Why is uranium fragile?
The Wikipedia entry for uranium describes it as 'malleable and ductile'. This seems the opposite of fragile. Considering that depleted uranium is used in armor piercing munitions, this does not indicate a fragile material.
Perhaps the "idea" behind the question relates to the fact that uranium is a fairly reactive metal. It's actually pyrophoric, meaning that when it is finely diveded, it will react spontaneously. If we could throw a spoonful of uranium powder into the air, it would react and burn in that air. This would not be smart, of course. It would, in fact, be a disasterously foolish thing to do as the resulting uranium compounds would pose a serious health risk. This is because uranium, though mildly radioactively, is a seriously toxic heavy metal. The combustion products would be airborne, and if inhaled, woe be unto the person who breathed much of it in.
Uranium is a chemical element with three natural isotopes (234, 235, 238). The natural uranium has cca. 0,72 % uranium-235; uranium with a concentration of uranium-235 under 0,72 % is called depleted uranium; uranium with a concentration of uranium -235 above 0,72 % is called enriched uranium. Uranium in nuclear power and research reactors is used as metal, aloys, uranium dioxide, uranium carbides, uranium silicides, etc.