The Analysis of Linear and Nonlinear Instability Phenomena in Heated Channels

摘要

This topical report presents the results of an analytical investigation into thermal-hydraulic instability modes in boiling heated channels. In particular, both linear and nonlinear analysis was performed on density-wave and excursive (Ledinegg) instability modes. Several new and important phenomena were discovered during this investigation. First, it was found that when frictional gravitational effects are properly considered, 'islands of instability' may occur in linearly stable regions. In addition, the nonlinear analysis indicated that finite amplitude disturbances in the flow could excite precipitous instabilities for conditions which are linearly stable (subcritical), while limit-cycle oscillations of small amplitude are possible for conditions which are linearly unstable (supercritical). The implications of these new findings on light water nuclear reactors (LWRs) safety is not clear; however, it is clear that such phenomena should be considered in the evaluations of LWR stability.