Large cemented gibbsite agglomerates in alkaline nuclear waste at the Hanford site and the impacts to remediation

Abstract

Recent work with the remediation of legacy alkaline nuclear waste has focused on nanometer and micrometer particle sizes, emphasizing how these small particles can impact efforts to treat the waste. Building upon this work, we present here findings that show very large particles (several centimeters in size) also exist in these waste which likewise play an important role in the remediation process. While large cemented gibbsite nodules have been periodically reported in acid soils in the literature, this study found similar large gibbsite agglomerates (7 cm in diameter) in alkaline nuclear waste, the first time that such large agglomerates have been identified in an alkaline environment. The morphology of the gibbsite in the agglomerates that were grown over more than 40 years of storage in the waste tank were similar to the much smaller agglomerates that have been reported in previous shorter term studies. Fluid dynamics calculations indicate that these cemented particles would be difficult to mobilize with standard jet slurry technologies, which is consistent with their persistence in the waste heel after jet sluicing of the tank.

Keywords: Agglomeration; Cemented particles; Gibbsite; Hanford; Nuclear waste.