The Laguna verde BWR/5 instability event. Some lessons learnt

There have been several BWR instability events reported in the past. Among them, the one occurred on January 24, 1995 at Laguna Verde BWR/5, Mexico is studied here. The power signal was divided into small blocks and each block was considered from the point of view of the noise analysis. Reactor was stable within the preliminary blocks and unstable at the final blocks, so noise signal characterisation allows us to describe the transition to instability from stability. The lessons learned serve as a way to design very early alarm procedures.