Information On The Use Of Boron Carbide As A Nuclear Control And Poison Material PDF Download

Boron carbide-graphite nuclear control-rod materials containing up to 45 wt% B were prepared by hot-pressing techniques. The densities of these compacts decreased with increasing B content. Compact strengths, however, were noticeably increased with B content of 20 wt%, suggesting that the B acts as a sintering aid. Thermal stability was evaluated by annealing compacts under a variety of temperature and atmospheric conditions. The upper limit of the ioss of 13 was 5% to 10%~ in 200 hr at 2000 deg C--considerably less than would be predicted from the Langmuir evaporation equation. Diffusion of B atoms through the pores of the graphite, rather than evaporation from the surface, was found to be the rate- controlling step in the loss of B. Compacts containing 20, 30, and 40 wt% B were irradiated at 350 and 700 deg C to 1.0 and 2 4 x 10/sup 21/ nvt(fast). Physical integrity of the compacts was good after irradiation. Slight increases in tensile strength were noted in several instances. (auth).