Oversight of the Flamanville EPR reactor

The EPR reactor is a pressurised water reactor (PWR) whose design meets more stringent safety objectives than the reactors previously built in France.

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Background and current situation:

Following issue of the creation authorisation decree and the building permit, construction of the Flamanville 3 reactor began in September 2007 and was completed in early 2024. ASN monitored this construction phase by means of nearly 600 inspections. At the same time, ASN reviewed the reactor commissioning authorisation application, analysed the issues encountered during equipment manufacturing, construction and testing, and assessed the results of the start-up tests. At the end of the construction worksite, ASN carried out detailed monitoring of the preparations by the future licensee. In 2020 ASN authorised the arrival of fuel on the site (partial commissioning) and, in May 2024, the introduction of fuel into the reactor vessel (commissioning).

Main steps following commissioning of the Flamanville EPR reactor

Performance of the start-up tests

The start-up tests contribute to verification of the conformity of the installation once it has been built. 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 these tests for the Flamanville EPR reactor.

After loading the nuclear fuel into the reactor, EDF initiated a pre-critical tests phase, in other words, without triggering the nuclear chain reaction. The licensee will then proceed with reactor divergence, that is the initiation of the nuclear chain reaction process, with a gradual increase in reactor power, so that the installation’s start-up tests can be carried out.

With the support of IRSN, ASN reviewed this test programme, along with the conditions in which it is to be carried out in order to ensure the safety of the installation.

Steps requiring ASN approval

During the tests phase, several milestones will require ASN approval.

In accordance with technical prescription [INB167-73] of the commissioning authorisation, EDF sent ASN a file before reaching the temperature of 110 °C[1] in the main primary system. This file notably listed the operations carried out by EDF on the main primary system and the main secondary systems and described the results of the checks it carried out on the equipment.

Reactor divergence requires approval from ASN (see technical prescription [INB167-74] of the commissioning authorisation). Prior to reactor divergence, EDF will send ASN a file, the contents of which are specified by technical prescription [INB167-75]. This prescription subjects the Flamanville EPR reactor to the same requirements as those applicable to the restart of the other EDF reactors in operation.

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Two hold points are defined for the start-up tests after divergence of the Flamanville EPR reactor:

• continuation of the start-up tests at a power more than 25% of the rated power, subject to ASN prior approval (see technical prescription [INB167-178]). The main purpose of this hold point is to check the calibration of the reactor protection system. The data to be transmitted in order to lift this hold point are defined in technical prescription [INB167-78].

• continuation of the start-up tests at a power more than 80% of the rated power is also subject to prior ASN approval (see technical prescription [INB167-79]). At this stage, a large part of the start-up test programme will have been completed and the results obtained will make it possible to check the installation’s conformity with its safety case.

ASN oversight

In addition to the steps requiring its approval, ASN reviews the test results and any significant events that may have occurred.

At the same time, ASN defined a specific inspection program to monitor reactor start-up. For example, it carried out or will be carrying out inspections relating to fuel handling, reactor loading, reactor divergence and performance of the test programme at power. ASN also checks the conditions for EDF operation of the reactor during the start-up phase.

ASN will then implement the thematic inspection programme which it carries out on all the EDF reactors in operation.