A hybrid-type approach for plant layout design is pressented with a constraint-directed search procedure and a mathematical optimization technique. In layout design, a plant must be arranged to satisfy spatial constraints imposed by its components. In our approach, the whole space of a plant building is divided into the finite compartments with a modular size in order to separate the description of the layout into the combinational part and the dimensional part. According to this, the approach consists of two steps. In the first step, a constraint-directed search procedure is applied for fixing the combinational relations among plant components so as to satisfy the spatial layout conditions. In the second step; an optimization technique is applied for determining the actual dimensions of compartments so as to minimize the size of a plant building considering the size of components. In the optimization, mixed-integer programming and sequential linear programming are combined and the formulation is carried out automatically from the result of the first step. This hybrid approach has been applied to the design of a nuclear power plant in order to check its validity and effectiveness.
