Feasibility Study of a Passive DHR System with Heat Transfer Enhancement Mechanism in a Lead-Cooled Fast Reactor

The KLFR is a pool-type lead-cooled fast reactor, which has a core thermal output of 900 MW(thermal), and a reactor vessel auxiliary cooling system (RVACS) is employed to secure reliable decay heat removal (DHR) during the worst anticipated design-basis condition. Since the RVACS design is based on reliable and economic considerations, a sufficiently large DHR capacity and compact reactor vessel size are desirable. However, these two requirements compete with each other because a sufficient DHR capacity can be achieved by a larger vessel size with a consequential heavy lead coolant weight. An advanced RVACS concept that has a larger capacity with a more compact vessel size was developed. To increase the DHR capacity of the KLFR, which uses natural-air circulation cooling, the feasibility of heat transfer enhancement by introducing new design concepts to essentially reduce the heat transfer resistance of the radial heat transfer elements was investigated. As a result of this work, the parametric analysis results showed that the passive DHR capacity of the KLFR can be substantially increased by up to 24% when compared with the classical RVACS concept, and this feature makes a compact reactor vessel very feasible. With the proposed advanced RVACS concept, one could expect that the heat removal capacity of an RVACS-type passive DHR system will be increased.