Jargon Series: Fissile vs Fertile

I’ve been seeing another lie popping up about nuclear energy lately. People saying that Even though Nuclear Energy is low carbon, we lack the accessible supplies of Uranium to supply our power requirements for enough time to help combat climate change. ( I plan on touching on those other points in other articles.)

Let’s be generous to the anti-nuclear people and say sure, ignoring all the recyclable spent fuel we have sitting around, and the fact that uranium prospecting has been basically stalled for 30 years because our current known reserves have been more than enough to supply the demand and give them that point. Uranium 235 is only about 0.71% of all uranium, so sure we will say that our fissionable/fissile material supplies will only last us another say 80 years at current rates.

I mean unless there was a way to make fissile material…

Lets make a baby with a Bang!

Uranium-238, Thorium-232, Uranium-234, Plutonium-240, and Americium-241 are all elements that are called Fertile Isotopes. Meaning that by hitting them with a neutron moving at the right speed, it is possible to transmute them into another element/isotope that Can be used as nuclear fuel in a reactor. of those 5 listed, only U-238, U-234 and Th-232 exist naturally, the others having all decayed away in our solar system billions of years ago.

So what does this mean? Well if we accept that claim that there is only enough Uranium -235 for 80 more years of current consumption levels, then just by using all the Uranium-238 as a fertile fuel source to breed Plutonium -239 we would get enough fuel for 80 years x (99.28%/0.71%) = 11,186 years at current consumption levels. Just as a bit of perspective, the entirety of archaeological human history is approximately that long, with structures found dating back to about 10,000 BC.

Some people think it might be way older, which would be super interesting. But it still wasn’t Aliens.

And that amount of time is Just from the reserves we know about. The vast majority of the energy we extract from nuclear fuels is going to be from breeding fertile fuels. And that’s a good thing because it is Way more technically challenging to use a breeder for anything other than power generation than it is to simply purify fissile material.

Now just to finish off, I want to do some quick and dirty napkin math. I said there were three naturally occurring fertile isotopes, U234, U238, and Th232. U234 doesn’t really count because there is even less of it than there is U235 and it decays quite quickly it is just being continually replenished from the decay of other radioactive elements. So let’s figure out how much energy there is in just our two fertile fuels.

Currently, the world uses ~14 TW of electricity, of which approximately 11% is nuclear. So if 11% of 14 TW is the rate that we will run through our current explored reserves in 80 years, if we upped that to the full 14 TW then we would run through our reserves in about 8 years. if we had U238 breeders then we would have only 1118.6 years of nuclear fuel available to us.

But if you are a bit anxious about only having 1100 years of fuel reserves then we could fix one problem that I have touched on before, namely that we currently don’t reprocess our nuclear fuels and only use about 3% of the energy in them before storing them away. so if we did that with all of our known fuel reserves that would give us at least 30x more fuel to use which brings that measly 1100 years up to 33,000 years.

Now we know that we aren’t going to stay at 14 TW because as Asia and Africa climb out of energy poverty and start to use resources at western levels then predictions are for energy consumption to rise to between 18 – 20 TW by 2040. Even if we decide that we want to have an energy abundance beyond imagining and push it up to 50 TW that would still only lower the amount of energy from known uranium reserves to a staggering 9240 years.

I will follow your advice wise sir

I think I’ve already proven that there is enough energy for nuclear power plants to fulfill every wild fantasy of energy abundance but I’m not one to leave a job half-assed so here are the rapid-fire final nails in the coffin:
1. Projected reserves of uranium on land would triple Known reserves (10.5 million tonnes on top of current 5 million tonnes) (back up to ~30,000 years)
2. If we can extract uranium from seawater that would give us an estimated reserve of 4 Billion tonnes of uranium which according to our energy utopia numbers would only be enough for 24 million years at 50 TW of usage. Whatever will we do?
3. Thorium is 3-4x more common than uranium. And it is effectively identical in terms of energy density. (96-120 Million years for those keeping count.)

I really hope we can solve climate change before that runs out. Otherwise, we really don’t deserve this lovely planet of ours.

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