Searching the beginning of BWR power instability events with the Hilbert Huang transform

When a BWR instability takes place, the Regulator usually demands a report which must include many aspects such as the initial time of the instability and also the measurements adopted by the operator at that time. This initial time normally is difficult to know from the available data. In this work, a methodology is proposed to determine accurately when the instability began based on the Hilbert–Huang transform. The Empirical Mode Decomposition is applied to neutron detector signals coming from two plants which have recorded them during real instability events. The first intrinsic mode function shows sharply the beginning and the end of the incident. Besides, through the instantaneous amplitude and frequency of the first mode a kind of Decay Ratio can be assigned allowing us to obtain a sharper description of the instability.

► The report of the instability is enriched by including its beginning and its end.
► The Hilbert Huang transform (HHT) is used for indentifying both.
► The first Intrinsic Mode Function (IMF) detects both.
► The methodology is applied to neutron detector signals from two plants.
► The Decay Ratio of IMF 1 is calculated.