Strictly speaking, we CAN use most nuclear waste. Breeder reactors can be used to consume pretty much all usable fissle materials and produce a much lower volume of equivalent waste with different properties.
Breeder reactors can be used to manufacture weapons grade fissile material though, so there's political aspects, as well as economic ones-- uranium is fairly abundant.
Edit: spelling errors.
Radioactivity, by itself, is not that useful for generating power. What is useful for generating power is the induced splitting of _lots_ of atoms at the same time, not the slow trickle of energy release you get from radioactive decay alone. To put it another way: nuclear reactors don't work because their fuel is radioactive, they work because their fuel is splittable by neutrons. Those are not the same thing (all fuel splittable by neutrons is radioactive, but not all radioactive atoms are splittable by neutrons).
Check out "Reprocessing"; it's the step we removed from the current nuclear power cycle, and a major reason why our nuclear waste is so hard to store.
Basically you take the used fuel rods and extract the parts that can be reused in reactors as fuel, separate the super-highly radioactive stuff that can't be used in a reactor for short term storage, and then you're left mostly with stuff that's more dangerous from heavy metal poisoning than the radiation (U-238 eg).
It was stopped in the us by president Carter because of concerns about nuclear proliferation; I guess he thought we'd be clever enough to figure out how to safely store nuclear waste without a reprocessing industry, but so far we haven't, which is why we have spent fuel rods piling up.
It is very usable, just not in our current nuclear reactors. Uranium fuel rods are pellets of uranium held together by a metal casing. Being inside a reactor causes the metal to become brittle, and the life of the fuel rod is determined by the life of that casing.
In other reactor designs, like molten salt reactors, this casing is not used. The fuel stays in the reactor for much longer and much more of the potential energy is extracted. This results in lower volumes of waste that is much less radioactive for much less time than that coming from traditional reactors.
Learn more about molten salt reactors [here](https://en.m.wikipedia.org/wiki/Molten_salt_reactor
). They’re pretty awesome!
Nuclear fuel becomes “waste” when it no longer produces enough neutrons to sustain a nuclear chain reaction. The kinetic energy of neutrons drives the heat cycle that produces power. The gamma and beta radiation produced by “waste” isotopes contribute very little.
American scientists developed a nuclear reprocessing system called PUREX (Plutonium-Uranium Extraction) to resume spent nuclear fuel rods. But Ford suspended it and Carter ended it permanently because of the plutonium by-product and the Non-Proliferation Agreements. Now France reprocesses many nation's fuel for reuse using this 50 year old technology.
There are lots of things classed as “nuclear waste”. Some of those things can be used as fuel, or for other purposes.
The devil is in the details. Which materials? Used for what? At what cost? Etc.
Most reactors are metal reactors and using these materials is either technically infeasible or economically infeasible.
But Liquid Fluoride Thorium Reactors (LFTRs) can use many nuclear waste materials as fuel. They are an interesting technology I expect to see make an impact in the coming years.
A lot of good answers here. But also in the US, there are actually laws in place that hinder our ability to even push for nuclear fuel recycling technologies. It's mostly dueto the Ford/Carter fear of fissile by-products and the cold war as some have pointed out.
My company, in France, is all about pushing for recycling their waste.
That said, you need the right products left to split for heat production to make energy worth the effort. It's not about that they give off radiation, so this will only help so much.
TBH it is a conversation I would LOVE to see more of though as it is a real way we can promote the energy and make it a bit safer considering how much the world is relying on it while fearing it lately.
In a nuclear reactor, energy is released via fission. Some nuclides, such as U-235, are fissile, meaning they can easily undergo fission. Other nuclides, like U-238, are fertile; this means they can be converted to a fissile material by absorbing neutrons.
Nuclear waste consists of many different nuclides. There is some uranium left in the waste, and it is possible to reprocess the spent fuel to retrieve it. This is pretty expensive, and the US doesn't currently do this. Many of the other components of nuclear waste (Cs-137, Sr-90, ...) are not fissile or fertile, so they aren't useful for generating nuclear power even though they are still highly radioactive.