Is there anyone who is well versed in what exactly happens during nuclear activity? I'm specifically looking at nuclear fusion and nuclear fission. I am also looking for anything else that could be used in conjunction with nuclear physics or nuclear power.

The premise is that a certain body can with great effort and esoteric physical organs and metaphysical gifts, be able to manipulate energy on the atomic scale via nuclear fusion and or fission to generate energy within the body, making the eyes glow white ish.

This energy can immediately be catabolized by the body and appropriated to any part or organ system that needs it. Because this is a semi nuclear reaction, mass amounts of energy can be produced over a short time, but not over a long time due to over heating.

If the body over heats its nuclear energy production it literally melts under the heat and detonates as the concentrated atoms are released from the body.

However this energy can also be used in situations almost akin to magic, but really is just raw energy.

Thoughts?

Sounds like an interesting take on an energy-mage concept. I think the most interesting part of this is the notion of overheat; it provides the usual gate to magician power that is required by the genre.
So in your system do energy-wielders actually consumer part of their body via fission to get the energy, or is that just a helpful metaphor for understanding the limitations to their quasi-magic?

Not really.

Real nuclear fission plants work by using nuclear rods and a ton of water. When the rods are brought together, energy is radiated, and when they are separated, energy production slows down.

It's sort of a metaphor for how the energy is made. When the nuclear energy is activated, the person's eyes glow white, signaling the reaction. Their body is biomechanics lily constructed to withstand the internal nuclear radiation, and possesses an internal...shall we say nervous system apart from the CNS and PNS that regulates energy.

For example, muscle cells require ADP and ATP in order to contract. The energy would provide a substitute to ATP if needed, without lactic acid build up.

Or, for eyesight. Images are detected through rods and cones in the eye. The energy allow for microscopic changes to happen inside the eye and perfect transfer of information from the optic nerve to the brain. It also ennervates the iris to dialate or expand a hundred times faster than normal. (At max. Like vampire eyesight from those-books-that-shall-not-be-named.)

The draw back is the energy feedback. The person's cells can handle radiation at any given level, but prolonged radiation will kill them.

15 mins after full power production, eyesight begins to fade and the potential for cramping may occur

30 mins after full power, and decay at the cellular level begins to happen. Cancer is possible here as cells are now burning under the energy.

45 mins is overheat mode, where the body's internal temperature regulator cannot keep up with the demand on cooling as the cells start to die off very rapidly. Blackout actually is common here, as the body's own safety mechanism kicks in, forcibly shutting down the reaction. Kind of like how someone cannot choke themselves manually, because the body will black out and they can't hold on.

Should the person remain conscious, however, anytime after an hour is when critical mass is reached. The Body ignites, cells ALL die, and the excess energy is released through the skin. Right now, they're a walking disaster, releasing potent amounts of radiation as far as 40-100KM.

Then the body will either melt into a glob of radioactive goo. Or detonate with the force of a Tsar Bomb. (Near largest nuclear bomb ever produced)