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.