I don’t know for sure, but my guess was that the thorium sits in a gas chamber, and every time it decays the decay product excites the gas which eventually settles back down and emits a photon. The photons are shot into the water to heat it. I’m guessing they’re doing this setup to avoid creating heavy water in your vehicle.
I also appreciate that the concept artist for this car designed something that looks as hideously impractical as a nuclear powered car should.
