BNFL owns and operates the UK’s principal solid Low Level Radioactive Waste disposal site at Drigg in Cumbria, north west England. Drigg has been receiving waste since 1959 with approximately 900,000 m3 of waste disposed of to date. Waste accepted for disposal at Drigg comes in a variety of forms including rubble, spoil, redundant equipment, scrap and process waste, and typically contains significant metallic and cellulosic components. The organic content of the waste means that microbial activity plays a significant role in the development of the repository environment. Consequently, microbial processes are integrated into many aspects of the Drigg Post-Closure Radiological Safety Assessment (PCRSA). This begins with the identification and screening of relevant features, events and processes, through supporting research, engineering designs and finally integration into radiological safety assessment modelling. This paper outlines how and where microbiology is integrated into the Drigg PCRSA and indicates areas of active research.