The aim of this paper is to fill the gap in data relating to local supply chains in the proximity of nuclear sites by investigating the site of Sellafield in West Cumbria, UK. Using information obtained from invoice data provided by Sellafield Ltd, the site-licenced company, and from primary research, the authors explore the relevance of nuclear procurement within the area, by evaluating levels of economic leakage and seepage resulting from suppliers’ subcontracting and work carried out locally. The study shows that the presence of a nuclear site has a crucial role for the surrounding area and for its economy. The results indicate a significant level of financial retention in the area with regard to work carried out in-house and local subcontracting at a first tier. In particular, the results identify cash flows related to second-tier suppliers located in West Cumbria, demonstrating that about a third of the total work carried out or subcontracted at the nuclear site stays in the area. These findings underline the significant impact of Sellafield on the West Cumbria economy and, more generally, provide an overview of the importance of nuclear sites for local supply chains in peripheral and remote areas.