Current technologies for the remediation of difficult-to-measure radionuclides at nuclear sites - 22224

Difficult-to-measure radionuclides (DTMRs), defined by an absence of high-energy gamma emissions during decay, are problematic at nuclear sites. They are common contaminants at many facilities, including Hanford (WA, USA) and Sellafield (Cumbria, UK), that often have long half-lives and can potentially result in adverse health effects in humans, e.g. thyroid cancer from I-129 exposure. Effective remediation is therefore essential if nuclear site end-state targets for return to safe use are to be met. However, due to a lack of techniques for their in-situ detection, technologies designed to remediate these DTMRs are chronically underdeveloped and tend to be labour intensive and environmentally invasive (e.g. excavation), which can lead to further complications including elevated worker exposure doses during decommissioning. This, plus an emerging emphasis on sustainable remediation (e.g. ISO 18504, ASTM-E2876), means there is a renewed focus on less invasive technologies for radionuclide clean-up, and specifically for DTMRs.In this paper, we outline current technologies (Figure 1) for the remediation of DTMRs I-129, Tc-99, Sr-90 and H-3. These radionuclides have been selected based on their < 100 keV gamma emissions during decay, in combination with their high mobilities in groundwaters and prevalence at nuclear sites. We focus on the strengths and weaknesses of common remediation techniques that include ‘pump-and-treat’ (P&T) for contaminated groundwaters, in addition to permeable reactive barriers (PRBs) that are planted into spoilt land as engineered barrier systems to treat contaminated waters in-situ. Phytoremediation, which uses plants to extract, stabilise or degrade contamination, is also assessed as an emerging DTMR clean-up technology, with continuing development being driven by sustainability concerns and rising costs for traditional remediation methods. We supplement this discussion with examples from nuclear sites that are currently undergoing, or have previously undergone, decommissioning. We then conclude with our assessment on the future directions for these technologies and how they, either by themselves or in combination with others, may evolve over time to give more sustainable and less intrusive remediation options for assessors at nuclear or contaminated sites