Understanding Radioactive 'Hot' Particle Evolution in the Environment

Whilst radioactivity has always been present in the environment, industrial and military use of nuclear materials over the past 70 years has led to numerous deliberate and accidental releases of radioactive materials. The impact of these materials on humans and wider ecosystems is controlled by the behaviour of the radionuclides in the environment. In turn, radionuclide behaviour and resultant bioavailability is dictated by their concentration and chemical form.

Radioactive 'hot' particles are often an important part of releases to the environment and thus they are commonly found at nuclear sites (e.g. Sellafield) or in areas impacted by deliberate releases (e.g. Ravenglass and Eskmeals, UK) or accidents (e.g. Chernobyl and Fukushima). After release, particle-bound radionuclides have been shown to behave very differently in the environment when compared with homogeneously dispersed contamination. However, there is a distinct lack of knowledge about the composition of, and chemical form of radionuclides in hot particles, or of the processes that control their longer-term stability, fate and impact, particularly at the molecular scale. This leaves significant gaps in our conceptual models of radionuclide environmental behaviour, making it difficult to facilitate robust, long-term predictions of radionuclide transport and fate. Ultimately, the impact of these uncertainties is profound: a lack of confidence in our ability to predict radionuclide behaviour in the environment impacts on the public perception of priority issues, for example, the geological disposal of nuclear waste and the implementation of new nuclear build. As a result, better quantification and understanding of the short- to long-term behaviour and potential impacts of hot particles in the environment is crucial.

Reflecting the above, we will use a range of laboratory experiments and field samples combined with state-of-the-art characterisation tools, to develop a clear understanding of hot particle evolution in the environment over timescales ranging from months to decades. The majority of our experimental work will focus on uranium-rich hot particles due to their prevalence in the environment, and we will alter these under a range of environmental conditions in flowing columns, for periods of > 1 year. Throughout, we will monitor changes in solution chemistry; further, we will use a range of synchrotron, mass spectrometry, and electron microscopy techniques to assess changes over time in particle structure, chemistry, and isotopic composition, as well as characterising the formation of any secondary phases. Complementary to our column experiments, and in an effort to understand longer timescale reactions (years to decades) and assess processes across a wider range of particle types, we will use the same techniques to characterise particles from contaminated field samples (e.g. from the Sellafield area and Eskmeals firing range).

The information from this work will lead to a much-improved conceptual model of radionuclide behaviour when hot particles are present in the environment. Further, by working with a range of key stakeholders (e.g. EA, DSTL), we can use this knowledge to predict radiological risk at contaminated sites better and inform land management / monitoring practices.

The risk associated with nuclear material use always presents a major concern. Whether or not such perceptions are justified, they influence the public and decision-makers very heavily. Moreover, there are major uncertainties associated with radioactivity and the environment (especially radioactive 'hot' particles) and this may lead to a very conservative approach to risk. In turn, this may lead to incorrect estimates of doses and impacts, potentially leading to inappropriate decison making and excessive costs for little benefit. A proportionate understanding of risk in any nuclear programme is therefore essential for public acceptance, political support and proper cost-detriment analysis. Ultimately, the behaviour of radionuclides in the biosphere dictates the radiological risk they represent, and the proposed study of 'hot' particles will substantially improve our understanding of radionuclide behaviour in the environment, and therefore any associated risk assessments.

We have identified three main stakeholder groups who will benefit from this project; namely, Industry/Military, Regulators, and the UK National Security community (see letters of support). For Industry/Defence, several NDA Site Licence Companies (SLCs) and the MOD (or their contractors) have operational responsibility for land that is contaminated with hot particles. Our research findings will allow these stakeholders to make more informed management and remediation decisions regarding this existing legacy whilst also increasing preparedness for any future events (e.g. very severe reactor accidents). For Regulators (e.g. EA), our findings will permit better assessment of risk, across a range of timescales, thus facilitating more efficient regulation of nuclear sites. In the security area, as noted in the proposal, our research has a number of potential spin-offs in nuclear forensics (e.g. better identification of illicit nuclear materials brought into the UK). To ensure knowledge transfer to these stakeholder groups, we will engage with representatives of the EA, DSTL, AWE, and Sellafield Ltd., holding regular 'stakeholder' meetings where we report progress. As identified in the 'Pathways to Impact' (PTI) document, our representative stakeholders will then be able to disseminate this knowledge to others in their field (both nationally, and internationally). Finally, during month 30 of the project, we will hold a workshop with stakeholders to exploration potential continuation of this work and identify elements suitable for deployment.

Several other stakeholder groups may also benefit from our research findings. These include Government, Non-Governmental Organisations (NGOs), and the Wider Public. For Government and NGOs, knowledge transfer will mainly be facilitated through investigator participation in advisory bodies and learned societies (e.g. Committee for Radioactive Waste Management and Nuclear Innovation Research Advisory Board; Cabinet Office Science Advisory Committee via Livens; RSC and STFC Env-Rad-Net via Law; RCUK Energy Strategic Advisory Committee & MinSoc via Morris). To ensure engagement with the wider public, the team will participate across a range of outreach activities organised at The University of Manchester (identified in the PTI document).