Flamanville EPR reactor: design deviation of three main primary circuit nozzles. On March 3, 2021, EDF notified ASN of a significant event relating to a design deviation concerning three taps1 of the main primary circuit of the EPR reactor under construction on the Flamanville site. The primary primary circuit contains water that cools the reactor core and transfers energy from the nuclear reaction to the steam generators. This circuit is made up of four piping loops which are installed in the reactor building. Several auxiliary circuits are connected to the main primary circuit, through nozzles. The most important nozzles are integrated by forging during the manufacture of the main piping. Small diameter connections (less than 150 mm) are connected to the main primary circuit piping by means of a connection welded to the main piping called “set-in”. Three of these taps are affected by the declared deviation. In 2006, in order to make it easier to check the “set-in” weld on the main piping, EDF and Framatome changed the design of these three nozzles by widening the diameter of this weld. They did not then identify that the size of the breach to be taken into account in the event of a rupture of this weld then became greater than that considered in the safety studies.
ASN 16th March 2021 read more »