In a decree dated 25 March 2020, the commissioning deadline specified in the Authorisation Decree (DAC) was extended until 11 April 2024, to take into account the weld repairs in the main secondary circuit whilst maintaining flexibility.
On 7 April 2021, EDF submitted an operation authorisation application in compliance with the 18-month period before fuel loading required by the Energy Code. The application submitted ensures that the national energy policy guidelines are taken into account (in particular, compliance with the 63.2GWe nuclear power ceiling). EDF received this operating authorisation on 30 August 2021, in an order issued by the Minister for the Ecological Transition.
The year 2021 was marked by the following achievements:
In the first half of 2017 the ASN examined “higher-than expected” carbon levels in the vessel head and bottom on the basis of documentation submitted by Framatome, under the supervision of EDF. Based on the opinion of a group of ASN-appointed experts, the ASN concluded that the mechanical properties of the vessel head and bottom were adequate for their uses, including in the event of an accident (1). On 9 October 2018, the ASN authorised:
The project is now focused on replacing the vessel head by the end of 2024, the supply of a new equipped vessel head having been ordered from Framatome.
Therefore, the costs incurred for the manufacture of a replacement vessel head arenot included in the target construction cost. Furthermore, arbitration proceedings have been engaged with respect to this matter by EDF, AREVA SA, AREVA NP, and Framatome. The arbitration tribunal issued its decision on 30 June 2021 and denied EDF’s claims. It held that Framatome was not required to compensate EDF for the loss sustained due to the obligation to replace the reactor vessel cover.
On 30 November 2017, EDF declared a significant event to the Nuclear Safety Authority regarding the detection of a quality deviation in the welding of the main secondary pipes that transfer the steam from steam generators to the turbine (VVP pipework circuit).
This system was designed and manufactured according to the “break preclusion” concept. This approach consists of strengthening requirements for design, manufacture and monitoring in service. These strengthened requirements, requested by EDF, also involve a “high quality” requirement in the building of these systems (2). Although these requirements were applied during the design phase, they were not properly incorporated into the welding work. Failure to meet these requirements does not necessarily entail non-compliance with the nuclear pressure equipment regulations.
On 10 April 2018 (3), EDF notified the ASN of a significant event relating to the detection, during the initial comprehensive inspection (4), of deviations in the inspection of the welding of the pipes of the main secondary circuit. In accordance with industrial procedures, the welds had been inspected by the consortium of contractors in charge of manufacturing system. Each weld had been declared compliant by the consortium just as they were being completed.
EDF began a further inspection during the second quarter of 2018 of all welds concerned in the main secondary system. For eight of these, known as reactor containment building penetration welds, on 3 December 2018 EDF suggested providing a specific ‘as-is’ design calculation file to the ASN. In a letter dated 19 June 2019, the ASN asked EDF to rework the eight penetration welds (5) before commissioning.
EDF’s proposal for reworking the penetration welds is the use of remotely controlled robots, designed to conduct high-precision operations within the pipe work in question. The ASN approved this process on 19 March 2021. The 8 penetration welds concerned were all upgraded in 2021 and checked by EDF before stress-relieving heat treatment.
4 ARE penetration welds (on the steam generator water supply lines) are also subject to repair. The qualification of the repair process by the ASN is underway. This process is an adaptation of the one used for VVP penetration repairs.
The technical investigation into reworking the welds located on the main secondary circuit with quality deviations and/or not complying with the requirements of the break preclusion reference is ongoing. 45 VVP and 32 ARE welds are involved. The rework on these welds started in the summer of 2021. Seventy per cent of the welds concerned (VVP and ARE) are currently being upgraded. Twelve VVP welds are completed to date before stress-relieving heat treatment.
In total, about 100 welds in the main secondary circuit (penetration and non-penetration) are concerned by the repairs to the VVP and ARE piping. As a last step, most of the welds will have to undergo an optimised stress-relieving heat treatment before a final conformity inspection. Repairing the penetration welds is one of the key challenges on the critical pathway of the project.
Deviations observed in the stress-relieving heat treatment historic process
Stress-Relieving Heat Treatment (SRHT) is a manufacturing operation that, in addition to giving the welded joint the expected mechanical properties, aims to reduce the residual stresses that develop within a material during a welding operation. SRHT is performed by heating the welded joint for a determined period of time at a temperature of about 600°C (+/-15°C).
In late 2020, Framatome reported to the ASN a deviation in the SRHT process historically used on the welds of the main secondary circuit of Flamanville 3. Framatome the developed an “optimised” process to ensure compliance with the required temperature range.
The demonstration of the qualification of the SRHT processes must be approved by the ASN on the basis of supporting documentation.
In late 2021, the ASN approved this qualification demonstration of optimised SRHT processes for VVP penetration welds, as well as for “simple geometry” non-penetration welds.
ASN approval is expected for some 60 other welds (ARE penetration welds and other non-penetration welds, other than “simple geometry” welds).
(1) Opinion dated 11 October 2017.
(2) Given that these requirements were stated, the potential for pipes rupturing did not have to be considered during the safety demonstration. This proves, with a high degree of confidence, that accidents are physically impossible or extremely unlikely and that their consequences are limited to acceptable economic conditions.
(3) See EDF press release of 10 April 2018 “EDF has detected quality deviations on certain welds of the main secondary system of the Flamanville EPR and has begun additional controls”.
(4) The initial comprehensive inspection is a regulatory requirement prior to the plant commissioning, which consists, in particular, in examining the welds of the primary and secondary systems.
(5) See EDF’s press release of 20 June 2019: “Flamanville EPR: EDF notes the French Nuclear Safety Authority’s decision”.
