France's Autorité de Sûreté Nucléaire (ASN) has issued a draft decision which should allow EDF to use the current reactor pressure vessel (RPV) head of the 1650 MWe EPR under construction at unit 3 of the Flamanville NPP until the end of the reactor's first operating cycle. Previously ASN had ruled that the vessel head should be replaced by the end of 2024. In 2015, Areva NP (now Framatome) discovered an anomaly in the composition of the steel in certain zones of the RPV's closure head and bottom head of the EPR. A test programme indicated that the mechanical strength of the steel was sufficient in all operating situations, including accident situations and the results were sent to ASN in 2016.

In June 2017, ASN provisionally ruled the unit could start up safely, at the end of 2018 as planned, but that the RPV head would need to be replaced as soon as a new one could be produced. Delivery of the replacement lid is scheduled for October 2024. In October 2018 ASN authorised the commissioning and use of the RPV, subject to implementation of a thermal ageing monitoring test programme and on specific controls during the operation. ASN said that “if no mechanism has been identified that can lead to the rapid creation or propagation of a fault during operation of the reactor … it is therefore acceptable that no control is implemented before the end of 2024 and … consequently, the use of the lid until such a deadline is acceptable from the point of view of nuclear safety".

At that time, commissioning of the reactor was scheduled for October 2019. However, ASN notes that because of “hazards that have occurred since”, commissioning of the reactor is postponed to the first quarter of the year 2024. “The first operating cycle of the reactor, which includes a testing phase, is planned to last between 15 and 18 months”. This first scheduled shutdown is the one during which the first complete requalification of the primary circuit of the reactor is made.

ASN says “removal of a stop in progress of the first cycle dedicated to the replacement of the lid, will prevent a possible interruption of the reactor start-up tests, to avoid carrying out sensitive operations of shutting down and restarting the reactor and reducing the collective exhibition linked to additional operations, which constitute elements favourable in terms of nuclear safety and radiation protection”.

ASN explained that the postponement requested by Framatome would “lead to a duration of use of the cover of approximately 18 months, ie a shorter period than that envisaged when ASN took its decision in… October 2018, which, given the date then envisaged for the start of the reactor, was about four years”.

ASN’s draft decision therefore recommends that the December 2024 deadline for replacement of the RPV head are replaced by the words: "from the [first] shutdown of the reactor during which the first complete requalification of the primary circuit is carried out ".

However, the ASN added that, “in the event that the project suffers a significant delay again, the operator will have to re-examine the possibility of replacing the cover before the commissioning of the reactor”. Flamanville 3 has suffered a long series of delays. Construction began in December 2007 and the reactor was originally expected to start commercial operation in 2013. ASN has launched a public consultation on its proposed decision. which will run until 31 March.

Image: Illustration of the current EPR reactor vessel head seen from below (courtesy of ASN)