What are the most common materials used? How important are Ag-In-Cd alloys in control rods? Have they been superceded by other materials in newer designs?
In my experience with BWRs, boron carbide (b4c) powder in tubes; once the boron absorbs a neutron, it is "used up"; newer designs use hafnium, because after absorbing neutrons, it becomes other isotopes of hafnium that are also good neutron absorbers.
