Dynamic evaluation of a scaled-down heat pipe-cooled system during start-up/shut-down processes using a hardware-in-the-loop test approach

Based on the OpenMC simulation results, the relationship between the calculated reactivity and CD angle is shown in Fig. 5(a). A total external reactivity of approximately 9 $ is added into the nuclear system as the CDs rotate from 0° to 180°. However, the rate of the external reactivity increase is uneven; for instance, this process is faster when the CD angle is approximately 90°. According to past mechanical designs of small solid-state nuclear reactors and CDs, the maximum rotating speed of CDs should be 1°/s. Therefore, the mean rate of external reactivity insertion among different ranges of the CD angle is shown in Fig. 5(b). Here, the maximum value is less than 0.1 $/s. The trends in the characteristic parameters, as functions of the neutronics period, are shown in Fig. 15. As the external reactivity increases and neutronics period shortens, the first overshoot seems to occur earlier, and the amplitude of oscillation increases. In addition, the oscillations during long neutronic periods lasted longer. Fig.15(c) demonstrates a strong linear correlation between the characteristic oscillation time and neutronics period.

基于OpenMC模拟结果，计算得到的反应性（reactivity）与控制鼓（Control Drum，CD）转角的关系如图5(a)所示。当控制鼓从0°旋转至180°时，核系统总共引入了约9个反应性单位（$）的外源性反应性。但外源性反应性的增长速率并不均匀，例如当CD转角约为90°时，反应性增长更快。根据以往小型固态核反应堆及控制鼓的机械设计方案，控制鼓的最大旋转速率应为1°/s。因此，不同CD转角区间内的外源性反应性平均引入速率如图5(b)所示，该图中最大速率小于0.1 $/s。特征参数随中子学周期（neutronics period）变化的趋势如图15所示。随着外源性反应性提升、中子学周期缩短，首次超调现象出现的时间更早，且振荡幅值随之增大。此外，长中子学周期下的振荡持续时间更长。图15(c)则表明特征振荡时间与中子学周期之间存在显著的线性相关性。