- 153 - Loss of the primary heat sink, reactor in state A, B or C with primary system closed or just open Extension of the incident to the entire site does not change the scenario described previously, given that operation of the Flamanville 3 EPR does not require equipment common to plant units 1 and 2. Damage to the fuel of the Flamanville 3 EPR will start about 9 days after loss of the heat sink. Loss of the primary heat sink, reactor in state C, primary system not pressurisable or in state D Extension of the incident to the entire site does not change the scenario described previously, given that operation of the Flamanville 3 EPR ensures the long-term removal of the residual power and does not require equipment common to plant units 1 and 2. EDF has not studied the situation of combined loss of the primary and alternate heat sinks. For the EPR, EDF therefore considers that in all cases the heat sink will have been restored before the core becomes exposed. When the JAC tanks are empty (about 7 days after loss of the heat sink), replenishing of the EFWS tanks of the Flamanville 3 EPR from the freshwater ponds of the SEA (demineralisation plant water supply system) is envisaged. This resource, which is shared between the three plant units and the replenishing of the EFWS and BK building tanks, could be called up at the request of the national crisis team to provide several days of additional autonomy. To conclude, when the primary system is closed, the residual power is removed from the reactor core by the secondary system. In this case EDF identifies a cliff-edge effect related to the exhaustion of the feedwater reserves. This time this would take is evaluated at "several days". EDF considers that the heat sink (which can be restored in one or three days depending on the site) will in all cases have been restored before the core becomes exposed. In situations where the primary system is not pressurisable, the residual power is removed by vaporisation of the reactor cavity water in the containment. In such cases, the primary system is provided makeup via the CVCS system. The cliff-edge effect is not detailed by EDF. In the particular case of the EPR, a cliffedge effect is associated with the feedwater autonomy, evaluated at about 2 days. This corresponds to the specified autonomy of the EFWS tanks, which can subsequently be replenished by the tanks of the JAC system which is dedicated to this, increasing the autonomy to 9 days. ASN considers that the heat sink loss accident situations analysed by EDF in its complementary safety assessments correspond to the requirements of ASN decision 2011-DC-0213 for the existing reactors and just for the Flamanville 3 EPR. As required by the specifications, they are established considering gradual losses of the water resources, with the exception of the following cases which EDF should have studied: total loss of the primary heat sinks combined with loss of the alternate heat sink on the Flamanville 3 EPR (situation only studied for the spent fuel pool in building BK) situation H1 (total loss of the heat sink) on the Civaux NPP site. This situation was only studied for one plant unit on the Civaux site and not for the entire site. Apart from the H1 situation on the Civaux site, the postulated situations are examined considering first one plant unit, then all the plant units of a site as being affected, as required by the specifications. Pursuant to ASN decision 2011-DC-0213, the site H1 situation should be explicitly studied for all the plant units on the Civaux site. ASN is going to ask EDF to evaluate the robustness of the Flamanville 3 EPR reactor with respect to complete loss of the primary and alternate heat sinks, and the combination of this with a general electrical power loss situation . If only one plant unit was affected, ASN considers the EDF's estimate of the time before the heat sink is restored (several days) to be plausible, as the baseline safety standard currently in effect already requires an autonomy of 100 hours for total loss of the heat sink on one reactor.
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