Exploring the dodewaard type-I and type-II stability; from start-up to shut-down, from stable to unstable

Stability measurements on the Dodewaard natural circulation boiling water reactor have been performed for five years, covering the entire operational map. A data base of stability characteristics for testing of analytical models and for computer-code benchmarking has been set up. Type-I natural-circulation-flow stability and Type-II reactor stability have been investigated, Flashing turned out to be an important phenomenon. At a Type-II instability, the oscillating reactor power showed a peculiar modulation before the divergence to the scram level. The decay ratio was found to be an unpractical and unsafe stability indicator for reactors with a decay ratio larger than 0,6