In late 2021, during preventive maintenance checks on reactor 1 at the Civaux nuclear power plant, scheduled as part of its ten-year inspection, defects were detected close to welds on the pipes of the safety injection system (SIS) circuit. Preventive checks were then carried out on the Civaux 2, Chooz 1 and Chooz 2 reactors, which also belong to the N4 series, and similar defects were identified. Preventive maintenance checks conducted during the ten-year inspection of reactor 1 at the Penly nuclear power plant also found similar defects on the SIS circuit.
Through expert assessments and analyses conducted during 2022, EDF identified the reactors where the SIS circuit pipes are the most susceptible to stress corrosion. They are the 16 most recent reactors: the four N4- reactors, and twelve P’4 1300MW reactors.
In its press release of 27 July 2022, the ASN declared its position reached on 26 July 2022 regarding EDF’s proposed inspection strategy for the stress corrosion affecting its reactors. The ASN considered EDF’s strategy appropriate given the knowledge learned about this phenomenon, and the related safety issues.
Of the 16 reactors identified as the most susceptible to stress corrosion, 10 were treated in 2022 or are currently being treated. All these reactors will have been treated by the end of 2023:
Discussions continued with the ASN about the treatment programme for stress corrosion.
Given the outages for inspections and repairs, in 2022 EDF regularly released information about adjustments to nuclear output estimates (see the press releases of 13 January, 7 February, and 19 May mentioned in note 2). As stated in the press release of 3 November 2022, all this information finally led EDF to revise its nuclear power output for 2022 downwards, to a range of 275-285 TWh. The final volume was 279TWh, down by 81.7TWh or 23% from 2021.
The fuel assemblies required for the first fuel load continued to arrive during the first half of the year, and the entire first core is now stored in the Flamanville 3 reactor building pool.
The process of repairing the penetration welds on the main secondary circuit using remote-controlled robots was approved by the ASN on 19 March 2021, several weeks behind the expected date, and work began on the eight welds that were not compliant with the break preclusion principle. All eight were repaired in 2021, then subjected to stress-relieving heat treatment. Demonstration of the qualification of the stress-relieving heat treatment for repairs of VVP (steam discharge pipework circuit) penetration welds was validated by the ASN, which issued authorisation for its use in late 2021. Furthermore, four ARE (steam generator water supply circuit) penetration welds also require repair, and qualification of the repair process is under way at the ASN. This process is an adaptation of the process used for VVP penetration weld repairs.
For the non-penetration welds located on the main secondary circuit that had quality deviations (this concerns 45 VVP welds and 32 ARE welds), the ASN issued approval in April 2021 for the repair of a third batch of 6 welds. In the 3 batches authorised to date, 12 weld upgrades have been completed. In April the ASN gave approval for the related regulatory checks, which are currently in process.
In total, a hundred welds (penetration and non-penetration) on the main secondary circuit were concerned by repairs to the VVP and ARE pipework. The final stage of repair for most of these welds will be an optimised stress-relieving heat treatment, prior to the final verification. Repairing these welds remains one of the key challenges on the Flamanville 3 critical pathway.
On 2 March 2021 EDF declared a significant event to the ASN, concerning incomplete application of the 2006 design standards when installing three nozzles on the main primary circuit (these nozzles connect auxiliary circuits to the primary circuit). At the request of the ASN, three scenarios were examined by the Group’s engineering teams. A file was sent to the ASN on 21 June 2021, stating that EDF’s chosen solution is to install a “containment collar”, and asking the ASN for its position on this solution, so that all the design and procurement activities could be launched by the end of 2021. In a letter of 8 October 2021 the ASN indicated that it had no objections to this solution in principle. Nonetheless the design file for the containment collar will be examined by the French Radiation Protection and Nuclear Safety Institute IRSN (Institut de radioprotection et de sûreté nucléaire).
After corrosion was observed on pressuriser valves at the EPR at Olkiluto (Finland), the Group carried out equipment checks and also detected traces of corrosion on the Flamanville EPR’s valves. The material used for certain components of the pilots control valves was changed accordingly. Several corrosion stress tests were conducted to select the best material. The ASN was regularly informed of the technical choices, and made no objection to this strategy. The ASN and the IRSN also continued their examination of the operation and reliability of the pressuriser valves. EDF is due to respond to the IRSN’s most recent questions so that it can finalise examination of the valve design.
As the work advanced, new technical matters emerged that could increase the completion cost and the risk of deferred timelines. In view of the progress made on operations and preparations for start-up, on 12 January 2022 EDF adjusted the schedule for the Flamanville 3 project. The fuel loading date was deferred from late 2022 to the second quarter of 2023, and the estimated completion cost revised from €12.4 billion to €12.7 billion (in 2015 euros, excluding interim interest). The project has no remaining margin in its schedule or completion cost.
Before loading the fuel into the reactor vessel and carrying out the overall start-up tests, several operations remained to be carried out, mainly:
The main progress on the Flamanville 3 project in 2022 were:
As announced in January 2022, inspections of the Taishan 1 reactor’s fuel assemblies following the technical issue encountered during its second operating cycle showed mechanical wear on certain assembly components. This kind of wear has already been observed in several reactors of the French nuclear fleet. For the future commissioning of Flamanville 3, a solution has been examined with the ASN. EDF’s proposed strategy for the Flamanville EPR (supply of around sixty reinforced fuel assemblies) was presented to the High Committee for Transparency and Information on Nuclear Safety (Haut comité pour la transparence et l’information sur la sécurité nucléaire, HCTISN) on 7 June 2022. In January 2023, the IRSN issued a favourable opinion of EDF’s proposed strategy, and the ASN will finalise its examination by the end of the first quarter of 2023.
