In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and leave an energy profit for power generation. The concept has more recently been referred to as an accelerator-driven system (ADS).
The concept is credited to Italian scientist Carlo Rubbia, a Nobel Prize nuclear 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.
 Principle and feasibility
The energy amplifier uses a synchrotron or other appropriate accelerator (e.g. cyclotron, fixed-field alternating-gradient) to produce a beam of protons. These hit a heavy metal target such as lead, thorium or uranium and produce neutrons through the process of spallation. 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.
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 (although the question of uranium-233 as nuclear weapon material must be assessed carefully).
- The possibility exists of using the reactor to consume plutonium, reducing the world stockpile of the very-long-lived element.
- Less long-lived radioactive waste is produced — the waste material would decay after 500 years to the radioactive level of coal ash.
- No new science is required; the technologies to build the energy amplifier have all been demonstrated. Building an energy amplifier requires only some engineering effort, not fundamental research (unlike nuclear fusion proposals).
- Power generation might be economical compared to current nuclear reactor designs if the total fuel cycle and decommissioning costs are considered.
- The design could work on a relatively small scale, making it more suitable for countries without a well-developed power grid system
- Inherent safety and safe fuel transport could make the technology more suitable for developing countries as well as in densely populated areas.
- General technical difficulties.
- Each reactor needs its own facility (particle accelerator) 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 (> ~12 MW at 1GeV) has ever been built. Currently, the Spallation Neutron Source utilizes a 1.44 MW proton beam to produce its neutrons, with upgrades envisioned to 5 MW. Its 1.1 billion dollar cost included research equipment not needed for a commercial reactor.
 See also
- Alternative energy
- Thorium fuel cycle
- Breeder reactor, another type of nuclear reactor that aims for an energy profit by creating more fissile material than it consumes.
- "Neutron amplification in CANDU reactors". CANDU.
- "大電流電子線加速器の性能確認試験" [Performance of Ｈigh Power CW Electron Linear Accelerator] (pdf) (in Japanese). Ōarai, Ibaraki: Japan Atomic Energy Agency. December 2000. Retrieved 2013-01-21.
- David JC McKay Sustainable Energy - without the hot air'
- A PRELIMINARY ESTIMATE OF THE ECONOMIC IMPACT OF THE ENERGY AMPLIFIER - An in-depth review of the Energy Amplifier co-authored by Rubbia (pdf download available from the CERN document server)
- Christoph Pistner, Emerging Nuclear Technologies: The Example of Carlo Rubbia's Energy Amplifier, International Network of Engineers and Scientists Against Proliferation
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