Insufficient seismic resistance of a part of the Donzère-Mondragon canal embankment: ASN imposes temporary shutdown of the Tricastin nuclear power plant
In a resolution dated 27 September 2017, ASN required that EDF temporarily shut down the four reactors of the Tricastin nuclear power plant as rapidly as possible.
On 18 August 2017, EDF notified ASN of a significant safety event relating to a risk of failure of a part of the embankment of the Donzère-Mondragon canal with regard to the most severe earthquakes studied in the nuclear safety case.
The resulting flooding could lead to a nuclear fuel melt accident in the four reactors of the Tricastin NPP and would make it particularly difficult to implement on-site and off-site emergency management resources.
At the request of the ASN Commission, EDF was given a hearing on 26 September 2017 and provided additional data. ASN considers that these data are unable to rule out the risk in the short term.
EDF is required to conduct further geotechnical investigations in order to make a more detailed characterisation of the composition of the part of the embankment concerned and carry out the necessary reinforcement works before the reactors are restarted, to ensure that the embankment is able to withstand the maximum earthquake considered in the nuclear safety case.
Areva was also given a hearing by the ASN Commission on 26 September 2017 regarding the consequences of failure of a part of the embankment on the facilities it operates on the Tricastin site.
ASN prescribes measures appropriate to the risks relating to the Areva facilities. It thus requested upgrading of the systems designed to mitigate the consequences of chemical releases by the W and Comurhex 1 facilities. The resumption of activities at Comurhex 1, which is currently shut down, will depend on this upgrade being carried out.
ASN reclassifies the significant event notified by EDF at level 2 on the INES scale.
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