Dounreay's plutonium criticality research facility, D8550, comprised plutonium contaminated equipment within grossly contaminated, highly shielded structures. It owed its existence to the passing of the McMahon Act in the US in 1946, which effectively ended collaboration between the UK and the US in nuclear energy. Because experimental data gathered in the US on uranium and plutonium criticality was unavailable to the UK, a new experimental complex was built at Dounreay to carry out a major programme of criticality experiments on uranium and plutonium-bearing materials for the benefit of the UK nuclear industry as a whole. Criticality in D8550 was first reached in November 1960.

Despite suggestions in the past that a building like D8550 plutonium criticality facility could never be decontaminated, this decommissioning project shows that even the most contaminated of areas can
now be decommissioned safely and efficiently.