Modeling and analysis of tritium behavior in ceramic breeder single crystal and beryllium in fusion blanket applications

摘要

Tritium transport and release is an important issue for both ceramic breeders and beryllium multiplier in fusion blanket. In order to address this issue, a thorough understanding of the mechanisms of tritium transport is required. For ceramic breeders, basic studies on the tritium behavior in single crystal will help understand the overall behavior in the solid breeders. Simple diffusion/desorption models have been suggested for tritium release from a solid breeder single crystal and beryllium. However, they were found not to adequately reproduce recent tritium release data for LiAlO$sb2$ single crystal and beryllium, indicating the need for a more comprehensive model.;The objectives of this work are: (1) to develop models for better characterization and understanding of tritium transport and release mechanisms in a single crystal ceramic breeder and in beryllium, and (2) to use such models to analyze the tritium release experimental data in order to help estimate fundamental properties to be used in blanket tritium analysis.;The model developed in this work for solid breeder single crystal, MISTRAL-SC, incorporates bulk diffusion as well as the four major surface processes and allows for the variation of surface activation energies with coverage and for the presence of H$sb2$ in the purge. Based on the analysis of experimental data, the four major surface processes were found to be important release mechanisms. The diffusion coefficient for LiAlO$sb2$ was determined by matching the modeling results to the experimental data. Also, a new model for tritium release from Be, BETTY, has been developed to analyze the recent tritium release data from high density and porous Be. The model includes diffusion through Be and BeO, surface processes and diffusion through inter-connected porosity (as-fabricated or radiation-induced). Due to the lack of property data for different surface processes, only second order desorption was considered among the surface processes. Tritium diffusion and desorption coefficients for Be and BeO were estimated by reproducing the experimental data.;These values are compared to previously estimated fundamental properties from past experiments. Discrepancies are discussed and recommendations are proposed for values of the fundamental properties to be used for analysis of blanket with LiAlO$sb2$ solid breeder and beryllium.