With the current debate about climate change and carbon emissions as well as soaring oil prices, it is feasible that nuclear energy will play a central role in power generation in years to come.
Gradually people are starting to accept that provided it’s done correctly, nuclear power is a very viable and potentially safe alternative to fossil fuels. But the subject of what happens to the waste is one of pressing and ongoing concern.
“In some people’s case there are very deep beliefs that the slightest sniff of radiation is instant death,” says David Horsley, a fellow with the Royal Academy of Engineers and formerly head of fuel development with British Nuclear Fuels.
The earliest accumulated nuclear waste is about to turn 50. Mainly generated in power reactors it is mostly stored in water cooling tanks of an average depth of 7m. Improved technology and a better understanding of the fuel cycle has meant that waste generated today is easier to handle than it used to be. Yet the question of what to actually do with it all can no longer be avoided.
THE WASTE DEBATE
While there are all sorts of ideas for how best to deal with nuclear waste, the overwhelming consensus is to stick it in the ground. Russia’s long-held practise of dropping it in the sea certainly hasn’t improved its environmental credentials.
But there are countless styles of nuclear burial repositories depending on the sorts of materials used to build them (i.e. concretes, metals, synthetic plastics etc).
Then there’s the environmental and geological characteristics of sites; are they existing sites such as ex-mines? What about seismic activity, temperature and water levels. Then of course there’s the waste itself.
Probably one of the easiest types of waste to handle is spent fuel cells. These are solid and tend to be heavily compacted into ceramic form. But nuclear operations aren’t always neat and tidy, producing a smorgasbord of radioactive materials from clothing, soils, metals, concretes, timbers, and the most dreaded of radioactive substances – liquids.
The materials used to contain waste also demand careful consideration. For instance, metal corrosion is a big cause of gas which can destabilise repositories. This has emerged as a key issue in the UK.
Nuclear waste is generally divided into three categories; high-level waste (HLW); intermediate-level waste (ILW); and low-level waste (LLW). Some countries have added a classification for very-low-level waste (VLLW).
LOOKING TOWARDS THE FUTURE
While it is hard to say exactly how much of it there is around, some estimates now show there could be, with the rising interest in nuclear energy, about 250,000t of spent fuel and HLW by the year 2015. Such waste is presently held in temporary storage, often close to one of the 400 nuclear power stations around the world or in military bases where it is the result of the production of nuclear weapons.
The International Atomic Energy Agency recently conducted the most extensive survey of nuclear-powered countries and their strategies for handling radioactive materials in the decommissioning of nuclear power plants.
The overwhelming consensus with regard to the handling of decommissioning nuclear waste is that it should be buried. Much of the LLW and MLW accumulated at nuclear power plants, research laboratories and other sources have been slated for burial in so-called near-surface repositories.
One reason why burial is supported so widely is because of the high levels of expertise and advanced technologies for drilling.
“Technological capability for the construction of geological facilities is available, as it is based on current drilling, tunnelling, backfilling and sealing technologies,” says the IAEA.
Several countries are researching deep underground disposal facilities for HLW. Belgium, Canada, Finland, France, Germany, Sweden, Switzerland, the UK and the US have all performed detailed studies, or characterisations, drilling numerous boreholes and exploratory shafts and ramps in underground research laboratories.
Sweden is seen as the most advanced with its plans for a final, underground repository, while US plans to dispose of nuclear waste at Yukka Mountain in Nevada have met with fierce opposition.
Currently the US government’s Waste Isolation Pilot Plant in New Mexico is the only repository in a deep geological formation.
Governments in Romania, Lithuania, Iran and the US are considering building repositories for the disposal of operational and decommissioning waste in surface-engineered constructions. Proposed depths range from tens to hundreds of metres. Repositories are in different stages of development in Canada, Hungary and the UK.
Germany has a strict policy of sticking all of its nuclear waste in deep geological formations and planning has started for the proposed Konrad repository which will operate at depths of between 800m and 1,300m and store both operational and decommissioning waste. Construction has been delayed however, pending a court examination.
New facilities designed for the disposal of decommissioning wastes are planned in Japan and France. France’s Morvilliers facility, opened in 2003, is designed to handle 650,000m³ of VLLW in excavated cells within a clay formation.
Monitoring of sites is of course crucial and some countries including Lithuania are developing new software for advanced computer-based monitoring.
With regard to nuclear reactors, many of the current designs focus on allowing for the storage of more waste on site. Also suggested recently was the possibility of sinking and covering reactors themselves so that they become in effect a near-surface repository. This process is referred to as entombment in the industry.
BUT HOW BIG IS THE PROBLEM?
HLW is accumulating at about 12,000t a year worldwide. High-level wastes are highly radioactive for a long time, so must be isolated from people for thousands of years while their radiation levels drop. But it’s a fact seemingly little known outside of the nuclear industry that of the total quantity of nuclear waste thus far accumulated, HLW makes up only a fraction. In fact, only about 3% of all radioactive waste is HLW.
Of course this shouldn’t provide grounds for complacency; this small proportion of waste holds something like 95% of the total radioactivity of nuclear waste. About 90% of the world’s radioactive waste is LLW, yet it constitutes only 1% of total radioactivity.
Hospitals, universities, research reactors and industries that use radioactive isotopes have to handle LLW. It is also produced by the nuclear power industry, mostly as metals and organic materials in lightly contaminated scrap and other soft items such as protective clothing and cleaning materials.
According to Australia’s peak nuclear body, ANSTO (Australian Nuclear Science and Technology Organisation), a person standing for an hour 2m from a truck laden with LLW would absorb about as much radiation had they just taken a flight from Sydney to Los Angeles, which takes about 16 hours.
It points out further, that contrary to popular belief, LLW cannot be used to make dirty bombs, it would also pose little threat if struck by missiles or was set alight in some other manner.
ILW is another case altogether. It typically comes from production of radiopharmaceuticals, waste from reprocessing of spent research reactor fuel, and disused radioactive sources from industry and medicine. Worldwide it makes up 7% of the volume of radioactive wastes and has 4% of the radioactivity.
One thing that makes the treatment and disposal of nuclear waste so challenging is the fact that different reactions occur when different materials are irradiated. Concretes, metals such as steel and aluminium, and just about anything in the periodic table may decide to alter its behaviour.
Further, there are several different nuclear power plant designs, each of which produces waste with different characteristics. For instance, reactors made with graphite moderators create waste with unique challenges.
In addition to contamination problems, graphite also tends to accumulate energy. Several countries are trialling solutions to this problem although none yet claims to have found the answer. Options being investigated include encapsulation of solid graphite, incineration, hydrolysis and recycling.
DIGGING DEEP FOR THE ANSWER
It is widely felt that all forms of HLW should be stored in deep geological repositories. The less-radioactive ILW and LLW have for decades been placed in various types of ‘near-surface’ repositories, which can mean anything from storage containers made from concrete, steel, aluminium or other materials to relatively shallow trenches with designs several metres deep.
But of course it’s all a lot easier said than done. Burial of nuclear waste is not only enormously scientific but it is politically difficult as well as potentially very expensive.
A recent Deloitte survey stated that Britain’s nuclear waste legacy will cost around $50bn. “We haven’t really touched on the nub of the [nuclear] waste management problem in the UK,” says the Royal Academy of Engineer’s Professor Horsley.
Canada’s Nuclear Waste Management organisation recently concluded that deep geological disposal would cost its country C$24bn and require 60 years of additional study before the first bundle of waste is dealt with.
Several years ago, there were plans for Australia to provide a major repository for the world’s nuclear waste. The Pangea project, located in the remote deserts in Western Australia, would have seen Australia take around a fifth of the world’s nuclear waste. However, the project became a political nightmare and was swiftly scuttled. “It was just too far fetched,” says Lubi Dimitrovski, ANSTO’s manager for waste operations and technology development.
In our second instalment of this article we look at how countries are not only taking more responsibility for spent fuel but designing plants that can help reduce waste in the first place.