- 185 - In the CSA reports on the reactors in the fleet, EDF states that in situations involving a total loss of electrical power sources, the pressure measurement in the containment is lost. It is then possible to use the containment pressurisation kinetics charts available for the various plant series. In situations involving a total loss of electrical power sources, the unit having lost all its means of injecting water into the core, pressurisation of the containment is slow and opening of the U5 venting device therefore takes place after a few days. This time can be used to restore the unit's electrical power sources or deploy the mobile resources provided by the FARN. EDF states that the Ultimate Backup Diesel Generator (DUS) will be able to provide electrical back-up for the instrumentation enabling operation to continue in a severe accident situation. This is satisfactory in principle. ASN will examine whether the information backed-up by the SBO diesel generator is complete, based on the proposals submitted by EDF for the hard-core. In the meantime, ASN also considers that the operations shift crews must be able to access the containment pressure and vessel pressure measurements as of the first hours, in all circumstances, without waiting for the FARN. In addition, EDF undertook to guarantee that as of the first hours of an accident, the primary system pressure and containment pressure measurements would be available, including in the event of failure of the LLS turbine generator set, by deploying a small generator pending the installation of the Ultimate Backup Diesel Generator (DUS). With regard to the robustness of this instrumentation, EDF states in the CSA reports for the reactors in the fleet that this entails no risk of unavailability in a flooding situation, but that it is not classified for the seismic risk. EDF will study its seismic resistance on the basis of the conclusions regarding the content of the hard-core. Moreover, the installation of instrumentation dedicated to severe accident management, able to detect reactor vessel melt-through and the presence of hydrogen in the containment is currently planned for the third ten-yearly inspections for the 900 MWe and 1300 MWe reactors and the first ten-yearly inspections for the 1450 MWe reactors. ASN considers that these elements would facilitate management of the situation by the licensee and the public authorities. ASN will require that the implementation of this instrumentation be accelerated and that it shall also be redundant. 6.3.8 Ability to manage several accidents in the event of simultaneous core melt / fuel damage in different units on the same site Feasibility of immediate GIAG actions Assuming an event leading to simultaneous loss of all electrical power supplies and cooling for the reactor coolant system on all the reactors of a site, ASN considers that, for each reactor, the feasibility of all the immediate actions provided for in the GIAG must be guaranteed, in particular depressurisation of the reactor coolant system, with the operations and emergency crews present on the site. In this respect, following the CSAs, EDF undertook to study the adequacy of the resources, both human and material, for the activities involved in implementing the equipment of the hard-core (including the immediate actions of the GIAG) and the additional equipment proposed following the CSAs. The main steps in this study are as follows: identification of the missions to be performed (emergency management, operation of facilities, etc.) on all the units; identification of the activities to be performed, with their main characteristics in terms of duration, intervention conditions, etc.; consideration of the additional equipment to be implemented, with its implementation constraints being incorporated into its design; final check on the adequacy of the human resources (numbers and skills) for all the activities to be carried out; identification of any additional training requirements.
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