Expensive and dangerous: The arguments against nuclear power in the UK haven’t changed all that much in half a century, arguably because the nuclear industry has yet to conclusively put to rest public fears over reactor safety and the ongoing issue of how best to dispose of radioactive waste.
The disasters at Chernobyl and Fukushima Daiichi, as well as two high-profile radioactive leaks in the UK in 1957 and 2005, are regularly cited as proof that nuclear power generation is inherently unsafe.
But equally headline-worthy is the problem of how to safely store and dispose of spent radioactive fuel from the 15 nuclear reactors that remain operational across the UK, the majority of which are earmarked for retirement by 2023 and still generate around 18% of the UK’s electricity supply.
Overseeing this mammoth task is Radioactive Waste Management (RWM), a subsidiary of the UK Nuclear Decommissioning Authority (NDA). As RWM’s waste management director Ann McCall explains, the problem has as much to do with public perception – most people do not know what constitutes radioactive waste, its toxicity or how it is stored − as it does with science.
“RWM has two parts to its mission and the first is that we provide waste management solutions and help the nuclear industry package waste,” McCall explains. “The second part is to deliver a long-term geological disposal facility (GDF) in the UK for higher activity waste. In 2017 we begin working with local communities across the UK to investigate potential sites and this is very much a social issue.
“Some say waste should be left in interim stores on the surface for long periods; I would argue that geological barriers have been stable for millions of years, whereas society has changed substantially.
“Radioactive waste requires geological timeframes in which it is managed and in the UK we think we are taking a responsible approach to higher activity nuclear waste by saying that you cannot rely on society to carry on looking after these hazardous materials for hundreds, if not thousands of years.”
Capacity issues: the packaging and interim storage of radioactive waste
Radioactive wastes include everyday items such as equipment and tools, water and air filters, and the protective clothes that workers wear. In nuclear reactors, most internal components such as tanks and pipes will come into contact with radioactive materials and become contaminated.
If a material is also in contact with (or close to) neutron radiation, the free neutrons may interact with the nuclei of other atoms to form unstable isotopes that decay and release further radiation, such as in a nuclear reactor core when free neutrons are released by the fission of uranium in fuel.
Most radioactive waste produced in the UK is solid and made from a variety of materials, including concrete and steel from dismantled buildings. Some wastes take the form of liquids or sludges, and are usually turned into solids by drying them or incorporating them into cement or glass.
The NDA differentiates between higher activity waste (HAW), low level waste (LLW) and other radioactive materials such as spent nuclear fuel, plutonium and uranium. The disposal options are dictated by the safety cases of the facilities where such materials are stored, as McCall explains.
“LLW is defined as radioactive waste with a radioactive content not exceeding four gigabecquerels per ton (GBq/te) of alpha or 12 GBq/te of beta/gamma activity,” McCall explains. “In the UK, LLW is packaged and sent directly, as it has been since the 1950s, to a shallow disposal facility in Cumbria.
“Plutonium and uranium are considered to be potential assets and so we look at their interim storage as well as at longer term options such as their potential reuse in fuel fabrication. Spent nuclear fuel is currently housed in interim stores pending the availability of a GDF.
“HAW requires a geological as well as an engineered barrier to retard the radionuclei and also has to go into interim storage before it goes to a GDF. However, such facilities have design lives of around 50−100 years, while radioactive waste contains radionuclides with half lives of millions of years; interim storage is not feasible over such time frames as it requires continuous waste management.”
How does the NDA ensure safe storage for 100 years, and that waste packages will be disposable at the end of the storage period and unaffected by any variance in the availability of disposal routes?
“RWM assesses the waste producer’s plans for the packaging and storage of the waste to ensure that these plans are compatible with geological disposal,” McCall states. “This means that waste being packaged today in the UK does not become a new nuclear legacy for future generations.”
Innovations in waste disposal: modular storage and success at Sellafield
Storing radioactive waste typically involves mixing it with cement and pouring into 500L stainless steel drums or boxes that are then placed underground, but innovations in the field are emerging.
“One option involves robust packaging containers that provide a stronger barrier,” explains McCall. “Unlike a thin-walled cement package, they may not require the waste to be cemented inside them. Instead, it can be dried or thermally treated or vitrified (glassified), thus reducing the volume.
“There is also a move to a more modular approach to interim storage. The Magnox power sites around the UK keep a standard cross section to the building and then make the buildings longer or shorter as required and so the stores are cheaper to run since they are more standardised.”
The waste from an operational site such as Bradwell is far simpler to deal with than the waste from Sellafield, which contained reprocessing technology, a power plant and research facilities, McCall explains.
“The large Magnox Swarf Storage Silos there were built over 60 years ago and contain a significant amount of radioactivity in deteriorating surface facilities.” she adds. “RWM has collaborated with Sellafield to bring forward the emptying of the facility by five years and save billions for the taxpayer by retrieving the waste and storing it in robust stainless steel boxes ready for geological disposal.
“Other innovations in the field include the partitioning, transmutation and utilisation of spent nuclear fuel in the PRISM reactor, but such solutions would still require a GDF.”
Going underground: the search for a geological disposal facility in the UK
The search for a permanent GDF on UK soil continues. The total cost of disposing of radioactive waste accumulated to date could hit £12bn, with £4bn estimated to be spent before the waste can be buried. Around 30% of the UK, excluding Scotland, could be geologically suitable for such a site.
“Geological disposal is internationally accepted as the safest option for the permanent disposal of HAW,” says McCall. “It provides a secure environment which isolates the waste and contains the radioactivity so that no harmful quantities can reach people and the surface environment.
“Multiple man-made barriers − the solid form of the radioactive waste itself; the metal or concrete package containing the waste; the protective buffer or backfill around the containers; and filled and sealed tunnels or vaults − work with the stable natural rock to provide safety now and in the future.”
China does not have an enviable nuclear safety record. Given the nation’s investment in the UK industry, what measures need to be in place to ensure that waste maintenance standards are met?
“If China operates a plant in the UK and packaging waste suitable for geological disposal, they will have to meet the very high standards of UK regulators,” says McCall. “We comply with international standards as set out by both the International Atomic Energy Agency and the International Commission on Radiological Protection and convert these into national legislation.
“These in turn are enforced and overseen by both the nuclear safety regulator – the Office of Nuclear Regulation − and the environmental regulator, the UK Environmental Agency.
“Current interim storage waste management strategies are fit for purpose and the UK is making good progress with the clean-up and decommissioning of the nation’s nuclear legacy.”