The Dounreay dome has been a local landmark for many years

Up until recently, the iconic sphere of the world's first fast breeder reactor was due to be kept for posterity.

Many locals support its retention while Historic Scotland had been keeping its future listing under review.

The dome's fate is being discussed along with what state the site should be left in after its �2.9bn clean-up.

The Nuclear Decommissioning Authority (NDA) said it was likely there would not be a sphere at the end of the site's decommissioning.

The UKAEA is carrying out a consultation exercise on behalf on the NDA, which is in overall charge of Dounreay and the UK's other 19 defunct reactor sites.

The most prudent strategy radiologically is to arrange to dismantle it - to get rid of it John Farquhar NDA

In all five "endgame" scenarios set out by the agency, the former fast reactor complex has been levelled, apart from the dome.

However, the NDA said it saw no case for the dome's retention after the internal plant, fittings and equipment are stripped out.

Scottish regional director John Farquhar said he understood the historical and emotional case for keeping the landmark sphere, but added that his organisation must observe its remit to oversee the safe clean-up of the site.

He said: "The most prudent strategy radiologically is to arrange to dismantle it - to get rid of it."

Maintenance costs

Mr Farquhar said the Dounreay fast reactor, which ran from 1959 to 1977, handled some of the highest hazard material on the site.

The stainless steel sphere is contaminated with tritium, which is said to be notoriously hard to clean up.

Mr Farquhar said there was also evidence of corrosion to the structure.

If kept the shell would be costly to maintain, with painting it alone costing �250,000 every five years.

Mr Farquhar added that neither the NDA nor any other government body would pick up the bill associated with the sphere's retention beyond the site clean-up.