ASN monitoring of the EPR Flamanville reactor construction site: notable points
In the second half of 2012, ASN conducted several inspections for continued 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.
Filling with water and modification of the pumping station intake channel
The seawater intake channel for the pumping stations1 of the two reactors in operation needed to be extended in order to be able to supply the EPR reactor pumping station, for which the civil engineering work is now complete. The channel extension work comprised three steps:
- construction of a new dam closing off the intake channel beyond the EPR reactor platform. This first step was carried out from April to November 2012;
- filling with water of the portion of the channel located in front of the EPR reactor pumping station. This second step took place on 29 November 2012;
- complete removal of the dam between reactor 2 and the EPR reactor, which began on 10 December 2012.
During preparation for and performance of these operations, ASN was particularly attentive to maintaining the safety of Flamanville reactors 1 and 2, which must be guaranteed by EDF. An unannounced inspection was therefore carried out on 10 December 2012, the date on which the breach was opened in the dam to be removed; this inspection verified the technical and organisational measures taken by EDF for performance of these operations. In particular, the removal of the dam during this third step entails the dispersion of suspended solids (sand, earth, etc.) into the water of the channel from the structure. EDF must minimise the dispersion of these solids, in order to limit their impact on the reactors in operation. The licensee must in particular avoid a malfunction of the reactor cooling water filtration systems. The measures taken by EDF were inspected by ASN and found to be satisfactory.
ASN remains attentive to the satisfactory performance of this phase of the construction site, which will require the use of heavy site machinery in order to achieve the final elevation of the channel bottom.
Manufacture of the polar crane supports
During the inspection of 14th December 2011, on the Flamanville 3 site, ASN was informed of a number of deviations that occurred during the manufacture of the polar crane supports2. EDF discovered defects in the support welds in the factory before painting, then again on the Flamanville site during complementary inspections. ASN asked EDF to inspect a larger number of supports in order to identify the scale of the defects. These additional inspections demonstrated the presence of defects on a large number of supports, so EDF decided to replace them all and have new polar crane supports manufactured. At ASN’s request, EDF presented ASN and its technical support organisation, the Institute for Radiation Protection and Nuclear Safety, with 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.
On 10 October 2012, ASN carried out an inspection to check that the steps actually taken by EDF to prevent defects of the same type on the new supports were implemented in good conditions. The inspectors also examined the steps taken by EDF to analyse whether other equipment intended for Flamanville 3 was affected by similar defects. The analysis did indeed reveal defects on certain items (especially on several handling cranes or their carriages), so EDF returned some of the equipment concerned to the factory for repair, while dealing with other items in situ.
At the end of January 2013, EDF had completed the installation of all the new supports in the reactor building.
Repair of the reactor vessel closure head
Since the end of 2010, AREVA NP has been involved in a process to repair deviations on the Flamanville EPR reactor vessel closure head. These repairs consist in removing and then completely re-doing all the welds and buttering on all the closure head adapters3.
During the second half of 2012, AREVA NP completed the welds and buttering removal phase and carried out a complete inspection of the closure head base metal. In December 2012, ASN carried out checks on these inspection operations and in January 2013 conducted an exhaustive examination of the results of these operations. No deviating indication was observed, so ASN authorised the start of the second phase of the closure head repair work, which involved the new buttering and welding of the closure head.
At the request of ASN, AREVA NP improved the closure head manufacturing processes and the manufacturing inspection processes that had initially been followed. These improvements concern the adapter welding procedures and the scope of the checks carried out on the welds. ASN tasked the APAVE Group, an organisation approved by ASN for inspection of pressure equipment, with monitoring of the closure head repair phases, which will also be inspected by ASN. Following these repairs, the closure head will undergo a final check and a pressure test.
Identification of the requirements associated with the assembly of the nuclear steam supply system (NSSS) pressure equipment
In addition to the regular checks carried out by ASN on EDF, ASN also examines the steps taken by AREVA NP, the NSSS manufacturer, to prevent the risk of any damage to the equipment during transport to the Flamanville site and during assembly. ASN is thus continuing to examine the documentation required for authorisation of the on-site assembly operations for the NSSS equipment. Together with the organisations responsible for assessing equipment conformity, ASN is also examining the monitoring measures required during the on-site assembly operations.
In December 2012, the first assembly operations for the NSSS, in particular the installation of certain concrete containment penetrations, were authorised by ASN on the Flamanville site. In January 2013, ASN carried out an inspection of these operations, which confirmed compliance with the construction procedures that had been validated by ASN beforehand.
To find out more:
1. The pumping stations take seawater and use it to cool some of the systems.
2. The polar crane is a handling crane located under the reactor building dome. It rests on metal supports secured to the structure of the reactor building. It is used to handle heavy loads above the reactor and is thus subject to exhaustive checks.
3. See the information notice published by ASN on 19 October 2011 ("ASN monitors AREVA NP repair of the vessel closure head intended for the Flamanville EPR" (French only)) and EPR information notice No. 12 (October 2012).