Investigation of migration an actinide imitator (Ce) in synthesis glass ceramics with a nuclear microscope

Full text: The generally accepted conception of radioactive waste (RAW) safe disposal, so-called 'multibarrier strategy', assumes construction of several protective barriers in a geologic burial. One of these barriers is is a durable corrosion-resistant container of RAW. The glass ceramics (syntetic alumina silicate) is considered as promising material for such containers. An important parameter for long term reduction of behavior for such materials is rate of radionuclide emanation from the container. As an element whose migration in solids is analogous as that of actinide, one generally uses Cerium. For investigation of transuranium element migration Ce is used as an analogue. Accordingly, CeO2 may serve as an imitator of transuranium oxides. In the present work Ce migration in glass ceramics has been investigated with a nuclear microprobe which is more sensitive instrument than an electron microscope. The glass ceramic material was prepared from mixture of materials powders (70 % mas. of red granite and 30% mas. of kaolin) by sintering under pressure. The hot pressing was conducted at 1050 deg. temperature and 40 MPa pressure. The endurance time continued 15 min. Manufactured alumina silicate samples were in the form of a pellet. The material density was 2.5-2.7 g/cm3. Pellets of imitator substance were made of CeO2 powder by the same method. After polishing, aluminosilicate and imitator pellets were pressed together and annealed in the temperature range from 600 to 750 deg. C in vacuum during 10 hours. As a result of annealing, Ce penetration occurred thought the interface into the depth of the alumina silicate pellet. After that the pellets were separated, and the alumina silicate pellet was cleaved in the direction transversal to the former interface. The surface of cleavage of alumina silicate pellet was studied with a nuclear microprobe. For measurement of Ce diffusion distribution in alumina silicate samples we applied a nuclear microprobe on the basis of a magnetic quadrupole lenses doublet and an X-ray spectrometer were used. A 10 μm proton beam of 1.8 MeV energy and 2 nA current was applied. The X-ray spectra were measured with Ge(HPGe) detector with 155 eV energy resolution for the Mn Kα line. The profile of Ce distribution was measured by moving discretely the microprobe beam on cleavage of alumina silicate pellet in the direction from the former interface. The Ce concentration at the corresponding depth, counted from the interface surface, was determined by Ce Lβ line. The measurements showed that maximum Ce content in the alumina silicate matrix after the diffusion annealing was about 0.03 % mas. The depth of Ce penetration into matrix was about 130 μm. At the 150 μm depth the Ce content decreased to 0.003 % mas. that was the background level of Ce content in the alumina silicate