The concept is credited to Italian scientist Carlo Rubbia, a Nobel Prize particle physicist and former director of Europe's CERN international nuclear physics lab. He published a proposal for a power reactor based on a proton cyclotron accelerator with a beam energy of 800 MeV to 1 GeV, and a target with thorium as fuel and lead as a coolant. Rubbia's scheme also borrows from ideas developed by a group led by nuclear physicist Charles Bowman of the Los Alamos National Laboratory
Principle and feasibility
The energy amplifier first uses a particle accelerator to produce a beam of high-energy protons. The beam is directed to smash into the nucleus of a heavy metal target, such as lead, thorium or uranium. Inelastic collisions between the proton beam and the target results in spallation, which produces twenty to thirty neutrons per event. It might be possible to increase the neutron flux through the use of a neutron amplifier, a thin film of fissile material surrounding the spallation source; the use of neutron amplification in CANDU reactors has been proposed. While CANDU is a critical design, many of the concepts can be applied to a sub-critical system. Thorium nuclei absorb neutrons, thus breeding fissile uranium-233, an isotope of uranium which is not found in nature. Moderated neutrons produce U-233 fission, releasing energy. This design is entirely plausible with currently available technology, but requires more study before it can be declared both practical and economical. OMEGA project is being studied as one of methodology of accelerator-driven system in Japan. Richard Garwin and Georges Charpak describe the energy amplifier in detail in their book Megawatts and Megatons A Turning Point in the Nuclear Age?" on pages 153-163. Earlier, the general concept of the energy amplifier, namely an Accelerator-driven sub-critical reactor, was covered in "The Second Nuclear Era" pages 62–64, by Alvin M. Weinberg and others.
Advantages
The concept has several potential advantages over conventional nuclear fission reactors:
Subcritical design means that the reaction could not run away — if anything went wrong, the reaction would stop and the reactor would cool down. A meltdown could however occur if the ability to cool the core was lost.
Thorium is an abundant element — much more so than uranium — reducing strategic and political supply issues and eliminating costly and energy-intensive isotope separation. There is enough thorium to generate energy for at least several thousand years at current consumption rates.
The energy amplifier would produce very little plutonium, so the design is believed to be more proliferation-resistant than conventional nuclear power.
The possibility exists of using the reactor to consume plutonium, reducing the world stockpile of the very-long-lived element.
No new science is required; the technologies to build the energy amplifier have all been demonstrated. Building an energy amplifier requires only engineering effort, not fundamental research.
The design could work on a relatively small scale, and had the potential to load-follow by modulating the proton beam, making it more suitable for countries without a well-developed power grid system.
Each reactor needs its own facility to generate the high energy proton beam, which is very costly. Apart from linear particle accelerators, which are very expensive, no proton accelerator of sufficient power and energy at has ever been built. Currently, the Spallation Neutron Source utilizes a proton beam to produce its neutrons, with upgrades envisioned to Its cost included research equipment not needed for a commercial reactor.
The fuel material needs to be chosen carefully to avoid unwanted nuclear reactions. This implies a full-scale nuclear reprocessing plant associated with the energy amplifier.
