[en] Although Hypothetical Core Disruptive Accidents (HCDAs) are not Design Basis Accidents for the Clinch River Breeder Reactor Plant, extensive assessments of HCDA consequences have been made. Prudent margins beyond the design base have been included in the design to further reduce the risk to the public from highly improbable occurrences. These margins include Structural Margin Beyond the Design Base to address the energetics aspects and Thermal Margin Beyond the Design Base to address the longer term thermal and radiological consequences. The assessments that led to the specification of these margins are described, along with the experimental support for those assessments