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Wednesday, February 10, 2010

Driven Nuclear Reactions

Driven nuclear reactions -
  • Do not rely on spontaneous fission, 
  • Produce no radioactive waste, and 
  • Do not have the potential to create a nuclear weapons capability.

The principles of operation of reactors based on driven nuclear reactions are straightforward.

Overview of Driven Nuclear Reactors

A. Source of Energy and Fuel-Cost Considerations
About 1% of the mass of neutrons is typically converted into energy when they are absorbed into atomic nuclei. For each 100 grams of neutrons absorbed, about 1 gram will be converted into energy:
90 million megajoules (1 x 10-3 kg x (3 x 108)joules),
which is similar to the amount of energy produced by burning about 2,700 tonnes of coal. If coal costs around $120/tonne, the fuel-cost for this amount of energy would be nearly $324,000.

B. Reaction Steps
  1. Mechanism to induce ejection of neutrons.
  2. Ejection of neutrons from suitable sources.
  3. Absorption of neutrons into suitable target, with extraction of thermal-energy to drive conventional steam-turbine power station.
In neutron absorption, the nucleus absorbs the neutron and becomes excited, typically emitting capture gamma rays.

C. Feasibility Assessment and Possible Unintended Benefits
For assessment of reaction steps “2” and “3”, it may be expedient to substitute a radioactive isotope produced in a research reactor for the eventual mechanism that is to be used to induce ejection of neutrons.
For example, Antimony 124 (half-life 60 days) produces high-energy photons that are only slightly above the energy-level needed to eject neutrons from Beryllium. (Note: Of all the naturally occurring, non-radioactive elements, Beryllium is quite unusual in possessing a neutron which requires relatively little energy to remove it from its nucleus.) The by-product is Helium – each Beryllium atom splitting into 2 Helium atoms after losing a neutron. About 1 kilogram of Beryllium would yield about 100 grams of neutrons, which, on being absorbed by a suitable target, would release about the same amount of energy produced by burning 2,700 tonnes of coal.
For absorption of neutrons, naturally occurring Cadmium contains about 12% Cadmium 113 and 28% Cadmium 114. Cadmium 113 readily absorbs neutrons and is converted to Cadmium 114.

The long-term storage of radioactive waste from conventional nuclear reactors is not an issue for driven nuclear reactors. It is worth observing that the timescales involved in storage of radioactive waste are related to the time in which radioactive decay takes place under natural conditions.
Radioactive isotopes either possess an excess of neutrons – which tends to make them potentially useful sources from which to induce ejection of neutrons; or they possess an excess of protons – which tends to make them potentially useful as neutron-absorbing targets.

One implication of this is that it may be convenient for the foreseeable future to fuel driven nuclear reactors with radioactive waste from conventional nuclear reactors.

A further possibility is the operation of driven nuclear reactors primarily to produce valuable materials, with energy output as a by-product.

Related article: Nuclear Power and Nuclear Energy versus Nuclear Technology