Neutron economy is defined as the ratio of an adjoint

weighted average The weighted arithmetic mean is similar to an ordinary arithmetic mean (the most common type of average), except that instead of each of the data points contributing equally to the final average, some data points contribute more than others. The ...

of the excess

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...

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 Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rubber used to hold objects togethe ...

and

inelastic collision An inelastic collision, in contrast to an elastic collision, is a collision in which kinetic energy is not conserved due to the action of internal friction. In collisions of macroscopic bodies, some kinetic energy is turned into vibrational ene ...

s with fuel, coolant and construction material. Neutrons slow down in elastic and inelastic collisions, until they are absorbed via

Neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons ...

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 A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...

elements, resonance absorption by fuel, and leakage while fast and thermal energy ranges. Heavy water is an extremely efficient moderator. As a result, reactors using heavy water, such as the

CANDU The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...

, also have a high neutron economy. The quantity that indicates how much the neutron economy is out of balance is given the term reactivity. If a reactor is exactly

critical Critical or Critically may refer to: *Critical, or critical but stable, medical states **Critical, or intensive care medicine * Critical juncture, a discontinuous change studied in the social sciences. *Critical Software, a company specializing ...

—that is, the neutron production is exactly equal to neutron destruction—the reactivity is zero. If the reactivity is positive, the reactor is supercritical. If the reactivity is negative, the reactor is

subcritical In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fissi ...

. 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 A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

design.

References

Economy An economy is an area of the production, distribution and trade, as well as consumption of goods and services. In general, it is defined as a social domain that emphasize the practices, discourses, and material expressions associated with th ...

Nuclear technology {{nuclear-stub

See also

References