ASN requires additional reinforcement of the embankment protecting the Tricastin NPP
In a resolution dated 25th June 2019, ASN requires that EDF carry out additional reinforcements on a portion of the Donzère-Mondragon canal embankment protecting the Tricastin nuclear power plant (NPP) and ensure that this portion of the embankment is monitored.
On 27th September 2017, ASN ordered temporary shutdown of the four reactors of the Tricastin NPP owing to the risk of failure of a 400-metre long portion of the Donzère-Mondragon canal embankment in the event of an earthquake. The assessments carried out showed that the flooding resulting from failure of the embankment could lead to a nuclear fuel melt accident in the four reactors, while at the same time making it particularly difficult to deploy the on-site and off-site emergency management resources.
In 2017, EDF reinforced the portion of the embankment concerned, to ensure that it could withstand the safe shutdown earthquake. On this basis, ASN approved restart of the reactors in December 2017.
EDF plans to carry out additional work on this embankment so that it can withstand the extreme earthquake defined after the Fukushima accident. The resolution adopted by ASN on 25th June 2019 requires that this reinforcement work be completed no later than the end of 2022. In the meantime, it also regulates some of the actions to be carried out by EDF, more particularly:
- tightened monitoring of the embankment;
- the steps to be taken in the event of a rise in the piezometric level;
- retaining the human and material resources (backfill, construction machinery, etc.) so that the necessary work could be carried out to repair any damage resulting from an earthquake.
This resolution was opened to public consultation from 4th to 18th April 2018 on the ASN website.
 The earthquake considered in the nuclear safety case of basic nuclear installations is called the safe shutdown earthquake (SSE). It is calculated using a deterministic approach detailed in basic safety rule n° 2001/01 of 31st May 2001.
 ASN asked EDF to check the resistance of the existing equipment in the “hardened safety core” to an extreme earthquake. The intensity of this earthquake is greater than that of the safe shutdown earthquake.
 Water level inside the body of the embankment.