EPR Reactor: Information Letter n°12 - ASN’s supervision of the Flamanville-3 reactor construction (EPR)

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ASN oversight of the Flamanville 3 EPR construction site continued during the second half of 2011. Details of recent findings are provided below.

Inspection of prestressing tendon duct installation work

Since 2008, several ASN inspections have been devoted to the prestressing tendon system^[1] of the reactor containment structure.

In June 2011, after the detection of new deviations in the positioning of the prestressing tendon ducts, ASN asked EDF to suspend concreting work for the inner containment wall.

At ASN's request, EDF has presented an action plan to prevent further deviations and resume concreting operations.

Subsequently, ASN inspectors have performed unannounced inspections of concrete lift 8
 (12 July 2011 - see Newsletter No. 11), concrete lift 10 (22 November 2011) and concrete lift 11 (15 February 2012). The results of these inspections demonstrate the adequate implementation of the various technical and organizational measures adopted by EDF to ensure proper construction of the inner containment wall.

 Manufacture of polar crane support brackets

In the course of the inspection conducted on 14 December 2011, ASN inspectors were informed of a number of deviations in the manufacture of the polar crane support brackets^[2] for the reactor building. EDF had detected welding defects in these brackets during factory inspections prior to painting, and again during additional on-site inspections. Although such defects were initially observed in a limited number of brackets, ASN has asked EDF to conduct additional inspections on other brackets. EDF is currently conducting these inspections, determining the cause of the defects and thereby defining a corrective strategy. ASN will also conduct inspections on this issue. The construction of concrete lift 11 (inner containment wall) will only be initiated after implementation of the solution adopted by EDF to ensure construction quality.

Oversight of complex concreting operations

In July 2011, EDF informed ASN of the detection of rock pockets^[3] in certain concrete walls of the reactor building spent fuel pools. Further to an inspection conducted on 12 July 2011 (see Newsletter No. 11), and after technical analysis, ASN asked EDF to provide additional information, particularly regarding the following:

• final (post-repair) construction quality of affected concrete walls,
• identification of appropriate preventive measures, particularly regarding proper assessment of worker qualifications, with a view to ensuring full control of future complex concreting operations.

Based on the information submitted by EDF and the results of inspections conducted on 22 November and 20 December 2011, the technical and organizational measures adopted by EDF to detect and repair such defects and ensure full control of future complex concreting operations appear to be satisfactory.

Quality control of tank, pool and liner welding operations

Tank liner installation operations were initiated in late 2010 for certain safety-related tanks^[4], with particular emphasis on spent fuel pool tanks located in the reactor building and fuel building. Given the large number of tanks to be manufactured, and their importance for safety, ASN attaches particular importance to the oversight of tank manufacturing processes. ASN inspections regarding this issue were therefore conducted on 12 January, 22 June, 16 November and 23 November 2011, and 25 January 2012.

Based on the results of these inspections, the organizational measures implemented by EDF and the main construction contractor appear to be satisfactory. However, EDF must pay careful attention to stainless steel sheet metal contamination risks and to ensuring adequate control of sheet metal welding operations, particularly during repair work. ASN will continue to monitor the proper execution of these activities and the proper implementation of tank lining procedures for spent fuel pool tanks in the reactor building and fuel building.

ASN report on the complementary safety assessments conducted by EDF after the Fukushima accident

On 3 January 2012, ASN issued a report on the complementary safety assessments conducted after the Fukushima incident.

This report presents the complementary safety assessment results for all basic nuclear installations examined in 2011 (including the Flamanville 3 EPR site), and the actions to be taken by ASN based on these results. Specific requirements are to be imposed on EDF in order to improve the robustness of nuclear facilities (beyond existing safety margins) under extreme conditions.

ASN opinion and report on complementary safety assessments are available for public consultation.

Repair of reactor vessel head

AREVA NP has informed ASN of the detection of two significant quality non-conformances during manufacture of the reactor vessel head for the Flamanville 3 EPR. In order to address these non-conformances, AREVA NP submitted a proposal to ASN in July 2011. The proposed solution consists of reworking several steps of the reactor vessel head manufacturing process.

Non-conformances were the following:

• initial detection (in the fall of 2010) of welding defects in the reactor vessel head adapters,
• subsequent detection (in June 2011, during repair operations intended to correct the previously detected non-conformance) of insufficient base metal thickness (buttering).

ASN asked AREVA NP to conduct a detailed assessment of the potential impact of the proposed operations on the construction quality of the reactor vessel head. ASN also asked AREVA NP to propose specific measures to ensure the quality of repairs. After detailed examination of the information received from AREVA NP and receipt of a report issued by the Advisory Committee for Nuclear Pressure Equipment, ASN informed AREVA NP that it could proceed with reactor vessel head repair operations using the proposed method.

Detailed procedures are to be prepared for each step of the repair process. These procedures must demonstrate that AREVA NP is taking all necessary measures to mitigate potential risks and ensure the detection of non-conformances. Operations are currently being conducted without major difficulties, under the strict supervision of ASN and APAVE^[5] (inspection authority appointed by ASN). ASN will assess the acceptability of the reactor vessel head after successful completion of all repair and manufacturing operations.

Non-conformances detected during the pipe manufacturing process

In the course of a manufacturing inspection conducted in March 2011, AREVA NP detected a non-conformance of the internal surface condition of certain auxiliary pipes. The affected components exhibited small metal tears and scratches. AREVA NP proceeded with the repair of these components. In September 2011, ASN ordered the suspension of repair operations due to non-consideration of certain requirements intended to improve radiation protection performance for the future reactor. AREVA NP subsequently proposed appropriate measures, and repairs were resumed in November 2011.

In November 2011, the EDF-appointed user inspectorate^[6] in charge of verifying the regulatory compliance of certain piping components informed ASN of the inadequacy of weld repair operations performed by an AREVA NP subcontractor. In particular, the tools used and the inspections conducted were insufficient to ensure proper thickness of regions adjacent to welds. On 22 December 2011, ASN conducted a reactive inspection and suspended pipe manufacturing operations (subsequently resumed in February 2012 after effective implementation of ASN requests).

ASN considers that these non-conformances illustrate how essential it is for manufacturers to stipulate specific requirements to their suppliers and to ensure that they are met. ASN has also asked AREVA to verify that manufacturing processes generate no risk of degradation and are adequately monitored.

[1] Prestressing is a construction technique used to improve the structural performance of a building. It is achieved by means of prestressing tendons running through ducts embedded in the concrete. The EPR containment structure is composed of two containment walls separated by a space between them. The inner containment wall is made of prestressed concrete lined with steel on the inside.

[2] The polar crane is an overhead handling crane located below the reactor building dome. It is supported by brackets secured to the building structure. It is used to handle heavy loads above the reactor and is therefore subject to detailed inspections.

[3] Concrete lift areas exhibiting a concentration of agglomerates and a lack of cement, and therefore requiring repair.

[4] Sealed storage tanks with stainless steel walls, located within facility buildings.

[5] http://www.apave.com

[6] User inspectorate: Approved organization responsible for conducting compliance assessment activities in accordance with nuclear pressure vessel regulations.