We investigated the characteristics of reactivity change due to fuel debris falling into water. The impact of each parameter on criticality was evaluated using a basic parametric survey. The results clearly indicated that when a large number of fuel debris pieces suddenly sediment in water, the reactivity increases rapidly. It suggested that this situation must be avoided to prevent criticality accidents during fuel debris retrieval operations. On the other hand, when fuel debris pieces gradually sediment, falling from a low height onto a floor with high friction, the sedimentation shape can easily condense to a significant height. In such cases, the criticality risk might become large once the sedimentation process is complete. Our findings indicate that this situation should also be avoided.

我们研究了燃料碎片落入水中引起的反应性变化特征。使用基本参数调查评估每个参数对关键性的影响。结果清楚地表明，当大量燃料碎片碎片突然在水中沉淀时，反应性迅速增加。它建议必须避免这种情况，以防止在燃料碎片回收作业中发生临界事故。另一方面，当燃料碎片逐渐沉淀，从低高度落到摩擦力大的地面上时，沉淀形状很容易凝结到一个显着的高度。在这种情况下，一旦沉淀过程完成，临界风险可能会变大。我们的研究结果表明，这种情况也应该避免。