Editing Neutron reflector (section)

==Nuclear reactors==
In a [[uranium]] graphite chain reacting pile, the [[critical mass|critical size]] may be considerably reduced by surrounding the pile with a layer of graphite, since such an envelope reflects many neutrons back into the pile.

To obtain a 30-year life span, the [[Small, sealed, transportable, autonomous reactor|SSTAR]] nuclear reactor design calls for a moveable neutron reflector to be placed over the column of fuel. The reflector's slow downward travel over the column would cause the fuel to be burned from the top of the column to the bottom.

A reflector made of a light material like [[graphite]] or [[beryllium]] will also serve as a [[neutron moderator]] reducing neutron kinetic energy, while a heavy material like [[lead]] or [[lead-bismuth eutectic]] will have less effect on neutron velocity.

In power reactors, a neutron reflector reduces the non-uniformity of the power distribution in the peripheral fuel assemblies, reduces neutron leakage and reduces a coolant flow bypass of the core. By reducing neutron leakage, the reflector increases reactivity of the core and reduces the amount of fuel necessary to maintain the reactor critical for a long period. In [[light-water reactor]]s, the neutron reflector is installed for following purposes:
* The neutron flux distribution is "flattened", i.e., the ratio of the average flux to the maximum flux is increased. Therefore, reflectors reduce the non-uniformity of the power distribution.
* By increasing the neutron flux at the edge of the [[Nuclear reactor core|core]], there is much better utilization in the peripheral fuel assemblies. This fuel, in the outer regions of the core, now contributes much more to the total power production.
* The neutron reflector scatters back (or reflects) into the core many neutrons that would otherwise escape. The neutrons reflected back into the core are available for chain reaction. This means that the minimum critical size of the reactor is reduced. Alternatively, if the core size is maintained, the reflector makes additional reactivity available for higher fuel burnup. The decrease in the critical size of core required is known as the reflector savings.
* Neutron reflectors reduce neutron leakage, i.e., to reduce the neutron fluence on a reactor pressure vessel.
* Neutron reflectors reduce a coolant flow bypass of a core.
* Neutron reflectors serve as a thermal and radiation shield of a reactor core.