Fertile material

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Transmutation flow between 238Pu and 245Cm in LWR.[1] Speed of transmutation varies greatly by nuclide, and percentages are relative to total transmutation and decay. After removal of fuel from reactor, decay will predominate for shorter-lived isotopes such as 238Pu, 241Pu, 242–244Cm; but 245–248Cm are all long-lived.

Fertile material is a material that, although not itself fissionable by thermal neutrons, can be converted into a fissile material by neutron absorption and subsequent nuclei conversions.

Naturally-occurring fertile materials[edit]

Naturally-occurring fertile materials that can be converted into a fissile material by irradiation in a reactor include:

Artificial isotopes formed in the reactor which can be converted into fissile material by one neutron capture include:

Some other actinides need more than one neutron capture before arriving at an isotope which is both fissile and long-lived enough to probably be able to capture another neutron and fission instead of decaying.

Since these require a total of 3 or 4 thermal neutrons to eventually fission, and a thermal neutron fission generates only about 2 to 3 neutrons, these nuclides represent a net loss of neutrons. In a fast reactor, they may require fewer neutrons to achieve fission, as well as producing more neutrons when they do fission.

Fissile materials from fertile materials[edit]

A fast-neutron reactor, meaning one with little or no neutron moderator and hence utilising fast neutrons, can be configured as a breeder reactor, producing more fissile material than it consumes, using fertile material in a blanket around the core, or contained in special fuel rods. Since plutonium-238, plutonium-240 and plutonium-242 are fertile, accumulation of these and other nonfissile isotopes is less of a problem than in thermal reactors, which cannot burn them efficiently. Breeder reactors using thermal-spectrum neutrons are only practical if the thorium fuel cycle is used, as uranium-233 fissions far more reliably with thermal neutrons than plutonium-239.

Applications[edit]

Proposed applications for fertile material includes a space-based facility for the manufacture of fissile material for spacecraft nuclear propulsion. The facility would notionally transport fertile materials from Earth, safely through the atmosphere, and locate them at a space facility at the Earth–Moon L1 Lagrangian point where manufacture of fissile material would occur, eliminating the safety risk of transport of fissile materials from Earth.[2]

References[edit]

  1. ^ Sasahara, Akihiro; Matsumura, Tetsuo; Nicolaou, Giorgos; Papaioannou, Dimitri (April 2004). "Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels". Journal of Nuclear Science and Technology 41 (4): 448–456. doi:10.3327/jnst.41.448. 
  2. ^ Dodd, Jake; Thangavelu, Madhu (January 2012). "SNAP-X: The Space Nuclear Activation Plant". AIAA Space 2012 (Conference issue). doi:10.2514/6.2012-5329. Retrieved 2012-12-18.