A NUCLEAR reactor at Hunterston in Ayrshire is to be shut down because of safety fears.

The decision by British Energy, the UK's biggest power generator, to shut down the Scots reactor and another at Hinkley in Somerset wiped GBP800m off its value as its shares fell by 25per cent.

It followed the discovery of cracked pipes at two other power stations. British Energy also said it was also examining a "significant leak" in the cooling systems of a third power plant.

The Department of Trade and Industry insisted that the reactor closures would not leave the country short of electricity.

The decision to prepare to shut down reactors at Hunterston and Hinkley was taken after an inspection at the Hinkley Point B R3 plant found cracking which was "at the high end of the range previously experienced". Boiler tube cracking had been discovered at Hunterston in September.

The discoveries prompted British Energy to prepare to shut down one reactor at Hunterston and one at Hinkley for early inspection. The output of both reactors has been lowered while plans are made to shut them down ahead of inspections.

It was also revealed that a leak had been discovered in an underground pipe at the company's power station in Hartlepool, but it insisted last night that this was non-nuclear. Repair and assessment work is being carried out.

British Energy, which can generate one-fifth of the UK's energy requirements from eight nuclear power stations and one coal-fired plant, will now have to buy electricity on the wholesale market to fulfil its contracts, according to its finance director.

A DTI spokeswoman said: "National Grid is there to balance supply and demand. We would expect the market to respond by bringing on other sources of generation to fill this gap."

Output problems have dogged British Energy in recent years, after previous boiler unit closures at one of its plants at Heysham in Lancashire and other supply breaks at Hartlepool.

Meanwhile, another nuclear power generator, British Nuclear Group, was fined GBP500,000 yesterday for an incident in which around 83,000 tonnes of acid containing 20 tonnes of uranium and 160kg of plutonium escaped from a broken pipe into a sealed concrete holding site at its Sellafield nuclear reprocessing plant.

Opponents of nuclear power said the current problems of British Energy highlighted its unreliability.