Studies have been conducted to demonstrate that weapons-grade plutonium can be readily disposed of by utilizing it as a fuel in pressurized water reactors (PWR). The disposition can be achieved by first fabricating the weapons-grade plutonium into a mixed-oxide (MOX) fuel form and then irradiating it in either advanced or existing PWRs to a depleted level similar to commercial spent fuel. Preliminary neutronics studies pertaining to safety-related core design using 100% weapons-grade MOX fuel are presented. The results demonstrate the feasibility of a small plutonium disposition reactor of 600-MW(electric) capacity called the PDR600, a large plutonium disposition reactor of 1400-MW(electric) capacity called the PDR1400, and a typical four-loop modified Westinghouse reactor. Feasible loading patterns are obtained for the initial and equilibrium cycles using discrete borosilicate glass burnable absorbers and a heavy loading of zirconium diboride integral fuel burnable absorbers in every fuel rod. The preliminary core physics results include information on soluble boron concentration, peaking factors, Doppler and moderator reactivity coefficients, boron, xenon and control rod worths, shutdown margin and delayed neutron parameters. The core design for weapons-grade plutonium disposition can be achieved with minimum changes in the present safety and licensing criteria of advanced or existing PWRs.