Corrosion and Metal Release of Copper and Stainless Steel Exposed to Ultrapure Water

Abstract

Source for Production of Ion of Deuterium Extracted from Rf plasma (SPIDER) and Megavolt ITer Injector and Concept Advance (MITICA) experiments are actively cooled by ultrapure water (UPW) to electrically insulate in-vessel components that are polarized to high voltage levels. Water circulating in cooling pipes reacts with wetted surfaces made of copper and stainless steel, causing water resistivity degradation. First investigations on the causes that might determine water degradation highlighted the necessity to measure release rates of the main materials (copper and stainless steel) exposed to UPW as a baseline study to better understand the release rates measured during experimental campaign in the real cooling circuits in SPIDER and MITICA. This article presents first the experimental results of stainless steel and copper samples exposed to stagnant UPW at ambient temperature and high oxygen environment to measure the ion release behavior. Trace metal analysis using inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify metals released in solution, and scanning electron microscope (SEM) was used to characterize the oxide formed on the sample surface after the exposure.