The six-factor formula is used in nuclear engineering to determine the multiplication of a nuclear chain reaction in a non-infinite medium.
The symbols are defined as:
- , and are the average number of neutrons produced per fission in the medium (2.43 for uranium-235).
- and are the microscopic fission and absorption cross sections for fuel, respectively.
- and are the macroscopic absorption cross sections in fuel and in total, respectively.
- is the macroscopic fission cross-section.
- is the number density of atoms of a specific nuclide.
- is the resonance integral for absorption of a specific nuclide.
- is the average lethargy gain per scattering event.
- Lethargy is defined as decrease in neutron energy.
- (fast utilization) is the probability that a fast neutron is absorbed in fuel.
- is the probability that a fast neutron absorption in fuel causes fission.
- is the probability that a thermal neutron absorption in fuel causes fission.
- is the geometric buckling.
- is the diffusion length of thermal neutrons.
- where is the diffusion coefficient.
- is the age to thermal.
- is the evaluation of where is the energy of the neutron at birth.
Multiplication
The multiplication factor, , is defined as (see nuclear chain reaction):
- If is greater than 1, the chain reaction is supercritical, and the neutron population will grow exponentially.
- If is less than 1, the chain reaction is subcritical, and the neutron population will exponentially decay.
- If , the chain reaction is critical and the neutron population will remain constant.
See also
References