PHASE-EQUILIBRIA IN THE UO2-AUSTENITIC STEEL SYSTEM UP TO 3000-DEGREES-C

The pseudobinary UO2-austenitic steel system was investigated by DTA u p to 1500 degrees C, by isothermal annealing up to 2000 degrees C, by induction heating up to 2850 degrees C and by are melting up to about 3000 degrees C. The system is characterized by a degenerate eutectic a t 1433 degrees C on the steel side and a monotectic at 2830 degrees C and about 1 mol% steel. The maximum solubility of steel in solid UO2 i s 0.6 mol%, that in liquid UO2 at 3000 degrees C is about 4 mol%. UO2 and steel form (Fe, Mn, Cr)(2)O-3 precipitates between 1300 and 2600 d egrees C as UO2 becomes hypostoichiometric. Liquid steel is stabilized to higher temperatures above its boiling point at 2790 degrees C by d issolution of uranium and decomposes peritectically to liquid UO2-x an d gas at estimated 3200 degrees C. The critical data of the single-pha se UO2-steel melt based on the application of the Redlich-Kister model are T-c = 4900 degrees C, p(c) = 300 bar and x(c,steel) = 0.41. (C) 1 997 Elsevier Science B.V.