December 07, 2017

The French nuclear safety authority ASN (Autorité de Sécurité Nucléaire), examined the data provided by EDF (Electricité de France) to demonstrate the seismic resistance of the Donzère-Mondragon canal embankment which protects the Tricastin NPP. ASN considers that, following the investigations and repairs carried out by EDF, the condition of the embankment allows the restart of the EDF reactors and gave its consent for the restart of reactors 2, 3 and 4.
On 27 September 2017, ASN ordered temporary shutdown of the Tricastin NPP due to the risk of failure of a 400 metre long portion of the Donzère-Mondragon embankment in the event of an earthquake. The assessments carried out showed that the flooding that would result from failure of the embankment would have caused a nuclear fuel melt accident in the four reactors of the Tricastin NPP and would have made deployment of the on-site and off-site emergency management resources particularly difficult.
EDF strengthened the portion of the embankment concerned, after having carried out geotechnical surveys to obtain a more detailed characterisation of its composition. The assessment carried out by IRSN at the request of ASN on the strengthened embankment confirms that there would be no failure in the event of a safe shutdown earthquake (SSE), which is the largest earthquake studied in the nuclear safety case. It however revealed that, in certain conditions, there is a risk of localised landslips which, without compromising the stability of the embankment, would require repair work to be carried out subsequent to an earthquake. EDF has therefore pre-positioned equipment in the vicinity of the embankment, in order to be able to carry out these necessary works to repair any landslips observed following an earthquake.
EDF has undertaken to implement enhanced monitoring of the embankment and has defined the relevant measures. Finally, EDF intends to further strengthen the embankment so that it can withstand the extreme earthquake defined in the stress tests performed in the wake of the Fukushima Daiichi accident.
The Tricastin Nuclear Power Plant is a nuclear power plant consisting of 4 pressurized water reactors with 915 MW electrical power output each. The power plant is located in the south of France (Drôme and Vaucluse Department) at the Canal de Donzère-Mondragon near the Donzère-Mondragon Dam and the commune of Pierrelatte. (Source: ASN)