Boron may also be used as a burnable poison to compensate for the change in reactivity with
lifetime. In this scheme, a small amount of boron is incorporated into the fuel or special
burnable poison rods to reduce the beginning-of-life reactivity. Burnup of the poison causes a
reactivity increase that partially compensates for the decrease in reactivity due to fuel burnup
and accumulation of fission products. Difficulties have generally been encountered when boron
is incorporated directly with the fuel, and most applications have used separate burnable poison
The important information in this chapter is summarized below.
Control Materials Summary
Excellent control for water-cooled, water-moderated reactors
due to neutronic, mechanical, and physical properties.
Limited availability and high cost.
Highly effective neutron absorber.
Control effectiveness in water-moderated reactors is close to
hafnium. Used in pressurized-water reactors.
Easily fabricated and adequate strength
Must be enclosed in stainless steel tube to protect it from
Very high thermal-absorption cross-section and low cost.
Commonly used in thermal reactors for control rods and
Nonmetallic thus must be incorporated into a metallic
material for use as control rod.