Neutron economy
Encyclopedia
Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron
production divided by an adjoint weighted average of the fission
production.
The distribution of neutron energies in a nuclear reactor differs from the fission neutron spectrum due to the slowing down of neutrons in elastic and inelastic collisions with fuel, coolant and construction material. Neutrons slow down in elastic and inelastic collisions, until they are absorbed via Neutron capture
or lost by leakage. Neutron economy is the balanced account, in a reactor, of the neutrons created and the neutrons lost through absorption by non-fuel elements, resonance absorption by fuel, and leakage while fast and thermal energy ranges.
The quantity that indicates how much the neutron economy is out of balance is given the term Reactivity. If a reactor is exactly critical - that is, the neutron production is exactly equal to neutron destruction - then the reactivity is zero. If the reactivity is positive - then the reactor is supercritical. If the reactivity is negative - then the reactor is subcritical.
However the term neutron economy is used not just for the instantaneous reactivity of a reactor but also to describe the overall efficiency of a nuclear reactor
design.
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
production divided by an adjoint weighted average of the fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
production.
The distribution of neutron energies in a nuclear reactor differs from the fission neutron spectrum due to the slowing down of neutrons in elastic and inelastic collisions with fuel, coolant and construction material. Neutrons slow down in elastic and inelastic collisions, until they are absorbed via Neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
or lost by leakage. Neutron economy is the balanced account, in a reactor, of the neutrons created and the neutrons lost through absorption by non-fuel elements, resonance absorption by fuel, and leakage while fast and thermal energy ranges.
The quantity that indicates how much the neutron economy is out of balance is given the term Reactivity. If a reactor is exactly critical - that is, the neutron production is exactly equal to neutron destruction - then the reactivity is zero. If the reactivity is positive - then the reactor is supercritical. If the reactivity is negative - then the reactor is subcritical.
However the term neutron economy is used not just for the instantaneous reactivity of a reactor but also to describe the overall efficiency of a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
design.