Diffusion of some critical radionuclides in mineral-like ceramic materials

Abstract

The diffusion coefficients and activation energy of diffusion of ²²Na, ⁹⁰Sr, ¹⁵²Eu, and ²⁴¹Am radionuclides in zirconolite ceramics prepared by cold crucible induction melting (CCIM), of ²²Na, ⁹⁰Sr, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am in Synroc-C ceramics prepared by hot pressing (HP) and CCIM, and of ²²Na and ¹⁵²Eu 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 ⁹⁰Sr, ¹³⁷Cs, and ²⁴¹Am 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 ²²Na radionuclide is the most mobile and ²⁴¹Am 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 ²²Na, ⁹⁰Sr, ¹⁵²Eu, and ²⁴¹Am 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).