Influence of material choice on the release and speciation of 14C (D2.15)

In the framework of Work Package 2 of the international CAST project, partially funded by the European Commission, laboratories in Belgium, Finland, Germany, Japan, and the Netherlands each investigated, independently, the release of 14C from steels used in nuclear power plants and its speciation in environments representative for geological disposal. The materials investigated ranged from carbon steels representative for the reactor pressure vessel to stainless steels used as reactor internals. The researchers used a plethora of analytical techniques, including mass spectrometry, gas chromatography, TIC/TOC determination, liquid scintillation counting, ion chromatography, etc. There is a clear distinction in the corrosion rate: the corrosion rate of stainless steel is an order of magnitude lower than that of carbon steel, which confirms literature data. With regards to speciation, it seems that the majority of the carbon compounds are volatile and are found in the gas phase after the leaching tests. The main carbon species is methane, both for stainless steel as for carbon steel. When comparing the speciation of 14C released from carbon steel and Zircaloy-4, we find little differences. It appears that the speciation is not material-dependent.