INTRODUCTION
The purpose of this study was to examine the far-field thermal/thermoelastic behavior of a radioactive waste repository as a function of the rock type, gross thermal loading, waste type, waste age, repository depth, and in situ stress state. The finite element method of analysis was used to perform this study. The study was undertaken in two phases:
a preliminary investigation of the thermal behavior of a repository with respect to host rock type was made using thermal properties typical of a uniform rock mass composed of either granite, limestone, or shale;
a thermoelastic analysis, including an assessment of the potential for rock failure, was made using typical thermo-mechanical properties of granite.
The principal objective of the first phase of the study was to relate the thermal behavior of the host rock mass to its thermal properties.This relationship, based on a non-dimensional scaling technique commonly used in transient conduction analysis, was verified by numerical results from the finite element analysis.
The second phase of the study involved a thermoelastic analysis of a repository in granitic rock. In this analysis, it was assumed that the rock mass behaves in a linear elastic fashion. The potential for rock failure was evaluated by use of the Mohr-Coulomb criterion. Most of the analyses were based on the emplacement of 10-year-old spent unreprocessed fuel (SF) and high level waste (HLW) from pressurized water reactors (PWR). Gross thermal loadings of 12.4, 24.8, and 37.2 W/m2 were considered.
Peak temperatures predicted for various combinations of the parameters received special attention with regard to their location and time of occurrence. Displacements and the failure potential of granite as a result of the temperature distributions are determined in the far-field region surrounding the repository.
The purpose of this analysis was to examine the far-field thermomechanical behavior of a radioactive waste repository considering such parameters as rock type, gross thermal loading (GTL), waste type, waste age, repository depth and in situ stress state. The numerical analyses were performed in axisymmetric geometry using the finite element method (1,2,3).* The parametric analyses were completed in two phases:
a preliminary investigation of the thermal behavior of a repository with respect to host rock type was made using thermal properties typical of a uniform rock mass composed of either granite, limestone, or shale;
a thermoelastic analysis, including an assessment of the potential for rock failure, was made using typical thermomechanical properties of granite.
The principal objective of the first phase of the study was to relate the thermal behavior of three rock types to their respective thermal properties. A non-dimensional scaling technique was used to establish this relationship and was verified by numerical calculations from the finite element analysis. Upon establishig the correlation between the scaled and finite element calculations, the influence of GTL, waste type, waste age, and repository depth on the far-field thermal response was investigated for a granitic rock type.
