Yet another fictious piece of military technology.
Nuclear handgrenade seems to be a perfect weapon for killing a lot of enemies, but it seems to have certain drawbacks:
- It's probably pretty hard to make a functional nuclear weapon of that size, and
- The effective blast radius of the grenade will probably be a bit larger than the range it can be thrown.
However, there seems to be at least some evidence that there have been efforts to make nuclear handgrenades, or at least something related (small nuclear weapons can be a fairly scary thought).
On related military technology, see: Helicopter Ejection Seat, suitcase nuke.