Actinides and Lanthanides

The lanthanides and the actinides are usually shown as two additional rows below the main body of the periodic table. Actinides are 15 radioactive metallic chemical elements with atomic numbers from 89 to 103, including thorium, uranium, plutonium and curium. The most abundant actinides on Earth are naturally-occurring uranium and thorium and synthetically-produced plutonium. At least 6 actinides heavier than plutonium have been released into the environment by nuclear weapons tests.

Lanthanides are the 15 metallic chemical elements with atomic numbers 57 through 71, including cerium, neodymium, erbium, thullium and ytterbium. Most of the world's lanthanides are extracted from mineral deposits in Inner Mongolia, in the People's Republic of China.

The use of nuclear energy to produce electricity has avoided the release of an estimated 56 gigatonnes of carbon dioxide since 1971. With the increased focus on reducing carbon emissions, the International Energy Agency (IEA) has projected that the proportion of energy derived from nuclear sources needs to more than double from 396 gigawatts (GW) in 2012 to 930 GW by 2050.

As demand for nuclear energy increases, so does the amount of radioactive waste being generated, and research is focusing on how we can safely store and dispose of this waste. Diamond has been helping a handful of pioneering nuclear researchers undertake a wide range of research, 2-year geological disposal experiments, to analysing container corrosion and investigating safe decommissioning processes. Scientists coming to the synchrotron are not only ensuring the future protection of our environment, but also saving the UK economy hundreds of millions of pounds by simplifying storage solutions. Read more here.

A sample of grout and uranium ready for examination at the JEEP beamline, I12.

The timescale and costs of cleaning up one of the UK’s most hazardous buildings, Magnox Swarf Storage Silo at Sellafield, could be significantly reduced, thanks to a study carried out at Diamond by researchers from the University of Bristol. Their research focussed on the chemical behaviours of intermediate level waste (ILW) at the site and unearthed previously unknown information about the long-term corrosion behaviours of magnesium and uranium.

The groundbreaking research, which took place on Diamond’s Joint Engineering and Environmental Processes beamline (I12), points the way to a radically simplified approach to the packaging and disposal of ILW. Previously, a 22-step mechanical treatment and encapsulation process was thought necessary to manage and ultimately dispose of ILW stored in silos constructed over 50 years ago. The study’s findings suggest this could be replaced with a 3-step solution which stores the waste ‘raw’ with concrete grout inside a shielded container. Switching to this new method could speed up the decommissioning of the silo by several years and provide huge savings to the taxpayer. The technique could also be applied to other redundant nuclear facilities in the UK and around the world. Read more here.

X-ray spectroscopy techniques at Diamond have given scientists a new insight into the behaviour of uranium during deep disposal of radioactive waste.

Many countries will use geological disposal facilities as the final way to dispose of radioactive wastes and so it is important to be able to predict the behaviour and potential impacts of uranium under alkaline conditions relevant to deep disposal. The effectiveness of iron (oxyhydr) oxides to reduce the mobility of uranium is well known due to their high surface reactivity. However, the fate of surface bond uranium during the crystallisation of these minerals is poorly understood.

A team of researchers from the University of Manchester and Diamond used spectroscopy techniques on the B18 beamline to explore these processes. Combining X-ray Absorption Spectroscopy alongside chemical extraction and transmission electron microscopy techniques at the labs in Manchester, they were able to gather the first evidence for how absorbed U(VI) – uranium in its more mobile oxidation state – becomes incorporated into hematite. The Extended X-ray Absorption Fine Structure (EXAFS) technique also allowed them to determine the exact mechanism of uranium incorporation, showing that it directly substitutes for iron, with little distortion of the surrounding crystalline structure. The combined results of the study have afforded a full mechanistic understanding of uranium incorporation into hematite, and the nature of uranium bonding within the mineral structure. Together these findings highlight that minerals can be used to lock away radioactive contaminants and thus may contribute to controlling the environmental impact of radioactive waste disposal. Read more here.

The management and disposal of higher activity radioactive wastes is a significant issue for countries with a history of nuclear power generation and military activities. The most common long-term disposal choice is containment within a deep geological disposal facility (GDF), but to remain effective over the long term, GDFs must limit the mobility and migration of radionuclides. To understand how radionuclides can become mobile, we need to investigate the interaction of radionuclides with geological materials.

A team from The University of Manchester worked with Diamond scientists to use Small angle X-ray Scattering (SAXS) to characterise the formation of uranium (U) colloids in synthetic cement leachate systems. They observed nano-particulate U-colloid formation occurring within hours, and by measuring aged samples, showed that the colloids were stable for several years under some conditions. Read more here.

In 1986, the worst nuclear accident in history sent up to 30% of the 190 metric tons of uranium at the Chernobyl nuclear power plant into the atmosphere. The Soviet Union eventually established a 19-mile-wide exclusion zone around the reactor, evacuating 335,000 people. Clean-up is expected to last until at least 2065 and the full health consequences of the accident, including impacts on mental health and subsequent generations, remain highly debated.