Assuming the spontaneous fission neutron level as a neutron source, and using point kinetic methods in the course of the analytical treatment, the energy excursion of hypothetical nuclear explosives with mixed plutonium of various isotope compositions has been investigated. The α-Rossi values for the metallic density of different configurations have been evaluated with multigroup SN methods. Commercial plutonium from relatively low burned-up nuclear fuel, containing 5% 240Pu, is shown to reveal similarities with high weapons-grade plutonium, thus making possible a nuclear explosion (in combination with a sophisticated conventional implosion technique). On the other hand, commercial plutonium from moderately to highly burned up (containing 15 or 25% 240Pu nuclear fuel) will have a small probability for an energy excursion up to 100 tons TNT, even by extremely improved implosion techniques.