Michael Woods

Abstract Fluoride-based molten salts are candidate coolants and fuel salts in certain Generation IV molten salt reactors (MSRs). Effective monitoring of these salts is crucial, because salt composition plays a key role in reactor safety and efficiency. Optical probes offer a potentially powerful method of remotely monitoring fission and corrosion products within these salts, providing valuable data for reactor process control. However, performing spectroscopic measurements of fluoride-based salts is particularly challenging due to their highly corrosive nature, which can degrade many common optical materials. In this work, we present a novel optical cell design that enables spectroscopic measurements of transition-metal analytes in LiF-NaF-KF eutectic salt (i.e., FLiNaK). This innovative cell design overcomes the challenges posed by the corrosive nature of the salts, allowing for accurate and consistent spectroscopic analysis. This work reports temperature dependent absorption measurements for Co2+, Ni2+, and Cr3+ analytes, which are common corrosion products originating from structural alloys in MSR systems. Absorption spectra were used to understand interactions of these analytes with FLiNaK, particularly ligand field coordination. The analysis of absorption spectra was complemented by structural analyses using ab initio molecular dynamics (AIMD) simulations, providing deeper insights into the behavior of the analytes in FLiNaK. Our findings indicate that the analytes studied in this work exist in octahedral or near-octahedral coordination states that remain stable across the temperature range of 500-600°C.

A multi-modal approach combining in situ X-ray absorption spectroscopy, optical spectroscopy, and ab initio molecular dynamics simulations was used to investigate and understand nickel metal speciation in molten salt systems.

Reactions of Cr(ii) and Cr(iii) with the primary radiolytic transient species (solvated electron and Cl₂˙⁻) in molten eutectic LiCl–KCl were characterized, including the reactivity of their products.

Reactions of Cr(ii) and Cr(iii) with the primary radiolytic transient species (solvated electron and Cl₂˙⁻) in molten eutectic LiCl–KCl were characterized, including the reactivity of their products.

This work reports the wettability characteristics of LiCl-KCl and FLiNaK on various substrates to address the gap in contact angle measurements.

Innovative solutions are needed to reduce the amount of high-level waste generated by used nuclear fuel recycling strategies to support the widespread adoption of sustainable nuclear fission energy technologies. To this end, a new sulfur chloride-based process has been developed to recycle zirconium alloy-based materials, which make up a significant fraction of high-level radioactive waste. To support the continued development of this process, we present new data on the potential reaction pathways over time of the products arising from the gamma and electron beam radiolysis of neat thionyl chloride (SOCl₂). Interrogation of the gamma irradiated liquid by Raman spectroscopy provided more conclusive identification of the SOCl₂degradation products, specifically sulfur dichloride (SCl₂), molecular chlorine (Cl₂), sulfur dioxide (SO₂), and sulfuryl chloride (SO₂Cl₂). In comparison, the high dose rate (∼10⁷ Gy s⁻¹) electron beam irradiations formed significantly more degradation products. For both cobalt-60 gamma and electron beam irradiations, the observed degradation products were found to evolve as a function of time post-irradiation via the same reaction pathways, with indication of a solvent regeneration mechanism. These findings are fortuitous for process development, as such a mechanism would be beneficial for process longevity and cost effectiveness.

Innovative solutions are needed to reduce the amount of high-level waste generated by used nuclear fuel recycling strategies to support the widespread adoption of sustainable nuclear fission energy technologies. To this end, a new sulfur chloride-based process has been developed to recycle zirconium alloy-based materials, which make up a significant fraction of high-level radioactive waste. To support the continued development of this process, we present new data on the potential reaction pathways over time of the products arising from the gamma and electron beam radiolysis of neat thionyl chloride (SOCl₂). Interrogation of the gamma irradiated liquid by Raman spectroscopy provided more conclusive identification of the SOCl₂degradation products, specifically sulfur dichloride (SCl₂), molecular chlorine (Cl₂), sulfur dioxide (SO₂), and sulfuryl chloride (SO₂Cl₂). In comparison, the high dose rate (∼10⁷ Gy s⁻¹) electron beam irradiations formed significantly more degradation products. For both cobalt-60 gamma and electron beam irradiations, the observed degradation products were found to evolve as a function of time post-irradiation via the same reaction pathways, with indication of a solvent regeneration mechanism. These findings are fortuitous for process development, as such a mechanism would be beneficial for process longevity and cost effectiveness.

A new transient interhalogen species (ICl^•−) has been identified in electron pulse irradiated molten chloride salt mixtures. This species has significant implications for the transport of fission-product iodine in molten salt reactor environments.

A new transient interhalogen species (ICl^•−) has been identified in electron pulse irradiated molten chloride salt mixtures. This species has significant implications for the transport of fission-product iodine in molten salt reactor environments.