BWR Parametric Sensitivity Effect of Regional Mode Instability on Stability Boundary

Abstract

Both in-phase (core wide mode) instability and out-of-phase (regional mode) instability are of great concerns in BWR stability issues. Normally, decay ratios for regional mode oscillations are much less than those under core wide conditions. However, under certain observation mode, the regional mode instability has the phenomenon of power increasing in one half of the core and at the same time, it decrease in the other half, so it looks like that the average power remains essentially constant. This research presents a study of fractional change of decay ratio to evaluate parametric effects of regional mode instability on reload core design power/flow stability boundary for the Chinshan Nuclear Power Plant Unit 2 Cycle 21 (BWR4). Making use of LAPUR5.2 and SIMULATE-3 codes, we have established a methodology to conduct such out-of-phase stability analysis. Many important parameters, such as system pressure, core flow rates, moderator void fraction, fuel physical and geometrical properties, have strong influences on regional mode stability. Current investigations have shown that at some operation points along the stability boundary, certain parameters present more sensitive characteristics.

A Study on the Effect of Geometry and Operating Variables on Density Wave Oscillation in a Supercritical Natural Circulation Loop

“…However, the difference in MSBs becomes pronounced at higher N psub , and the stability zone becomes reduced with the decrease in the inlet pressure. It should be noted that the increase in the exit pressure makes the BWR more stable [39][40][41], and a similar pattern is also observed for the SCWNCL.…”

Analysis of flow induced density wave oscillations in the CANDU supercritical water reactor

“…However, the difference in MSBs becomes pronounced at higher and the stability zone gets reduced with the increase in the exit pressure. It should be noticed that the increase in the exit pressure makes a BWR more stable [25][26][27][28], but the reverse is observed for the CANDU SCWR.…”