Solidus and liquidus temperatures of core-concrete mixtures

Solidus and liquidus temperatures were measured for four types of concrete (limestone, limestone sand, basalt, and siliceous) and for their mixtures with urania and zirconia. Differential thermal analysis (DTA) was generally employed to determine the solidus and liquidus temperatures. However, some liquidus temperatures were also measured by rotational viscometry. The measured solidus temperatures for the urania-zirconia-concrete mixtures were significantly lower (hundreds of degrees) than those employed in the CORCON-Mod 2 thermal hydraulic code, and the measured liquidus temperatures were significantly higher (also hundreds of degrees). The liquidus temperatures for urania-zirconia-concrete mixtures containing limestone or limestone-sand concrete were generally above 2850 K, which was the upper temperature limit of our experiments. The revised solidus and liquidus temperatures are to be incorporated in the CORCON-Mod 3 thermal hydraulic code which is an integral part of the US Nuclear Regulatory Commission's NELCOR Code. MELCOR computes the consequences of severe accidents at nuclear reactors. DTA was also employed to redetermine the calcia-urania (CaO-UO2) phase diagram. Earlier data were not in agreement, and this binary phase diagram is required in computer programs that calculate the phase diagrams (and solidus and liquidus temperatures) of urania-zirconia-concrete systems from the phase diagrams of simpler systems. A eutectic temperature and composition of 2218±5 K and 37 mol% U02, respectively, were determined for the CaO-U02 system. The solubility of CaO in U02 at the eutectic temperature was 30 mot% CaO