Reactor Theory (Nuclear Parameters)
DOE-HDBK-1019/2-93
NEUTRON LIFE CYCLE
Neutron Life Cycle Summary
The infinite multiplication factor, k
, is the ratio of the neutrons produced by fission
in one generation to the number of neutrons lost through absorption in the preceding
generation.
The effective multiplication factor, keff, is the ratio of the number of neutrons
produced by fission in one generation to the number of neutrons lost through
absorption and leakage in the preceding generation.
Critical is the condition where the neutron chain reaction is self-sustaining and the
neutron population is neither increasing nor decreasing.
Subcritical is the condition in which the neutron population is decreasing each
generation.
Supercritical is the condition in which the neutron population is increasing each
generation.
The six factor formula is stated as keff = f p t f h. Each of the six factors is
defined below.
number of fast neutrons produced by all fissions
number of fast neutrons produced by thermal fissions
f
number of fast neutrons that do not leak from reactor
number of fast neutrons produced by all fissions
p
number of neutrons that reach thermal energy
number of fast neutrons that start to slow down
t
number of thermal neutrons that do not leak from reactor
number of neutrons that reach thermal energies
f
number of thermal neutrons absorbed in the fuel
number of thermal neutrons absorbed in all reactor materials
h
number of fast neutrons produced by thermal fission
number of thermal neutrons absorbed in the fuel
Rev. 0
NP-03
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