Experimental study on thermal stratification phenomena in reactor vessel in fast reactors; Evaluation of rising rate of straticication interface using multi-dimensional thermal-hydraulic code

Kimura, Nobuyuki; not registered; Hayashi, Kenji; Kamide, Hideki 

In a fast reactor, the thermal stratification phenomena occur in thc reactor vessel when a scram shutdown is imposed. The thermal stratification phenomena can induce thermal fatigue in structural components in the reactor vessel. It is necessary for designs of real reactors to quantify an occurrencc condition, a position, a rising velocity and a temperature gradient of the stratification interface. To study the thermal stratification phenomena, sodium experiments were performed using PLANDTL-DHX facility. Also, two dimensional analyses were carried out using a multi-dimensional thermal-hydraulic code AQUA with an algebraic stress turbulence model and compared to the sodium experiments. Influence of Richardson (Ri) and Reynolds (Re) numbers were cxamined by experiments and calculations. In the cases of high Ri, the calculated temperature distributions were in good agreements with the cxperimental results. In the cases of low Ri, on the other hand, the analyses had milder temperature gradients in the stratification interface, compared to the experiments. The analyses, however, could simulate the trend; the level of the interface rises with decreasing Ri. The analysis using k- two equation turbulencc model was also carried out. The ASM could simulate the cxperimental temperature distributions and thus the level of the interface better than the k- two equation turbulence model.