- 154 - If all the reactors on a site were to be affected simultaneously, the feedwater volumes (EFWS + SER) would be reduced, as the SER tank is divided between several plant units. The last periodic safety reviews evaluated the autonomy at 24 hours (can reach 2 to 3 days on certain sites). ASN considers that the times before the core becomes exposed should have been clearly indicated. ASN will ask EDF to give a qualitative evaluation of the times. In states where the primary system is not pressurisable, ASN observes that EDF has not calculated a cliff-edge effect for the H1 situation. ASN agrees that the time before the core becomes exposed would be longer in an H1 situation than in a situation of total loss of the electrical power supplies (see § 5.1.of this chapter), due to additional possibilities of making-up the primary system from the PTR tank. More precisely, the times calculated in the "H3" situation are from 70 to 80 hours when the reactor cavity is full; more than one day when the reactor cavity is not full, subject nevertheless to the robustness of the equipment used for H1 management (CVCS pumps, electrical panels, etc.). Reservations on this point are made in the following paragraph. In states where the primary system is pressurisable, a cliff-edge effect associated with feedwater exhaustion is observed. ASN estimates the time before core exposure, evaluated at several days, to be acceptable given the water quantities regularly observed and prescribed in the operating technical specifications: 100 hours of autonomy if a single plant unit is affected, and at least 24 hours (possibly more) if a whole site is affected. ASN considers that EDF's proposal to re-assess the minimum required water reserves and study additional means of resupplying water is satisfactory. EDF has not examined in the H1 situation the case where the primary system vents remain open, whereas failure of the vents to close was examined for the H3 situations. Given the additional available sources of make-up for the primary system, such a situation appears to be covered by the "primary system not pressurisable" states. Assessment of the impact of an H1 situation on the spent fuel pools: EDF has chosen the operating ranges of APR40 or RCD41 at end of unloading as states that are penalising to consider for an accident situation affecting only one plant unit. This is because it is in these plant unit states that the residual power of the fuel stored in the spent fuel pool is at maximum level. For the analysis of an accident scenario affecting the entire site, EDF has taken a situation where one of the site plant units is in APR or RCD (states penalising for the spent fuel pools) while the others are under power. EDF also studied the case where a fuel assembly is being handled in the spent fuel pool. With a single plant unit affected: Loss of the heat sink induces a total loss of spent fuel pool cooling. The procedure applied in this situation provides for: stopping of the fuel handling operations and placing those fuel assemblies actually being handled in safe condition; alignment of spent fuel pool make up in priority by SED42, then by JPI43. The other measures aiming at guaranteeing the accessibility of the premises adjacent to the BK hall, and that the pressure in the hall does not rise, are equivalent to those for situation H3 - total loss of electrical power supplies. Loss of spent fuel pool cooling results in gradual heating of the water. The JPP44 system guarantees permanent make up of the spent fuel pool. Throughout this period where topping up is guaranteed, the level of water in the 40 APR: Refuelling shutdown 41 RCD: Reactor completely unloaded 42 SED: Reactor dimineralised water distribution system 43 JPI: Nuclear island fire protection system
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