- The way in which neutrons are increased and absorbed can be
described by a combination of factors in the 'four factor formula'
- Neutrons are increased in two ways
- Thermal fission factor h
- Fast fission factor e
- Neutrons are absorbed in two ways
- Resonance escape probability p
- Thermal utlisation factor f
h = the average number of neutrons produced
per thermal neutron absorbed in the fuel.
e = the number of fission neutrons produced
by fast neutrons before they are moderated. This will be largely in the ^{238}U.
f = the fraction of thermal neutrons absorbed in the reactor that are
absorbed in the fuel.
p = the fraction of neutrons that are in the course of thermalisation
escape being captured by the resonance structure of ^{238}U.
L = combined leakage factor L
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