Nuclear fission reactors are absolutely necessary, if we're going to decarbonize our energy sector. Unfortunately, the details are not pretty.
Leaving aside the spent fuel rods (and the
much larger amount of radioactive waste that you get when you disassemble the reactor itself after its 40 year useful lifetime is up), you need to think about the input, namely the uranium itself.
The first thing you need to know is that natural uranium is 99.3% ²³⁸U, and only 0.7% ²³⁵U. It's only the ²³⁵U that participates in fission.
You
could use the fast neutrons produced in the fission reaction to convert ²³⁸U to Plutonium-239 (neutron capture, followed by beta decay). ²³⁹Pu does undergo fission. In the most efficient designs, a "fast breeder reactor" produces more fissile material than it consumes. That can be reprocessed to fuel other (non-breeder) reactors.
For decades, France was big into breeder reactors, but their last one was shut down in 1997 and no new ones are planned. More modestly, Canada's
CANDU reactors burn unenriched natural uranium. Just enough ²³⁸U is converted to ²³⁹Pu to keep the fission reaction going longer. Because of that, they use 30-40% less mined uranium per MWhr of electricity generated than do light-water reactors.
The US and most of the rest of the world use light-water reactors. They burn enriched uranium, whose ²³⁵U content has been increased to 2%-5%. What you do with the depleted uranium that's left over is an interesting question. Traditionally, it's been used for artillery shells (14% heavier than lead). Maybe there are other,
less problematic uses.
But, in any case, the takeaway is that
at most 0.7% of the uranium that's dug out of the ground is used to produce energy in an LWR. I say "at most", because there's one thing I haven't told you yet:
neutron poisoning means that in conventional LWRs, the fission reaction shuts down long before all the ²³⁵U is consumed. In some designs,
as little as 5% of the available ²³⁵U is consumed (that's 5% of 0.7% = 0.035% of the uranium dug out of the ground).
There are ways around this. The biggest neutron poison is ¹³⁵Xe (followed by ⁸³Kr). Both of those are gases. In a
molten salt fission reactor, the nuclear fuel is in liquid form (rather than the solid form in conventional fuel rods). There, the Xenon and Krypton, which would otherwise poison the fission reaction, just bubble to the surface and disappear. Of course, this is just a design proposal and no such power plant has been built yet.
So, barring a dramatic resuscitation of the breeder reactor program, we are actually facing a problem. The world runs out of exploitable ²³⁵U
in less than a century at current rates of usage, and a lot faster if we launched a building spree of LWRs.
