France’s nuclear safety authority (ASN) has reclassified an incident at Dampierre earlier this year as INES level 2.
ASN said the incident, which occurred in April during a routine refuelling at unit 4, had been given a provisional rating of INES level 1 by EdF. EdF subsequently proposed that the incident, in which an error in the loading sequence led to incorrect positioning of 113 fuel elements, be reclassified as level 2.
Preliminary results of EdF’s analysis sent to the ASN showed that, under different conditions, the incorrect position of the fuel assemblies could have initiated the initial stages of an unplanned chain reaction. Further studies requested by the ASN from EdF showed that the measuring instruments in use would not have been able to detect the rise in power and thus alert the operators before the chain reaction began. Other safety systems would have prevented any such power surge taking place under the applicable conditions. EdF has, nonetheless, implemented measures to ensure that the error could not be repeated.