| Abstract: | This paper discusses the development of the core support structure design from that employed on Fort St Vrain to recently announced contracts by Philadelphia Electric, Delmarva Power and Light and Southern California Edison for the large HTGR. Particular emphasis is given to the seismic considerations in the design of the structure for the large HTGR. The overall configuration of each reactor type is critically compared. Although similar components are employed, the basic difference in layout configuration results in significant conceptual differences in the structural and mechanical requirements of the core support components. The configuration and major components for the large reactor are described in some detail. The essential features and function of components are discussed. The graphite components in the core support floor and permanent reflector are designed to form a tight array during reactor normal operating conditions. This composite structure resists compressive loading due to differential gas forces and concrete pressure vessel movement. This tight array concept has important advantageous effects on primary coolant flow distribution and seismic capability.The paper discusses the inherent requirements and methodology in developing a standard plant design for high seismic sites. A design suitable for 0.15 g operating basis earthquake and 0.25 g safe shutdown earthquake has been developed which is applicable for over 80% of the expected sites in the USA. The HTGR core and support structure consists of many thousand graphite elements. It behaves as an inelastic body having random response when subjected to seismic excitation. The paper describes simplified analytical models which have been developed to investigate this phenomenon. An overview of a test program to substantiate and correlate with the analytical models is provided. The program addresses the interelement collision forces and frequencies of elements within the core and the load/deflection at the boundary. Various one, two and three-dimensional scale models have been tested. A summary of the objectives of the program is provided. |
