Comparison with Uranium?

The problem of the actual nuclear energy is that those reactors have the Rickover's design as a nuclear bomb.

By controlling the amount of neutrons generated by the nuclear reaction, the engineers can regulate the power of the reactors.

Until 3 big accidents have brought some doubt in this technology : Three Mile Island (USA),  Tchernobyl (USSR) or Fukushima (JP).

Trouble free

Thorium is safer than Uranium because Thorium is not fissile, but fertile. The fission reaction requires 2 steps which gives more possibility to control it. Furthermore, the characteristics of Thorium dioxide make it a very safe nuclear fuel

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Thorium is not fissile but fertile.

It means that the capture of a neutron doesn't start the fission processe but it transforms Th232 into a fissile isotope of Uranium, U233. In this configuration, the capture of a new neutron results in the fission of this element.

There are also other features

"There are three main safety features to thorium dioxide, the form of thorium used in nuclear reactors, which set it apart from conventional nuclear fuels: its melting point, stability, and thermal conductivity are all significantly higher than that of uranium oxide.

Thorium dioxide has a melting point 500 degrees Celsius higher than the melting point of uranium oxide, reducing the risk that an accidental power surge or loss of coolant inside the reactor will result in temperatures high enough to trigger a meltdown.

As an extra margin of safety, the thermal conductivity of thorium dioxide is 30 percent higher than its uranium counterpart at 100°C, and 8 percent higher at 650°C. Thus the plant can be operated at lower temperatures, even further below the melting point of the fuel.

Lastly, the compound's higher stability reduces the risk of the fuel pellets reacting to and therefore oxidizing their metal claddings, which would produce highly explosive hydrogen gas. Thorium dioxide is in fact the most stable solid oxide at high temperatures, making it the best choice to resist highly reactive metals."

Extracted from "The Accompanying Safeties and Risks of Thorium Fuel" from Isabel Gueble.