The modular high temperature gas-cooled reactor (MHTGR) is an advanced reactor concept under development in a cooperative program involving U.S. government, the nuclear industry, and the utilities. The design utilized the basic hig-temperature gas-cooled reactor features of ceramic fuel, helium coolant, and a graphite moderator. The key design parameters, including power, power density, and core and configuration of the MHTGR are selected to utilize the inherent properties of these materials to develop passive safety features that provide a significantly higher margin of safety than current generation reactors. In this paper the reference MHTGR module is combined with several alternatives, each characterized by an alternative containment building structure providing differing degrees of radionuclide containment. The reference design and each alternate are described and their performance compared. The MHTGR radionuclide source and how it related to the radionuclide retention provided by buildings and building features are discussed. This is followed by more detailed considerations leading to the selection of five alternatives. The underlying assumptions and approach employed in assessing alternative designs are summarized. The evaluation of the cost and offsite does reduction benefit of the reference design and selected alternatives are described. Finally, the various alternatives are compared with each other allowing conclusions to be drawn. All design concepts meet the U.S. Environmental Protection Agency's Protective Action Guidelines at the site boundary hence precluding the need for emergency drills, sheltering, or evacuation of the public.