Some large buildings can be demolished in a few days, but to remove a nuclear power station may take a century or more because of the danger from radioactivity.
When a nuclear power station is shut down. The first step is to remove all the nuclear fuel. It is taken out of the reactor —the heart of the power station — by the same machinery that has been used throughout its operating life to regularly replace old fuel with new. This remotely operated equipment place–; the old fuel into special: containers for taking to a reprocessing plant. There it is turned into enriched fuel for use in other reactors_ A small amount of radioactive waste is also produced and stored for future.
As a reactor contains anything from 23,000 to 43.000 highly radioactive fuel rods — depending upon its design — and each has to be removed separately, this part of the job may take up to five years. But with the fuel gone, 99 per cent of the site’s radioactive content has been removed.
The next stage is to remove all the conventional plant, equipment and buildings. This will involve some radioactivity —in the boilers, for example — and will take another five to seven years to finish.
The final stage is the most controversial, and plans vary from country to country. Usually, a sealed reactor will be left for 100 years or more to ‘sleep it off, so that the radioactivity inside it can decay. Although remote-controlled robot equipment already exists to demolish the reactor from the inside out, other robots would be needed to service and maintain them. In 100 years’ time, radioactivity will be low enough for human maintenance teams to look after the robots in the reactor. So in most cases the reactor will remain encased in concrete like some ancient monument 160ft (50m) high. By 1986, 34 nuclear power stations had been taken out of service round the world. Most are beginning to ‘sleep off the radioactivity.
French nuclear specialists are content to leave their sleeping reactors to be dealt with by a future generation with more advanced techniques.
The British, however, are undertaking a demonstration project to show that a reactor can be dismantled faster. At Sellafield in Cumbria, the Windscale advanced gas-cooled reactor is planned to be returned to green-field status by 1996. Work began in1982. Dismantling is being carried out inside the steel dome under reduced air pressure so that radioactive gas cannot leak. A remote-controlled manipulator —like a giant arm and hand — will be lowered down inside the reactor to cut it into pieces weighing about a ton, using oxypropane cutting equipment. The operations will be monitored on closed-circuit television.
Each piece will be carried to a ‘sentencing cell’, where it will be weighed and its radioactivity measured. It will then be lowered into a reinforced concrete box, and the remaining space will be filled with concrete to form a 50 ton cube.
Nearly 1900 tons of radioactive waste will have to be dealt with in this way. The cubes will be kept in a building on the site until a repository is built for the waste. Methods of breaking up the concrete shield remotely are still being tried out.
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