The microhomogeneity of UO 2 PuO 2 sintered fuel pellets has been determined autoradiographically from data obtained from the “stars” produced by high local concentrations of PuO 2. The method involves the counting of the α tracks, in “stars”, of projected length greater than a certain fraction, x, of the maximum track length, R e , in the emulsion. The value of x chosen, 0.4 R e , limits the depth of the section being examined and is a compromise between obtaining the thin section required by the method used in interpreting the results, and obtaining a reasonable number of tracks. The number of tracks, of length x⩾0.4 R e , associated with particular “stars” is used to calculate the volume of PuO 2 in the sectioned particles and the true particle size distribution in the fuel calculated from the size distribution of the sectioned particles in the plane of observation. The final results are in the shape of statistical information about the particles as an assembly, and not about individual particles. The method gives a semi-quantitative picture of the particle size distribution and is applicable to loadings of up to 3 wt % Pu 239O 2.
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