Round Robin Analysis of Small Punch Testing on 15Kh2NMFA Reference Material

Miniature / sub-sized specimen test methods for the mechanical characterization of metallic alloys like the small punch test (SPT) have the benefit that only small quantities of material are needed to perform a reasonable number of tests. This makes such tests in particular interesting if only limited quantities of material are available for mechanical characterization, like irradiated specimens from reactor pressure vessel (RPV) surveillance programs of light water reactors (LWRs). The SPT only requires small discs of 8mm diameter and 0.5mm thickness and such specimens can be manufactured from broken Charpy impact test specimens that were previously tested within RPV surveillance programs. With the publication of EN 10371 earlier in 2021 the SPT is now a standardized test that can be used in principle to determine tensile, creep, fracture toughness properties and ductile-to-brittle transition temperatures (DBTTs). However, fabrication and testing of irradiated SPT specimens remotely in hot cell environments has several practical challenges. Any deviation in specification as laid down in the standard can lead to variations in test outcome. To address this issue an SPT Round Robin exercise on VVER RPV steel 15Kh2NMFA reference material has been performed in the context of the Horizon 2020 Euratom project STRUMAT-LTO. Several research organizations, namely NRG, EK/CER, JRC, VUJE, CIEMAT and UJV, have participated in this round robin exercise to validate sample manufacturing, test procedures and test equipment and to determine tensile properties and DBTTs of the above RPV steel. In this paper results and conclusions of the STRUMAT-LTO SPT round robin exercise are presented.