Flow instability analysis of supercritical water-cooled reactor CSR1000 based on frequency domain

Flow instability was studied for supercritical water-cooled reactor CSR1000 based on frequency domain method in this paper. A code named FREDO-CSR1000 (Frequency Domain Analysis of CSR1000) has been developed. The analysis of flow instability for CSR1000 both in average channel and hot channel within rated power and flow has been performed with the FREDO-CSR1000 code. The key parameters including decay ratio, the maximum cladding surface temperature and the proper orifice pressure drop coefficient were obtained as well. The calculation results indicated that the decay ratio of the first flow path varies with power and flow monotonically. However, the decay ratio of the second flow path ascends first and then descends, the trend of which is fluctuant because of the simultaneous influence of a multitude of variables. Besides, it is found that the location where the flow instability happened is directly determined by the point at which the pseudo-critical temperature reached. Moreover, the neutral stability boundary for hot channel of CSR1000 was obtained so that the threshold of flow instability can be predicted.