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Comment by DisjointedHunt | Hacker News Reader

It’s not one dimensional.

Energy density can be both important for transportation and also be important for the ability to accelerate energy production without a proportional growth in mining/resource harvesting that harms the planet.

A melon sized chunk of uranium powers an Aircraft carrier of the US navy for over 2 decades while it circumnavigates the globe hundreds of times, launching aircraft off its deck and powering remarkable levels of energy demand from on board systems.

For comparison, a single trip around the pacific for a conventionally fueled aircraft carrier costs 125 MILLION GALLONS of fuel.

It’s incredibly hard to wrap one’s head around what 20 years x 125 Million Gallons x Num_trips per year looks like.

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I think you added some zeroes there. HMS Queen Elizabeth carries about 1.75 million gallons of fuel [1]. she has to fuel up about twice to sail 26,000 Nmi [2]. Pacific is about 8000 Nmi, so round tripping would be roughly a full tank.

1) https://www.royalnavy.mod.uk/news-and-latest-activity/news/2...

2) https://declassifieduk.org/royal-navys-gunboat-diplomacy-is-....

> important for the ability to accelerate energy production without a proportional growth in mining/resource harvesting that harms the planet.

I agree.

> A melon sized chunk of uranium powers an Aircraft carrier of the US navy for over 2 decades … a single trip around the pacific for a conventionally fueled aircraft carrier costs 125 MILLION GALLONS of fuel.

Are you sure you didn't add a few zeros in there? I think the real energy density difference there is about a million, but you're at least 200 times more than that, depending on Num_trips?

(But yes, to the core point, transport is the one thing where energy density matters, and a nuclear powered aircraft carrier, or sub, is totally a thing where atomic power shines. Subs especially. Just that they're not a major part of the problem, and while this is a fun diversion I had been more interested in baseload here).

> Energy density can be both important for transportation and also be important for the ability to accelerate energy production without a proportional growth in mining/resource harvesting that harms the planet.

>A melon sized chunk of uranium powers an Aircraft carrier of the US navy for over 2 decades while it circumnavigates the globe hundreds of times, launching aircraft off its deck and powering remarkable levels of energy demand from on board systems.

You've made a bit of a mistake here, thinking that energy density and resource harvesting are always opposed. They're not. The aircraft carrier uses 93% HEU, while most reactors use uranium that is 10-20x less enriched. The same amount of earth has to be mined either way, but the HEU used in the core of an aircraft carrier or nuclear sub has to undergo a lot more expensive and resource intensive (and downright dangerous) post-processing.

> A melon sized chunk of uranium powers an Aircraft carrier of the US navy for over 2 decades while it circumnavigates the globe hundreds of times, launching aircraft off its deck and powering remarkable levels of energy demand from on board systems.

And how much does a civilian nuclear reactor weigh?

Even compare a solar panel (there are panels on the market that produce 50GJ/kg over their life, and it's almost all sand) to the fuel assembly plus a type A storage cask.

Even if we accept your ridiculous premise, solar wins.

Depends on the details. For land use, as I said in my other comments, the energy density is a red herring — the mass (and the area) aren't what we're limited by anyway.

For transport, the limits depend on the nature of the transport. Cars are fine with LiIon; aircraft can be fine with LiIon for a few hundred miles but not thousands; hydrogen from electrolysis can power aircraft or rockets but are a bad choice for submarines; PV in a spacecraft means an ion drive and not a launch, the higher specific impulse doesn't make up for the lower absolute thrust in that scenario; nuclear spacecraft would be great except everyone's terrified of it.

But none of this matters either way with the power grid.

> For land use, as I said in my other comments, the energy density is a red herring — the mass (and the area) aren't what we're limited by anyway.

My point is, even if we accept the broken premise then the conclusion is still to plan and fund as much solar and wind as possible until we've provisioned about 80% of net energy. At that point you consider the tradeoff between LCOS of whatever battery tech can be scaled and the cost of nuclear (or if we're still operating under the faulty premise, the extra land and mass the reactor will consume).

Just the fuel and storage cask of nuclear fuel weighs almost as much a solar panel for the same energy content -- the discarded depleted uranium weighs more.

If you look at low concentration Uranium mines like Inkai (which are already close to a majority and will be comparatively high yield if nuclear is expanded) you have hundreds of square kilometers of poisoned and unusable land and poisoned ground water that will probably never be properly remediated producing about 15W/m^2 . Even Husab which is open pit only produces about 180W/m^2 from the currently occupied land and 30W/m^2 from the whole strike.

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