Pre-qualification of cladding materials for SCWR fuel qualification testing facility – stress corrosion cracking testing

The main target of the HPLWR Phase 2 follow-up FP7 project “Fuel Qualification Test for Super Critical Water Reactor” is to make significant progress towards the design, analysis and licensing of a fuel assembly cooled with supercritical water (SCW) in a research reactor which also includes the material research on those in-core materials which could be licensed in near future. In frame of WP4 - Pre-qualification, stress corrosion cracking (SCC) resistance of three selected austenitic stainless steels 08Cr18Ni10Ti (equivalent of 321), 347H and 316L was evaluated. Presented work summarizes preliminary results of slow strain rate tensile tests (SSRT), performed using a step-motor controlled loading device in an autoclave at 550°C SCW. Susceptibility to SCC was examined by SSRT tests with constant elongation rate of 5.2·10-7s-1 in an autoclave connected to recirculation loop allowing continual water chemistry control during the test. Furthermore, reference tests under the same temperature and loading conditions were conducted in inert nitrogen atmosphere, in order to distinguish the effect of environment. On the top of that, in all tests, the loaded tensile specimens were continually monitored by acoustic emission (AE) measurement with 1-D linear location mode in order to determine the time of crack initiation. Obtained stress-strain curves didn’t indicate any significant change of mechanical properties of the examined materials in 550°C SCW compare to those measured in inert atmosphere. Nevertheless, post-test SEM fractographic analysis showed evidences of SCC initiation areas on main fracture surface and elevated number of secondary cracks along gage section of the tensile specimen. Sudden release of significant number of high energy AE signals, observed during the SSRT tests in SCW, was probably caused by initiation of SCC cracks because such AE signals were not detected within reference tests. Correlation between burst AE events and numbers of secondary cracks is discussed.

JANIK Premysl;  NOVOTNY Radek;  NILSSON Karl-Fredrik;  SIEGL J;  HAUSILD P; 

2014-01-30

China Guangdong Nuclear Power Holding Co., Ltd (CGNPC)

JRC86803