In order to ensure continued safe operation of European nuclear reactors, it is necessary to solve specific issues that arise from irradiation induced reactor pressure vessel (RPV) embrittlement under long term operation. This requires an extension of the RPV surveillance programs to cover longer operation times than originally planned. The limited availability of surveillance materials poses a challenge for the feasibility of such programs. Among others, the use of the small specimen technology is a promising option to overcome the lack of materials. For example, a number of not less than 16 sub-sized 0.16 C(T) specimens (4 mm thickness) can be manufactured from two tested Charpy sized (10 mm × 10 mm × 55 mm) specimens, allowing a reliable determination of the reference temperature T0. Such Charpy sized fracture mechanics specimens are currently widely used in the RPV surveillance programs.
To establish the methodology for fracture mechanics testing of irradiated and unirradiated RPV steels using sub-sized specimens, a joined R&D project was launched partly financed by the German Federal Ministry for Economic Affairs and Energy. Moreover the following points shall be addressed:
• Manufacturing, pre-cracking procedure, measurement of the crack opening displacement and load line displacement under hot cell conditions
• Demonstration of the transferability of fracture mechanics data
The purpose is to demonstrate that the results measured on sub-sized specimens can safely be used in the safety assessment of RPVs. In addition, the results will establish a basis to assess results from international projects regarding sub-sized fracture mechanics specimens.