They had to cancel a previous bid competition to deliver the £120m Box Encapsulation Plant Product Store and Direct Import Facility earlier this month after failing to attract sufficient interest.

One contractor told the Enquirer: “There have been several challenges on other jobs, particularly Laing O’Rourke’s Encapsulated Product Store 3, which is running four years late.

“The procurement problem is of Sellafield’s own making. This is causing other contractors to be reluctant to repeat Laing O’Rourke’s experience.”

Now small teams of contractors are being invited to look around the half-finished project ahead of Sellafield deciding on how to handle another bid race.

The “Big Box” project to encapsulate intermediate level waste in cement for above ground storage at the site has suffered a chequered history.

A Jacobs, Atkins and Carillion joint venture started work on the project back in 1997.

But the job was halted in 2002, due to technical uncertainties, and the partially completed on-site facilities put in mothballs.

After a project rethink in 2010 Balfour Beatty in joint venture with Babcock secured the early contractor engagement phase of the Box Encapsulation Plant Product Store and Comprehensive Import Export Facility, as the waste store project became known.

Following another strategic review in the face of rising costs, Sellafield bosses decided to cancel this planned expansion and replace it with an alternative simpler facility known as the BEPPS and Direct Import Facility, which formally went to prequalification stage before being cancelled because of insufficient interest.

Firms wishing to visit the site will be allowed a maximum of three staff and should in the first instance contact Kate Woodend  or Michele Burns. Security clearance will be required for any person looking to attend the site visit so emails need to be sent by 25 November.