why splitting uranium releases energy but we haven’t see any stray (random) nuclear explosion in natural ore deposits?

Question

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?

In: 508

Answer 1

Individual uranium atoms split (fission) all the time. You can measure this with the right tools. The reactions release a microscopic amount of energy.

The energy released in a nuclear explosion or nuclear reactor is a _chain reaction_ of those fission events. So one atom fissions, and its neutrons cause other atoms to fission, and their neutrons cause other atoms to fissions, and so on. In a reactor this is slow and controlled, in a bomb is very fast.

There are specific conditions that need to be created for these kinds of chain reactions to exist. At the most basic level, you need enough of the right kind of uranium (U-235) near itself, without too much stuff around it that will also absorb the neutrons. If you want an explosive reaction, you need almost entirely U-235 by itself.

There are other things you can do to change the conditions to make these reactions happen — there are many ways to design nuclear reactors. The long and short of it, though, is that uranium as it is today found in nature requires very, very specific conditions to work in a nuclear reactor, because its concentration of U-235 is very low. As others have noted, 1.7 billion years ago, the concentration of U-235 was higher in natural ore, and enough that natural conditions could produce a sort of nuclear reactor. But because of nuclear decay, natural uranium ore today could not produce those conditions in nature. It is possible to use uranium with the same enrichment as natural ore in a reactor, but it requires creating very artificial conditions (like rendering all of that ore into metal, putting it into very specific geometries, having very specific “moderators” that increase the chance of fission).

At no point in the past was it ever possible to have a natural nuclear explosion. The requirements for a nuclear bomb are very specific and very artificial. They can be achieved — a nuclear bomb is just an engineering device for achieving those conditions — but you will not find them in nature.