The Accelerator Driven System, or ADS, is a form of nuclear reactor that does not require Uranium or Plutonium as nuclear fission fuel.
The main proponent of ADS technology is physicist Carlo Rubbia. ADS technology relies very heavily on isotopic elements wich are fertile rather than fissile.
The intervention of an accelerator transmutes these elements from fertile to fissile by the capture of neutrons. Protons are fired at the fertile fuel to excite energy levels thus causing expulsion, or capture of neutrons in a process of fission which can be switched off at will.
The ADS system uses radionucleides further down the periodic table of elements than Uranium, such as Radium or Thorium, neither of which are capable of self sustaining nuclear chain reactions. What this last point means in practice is that when the reactor is switched off, the radioactivity is switched off also.
The Thorium core is submersed in a deep column of lead, inside a metal container with much higher melting temperature than lead. A shaft from the top of the column is free of lead and leads to a vertically positioned particle accelerator. The Particle accelerator is driven by electricity to fire a continuous beam of protons down into the Thorium Core, without which sustained nuclear fission is impossible. The accelerator can be switched off at any moment.
When activated the Thorium core heats the lead surrounding it to make the lead molten. Natural convection causes the molten lead to rise through a thermal exchanger where water is heated to make steam for turbine power generation. As the lead cools it drops back down to the Thorium Core to be reheated.
This system relies on no pumps, pipes, or valves. If shut down the Thorium Core remains enclosed in it's own lead shield.
The ADS system is said to generate 60 times more net energy output than that which is imputted by the particle accelerator.
Another advantage of ADS is that it could make possible the global outlawing of all uranium mining and plutonium production. Eventually it could lead to the disarmament of all nuclear weapons provided there was the political will.
ADS technology is best suited to Radium, or Thorium which are two types of radionuclides which cannot fuel sustained nuclear reaction without Accelerator intervention. India and Brazil are two countries with mineral reserves best suited to exploit this technology.
ADS technology however can also be used to burn off Uranium and Plutonium radioactive wastes and reduce them to more manageable isotopic elements.