Diffusion of Some Critical Radionuclides in Mineral-Like Ceramic Materials

摘要

The diffusion coefficients and activation energy of diffusion of ~(22)Na, ~(90)Sr, ~(152)Eu, and ~(241)Am radionuclides in zirconolite ceramics prepared by cold crucible induction melting (CCIM), of ~(22)Na, ~(90)Sr, ~(137)Cs, ~(152)Eu, and ~(241)Am in Synroc-C ceramics prepared by hot pressing (HP) and CCIM, and of ~(22)Na and ~(152)Eu in the ceramic from the Lawrence Livermore National Laboratory (the United States), synthesized by cold pressing (CP) and sintering, and also the diffusion mobility of ~(90)Sr, ~(137)Cs, and ~(241)Am in the chromium-containing sphene glass ceramic prepared by CCIM were determined by the method of integral residual activity. In the temperature interval 573-923 K, the ~(22)Na radionuclide is the most mobile and ~(241)Am is the least mobile. The differences between the diffusion coefficients reach 4-5 orders of magnitude. The diffusion coefficients of the examined radionuclides in the ceramic depend both on the preparation procedure (HP, CP, or CCIM) and on the initial charge components when the same procedure is used for preparing the ceramic. Negative values of the activation entropy of the diffusion of ~(22)Na, ~(90)Sr, ~(152)Eu, and ~(241)Am in ceramics suggest that the mass transfer of radionuclides in them occurs not by the vacancy mechanism but by the interstitial mechanism and, probably, in part along the facilitated migration pathways (grain boundaries, pore surfaces, micro- and macrocracks).