Prefiltering devices for gaseous effluents from dismantling operations

Dismantling processes produce emissions of aerosols which can disseminate contamination in the cell where the cutting operation takes place, and in the ventilation ducts up to the HEPA filters, the last barrier before releases into the environment. Cutting processes, and mainly thermal ones, cause rapid plugging of HEPA filters because of the high concentrations of ultrafine particles produced. To increase the life of HEPA filters and thus to reduce the amount of solid wastes, an efficient cleanable prefiltering device is necessary. The object of this work was to select one or several cleaning devices, selection that can be done from the knowledge of the physico-chemical characteristics of the gas and aerosols to deal with, the range of the available cleaning devices and the implied facility. Thus, we: - collected data on secondary emissions produced by various cutting techniques of metallic structures and made complementary experimental studies. Underwater plasma cutting and especially the influence of water depth have been studied jointly with Heriot-Watt University (Edinburgh), -designed and built a prefiltration test rig, which has been used at Windscale, in cooperation with UKAEA, on a facility simulating the Advanced Gas Cooled Reactor in dismantling stage, in order to select an appropriate cleaning device, - made an assessment of a selected captation and prefiltration device by application to radioactive secondary emissions in an underwater plasma dismantling facility of the CEA/STEC of Cadarache. (author)