Communities of nuclear workers have evolved in distinctive contexts. During the Manhattan Project the UK, USA and Canada collectively developed the first reactors, isotope separation plants and atomic bombs and, in the process, nurtured distinct cadres of specialist workers. Their later workplaces were often inherited from wartime facilities, or built anew at isolated locations. For a decade, nuclear specialists were segregated and cossetted to gestate practical expertise. At Oak Ridge Tennessee, for example, the informal ‘Clinch College of Nuclear Knowledge’ aimed (...) to industrialise the use of radioactive materials. ‘We were like children in a toy factory’, said its Director: ‘everyone could play the game of designing new nuclear power piles’. His counterpart at Chalk River, Ontario headed a project ‘completely Canadian in every respect’, while the head of the British project chose the remote Dounreay site in northern Scotland because of design uncertainties in the experimental breeder reactor. With the decline of secrecy during the mid-1950s, the hidden specialists lauded as ‘atomic scientists’ gradually became visible as new breeds of engineers, technologists and technicians responsible for nuclear reactors and power plants. Mutated by their different political contexts, occupational categories, labour affiliations, professional representations and popular depictions, their activities were disputed by distinct audiences. This chapter examines the changing identities of nuclear specialists and the significance of their secure sites. Shaped successively by Cold War secrecy, commercial competition and terrorist threats, nuclear energy remained out of site for wider publics and most nuclear specialists alike. The distinctive episodes reveal the changing working experiences of technical workers in late-twentieth and early twenty-first century environments. (shrink)