Project FRACTESUS: Fracture toughness round robin on a high copper weld using miniature C(T) specimens - results and discussion

The present FRACTESUS project aims to determine the effect of specimen size on the fracture toughness properties. Finite element models (FEM) are used to investigate the difference between large-size and miniature compact tension (MC(T)) specimens and quantitatively assess the resulting loss of constraint due to size reduction. The optimal range of usability of MC(T) specimens can therefore be determined and evidenced with experimental results. Large inter-laboratory testing is included in the FRACTESUS project to prove the repeatability and reproducibility of the small-scale testing of fracture toughness properties. Various materials relevant for most of the available reactor materials and irradiation conditions are investigated. The experimental round robin on unirradiated materials has been completed by 13 different laboratories. The reference temperatures T0 obtained from MC(T) specimens by the different laboratories are compared to the one obtained from larger (mostly 1T-C(T)) specimens for six different materials. The considered materials are relevant for the nuclear industry and consist of four base (15Kh2MFAA, A533B LUS, A533B JRQ, A508 Cl.3) and two weld (ANP-5 and 73W) materials. In this regard, the present publication will elaborate on the investigations and the results achieved during the round robin of the material ANP-5. The ANP-5 weld metal is a modified NiCrMo1 UP weld belonging to a 6-meter (236 inch) reactor pressure vessel (RPV) test weldment. This test weldment was manufactured and post weld heat treated by Klöckner Werke AG and is supposed to be representative for RPV weldments of 1^st generation pressurized water reactors (PWR). The special feature of this material is the high copper content, which makes it particularly susceptible to irradiation-induced embrittlement. In the framework of the FRACTESUS project the material was investigated according to the ASTM E1921 standard by five partners: SCK CEN, University of Cantabria, Helmholtz-Zentrum Dresden-Rossendorf, United Kingdom Atomic Energy Authority and the Framatome GmbH. Nearly 100 miniature C(T) specimens were tested to determine the transition temperature T0 and to compare it with the results of standard sized specimen. Within this ANP-5 test program two test series performed different than expected. A sharp transition from brittle to ductile without a distinct transition range was observed. The results of the test program and reasons for the unexpected material behavior will be discussed hereinafter.