Lessons learnt over 30 years of air filtration in the nuclear industry

The more than 30 years since the inception of the High Efficiency Particulate Air filters (HEPA) provide an incredible story. The filter's application to nuclear air cleaning and reciprocal effect on nuclear programme upon its development is even more interesting. The HEPA filter provided the capacity needed to intercept extremely small particulate matter in the airstreams of nuclear plants and laboratories. When some of the particulate matter potentially might be plutonium or other alpha radiation bearing particles in the air exhausted to the environment, the critical importance of the filter becomes obvious. From a crude and weak initial concept, the HEPA filter has developed into the backbone of particulate air cleaning for nuclear ends and has become most essential to environmental cleaning for other industrial pursuits as well. In the nuclear industry, High Efficiency Particulate Air filters (HEPA) were the need for the containment of radioactive aerosols within the nuclear facilities. Air filtration theory has been very important in the development of HEPA filters. The early air filtration theories model air filters as the air flow around single fibres and the particle capture by these single fibres. The single fibre theories included the interference effect of neighbouring fibres by using cell flow models. Equations were derived to describe particle capture efficiency as function of system variables (air flow temperature and pressure), particle variables (size, density...) and filter characteristics (fibre diameter, fibre volume fraction, filter thickness...).