EPR Information Letter No.17: ASN monitoring of the Flamanville EPR reactor construction site: notable points.

Published on 23/06/2015 • 05:30 pm

Information notice

In the second half of 2014 and early 2015, ASN continued its monitoring of the Flamanville 3 EPR reactor and the various manufacturing operations for this reactor. The notable points observed over these last few months are detailed below

Monitoring of the initial start-up tests of the Flamanville 3 EPR reactor.

The purpose of the start-up tests on the Flamanville 3 EPR construction site is to help demonstrate that the equipment installed complies with the relevant safety requirements. In its resolution 2013-DC-0347 of 7th May 2013, ASN set prescriptions applicable to EDF’s organisation for the production of the test documentation, the performance and scheduling of the tests and the analysis of the test results.

In 2014, ASN continued its oversight of the preparations for the start-up tests and the organisation defined on the site for performance of these tests. Through an inspection of the EDF head office departments on 2nd October 2014, and two on-site inspections on 4th September and 11th December 2014, ASN focused on checking that EDF’s organisation was compatible with the prescriptions issued.

Following these inspections, ASN considers that the organisation defined and implemented in the EDF head office departments and on the construction site for drafting of the documentation and performance of the start-up tests is on the whole satisfactory. EDF will however be required to remain vigilant in order to record any deviations encountered, more specifically when the preconditions defined for performance of a start-up test are not met.

The continued work on the construction site will be accompanied by an increasing number of start-up tests and, more specifically on the occasion of its inspections, ASN will remain attentive to compliance with the prescriptions it has issued.

Deviations concerning prestressing of the inner containment of the reactor building.

Deviations concerning prestressing of the inner containment of the reactor building

The initial prestressing[1] work led to two deviations notified to ASN by EDF in July 2014[21]. In February 2015, EDF informed the ASN Caen division of further difficulties during the tensioning of a “gamma”[3] cable. The analysis carried out by EDF identified the fact that clamping jaws - metal parts designed to clamp the cable while it is being tensioned – were incomplete or even totally absent from some of the 54 strands[4] making up the cable. The strands which were not equipped with clamping jaws were therefore not tensioned sufficiently to obtain the expected prestressing force. EDF suspended the work until an action plan could be implemented to avoid this anomaly from happening again. The strands concerned will be re-tensioned.

EDF periodically informs ASN of the deviations observed in the prestressing activity. ASN therefore adapted its oversight of this activity, in particular with regard to inspections. Since the beginning of the prestressing work on the inner containment, four dedicated inspections have been carried out between July 2014 and March 2015.

In the light of the conclusions of these inspections, it was found that the organisation defined and implemented on the site for performance of the prestressing operations could be further improved. ASN in fact noted a large number of deviations in these complex activities, which meant that EDF frequently had to adapt the performance methods to take account of the experience feedback obtained. EDF will need to ensure that full account is taken of the cumulative effect of these deviations on the quality of construction of the inner containment. However, ASN observes that there is effective detection of the deviations and appropriate suspension of the activities concerned by EDF, pending the adoption of corrective measures to prevent any reoccurrence of the deviations observed.

Assembly of the main primary system.

The construction of the EPR reactor’s nuclear steam supply system involves the successive assembly of nuclear pressure equipment items; to check the correct performance of these assembly operations and assess the conformity of the nuclear pressure equipment with the requirements applicable to them, ASN relies on the services of approved organisations. These requirements more specifically concern giving consideration to the risks inherent in the assembly operations, the checks to be performed on-site by the manufacturer, the organisation set up 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. During these inspections, ASN and the approved organisations carry out and monitor the assembly operations or the operations involved in the on-site manufacture of nuclear pressure equipment and also review the technical documentation.

 

Between February and July 2014 AREVA carried out an initial assembly sequence on the reactor primary system, consisting in bringing several components of reactor primary system loop n°2 into the reactor building and then interconnecting them: the vessel body, the crossover leg, the hot leg and the primary pump casing[5].

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 n°2, the pressuriser and its expansion line into the reactor building and welding them to the primary system.

The X-ray inspections carried out on the welds revealed in October 2014 a defect indication on the weld between steam generator n°2 and the hot leg. Welding operations were then suspended and in-depth investigations were carried out by AREVA to characterise this indication and its origin. After analysis of this characterisation work and the proposals for corrective measures from ASN, the proposed repair for this weld was carried out and the operations continued.

During the month of March 2015, AREVA continued to bring the main components of the primary system into the reactor building and positioned steam generators 1, 3 and 4 in their respective bunkers. On 27th March 2015, AREVA suspended welding work following a deviation that occurred during the welding of steam generator 1. A further analysis of the welding conditions was carried out by AREVA and presented to the approved organisations and ASN. After examining this analysis, ASN had no objection to continuation of the operations. AREVA in particular provided additional data concerning the inspection methods used to guarantee the conformity of these welds.

During this period, ASN carried out two inspections, of EDF and AREVA respectively - concerning the assembly of the primary system - and two inspections on the monitoring of these activities by BUREAU VERITAS in its capacity as an ASN approved organisation. In the light of these inspections, ASN considers that the assembly operations involving the large components of the primary system and carried out between the summer of 2014 and April 2015, took place in satisfactory conditions.

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

ASN was informed by AREVA of an anomaly in the composition of the steel in certain areas of the Flamanville EPR reactor vessel head and bottom head. This anomaly was detected during tests performed in accordance with the nuclear pressure equipment regulations, which require that the manufacturer control the risks of heterogeneity in the materials used to manufacture those components most important for safety. In order to address this technical requirement, AREVA conducted chemical and mechanical tests on a vessel head similar to that of the Flamanville 3 EPR reactor. At the end of 2014, the results of these tests showed the presence of an area with a high concentration of carbon, giving lower than expected mechanical toughness[6] values. The first measurements confirmed the presence of this anomaly in the vessel head and vessel bottom head already installed in the Flamanville 3 EPR. AREVA submitted a proposal to ASN that it carry out a further detailed test campaign on a representative vessel head to precisely identify the location of the area concerned and its mechanical properties.

ASN will issue a ruling on the test programme, check that it is correctly implemented and examine the file to be presented by AREVA, in order to demonstrate the strength of the Flamanville EPR reactor vessel. It will in particular call on the help of its technical support organisation, IRSN, and the Advisory Committees for nuclear pressure equipment and for other reactors.

ASN has informed its counterparts in other countries concerned by the construction of an EPR reactor.

On its website ASN has published a press release and a technical notice.

Meeting between ASN and the Finnish nuclear safety regulator.

The inspectors from the Finnish nuclear safety regulator (STUK) and ASN in the future Flamanville 3 EPR reactor control room.

ASN and the Finnish nuclear safety regulator (STUK) met in France in March 2015. Their regular exchanges enable the two authorities to share their experience of construction oversight and the technical design review for the EPR type reactors, as a reactor of this type is currently under construction on the Olkiluoto site in western Finland. Technical meetings were held regarding the preparation for the start-up tests, the problems linked to the civil engineering work, reactor instrumentation and control (I&C) and the manufacture and installation of the large mechanical components. A visit to the Flamanville 3 construction site was also organised.

Submission of the Flamanville 3 commissioning authorisation application.

On 19th March 2015, ASN received the Flamanville 3 commissioning authorisation application file. This file was sent by EDF in accordance with Article 20 of Decree 2007-1557. It contains a safety analysis report, general operating rules, a waste management study, a decommissioning plan, an on-site emergency plan and an updated version of the impact assessment.

Commissioning of the facility corresponds to the introduction of the first fuel assembly into the reactor vessel. It is dependent on prior issue of the facility commissioning authorisation by ASN.

ASN considers that the file submitted by EDF is acceptable. ASN however considers that it needs to be added to so that the technical review can be carried out. In a letter dated 12th June 2015, ASN notified EDF of its conclusions and drew up the list of additions, corrections and justifications required concerning the various parts of the commissioning authorisation application file. Pending these additions, the time allocated for the review as stipulated by the regulations has been placed on hold.

On the same date, EDF submitted the partial commissioning authorisation application file to ASN (a step which corresponds to the introduction of fuel within the BNI perimeter of Flamanville 3). ASN has begun to analyse this application in order to determine whether it contains all the items needed to allow its technical review to be carried out.

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Reference texts

Inspection follow-up letters (French version)

  • Consult inspection follow-up letter CODEP-CAE-2014-043578 of 24th September 2014
    with regard to the inspection of 4th September 2014 on the Flamanville 3 site and concerning the preparation for and performance of the start-up tests on the pumping station equipment.
  • Consult inspection follow-up letter CODEP-DCN-2014-049029 of 29th October 2014
    with regard to the inspection of 2nd October 2014 in the EDF head office departments and concerning the drafting of the documentation for the start-up tests.
  • Consult inspection follow-up letter CODEP-CAE-2014-057289 of 19th December 2014
    with regard to the inspection of 11th December 2014 on the Flamanville 3 site, and concerning the performance of start-up tests on the pumping station equipment.
  • Consult inspection follow-up letter CODEP-CAE-2014-038746 of 2nd September 2014
    with regard to the inspection of 17th July 2014 on the Flamanville 3 site, and concerning the prestressing of the reactor building inner containment.
  • Consult inspection follow-up letter CODEP-CAE-2014-048635 of 24th October 2014
    with regard to the inspection of 17th October 2014 on the Flamanville 3 site, and concerning the prestressing of the reactor building inner containment.
  • Consult inspection follow-up letter CODEP-CAE-2015-004887 of 5th February 2015
    with regard to the inspection of 22nd January 2015 on the Flamanville 3 site, and concerning the prestressing of the reactor building inner containment.
  • Consult inspection follow-up letter CODEP-CAE-2015-013684 of 14th April 2015
    with regard to the inspection of 25th March 2015 on the Flamanville 3 site, and concerning the prestressing of the reactor building inner containment.
  • Consult inspection follow-up letter CODEP-CAE-2015-006724 of 17th February 2015
    with regard to the inspection of 10th February 2015 on the Flamanville 3 site, and concerning the construction of the limonite ring.
  • Consult inspection follow-up letter CODEP-CAE-2015-011613 of 23rd March 2015
    with regard to the inspection of 6th March 2015 on the Flamanville 3 site, and concerning the performance of mechanical assembly and management of the cleanness relating to these activities.
  • Consult inspection follow-up letter CODEP-CAE-2015-014169 of 9th April 2015
    with regard to the inspection of 1st April 2015 on the Flamanville 3 site and concerning the organisation of EDF and its contractors regarding the mechanical assembly work for the nuclear pressure equipment of the main primary system.
  • Consult inspection follow-up letter CODEP-DEP-2015-01206 of 5th May 2015
    with regard to the inspection of 1st April 2015 on the Flamanville 3 site and concerning the monitoring of the manufacture of nuclear pressure equipment – conformity of main primary system welding operations.
  • Consult inspection follow-up letter CODEP-DCN-2015-016930 of 2nd June 2015
    with regard to the inspection of 15th April 2015, at the EDF Corporate Nuclear Engineering Unit (CNEN) and concerning the drafting of the partial commissioning authorisation application file.

 
 

[1] The building housing the EPR reactor comprises a double containment. The function of the outer containment, made of reinforced concrete, is to protect the equipment from external hazards. The inner containment is made of prestressed concrete, which makes it able to withstand the pressure increases liable to occur in an accident situation. This prestressing is by means of cables inserted into sleeves incorporated into the concrete, which are then tensioned such as to apply a compression force to the concrete, able to counter any internal overpressure. Finally, a cement grout is injected into the sleeves, to protect the cables from corrosion.

[2] Consult the EPR Information letter of July 2014

[3] The “gamma” cables in particular prestress the dome of the inner containment and their name is due to their characteristic geometry (upper case Greek letter “gamma”: Γ)

[4] A strand is one of the 54 metal wires making up a prestressing cable.

[5] Consult Information letter n°16

[6] Toughness is an indicator of the ability of a material to withstand crack propagation. In the case of a reactor vessel, this property is particularly important in the event of a thermal shock, for example following the injection of cold water into the reactor primary system.

Date of last update : 05/12/2017