Stability analysis of Generation IV Supercritical Water Reactors

The Supercritical Water Reactor (SCWR) is one of several reactor design concepts included in the Generation IV International Advanced Reactor Design Program. This reactor concept capitalizes upon the experience gained to date in the technology of the current light water reactors and of the supercritical fossil-fuel power plants. In SCWRs, water at supercritical pressures is used as the reactor coolant. At these conditions, there is no phase change in the coolant; however, the fluid properties undergo significant variation, particularly in the pseudo-critical region. In particular, the fluid density decreases by a factor of nearly six with increasing temperature. It has been seen for two- phase flow that variations in the fluid density can lead to density-wave oscillations, which may cause many undesired problems in system's performance. Similar issues must be addressed for flows at supercritical conditions because of the fluid property variations with temperature. The stability studies for supercritical water systems which been performed before have been typically based on oversimplified models and their results are often not fully consistent and incomplete. The objectives of the present paper are twofold. First, the effect of local (multidimensional) property variations of fluids at supercritical pressures (such as water and CO2) and their impact on the dynamic response of heated channels is discussed. Secondly, the methodology and results are shown of the analysis of density-wave oscillations in SCWRs using a complete one-dimensional model of reactor coolant channels. The results of parametric testing and validation of the proposed model will be discussed in the full paper, including a sensitivity analysis to major modeling assumptions. These results include comparisons between time-domain integration of the governing equations, and the frequency - domain analysis using two different approaches to quantify the effect of axial distributions of: fluid properties, power distribution and transient heat transfer across fuel elements. Newly developed SCWR stability maps will also be shown. They will be compared against similar results available in the literature. (author)