- 36 - 2.3.8 General evaluation of the "loss of heat sink" topic ASN finds that the heat sink, which is an important system, demands particular vigilance. The recent heat sink clogging or partial loss events, at Cruas and Fessenheim in December 2009 especially, demonstrated its vulnerability and led EDF to initiate an action plan to reinforce the robustness of all the heat sinks. ASN specifically asked EDF to initiate a design review of all the heat sinks. ASN will be asking EDF for the detailed conclusions of the heat sink design review site by site, along with the corresponding action plan with completion dates. The inspections carried out by ASN in 2011 showed that the general condition of the heat sinks was good but that a certain number of nonconformities persisted on certain sites. Stringent operation and maintenance, close monitoring of the condition of equipment and structures and exhaustive implementation of national directives are as a general rule the areas for improvement for many sites. On numerous sites, maintenance of the SEC system was deficient and thus requires particularly close attention. EDF intends to strengthen the safety frame of reference for the heat sink, estimated for early 2013. 1.42.4 Loss of electrical power supplies 2.4.1 Introduction Each reactor is connected to the electricity grid by a line called the "main line". Before sending the grid the electrical energy it has produced via the generator, the reactor uses the step-down transformer (TS) to draw off the electrical energy needed to power the panels and switchboards providing the energy required by the equipment it needs in order to function, as well as the equipment needed for the safety of the facility. If there is an incident on the main line, it is capable of isolating itself from the electricity grid via its step-down transformer and can continue to supply its panels and switchboards itself. When the reactor is not producing electricity, or if the main line is unavailable, the panels and switchboards are then supplied via a second line, called the auxiliary line. The reactor is then powered directly from the electricity grid, via the auxiliary transformer (TA). Failure of the off-site sources is considered in the design of the reactors. To take account of this risk, each reactor has on-site energy sources capable of supplying the electrical panels and switchboards essential to the correct working of the safety equipment. The reactor's on-site sources thus consist of two diesel electricity generating sets. Each nuclear power plant has an additional on-site energy source, the technology of which differs according to the plant series to which it belongs: a station blackout diesel (SBO) for the 900 MWe NPPs or a combustion turbine (TAC) for the 1300 MWe and N4 series. In the event of total loss of both off-site and on-site electrical sources, there is one final backup turbine generator (LLS) type electrical power source which runs on the steam produced by the reactor itself. The goal of the inspections was to examine NPP practices with regard to the operation, maintenance and enhanced reliability of the equipment contributing to the electrical power supply for the equipment necessary for the safety of the facilities. Application of the EDF technical frame of reference was verified by means of spot-checks, particularly with regard to the general operating rules and the maintenance programmes. Field visits were also carried out on the electrical buildings, the backup electricity generating sets and the TACs, in the control room and in the battery rooms. Finally, a real-situation exercise was held with the EDF operating crews, who were asked to align and start-up a backup electricity generating set, during the course of certain inspections. 2.4.2 Organisation and operation ASN considers that the documentation associated with the operation and maintenance of the electrical power supplies could be improved. Formal structure of documents During the spot-checks of the operating documents, the inspectors found a lack of rigorous structuring of these documents on most sites, in particular: the particular requirements and the limiting conditions of chapter III of the general operating rules (RGE) are not always included in the maintenance operation files (especially at Bugey, SaintAlban);
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