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Reactor Theory (Neutron Characteristics)
DOE-HDBK-1019/1-93
NEUTRON SOURCES
Rev. 0
Page 1
NP-02
NEUTRON SOURCES
Neutrons from a variety of sources are always present in a reactor core. This is
true even when the reactor is shut down. Some of these neutrons are produced by
naturally occurring (intrinsic) neutron sources, while others may be the result of
fabricated (installed) neutron sources that are incorporated into the design of the
reactor. The neutrons produced by sources other than neutron-induced fission
are often grouped together and classified as source neutrons.
EO 1.1
DEFINE the following terms:
a.
Intrinsic neutron source
b.
Installed neutron source
EO 1.2
LIST three examples of reactions that produce neutrons in
intrinsic neutron sources.
EO 1.3
LIST three examples of reactions that produce neutrons in
installed neutron sources.
Neutron Sources
In addition to neutron-induced fission, neutrons are produced by other reactions. The neutrons
produced by reactions other than neutron-induced fission are called source neutrons. Source
neutrons are important because they ensure that the neutron population remains high enough to
allow a visible indication of neutron level on the most sensitive monitoring instruments while the
reactor is shutdown and during the startup sequence. This verifies instrument operability and
allows monitoring of neutron population changes. Source neutrons can be classified as either
intrinsic or installed neutron sources.
Intrinsic Neutron Sources
Some neutrons will be produced in the materials present in the reactor due to a variety of
unavoidable reactions that occur because of the nature of these materials. Intrinsic neutron
sources are those neutron-producing reactions that always occur in reactor materials.
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