- 156 - 5.2.2 Loss of the primary heat sink and the alternate heat sink No reactor in operation has an alternate heat sink. Only the EPR has an alternate heat sink. It comprises two independent systems (EVU and SRU) which themselves are made up of two redundant channels in the pumping station. The SRU system can draw in raw water from the main pumping station ("normal" mode) or from the outfall structure in the sea ("diversification" mode). EDF has not studied the consequences of loss of the alternate heat sink on the safety of the EPR reactor. Consequences of loss of the heat sink on the spent fuel pools: In this scenario, the 3 PTR cooling trains are lost due to the loss of the CCWS/ESWS and EVU/SRU trains. In states A, B, C with the primary system pressurisable, the 2600 m3 JAC tank is dedicated to replenishing the ASG tank. Making up by JAC gives a time lapse of about four days before the fuel assemblies stored in the rack become exposed, which is compatible with an external intervention. In states C with the primary system not pressurisable, D, and potentially part of state E, the topping up by JAC enables the level in the spent fuel pool to be maintained for: about four days with the JAC tank of 1000 m3; more than ten days with the JAC tank of 2600 m3. The time lapse before the fuel assemblies stored in the rack become exposed is about 18 days, compatible with an external intervention. In states E and F46, making up by JAC enables the level in the reactor cavity to be maintained for: more than one day with the JAC tanks of 1000 m3; more than three days with the JAC tank of 2600 m3. The time lapse before the fuel assemblies stored in the rack become exposed is about 5 days, compatible with an external intervention. ASN observes that for the Flamanville EPR, EDF has not studied the consequences of the successive loss of first the primary heat sink, then the alternate heat sink on the safety of the reactor. This configuration was only studied for the spent fuel pools. This scenario should also have been combined with a total loss of the electrical power supplies. ASN will ask EDF to conduct complementary studies to assess the consequences of a complete loss of the primary heat sink (ESWS) and alternate heat sink (SRU) of the Flamanville 3 EPR on the damage to the reactor core. Regarding the assessment of the consequences of heat sink loss on the spent fuel pools, ASN observes that the time lapses before the core becomes exposed are purported to be longer than the time specified in the baseline safety standard: a few days with maximum residual power in the BK building spent fuel pool, and about one week in the states other than APR - RCD. These times seem compatible with an external intervention and with the means that EDF envisages implementing to make an additional water make-up. If the make-up means are lost, the times and consequences are identical to those for an electrical power loss situation. 46 State "F" of the EPR: Cold shutdown with the reactor core completely unloaded. This state is used to carry out work on the primary system components. This state is not to be analysed with respect to reactor core protection.
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