PNNL

Abstract

Radiolytic hydrogen (H2) generation in nuclear waste sludges like gibbsite (a-Al(OH)3) is a safety hazard modulated by impurities. To understand why nitrate-bearing gibbsite produces less H2 than chloride-bearing analogues, we paired ²7Al multiple quantum magic angle spinning (MQMAS) NMR spectroscopy to determine structural heterogeneity with transverse-field muon spin rotation (TF-µSR) to probe electron availability. MQMAS revealed greater structural disorder in the nitrate sample. Correspondingly, TF-µSR showed a larger diamagnetic fraction (?Adia ˜ 0.026) for nitrate, signifying suppressed muonium (Mu) formation and thus reduced electron survival on the microsecond timescale. This establishes a correlation between impurity-induced disorder and electron loss. The diamagnetic fraction serves as a benchmark for this effect, as it provides a key constraint for predictive models without currently resolving whether the electron is lost to direct chemical scavenging or trapping at lattice defects.