In essence, thorium reactors are a kind of molten salt reactor. The fuel is a molten salt which is pumped from the critical core to a heat exchanger that heats water, converting it to steam, and working the turbine generator much like how current light and heavy water reactors work.
The nuclear fuel itself is mixed into a molten salt. This means that the thorium is turned into uranium rather than directly using uranium, pumping fuel without shutdowns, and using a salt coolant to operate at higher temperatures.
These aspects of thorium reactors could make nuclear energy far safer. Rather than attempting to control a reaction, some energy is spent to keep the reaction going.
Thorium accepts more neutrons if the salt does overheat, meaning there is less of it firing around that would otherwise cause more chain reactions. It also expands considerably if it overheats, which would push the fuel out of the critical core, stopping the reaction.