- 84 - As from the 1300 MWe series reactors, the fuel pool storage racks have been manufactured in a neutron-absorbing material in order to guarantee sub-criticality in spite of a denser storage arrangement than for the preceding reactors. The fuel pools of the 1300MWe P4 series reactors have 459 storage compartments. As from the P4 series, the transportation containers are loaded beneath the loading pool. This means that the heavy handling crane used in the CP0, CPY and P4 series reactors is not necessary, allowing the height of the fuel building to be lowered. The fuel storage pools have capacities of 630 compartments for the P4 series reactors, 612 for the N4 series reactors, and 1167 for the EPR reactor. For the EPR reactor, the reactor cavity and spent fuel pool cooling and treatment system (PTR) has an additional train with a diversified heat sink and can be resupplied with electricity by the ultimate backup generator sets. 1.3 The periodic safety reviews The French safety standard requires French nuclear installations to be designed and built to withstand - without jeopardising their safety - the most severe natural phenomena (earthquakes, floods, etc.) that have already occurred in the surrounding area, with an additional safety margin. Moreover, it requires the implementation of a system of "defence in depth" that consists of a series of redundant and diversified measures (automatic mechanisms, systems or procedures) to prevent the occurrence of an accident or to mitigate its consequences. These measures are checked at each stage in the life of the nuclear installations (examination of the safety options, creation authorisation, commissioning authorisation, etc.) and re-examined systematically during the 10-year safety reviews instituted by article 29 of the act of 13 June 2006. This periodic safety review provides the opportunity for an indepth examination of the condition of the NPPs, to check that they comply with all the safety requirements. An additional aim of the review is to improve the safety of the installations, particularly by comparing the applicable requirements with those applied by the licensee to more recent NPPs. The periodic safety reviews therefore constitute one of the cornerstones of safety in France, by obliging the licensee not only to maintain the level of safety of its NPP but also to improve it. The review process The periodic safety review comprises a number of successive steps. 1. The conformity review: this consists in comparing the condition of the installation to the applicable safety requirements and regulations including, notably, the creation authorisation decree and ASN's requirements. This step ensures that changes to the installation and its operation, as a result of modifications or ageing, comply with applicable regulations and do not compromise the installation's safety requirements. This tenyear conformity check does not relieve the licensee of its permanent obligation to guarantee the conformity of its installations. 2. The safety review: this aims to appraise the safety of the installation and to improve it with respect to: French regulations and the most recent safety objectives and practices in France and abroad; operating experience feedback from the installation; operating experience feedback from other nuclear installations in France and abroad; lessons learned from other installations or equipment prone to risk. ASN may rule - possibly after consulting the GPR (advisory committee for safety of nuclear reactors) - on the study topics envisaged by the licensee before the launch of the safety reassessment studies, during the phase known as the periodic safety review orientation phase.
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