Class Notes on Fission Reactors, Nuclear Accident, and Neutron Detector
See also the links and references in 1 and 2 above.
: Advanced Nuclear Power Reactors
A nuclear reactor, in its basic form, consists of four parts:
Fuel (usually enriched uranium);
A moderator, usually made from low atomic mass materials, to thermalize
neutrons (how about the fast reactors?);
Control rods made of materials with a high neutron capture
(e.g., Cd or
A coolant to remove heat
is contained in the
The core is where the fission chain is
sustained and the energy of fission is released as heat.
Since the most of the
fissions result from the absorption of slow neutrons, the
must also be in
the core (recall that the function of the moderator is to slow down the fission
neutrons through the elastic scattering reactions).
The core is surrounded by a
of a material determined largely by the energy distribution of the
neutrons in the reactor.
The purpose of the reflector is to decrease the loss of
neutrons from the core by scattering back many of those which escaped.
of heat generation is proportional to the nuclear fission rate and this is determined,
in a given reactor core, by the neutron density, i.e., the number of neutrons per unit
Control, including startup, operation at any desired power level, and shut
down, is thus achieved by varying the neutron density in the core.
generally done by moving rods of a material that absorbs neutron readily, i.e., a
Insertion of a poison results in decrease in the reactivity (or
neutron multiplying property) of the core and, consequently, in a decrease in the
Note: some reactors (e.g., research, teaching, Naval) use Fuel Rods for control of
The heat generated in the reactor core is removed by circulation of a suitable
Heat must be removed from the core at a rate that permits the coolant to
attain a high temperature without the development of such thermal stresses and
internal temperatures as to cause the reactor to suffer damage.