- 169 - Furthermore, concerning the reactors in operation, the venting-filtration system U5 (described in § 6.2.2), reserved for the ultimate safeguarding of the reactor containment, once the gas plume induced by its opening has gone, enables the off-site radiological consequences to be limited. This system, which filters the aerosols that form in the reactor containment in the event of loss of reactor vessel or primary cooling system leaktightness, retains a large proportion of the radionuclides. If U5 is opened, the population protection measures would be implemented around the nuclear site during the radiological emergency phase. To limit iodine releases and reduce the radiological impact on the site and the populations in a severe accident situation, EDF indicates in the CSA reports that it plans studying a passive device for increasing the pH in the reactor building sumps, including in a situation of total loss of the electrical power supplies (SBO - site blackout). As the earthquake was not considered a plausible severe accident initiating event at either the design stage or during the periodic safety reviews (see § 6.1), given all the design measures taken on the structures, systems and components classified for safety, the U5 system components - apart from the containment penetration and the isolation valves - are not seismic classified. The U5 system sand filter was therefore not subject to specific requirements with respect to the seismic risk when it was installed. Consequently, this system could, in the event of an SA further to an earthquake, cease to be operational or even become prejudicial for other safety-classified equipment items. EDF has undertaken to conduct a study on the earthquake resistance of the U5 system. It has also announced the launching in a second phase of a broader reflection on the U5 system filtration that could, if necessary, lead to changes in this system in the longer term. ASN will issue a requirement on this subject. Insofar as they were not subject to specific design requirement with respect to external hazards, ASN considers that at present, the means for limiting releases in the event of core meltdown are not resistant to the hazard levels adopted for the CSAs, particularly for earthquake levels exceeding the design-basis earthquake. The changes resulting from the studies announced by EDF will have to guarantee the resistance of these means. ASN will thus require EDF to carry out a detailed study of the possibility of improving the U5 ventingfiltration system, taking into account hazard robustness, filtration efficiency if used on two reactors simultaneously, the improvement in the filtration of the fission products, especially iodine isotopes, and the radiological consequences of opening, notably on accessibility of the site, of the emergency management rooms and of the control room. The communication and information systems (internal and external): In the CSA reports, EDF gives the communication objectives and principles applied to ensure on-site communication between the emergency teams and the grouping areas, and communication with the off-site players. The objectives of these systems are to alert the on-site and off-site players as quickly as possible (EDF staff and public authorities alike), to alert the populations if a reflex response phase PPI (off-site emergency plan) criterion is attained, to exchange information with the various emergency management centres both on site and off site, and to inform the public and the medias. EDF indicates that the means of communication used when deploying the organisation can be deficient (either following immediate degradation as a result of an initiating event, or by exhaustion of the batteries ensuring their operation). To enhance the reliability of these various means of communication, EDF undertakes to study the reinforcement of the strategic connections by communication means that have greater autonomy and are resistant to earthquakes and flooding (i.e. totally independent of hard-wired communication links). The aim is to equip the emergency management rooms with satellite-link telephones with greater autonomy enabling the shift operations supervisor to give the alert, the local and national players to establish or continue their communications, and the FARN (nuclear rapid intervention force) - if it should be required to intervene - to establish contact with the on-site participants. The FARN is a national EDF entity currently being set up, which will be capable of rapidly providing material and human aid to a site in serious difficulty. This entity is described in greater detail in the paragraph "Extensive destruction of infrastructures around the facilities" below. ASN considers that communication is a primary element in emergency management and that it is essential for EDF to be able to alert the public authorities and, if delegated power by the prefect, to alert the populations in order to protect them, inform on-site personnel of the situation, particularly if the site has to be evacuated, and
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