The French Nuclear Safety Authority (ASN) has been informed by AREVA of an anomaly in the composition of the steel in certain zones of the reactor vessel head and reactor vessel bottom head of its European Pressurized Reactor (EPR).
The nuclear pressure equipment regulation requires that the manufacturer limits the risks of heterogeneity in the materials used for manufacturing the components most important for safety. In order to address this technical requirement, AREVA carried out chemical and mechanical tests on a vessel head similar to that of the Flamanville EPR. The results of these tests, in late 2014, revealed the presence of a zone in which there was a high carbon concentration, leading to lower than expected mechanical toughness1 values.
Initial measurements confirmed the presence of this anomaly in the reactor vessel head and reactor vessel bottom head of the Flamanville EPR. ASN received a proposal from AREVA for a further detailed test campaign on a representative vessel head, starting in April 2015, in order to precisely identify the location of the zone concerned and its mechanical properties.
ASN will make a decision on the acceptability of the test program, check its correct performance and examine the file to be submitted by AREVA to demonstrate the robustness of the Flamanville EPR reactor vessel. It will also call on the services of its technical support organization, IRSN (Institute of Radiation Protection and Nuclear Safety), and the Advisory Committee of Experts for Nuclear Pressure Equipment.
The vessel of a pressurized water reactor is equipment that is particularly important for safety. It contains the fuel and takes part in the radioactivity second containment barrier.
The reactor vessel head and reactor vessel bottom head of the Flamanville EPR are partially spherical forged steel parts.
ASN has informed its foreign counterparts which are concerned by the construction of an EPR. Currently, AREVA’s EPR is central in the construction of two nuclear power plant projects, the 1,650 MW Flamanville 3 project in France and the 1,600 MW Olkiluoto 3 project in Finland. Both projects have been plagued with delays and ballooning costs.
1. Toughness is an indicator of the ability of a material to withstand the propagation of cracks. For a reactor vessel, this property is in particular significant regarding thermal shock, for instance following the injection of cold water in the primary circuit of the reactor.