反应堆的自然循环能力是其固有安全性的一项重要特征参数，利用RELAP5/Mod 3.4程序计算了JRR-3M池式研究堆在无应急冷却系统和有应急冷却系统条件下失去场外电源的事故工况，分析了冷却剂流动方向反转过程中的瞬态自然循环能力，并得到了最大自然循环载热能力。计算结果表明：应急冷却系统的投入明显地降低了燃料和冷却剂的温度，提高了反应堆的安全性；当衰变功率降低至590 kW时关闭辅助泵，利用自然循环能力可使反应堆达到安全状态。通过此研究堆的自然循环能力计算，验证了计算模型、计算方法的可行性，可进一步应用于此类型的研究堆。

The natural circulation capacity is an important parameter that characterizes the safety capability of a nuclear reactor. We calculated the transient characteristics under the conditions with and without emergency cooling system by RELAP5/Mod 3.4, analyzed the transient natural circulation capability of the coolant flow direction reversal process, and acquired the maximum transient transfer capability. The results show: the emergency cooling system reduced fuel and coolant temperatures significantly and improved the safety of the reactor; when the decay power was reduced to 590 kW, the auxiliary pump was turned off and the reactor could be brought into a safe state with natural circulation.