associated facilities cost £15million to build in late 1950s money (equivalent to £370million in 2021). It was designed to generate 60MW thermal power and achieve a 2% fuel burn up. It reached 30MWt in August 1962, and 60MWt in July 1963 allowing it to produce its rated 14MWe (electrical). The reactor was surrounded by a steel sphere, still a prominent feature of the landscape, which was constructed by the Motherwell Bridge Company. DFR was a loop-type FBR cooled by primary and secondary NaK circuits, with 24 primary coolant loops. The reactor core was initially fuelled with uranium metal fuel stabilised with molybdenum and clad in niobium. The core was later used to test oxide fuels for PFR and provide experimental space to support overseas fast reactor fuel and materials development programmes. It had over 5,000 breeder elements of natural uranium in stainless steel arranged in an inner and outer breeder sections. Many were replaced in 1965. Prototype Fast Reactor (PFR) The third and final UKAEA-operated reactor to be built on the Dounreay site was the Prototype Fast Reactor (PFR). In 1966, it was announced that the PFR would be built at Dounreay. PFR was a pool-type fast breeder reactor, cooled by 1,500tonnes of liquid sodium and fueled with MOX. The design output of PFR was 250MWe (electrical). It achieved criticality in 1974 and began supplying National Grid power in January 1975. There were many delays and reliability problems before reaching full power. It had three cooling circuits. Leaks in the sodium water steam generators shutdown one and then two of the cooling circuits in 1974 and 1975. By August 1976 it had reached 500MWt, (to produce about 166 MWe) and in 1985 it first reached its design output of 250MWe. In 1988, it was announced that funding for FBR research was being cut from £105million to £10million per year, and the PFR funding would end in 1994. The reactor was taken offline in 1994, marking the end of nuclear power generation at the site. It had supplied 9,250GWh in all. The lifetime load factor recorded by the IAEA was 26.9%. The control panel for the reactor was earmarked for an exhibition on the reactor at the London Science Museum in 2016. Subsequent activity Since the reactors have all been shut down, care and maintenance of old plant and decommissioning activities have meant that Dounreay has still retained a large workforce.