Abstract
ABSTRACTThe chemical form of14C released from irradiated stainless steel is a key parameter in the safety assessment of the subsurface disposal system in Japan. In this study, to identify the chemical form of the released carbon, unirradiated stainless-steel powders, which were found to be water-atomized powders with a silicon oxide film, were immersed in NaOH and HCl solutions under low-oxygen conditions for approximately 25 days. The results showed that the main chemical forms of the carbon were colloidal carbon in the NaOH solution and colloidal carbon and formic and acetic acids in the HCl solution. Almost no hydrocarbons were detected in both solution systems. Concerning the source of the colloidal carbon and carboxylic acids, the hypothesis that carbon in the oxide layer is released is considered to be reasonable. The very small amounts of hydrocarbons generated prevented us from discussing the source of the hydrocarbons. To validate the hypothesis and obtain further information on the hydrocarbons, additional experiments are necessary. In particular, for long-term safety assessment, it is important to determine whether the colloidal carbon, carboxylic acids and hydrocarbons are continuously released during the corrosion process. Therefore, information on the temporal evolution of the carbon should be obtained.
Highlights
IntroductionThe chemical form of radiocarbon (14C) released from low-level waste (e.g., irradiated control rods, channel boxes and burnable poisons of spent fuel, which are composed of stainless steel) is a key parameter in the safety assessment of the sub-surface disposal system in Japan (Yamato 2006; Nuclear Safety Commission of Japan 2007)
The chemical form of radiocarbon (14C) released from low-level waste is a key parameter in the safety assessment of the sub-surface disposal system in Japan (Yamato 2006; Nuclear Safety Commission of Japan 2007)
The oxide layers are mainly composed of Si, which implies that these powders are water-atomized stainless-steel powders (Klar and Samal 2007; Hedberg et al 2012, 2013), meaning that the stainless-steel powders used
Summary
The chemical form of radiocarbon (14C) released from low-level waste (e.g., irradiated control rods, channel boxes and burnable poisons of spent fuel, which are composed of stainless steel) is a key parameter in the safety assessment of the sub-surface disposal system in Japan (Yamato 2006; Nuclear Safety Commission of Japan 2007). Whether or not 14C, which has a long radioactive half-life (5730 yr), will sufficiently decay in the disposal facility depends on its chemical form This indicates that it is necessary for the safety assessment to determine the chemical form of 14C released from the waste under the disposal conditions (highly alkaline and low-oxygen conditions). Given the low corrosion rate of stainless steel in alkaline solutions under low-oxygen conditions (Blackwood et al 2002; Mihara et al 2002) and the low carbon content (
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