ASSESSMENT OF THE SCC MITIGATION CAPABILITIES OF THE NOBLE METAL CHEMICAL APPLICATION TECHNOLOGY IN A SIMULATED BWR ENVIRONMENT

摘要

To mitigate stress corrosion cracking (SCC) inboiling water reactors (BWRs), the noble metal chemicalapplication (NMCA or NobleChemTM) technology wasdeveloped. Pt solution is injected into the feed water ofBWRs and Pt particles are formed which deposit on allwater-wetted surfaces of the primary circuit. Together withinjected hydrogen (hydrogen water chemistry, HWC) thePt particles catalyze the consumption of oxygen andhydrogen peroxide (produced by radiolysis in the core).Thus the electrochemical corrosion potential (ECP) on thesteel surfaces is lowered, thereby mitigating SCC. To dateno universal parameters have been defined to what extendPt particles need to be present on the surfaces of thestructural materials to reach a sufficiently low ECP.A test series in PSI’s experimental facilities, simulatingBWR conditions, has revealed that the Pt surface loadingalone is not sufficient to assess the SCC mitigationcapabilities. Pt particle size and inter-particle distancescorrelate much better with the lowering of the ECP. Tofurther verify SCC mitigation on Pt-treated Inconel 182specimens, a series of SCC initiation tests was carried outas well. Constant extension rate tensile tests with flat,tapered specimens seem to confirm the reduced SCCinitiation susceptibility of Pt-treated Inconel 182 (i.e.,lower ECP) as compared to non-treated ones (i.e., higherECP) in a simulated BWR/HWC environment.