Simplified flow instability analysis of a natural circulation system with parallel boiling channels

Regional flow instability in two-phase flow system is attracting much interest. In this flow instability mode, flow fluctuations are limited, e.g. only in the core region of BWR, but without fluctuation of the total inlet flow. Thus the flow instability may cause a significant problem related to system safety. Many investigations on the flow instabilities have been conducted so far, and respective stability criteria have been proposed, while these investigations focused normally on the one-chemical system without flow maldistribution, and the resulting stability criteria are hardly applied to the regional flow instability. Thus in the present investigation, analytical investigation was conducted focusing not only on the flow instability in a whole system but also on the regional flow instability. The stability analysis was based on a lumped-parameter model of parallel boiling channels. Finally the stability criteria for the two types of the flow instabilities and the stability maps were obtained. (author)