The use of the noise analysis for the detection of the pellet- cladding mechanical interaction

The pellet-cladding mechanical interaction (PCMI) has been classically studied with the cladding elongation signal versus the rod power, but a different method can be used to evaluate the PCMI. It is based on the noise analysis techniques and uses the coherence function between the neutron flux and the cladding elongation noise signals detecting PCMI. This technique has been studied in the Halden experimental reactor. The mean coherence versus average linear heat rate shows two different regions that can be fitted with two straight lines, with the crossing point between them being taken as the threshold for PCMI. In addition, noise analysis in the time domain allows us to measure an elongation response time to a power step. This result can be applied to power instability events in BWRs.