Experimental reactivity worth of UO₂ pellets containing 3% of Gd₂O₃ dispersed in the form of microspheres with diameters of 80, 120, 190 and 380 μm [13]. Measurements were carried out at the zero-power reactor MINERVE of CEA Cadarache by the oscillation technique [12]. The experimental values $\mathrm{\Delta }{\rho }_{\mathrm{i}}$ are normalized to the nominal value $\mathrm{\Delta }{\rho }_0$ measured in the case of UO₂ pellets containing 3% of homogeneously mixed Gd₂O₃ powder.