PROPOSAL OF BENCHMARK PROBLEM OF THERMAL STRIPING PHENOMENA IN PLANAR TRIPLE PARALLEL JETS TESTS FOR FUNDAMENTAL CODE VALIDATION IN SODIUM-COOLED FAST REACTOR DEVELOPMENT

摘要

Numerical simulation is recognized as an essential tool for the physical phenomena analysis and plant design study of sodium-cooled fast reactors (SFRs). In order to enhance credibility of the numerical results in the activities for plant design by using numerical simulations, it is recognized that verification and validation (V&V) process is very important. In this study, experiments for planar triple parallel jets mixing phenomena conducted in JAEA were proposed as benchmark problems for the code validation in the area of thermal striping study in SFR development. In the experiment, triple jets were simulating a control rod channel and two fuel assemblies on both sides of the channel because thermal striping can be caused in the region where the temperature fluctuation is induced by mixing of fluids at different temperatures. Since high cycle thermal fatigue in structure may be caused by thermal striping, investigation of mixing process of the jets and attenuation process of the temperature fluctuation from fluid to structure is highly required. The sodium experiment PLAJEST and the water experiment WAJECO were selected as the benchmark problem. A cold jet and two hot jets flow out vertically from the center nozzle and the neighbor nozzles. In a typical boundary condition at 0.5 m/s in axial velocity through the nozzle of 0.02 m in width, the Reynolds numbers were 2.8×10~4 and 1.5×10~4 at 348 °C in PLAJEST and at 40 °C in WAJECO, respectively. In the both experiments, die mixing area was located between the two parallel vertical walls and a metal test plate made of the stainless steel No.316 (SS316) with thermocouples in it was set on one side in order to investigate the transfer characteristics of temperature fluctuations from fluid to structure.