Current nuclear waste storage methods are less stable than previously thought and could be leaking harmful radioactive material, scientists have warned.
Disposal of nuclear waste involves mixing it with other materials to form glass or ceramics, and then encasing those pieces of glass or ceramics – now radioactive –inside metallic canisters.
These canisters can then be buried deep underground in a repository to isolate the radioactive material and prevent it from interacting with the environment.
However, the team found that the glass and ceramic materials holding nuclear waste can interact with the stainless steel used to make the canisters, accelerating corrosion.
This could affect the service life of nuclear waste storage and exacerbate radioactive contamination into the environment – potentially polluting water sources and risking chronic disease in humans.
Stainless steel canisters used to store vitrified high-level waste (HLW), which is usually stored deep underground for at least 50 years before disposal
‘In the real-life scenario, the glass or ceramic waste forms would be in close contact with stainless steel canisters,’ said Xiaolei Guo, lead author of the study and deputy director of Ohio State’s Center for Performance and Design of Nuclear Waste Forms and Containers.
‘Under specific conditions, the corrosion of stainless steel will go crazy.
‘It creates a super-aggressive environment that can corrode surrounding materials.’
Radioactive waste – by-products of nuclear power generation and nuclear fission – can remain hazardous to humans and the environment for hundreds of thousands of years.
As a result, countries have developed plans to store this so-called high level waste (HLW) up to around 3,200 feet deep in what is called a deep geological repository.
Radioactive waste stored at such depths helps prevent any chance of radiation exposure to people.
HLW typically arises in liquid form, generated as a by-product during the reprocessing of spent fuel from nuclear reactors.
‘In the current disposal plan for many countries, the high level nuclear waste will be primarily mixed with other materials to form glass or ceramic waste forms,’ Guo told MailOnline.
For the study, Dr Gerald Frankel at Ohio State University and his team pressed stainless steel – a so-called ‘barrier metal’ – against materials used to immobilise nuclear waste – a borosilicate glass and titanate-based ceramics.
Aerial photograph of the nuclear fuel processing site of Sellafield, Cumbira, which is Europe’s largest nuclear site
They then studied the rate of corrosion under simulated repository conditions, and found that both materials corroded much faster in the areas where they were in contact with the stainless steel.
‘Severe’ corrosion was found between stainless steel and both borosilicate glass and the ceramic waste form.
‘Our study showed that the release rate could be enhanced due to the corrosion interactions between different materials used to isolate these wastes,’ Guo said.
‘Specifically, the corrosion of metallic canisters creates a highly aggressive environment that can corrode the surrounding materials faster than what was predicted.’
The accelerated corrosion can be attributed to chemical changes that occur within a confined space over time.
This research should be carefully considered when assessing the safety of nuclear waste disposal and when selecting barrier materials, the team say.
‘The corrosion that is accelerated by the interface interaction between dissimilar materials could profoundly impact the service life of the nuclear waste packages, which, therefore should be carefully considered when evaluating the performance of waste forms and their packages,’ the team said in their research paper, published in Nature Materials.
‘Moreover, compatible barriers should be selected to further optimise the performance of the geological repository system,’ they add.
In the UK, HLW treatment takes place at Sellafield, a two-square-mile site close to Seascale on the coast of Cumbria – but the site doesn’t have a deep geological disposal unit.
Seallfield confirmed to MailOnline that the government’s search for a deep geological disposal unit in the UK is ongoing, although HLW is still stored at the site.
The US, meanwhile, has over 90,000 metric tons of nuclear waste that requires disposal, and according to the US General Accountability Office, it is typically stored near the plants where it is produced.
A permanent site has been proposed for Yucca Mountain in Nevada, though plans for a deep geological repository have stalled.
Only Finland has started construction on a long-term repository for high-level nuclear waste, according to the research team.
‘At this stage, it is still a plan for most countries, but there have been continuous research and risk assessment efforts on this topic. Eventually, it is very likely to occur,’ Guo said.
WHY IS RADIOACTIVE WASTE DANGEROUS?
Radioactivity is the process of an unstable atomic nuclei loses energy through radiation.
It damages the cells of the human body, causing a mutation, which can make them cancerous.
Radioactive waste, formed as a by-product of nuclear processes, can take the form of different states of matter, including gas, solids and liquids.
Depending on the waste’s source, the radioactivity can last from a few hours to hundreds of thousands of years.
If disposed of improperly, radioactive waste can devastate the environment, ruining air, water and soil quality.
These materials can have long-term negative effects on human health, and can be fatal.
Source: Nuclear Energy Institute/How Stuff Works