Rapid determination of iodide ion content in chloride molten salt by ascorbic acid reduction

Abstract

This study aimed to establish an alternative method for assessing the efficacy of removing fission product iodine from molten salt spent nuclear fuel under acidic conditions. In the pretreatment stage, ascorbic acid with a mass fraction of 0.5 wt% was used instead of dilute nitric acid with a volume fraction less than 2 vol%. The iodide content of molten salt samples dissolved in various ratios of Cl⁻ to I⁻ was determined and compared by inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC). The iodide ions in simulated chloride salts containing LiI were tested after pretreatment. It was found that at 1.0 mg L⁻¹ chloride ion concentration, the detection limit of this method was 0.255 μg L⁻¹, with a spike-and-recovery experience between 103.3% and 102.8% and a relative standard deviation of less than 3% (n = 6). The average spike-and-recovery experience was 104.3%, and the limit of detection was 0.472 μg L⁻¹ at a concentration of 100.0 mg L⁻¹ with RSD of less than 5%. When the concentration ratio of Cl⁻/I⁻ in the molten salt was less than two orders of magnitude, the analytical value of this technique was comparable to the measurement result by IC. Furthermore, the accuracy of ICP-MS was superior to that of IC when the concentration ratio of Cl⁻/I⁻ was higher than two orders of magnitude. The results indicate that the improved pretreatment method with ascorbic acid can eliminate inaccuracies caused by the iodide memory effect. The method has been verified to determine iodide content in high chloride molten salt under acidic conditions and will be used in the treatment of spent fuel from molten salt reactors.