5 Dec (NucNet): French nuclear regulator ASN has examined documents submitted by state-controlled nuclear operator EDF to justify the earthquake resistance of a canal dyke protecting the Tricastin nuclear power station and has said that three reactors at the site can restart. ASN said it considers that the state of the dyke, after the investigations and repairs carried out by EDF, allows the restart of Units 2, 3 and 4 at the four-unit facility. Unit 1 will remain shut down for maintenance, ASN said. In September 2017 ASN ordered EDF to temporarily shut down all four reactors at Tricastin in the south of France following the discovery of flaws in the canal dyke bordering the facility. ASN said at the time that Tricastin had failed to pass safety tests involving above-average earthquakes. EDF said the shutdown would allow it to strengthen a small section of the dyke to the north of the station. “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,” said the company at the time. According to EDF, geotechnical surveys carried out on the dyke in 2015 and 2016, supplementing those performed in 2013 and 2014, revealed that a small section of the dyke required reinforcement. However, EDF said it had demonstrated to ASN that the dyke was capable of withstanding an earthquake known as a “maximum historically probable earthquake”, or MHPE. ASN classified the incident as Level 2 on the International Atomic Energy Agency’s International Nuclear and Radiological Event Scale (INES). Events are rated at seven levels, ranging from 1 (anomaly) to 7 (major accident). The Tricastin station has four pressurised water reactors that began commercial operation from 1980 to 1981.