On June 28, the French Nuclear Safety Authority (Autorité de Sûreté Nucléaire – ASN) presented its draft opinion concerning the toughness of the upper and lower domes (vessel head and bottom head) of the Flamanville EPR reactor pressure vessel. The ASN will submit its draft opinion for public consultation during the course of the summary and shall give its definitive opinion in the fall.
The ASN based its opinion on the analysis carried out by the ASN's Nuclear Pressure Equipment Department (ASN/DEP) and by the French Institute for Radiological Protection and Nuclear Safety (Institut de Radioprotection et de Sûreté Nucléaire – IRSN), of elements provided by AREVA NP and EDF, as well as on the opinion of its Advisory Committee of Experts for Nuclear Pressure Equipment which met on June 26 and 27.
The ASN concluded that the mechanical properties of the two parts are adequate, including in extreme situations, and that they are thus serviceable. Given the uncertainty relating to the feasibility of certain inspections on the closure head, and in accordance with the principle of defense in depth, the ASN considers that this component should not be operated beyond 2024.
These conclusions are based, amongst other things, on the opinion of the Advisory Committee of Experts for Nuclear Pressure Equipment which also indicates that the approach presented makes it possible "to conclude that the material has mechanical properties that are sufficient to rule out the feared risks and guarantee the serviceability of the domes". The report by the latter also underlines the scale of the test program carried out by AREVA NP and the conservative margins employed in the file.
AREVA NP produced these two components in 2005 and 2006 in accordance with the regulatory requirements in force at the time. Following the detection by AREVA NP at the end of 2014 of anomalies in the composition of the steel of the reactor pressure vessel head and bottom head, AREVA NP, in partnership with EDF, prepared and deployed a large-scale additional test program. Before implementation, the program was validated by the ASN in September 2015, and a supplement to this test program was presented and validated by the ASN in June 2016. AREVA NP completed the program and submitted its report to the ASN in mid-December 2016.
Tests were performed on vessel heads and bottom heads similar to those on the Flamanville 3 EPR reactor. Three sacrificial domes were used and more than 1,700 samples were taken. The program has mobilized a wide range of skills and involved many AREVA NP experts over two years. An external and independent body was appointed by the ASN for the oversight of these tests, in addition to the customer EDF. The resulting file also takes into consideration additional tests performed on the two Flamanville 3 domes (non-destructive testing via ultrasonic or magnetic particle testing), together with calculations.
AREVA NP has been able to use all these elements gathered over a period of more than two years to conclude that the reactor vessel demonstrates sufficient toughness.
The Flamanville 3 EPR reactor is a generation III+ 1650 MWe reactor benefiting from major technological advances and optimal safety, endurance and performance.