Flow characteristic of single-phase natural circulation under ocean motions

Natural circulation is widely used in nuclear reactor systems as the passive safety system. With the development of the floating nuclear power plant (FNPP), researchers should pay more attention to flow and heat transfer characteristics for the natural circulation under ocean conditions for the safety of FNPP. In this paper, the flow characteristics in a single-phase natural circulation system were investigated and the effects of heaving, rolling and coupled motions were analyzed. The oscillation amplitude of flow rate increases with the increase of period in a certain range and maximum acceleration under heaving motions. With the increase of oscillation intensity (higher frequency and larger maximum rolling angle), the oscillation amplitude increases and the average flow rate decreases under rolling motions. Moreover, the lateral displacement of rolling center changes the oscillation period and induces larger amplitude oscillations. The flow characteristic becomes more complex when the system is subjected to coupled motions. The oscillation period is the least common multiple of two motions’ periods. The oscillation induced by coupled motions makes the system more unstable than that induced by an individual motion. The potential superposition effect exists under coupled motions and needs to be addressed for the operation safety.