[en] Durability of an La₂Zr₂O₇ waste form containing various amounts of simulated HLW elements was examined at 90 C in three kinds of solutions. In HCl solution of pH=1, the leach rates of La, Nd and Ce from the La₂Zr₂O₇ waste form decreased with increasing concentration of Nd and Ce which were solved in La₂Zr₂O₇ yielding solid solutions. In deionized water of pH=5.6 and NaOH solution of pH=10, however, such a compositional effect on leach rates was not observed because of the formation of hydroxides or cabonates on the surface of the solid. (orig.)