ASN considers that, further to the investigations and repairs carried out by EDF, the condition of the Donzère-Mondragon canal embankment allows restart of the reactors of the Tricastin nuclear power plant (NPP).
With the support of IRSN, ASN examined the data provided by EDF 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.
ASN has initiated a process to issue prescriptions, which will be the subject of a public consultation, to regulate the steps to be taken by EDF, in particular the enhanced monitoring of the embankment, the deployment of permanently pre-positioned equipment and the final strengthening of the embankment, as rapidly as possible, so that it can withstand the extreme earthquake.
Furthermore, with regard to the Comurhex 1 uranium conversion facility, ASN authorised its restart on 23 October 2017 in the light of the steps taken to reinforce the means of controlling chemical release if the embankment were to fail after an earthquake. This restart means that the hazardous substances can be removed from the site with a view to final shutdown of the facility scheduled for the end of December 2017.
To find out more:
Consult the public information notice published by ASN on 28 September 2017 and the ASN resolution of 27 September 2017 ordering temporary shutdown of the 4 reactors of the Tricastin NPP
Consult the 23 October 2017 resolution allowing restart of the Comurhex installation.
Consult the IRSN public information notice on 5 december 2017 :
 Reactor 1 remains shut down as EDF intends to carry out maintenance on it.