An assembly containing strong neutron absorbers such as boron carbide, silver-indium-cadmium alloy or hafnium, moved into or out of the core to change reactivity. PWRs use clusters of thin rods lowered from above into fuel assemblies and arranged in banks; BWRs use cruciform blades inserted from below between bundles. Rod positions, insertion limits and rod-drop times are tightly controlled by technical specifications.
Control rod H-8 is reading 6 steps out of alignment with its bank, call I&C before we move anything.
Also heard as
- rod
- control rod assembly
Related terms
Scram
The rapid automatic or manual insertion of all control rods to shut a reactor down in seconds.
Reactivity
A measure of how far a reactor is from criticality, positive when power will rise and negative when it will fall.
Shutdown margin
How far subcritical a reactor would be with all rods inserted except the single most valuable one stuck out.
Criticality
The state in which a chain reaction sustains itself at a steady rate, with each fission causing on average exactly one more.