Plant MaterialsDOE-HDBK-1017/2-93CONTROL MATERIALSBoron may also be used as a burnable poison to compensate for the change in reactivity withlifetime. In this scheme, a small amount of boron is incorporated into the fuel or specialburnable poison rods to reduce the beginning-of-life reactivity. Burnup of the poison causes areactivity increase that partially compensates for the decrease in reactivity due to fuel burnupand accumulation of fission products. Difficulties have generally been encountered when boronis incorporated directly with the fuel, and most applications have used separate burnable poisonrods.SummaryThe important information in this chapter is summarized below.Control Materials SummaryHafniumAdvantages:Excellent control for water-cooled, water-moderated reactorsdue to neutronic, mechanical, and physical properties.Disadvantages:Limited availability and high cost.Silver-Indium-Cadmium AlloysAdvantages:Highly effective neutron absorber.Control effectiveness in water-moderated reactors is close tohafnium. Used in pressurized-water reactors.Easily fabricated and adequate strengthDisadvantages:Must be enclosed in stainless steel tube to protect it fromcorrosion.BoronAdvantages:Very high thermal-absorption cross-section and low cost. Commonly used in thermal reactors for control rods andburnable poison.Disadvantages:Nonmetallic thus must be incorporated into a metallicmaterial for use as control rod.Rev. 0Page 17MS-05
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