The job of recovering the fissile material which accidentally spewed on to the floor of a shielded cell in September 2005 has been much tougher than initially envisaged.

A failure of management systems led to intermediate-level active liquid waste spilling over a steel drum after an automatic mechanism to release its lid failed to activate.

Before the flow was stemmed, 58 gallons had poured out, much of it mixing with a separate feed of cement powder.

The embarrassing blunder has been a major blot on the UKAEA's improving safety record at the Caithness site in recent years.

It has also halted operation at the plant where the highly-active liquor – viewed as the site's highest hazard – is cemented in drums before being put in long-term storage.

Those dealing with the clean-up initially envisaged having the plant back in action in the summer of last year at a cost of about £1 million.

But it has proved much trickier than anticipated.

The first phase, involving the extraction of the contaminated drum and pumping out material still in liquid form, was relatively straightforward.

The job to recover the spent fuel liquor which had drained into the sump below the cell and mixed with the powder was much more challenging.

This has involved extended-reach manipulator tools as well as personnel in airline suits going into the cell.

The clean-up team has also had to remove and replace the contaminated section of the conveyer belt on which the waste drums are moved.

A milestone was reached earlier this month with the removal of the solid aggregation of cement from the bottom of the four-feet-deep sump. Personnel are currently swabbing the area to remove remaining hot spots of contamination.

Site decommissioning manager Steve Beckitt, who has been overseeing the recovery operation, yesterday said the job has so far been completed without any significant incidents.

There has been a total of 1000 entries into the cell though no worker has been exposed to more than a tenth of the site's radiation limit.

There was a mishap in the summer when clean water accidentally spilled into the sump but it was quickly dealt with.

Mr Beckitt said: "We're close to getting the radiation levels in the cell down to where they need to be.

"We've also been busy with the all-important task of ensuring the paperwork and revised operating instructions are in place and all the operators are fully trained and familiar with the procedures."

Mr Beckitt said the electronics controlling drum-handling in the cell have been upgraded to ensure there can be no repeat of the spillage.

Subject to the approval of regulators, the UKAEA is gearing to have the £15 million cementation plant back up and running by May.

Before the spillage it had processed 1850 drums – comprising about a third of the site's stockpile of the liquid waste from historic reprocessing activities.

Mr Beckitt said the lengthy stoppage is not holding up the £3.6 billion clean-up of Dounreay.

He said: "It has not had an impact on the overall decommissioning programme. The plant was never on a critical pathway though we are keen to deal with the remaining intermediate liquid waste on the site as quickly as we can."

The spillage led to the Nuclear Installations Inspectorate serving enforcement notices on the UKAEA.

An internal UKAEA probe found there to be no single cause but a build-up of circumstances including poor communications, an over-reliance on automated controls and a tolerance of defects.

Four employees were suspended on full pay during the initial investigation but were later reinstated. No disciplinary proceedings were taken.

iain-grant@ukf.net

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