- 187 - ASN considers that the proposed improvements, which meet the CSA specifications, should be implemented. It will issue a requirement on this subject. With regard to the Flamanville EPR reactor, the design of which already offers improved protection against severe accidents, EDF will identify which among the planned equipment is to be included in the hard-core for the prevention and mitigation of the consequences of a severe accident, including systems or equipment allowing depressurisation of the reactor coolant system, isolation of the containment and control of the pressure in the containment. ASN will issue a requirement on this subject. By virtue of its design, the Flamanville EPR reactor has no containment venting and filtration system. The EVU system has the role of removing heat from the containment and controlling its pressure, with the residual power being evacuated to the diversified ultimate heat sink SRU. To prevent a cliff-edge effect in the event of total and prolonged loss of electrical power, EDF envisages adding a mobile and independent water makeup system in the reactor building, via the EVU spray nozzles, which would be deployed within 48 hours of the beginning of the accident. This arrangement extends the 5-day period, beyond which the FARN would be responsible for providing a high-power mobile electrical device for resupplying the EVU/SRU chain. ASN has no objection to this additional system, but considers that EDF could go further (see following paragraph). 6.3.10 Steps envisaged for strengthening maintained containment integrity after fuel damage In general for the reactor fleet, concerning the equipment designed to limit the consequences of a severe accident and radioactive releases, the current baseline safety requirements make no provision for off-site hazards. EDF shall, in response to a requirement to be issued by ASN concerning the hardcore, specify the hard-core equipment (existing equipment and additional countermeasures) preventing and mitigating the consequences of a severe accident. This equipment shall be robust to hazards beyond the current hazard level considered for the facilities. This in particular applies to the hydrogen recombiners and the U5 systems in use on the reactor fleet. Moreover, in the light of the cliff-edge effect on the consequences of a reactor core melt, when a containment is already open, EDF undertook, after the CSAs, to study the feasibility of measures to guarantee the time needed to close the equipment hatch (TAM) in the event of total loss of electrical power. With regard to the EPR, in addition to the steps planned to maintain the integrity of the containment, assuming the possibility that a heat sink might not be restored with certainty in the scenarios envisaged by the CSAs, ASN will be asking EDF to identify the existing or additional systems to be included in the hard-core to ensure management of pressure in the containment in the event of a severe accident and to perform a study of the advantages and drawbacks of the various possible systems. With regard to the ability of the EPR's severe accident equipment to withstand hazards, the systems participating directly in heat removal and thus in maintaining the integrity of the containment have a seismic safety classification SC151. In the Flamanville EPR's CSA report, EDF states that this equipment is robust to seismic levels beyond their design basis. As part of the Flamanville EPR commissioning review, EDF will send ASN a demonstration of the robustness of the hard-core equipment. 6.4 Measures to limit radioactive releases in the event of a severe accident 6.4.1 Radioactive releases after loss of containment integrity In the CSA specifications, ASN asked EDF to tackle the steps planned to limit radioactive releases from the facilities in the event of a severe accident. In the CSA reports on the reactor fleet, EDF states that the U5 venting-filtration device, even though reserved for ultimate safeguard of the containment and concerning which all the countermeasures are designed to prevent it from opening, can once the gas plume resulting from its opening has passed help limit the radiological 51 The requirements for seismic class 1 are, whenever required, operability during or after an earthquake, functional capacity, integrity and stability.
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