Fluctuations neutroniques observees sur les reacteurs 900 MW and 1300 MW a partir des systemes de surveillance en exploitation

Abstract

This paper presents a survey about the use of neutron noise surveillance techniques on French PWRs. It rests upon a data base built from informations (Power Spectral Densities), that are being collected in nuclear power plant by the plant technicians every month. A first study concerns 14 reactors with partial thermal shield and 27 fuel cycles : the evolution of neutron noise fluctuations within several frequency bands has been followed versus time, boron concentration and burn up. An experimental estimation of the burn up influence has been made. Reference signatures related to internal components'behaviour are quantified. The anomalies detected on all 900 MW units from their first start up (about 80 cycle-reactors) are briefly presented. First results recently obtained on the new 1300 MW nuclear plants confirm that neutron noise analysis combined with the vessel vibration analysis is a valuable tool for internal components monitoring and diagnosis.