Reactors for which the provisional shutdown times were significantly exceeded (by over 50 days) included Bugey 5 (ten-year inspection, VD), Gravelines 1 (VD), Cattenom 2 (SRS), Cruas 4 (VP), Dampierre 1 (VD) and Gravelines 5 (VP). The longest shutdown extensions therefore involved mainly sites with an especially significant industrial programme, such as Dampierre and Gravelines.
Nuclear generation expressed in annual energy is based on a generation rate for the French nuclear fleet as a whole. This is defined as the ratio of energy generated to the maximum theoretical energy (the energy generated if the installed capacity were operated year-round), also known as the load factor (Kp). This rate is obtained by multiplying two coefficients (Kp = Kd x Ku):
In 2022, the Kp factor reached 52%, a decrease compared with that of 2021 (67%). This results from a Kd of 58.1%, lower than in 2021 (72.9%) and a Ku of 89.6%, also lower than in 2021 (92.2%).
On the occasion of the scheduled controls during the ten-year inspection of the Civaux 1 reactor in late 2021, stress corrosion was identified on parts of the pipework in the reactor’s main primary circuit’s auxiliary circuits. EDF immediately carried out inspections and expert appraisals of the 4 series making up the French nuclear fleet (900MW, 1,300MW-P4, 1,300MW-P’4 and N4).
In 2022, over 112 metallurgical expert appraisals were performed on pipework samples, a new inspection method using ultrasound was developed, and a strategy to repair welds affected by the phenomenon in question was implemented after instruction by the French Nuclear Safety Authority (ASN).
Out of the 56 reactors in the nuclear fleet, 40 were identified as being not vulnerable or only slightly vulnerable to the phenomenon of stress corrosion. These are the thirty-two 900MW series and the eight 1,300MW-P4 series reactors. 16 reactors were identified as being vulnerable or highly vulnerable to the phenomenon of stress corrosion: the twelve 1,300MW-P’4 series reactors and the four N4 series reactors.
In 2022, sections of pipework were replaced on 10 reactors. 6 other reactors should be treated in 2023 with the preventive replacement of the potentially impacted lines.
From 1 January 2023 onwards, EDF has included stress corrosion inspections using the improved ultrasound technology as part of its preventive maintenance plan.
For the 1300 MW-P'4 reactors, EDF has adapted its treatment strategy for the entire series. This strategy, presented to the ASN at the end of 2022, aims to address the stress corrosion issue for all 1300 MW-P'4 reactors by the end of 2023. For these reactors, EDF plans to proceed with the complete preventive replacement of safety injection line pipes whose welds could be affected by the stress corrosion phenomenon.
As part of the inspection and assessment program initiated by EDF, analyses were carried out on a particular weld in the RIS system of the Penly 1 reactor. This weld had the particularity of having been repaired twice during the initial assembly of the circuit at the time of construction, making it sensitive to the stress corrosion phenomenon. Metallurgical expertise revealed a stress corrosion defect.
On 10 March 2023, EDF proposed to the ASN an evolution in its stress corrosion control strategy and is accelerating the inspection of the concerned welds of the RIS and RRA systems, in order to include the elements identified on the weld repaired at Penly 1(2). The ASN announced to have taken note of this evolution in the strategy and to continue the technical dialogue with EDF. This evolution aims to accelerate the inspection of repaired welds during scheduled maintenance outages of reactors in 2023, 2024 and 2025.
320 welds in the RIS and RRA systems have been identified as having been repaired at the time of reactor construction, of which 69 are identified as the most sensitive to stress corrosion. The revised strategy will result in more than 90% of these priority welds being inspected by the end of 2023, and 148 welds repaired at the time of reactor construction, being inspected by 2023.
The risks relating to the phenomenon of stress corrosion are described in section 2.2.5 under risk 5A “Failure to comply with the objectives for operation and/or for extending the operating life of nuclear power plants (France and United Kingdom)”.
The risks related to the environment, nuclear safety and radiation protection are described in section 2.2.5 under risk 5C “Nuclear safety violations during operations resulting in nuclear civil liability”.
EDF’s environmental procedure was introduced in 2002 on a few sites, then extended to all nuclear generation units. It is based on an ISO 14001-certified SME environmental management system (see section 3.5.4.2 “Environmental management system (EMS)”). For a description of radioactive waste processing downstream of the fuel cycle as well as decommissioning, see section 1.4.1.1.2.3.
EDF, in its capacity as a nuclear operator, takes responsibility for nuclear safety and, in a rapidly-changing context (market competition, environmental issues, European connection, etc.), reaffirms as its absolute priority the protection of the human and environmental health, among other things, through the prevention of accidents and the limiting of their consequences as regards nuclear safety. The implementation of the French nuclear power programme led EDF to establish a safety procedure that:
Regulatory notice
Articles L. 125-10 et seq. of the French Environmental Code includes specific provisions on the right to information regarding the nuclear industry aimed at guaranteeing the public’s right to reliable, accessible information. In particular, the operator of a BNF is required to declare any accidents and incidents occurring as a result of the operation of the facility that could potentially be detrimental to the interests referred to in Article L. 593-1 of the French Environmental Code, namely public health and safety and/or the protection of nature and the environment, and to do so speedily to the ASN and the competent administrative authority.
Other authorities also contribute to transparency for the nuclear industry. They include the High Committee for Transparency and Information on Nuclear Safety (Haut Comité pour la transparence et l’information sur la sécurité nucléaire, HCTISN) as well as local information Committees formed for any site housing one or more BNFs.
(1) Available energy is equal to the maximum theoretical energy less generation losses due to technical reasons inherent to power plants, such as planned outages, unplanned outages due to failure or safety requirements, and performance of regulatory tests.
(2) See EDF’s press release of 16 March 2023 “Clarification on the stress corrosion phenomenon detected on parts of the auxiliary circuits of the main primary circuit of several nuclear reactors”.
