EPR Reactor: Information Letter n°13 - ASN monitoring of the EPR Flamanville reactor construction site: notable points

Since the end of 2011, ASN has conducted several inspections [link to inspection follow-up letters posted on line on asn.fr] that continue its monitoring of the construction of the Flamanville 3 EPR reactor and various other manufacturing operations for this reactor. The notable points observed over these last few months are detailed below.

Manufacture of the polar crane supports

During the inspection of 14th December 2011, ASN was informed of a number of deviations that occurred during the manufacture of the supports of the reactor building polar crane[1]. EDF discovered defects in the support welds in the factory before painting, then again on the Flamanville site during complementary inspections. While these defects were initially discovered on a limited number of supports, ASN asked EDF to carry out additional inspections on other supports. These additional inspections revealed defects on a large number of the supports. EDF then informed ASN of its decision to have all the polar crane supports re-manufactured. Meetings were held between ASN, the IRSN and EDF to that EDF could present the work undertaken to understand the origin of these numerous defects and to prevent identical defects occurring on other components intended for the Flamanville 3 reactor.

Manufacture of the new consoles is currently in progress. ASN will be attentive to the quality of the new supports and, at the appropriate time, to the conditions of resuming the installation and concreting activities within the reactor containment.

Cooperation with the Finnish safety Authority (STUK) and monitoring of the complex concreting activities

In July 2011, EDF informed ASN that it had discovered localised honeycombing[2] in certain concrete walls of the pools in the reactor building. ASN asked EDF to implement measures to enhance the quality of the following complex concreting operations, and conducted inspections in this respect on 19th October, 22nd November and 20th December (see information letters No. 11 and 23). These inspections were continued in 2012.

On 13th March 2012 ASN thus performed an inspection to check the technical and organizational measures adopted by EDF for the fabrication of APC shell[3] roof of the safeguard auxiliary building. The technique used at Flamanville to produce this complex structure is similar to that used in Finland on the Olkiluoto EPR reactor construction site. The ASN inspectors conducted this inspection in the presence of their Finnish counterparts, in the framework of frequent exchanges with STUK, the Finnish safety Authority. On completion of this inspection, ASN considers that EDF's organisation for the construction of this structure is on the whole satisfactory, as is EDF oversight of its contractors.

In addition, in March 2012 EDF informed ASN of the presence of "empty spaces" behind the recesses accommodating the gates[4] of the reactor building pools; this partial filling with concrete results from activities that took place in the summer of 2011, before the implementation of additional measures for complex concreting work. EDF detected this defect at Flamanville through application of experience feedback from the Olkiluoto reactor, where a similar anomaly had been observed. The repairs undertaken by EDF were subject to unannounced inspection by ASN on 21st August 2012. Although ASN notes that EDF has endeavoured to turn the experience feedback from the Olkiluoto construction site to good account, it will remain attentive to the final construction quality - that is to say after inspection and repair – of the EPR reactor pools.

Repair of the reactor vessel closure head 

AREVA NP informed ASN, first at the end of 2010 and then in 2011, of the detection of two major quality deviations during manufacture of the Flamanville EPR reactor vessel closure head. The deviations concerned:

• firstly, in autumn 2010, detection of a large number of defects in the adapters’ welds located on the vessel closure head;
• secondly, in June 2011, during repair operations to correct the previous defects, detection of insufficient thickness in the buttering metal layer located under these welds.

The processing of these deviations led AREVA NP in July 2011 to propose a large-scale repair solution to ASN, involving completely redoing several steps in the vessel head manufacturing process. The first of these steps consisting in eliminating all the welds and the buttering-metal of 50 adapters out of a total of 105.

During this step AREVA NP was specifically monitored by the APAVE[5] and ASN. The operations ran with no major difficulties other than a machining machine programming anomaly, which had no impact on the quality of the vessel closure head but led ASN to suspend the closure head repair operations. AREVA NP proposed corrective and preventive measures involving introducing safety mechanisms in the machining programs, stepping up internal monitoring and implementing additional checks. ASN approved this plan of actions and authorised resumption of the repair operations, two months after their suspension.

An inspection carried out in July 2012 confirmed the progress of the operations following the implementation of these actions and allowed AREVA NP's experience feedback to be examined during this first phase of machining of the welds and butterings. No corrective actions were demanded further to this inspection. ASN approved the continuation of the repair operations consisting in eliminating the welds and buttering metal from the remaining 55 adapters.

At the end of this second phase, AREVA NP will perform a complete inspection of the closure head base metal under the removed welds. After examining the results of these inspections, ASN will decide on the continuation of the repair operations which will involve resuming fabrication of the closure head, still with tightened monitoring.

 Identification of the requirements associated with the assembly of the equipment

The nuclear steam supply system of the Flamanville EPR reactor comprises a large number of nuclear pressure equipment items (containers under pressure, pipes, cocks, safety valves). These equipment items are assembled together to form integrated and functional units. The first unit assembly operations are starting on the Flamanville site.

In addition to its regular inspections of EDF, the nuclear installation licensee, ASN also examines the measures taken by AREVA NP, the assembly unit manufacturer, to prevent the risks of the units getting damaged during transport and assembly on site. The risks of impacts, deformation, chemical pollution, corrosion, etc. must be taken into account.

ASN has asked AREVA NP to carry out a risk analysis of these transport and on-site installation phases, and to clearly identify the measures planned to reduce or eliminate these risks. At the same time, ASN began its inspections on this theme in June 2012 in the AREVA NP premises on the Flamanville EPR site, and on the actual construction site itself. These first on-site inspections of AREVA NP revealed that progress remains to be made:

• in the identification of the documents drafted by the equipment manufacturers and defining the precautions to take to prevent equipment damage during transport and assembly;
• in the defining and compliance with the conditions of conservation of the equipment in the buildings after their installation until they are commissioned, notably with regard to temperature and relative humidity.

After examining the measures presented by AREVA NP, and in agreement with the organisations responsible for assessing the conformity of the pressure equipment, ASN will state its position regarding the continuation of the on-site assembly operations.

Additional requirements applicable to Flamanville 3 in the light of the conclusions of the Complementary Safety Assessments (CSA). 

After the publication on 3rd January 2012 of the conclusions of the CSAs carried out in 2011, ASN took 32 resolutions on 26th June 2012, each of which sets some thirty complementary prescriptions relative to the EDF nuclear power plants, the AREVA facilities and some of the CEA (French Alternative Energies and Atomic Energy Commission) reactors. Resolution No. 2012-DC-0283 concerns the Flamanville site. Its appendix No.2 sets additional requirements applicable to the Flamanville 3 reactor.

The file that EDF will submit on account of article 20 of decree 2007-1557 for the commissioning of Flamanville 3 must provide proof that these requirements have been taken into account.

Flamanville 3 reactor instrumentation and control system

Refer to the information notice of 16th April 2012: "ASN lifts its reservations on the Flamanville 3 EPR instrumentation & control architecture".