Long-term storage of Kr-85 in zeolite 5A

From experiments on the fixation of Ar, Kr and Xe in the temperature range 400 to 5500C and pressures between 100 and 2000 bar in zeolites of type A, it was discovered that, when the zeolite is exchanged with divalent cations (Mg, Ca and Sr), the encapsulated noble gas brings about a collapse of the crystalline structure (glassification or sintering.). This effect is essentially independent of the amount of gas sorbed. In addition, the zeolite containing trapped gas looses its ability to sorb H2O. CO2 and other gases. Since a reloading after desorption at elevated temperatures is not possible, it may be concluded that the alteration of crystal structure after encapsulation is permanent. The obtained product has remarkable properties with regard to the long-term storage of Kr-85, i.e. no significant gas leakage is apparent even after 8 month at 4500C, several days of storage under water or irradiation with γ-rays within the dose range 0.3-3.0x108 rad. Systematic experiments were carried out to optimize the encapsulation. In this context the effect of the cationic composition, the pretreatment, the fixation temperature, the fixation pressure, the type of noble gas, etc. was examined. The results indicate that an adequate loading (20 to 30 cm3 STP Kr/g) can be obtained at 5200C and pressures well below 500 bar. A further improvement can be achieved with a monolithic block (density increase by a factor of about 2). It was demonstrated that, instead of mechanical compression, cryogenic pumping followed by PVT compression can be employed for the encapsulation of Kr. The result is a simplified process with improved safety