DOUNREAY's leading critic is seeking assurances from the Government nuclear watchdog over the 170kg of highly enriched uranium which may or may not have been lost 30 years ago, writes David Ross, Highland Correspondent.

As a team of 10 inspectors from HM Nuclear Installations Inspectorate began work on a major safety audit at the beginning of this week, the plant was plunged into new controversy.

A report prepared by Dounreay's operators, the UK Atomic Energy Authority had quoted estimated losses of HEU of 170kg - 22kg of which was estimated to have gone into the plant's shaft, with the balance spread around different facilities at the site.

The following day, the authority's chief executive, Mr John McKeown, insisted the 170kg had never existed, but had been an accounting error. But others remain convinced that the material ended up in the UK nuclear weapons programme.

Mrs Lorraine Mann, of Scotland Against Nuclear Dumping, has now written to Dr David Turton, HM Principal Inspector at the watchdog's Merseyside headquarters, stating: ''I wish to draw your attention to the contents of UK Atomic Energy Authority's recently released document which outlines the inventory of materials in the Dounreay Shaft. In particular, I wish to draw your attention to pages 35 and 36 where the presence of fissile materials in the shaft is discussed.

''During the discussion, reference is made to large quantities of U-235 MUF (Material Unaccounted For) which accumulated during the 1960s. Assumptions are made as to how much of the MUF may be in the shaft and it is stated, 'unaccountable losses are likely to be spread over various facilities and are likely to be recovered during their decommissioning.'

''I seek reassurance that the amount of MUF lodged in pipes, dissolvers and other parts of plant in FCA is well known and clearly identified. If such assurance cannot be given, I am interested to know on what basis it could be considered safe to operate any of the plants involved in the future.

''I wish to know whether NII has also been aware of this information and UKAEA's view that the materials are likely to be lodged in facilities on the Dounreay site. If so, on what basis has UKAEA been permitted to use these facilities for further work on fissile material over the past 30 years?''