Reactor Theory (Reactor Operations)
DOE-HDBK-1019/2-93
SUBCRITICAL MULTIPLICATION
Example:
Calculate the subcritical multiplication factors for the following values of keff.
1)
keff = 0.6
2)
keff = 0.986
Solution:
1)
M
1
1 keff
1
1 0.6
2.5
2)
M
1
1 keff
1
1 0.986
71.4
The example above illustrates that the subcritical multiplication factor will increase as positive
reactivity is added to a shutdown reactor, increasing the value of keff. If the source strength of
this reactor were 1000 neutrons/sec, the neutron level would increase from 2500 neutrons/second
at a keff of 0.6 to a neutron level of 71,400 neutrons/sec at a keff of 0.986.
Effect of Reactivity Changes on Subcritical Multiplication
In a subcritical reactor, the neutron level is related to the source strength by Equation (4-2).
(4-2)
N (S) (M)
where:
N
=
neutron level
S
=
neutron source strength
M
=
subcritical multiplication factor
Rev. 0
NP-04
Page 3
