In February 1985, work was initiated to develop a three-dimensional computerized solids model of the Three Mile Island Unit 2 (TMI-2) reactor building (RB) systems and facilities. Although it was initially planned to use this model to support the acquisition of data for radiological characterization purposes, the unique ability of the solids modeling system to integrate plant configuration data into a single source made it an ideal tool for supporting various other TMI-2 recovery engineering activities as well. In addition to the RB model, a model of the auxiliary and fuel-handling buildings and a very detailed model of the TMI-2 reactor have also been developed. The application of the reactor model to support activities related to reactor vessel defueling and reactor components disassembly is the primary subject of this paper.