FA3 RPV Carbon Segregation Issue: Representativeness and Transferability of Sacrificial Parts

In order to demonstrate that the cover head and bottom head of the FA3 Reactor Pressure Vessel (RPV) exhibits sufficient toughness to withstand operational (from normal up to faulted) conditions, a dedicated experimental program was performed for three sacrificial forged parts (two cover heads and a bottom head) manufactured in Creusot Forge as-well, according to a similar process. In order to be allowed to consider the mechanical properties (toughness) measured on these sacrificial parts, it was necessary to prove that they were representative of the FA3 ones. Among all the parameters influencing the toughness properties it was defined that two of them had a major impact: the carbon content and the quenching effects. For the first one, it was identified that it could be influenced by pouring conditions, forging conditions, including discard and upsetting ratios and machining (thickness). For the second one, it was identified that it could be influenced by post-heat treatment machining and by quenching conditions. Regarding these factors, for the five parts: manufacturing parameters and acceptance test results were compared, taking into account uncertainties. In addition, for the three sacrificial parts, carbon content measured for various depths in the thickness were compared, after a transformation methodology allowing to convert depth inside part to ingot vertical location. Finally, it was shown that the sacrificial parts could be considered to be representative of the FA3 parts to be used, for their mechanical properties.