Research on Depressurization Strategy of AP1000 Automatic Depressurization System Under DVI Pipeline Break Accident

Abstract In this paper, based on the system analysis program, the AP1000 nuclear power plant is taken as the research object, and the AP1000 system analysis model is built. Taking the DVI pipeline break accident as the starting event, the depressurization strategy of the ADS is studied. The results show that after the DVI pipeline break accident, the primary loop’s pressure can be gradually reduced to the input pressure of the in-containment refueling water storage tank (IRWST) through the multi-stage pressure relief of ADS, so that the three types passive water tanks can be orderly injected to ensure that the cladding does not overheat. There is a flow suppression area in the safety injection process of the core make-up water tank (CMT). In the DVI pipeline break accident, the first three levels of ADS have little effect on the input of high-pressure and medium-pressure safety injection, and the input time of ACC in different ADS pipeline fault conditions is only 2 seconds apart. In the DVI pipeline break accident, under the ADS pipeline fault conditions simulated in this paper, the low-pressure safety injection can be successfully put into operation to ensure the safety of the core. The multi-stage design of ADS can gradually increase the inlet pressure of the sparger. Opening ADS-2 or ADS-3 with larger size at the initial time can keep the sparger in a stable critical jet state for a short time. However, in the DVI pipeline break accident, the sparger cannot maintain a stable critical jet for a long time due to the large break of the pipeline and the strong pressure relief ability. Therefore, at the beginning of nuclear power design, it is necessary to consider that the jet flow pattern of the sparger in the DVI pipeline break accident will be in the chugging and condensation oscillation area, accompanied by large dynamic load and noise, which poses a potential threat to the integrity of the sparger and the safety of the nuclear power system.