4.1.1 Gaseous and airborne waste treatment

Operations involving the handling of radioactive material may generate airborne radioactive contamination. The basic difference between airborne effluents and RAW in condensed (i. e., liquid or solid) phase is that airborne material has no definite volume and its dispersion in the environment is very fast. Gaseous and airborne wastes are discharged to the environment through ventilation and air-cleaning systems, which are a vital part of the general design of a nuclear facility [ 11-14] . The combination of a well — designed ventilation system with thorough cleaning of exhaust air is the main method of preventing radioactive contamination of the air in working areas and in the surrounding atmosphere. Ventilation and air-cleaning systems should provide efficient treatment of gaseous streams under normal operations, maintenance and accident conditions. High efficiency particu­late air (HEPA) filters are most commonly used for removal of radioactive particulates and aerosols from gaseous streams [12, 14]. Sorption beds charged with activated charcoal are common for removal of volatiles (e. g. iodine) and as delay beds for noble gases. Wet scrubbers are used for the removal of gaseous chemicals, particulates and aerosols from process off­gases. Additional components of the air-cleaning system include pre-filters, and temperature and humidity control systems, as well as monitoring equip­ment such as gauges that show pressure differentials. The treatment of gaseous streams results in secondary waste either solid (spent filters or sorption beds) or liquid (scrubbing solutions). The physical and chemical properties of the selected air-cleaning media should therefore be compat­ible with the treatment and conditioning processes for the solid or liquid waste streams in which they will be treated.