A dose reconstruction case study - the retrospective assessment of neutron dose for workers on the Windscale Piles at Sellafield

The Windscale Piles were air-cooled reactors which started operation in 1951 to irradiate natural uranium fuel elements. It is now nearly 40 years since the Windscale Piles ceased operation after a fire during the release of Wigner energy in Reactor 1 on 10 October 1957. The spotlight returned to the Windscale Piles during the recent childhood leukaemia cases because the two fathers concerned worked there during the 1950s. Operators working on the Piles wore film badges and QFEs, but no suitable personal neutron dosemeter was available at that time and no neutron doses were entered onto dose records. For the purposes of litigation, a major dose reconstruction exercise was carried out to retrospectively assess the likely neutron doses received by the two individuals. The paper describes the main steps and processes required to carry out the reconstruction exercise. Within the overall exercise, two technical aspects required particular attention. Firstly, expert interpretation was used to convert contemporary survey measurements into useable data requiring some knowledge of the neutron spectrum and the capabilities of the early neutron instruments. Secondly, it was necessary to model the reactors to predict neutron dose rates for key scenarios identified in the dose reconstruction process for which archive survey information was not located. Finally, the methodology used to convert the survey data and model predictions into neutron doses for the individuals concerned is discussed and contrasted with other potential approaches. (author)