The energy that I am talking about is the potential energy that is converted to kinetic energy in fission reactions. There are many web sites that explain the fission reaction and the amount of power that can be released in the conversion process.
One such site is the following.

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fission.html

If you read the information on that web site you will get a better understanding of the premise that I am trying to explain.
On that site under “Uranium Fuel” it says:
“ Natural uranium is composed of 0.72% U-235 (the fissionable isotope), 99.27% U-238, and a trace quantity 0.0055% U-234“

Under the heading “Fissionable Isotopes” it says:
“While uranium-235 is the naturally occuring fissionable isotope, there are other isotopes which can be induced to fission by neutron bombardment. Plutonium-239 is also fissionable by bombardment with slow neutrons, and both it and uranium-235 have been used to make nuclear fission bombs. Plutonium-239 can be produced by "breeding" it from uranium-238. Uranium-238, which makes up 99.3% of natural uranium, is not fissionable by slow neutrons. U-238 has a small probability for spontaneous fission and also a small probability of fission when bombarded with fast neutrons, but it is not useful as a nuclear fuel source.”

That brings me to a thought of a very BRIEF HITORY OF THE EARTH
The scenario that I can imagine for the Earth goes somewhat like this: Four billion years ago when the Earth was being born, there was more radioactive Uranium 238 and a greater than 0.72% of it was U-235. Over millions of years the uranium was shifted from place to place by tectonic activity, and the lighter elements such as silicon rose to the top and covered the radioactive materials. The fission material remained underground and simply heated the material in the vicinity where it existed. Millions of years passed and the amount of fissionable U-235 decreased in quantity to the 0.72% of the present day U-238.

Then man came along and saw that there was heat energy coming from the uranium and figured that the energy was “free” just for the taking. When he took it out of the ground into the atmosphere and studied it, he realized that it can be made into very destructive bombs, he also noticed that there is a way to release more of the potential energy by “breeding” the U-238 atoms into plutonium atoms.
All this activity happened above ground in the atmosphere, for every atom that was converted to another atom there was a release of energy and that energy entered the atmosphere and the surrounding environment, this energy then heated the surrounding environment including the air.
Man noticed the heat and said “heat is valuable” we can make electricity with it, they then made many electricity generators using nuclear power. Such world wide activity needed thousands of tons of U-238 atoms, which they were able to dig up from the ground and bring to the surface environment. At the surface, the potential energy of natural uranium was converted into more potent energy within the electricity generator buildings. The “more potent” material could be used for bombs, and many nations constructed and exploded such bombs, many more nations desired to own such bombs.
While this feverish nuclear activity was going on, it seems that some of the laws of physics were forgotten by the people involved in engineering and physics.

Although every atom that broke apart in the nuclear process imparted its kinetic energy to the surface environment, it was considered as miniscule amount and of no consequence to the global environment. Even when evidence surfaced that the global temperature was increasing and atmospheric molecules were escaping Earth’s gravitational field, it was simply attributed to some other cause, rather than the kinetic energy that originates in the conversion process within the nucleus of an atom.
According to the laws of physics, this extra (man made) energy eventually created impossible living conditions on the planet. Thousands of years passed before the planet became habitable again. THE END

From:

http://en.wikipedia.org/wiki/Nuclear_fission

“Typical fission events release about two hundred million eV (200 MeV) of energy for each fission event. By contrast, most chemical oxidation reactions (such as burning coal or TNT) release at most a few eV per event. So, nuclear fuel contains at least ten million times more usable energy per unit mass than does chemical fuel. The energy of nuclear fission is released as kinetic energy of the fission products and fragments, and as electromagnetic radiation in the form of gamma rays; in a nuclear reactor, the energy is converted to heat as the particles and gamma rays collide with the atoms that make up the reactor and its working fluid, usually water or occasionally heavy water.”

I assume that by “each fission event” they mean the break up of one atomic nucleus.
What is not pointed out there is that the “parts” that come from the break up are radioactive, and impart kinetic energy to the surroundings, as explained at the following web site.

http://mitnse.files.wordpress.com/2011/03/fission_02.pdf

“When an atom decays, it gives off energy or particles to become more stable. The energy or particles then interact with the surroundings to generate heat.”

In other words, the first fission event causes the remaining parts to be very unstable, and the unstable parts cause instability in their surroundings until everything settles down.

It is somewhat comparable to burning a log in a fire, the heat advances until the fuel runs out, the only difference is that a log burns to ash and cools down quickly, whereas the radioactivity, with its ability to heat the surroundings, will continue and accumulate for a very long time.
U-235 has a half life of 700 million years. Plutonium-239 has a half-life of 24,200 years.

From:
http://en.wikipedia.org/wiki/Uranium_mines

“Uranium mining is presently carried out in about 15 countries around the world, producing a cumulative total of 53663 tonne uranium (tU).”

How many “fission events” of two hundred million electron volts each, can be created from 53663 tonnes of uranium?
How many Plutonium-239 atoms and other radioactive elements can be “bred” from 53663 tonnes of uranium?
How much energy will be inserted into the atmosphere from the 53663 tonnes of uranium, after it has been converted and intensified in the nuclear furnace?

It is a good thing that the Earth has a way of dealing with a little bit of extra heat (energy) otherwise we would be toast all ready.

Nuclear bomb
http://www.atomicarchive.com/Fission/Fission10.shtml