characteristics in the transition flow region defined between the quench front and the dispersed flow region. The calculation was relatively stable and the computing time is about the same as a real time for a IBM 370-158 computer. (Atomindex citation 09:395344)