Radiolytic evaluation of select sulfur chlorides (S2Cl2 and SOCl2) for advanced low temperature chlorination of zirconium-based used nuclear fuel cladding

Abstract

New sulfur chloride compounds—sulfur monochloride (S2Cl2) and thionyl chloride (SOCl2)—have been proposed as alternative chlorinating agents for the chemical decladding of zirconium-based used nuclear fuel cladding materials. However, the radiation stability of these compounds has not been thoroughly evaluated, despite envisioned process conditions involving intense, multi-component radiation fields. Knowledge of the radiation chemistry of these sulfur chlorides is essential for the development and optimization of alternative chlorination technologies. To this end, we present preliminary findings on the gamma radiolysis of neat S2Cl2 and SOCl2 at ambient temperature up to ∼ 34 MGy. In this study, Raman spectroscopy and density functional theory calculations were used to identify the Raman-active degradation products from S2Cl2 and SOCl2 radiolysis. Both sulfur chloride compounds exhibited significant radiation resistance, with respect to changes in the Raman signatures of the parent compounds and the ingrowth of Raman-active degradation products. For S2Cl2, molecular chlorine (Cl2) was directly identified as the predominant degradation product, which was completely consumed at higher absorbed doses (> 9 MGy). Similarly, the main degradation product from SOCl2 radiolysis was also Cl2, although in this system it continued to grow in with dose over the entire dose range. An “SO” containing degradation product(s) was also identified as a compliment to Cl2. Overall, the perceived radiation resistance of these sulfur chloride compounds makes them suitable for inclusion in a used nuclear fuel chemical decladding process, especially as radiolytically formed Cl2 can be used to reform the parent compounds, thereby increasing the longevity of the solvents used.