Mechanical properties of BeO-(UTh)O2 dispersion fuels.

Abstract

Dispersions of (UTh)02 in BeO were fabricated using (UTh)02 particles made from mixed powders of U02 and Th02 or by co-precipitation of U02 and Th02. The behaviour of the dispersions was studied by measuring the modulus of rupture and Young's modulus. Modulus of rupture measurements were made by four-point bending of cylindrical specimens, and Young's modulus was calculated from the deflection of rectangular beams. The out-of-pile control specimens for two irradiation experiments, X121 and X105, were also tested. Examination of matching fracture faces showed that cracks passed through (UTh)02 particles, indicating that they were bonded to the matrix. The results were compared with previous results on BeO-Th02 dispersions. The strength of dispersions of (UTh)02 in BeO decreased with increasing (UTh)02 particle size and increasing (UTh)02 concentration. For dispersions of 1.7 v/o (UTh)02 made from mixed oxides in BeO, the strength increased with increasing temperature while for dispersions of (UTh)02 made by co-precipitation, the strength remained unchanged with temperature up to 500ºC and decreased as the temperature was raised to 1000ºC, Young's modulus decreased with increasing (UTh)02 concentration. Young's modulus of 1.7 v/o (UTh)Oa dispersions remained unchanged up to about 600ºC} then decreased slightly as the temperature was raised to 1000ºC, Increasing the (UTnJOa concentration from 1.7 to 20 v/o displaced the curve to lower values. In general, the behaviour of dispersions of (UTh)02 in BeO was similar to that of ThOa in BeO. The differences in behaviour between dispersions of (UTh)Oa made from mixed oxides and by co-precipitation, observed in modulus of rupture tests, were attributed to variations in matrix grain size caused by iron cexamination of the co-precipitated (UThJOg. It was concluded that to obtain maximum strength, the particle size of the (UThJOg should not exceed 5jj., and the particles should contain no impurity which could cause grain growth in the beryllia matrix