With this perk you erupt into a devastating nuclear explosion similar to the explosion of a car or mini nuke whenever your health is reduced to 20 or less. Any allies in the vicinity will also suffer the effects of the blast.
You will be healed by a certain amount of health (to make your health 20+) when this perk activates. The amount of damage dealt and healing received is determined by your damage resistance. Radiation is reset to 0 after exploding (although you're likely to collect some radiation from the explosion itself).
You will continue to explode every 10 seconds until your health is 20+.
The explosion damages armor. This is important if you have rare kinds of armor, or if your repair skill is low.
The blast radius damages/cripples your limbs.
This is a relatively useless perk. As being about the power of a mini-nuke, it isn't much to look at and its range is quite limited as well as the player hurting any nearby allies including companions. When playing on harder difficulties, it is very hard to get to just under 20 health because only on very low difficulties weapons would do little enough damage so you wouldn't die before reaching this state.
Even though all radiation is released when you explode, having a higher radiation level when the explosion occurs does not increase damage at all.
PCXbox 360 When playing on normal difficulty or higher, you can be killed by the explosion before the health regain activates. This makes the perk entirely useless at higher difficulties (the perk merely kills you when your health reaches 20).