Operational feedback on internal structure vibration in 54 French PWRs during 300 fuel cycles

Abstract

EDF has acquired extensive feedback on vibration of reactor vessel internals by analysing ex-core neutron noise on its 54 pressurized water reactors during the course of over 300 fuel cycles. This feedback has been built up by processing more than 3,000 vibratory signatures acquired since the startup of its reactors. These signatures are now centralized for the whole of France in the “SINBAD” data base. Signature processing has enabled: 1. • distinguishing between mechanical phenomena and signature variation linked to unit operation: in particular, the impact on signature level of unit operating parameters such as initial fuel enrichment and burn-up rate was assessed; 2. • among the purely mechanical phenomena, pointing up slight changes in position of vessel internals and the first signs of structural wear: relaxation (in the hold-down spring and fuel rod assemblies) and wear on surfaces of contact between internals and reactor vessel were detected; 3. • lastly and most importantly, automatic recognition of the various types of vibratory behavior of internals. It was consequently possible to draw up user requirement specifications for automated monitoring of internals, which should soon be integrated in PSAD, a system which groups several reactor monitoring functions.