NEUTRON LIFE CYCLE
DOE-HDBK-1019/2-93
Reactor Theory (Nuclear Parameters)
Neutron Life Cycle Summary (Cont.)
The thermal utilization factor can be calculated from the macroscopic cross section
for absorption of reactor materials using Equation (3-1).
f
S
U
a
S
U
a
S
m
a
S
p
a
The reproduction factor can be calculated based on the characteristics of the reactor
fuel using Equation (3-2).
h
N
U 235
s
U 235
f
n
U 235
N
U 235
s
U 235
a
N
U 238
s
U 238
a
The number of neutrons present at any point in the neutron life cycle can be
calculated as the product of the number of neutrons present at the start of the
generation and all the factors preceding that point in the life cycle.
The thermal utilization factor is effected by the enrichment of uranium-235, the
amount of neutron poisons, and the moderator-to-fuel ratio.
The reproduction factor is effected by the enrichment of uranium-235.
The resonance escape probability is effected by the enrichment of uranium-235, the
temperature of the fuel, and the temperature of the moderator.
An increase in moderator temperature will have the following effects.
Increase the thermal utilization factor
Decrease resonance escape probability
Decrease fast non-leakage probability
Decrease thermal non-leakage probability
NP-03
Rev. 0
Page 16
