Incident of 9 April 2014 on reactor 1 of the Fessenheim NPP: ASN actions

On 9^th April 2014, ASN was informed by EDF that internal flooding in the non-nuclear part of reactor 1 in the Fessenheim nuclear power plant had damaged the safety electrical systems, leading to shutdown of reactor 1.

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The repair and requalification of the equipment affected by splashing water lasted nearly 50 days. After the restart operations and the testing of the repaired equipment, EDF reactor 1 was reconnected to the grid on 28^th May 2014.

EDF informed the ASN Strasbourg division in the afternoon of 9^th April 2014 and then kept them informed for the entire duration of the event. In order to observe the consequences of the incident and analyse its management by the licensee, ASN conducted an immediate inspection on the Fessenheim site on 10^th April 2014. ASN then carried out daily inspection and monitoring of the repair and requalification operations performed in the following weeks.

ASN considered that reactor operations during the event and equipment repair and requalification operations were carried out satisfactorily by EDF.

ASN did however observe inadequacies in the filling procedure for the SNO tank^[1], located in the non-nuclear part of the site, which led to an overflow of water and it submitted requests for corrective measures to improve the reliability of this operation.

ASN also made sure that the licensee learned the lessons from this event with regard to the risk of internal flooding of the installation. Following the event which occurred on the Fessenheim site, EDF carried out “internal flooding reviews” on all French NPP sites during the course of 2014, in order to identify the potential sources of internal flooding and the equipment which could be damaged. It also checked the condition of the water drainage systems and the flood protection systems. These reviews led to the implementation of action plans on the various sites, in order to restore the conformity of certain equipment (tightness of openings, renovation of piping for example) and carry out additional inspections.

ASN informed the public and the various stakeholders of the occurrence of this event on the Fessenheim site, as of April 2014. As with any event rated 1 on the INES scale, ASN published an incident notice on its website on 17^th April 2014. The follow-up letter for the 10^th April 2014 inspection was also published on the ASN website, on 24^th April 2014. The event was presented and discussed on two occasions during plenary meetings of the Fessenheim NPP’s local information and surveillance committee (CLIS) on 23^rd June and 2^nd October 2014.

This event was also covered in the section, devoted to the assessment of the Fessenheim site^[2], of the 2014 ASN annual report on the state of nuclear safety in France presented to Parliament.

It was also presented to the members of the Franco-German reactor safety committee (DFK^[3]) during two meetings of this committee, on 22^nd May and 16^th September 2014. These exchanges enabled the questions by the German participants concerning this event to be answered.

Similarly, the Franco-Swiss nuclear safety committee (CFS) meets yearly, bringing together ASN and its Swiss counterpart, ENSI, plus a representative from the Swiss cantons, the federal nuclear safety inspectorate, the federal office of energy and the federal office of health. The 9^th April 2014 event was presented to the members of this committee at its meeting of 4^th September 2014.

Finally, IRSN published its analysis of this event in its report on the safety and radiation protection of the French NPP fleet in 2014