Temporary shutdown of the four generation units of the Tricastin nuclear power plant

EDF takes note of the decision taken by the French Nuclear Safety Authority (ASN) on 28 September 2017 requesting that EDF temporarily shut down the four generation units of the Tricastin nuclear power plant (Drôme, France), while strengthening work is carried out on a small section of the dyke located to the north of the power plant bordering the Donzère-Mondragon canal.

As an operator that takes responsibility for the safety of its installations, EDF does not share the view that the four reactors need to be shut down for the duration of the work. EDF will nevertheless implement the ASN decision without undue delay.

The geotechnical surveys carried out on this dyke in 2015 and 2016, supplementing those performed in 2013 and 2014, revealed that a small section of the dyke required reinforcement. EDF has however demonstrated to the ASN that the dyke is capable of withstanding an earthquake known as a "Maximum Historically Probable Earthquake" (MHPE). This is an earthquake that is more severe than the historical earthquakes observed in the vicinity of the power plant, located in the most damaging position for the installations.

On the basis of the analyses and calculations performed it was not possible to unequivocally demonstrate the robustness of the dyke in the event of an earthquake known as a "Safe Shutdown Earthquake", a hypothetical earthquake releasing energy five times greater than that of an MHPE. On 18 August 2017, EDF therefore declared a "significant safety event" at level 1 on the INES scale (the 8-level International Nuclear Events Scale).

EDF submitted a two-phase reactive action plan to the ASN:

• Within one month, dyke strengthening work will be carried out in order to guarantee its resistance in a Safe Shutdown Earthquake situation.
• Ahead of this strengthening work, additional protection is currently being installed on the existing peripheral protective wall and will be operational within a few days. This measure ensures that no water would reach the reactors in the event of a Safe Shutdown Earthquake during the work period.

Given these arrangements, EDF is convinced that the safety of the installations is guaranteed and considers the reactors’ shutdown unjustified.

The shutdown of the reactors required by the ASN has led the Group to revise its nuclear generation target for the year 2017 to 385-392 TWh, depending on the actual duration of reactors’ shutdown, compared with a previous target of 390-400 TWh.