EPR Reactor: Information Letter n°25

• the preparation for and performance of hot testing at the end of 2023, to verify the ability of the systems to perform their safety functions during hot operation of the reactor, prior to commissioning,
• preparedness of the teams who will be operating the reactor, prior to commissioning,
• the conformity of the nuclear pressure equipment, which notably includes completion of the quality review, the processing of the irregularities affecting certain equipment, and equipment conservation,
• completion of the installation before commissioning, whether in terms of works, processing of anomalies and start-up tests, with detailed monitoring of the progress of these actions, up until reactor commissioning,
• the start-up operations following commissioning, notably loading of fuel into the reactor vessel and analysis of the experience feedback from the significant events reported.

ASN had no objection on the transition of the main primary system to 110 °C (commissioning of primary and secondary circuits according to nuclear pressure vessel regulation) and is continuing its monitoring prior to reactor divergence.

Monitoring the start-up tests

In its resolution of 7 May 2013, and then in its commissioning resolution of 7 May 2024, ASN issued a number of prescriptions regulating the preparation for and performance of the Flamanville EPR reactor start-up tests.

These tests contribute to verifying the conformity of the installation. Therefore the adequacy of the start-up tests programme, the correct performance of the tests in the intended performance conditions and the result of these tests were examined by ASN so that it could issue a position statement on the commissioning authorisation. ASN oversight of the subject is detailed in the commissioning authorisation application review report.

In late 2023 and early 2024, ASN continued its monitoring of the start-up tests, notably the preparation for and performance of the hot tests. This monitoring involved:

• two one-day inspections on the topic of preparation for the tests;
• one tightened inspection on the topic of performance of the tests (this inspection involved eight ASN inspectors and four IRSN experts for three days);
• a review of the test results.

In addition, in early 2024, two of the fuel loading inspections focused on the in-core instrumentation tests and on completion of the tests prior to fuel loading.

Finally, ASN checked the sustainability of the test results, notably by monitoring EDF's performance of certain periodic tests. These tests were able to check that the safety criteria, verified during tests performed sometimes several years previously, were still being met. ASN also checked that the equipment was maintained in good condition through inspections on its conservation.

At the same time, ASN is continuing to monitor the start-up tests in progress with a view to reactor start-up.

Preparedness of the teams who will be operating the reactor

In parallel with the Flamanville EPR reactor construction and start-up tests, an EDF entity has been gradually set up over the past few years, as the project progressed on the site of future reactor operations. The role of this entity was notably to define the organisations, manage the skills of the staff, and produce the documentation and the operational tools needed to use it.

With a view to reactor commissioning, a process was implemented for gradual transfer of responsibility for operation of the installation to this entity. The steps in this transfer process enabled the personnel to acquire skills, learn how to operate equipment, draw up operating documentation and develop tools needed for future operation of the reactor.

In late 2023 and early 2024, ASN continued its monitoring of the preparedness of the teams who will be operating the reactor, notably through:

• an inspection devoted to emergency management, taking account of a significant amount of work to be done on this subject, as identified by an inspection in 2022,
• a tightened inspection involving six ASN inspectors and one IRSN expert for two days, covering actions to prepare for operation; this tightened inspection was held in response to ASN's requests made following the in-depth inspection carried out from 22 to 26 May 2023, the results of which were closely monitored up until commissioning,
• an inspection devoted to the pre-service inspection of the main primary system and the main secondary systems,
• an inspection devoted to radiation protection, for the opening of the "controlled area".

On the basis of this oversight and prior to commissioning, ASN considered that EDF had taken appropriate measures in response to its requests in order to be ready to operate the reactor.

Conformity assessment of nuclear pressure equipment

The regulations applicable to nuclear pressure equipment include nuclear safety issues, which lead to design, manufacturing and in-service monitoring rules for this equipment, in order to ensure its integrity throughout its operating lifetime. For some equipment, these provisions are reinforced such as to make any failure highly improbable when this is not considered in the safety case.

The French regulations require the issue of conformity reports or certificates for pressure equipment before it enters service.

ASN continued the conformity assessment of the equipment until May 2024, by means of reviews and inspections. Some of these inspections concerned the processing of irregularities, detected as of 2023 and affecting certain equipment, the conservation of equipment, or certain issues encountered during the hot tests performed at the end of 2023.

Following these controls, the broad outlines of which are presented in the commissioning authorisation application review report, ASN issued the conformity assessment reports for the N1 level nuclear pressure equipment, as well as the report for the reactor's nuclear steam supply system (NSSS).

Completion of the installation

In 2022, ASN initiated a monitoring programme comprising several inspections dedicated to completion of the installation. This programme continued in 2023, notably involving an inspection and various monitoring actions carried out during the inspection campaign run prior to fuel loading.

ASN also carried out detailed monitoring of the work still to be done on the reactor before it is commissioned.

On the basis of this monitoring and prior to commissioning, ASN considered that EDF had taken appropriate measures to complete the installation and thus demonstrate its conformity.

Oversight of start-up operations following commissioning

In a resolution of 7 May 2024, ASN authorised commissioning of the Flamanville EPR reactor. This authorisation enabled EDF to begin loading of 241 nuclear fuel assemblies into the reactor: these operations ended on 15 May 2024. They were inspected on 10 May 2024 and ASN considers that they were well prepared and carried out.

The licensee periodically submits operating and testing information, which notably enables ASN to carry out its oversight work. The reactor pressure vessel was closed at the end of May 2024: this step enabled EDF to begin the cold and then hot pre-critical tests, prior to divergence and then reactor power increase. These activities are covered by a campaign of ASN inspections related to divergence.

In accordance with technical prescription [INB167-73] of the commissioning authorisation, EDF sent ASN a file notably listing the operations carried out by EDF on the main primary system and the main secondary systems, describing the results of the checks it performed on the equipment before the temperature of 110°C was reached in the main primary system and main secondary systems (according to the regulations, this temperature corresponds to commissioning of these systems). This file, which was reviewed and inspected on 28 May 2024, concluded with the issue by ASN of no objection to the transition to 110 °C.

Since commissioning of the reactor, the licensee has reported a number of significant safety events, three of which were rated level 1 on the INES scale. At the beginning of June 2024, as a result of the number and nature of the significant events reported since commissioning, EDF momentarily suspended the reactor start-up operations so that it could analyse the root causes of the events reported, put corrective measures into place and safeguard future activities for continued start-up of the reactor. ASN is particularly vigilant with regard to the analysis of the root causes of these events and the steps taken by EDF to learn all relevant lessons and safeguard the upcoming start-up activities.

International operating experience feedback follow-up

ASN participates in several international bodies and regularly organises meetings with the nuclear regulators concerned by the various EPR projects under construction or in service around the world.

ASN closely examines the conclusions of the operating experience feedback from EPR reactors in operation and regularly verifies that the lessons learned are taken into account by EDF at Flamanville. In particular, a number of phenomena linked to the physical behaviour of the core, observed at start-up of the first EPRs, were incorporated into the review of the commissioning authorisation application. These points are detailed in the commissioning authorisation application review report.

To find out more:

Reference texts (in french)

Incident notices (in french)

Inspection follow-up letters (in french)

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