United States Patent im [in 3,13,439 Stein [45] Aug. 27, 1974 [54] ATMOSPHERE PURIFICATION OF XENON, 3,377,136 4/1968 Morrow 423/262 RADON & RADON DAUGHTER ELEMENTS 3,778,499 12/1973 Stein 423/210 3,784,674 1/1974 Stein 423/210 X [75] Inventor: Lawrence Stein, Downers Grove, 111. [73] Assignee: The United States of America as Primary Examiner—Earl C. Thomas represented by the United States Attorney, Agent, or Firm—John A. Horan; Arthur A. Atomic Energy Commission, Churm; James W. Weinberger Washington, D.C. [22] Filed: Mar. 27, 1973 [57] ABSTRACT [21] Appl. No.: 345,419 A method of purifying an atmosphere of xenon, radon and radon daughter elements by passing the atmo- [52] U.S. CI 423/210, 423/249, 423/262, sphere containing these elements through a reaction 423/472, 176/37, 252/301.1 R bed of dioxygenyl hexafluoroantimonate, which oxi- [51] Int. CI BOld 53/34 dizes the xenon, radon and radon daughter elements [58] Field of Search 423/210, 262, 472, 249; to their respective fluorides which remain in the reac- tion bed and are thus removed from the atmosphere, 176/37; 252/301.1 R, 301.1 W and recirculating the purified atmosphere. The [56] References Cited method is also useful for separating the before-named elements from krypton. UNITED STATES PATENTS 3,185,548 5/1965 Fields et al 423/262 9 Claims, No Drawings 3,829,551 1 2 ATMOSPHERE PURIFICATION OF XENON, Radioactive noble gases are also found in the atmo- RADON & RADON DAUGHTER ELEMENTS spheres of nuclear reactor power facilities and nuclear reactor fuel reprocessing facilities. These gases gener- alI rnwTDAPTHAi nDirtK, ncTUc iw„cMTinM y consist of a number of isotopeP s of krypton and CONTRACTUAL ORIGIN OF THE INVENTION $ xe^on and range in half.,ife from sec0nds to years. The invention described herein was made in the Many of the krypton and xenon isotopes which have course of, or under, a contract with the UNITED short half-lives have radioactive daughter elements STATES ATOMIC ENERGY COMMISSION. having relatively long half-lives. In a boiling water reac- tor, the fission gases which have entered the water in BACKGROUND OF THE INVENTION 10 the reactor, either by diffusion through the fuel clad- This invention relates to a method for purifying an ding or through breaks in the cladding, are released at atmosphere of xenon, radon and radon daughter ele- the exit of the turbine condenser. These gases are nor- ments which may be contained therein and for the sep- mally discharged to the atmosphere after a short delay aration of these elements from krypton. time. In the pressurized water reactor, the gases are re- Radon is a heavy, radioactive, gaseous element 15 moved in the coolant loop and are stored for periods up formed by the alpha disintegration of radium. The most to months to eliminate the short-lived gases by radioac- common isotope, 222Rn, is an alpha emitter with a half- tive decay. In each case, the quantity of fission gas life of 3.8 days. Radon is inherently associated with ra- eventually released to the atmosphere depends upon dium in uranium ores and, with its short-lived radioac- the condition of the reactor fuel, and emissions could tive daughters, 2l8Po, 214Pb, 214Bi, and 214Po, constitutes 20 be increased greatly in the event of an accident such as a potential health hazard in uranium mining and ore- a fuel meltdown. Emissions from liquid-metal-cooled handling operations. The daughter elements are solids reactors, breeder reactors, and high-temperature-gas- and tend to be retained in the lungs, where they may cooled reactors will arise from the same general source ultimately cause cancer. but will vary as to nature and quantity from those ema- Forced ventilation is generally used to lower concen- 25 nating from light-water reactors, trations of the radioactive elements in the atmosphere Industrial sources of non-fission-product krypton and of a uranium mine, but it is often difficult to lower the xenon are liquid-air plants. Air contains only 1.14 ppm concentrations adequately in all parts of a mine by this krypton and 0.087 ppm xenon. The cost of obtaining method, since the gaseous radon diffuses continuously noble gases from liquidair plants is therefore high and from exposed veins of uranium ore and from piles of 30 the supply, particularly of xenon, is limited. Various the broken ore. methods have been developed for the treatment of Several methods have been developed for the re- these gaseous reactor wastes and the recovery of the moval of radon and its daughter elements from the at- fission product noble gases. Fixed adsorption beds have mosphere by contacting the atmosphere with various been used in a number of applications for the removal chemicals capable of reacting with the elements to re- ^5 Qf radioactive noble gases from dilute gas streams at move them from the atmosphere. room temperature. These adsorption beds may be ei- One of these methods uses a fluorinating solution to ther charcoal or molecular sieve. The advantages of the oxidize the radon and daughter elements to fluoride room temperature adsorption process are that it is sim- compounds which then dissolve in the solution. How- pie to operate and will accept very dilute feed material, ever, liquid fluorinating solutions pose several prob- 40 Disadvantages are the large volume of adsorbent re- lems. The liquids are highly corrosive and, in some in- quired and the potential fire hazard with charcoal. A stances, have high vapor pressures. Corrosionresistant low-temperature charcoal process can also be used for equipment is therefore required for contacting large noble gas recovery. It has the disadvantages of high op- volumes of air with the liquid phase. Additional equip- erating cost, requires pretreatment of the inlet gas to ment is also necessary to further purify the atmosphere 45 beds, and also requires extensive liquid nitrogen pro- (i.e., to remove any hazardous vapors picked up from duction capabilities and a steady flow and constant the fluorinating solution) before the atmosphere is re- composition of incoming feed gas. Low-temperature circulated. In another method, the atmosphere contain- adsorption beds are similar to room-temperature beds ing the radon and radon daughter elements is passed but are much smaller in size, since the noble gas capac- through a solid reaction bed of a fluorinating com- ity of adsorbents increases markedly as the bed temper- pound, as disclosed in applicant's copending applica- ature approaches liquid nitrogen temperature. Halo- tion Ser. No. 179,229 (70), filed Sept. 9, 1971. In this carbon solvents such as Freon have also been used for method, the elements are oxidized by the fluorinating selective adsorption of krypton and xenon. This compound to their respective fluorides and remain in 55 method utilizes the high solubility of krypton and the reaction bed; they are thus removed from the atmo- xenon in the solvent. In a continuous adsorption pro- sphere, which may then be recirculated. The fluorinat- cess, krypton and xenon are preferentially removed ing compounds disclosed therein are complex fluorides from an incoming gas stream by selective dissolution in formed by reaction of halogen fluorides and metal fluo- a Freon solvent at relatively low temperature and high rides such as ClF2SbF6, BrF2SbF6, BrF4SbFu, IF4 SbF6, 6Q pressure. and Br2BiF6. One problem with the use of the solid re- The recovery of xenon and krypton by treating gase- action compounds is that they release halogen fluoride ous radioactive wastes with fluorine is described in an vapors as reduction products in their reactions with ra- article entitled "Recovery of Xenon and Krypton in the don. These must be removed from the radon-free atmo- Treatment of Gaseous Radioactive Wastes" by J. Sliv- sphere before it can be recirculated. This removal re- 65 nik, Proceedings of Symposium on Treatment of Air- quires additional equipment and adds to the over-all borne Radioactive Wastes, Int. At. Energ. Agency, Vi- cost of radon and radon daughter element removal enna, 1968, pp. 315-321. In this study, an attempt was from the atmosphere. made to react xenon and krypton with fluorine at high 3,829,551 3 4 pressures and elevated temperatures. It was found that, thesis of Dioxygenyl Salts," Shamir and Binenboym, while the xenon would react with the fluorine, krypton Inorganica Chimica Acta, 2, 37, March 1968. The prod- would not, which permitted the separation of xenon uct obtained by photochemical reaction of oxygen, flu- from the krypton. However, fluorine is not a conve- orine and antimony pentafluoride is a white, crystalline nient reagent for this purpose, as it must be heated with 5 powder. the process gas and the excess fluorine must be re- The method of this invention is operable at tempera- moved afterwards. tures from about 0°C. to about 125°C., above which SUMMARY OF THE INVENTION temperature 02SbF„ begins to decompose. At these temperatures, the xenon, radon and radon daughter el- I have found a method for purifying an atmosphere 10 ements will react immediately with the hexafluoroanti- of xenon, radon and radon daughter elements by pass- monate compound. No reaction of krypton at 485 to ing the atmosphere containing these elements through 70Q mm pressure was observed from 23° to 150°C. a reaction bed of 02SbF6, whereby the xenon radon ,n the method of thjs invention> the atmosphere to be and radon daughter elements are oxidized to their re- fied .g d th h a reaction bed Qf Q SbFs in spective fluorides, which remain on the bed and are ° , , , .£. , . , n , , .