EPR Reactor: Information Letter n°18: ASN oversight of the Flamanville EPR reactor construction site: notable points

Published on 14/06/2016 at 11:00

Press release

In the second half of 2015 and early 2016, ASN continued its oversight actions on the Flamanville 3 EPR reactor construction site and the various manufacturing operations for this reactor. The notable points observed over the last few months are detailed below. 

Assembly of the main primary system

View over the Flamanville 3 EPR construction site from the cliff © EDF Médiathèque - Alexis Morin- Antoine Soubigou/All rights reserved

Production of the EPR reactor main primary system involves successive nuclear pressure equipment assembly sequences. To check the correct performance of these assembly operations and assess the conformity of the nuclear pressure equipment with the applicable requirements, ASN relies in part on the monitoring actions of accredited organisations. These requirements more specifically concern taking into account the risks inherent in the assembly operations, the checks to be performed on-site by the manufacturer, the organisation put in place by EDF and AREVA to limit the risks associated with the activities carried out by other contractors in proximity to the areas concerned, as well as the cleanness of the work areas and the assembled equipment.

Between February and July 2014, AREVA carried out a first assembly sequence for the reactor primary system. This consisted in introducing into the reactor building and then assembling together several components of loop 2 of the reactor primary system (the reactor vessel, the primary system pipes and a primary pump casing[1]).

After ASN analysed the results of this first assembly sequence, AREVA began a second assembly sequence which consisted firstly in carrying out these operations on the other three loops (1, 3 and 4) and secondly in introducing steam generator No.2, the pressuriser and its expansion line into the reactor building and welding them to the primary system. These operations could not be carried out in a continuous manner due to the discovery in October 2014 of a defect in a weld between steam generator No.2 and a pipe, and then, in March 2015, a deviation that occurred when making a weld between steam generator No.1 and another pipe. AREVA carried out a further analysis of the welding conditions which it presented to the accredited organisations and ASN. AREVA in particular provided additional information relative to the inspection methods used to guarantee the conformity of these welds[2]. In view of these measures, ASN did not formulate any objection to the continuation of the operations.

In May 2015 AREVA informed ASN that new defects had been discovered during inspections of the welds connecting primary system components. In June 2015 a defect was also discovered in the weld between the first and second section of the pressuriser expansion line[3]. AREVA conducted in-depth investigations into the cause of the defects, resulting in the defining of an action plan for carrying out the repairs.

These repairs were carried out, but further defects were detected on two occasions on a same given weld of loop No.1; this weld underwent a first repair in December 2015, then a second repair in March 2016. As the inspections carried out further to this second repair operation did not give full satisfaction, AREVA and EDF must further their analysis of the causes of these defects in order to successfully repair this last weld.

During 2014, 2015 and 2016, ASN performed six inspections - two of EDF and four of AREVA - focusing on the assembly of the primary system, and four inspections focusing on the monitoring of these same activities by BUREAU VERITAS as an ASN-accredited organisation. In the light of these inspections, ASN observes that the assembly operations involving the large components of the primary system have given rise - particularly since summer 2015 - to several deviations, which still require further analysis. ASN nevertheless considers that AREVA and EDF responded appropriately by suspending the activities in order to determine the causes of the deviations and deal with them.

Steel composition anomaly in certain areas of the reactor vessel head and bottom head

On 7th April 2015 ASN published a notice relative to the detection by AREVA of an anomaly in the composition of the steel in certain areas of the Flamanville 3 EPR reactor vessel head and bottom head. This anomaly appears to be linked to the presence of a higher than expected concentration of carbon in these areas, leading to mechanical characteristics which are lower than expected.

ASN adopted a position on 12th December 2015 on AREVA's proposed method of substantiating the mechanical properties of the Flamanville 3 EPR reactor vessel head and bottom head. On condition that its observations and requests are taken into account, ASN considers that the method proposed by AREVA is acceptable in principle and formulates no objection to starting the corresponding programme of tests. ASN published an information notice setting out this position on its website. (link to consult it).

ASN mandated an accredited organisation to monitor the test programme as a whole and conducted an inspection on 25th and 26th April in the AREVA test laboratory in Erlangen (Germany) which is performing some of these tests. No nonconformity was observed in the conducting of the tests or the management of the laboratory. The inspection also enabled to verify the technical competence of the laboratory, compliance with the required criteria of independence and impartiality.

ASN also made available to the public on its website several letters concerning the manufacture of the Flamanville EPR reactor vessel which have been sent to AREVA since 2006 and communicated to the monitoring group set up by the HCTISN (French High Committee for Transparency and Information on Nuclear Security) to ensure the transparency of examination of this anomaly and due transmission of the information to the civil society. (link to consult them).

"Complete initial inspection" of the main primary system

For several months ASN has been conducting random checks on the implementation of the non-destructive tests required for the "complete initial inspection" of the main primary system required by the regulations. During this inspection, the licensee must verify the applicability of the non-destructive test procedures that will be implemented during reactor operation. These procedures must first undergo a qualification process which consists in detailing the procedure performance levels and, when a risk of reduction in performance has been identified, demonstrating that the performances levels are sufficient to achieve the required objectives, and notably to allow the early detection of defects.

An inspection carried out on 12th April 2016 concerned a non-destructive test consisting in the ultrasonic inspection of the weld between the upper shell and the intermediate shell of the main primary system pressuriser. During this inspection, the organisational set-up deployed on the site by EDF for the implementation, technical verification and monitoring of the abovementioned activity did not seem satisfactory. The inspectors more specifically noted shortcomings in the identification and integration of the defined requirements for the ultrasonic inspection procedure which neither the technical verifications nor the associated monitoring actions had detected.

The inspectors also noted that the personnel tasked with this activity lacked specific training in this inspection process and that the associated procedure was not sufficiently operational, leading to difficulties in interpretation and even procedural errors on the part of the personnel.

Further to this inspection and in application of the prescription [BNI 167-2] of ASN Resolution 2013-DC-0347, EDF informed ASN of the suspension of the manual non-destructive testing activities for the initial complete inspection of the main primary system. EDF is working on determining and implementing preventive, corrective and curative measures before resuming these activities; ASN will be informed of resumption of the activities.

Oversight of the initial start-up tests of the Flamanville 3 EPR reactor

The aim of the start-up tests on the Flamanville 3 EPR reactor construction site is to help demonstrate that the installed equipment complies with the assigned safety requirements. Through its resolution 2013-DC-0347 of 7th May 2013, ASN has set prescriptions to govern the EDF organisation for the production of the documentation relative to the tests, their performance and sequencing, and the analysis of their results.

In 2015, ASN continued its oversight of preparation for the start-up tests and the on-site organisation for their performance. ASN thus endeavoured to verify the compatibility of EDF's organisation with the set requirements during the following inspections:

  • in the EDF central services on 30th September 2015, concerning production of the start-up test documentation. This inspection focused on the documentation concerning the tests of equipment contributing to the limitation of nuisance and inconveniences associated with normal operation of the installation;
  • on the site, on 4th November 2015, for the follow-up inspections of end-of-assembly of the ventilation system;
  • on the site, on 25th November 2015, for dealing with the deviations encountered during the start-up tests;
  • on the site, on 3rd December 2015, for the ventilation system start-up tests.

With regard to the inspection conducted in the EDF central services, ASN considers that the content of the examined documentation is generally satisfactory.

Regarding the on-site inspections, on completion of the inspection of the first start-up tests of the ventilation equipment and the tests of the equipment installed in the pumping station, ASN considers that EDF's organisational setup for the preparation and performance of the start-up tests can be improved. More specifically, EDF must be attentive to the rigour with which deviations encountered during the start-up tests are dealt with in order to decide, among other things, on the representativeness of the tests performed and the acceptability of their results, while at the same time integrating experience feedback for subsequent tests.

ASN will remain attentive to the smooth performance of the tests at Flamanville 3. The construction site will proceed with a growing number of start-up tests and ASN will verify, more specifically through its inspections, compliance with its prescriptions.

Oversight of the preparation of the future Flamanville 3 reactor licensee

ASN inspection at the EPR nuclear power plant in Flamanville - décember 2015

At the same time as it oversees the construction and start-up tests and examines the commissioning authorisation application, ASN oversees preparation of the future Flamanville 3 reactor licensee. The inspectors verify the operating organisational set-ups, management of the personnel's skills and their involvement in the construction of the reactor and its start-up tests. The inspectors also examine the conditions of production of the future documentation for reactor maintenance and operational control.

On this account, on 18th November 2015 an inspection of the organisation of the teams intended to ensure operational control of the reactor focused on the electrical distribution documentation. As the electrical distribution equipment is among the first to be put into service, when the future operating teams use it they are performing the first operational management and maintenance operations of the reactor equipment. ASN considers that in view of the sampling inspection results, the site's organisational set-up for producing the operating documentation is satisfactory.

In December 2015, the future operating teams carried out a fresh fuel reception exercise with dummy fuel. This exercise aimed at testing the planned means and procedures and observing the personnel in an operating situation. During the exercise on 2nd December 2015, the inspectors attended dummy fuel assembly handling operations and observed the setting up and functioning of a technical contingencies management team. They also looked into the production of the operating documents and the organisation of the exercise. The inspection revealed a satisfactory situation and confirmed the benefits of this type of exercise.

Analysis of the technical, organisational and human measures planned by EDF for operational control of the Flamanville 3 reactor

At the request of ASN, the Advisory Committee of Experts for Nuclear Reactors (GPR) met on 18th June 2015 to analyse the technical, organisational and human measures planned by EDF for the operational control of the Flamanville 3 EPR reactor.

As the control room and the organisation of the operating team differ from those of the EDF reactors in operation, a detailed analysis was carried out taking into account the results of various test campaigns carried out on a full-scale simulator, identical to the future Flamanville 3 control room.

On the basis of the GPR's opinion issued following this meeting and the detailed analysis carried out by IRSN, ASN considered (Insert link to the GRP follow-up letter) that the design approach for these measures was generally satisfactory.

Complementary tests will nevertheless have to be carried out before commissioning Flamanville 3, as much on the simulator as during the start-up tests to verify the compatibility of these different measures.


[1] Consult Information letter No.16

[2] Consult Information letter No.17

[3] The pressuriser expansion line links the bottom of this component to the primary system.


Date of last update : 26/11/2021