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用时域方法研究了低压低含汽量自然循环系统的非线性密度波不稳定性。发现存在于系统的两种密度波不稳定的非线性振荡形式,研究了两种振荡的特性、机理及其影响因素。得到如下一些重要结论:1.不稳定区域密度波振荡为有限的持续振荡。靠近稳定边界时,系统发展为等幅的持续振荡,且随着过冷度的增加振幅加大;远离稳定边界时,密度波振荡耦合可压缩性密度波振荡,呈变幅的有限振荡。2.核功率和空泡份额耦合反馈对密度波振荡的影响取决于热流密度滞后的相位,对5MW核供热堆主回路系统来说,起激励作用。3.加大堆芯出口水力提升段的质量惯性能有效地抑制可压缩性密度波振荡,提高系统的稳定性。
The time domain method is used to study the nonlinear density wave instability of low pressure and low volume natural circulation systems. Two kinds of nonstationary oscillatory forms of density waves existing in the system are found. The characteristics, mechanism and influencing factors of the two kinds of oscillations are studied. The following are some important conclusions: 1. Instability region density wave oscillation is limited continuous oscillation. When the stability boundary is approached, the system develops into constant amplitude oscillation and the amplitude increases with the increase of undercooling. When away from the stable boundary, the density wave oscillation decouples the compressible density oscillation with amplitude-limited finite oscillation. 2. The influence of nuclear power and bubble fraction coupling feedback on the density wave oscillation depends on the phase of the heat flux density lag, which is an incentive for the main loop system of 5MW nuclear reactor. 3. Increasing the mass inertia of the hydraulic lift section of the core outlet can effectively suppress the compressible density wave oscillation and improve the stability of the system.