USE OF ELECTROCHEMICAL NOISE TO DETECT STRESS-CORROSION CRACK INITIATION IN SIMULATED BWR ENVIRONMENTS

The objective of this research was to investigate the use of electroch emical noise (EN) for detecting stress corrosion crack (SCC) initiatio n in boiling water reactor (BWR) environments. Initial experiments exa mined the response of sensitized AISI Type 304 stainless steel (SS) in slow strain-rate tensile (SSRT) tests in oxygenated, 288 degrees C/10 .4 MPa water, a laboratory simulation of the normal BWR environment. T his combination of specimen condition and geometry assured abundant nu cleation of intergranular cracks, with controllable propagation and ar rest via changes in either loading or environment. In the latter case, addition of gaseous hydrogen was used to simulate BWR hydrogen water chemistry (HWC) and lower the specimen potential into a non-cracking r egion. The SSRT tests provided an ideal platform for optimizing the el ectrochemical cell configuration, while establishing the nature of ele ctrochemical potential and current noise (EPN and ECN) responses to cr ack initiation, propagation and arrest. The standard deviation of elec trochemical potential, a measure of EPN amplitude, proved to be the be st. indicator of SCC initiation, but the degree of correlation depende d upon both the periodicity of the calculation and the electrode confi guration. Further development work is expected to lead to a useful, in -plant sensor for real-time detection of SCC activity.