- 62 - the instrumentation system used to monitor the main parameters in the facilities (temperature, pressure, water level, radiological environment, etc.). Some equipment therefore has to be identified as important for safety and be the subject of particular monitoring in order to maintain its functions in both normal and accident conditions. It should be pointed out that electricity distribution comprises 3 modes: normal, backup, safeguard. The inspectors found that modifications to the electrical power supplies had been made with no checks on the quality of the work done or the requalification of the hardware (addition of electrical cabinets leading to the room heating up, with the cabinet doors then kept open for ventilation; transformation of a cloakroom into an equipment room, electrical modifications made with no checks subsequent to the works (in particular a change to the power balance). A known problem with the reliability of the measurement system (displacement type) for the fuel tank levels of the backup generator set (GES) meant that there was drift in their operating modes. Hardware changes were not made under quality assurance conditions in the manual mode restart procedure for the site's electrical power supplies in the event of loss of the ERDF grid (dating back to 1993, handwritten modifications). Furthermore, the resupply of the GES in a post-accident situation, given that the fuel tank is located outside the buildings, could be problematical if these areas are inaccessible, for instance following an earthquake. Identified operating experience feedback concerning circuit-breaker settings following unplanned ventilation losses (magnetic protection) has not in recent years always been integrated. Other feedback is being processed with regard to the premature wear of the connecting rod bearings of certain backup generating sets. The site visit in particular revealed advanced corrosion of the lines connecting the GES underground tanks to their motor unit and particularly high levels of corrosion on the backup generator sets' cooling water lines. The inspectors also found that several bargraph type indicators intended for operation of the safeguard systems were faulty in certain fall-back centres. Finally, the visits carried out were also an opportunity to question the licensee about the risk of loss of the fall-back centres for units R1 and R7, and thus of the electrical safeguard, in the event of on-site flooding, given the presence in adjacent premises of water pipes not qualified as seismic-resistant. To conclude, the accessibility of the safeguard electrical power supply resources would not always appear to be guaranteed in post-accident conditions, particularly with regard to fuel resupply. The advanced state of corrosion of some backup generator sets equipment requires action to remedy these anomalies rapidly. The inspections brought to light the need for improved requalification of the facilities and updating of the documentation, if the function is not to be degraded. Generally speaking: the organisation and the means for backup electricity supply on the site, and maintained operation of the equipment important for safety taking part in functions important for safety, sometimes with reliance on off-site resources, must be more formally structured, made more reliable and be more regularly tested (site accessibility, mobilisation of emergency teams in a large-scale incident situation, etc.); the actual self-sufficiency of the site with regard to its electrical power supply must also be reviewed in the light of the above. Tricastin site The subject of electrical power supplies is dealt with by the licensees in accordance with the safety report and the general operating rules in force. The inspections revealed no divergence from this frame of reference. The safety issues related to the loss of electrical power supplies, for the facilities themselves, are minor. However, if electrical power is lost, the facilities would lose their dynamic containment, environmental monitoring and means of communication. As the consequences of a loss of electrical power are highly limited in terms of the safety of the facilities, the licensees have made no provision for any specific organisation. Only the electrical power supplies of Eurodif are designed to minimise the risk of total loss of off-site sources (12 electrical sources are provided to supply the plants). However, according to the safety report, the "total loss of electrical power"
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