The Thorium Reactor

Thorium (232T) can be used to make a power reactor. Thorium is three times as abundant on earth than uranium. There is also no need for costly isotope separation as there is only one, stable isotope. Forty times the potential energy is available compared to uranium.

Thorium is not itself fissile. Exposed to some 235U or 239P, thorium absorbs neutrons to become first 233T, which loses one beta particle (electron) and then another from its nucleus to become 233U which is fissile. Alternatively, a thorium reactor could be energised by a low-powered proton accelerator. The protons generate neutrons from a pool of molten lead) to initiate the creation of 233U and the heat producing thermonuclear reaction. The latter method has the advantage that the reactor is controlled by the particle accelerator, almost like a dimmer control on a light.

The other advantage of the thorium reactor are that it cannot develop a runaway reaction. Where 235U fission generates 3 neutrons, 233U spits out just 2. One neutron could convert the next 232T into 233U, while the other could split a 233U atom – but only if all of the neutrons were 100% effective, which is impossible. So a thorium reactor needs to be constantly “primed” with neutrons from outside. That makes it safe and very controllable!

The thorium reactor does not produce materials which can easily be used to manufacture weapons. It creates far fewer radioactive wastes, which decay far more rapidly – estimated at 500 years. Finally, scientists believe that a thorium reactor should be able to “incinerate” plutonium – to irradiate it, generating more energy, and destroy it. That would be very useful as there are many tonnes of plutonium from dismantled warheads in storage. These pose a serious danger to the world!

“Megawatts & Megatons” Richard Garwin & Georges Charpak, Knopf, New York, 2001, p153-163.

Why Were Thorium Reactors not Developed?

The simple answer must be the very close relationship between nuclear weapons and uranium reactors. The same scientists worked on both. Weapons relied on reactors to produce plutonium – the best weapons material. The cold war fuelled this relationship for decades. Even today, nations like India, Pakistan, Iran, North Korea, and Israel (Israel vapourised Iraq’s “Osirak” reactor before it was complete, or Iraq would have joined this list) used their power reactors to produce weapons grade uranium and plutonium. Unfortunately, the Canadian CANDU design is particularly effective at yielding bomb grade plutonium!

Fuelled by the fear of proliferation and by the need for “low carbon” electricity, the world may now be ready for thorium technology – or perhaps not!

The Thorium Reactor