Summary of Studies Made With Miniature C(T) Specimens for Non-Irradiated and Irradiated Materials

Abstract Progress in the theory of fracture mechanics has enabled the development of miniature specimen testing techniques. Miniaturization of compact tension (C(T)) specimens offers an option to be used in surveillance monitoring tests of reactor pressure vessel steels in nuclear power plants. The amount of the initial surveillance reference material diminishes continuously during the operational lifetime of a plant and at the same time the need for the lifetime extension of operating plants is growing. Moreover, since nuclear power generates notable amount of electricity free from carbon dioxide emission, the evaluation of the long-term structural integrity and the support of the lifetime extension are utmost important. Miniature specimen test technique is crucial for ensuring that enough material is available in surveillance programmes. The primary objective is to evaluate the effect of radiation embrittlement on fracture toughness and ultimate strength. The benefit of miniature specimen test technique is the reuse aspect and ensuring the cost-effectiveness of the testing procedure. This paper is a summary of studies made with miniature C(T) specimens within the recent years on a national level in the Finnish nuclear safety research programme. The results of studies made in 2023 and 2024 will be reviewed in more detail, and the results of previously conducted tests are included in the discussions. Overall goal of 2023 and 2024 studies was to research the applicability of further reduced 3 mm thick miniature C(T) specimens by means of fracture mechanics tests, utilizing finite element modelling and microstructural characterization as supporting activities. The main result is that the applicability of 3 mm thick miniature C(T) specimens is very promising when studying non-irradiated and irradiated materials and welds.