FILTERED VENTING FOR GERMAN POWER-REACTORS

Light water reactors in the Federal Republic of Germany are being retrofitted with venting filters for use after serious reactor accidents. Deep-bed stainless steel fiber filters remove droplets and particles as well as high-efficiency particulate air filters. The deep-bed stainless steel fiber filters consist of two layers of fleece. The fiber diameter decreases gradually from 30 to 2 μm in the direction of flow. In addition to its high removal efficiency, its resistance to extreme loads, and its high dust loading capacity, the filter is important because it completely separates droplets. Even after 130 h of spraying with fine (2- to 5-μm-diam) droplets, a maximum increase in differential pressure of only 3 mbars was measured. No penetrating water was detected on the downstream side. Even at a flow of more than twice the recommended rate, the removal efficiency only dropped from ≥99.99 to approximately 99.95%. An iodine filter can also be installed in each of the venting filters. Iodine experiments were conducted to determine the design of the iodine filter. The data obtained in experimental work using special silver zeolites are reported.