Patent GB-1041800-A (GB)
Title: Method of reducing the radioactive contamination of gases containing radioactive impurities and apparatus for use therein
IPC: G21F9/02
Filed: 1963-08-08
Abstract: 1,041,800. Processing radioactive waste; nuclear reactors. LINDE A.G. Aug. 8, 1963 [Aug. 14, 1962], No. 31277/63. Headings G6C and G6R. The radioactive contamination of a gas containing radioactive impurities is reduced by passing it through one or more flow-retarding devices until its radioactivity has declined to the required level. The gas may be passed through an adsorber, preferably at low temperature, of appropriate size and alternatively, or in addition, the gas may be liquefied and passed through a container provided with flowretarding devices, this particularly commending itself if the adsorbers required for retaining the gas would be too large. A plant designed for the decontamination of air which may have entered the system of a boiling water reactor where it has become contaminated with radioactive gases, and which is to be discharged into the atmosphere at a safe level of radioactivity, is described with reference to Fig. 1. The same plant can also be used for the decontamination of gases circulating in nuclear reactors. The air is led by a pipe 1 and a compressor 2 to a water-cooler 3 and a countercurrent heat exchanger 7 in which it is cooled to about 0‹ C., the condensate-principally water-being discharged from separators 4, 9 and the air led through a pipe 11 to one (12a for example) of two alternately operable regenerators 12a, 12b where the temperature is reduced to about 105‹ K for the removal of further condensable impurities, e.g. CO2, and on through a pipe 13 to a flow-retarding adsorber 14. This comprises an assembly of serially connected tubes 15 filled with silica gel and housed within a casing 16 along with a countercurrent heat exchanger 17 for further cooling the air. The retention time in this adsorber is about 40 days for Xe and 2 days for Kr. The air is then taken through a pipe 18 to an evaporator-condenser 19 where it is liquefied by heat exchange with evaporating liquid air, the radioactivity of which has already been reduced, before being conducted through a pipe 20 to a continuous flow storage vessel 21. This comprises a jacket 22 containing tubes 23 which are packed with a flow-retarding packing for the purpose of impeding convection, the liquid being introduced into the bottom ends of the tubes and taking about 1 day to pass through while the radioactive argon present decays to the required level. The liquid leaves a pipe 24 and is evaporated in the head of the evaporator-condenser 19 by heat exchange with the condensing radioactive air, the gas thus formed being returned through the heat exchanger 17 and the casing 16 of the adsorber 14 whence a pipe 27 conducts it back to the regenerator 12b where it is warmed and entrains the deposited impurities before it is transferred through a pipe 28 to the heat exchanger 7 and through a pipe 29 into the waste air discharging system. An alternative embodiment (Fig. 2, not shown), is described in which no regenerators are used and in which the evaporator-condenser and the continuous flow storage vessel are combined in a single structural unit.