A universal cookoff model (UCM) is applied to the melt cast explosive Comp-B composed of RDX and TNT. The UCM uses a simple kinetic mechanism with rates and thermophysical properties determined specifically for Comp-B. The success of the UCM is primarily attributed to the flexible form of the rat e expression as well as accurate thermophysical properties obtained from small-scale experiments. The rate expressions use distributed activation energies in conjunction with rate multipliers to account for accelerations caused by 1) dissolved RDX, 2) liquid RDX, and 3) pressure. Our finite element model addresses Comp-B cookoff from the pristine state, through melting of the TNT binder, partial dissolution of RDX in the hot TNT, and melting of the remaining RDX as the Comp-B thermally ignites. Typically, the UCM is used for explosives that do not flow. However, we have included a buoyancy-driven flow model to account for multiphase fluid movement. Predicted temperature fields were sensitive to flow, which caused the hotter material to rise. Our predictions of ignition times were also sensitive to RDX dissolving in hot TNT causing an acceleration of the RDX decomposition. Published by Elsevier Inc. on behalf of The Combustion Institute.