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

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