- 99 - no simultaneous occurrence of earthquake and the following is postulated: o an independent incident or accident condition, o an independent internal hazard (for example fire), o another independent external hazard. An examination must be conducted on the possible hazards that non-seismic-classified equipment represents for seismic-classified equipment by: considering the potential hazards representing an effective risk for the target; checking that none of the equipment items performing safeguard, reactor protection and their support functions is jeopardized. The list of potential hazards identified in particular includes the structures and items (weighing more than 10 kg) not designed to withstand an earthquake (unfixed loads, handling machinery not tied down, cabinets, fans, civil engineering structures, tanks, large equipment on small piping, equipment running through the premises, false ceilings, piping with a diameter larger than 50 mm, etc.). The event earthquake approach was extended to the potential damage to the nuclear island buildings by the turbine hall. When the analysis leads to the need for protection, the measures taken can involve: relocating the target or the hazard source, installing reinforcements to ensure the hazard's ability to withstand the earthquake, installation of protection on the target, justification of the target's ability to withstand the hazard by analysis or by testing, modification of the operating conditions of these equipment items. Implementation of this approach is being requested by ASN on the occasion of the ten-yearly outage inspections (as of the 900 MWe VD2 ). The approach comprises two parts, one national, which can lead to modifications to a plant series, and one local. During the course of its inspections, ASN observed the difficulty experienced by the licensee with ensuring optimum integration of this requirement on certain sites on a day-to-day basis, in particular during maintenance operations, construction site operations, the use of scaffolding and the utilisation and conservation of handling resources. This is why ASN will be requiring that on each site, EDF ensure the effective implementation of the "event earthquake" approach. Loss of off-site power supplies: The PWR safety demonstration studies the simultaneous occurrence of a major earthquake and the loss of offsite power supplies, insofar as they are not designed to withstand a major earthquake. At the same time, EDF introduced the "LOOP combination" which simulates the consequences of an earthquake during an accident transient. The safety case thus gives the combination of incidents and accidents with a LOOP: these transients are only managed by means of seismic-classified equipment. The total loss of electrical power supplies (situation H3) to a single unit on the site is included in the baseline safety requirements. It is the result of the loss of off-site power supplies associated with the impossibility of restoring the switchboards backed up by the back-up generators in each unit. These backup sources comprise autonomous and functionally independent diesel generators. In the event of the failure of these unit diesel generators to start or connect, it is possible to connect a site emergency generator or a diesel generator belonging to a neighbouring unit.
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