Analysis of startup process of small modular reactor with OTSGs

The ACP100 adopts the design of Once-Through steam generators(OTSGs). During the startup process, it involves the complicated heat transfer phenomenon which changes from single phase flow heat transfer to two phase flow heat transfer on the secondary side of OTSGs. In order to avoid the OTSGs operating in the operating interval where flow instability will occur, the coolant temperature of primary side and the feedwater flow rate of secondary side are all strictly required in the two phase flow operating interval of OTSGs. Besides, the regulation and fluctuation of the reactor nuclear power during the startup process influenced the stability of OTSGs operation, which makes the development and the validation startup strategy more important. The OTSGs simulation model of Babcock & Wilcox company design has been developed with APROS, the simulation result shows that it has good accordance with the operation parameters in literature. This model can capture the two phase flow heat transfer phenomenon on the secondary side of OTSGs. On this basis, the ACP100 startup numerical model has been developed also with APROS. The key parameters influenced the OTSGs operation during the whole startup process has been acquired in simulation. The recommendation for improving OTSGs operation stability during ACP100 startup process has been given.