Convection heat transfer in fissured media is a transport process of great relevance in the design and licensing of underground nuclear waste repositories, and in several other fields such as geothermal energy extraction and petroleum engineering. Canisters containing either spent fuel rod bundles or high level immobilized waste may be buried in tight, fluid-bearing crystalline rock which is (characteristically) fissured, or else has the possibility of becoming fissured owing to thermal stresses created by decay heat generation. This paper presents a limited study of thermal convection through a system of rigid, idealized fissures. The results obtained are based on the simplifying assumptions of rigid fissures with uniform width and periodicity, and an impermeable matrix. Although highly idealized, the model is able to characterize the effects of varying fissure geometry and periodicity on convection in a fissured domain. Anisotropy in the horizontal and vertical fissures could significantly alter the heat transfer rate from the repository, as well as mitigate or enhance the spread of accidentally released radionuclides. Refs.