[aidenn0]

It needs a neutron source to start fission, but once it's going, in theory it can self-sustain as Th decay genearates radio-isotopes. Furthermore it can breed fissile fuel with thermal neutrons, which is generally seen as an advantage.

The neutron economy, however, is very slim. Several of the intermediate decay products are neutron absorbers. This is why you see a lot of proposed liquid thorium reactors, there are various proposals to use chemical reactions to remove neutron absorbers from the fuel while the reactor is running (something that would be challenging with a solid reactor).