In X-Men: First Class, Sebastian Shaw was the leader of the Hellfire club. He has the ability to absorb energy to keep him young and then use that energy to give him strength, or just release it.
At the end of the movie, he was murdered by Magneto in an act of revenge, but Shaw had absorbed an entire nuclear fusion reaction beforehand, and he never released the energy.
Why didn't he explode? Where did all of that excess energy go?
Sebastian Shaw: Mutant Powerhouse
In the canon X-men comics when we first meet Sebastian Shaw, he is the leader of the Hellfire Club. They are a group of businessmen whose inner circle included a band of incredibly powerful mutants who used their money, power and superhuman abilities to affect their fiscal opportunities in any number of financial markets. They tended to work undercover and had elaborate hideouts, often in major cities around the world.
Uncharged, Shaw is a very strong, highly conditioned and well trained martial artist, proficient in a number of hand to hand techniques, as well as ancient and modern weapons. In his uncharged state, he does not possess superhuman strength.
Sebastian Shaw's mutant ability is the ability to absorb kinetic energy and weapons that use kinetic energy such as bullets or explosives and transform it into superhuman feats of strength and resistance to injury. It is speculated that part of this is the transformation of energy into mass, making him denser and stronger.
In essence, the harder you hit him, the stronger he got as he converted the energy of being attacked into resistance to damage. He could absorb energy even if he was the one doing the hitting as well. He could charge himself by punching a wall and was seen to do so before starting his day.
When forced to engage in hand to hand, Shaw's most common tactic was to engage the physically strongest enemy and tie that enemy up in hand to hand combat, since he could not be harmed. Shaw was able to effectively resist Colossus whose strength was considered capable of lifting 100 tons and give as good as he got, without injury. His strength increase would allow him to become as strong as or stronger than the person he was fighting.
It was noted he avoided combat with Wolverine, so it was not clear if he could be cut by his adamantium claws. But he was tough enough to resist damage from swords and other normal cutting weapons.
Fighting Shaw was always a challenge for the X-men, and they learned after several encounters to remove him from the fight arena was the most effective means of dealing with him. Rogue threw him from one fight and Cyclops would use his optic blast to push Shaw far away from the fight since he had no extraordinary movement powers. It would not harm him but it could delay him giving them time to create a strategy to restrain him.
He was often slowed or stopped by mutants who could manipulate energy or could attack him without further enhancing his powers. Both Storm and Iceman were perfect for that job since they could bind him in ice or snow reducing his effectiveness. He could also be driven into unconsciousness by lightning strikes or the use of psionic powers of which he seemed to be no more resistant than any other human.
While supercharged, Shaw could resist sleep for extended periods and was noted to use psychology to taunt his enemies into attacking him before they realized what he was doing.It is not known if Shaw needs air or food to survive, or whether he could survive in space if he were supercharged.
Sebastian Shaw, X-men First Class
Shaw from the movie X-men, First Class was not quite the same as his Marvel Comics appearances as the leader of the Hellfire Club. In the comics, while Shaw could absorb kinetic energy and store it for his later conversion or use, he could not redirect energy into energy spheres, for example, to poison someone like he did with Darwin, nor could he redirect fire as he did when he was attacked by the security detail.
First Class' Shaw was more powerful than his comic counterpart, and that was likely to offset the fact the Hellfire club was far smaller on the screen than it was in the comics.
As to where the energy Shaw manipulated went, it is safe to say he was like all mutants and redirected energy he absorbed, first into his cells, supercharging his body's damage resistance and strength. Once his body peaked, and we are not sure what that peak was, he would likely store it in the same energy dimension as most mutants seemed to draw their energy from.
Since most mutants use far more energy than they could possibly be getting from their food (even if they utilized 100% of the energy used from their food, we for example, use about 14% of our food's energy) they must be drawing the remainder of the energy from somewhere else.
In the Marvel Universe, it is theorized that most metahumans draw their energy and their energy manipulating powers from a nearby, highly responsive, accessible, energy-based universe, that while it cannot support life, their mutant physiology allows them to access that energy for a limited number of superhuman abilities.
This same dimension or one very much like it is responsible for physical transformation such as Colossus' transformation to living Osmium (the metal that comprises his metallic form.)
Where does the energy of the food you consume go when you die?
I would assume the energy he absorbed is still there, stored in his cells. There will be some mighty powerful worms and bacteria wherever he ends up buried.
If a person with powers like Sebastian Shaw's existed, what effects would it have on him/her taking into consideration elements of mother nature?
An example; Sebastian Shaw absorbs kinetic energy. I think that he would have the ability to move exceptionally fast being the fact that he wouldn't necessarily have resistance from the air, thus absorbing air friction.