Loss of heat sink (LOHS) accident in a natural circulation system has a complex event sequence scenario. Flow instability phenomena in LOHS accident involves multiple flow patterns and variety instability mechanisms. Through experimental investigation, a methodology analyzing instability under LOHS is established. It is concluded while slug flow occurring in heating channel, the system falls into geyser instability region which is proven as pressure drop oscillations (PDO) accompanied by wave mode changing. While annular flow occurs, natural circulation system forms stable two-phase flow transitorily and losses stability again. The post-annular-flow instability cannot form a regular vibration wave mode, and annular flow absorbs flowrate oscillation instead of pressurizer. Finally, average flowrate approaches to 0 and critical heat flux (CHF) happens.

自然循环系统中的散热片丢失（LOHS）事故具有复杂的事件序列场景。LOHS事故中的流动不稳定现象涉及多种流动模式和多​​种不稳定机制。通过实验研究，建立了一种分析LOHS下不稳定性的方法。可以得出结论，当在加热通道中发生团状流时，系统落入间歇泉不稳定区域，这被证明是伴随波模式变化的压降振荡（PDO）。当发生环形流动时，自然循环系统会暂时形成稳定的两相流，并再次失去稳定性。环形流动后的不稳定性不能形成规则的振动波模式，环形流动代替了增压器吸收了流量振荡。最后，