Synthesis and Exchange Reactions of Methane Isotopologues for Impurity Removal and Recovery of Tritium

Abstract Next-generation diagnostics for tritium extraction, recycling, recovery, and storage increasingly rely on diagnostics within radiological environments in which noninvasive spectroscopic methods can operate. Here, controlled Sabatier reactions and hydrogen isotope exchange reactions were employed to generate distributions of methane isotopologues (CQ4, Q = H and D) and serve as calibration models for spectral deconvolution for radiological deployment. Methane isotopologues arise as unavoidable byproducts in tritium-handling systems through radiochemical interactions between tritium and carbon-containing materials that influence tritium inventory, process efficiency, and waste. Raman vibrational signatures corresponding to multiple isotopologues were experimentally resolved despite significant overlap. Quantitative analysis was achieved using multivariate curve resolution (MCR) coupled with partial least squares (PLS) regression for isotopologue discrimination and concentation modeling. Spectral assignments were further supported through high-level quantum chemical calculations, where anharmonic vibrational frequencies derived from quartic force fields computed using explicitly correlated coupled cluster theory [CCSD(T)-F12b] with composite corrections enable accurate treatment of isotopic substitution. Although Sabatier reactions are associated with synthetic gas and methane production, it is utilized here as a controllable pathway for synthesizing isotopic distributions relevant representative of tritium process streams, enabling calibration, validation, and machine-learning-assisted model development. The approach directly supports improved tritium accountancy, impurity removal, and recycling for efficient process control across the current tritium production infrastructure by advancing the deployment of predictive, data-driven diagnostics in radiological environments.