Search results
Results From The WOW.Com Content Network
In a nuclear reactor, the neutron population at any instant is a function of the rate of neutron production (due to fission processes) and the rate of neutron losses (due to non-fission absorption mechanisms and leakage from the system). When a reactor's neutron population remains steady from one generation to the next (creating as many new ...
Concentration/Density: Neutron reactions leading to scattering, capture or fission reactions are more likely to occur in dense materials; conversely, neutrons are more likely to escape (leak) from low density materials. Moderation: Neutrons resulting from fission are typically fast (high energy). These fast neutrons do not cause fission as ...
Fission occurs when a heavy nuclide such as uranium-235 absorbs a neutron and breaks into nuclides of lighter elements such as barium or krypton, usually with the release of additional neutrons. Like all nuclides with a high atomic number, these uranium nuclei require many neutrons to bolster their stability, so they have a large neutron-proton ...
A less moderated neutron energy spectrum does worsen the capture/fission ratio for 235 U and especially 239 Pu, meaning that more fissile nuclei fail to fission on neutron absorption and instead capture the neutron to become a heavier nonfissile isotope, wasting one or more neutrons and increasing accumulation of heavy transuranic actinides ...
The chance of fissioning on absorption of a thermal neutron is about 92%; the capture-to-fission ratio of 233 U, therefore, is about 1:12 – which is better than the corresponding capture vs. fission ratios of 235 U (about 1:6), or 239 Pu or 241 Pu (both about 1:3).
The fission process can be understood when a nucleus with some equilibrium deformation absorbs energy (through neutron capture, for example), becomes excited and deforms to a configuration known as the "transition state" or "saddle point" configuration. As the nucleus deforms, the nuclear Coulomb energy decreases while the nuclear surface ...
The multiplication factor, k, is defined as (see Nuclear chain reaction): = If k is greater than 1, the chain reaction is supercritical, and the neutron population will grow exponentially.
An exception is the uranium-233 of the thorium cycle, which has a good fission/capture ratio at all neutron energies. Fast-neutron reactors use unmoderated fast neutrons to sustain the reaction, and require the fuel to contain a higher concentration of fissile material relative to fertile material (uranium-238).