The Nuclear Frag is a secondary grenade that appears as a NukePower-Up, but can be retrieved from the Mystery Box and is thrown on demand. When thrown, the Nuclear Frag creates an instant Nuke, similar to the Nuke Power-Up. This may be used when a player needs to be revived, or when the players are being overrun by zombies.
The Nuclear Frag also appears in the Apocalypse IV: Imminent Impactstoryline, but its name has been slightly altered to "Nuclear Frag Grenade". It can be obtained only from the Mystery Box. When obtained, the player will have three of them. The Nuclear Frag Grenade is the replacement for the Gersch Device, as it kills any zombie on the map after three seconds. This effect gives players a chance to reload, revive a player, etc. Unlike regular grenades, it cannot be 'cooked'. The basic appearance of the grenade is similar to the M92 Fragmentation Grenade, except that it is black and has a more futuristic look to it. How the grenade does not kill the players is unknown. It is also unknown who created it.