- 188 - consequences off the site. Thanks to the effective filtration of long-lived products in the aerosols, such as caesium 137 with a radioactive half-life of about 30 years, the long-term radiological consequences of U5 opening are limited. If the U5 system were to be opened, population protection measures during the radiological emergency phase would be deployed around the nuclear site. For the Flamanville EPR, EDF states in the CSA report that the core melt accident is part of the EPR designbasis and complies with strong stringent requirements. The radiological objectives associated with a severe accident are that in these situations, only protection measures that are extremely limited in terms of space and time should be necessary: limited sheltering of the population, no need for emergency evacuation beyond the immediate vicinity of the facility, no permanent rehousing, no long-term restrictions on the consumption of foodstuffs (in accordance with the technical directives applicable to the EPR). Equipment and devices specific to the management of a severe accident (for example passive flooding of the corium following its spreading in the specific area provided and the EVU system to control the containment pressure) were thus defined in the EPR design. In the CSA reports, EDF conducted a deterministic study of a combined failures situation leading to total loss of the SBO diesels. Assuming the unavailability of the soda injection and the shutdown of the ventilation and filtration systems for 24 hours, the rise in effective dose for the population would remain limited, but this situation would lead to an iodine release level that would require the deployment of population protection measures during the radiological emergency phase, such as the distribution of stable iodine tablets. EDF stated that it was examining the possibility of making the IRWST water alkaline, including in situations involving a total loss of electrical power supply. 6.4.2 Accident management after uncovering of the top of the fuel in the pool For the purposes of the CAS, ASN asked EDF to "describe the measures taken to manage the consequences of the loss of the cooling function for the spent fuel pool or for any other fuel store (the following concern the storage of fuel): before and after the loss of appropriate protection against radiation; before and after uncovering of the top of the fuel in the pool; before and after severe damage to the fuel in the store." The approach adopted by EDF in its complementary safety assessments concerning the spent fuel pools is to examine the consequences of a major natural hazard on the systems capable of removing the residual heat from the fuel stored in the pool, by examining the consequences of the loss of heat sink or electrical power supplies (see § 5). In its CSA reports, EDF did not however study the possible consequences of a loss of the integrity of the pools or cavities in the fuel building or reactor building, as well as the systems connected to them. ASN considers that the natural hazards to be considered as part of the CSAs can induce risks other than the loss of electrical power sources or heat sinks, such as: the risk of deformation of the storage racks; the risk of falling loads; shaking of the civil engineering structures supporting the spent fuel pool; a breach of a pipe or leaktight barrier connected to the pool; the loss of integrity of a door or sluice. These risks were analysed by IRSN during the review prior to the meeting of the advisory committees in November 2011. The analysis focused on evaluating the existing or foreseeable lines of defence to prevent uncovering of the fuel assemblies and melting of the fuel in the fuel building. With this in mind and in order to limit the risk of accidental drainage of the spent fuel pool, several improvements to the material and organisational arrangements were mentioned for the NPP reactors in service: Doubling of the diameter of the siphon-breaker devices on the PTR system discharge line; Automation of isolation of the cooling system intake line.
RkJQdWJsaXNoZXIy NjQ0NzU=