Session: MF-06-01/11-01 Materials and Technologies for Nuclear Power Plants I and Small-scale and miniature mechanical testing (Joint with C&S)

Paper Number: 61027

Start Time: Tuesday, July 13, 2021, 05:00 PM

61027 - Development of Mini-Compact Tension Specimen Fabrication and Test Methods in Hot Cell for Post-Irradiation Examination of Reactor Pressure Vessel Steels 

Most standard surveillance programmes for PWR type reactors, do not contain enough surveillance specimen for their long term operation (LTO) beyond the original design life of 40 years.  The use of testing methods based on small/sub-sized specimen such as mini-CT (0.16 CT, 4mm thickness)  is considered a promising approach to overcome this limitation. The feasibility of fracture toughness testing using sub-sized CT specimen has been generally demonstrated in Japanese-US lead Round Robin programme for un-irradiated materials. However, application of miniature testing techniques on irradiated materials in hot cells comes along with several technical challenges such as remote controlled machining, application of the extensometers, manipulator sensitivity etc. In addition, the dimensional tolerances of the standard CT specimen defined in the ASTM E1921 standard are defined as function of specimen width, resulting in severer absolute tolerance for the miniature specimen. This paper presents an in-cell fabrication method of a modified mini-CT specimen and a testing facility suitable for hot cell use. This work is performed at NRG within the framework of the STRUMAT project, funded by the Netherlands Ministry of Economic Affairs. A slightly modified miniature CT specimen is chosen, which allows “outboard” clip gage mounting for direct load-line displacement (LLD) measurement. In addition, a wide notch configuration with a width of 0.6 mm, 0.1 mm wider than specified in the ASTM E1921 standard, is used. This modified specimen geometry facilitates the in-cell fabrication of the miniature CT specimen and eases the remote handling and testing procedure. Three-dimensional finite element analysis validation was carried out to determine the effect of these modifications on the stress state of the specimen and to establish the difference between the LLD measured for the new specimen geometry in comparison to the applied displacement. It is demonstrated, that for the adjusted specimen geometry the maximum stresses in the specimen regions other than the crack tip will not exceed the yield strength during testing conditions and therefore will not influence the testing results.

Presenting Author: Frideriki Naziris NRG

Authors:

Frideriki Naziris NRG
Casper Versteylen NRG
Frederick Frith NRG
Marcel Bregman NRG
Murthy Kolluri NRG