Corrosion Phenomena and Deposits in ITER Neutral Beam Test Facility Primary Cooling Circuits

The ITER Neutral Beam Test Facility (NBTF) is hosted in Padua and includes two experiments: MITICA, the 1 MeV full-scale prototype of the ITER HNB injector, and SPIDER, the 100 keV full-size ITER Radio Frequency (RF) negative-ions source. SPIDER and MITICA experiments are actively cooled by UltraPure Water (UPW) to electrically insulate in-vessel components that are biased to high voltage levels. Therefore, water conductivity is the main monitored parameter to ensure components insulation. First cooling plant exploitation have highlighted that water degrades more quickly than estimated by design either in SPIDER and MITICA, where a good water quality is a key feature to operate at 1 MeV. Careful selection of suitable materials for any functional component is of utmost importance, as interaction between the water and this component may affect the chemical and mechanical properties of the latter. Furthermore, this interaction can be severed influenced by chemical water haracteristics. The Primary Circuits (PCs) that showed the most severe water degradation during operation are SPIDER and MITICA power supply ones, called PC01 and PC08. Specific experimental tests were performed on these PCs to evaluate possible causes of the water degradation and detect sources of contaminant that might compromise future experimental campaigns. Water samples were collected and trace metal analysis using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to quantify the type and amount of metals released. Moreover, components samples collected along the circuits were characterize by Scanning Electron Microscope (SEM) technique to detect undesired contaminants.