[en] This report describes the development of availability estimates for the High Temperature Gas-Cooled Reactor steam cycle/cogeneration (HTGR-SC/C) Lead Plant. The HTGR-SC/C Lead Plant is designed to produce both process steam and electric power. The plant can operate in the full electric power mode in the full cogeneration mode, or at any point in between. This study has two objectives: estimate the equivalent availability of the present design for the Lead Plant based on the best current data; and allocate outages for systems and subsystems to obtain a preselected equivalent availability of 80% for electric power generation. These allocations are to serve as design targets for the various systems and subsystems. The report presents a brief description of the Lead Plant followed by a detailed discussion of availability, including terminology, availability allocations, reference data and experience, methodology, the concept of states and capabilities, and the availability results