Dounreay Site Restoration Ltd

Experimental criticality laboratory

For six years, at the height of Britain's expansion into nuclear energy in the 1950s and 60s, the experimental criticality laboratory carried out vital research.

A series of experiments with plutonium and uranium liquids provided invaluable data that helped to shape Britain’s nuclear production facilities for generations to come.

At the height of the Cold War, the priority was to secure Britain’s place in the world as a nuclear power. Decommissioning wasn’t important.

So when the laboratory became redundant in 1967, the door to the most hazardous area of the facility was locked and its radioactive legacy allowed to decay for the next 30 years.

As the facility deteriorated and more radioactive junk accumulated, its worsening reputation lead some to believe it could never be decommissioned safely.

Today, after an eight-year clean-up and some 25,000 separate clean-out shifts by staff working in difficult and uncomfortable conditions, the legacy has safely gone and little evidence now remains of this once historic site.

Few stories illustrate more vividly how attitudes towards decommissioning have changed than the experimental criticality laboratory at Dounreay.

The 1946 McMahon Act passed by the United States effectively destroyed collaboration between Britain and the USA on atomic research at an important time in the development of the UK’s civil and military programmes.

The ban on information sharing in the late 1940s was a setback to British ambitions of becoming a nuclear superpower.
It forced British engineers and scientists to rely on calculated estimates when developing plutonium and uranium production plants that had to be economical and efficient while “safe beyond all possibility of error” from an accidental chain reaction.

Their calculations contained too many uncertainties and by the early 1950s Britain realised it had to scale up its own experiments on the criticality of plutonium and uranium to validate their thinking.

In 1954, while planning was underway for the fast reactor experiment at Dounreay, an area of unallocated land at the eastern edge of the site was chosen for a British experimental criticality laboratory.

Four cells – three for uranium and one for plutonium – were built between 1956 and 1959 and fitted with experimental reactors and rigs in a complex of buildings.

The first experiment using uranium in solution went critical on August 13, 1957. This was the first nuclear reaction to take place in Scotland. Over the next six years, a series of experiments yielded valuable information about the behaviour of uranium and plutonium.

The rigs were known by their acronyms - ZETR, TESSIE, PUMA, PANTHER, SIRIUS, PHOENIX, and TOAD.

When the experiments finished in 1963, the uranium cells (known as D1249) were cleaned out and converted to a test facility for sodium while the plutonium building (D8550) was retained in case more experiments were needed.

Early attempts to clean up contaminated areas of the plutonium building resulted in a number of incidents that, looking back, seem to have made the problem worse. In 1967, the facility was deemed redundant and a decision taken to seal up what was left inside.

Archive records reveal the view of site management in March 1967. There was “no incentive for costly decontamination" and “the building should be made safe at minimum cost”. Access to the most contaminated areas – the shielded cell where the reactions occurred and an adjoining room where the plutonium was prepared – “should be permanently barred”.

Other radioactive junk accumulated in the building during the 1970s and 1980s while clean areas were converted to a training and conference centre and an apprentice training school. In 1987, the first serious attempt started to decommission the building but this came to a halt in 1994 when the fast reactor programme was being wound up on the rest of the site.

In 1999, following the decision to close down Dounreay, one of the facilities identified for early decommissioning was the plutonium criticality laboratory. The facility was still heavily contaminated, so workers who entered the building to begin dismantling the remaining test rigs and clean up the contamination all around had to wear full airline suits to protect them from any airborne radioactivity.

The cell was lined with 300 sq m of steel plate that had to be decontaminated and cut up. Large steel handling equipment and lifting frames were taken apart and the heavy airtight door to the cell was turned into waste. A13mm thick steel pressure vessel, which enveloped the cell, had to cut up, all of it by workers wearing uncomfortable but essential protective equipment.

By 2002, parts of the building could be entered without respiratory equipment for the first time in 40 years.

In 2008, the whole building was declared safe from the hazard of plutonium and it became possible to walk through it without respiratory protection. It had taken staff some 25,000 individual entries wearing respirators or fully protective airline suits since 2000 to decommission D8550.

“The reputation of D8550 as a place that was so dirty that some people thought it could never be cleaned up safely was at the forefront of our minds from the very start,” said Steve Beckitt, decommissioning project manager. “We recognised the hazard was extensive throughout the building, we planned for it and we took no risks with the safety of those workers who went inside to clean it up.

“In total, the team made some 20,000 entries wearing full airline suits or, latterly, respirators. None of them received any significant radiation dose. We had one lost-time accident when a worker bumped her head on a beam. It was a thoroughly professional job that the whole team – DSRL, Doosan Babcock, NDSL and Nuvia – are justifiably proud of.

“For me, the successful and safe completion of this job sends out two strong messages. From a site perspective, it demonstrates the quality of decommissioning skills we have built up. And from an industry perspective, it underlines the importance of decommissioning plant as soon as it becomes redundant instead of walking away for decades and allowing the liability to get worse.”

The D1249 complex that was converted to a sodium test facility in the 1960s was razed to the ground between 2001 and 2005. The D8550 complex was demolished in 2009.

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