[acidburnNSA]

Oil is about 40% of the primary energy used in the USA and primarily for transportation. So fewer cars, trucks, ships, and airplanes would help. One transatlantic flight uses an astounding amount of oil. So take very few of those! And live close to work and close to places you want to be.

On the other hand, electric vehicles can help a huge amount for cars and trucks at least. Then we shift the primary fuel to whatever being used by the utility company. That's mostly natural gas, coal, nuclear, and hydro in the USA, followed by a percent and growing of wind and solar.

Of dispatchable options, nuclear, wind, and solar have tiny carbon footprints. Nuclear has very small physical and fuel footprints and runs 24/7, so that's my current favorite. It's also way safer statistically than almost anyone thinks, having saved 1.8 million lives net by displacing air pollution deaths by 2013. Its fuel is also renewable because uranium dissolved in seawater will replenish through erosion faster than we could ever use it for billions of years.

Wind and solar are kicking ass right now. going global scale requires large footprints of storage, land, magnets, coils, etc. I imagine a future of 50/50 nuclear + various forms of solar harvesting.

[spynxic]

> Its fuel is also renewable because uranium dissolved in seawater will replenish through erosion faster than we could ever use it for billions of years.

It's been an hour and still no one's caught this but.. what exactly is this you're referring to? It'd be a fishy looking stoichiometric ratio if the fuel is produced from the seawater.

[acidburnNSA]

Good catch! This is a pretty epic idea but it is defensible. Here I quote from a paper linked below:

"One additional aspect of nuclear sustainability—noted long-since by Bernard Cohen—is that a significant fraction of the nuclear fission energy resource is in fact completely “renewable” in the same sense as wind and solar energy [32]. Wind and rain constantly erode the Earth’s crust, which contains an average uranium concentration of 3 parts per million. Rivers then carry this dissolved uranium into the oceans, at a rate of approximately 10,000 MT per year [33]. In a breeder reactor energy system, this is a sufficient rate to supply the world’s entire electricity demand at the present time more than five times over—or is roughly one quarter of what’s needed to supply a continual 100 TW to a hypothetical global civilization of 10 billion persons which is energy supply-replete by any contemporary measure.

As the crust is being eroded by rivers, it is constantly replaced by new layers of rock being pushed upward by plate tectonic processes. The supply of uranium in the Earth’s crust is effectively inexhaustible, on the order of 40 trillion metric tonnes, a factor of 10,000 more than is present in the oceans. At present erosion rates, this source of uranium would last on the order of 4 billion years, similar to the timespan over which the Sun will become a red giant.

Therefore, this assured source of “continually mined-by-Nature and oceanically presented” uranium will last as long as life on Earth does—even if burned at rates sufficient to supply a large fraction of a fully-developed human civilization—and represents an astronomical amount of nuclear energy, one that is in fact truly renewable and inexhaustible by any human measures."

[1] http://www.mdpi.com/2071-1050/4/11/3088/htm

[sbierwagen]

Note that uranium mined from seawater is about six times as expensive as conventional uranium: https://en.wikipedia.org/wiki/Brine_mining#Uranium

[acidburnNSA]

Indeed, which is why it's not done commercially today. Note also that total fuel cost is about 5% of the cost of a nuclear plant, and that includes mining, milling, enrichment, and fabrication. As seawater extraction becomes cheaper and uranium mines run low (no time soon), it will basically be a wash economically to switch to the renewable uranium. Also, breeder reactors don't need you to enrich the fuel, so that counterbalances any increased extraction cost. On the downside most (but not all) breeders require chemical reprocessing which so far has been very expensive. With development this too could go down.

The key point is that we would never run out of fuel as a species if we went big with nuclear.

[dredmorbius]

Keep in mind that coal, as of the late 1800s in the U.S., was seen as a multi-million year supply. At then-current rates of use.

Thing is that the rates of use ... increased somewhat.

Exponential growth has a way of catching up with you.

Nuclear has a very long-term footpring and some unusual aspects relative to other energy systems. Many of its more notable critics come from inside the industry, or were early pioneers. I'm not so sanguine.

[acidburnNSA]

My estimates assume us-level consumption (10kWh/yr/person) for 10 billion people, and that will last 4 billion years. Don't think I'm too worried about exponential growth catching up to that!

Nuclear waste lasts a long time but we know how to store it for geologic time frames in crystalline bedrock or salt deposits where we have evidence that nothing will move for 200million years. And we only need 1 million until it's safe again.

If you got all your primary energy from nuclear reactors for your entire life, you'd make about 3 soda cans of waste. That's tiny compared to all the alternatives.

[dredmorbius]

Projections of limited per-person energy growth have proved exceedingly unreliable.

[acidburnNSA]

You're right. In the 1970s people estimated continued exponential per-person growth in the USA and ordered power plants in accordance. But then demand leveled off and lots of power plant orders were canceled. It's been nowhere near exponential in developed nations for some decades and is currently not expected to return to exponential growth. Sure, teleportation could be invented and use lots of energy, though, so if that's your point, fair enough. Let me rephrase my estimate a bit then to reemphasize the magnitude of the nuclear resource:

With 10 billion people using 40,000x the current per-person USA energy usage, we could power the world for at least 100,000 years with the nuclear resource.