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

Abstract

Low- and intermediate-level (L/ILW) radioactive waste produced in Switzerland consists of large amounts of14C-containing irradiated steel.14C will be released during the anoxic corrosion of the steel in the cementitious near field of an L/ILW repository. In this study, a corrosion experiment with irradiated steel was carried out to determine the speciation of14C released during the corrosion process in conditions similar to those anticipated in the near field of a cement-based repository. The development of the experimental setup, including installation of the reactor and development of suitable analytical methods based on compound-specific14C analysis with accelerator mass spectrometry (CSRA AMS) is reported. Time-dependent increase in the total content of14C-bearing organic compounds in solution (TO14C) was determined by AMS and the main organic corrosion products that are14C-bearing formate, acetate and lactate were identified by CSRA AMS after a pre-concentration step. The concentration of the14C-bearing organic compounds was found to be very low (fmol to pmol14C/L). Stable carbon compounds were identified and quantified while the source of stable carbon in the system has not yet been identified and the temporal evolution of the concentration of these carbon species is presently not understood.

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

“…In the experiment of (Wieland et al 2017), 14 C-containing acetate, formate and lactate were identified and quantified (Cvetković et al 2018c). The proportions were as follows: acetate ~32%, formate ~40%, and lactate ~25%.…”

Carbon-14 Release and Speciation During Corrosion of Irradiated Steel Under Radioactive Waste Disposal Conditions

“…An artificial cement pore water (ACW) with pH 12.5, used to simulate pore water conditions in the near field of a cement-based DGR and corresponding to a solution saturated w.r.t. Ca(OH) 2 , was prepared as reported elsewhere (Cvetković et al, 2018c).…”

“…S1-1). Before starting the corrosion experiment, tests of the background 14 C activity and the concentrations of carbon compounds were carried out (Cvetković et al, 2018c) (S.I. S2).…”

“…The reactor was tightly sealed and purged with N 2 to ensure O 2 -free conditions. A volume of 300 mL ACW was injected via the in-house developed sampling system located outside the lead shielding (Cvetković et al, 2018c;Wieland et al, 2018;Wieland et al, 2017). After one day, the solution was replaced with a fresh one and the experiment started (Cvetković et al, 2018c).…”

“…Furthermore, a recent corrosion study using irradiated steel identified dissolved and gaseous 14 C-bearing small carbon compounds (de Visser-Týnová et al, 2018). In the present study on the corrosion of irradiated steel, we developed analytical methods that allow both oxidized and reduced 14 C-bearing carbon compounds to be identified and quantified at ultra-low concentrations in both the liquid and gas phases by accelerator mass spectrometry (AMS) (Cvetković et al, 2018b;Cvetković et al, 2018c;Guillemot et al, 2020b). The extremely low 14 C concentrations expected in this corrosion experiment are a consequence of the small size and low 14 C content of the irradiated steel samples, the extremely slow corrosion of stainless steel under alkaline anoxic conditions, and finally the small sample quantities available for analysis with the given experimental set-up.…”