Abstract
In BWR, the cooling water takes place of boiling phenomenon in the core. The flow instability can become a complicated instability phenomenon by coupling the reactor power via the void reactivity. The instability can mainly be divided in-phase and out-of-phase instability. In this research, we use frequency domain tool LAPUR5.2 to do stability analysis on the ChinShan NPP unit 2 cycle reload design stability boundary and compare the results with the vendor’s results. And then we choose a operation point on the stability boundary and discuss the parameter effects on regional mode instability . According the result, it can conclude that out-of-phase instability happen easily in begin of fuel cycle, many control rods inserted, large core size, axial power bottom-peak. According to parameter sensitivity study, we can find that except the parameters of recirculation loop gain and time constant, other parameters have the same influence between in-phase and out-of-phase instabilities. At the same time, we know the parameters of core power and flow have significant effect on out-of-phase instability, others influence can be ignored.