Mechanical surveillance of French PWR's

It is expected that, by the end of 1986, almost forty 900 MWe nuclear power plants would be operating in France. In order to increase their availability, a surveillance has been set from the startup of the first unit Fessenheim 1. Mechanical surveillance is only considered here, that is, the surveillance of internal structures vibrations, and the detection of loose parts. The surveillance of vibrations aims to detect an anomaly in internals vibratory behaviour. For that, signals are used from accelerometers located on the pressure vessel and from ex core ion chambers. Signatures of these signals (Power Spectral Densities) are obtained periodically on site and automatically compared with the initial reference signature. Their interpretation is based on theoretical and experimental studies. Early detection of loose parts also is important to maintain the integrity of internal structures. We use the impulses obtained by accelerometers located on the primary circuit, due to shocks of metallic parts and surface wave propagation. Tests have been performed on site to determine the system sensitivity: the detection of a loose part inside a steam generator hot box during the preoperational test and the malfunction of a valve. Now, the progressive commissioning of new 900 and 1300 MWe nuclear power plants has lead us to automatize on site anomaly detection, in order to reduce the operator's work. Other developments are being carried out, such as the realization of specific devices, the development of a data bank, including data from each reactor, from each family of identical reactors and data related to particular incidents