Krypton recovery

Kr, a 10-year half-life krypton isotope, is currently released from reprocessing plants to the atmosphere. There will probably be no urgent need in terms of radiation dose to the local population to retain Kr. However, in view of a worldwide accumulation of Kr in the atmosphere, krypton recovery from reprocessing plants is required or will be required in the near future. 

The latest of three ethylene recovery plants was started in 1991. Sasol sold almost 300,000 t of ethylene in 1992. Sasol also produces polypropylene at Secunda from propylene produced at Sasol Two. In 1992 Sasol started constmction of a linear alpha olefin plant at Secunda to be completed in 1994 (40). Initial production is expected to be 100,000 t/yr pentene and hexene. Sasol also has a project under constmction to extract and purify krypton and xenon from the air separation plants at Sasol Two. Other potential new products under consideration at Sasol are acrylonitrile, acetic acid, acetates, and alkylamines. 

Off-Gas Treatment. Before the advent of the shear, the gases released from the spent fuel were mixed with the entire dissolver off-gas flow. Newer shear designs contain the fission gases and provide the opportunity for more efficient treatment. The gaseous fission products krypton and xenon are chemically inert and are released into the off-gas system as soon as the fuel cladding is breached. Efficient recovery of these isotopes requires capture at the point of release, before dilution with large quantities of air. Two processes have been developed, a cryogenic distillation and a Freon absorption. 

Air separation industry, U.S., 27 754 Air-separation plants, 27 359, 750-751 Air-separation units, krypton and xenon recovery from, 2 7 362 Air-slaked lime, 15 26 Air slaking, 25 43 Air sparging... 

Krypton and Xenon are valuable gases present in very low concentrations in air. U.S. 6,662,593 assigned to Air Products describes a cryogenic distillation process for air separation with recovery of a stream concentrated in Kypton and Xenon. What would be the cost of producing purified Krypton and Xenon by this method Consider reactive methods for separating Krypton and Xenon from the concentrated stream as well as the methods suggested in the patent. 

Steinberg, M. The Recovery of Fission Product Xenon and Krypton by Absorption Processes, Report BNU542, 1959. 

Fig. 2. Temperature dependence of krypton Kr release from a corundum single crystal treated by ion bombardment 10 ionscm . The peak corresponds to the inert gas release accompanying the recovery of the metamict amorphous layer produced by the ion beam treatment of the sample surface...

Concentration and Recovery of Krypton Kr-85 has a half-life of the radioactive decay of 10.7 yr and is produced by both natural and man-made sources. The natural sources include the interaction of cosmic rays with stable isotopes of Kr in the atmosphere. The man-made Kr-85 is principally produced during the fission reactions in LWR or during nuclear atmospheric tests it is also released from nuclear-fuel reprocessing activities. Due to its atmophile nature, most Kr (>98%) resides in the atmosphere and becomes isoto-pically well mixed within a few years (Yokochi, ITeraty, and Sturchio, 2008). There are no... 

The cryogenic fractional distillation of large quantities of atmospheric air is the only practical means available for acquiring the rare gases krypton, neon, and xenon. The recovery of crude rare gases is accomplished in multiple cryogenic fractional distillation columns and... 

If, in addition, krypton, xenon or neon are produced, analytics will extend considerably (see Section 3.5). Due to the presently increasing size ofOj-produdng air separation units a krypton/xenon recovery is more and more of economical interest. Actually many Linde plants are equipped with such krypton/xenon-enrichment columns which are integrated in the main cold box and thus belonging to the main air separation unit. The enriched noble gas containing liquid is continuously directed to a tank and from there often shipped by road tank cars to a Kr/Xe-purification unit for further refurbishment... 

For smaller samples in which the rare gas partial pressures are higher over the possibility that a large fraction of the xenon may originally be condensed in at -195 C should he noted. (It seldom happens that this occurs with krypton since its vapor pressure is higher (2-3 mm Hg) at -195 C, but partial pressure of krypton over the trap should also be considered with each sample). If this occurs and one wishes quantitative recovery of the xenon one could distill xenon to before starting the elution from C. It is usually more convenient to recover the xenon from and separately however. 

The procedure described in this paper is for the recovery of fission product krypton from kilogram amounts of irradiated uranium-metal. A brief description of the operations involved is given below to point out methods which maybe applicable to smaller scale e3q>eriments. 

Recovery and purification subsystems for krypton and xenon are shown in Figs. 6.35 and 6.36, respectively. An auxiliary condenser-reboiler is used to evaporate some of the oxygen from the liquid oxygen-krypton-xenon stream removed from the main condenser-reboiler. Nitrogen gas from the lower column furnishes the heat for evaporation. To minimize explosion hazards, the presence of all hydrocarbons, especially acetylene ice, must be avoided in the oxygen mixture. The oxygen-krypton-xenon mixture from the condenser-reboiler is sent to a small stripping column where the krypton and xenon are further concentrated. 

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