France's nuclear safety regulator, the Autorité de Sûreté Nucléaire (ASN), has set the conditions for the continued operation of EDF's 900 MWe reactors beyond 40 years. The regulator said it considers the measures planned by EDF combined with those prescribed by ASN will ensure the safety of the units for a further 10 years of operation.
EDF operates three pressurised water reactor designs, known as the 900 MWe, the 1300 MWe and the 1450 MWe N4. Its 32 operating 900 MWe reactors came into commercial operation between 1977 and 1988, and include the oldest of the country's current nuclear fleet. Such reactors are in operation at EDF's Blayais, Bugey, Chinon, Cruas-Meysse, Dampierre, Gravelines, Saint-Laurent and Tricastin nuclear power plants.
ASN reviews all French reactors on a 10-yearly basis. In order to take advantage of the standardised nature of EDF's reactors, these reviews are performed in two steps. Firstly, the 'generic' review phase, which covers subjects common to all 900 MWe reactors. Secondly, the 'specific' review phase, which relates to each reactor individually, and which will run until 2031.
ASN noted the fourth periodic safety review of the 900 MWe reactors is "of particular importance because the service life hypothesis adopted at the design stage was 40 years. Continuing operation beyond 40 years necessitates the updating of the design studies or equipment replacements".
On 23 February, ASN issued a resolution prescribing the implementation of the major safety improvements planned by EDF, along with additional measures it considers necessary to achieve the objectives of the safety review.
"This resolution closes the 'generic' phase of the safety review, which concerns the studies and modifications of the installations common to all the 900 MWe reactors, as they all have a similar design model," ASN noted.
ASN examined the generic phase with the support of France's Institute for Radiological Protection and Nuclear Safety and the permanent groups of experts, which it brought together 12 times between 2018 and 2020. It took into account, during this investigation, the observations and questions collected during a public consultation held between September 2018 and March 2019. ASN also posted its draft resolution on its website for public consultation between 3 December 2020 and 22 January 2021. This consultation led ASN to change or clarify some of the requirements of its resolution.
"This is the case, for example, with certain studies prescribed by ASN, for which the completion deadlines have been brought forward," the regulator said. "ASN has also pushed back some deadlines on account of specific industrial and operating constraints when this was acceptable from the safety aspect."
The safety of the 900 MWe reactors will be greatly improved due to a number of measures, ASN said. These include verifying the conformity of the reactors with their reference system, as well as improving their ability to withstand more severe attacks "of internal or external origin". Modifications will also limit the radiological consequences of accidents without core meltdown. Additionally, improvements will be made in the arrangements for managing accidental or aggressive situations affecting the used fuel storage pools at the units.
ASN said the improvements and measures will be applied to each reactor individually during their fourth periodic safety reviews, scheduled to run until 2031. These reviews will take the particularities of each facility into account, it said. The measures planned by EDF for each reactor will be subject to a public inquiry.
"ASN considers that the measures planned by EDF combined with those prescribed by ASN open the prospect of continued operation of these reactors for a further 10 years following their fourth periodic safety review," ASN said.
The regulator requires EDF to report annually on the actions implemented to meet the requirements and their deadlines, and also on the industrial capacity of both EDF and its outside contractors to complete the modifications of the facilities within the set timeframes. ASN requires that this information be made public.
In a 23 February letter to EDF, ASN President Bernard Doroszczuk said: "I underline the particularly ambitious objectives of the fourth periodic review of the reactors of 900 MWe and the very substantial work you have done in the generic phase. I also note the extent of the changes you have planned, the implementation of which will bring very significant improvements to the safety of these reactors."
He added, "I encourage you to analyse the lessons from the generic phase of the fourth periodic review of the 900 MWe reactors with a view to that of 1300 MWe reactors. This concerns in particular additional provisions that ASN considered necessary to achieve the objectives of review and timing of the deployment of safety enhancements."
