Once an old building is past its shelf life, it’s usually time to bring in the demo guys. But what if a building has been housing a nuclear reactor and is radioactive? Not so simple, and a true test of our nuclear capabilities.
Nuclear power plants are designed to operate for about 40 years. Yet it takes about 90 years to fully decommission one. Many UK plants were built in the 1950s and 1960s, so decommissioning is still very much a work in progress.
Cleaning up nuclear facilities — which also include particle accelerators, weapons factories and uranium mines — is a huge and expensive task. Costs vary according to the type of reactor, its location and radioactivity levels; for example, Trawsfynydd, in Snowdonia, active between 1965 and 1991, will cost a relatively cheap £796 million to sort out. But closing down some reactors at Sellafield in Cumbria will cost £23.5 billion. For context, the Nuclear Decommissioning Authority, which oversees the UK’s 14 old reactors, has a budget of about £2.8 billion.
So what needs to happen for a nuclear power station to retire? First, turbines are disconnected from the national grid and reactors sealed. Then tens of thousands of extremely hot and radioactive rods, mostly made of uranium, are removed from the reactor, encased and placed in a special cooling pond, along with older spent fuel. The pond cools the fuel and locks in radiation. After several years, the spent fuel is transported to Sellafield, where it is either reprocessed or stored (see graphic below). It will be radioactive for hundreds of thousands of years.
After this removal of 99 per cent of the plant’s radioactivity, the focus turns to contaminated waste. This is classified as low-level waste (rubble, plastics, clothing), intermediate level (fuel casings and graphite from reactor cores) and high level (acids produced by the fuel that can take 50 years to cool). Low-level waste accounts for 90 per cent of waste volume but a tiny fraction of radioactivity. High-level waste accounts for 1 per cent of volume but 95 per cent of radioactivity.
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Low and intermediate waste is encapsulated in a cement mixture and stored above ground in shielded containers. High-level waste is stored with spent nuclear fuel at Sellafield. Once the moveable waste is removed buildings are demolished, leaving only the reactor and cooling ponds. The reactor is then sealed up and abandoned, and cleaning of the radioactive ponds is started.
A phase (usually about 50 years) of “care and maintenance” then begins. Once radioactivity has returned to normal levels, the reactor and ponds are demolished. Berkeley, in Gloucestershire, was active from 1962 to 1989. It will enter care and maintenance in 2021 and be the first UK site to be demolished, in 2079.
New techniques to speed up the process, “immediate dismantling”, are being studied. For example, rubble can be re-used in new reactors and steel can be sand-blasted to remove radioactive layers.
Once decommissioning is complete, sites can be safely redeveloped. In Colorado, for example, a wildlife refuge covers much of a former nuclear weapons factory at Rocky Flats. In other cases, decommissioning paves the way for new power stations. Six of the eight plants that are scheduled to be built in the UK by 2025 will be on sites where decommissioning is taking place, including Sellafield.
They need to go somewhere and sites with a qualified workforce, grid connection and well-accustomed locals seem to be obvious choices.
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Too much of a bad thing (amounts of spent nuclear fuel)
Spent nuclear fuel is about 95 per cent uranium. Another 1 per cent is made up of other heavy elements, such as curium, americium and plutonium, whose isotopes can take hundreds of thousands of years to decay to safe levels. The final 4 per cent is made up of by-products of fission that break down over shorter periods — for example caesium-137 and strontium-90, which break down in about 300 years.
Total spent nuclear fuel
US 71,000
Russia 18,000
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Japan 12,000
France 11,300
UK 10,000
Finland 1,700