Newsletter n°16 - ASN monitoring of the Flamanville EPR reactor construction site: significant points.

Published on 17/11/2014 • 03:20 pm

Information notice

In the second half of 2013 and early 2014, ASN carried out a number of inspections to continue its monitoring of the Flamanville 3 EPR reactor construction site and the various items being manufactured for it. The significant points over these recent months are detailed below. 

Monitoring of the Flamanville 3 EPR reactor first commissioning tests

The purpose of the commissioning tests on the Flamanville 3 EPR site was to help demonstrate that the installed equipment complied with the relevant requirements. To ensure that the goals set for the commissioning tests were met, ASN resolution 2013-DC-0347 of 7th May 2013 set prescriptions concerning EDF’s organisation for drafting the test documentation, the test procedures / sequences and the analysis of their results.

In late 2013, on the occasion of the first power-up operations for the electrical and I&C cubicles, which are classified owing to their importance for safety, ASN monitored the preparation for the commissioning tests and the organisation defined on the site for performance of these tests. Through two inspections in the EDF head office departments on 11th July and 26th November 2013, plus two site inspections on 5th November and 18th December 2013, ASN focused on checking that the organisation was in conformity with the prescriptions issued.

Following these first inspections, ASN considers that the organisation defined and implemented by the EDF head office departments for drafting the commissioning tests documentation is on the whole satisfactory. The commissioning tests phase began while certain systems were not yet in their final configuration. ASN considers that EDF must continue to demonstrate in all its activities that the hardware modifications made to the detailed design of Flamanville 3 have actually been taken into account.

The on-going construction work on the site will be accompanied by an increasing number of commissioning tests and ASN will remain vigilant, more specifically on the occasion of its inspections concerning the commissioning tests and compliance with the prescriptions it has issued.

Schema of the polar crane and lifting and handling equipment. In red additional trolleys.

Significant event concerning the “320t” trolley on the Flamanville 3 EPR reactor polar crane

On 16th October 2013, during a load test of the “320 t” trolley on the reactor building’s polar crane, an incident occurred, damaging parts of the trolley and projecting metal components beyond the safety perimeter that had been defined. This event had no impact on the workers. The load being handled during the test remained securely suspended at the end of the cable. ASN is responsible for labour inspectorate duties on the site and checked that EDF has taken the necessary steps and defined a specific plan of action to improve the safety and satisfactory coordination of the activities.

Some ejected parts struck the metal liner of the inner containment dome, creating two points of impact, one of which was penetrating. In early 2014, welding repair work was carried out on this second impact in order to restore the leaktightness of the liner.

The EPR dome and polar crane of Flamanville

The “320 t” trolley will mainly be used to handle the vessel head to allow reloading of fuel, once the reactor is in service. This trolley must function correctly in order to prevent any risk of the parts being handled damaging other equipment in the reactor building.

Following this incident and at the request of ASN, EDF declared a significant safety event. The first analysis data show that the cause of the event was inadequate calibration of the trolley’s measurement channel, designed to detect over-speeds. The parts damaged during the event will be replaced and EDF will be required to perform further load tests and qualification of the trolley. ASN asked EDF to conduct an experience feedback analysis and identify any necessary corrective measures. ASN will then examine this information.

Deviation concerning the quality of concreting of lift n° 14

On 16th January 2014, EDF informed ASN that a concreting deviation had been detected concerning lift n° 14, situated at the join between the cylindrical part and the dome of the reactor building’s inner containment. The deviation was detected once the concrete had set, primarily in three areas which appeared to be darker in colour.

EDF proceeded to remove the concrete from these areas, which were found to contain a lower density of aggregate. Margins were adopted during this removal process to ensure that the characteristics of the concrete which remained in place were in conformity with the specified requirements. Following these operations, the maximum dimensions of the defects appeared to be 10 cm high, 40 cm deep and about 10 centimetres long, except for one of them, which was 4 m long.

The analysis sent by EDF to ASN identified the fact that rain, which was heavier than expected at the time of pouring, had created run-off leading to an accumulation of water and fine particles in certain areas, as the accumulated water could not drain away owing to the small diameter of the orifices made in the formwork. These areas did not therefore receive the expected density of aggregate.

EDF presented ASN with a repair strategy involving the injection of microconcrete, comprising aggregates of smaller dimension, so as to optimise following of the contours of the removed concrete volumes. To prevent this deviation from happening again, EDF has reinforced the measures to allow the drainage of run-off water and to this end it improved the concreting procedure used.

ASN issued no observation on this strategy and its implementation by EDF was considered by ASN to be satisfactory.

The EPR double-wall containment

Deviations concerning pre-stressing of the reactor building inner containment

The building housing the EPR reactor comprises a double-wall containment. The function of the outer containment, made of reinforced concrete, is to protect the equipment from the effects of an external hazard. The inner containment is made of pre-stressed concrete, which enables it to withstand the pressure rises liable to occur in an accident situation. This pre-stressing is by means of cables, inserted into sheaths incorporated into the concrete, then tensioned so as to apply a compression force to the concrete which would counter any internal over-pressure. Finally, a cement grout is injected into the sheaths, so as to protect the cables from corrosion.

Strands oilig

In early 2014, EDF informed ASN of two deviations which had occurred during the pre-stressing operations. The first concerned the injection of grout into the sheath of a horizontal cable. The quantity of grout prepared in the injection device was insufficient and an incorrect decision was taken to use water to push the grout into the injection device. This then led to the injection of a mixture of water and grout into the pre-stressing sheath, giving rise to risks of long-term corrosion of the strands[1].

The second deviation concerned the tensioning of a vertical cable: the various strands making up the cable were tensioned to significantly different values, which reduces the effectiveness of the pre-stressing.

The Caen division carried out an inspection on 17th July 2014, to examine how EDF dealt with these deviations. The inspectors found that the incidents which affected the pre-stressing work were mainly the result of documentary inadequacies and non-compliance with procedures by an outside contractor. They did however observe that EDF’s management of these deviations was appropriate and in accordance with its internal procedures. EDF in particular informed ASN of the deviations detected and suspended the pre-stressing work as a precaution, until the causes of the deviations could be determined and a remedial plan of action established. This plan has now been defined and implemented and the pre-stressing operations can resume. With regard to the deviation on the horizontal cable, measures to characterise and repair the defect have yet to be taken by EDF. With regard to the deviation on the vertical cable, EDF decided to replace all the strands of the cable concerned and then re-tension it.

Beginning of construction work on the Flamanville site’s future emergency centre

In its resolution 2012-DC-0283 of 26th June 2012, ASN issued additional prescriptions for EDF applicable to the Flamanville site, in the light of the conclusions of the stress tests[2]. These additional prescriptions require the installation of a “hardened safety core”, which must in particular include measures to strengthen the licensee’s ability to perform emergency management duties in extreme conditions, the scope of which exceeds that considered in the design.

In response to this prescription, EDF decided in particular to build a new emergency management centre in Flamanville; it will be operational for the commissioning of Flamanville 3.

The construction of the future emergency management centre thus began on the North part of the site in late 2013. The earthworks and initial pouring of concrete took place in August 2014. The centre will be able to offer a high level of resistance to hazards, such as an earthquake, and remain permanently accessible and habitable by the personnel managing the emergency situations, including during long-duration emergencies and in the event of radioactive releases.

ASN remains highly attentive to the construction of the premises of the Flamanville local emergency centre, which is common to the site’s three nuclear reactors and which will replace the existing emergency management facilities. ASN intends to conduct an inspection when the progress of the construction work so permits.

Meeting between ASN and the Finnish safety regulator

ASN and the Finnish safety regulator (STUK) met in France in the autumn of 2013. These regular meetings enable the two regulators to share their experience concerning the oversight of the construction and technical examination of the design of EPR type reactors, as a reactor of this type is also being built on the Olkiluoto site in western Finland. Technical meetings were held regarding preparations for the start-up tests, the problems linked to civil engineering work and the manufacture and installation of large mechanical components.

In the autumn of 2013, two Finnish inspectors also took part in an ASN inspection on the Flamanville site concerning mechanical erection work.

In February 2014, two ASN inspectors accompanied IRSN experts to Finland to take part in inspections carried out by STUK, prior to acceptance testing of the reactor containment under construction at Olkiluoto 3. This visit enabled ASN to gain a clearer understanding of this operation and to prepare its oversight approach for the same test to be carried out on the Flamanville 3 reactor under construction.

Installation of the main primary system

The EPR reactor’s nuclear steam supply system is built in successive assembly stages. Together with the organisations approved for assessing the conformity of the nuclear pressure equipment, ASN ensures that the pre-requisites applicable to these operations are met. These pre-requisites in particular concern consideration of the risks inherent in electromechanical assemblies, the checks to be performed on-site, the organisation set up by EDF and AREVA to minimise the risks associated with activities carried out by other contractors in proximity to the premises concerned, as well as the cleanness of the work areas and assembled equipment.

ASN and the approved organisations review the technical documentation for the assembly operations and monitor the nuclear pressure equipment assembly or manufacturing operations on the site.

Between February and July 2014, AREVA carried out an initial reactor system assembly sequence which consisted in bringing the following components of reactor coolant system loop N°2 into the reactor building and assembling them together: vessel body, crossover legs, cold leg, hot leg and reactor coolant pump casing.

During this period, ASN carried out two inspections, on EDF and AREVA respectively, concerning the installation of the EPR’s reactor coolant system, plus two inspections on the monitoring of these activities by BUREAU VERITAS as an organisation delegated by ASN. Further to these initial inspections, ASN considers that the assembly operations carried out since the summer of 2014 and involving the large components of the reactor coolant system have been carried out in satisfactory conditions. They will be gradually extended, after ASN has checked that the experience acquired during the initial activities carried out has been taken into account.

En savoir plus

Consult the resolutions

All the publications below are available in French

Consult the follow-up letters

  • Preparation of the documentation for the start-up tests at the Centre national d'équipement et de production d'électricité (CNEPE)
    Inspection of 07-11-2013
    INSSN-DCN-2013-0634
    (125,47 ko)
  • Drafting of the start-up tests documentation at the Centre national d'équipement nucléaire (CNEN)
    Inspection of 11-26-2013
    INSSN-DCN-2013-0633
    (123,70 ko)
  • Assembly and power-up of the I&C cubicles on the EPR construction site
    Inspection of 08-29-2013
    INSSN-CAE-2013-0604
    (123,97 ko)
  • Preparation for and performance of the start-up tests on the EPR construction site
    Inspection of 12-18-2013
    INSSN-CAE-2013-0606
    (163,46 ko)
  • Initial mechanical assembly work on the EPR reactor main primary system equipment
    Inspection of 07-17-2014
    INSSN-CAE-2014-0629
    (129,28 ko)
  • Management of deviations in the pre-stressing of the EPR reactor building inner containment
    Inspection of 06-11-2014 to 06-13-2014
    INSSN-CAE-2014-0636
    (128,91 ko)
  • Conformity of welding operations on the Flamanville EPR reactor main primary system
    Inspection of 06-12-2014
    INSSN-DEP-2014-0742
    (106,11 ko)
  • Monitoring of the transfer of the EPR reactor vessel into the reactor building under construction
    BUREAU VERITAS - Brignais (69)
    Inspection of 02-12-2014 to 02-13-2014
    INSNP-DEP-2014-1235
    (129,85 ko)

[1] A strand is one of the 54 metal wires making up a pre-stressing cable.

[2] The stress tests were required for all BNIs by ASN in order to take account of the experience feedback from the Fukushima-Daiichi accident of 11th March 2011.

Date of last update : 20/05/2019