Clean-up job may never be finished

The immensely long life of some radioactive substances means the job of decommissioning a big nuclear reactor will not be completed for decades, and maybe centuries - if ever.

The immensely long life of some radioactive substances means the job of decommissioning a big nuclear reactor will not be completed for decades, and maybe centuries - if ever.

Although the spent atomic fuel can be removed easily, and other radioactive waste taken off site, the core of the reactor has to be left in situ. It is simply too massive and, after years of nuclear bombardment, too dangerously radioactive to shift. It could be cut up with robots, but this would magnify the problem, as encasing the scrap with enough steel and concrete to keep it safe would increase its volume tenfold.

The usual strategy is to make the reactor building secure and then simply wait. This approach is being adopted by British Nuclear Fuels (BNFL), which is already decommissioning three early nuclear power stations, Berkeley on the river Severn, Trawsfynydd in North Wales and Hunterston in Scotland.

The structures of their "piles", the reactors themselves, have been contaminated with cobalt-60, whose effects take years to decay away. The BNFL spokesman David Cartwright said: "It's up to society to decide when the radioactive hazards have fallen to acceptable levels. We think that will be around 100 years from now."

Dounreay's reactors were fuelled with plutonium, which is active for much longer. Its "half-life" - the time it takes for half of a given amount to decay to lead - is 24,000 years.

Green groups tend to agree with the storage policy, because there is no depository in which to keep scrap if the reactor is dismantled. But the length of time that may have to be allowed for that is well illustrated in a Friends of the Earth poster from the 1970s, showing a Roman centurion on guard. "If the Romans had had nuclear power," the caption ran, "we'd still be guarding their waste."