Patent Number: 044249039
Section: summary

This invention concerns a process for storing tritium, especially tritium wastes from nuclear power plants, and equipment for the implementation of this method. The long-term storage of radioactive materials, in particular wastes from nuclear power plants, requires compliance with strict safety demands. It is necessary for instance to enclose the materials in containers of the lowest possible permeation rates and with the highest possible tightness at the closure sites. The container material furthermore must evince high mechanical strength, high reliability to pressure and incombustibility or fire-retardant properties. If the containers are for the purpose of final storage, they must be optimally protected against the effects of corrosion as well. This corrosion protection must be comprehensive as the possible final deposition sites are not yet known individually today. Heretofore tritium has been cast in concrete for the purpose of final storage. This is permissible, however, only up to amounts of 10 millicuries due to the properties of concrete. Therefore the elimination of substantial amounts of tritium is very costly. This condition may assume significance when the technology of fusion shall have progressed, as it requires tritium. The object of the invention is therefore to provide a process by means of which tritium and substances containing tritium can be reliably stored in problem-free manner and be recovered at any arbitrary time. This problem is solved by the invention in that the tritium is oxidized to HTO or T.sub.2 O bound to an adsorbing agent having molecular sieve properties, and then enclosing this adsorbent in a corrosion-proof metal container impervious to hydrogen diffusion. Using this process, even substantial amounts of tritium can be relatively safely stored. An especial advantage is that tritium can be recovered in a simple manner. The tritium oxidation can be carried out for instance by oxidzing HT or of tritiated organic compounds on heated cupric oxide. The oxidized tritium can be easily bound to the adsorbent in a dry inert gas atmosphere. Appropriate inert gases include dry air, nitrogen or argon. The inert gas can be used in the same manner also in the recovery of the tritium. The equipment of the invention to store the tritium is characterized by a metal container hermetic to hydrogen diffusion, wherein a molecular sieve, loaded with tritium in the form of HTO or T.sub.2 O and surrounded by a filler is enclosed. Zeolites are contained in an envelope in the molecular sieve and for the purpose of the present application evince the highest possible selectivity for water vapor and a high thermal stability in the loaded state to above 300.degree. C. Other natural or synthetic molecular sieves may also be used. The container may consist for instance of pure aluminum, titanium or high-grade steel, as these metals are especially hermetic with respect to hydrogen diffusion and furthermore are corrosion-proof. Pure aluminum in particular is well suited, as it evinces a very low permeation rate for HT, a high flexibility and hence low risk of rupture, an insensitivity to radiolysis, incombustibility, and insensitivity to water on account of the formation of a cohesive aluminum oxide layer which should be 50 to 60 .ANG.. This layer can be made thicker by anodic oxdiation to 5 to 6 microns, thereby achieving additional inhibition of permeation. To achieve reliable and completely tight sealing, the container should be provided with a blind flange or be welded. Welding preferably is carried out by electron beams in a vacuum. The cavity so created offers high reliability with respect to pressure increase inside due to radiolysis or dissociation of gases at high temperatures. A possible additional safety measure may consist in jacketing the container with glass-fiber reinforced plastics, for instance resins of polyester, phenol or epoxy, or with material of the kind utilized in making heat-shields for space capsules (ablative compounds). Thereby the mechanical strength is increased further and the resistance to corrosive liquids or gases is still further improved. A cartridge of pure aluminum should enclose the molecular sieve. The cartridge also may be provided with an aluminum oxide layer 50 to 60 .ANG. thick, and where appropriate with an anodic oxidation coating. Quick-connect seals of a known type are used to fill the cartridge. These seals are so designed that they will automatically open only when connecting means adapted thereto are mounted on them. Otherwise they will be sealed in vacuum-tight manner, so that there is no danger of contamination. Moreover they can be opened anytime without risk of contamination, for instance to dilute the tritium to a lesser specific final storage activity or to withdraw it in controlled manner by passing through it a flow of an inert gas. When passing a flow of inert gas through it, the amount and the concentration of the tritium can be controlled by setting a selected temperature in the range from -190.degree. to +300.degree. C. The amount withdrawn can be precisely metered as desired. It is possible also to enclose more than one molecular sieve in one container. In such a case it will be appropriate to provide references sites of rupture in the region between the seives so these can be removed individually. The remaining molecular sieves then remain encased and can be stored again. Another feature of the invention provides that the filler consist of a plastic, for instance a resin of polyester, epoxy or phenol, and/or of plaster and/or cement. These materials, especially the last three cited, do not promote or sustain combustion. In addition, a wax partition should be provided between the molecular sieve and the filler. Due to the softer consistency of the wax, the molecular sieve, especially when provided with quick-connect seals will be protected against damage if there is subsequent opening, since the partition wax prevents a direct combining with the filler. Both the filler and the wax may absorb slight amounts of tritium that remained adhering at the closure means of the cartridge during the process. Due to the varied chemical corrosion possible, the multilayer design provides optimal protection against external corrosion. A plurality of the containers according to the invention may also be housed within 200-liter waste containers, which then are filled with concrete and moved to the final storage site, for instance a salt mine.