Development of BWR components SCC mitigation method by the TiO2 treating technique

Stress Corrosion Cracking (SCC) susceptibility of Boiling Water Reactor (BWR) materials is mitigated by reduction of the electrochemical corrosion potential (ECP). In the reactor there is a photo-excitation reaction between TiO2 and ultraviolet Cherenkov radiation. The TiO2 treatment technique plans to mitigate SCC by reducing the ECP without hydrogen addition. We conducted the demonstration tests of the TiO2 treatment technique in a test reactor and in BWR plant piping systems. The test results showed that the ECP of TiO2 treated type 316L stainless steel and the Ni based alloy 600 were reduced to -350 mV vs. the standard hydrogen electrode (SHE) in the reactor system in normal water chemistry (NWC). In the no Cherenkov radiation area, the ECP of the TiO2 treated stainless steel still decreased as the dissolved hydrogen concentration in feed water up to 0.3 ppm. (a condition that will be referred as 'low HWC.') (author)