Fertile material

From Wikipedia, the free encyclopedia
Jump to: navigation, search
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

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

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

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

  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. 







Creative Commons License