| 摘要 |
PURPOSE:To improve the rate of cooling a reactor core by varying the flow resistance of flow passage holes at the time of back flowing for each of the reactor core region thereby relieving the effect of suppressing gas-liquid counter current. CONSTITUTION:Curvature is provided to top end edges 8 of part of the flow passage holes 4 penetrating through a supporting plate 3 for the upper part of the reactor core. The flow resistance at the time of back flow decreases and the flow resistance at the time of forward flow is approximately the same when comparison is made with the case in which the edges 8 are not provided with the curvature. Emergency core cooling water 2 accumulated in an upper plenum 1 is liable to flow into the holes 4 of the smaller flow resistance at the time of the back flow in the event of a rupture of the piping. On the other hand, the cooling water hardly flows into the flow passages of the large flow resistance at the time of the back flow. A head difference between the holes 4 is, therefore, positively formed as compared to the case in which all the holes 4 have the same flow resistance at the time of the back flow. A descending water flow 6 is then formed in the holes 4 where the flow resistance is small and a rising steam flow 7 is formed in the holes 4 where the flow resistance is large. The flow passages are thus separated and the effect of suppressing the counter flow is relieved. The cooling water 2 accumulated in the plenum 2 is, therefore, capable of falling rapidly by gravity to the reactor core. The rate of cooling the reactor core is thus improved.
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