The role of the BR2 material test reactor to determine the material properties of the flaked RPV shells in support of the structural integrity assessment

During the in-service inspection in the 2012 summer outage of the Doel-III reactor, a large number of quasi-laminar indications were detected. These ultrasonic observations were, after inspection of the Tihange-II vessel which is very similar to the Doel-III vessel, confirmed a few months later. Those unforeseen in-service inspection results have led to an extensive testing and evaluation program to which the Belgian Nuclear Research Centre (SCK•CEN) made a significant contribution with the determination of the materials properties, required for the safety integrity calculations. Four irradiation campaigns on a variety of materials relevant for the concerned case were successively carried out under well-controlled conditions in the BR2 Material Test Reactor. Given the high flux of the BR2 reactor, typically more than two orders of magnitude higher than on the vessel wall, the 40 years end-of-life fluence is reached in less than 4 weeks. Thanks to the extensive database developed through few decades of irradiation of a large number of structural materials, the outcome from the BR2 irradiation could be reliably transferred to the reactor pressure vessel. A number of issues were addressed with in-depth analysis to support the experimental data that were produced. This paper illustrates the key role of the BR2 reactor with several examples taken directly from the experiments performed within this project to demonstrate the applicability of accelerated data to the integrity of actual reactor pressure vessels.