THE cost of decommissioning Oldbury Nuclear Power Station has been set at £954 million, latest figures have shown.

A revised document just published by the Nuclear Decommissioning Authority (NDA) gives the estimated sum for taking the plant out of action and clearing the site once it stops generating electricity.

But it will take about 90 years to achieve the "final end" status.

Oldbury is the oldest operating nuclear power reactor in the world, having started producing power in 1967. It has already exceeded its expected generating life by a couple of years and one of its two reactors will close down for good this summer.

A case is being made for the other reactor to carry on until the end of 2012 but by then there will be no fuel left and the station, near Thornbury, will have to go into the decommissioning phase.

The NDA said it would take two years to remove the spent radioactive fuel, with a further 14 years of work to be completed to reach the point when the site could go into the so-called "care and maintenance" phase.

Final site clearance is then estimated to start in 2092, with the task finished in 2101.

The NDA said the UK's civil nuclear legacy was a major public liability and its aim was to find safe, sustainable and publicly acceptable ways to deal with it.

In its document it said: "The high cost of dealing with the historic civil public nuclear liability reflects the emphasis at the time the facilities were built on operations and the lack of awareness or foresight of the importance and need to plan for eventual decommissioning.

"Our mission is a long-term one and some sites will not reach their planned end state for decades. Some wastes will remain hazardous for thousands of years. This is immensely technical and challenging."

Berkeley power station, which has been under decommission since 1989, will cost £608 million to reach final site status.

Meanwhile the Environment Agency revealed Magnox, which operates the Oldbury site, was sent a warning letter after oil was discharged into the river Severn.

Dr Robert MacGregor, of the agency, said staff at the site reported a failure of a seal oil cooler in February, resulting in the loss of around 350 litres of oil into the river via a cooling water discharge, which quickly dispersed the oil.

He said: "The site immediately took measures to isolate the system and undertook a full investigation. Subsequently we undertook a formal investigation.

"Our area enforcement panel agreed that the appropriate response was for a warning letter to be served to Magnox Ltd.

"We expect the site to improve arrangements as a result of the loss of oil and we will follow this up as part of our routine inspection activities."