And if splitting atom releases energy, why haven’t these energy break from their atom themselves? Isn’t that means the force that bind the atoms are bigger than the energy released?
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You do get spontaneous fission of uranium-235, it’s very rare but does occur. U-235 only makes up 0.7% of all uranium so it’s a rare occurrence in a rare isotope so only detected if you really go looking for it.
Nuclear explosions cannot occur with natural uranium, you need to enrich the U-235 isotope to above 75% and even then it doesn’t spontaneously explode as a mushroom cloud. As soon as the chain reaction starts the U-235 would heat up to a gas, expand and fission would stop.
The naturally occurring reactors in Oklo that have been mentioned were not explosions. The isotope ratio was sufficiently high 2 billion years ago that if water flowed through a concentrated pocket of uranium that it could sustain a chain of fission events like that used in commercial nuclear reactors. They lasted something like 30 minutes before the ore got hot enough to boil off the water and then they stopped. Fuel cooled, water flowed again and the processing repeated again.
The atoms after fission are arranged in a more stable manner than before fission. The difference in stability is the energy released (in the form of kinetic energy of the fission products-they are moving faster than the U-235 atom prior to fission).
Uranium is releasing energy every day, all over — and through — the Earth. It’s possible Earth’s core would have cooled by now if not for this natural radioactivity.
It’s just not enough for a self-sustaining chain reaction. You need lots of very pure uranium for that.
A nuclear explosion is kind of like a traffic jam. Radioactive atoms like uranium naturally emit high energy particles every so often, just like cars naturally have to brake quickly every so often on the freeway, maybe somebody cut someone else off or an animal ran across the road.
If another car is close enough behind the first car, that car will have to brake suddenly too. Similarly, if another nuclear fuel atom is close enough to the first one, it may get hit by the emitted particle and burst apart, releasing more high energy particles.
However, in normal circumstances, both cars on the freeway and nuclear fuel atoms are too spread out to sustain this chain reaction for very long, so nothing really happens. One car having to slow down briefly isn’t going to cause much chaos, and one uranium atom splitting won’t release much energy.
Only once you reach a certain density of cars all trying to use the freeway at once do you start to have the potential for major traffic buildup, and once you reach that point, BOOM. Traffic jams happen like that.
Likewise, once you get enough nuclear fuel atoms close together in high enough concentration, you reach a point called “criticality” when nuclear chain reactions can spontaneously occur.
The answer to your question is that viable nuclear fuels just don’t really exist in such high concentrations in nature. Specific isotopes of uranium are needed to sustain a nuclear chain reaction because the isotope determines the possible components they can break apart into when they split, and in nature those isotopes are found mixed together with lots of other uranium isotopes and minerals. Nuclear fuels undergo a refining process which removes all the other stuff and leaves mostly just the isotope we want, and then the fuel rods are put into specialized chambers with particle reflectors and other rods in the reactor in order to finally reach criticality and start the reaction.
We should also note that when the uranium was made in a supernova explosion, billions of years ago, the uranium was roughly an equal mixture of U-238 and U-235. While this is enriched uranium, it is not highly enriched. So if you get a moderator like water for the neutrons, you can form a reactor or even an “out of control” reactor which boils away the moderator and stops and starts again, but you can’t assemble enough U-235 to make a prompt critical explosion which goes off in microseconds.
Different types of uranium. Uranium ore we dig up is more stable and sheds radiations much less than the one we use for reactors.
Elements aren’t one-size-fits-all, contrary to common understanding. There are isotopes. An “element” is defined by the number of protons in its nucleus; isotopes will have the same number of protons, but varying numbers of neutrons.
The type of uranium we use for nuclear reactions is an unstable isotope that we have to make artificially. We make it by taking the naturally-occurring uranium and enriching it (we use a bunch of chemical reactions and lasers to isolate uranium atoms to, more or less, forcibly shove more neutrons into their nuclei).
Splitting the uranium atom releases energy because you’re breaking the strong nuclear force, the force that holds protons and neutrons together in the nucleus. Imagine it’s really strong glue that holds lego bricks together.
We haven’t seen a nuclear explosion in natural ore because it has decayed into a stable isotope. This is because the glue is so strong that the bricks don’t want to break apart.
>And if splitting atom releases energy, why haven’t these energy break from their watom themselves?
When a nucleus decays energy is conserved by the emission of a particle and EM radiation.
>Isn’t that means the force that bind the atoms are bigger than the energy released?
Yes. You have basically described the strong nuclear force.
In answer to your first question: Natural uranium decay is a slow process, and uranium tends not to be very concentrated in ore. So, the combination of slow decay and low concentration can’t really cause a runaway reaction.
As to your second and third questions: Imagine a bunch of strong springs stuffed into a box. That is similar to what is happening in a big atom, where there is a struggle between the binding “strong nuclear” force and the repulsive “electromagnetic force”. For reasons we do not fully understand, the lid of the box fails, and the springs all come flying out. The potential energy is turned into kinetic energy. The decay products of the uranium are like the springs, and they can collide into other atoms, or collide into electrons. The end result is a lot of ionizations, heat, photons of light, and in a highly enriched environment, the flying springs can start knocking the lids off other boxes, causing the decay process to accelerate.
If we assume such an event could happen, all the hypothetical uranium deposits that were sufficiently unstable enough to spontaneously explode did so when they formed back when the planet coalesced into a planet, or when the planets early geology shuffled subcritical masses into each other. What remains is the pockets of subcritical ore that have been subcritical long enough that enough of their unstable isotopes have slowly decayed and now they are very subcritical and no longer susceptible to causing such events. This has likely been the case for billions of years, if it ever occurred at all.
Sufficiently unstable naturally occurring radioactive ores are actually warm to the touch–so in a sense even the ore we’re left with *actually is releasing energy in exactly the way you describe*. It’s just not happening catastrophically fast any more (if it ever did at all).
An RTG (Radioisotope thermoelectric generator) is essentially a very simple generator that takes advantage of this heat to directly generate a small amount of electricity.
Shortest answer . . . it doesn’t currently exist in high enough concentrations to achieve the critical mass needed for an energetic reaction (heat) much less explosion. Critical mass is when the uranium atoms are close enough together that if one goes, it starts a chain reaction and they all do. Before it is mined, refined, and piled together, those single random decays just wander off into non-uranium matter and lose their energy before they can start something.
i mean i’m just asking but why is this labelled as physics when it is clearly a chemistry question
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