The following gives an overview of other reactivity coefficients defined according to features of the reactor type, regarding an increase in reactor power.

[1] Void coefficient

This coefficient describes a reactivity change due to formation of voids in a liquid coolant. It is used in BWRs to control the reactivity by changing the void fraction. The mechanism of the reactivity change is identical to that discussed in the moderator temperature coefficient.

In sodium-cooled fast reactors, the void reactivity of sodium is evaluated on the basis of coolant boiling caused by hypothetical accidents.

[2] Pressure coefficient

Since PWRs and BWRs are operated at high pressure, the reactivity coefficient to pressure change (pressure coefficient) should be defined. The coolant density increases with pressure and the voids in BWRs are collapsed. The mechanism of the reactivity change is diametrically opposite to that of the moderator temperature coefficient.

[3] Core expansion effect

In a system with a large neutron leakage, an increase in leakage due to expansion or deformation of structure can have a remarkable negative reactiv­ity effect. This effect is especially important for small fast reactors.