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Neutrons produced by fission have high energies and move extremely quickly. These so-called fast neutrons do not cause fission as efficiently as slower-moving ones so they are slowed down in most reactors by the process of moderation.17-Jul-2006
Why are fast neutron reactors not used?
All nuclear reactors produce heat which must be removed from the reactor core. Water, the most common coolant in thermal reactors, is generally not feasible for a fast reactor, because it acts as a neutron moderator. All operating fast reactors are liquid metal cooled reactors.
Why slow neutrons are used in nuclear reaction?
This slowing or moderation of the neutrons allows them to be more easily absorbed by fissile nuclei, creating more fission events (see Figure 1). Materials used for moderation need to a very specific set of properties. First, a moderator cannot absorb neutrons itself.
Why slow neutrons are more effective than fast?
Neutrons which are travelling at too high a velocity possess too much energy that they simply bounce off the nuclei. A slower moving neutron containing less energy will hit the nucleus and be overcome by the nuclear strong force which holds protons and neutrons together.
Can neutrons be used to produce energy in nuclear reactors?
All nuclear power plants use nuclear fission, and most nuclear power plants use uranium atoms. During nuclear fission, a neutron collides with a uranium atom and splits it, releasing a large amount of energy in the form of heat and radiation.
What are fast neutrons used for?
The use of fast neutrons in so-called 'fast reactors' allows for the production of more fissile nuclei than are destroyed, as the absorption of at least one neutron per fission by an uranium 238 nucleus transforms this uranium 238 into a fissile plutonium 239 nucleus.
Do fast reactors burn nuclear waste?
Fast reactors are capable of destroying the longest-lived nuclear waste, transforming it to waste that decays to harmlessness in centuries rather than hundreds of millennia. Fast reactors typically use liquid metal coolants rather than water.
How the slow and rapid neutron process differ?
The difference between the s-process and r-process nucleosynthesis is controlled by beta decay rates of nuclei. The s-process path lies in the valley of beta stability, but the r-process path is shifted by many units toward neutron-richness.
Why moderator is not used in fast breeder reactor?
No moderator is used in the breeder reactor since fast neutrons are more efficient in transmuting U-238 to Pu-239. At this concentration of U-235, the cross-section for fission with fast neutrons is sufficient to sustain the chain-reaction.
How fast is a fast neutron?
14,000 km/s A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (100 TJ/kg), hence a speed of 14,000 km/s, or higher.
