Two-phase flow in natural circulation system of the integrated modular water reactor (IMR)

Two-phase flow thermal-hydraulics in the design aspect of the Integrated Modular water Reactor (IMR) has being numerically analyzed assisted by the α-flow code. A basic design concept of this small-scale advanced light water reactor adopts the two innovative heat transfer and safety systems, one of which is the Hybrid Heat Transport System (HHTS). The HHTS, combining functions for power and pressure controls, utilizes a two-phase natural circulation passing through the riser and the downcomer section in the reactor vessel. Our concerns have been therefore focused on the analyses of phase distribution in these sections to assure stable reactor operations. The predicted results indicated fairly uniform void distributions in both sections. Degree of the vapor flowing into the downcomer section was also estimated, which is one of the important factors affecting the design of the HHTS. (author)