As part of the fourth periodic review of EDF's 900 MWe reactors, IRSN conducted an assessment of the suitability of these reactor vessels - initially designed for an operating life of 40 years - for continued operation for up to 50 years and presented its conclusions to the standing advisory group of experts on nuclear pressure equipment.

The reactor vessel, an essential safety component, is not replaceable. However, the steel that makes them up ages under the effect of neutrons from the reactor core.

As the 900 MWe reactors of the EDF fleet progressively reach 40 years of operation, the hypothesis initially taken into account for the calculation of the effect of neutron irradiation, the operator must demonstrate the aptitude of the vessels to operate for another 10 years, a sine qua non condition for the prolongation of reactor operation.

The safety file submitted by EDF was examined in depth by IRSN experts in several stages, focusing on the key elements of vessel performance: assessment of the quantity of neutrons received, changes in steel properties, generic and specific defects to be considered in the vessels, and quantification of the stresses to which the vessel is subjected in an accident situation.

At the end of this process, IRSN considers that the suitability of the vessels for continued operation for up to 50 years is justified, subject to the additional information expected from EDF for certain vessels affected by specific defects, as well as the results of the in-service inspections carried out during the 10-yearly inspection of each reactor.