No, this is a misunderstanding of how fission works.
When a nuclear reactor is run with mildly-enriched Uranium, which is a mixture of Uranium 235 and Uranium 238, it forms a self-sustaining chain reaction with the Uranium 235 (which is fissile) and a load of the spare neutrons get absorbed by the Uranium 238 (which is fertile), converting it into Plutonium 239, which is also fissile. But most Uranium 235 reactors use a moderator which slows down the neutrons, which makes them more likely to cause fission in Uranium 235 but less likely to transmute Uranium 238 to Plutonium 239. So most modern reactors don't produce much Plutonium. In any case, the fission you get from Uranium and the fission you get from Plutonium is from different source materials. Once an atom is fissioned, it is split into smaller atoms and can no longer be fissioned.
Thorium isn't fissile, it's fertile. That is, if you fire a neutron at Thorium 232, you get Thorium 233, which decays to Protactinium 233, which then decays into Uranium 233, which is fissile. You then fire another neutron at Uranium 233, which then fissions into much smaller nuclei, giving you energy and the neutrons to do the above. The Uranium is no longer around after that to form Plutonium. There is no way to get any significant amount of Plutonium 239 from this, because that would require adding 7 more neutrons to the original Thorium 232 and having none of them trigger a fission event. The fissions that do occur don't provide 7 neutrons anyway, so it wouldn't be possible to get a self-sustaining conversion of a significant amount of Thorium into Plutonium for final fission even if the previous sentence weren't true - it would have to be enhanced with some other provider of lots of neutrons.
When a nuclear reactor is run with mildly-enriched Uranium, which is a mixture of Uranium 235 and Uranium 238, it forms a self-sustaining chain reaction with the Uranium 235 (which is fissile) and a load of the spare neutrons get absorbed by the Uranium 238 (which is fertile), converting it into Plutonium 239, which is also fissile. But most Uranium 235 reactors use a moderator which slows down the neutrons, which makes them more likely to cause fission in Uranium 235 but less likely to transmute Uranium 238 to Plutonium 239. So most modern reactors don't produce much Plutonium. In any case, the fission you get from Uranium and the fission you get from Plutonium is from different source materials. Once an atom is fissioned, it is split into smaller atoms and can no longer be fissioned.
Thorium isn't fissile, it's fertile. That is, if you fire a neutron at Thorium 232, you get Thorium 233, which decays to Protactinium 233, which then decays into Uranium 233, which is fissile. You then fire another neutron at Uranium 233, which then fissions into much smaller nuclei, giving you energy and the neutrons to do the above. The Uranium is no longer around after that to form Plutonium. There is no way to get any significant amount of Plutonium 239 from this, because that would require adding 7 more neutrons to the original Thorium 232 and having none of them trigger a fission event. The fissions that do occur don't provide 7 neutrons anyway, so it wouldn't be possible to get a self-sustaining conversion of a significant amount of Thorium into Plutonium for final fission even if the previous sentence weren't true - it would have to be enhanced with some other provider of lots of neutrons.