Analysis of ¹⁴C-bearing compounds released by the corrosion of irradiated steel using accelerator mass spectrometry

Abstract

The combination of ion chromatography (IC) with accelerator mass spectrometry (AMS) was developed to determine the speciation of 14C-(radiocarbon) bearing organic compounds in the femto to pico molar concentration range. The development of this compound-specific radiocarbon analysis (CSRA) of carboxylic acids is reported and the application of the method on a leaching solution from neutron-irradiated steel is demonstrated. The background and the dynamic range of the AMS-based method were quantified. On using 14C-labelled standards, the measurements demonstrate the repeatability of the analytical method and the reproducible recovery of the main target carboxylic acids (i.e., acetate, formate, malonate, and oxalate). The detection limit was determined to be in the mid fmol 14C per L level while the dynamic range of the analytical method covers three orders of magnitude from the low fmol to the mid pmol 14C per L level. Cross contamination was found to be negligible during IC fractionation and was accounted for during eluate processing and 14C detection by AMS. The 14C-bearing carboxylates released from an irradiated steel nut into an alkaline leaching solution were analysed using the CSRA-based analytical method with the aim to check the applicability of the approach and develop appropriate sample preparation. The concentrations of 14C-bearing formate and acetate, the main organic corrosion products, were at a low pmol 14C per L level for convenient dimensions of the alkaline leaching experiment which demonstrates that compound-specific 14C AMS is an extremely sensitive analytical method for analysing 14C-bearing compounds. The content of total organic 14C in solution (TO14C) determined by the direct measurement of an aliquot of the leaching solution agrees well with the sum of the 14C concentrations of the individual carboxylates within the uncertainty of the data. Furthermore, the TO14C content is in good agreement with the calculated value using the corrosion rate determined from the 60Co release and the 14C inventory of the irradiated steel specimen.

Quantification of dissolved organic14C-containing compounds by accelerator mass spectrometry in a corrosion experiment with irradiated steel

“…Compound-specific radiocarbon analysis (CSRA) with AMS involved two analytical steps: Firstly, chromatographic fractionation of the individual 14 C-containing compounds and secondly, 14 C detection by AMS. Fractionation of the individual compounds was achieved by using the HPIEC system described previously herein and the analytical procedure reported by Cvetković et al (2018b).…”

“…The procedure is automated and controlled by a LabView program based on an earlier version reported by Wacker et al (2013). The results can be corrected for cross contamination thanks to the fact that the carry-over effect is relatively constant for the given working range of 14 C/ 12 C concentrations (Cvetković et al 2018b).…”

Release and speciation of14C during the corrosion of activated steel in deep geological repositories for the disposal of radioactive waste

“…• the development of compound specific separation and analysis methods for determining the speciation of 14 C releases from irradiated steels at the very low concentrations expected in experiments (Cvetković et al 2018b);…”

“…The experiments were sampled periodically up to 412 days. 14 C analysis was based on compound-specific 14 C AMS which allowed the concentration of the individual water-soluble carboxylic acids and the total organic 14 C fraction (TO 14 C) to be quantified (Cvetković et al 2018b). No quantification of the 14 C carbonate fraction or the volatile hydrocarbons was undertaken.…”

“…The scope of experimental work performed under CAST WP2 included:measurement of the long-term corrosion rate of stainless steel under anoxic high-pH conditions (Sakuragi 2017);leaching studies of inactive steels, iron and iron carbide to investigate the potential speciation of 14 C release from irradiated steels (e.g. Cvetković et al 2018a);the development of compound specific separation and analysis methods for determining the speciation of 14 C releases from irradiated steels at the very low concentrations expected in experiments (Cvetković et al 2018b);comparisons of measured 14 C inventories for small irradiated steel samples with inventories calculated using activation codes (Mibus et al 2018); andleaching experiments on activated steel samples, principally stainless steels, but also carbon steels, under a range of repository-relevant conditions (Mibus et al 2018). …”