Phase Analysis of Corrosion Products from Nuclear Power Plants

The variability of the properties and the composition of the corrosion products of the stainless CrNi and mild steels in dependence on the conditions (temperature, acidity, etc.) is of such a range that, in practice, it is impossible to determine the properties of the corrosion products for an actual case from the theoretical data only. Since the decontamination processes for the materials of the water-cooled reactor (VVER-440) secondary circuits are in a process of development, it is necessary to draw the needed information by the measurement and analysis of the real specimens [1]. The corrosion layer was separated by scraping the rust off the surface and the powder samples were studied by transmission Mössbauer spectroscopy. It should be noted that the gamma spectroscopic measurements give no evidence of the presence of low-energy gamma radiation emitted from the samples. The scrapped specimen powder was homogenised (using the 50 m sieve) and fixed into the special holder. The ⁵⁷Co in Rh matrix was used as the radioactive Mössbauer source. Measured spectra were fitted using program NORMOS SITE. According to the results obtained from Mössbauer spectra, it is possible to establish that the main component of secondary circuit's corrosion products is magnetite Fe₃O₄. Next components are hematite -Fe₂O₃ and hydroxide akagenite -FeOOH, which is characterised by a significant paramagnetic doublet in the middle of the spectra. The sextets corresponding to base materials (martensite and austenite steels) were identified in all measured spectra.