The results are presented of the first phase of a research project on the application of spatial modeling techniques to the process of planning and executing the construction of a nuclear power plant. A computer modeling technique, based on sets of polyhedra and spatial operations, was developed and applied to modeling the components of a nuclear power plant. The objectives of the modeling are: to store and retrieve information about the various systems in the facility; to produce drawings of those systems from any angle in differing amounts of detail; to aid in the search for interference among the parts of the plant by identifying those elements that occupy the same space or are too close to each other; to calculate information such as surface area, length, and volume of selected elements of the plant; and to aid in finding the optimum construction sequence by simulated construction of selected areas of the plant. Computer techniques are described for inputting information by digitizing directly from engineering drawings, for editing the spatial model, for management of the spatial and non-spatial data, and for graphic output from the model. The software is implemented on the University's central time-sharing computer system and on a mini-computer system in the Architectural Research Laboratory.