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I think this is an interesting development for smaller generating needs, maybe even personal, but:

> Ammonia can also be burned in modified gas turbines, which IMO would be a great way to quickly displace natural gas in peaker plants, to enable higher renewables penetration w/o relying on fossil fuels to take up the slack.

Nukes can operate as peaker plants. The feedback from the control rods is nearly instantaneous. It's just in some markets they must telegraph their moves and get approval, which can take ~4 hours or more.

I bring up nukes because how are we going to make the ammonia? Nitrogen fixing reactions take loads of power. You could get it from nukes until we figure out higher capacity solar collection, but I don't know of anything else that would work well.

“ Nukes can operate as peaker plants. The feedback from the control rods is nearly instantaneous.”

But the physical thermal stress from throttling it significantly shorten its lifespan.

Throttling nukes is not a trivial task; I know one plant (Bruce?) doesn't even bother changing the reactor power, they just inject steam into the bay instead of putto g it through a turbine

Sounds like red tape or other stupidity. Ramping up very hot yes, but matching loads like you would with a gas plant no.

Its a bit complicated. Disclaimer: Im not a nuke engineer, I just took some nuke classes and was surrounded by then for a while.

New reactor designs promise to throttle, but I don’t know if any have been deployed.

This is a bit more complicated than a gas turbine. With a gas turbine, you just inject more gas as needed to keep the turbine turning at a constant speed. The combustion chamber is a violently small part of the whole.

The heat producing part of a reactor, by contrast, is massive. As a result you have thermal gradients, and these gradients are different at different power. They’re also larger at larger power.

A large thermal gradient isn’t a huge problem by itself (engineers have been accounting for this since the steam engine). The problem is the change of gradient itself. As the gradient changes, the materials inside change shape and this causes large mechanical stresses.

The situation is pretty much the same as when you turn off an ICE car: ever hear those ringing or popping sounds it makes? That is the various hot parts cooling and changing shape abruptly.

The problem for a reactor is made worse because material selection is very difficult: you cant just pick any alloy that has good thermal expansion, or good fatigue characteristics. Every alloy must be from a very narrow set of isotopes (not elements!!) that are compatible with the reactor’s neutron environment (balance, distribution, energy spectrum, etc).

I know all of the basic science behind this, but there exist old test reactors that can respond to loads quickly enough to act as peaker plants. Your information is either absolutely ancient or propaganda.

A throttle-able test reactor can be as simple as a pool with no pressure vessel. There’s maybe 100 of those in univeristies throughout the US.

Now commercialize it.

Does this vary with nuke's design?

I'd expect some do better than others.

See answer to other comment.

Should put a bitcoin mine in the power plant to use the excess power.

>Nukes can operate as peaker plants.

Not in an economical fashion, though. Because the fixed costs dominate the variable costs, the less often the plant operates, the more it needs to charge for electricity when it is running. Gas peaker plants work the opposite way: low capital cost, significant variable cost (price of gas). That's more suited to the role.

>how are we going to make the ammonia?

From surplus renewables at other times of the year. Part of the solution is going to be overbuilding renewables by some factor, maybe 1.5x, compared to the total annual electrical energy demand. Ammonia is basically a way to store that surplus on a seasonal timescale for backup generation, in a more cost-effective way than batteries. Plus, we also need ammonia for fertilizer, and maybe it will be used for transportation (shipping especially).

You're not getting it. You keep the plant on all the time. When you need to reduce power you insert the control rods. You lose some efficiency, but you do burn the fuel less fast as well; you're getting so much energy out of the nuclear fuel it's irrelevant.

This is established science and reactor design, it's not new. What I learned from a friend who works in power is there's red tape constrains on doing power variation which is why they don't do it.

Technically, Ruthenium is a platinum group element, not a "rare earth" element, though it is rare.

https://en.wikipedia.org/wiki/Ruthenium

On this, supposedly STEM-oriented forum, such a grave violation of chemistry nomenclature should be a bannable offence.

I've lost count of how many times everything is "rare earth", including Magnesium. An alkaline earth metal that's nearly as common as iron.

Good, thoughtful, comment, but the statement that ammonia is more "energy dense than H2 is innacurate and misleading. Ammonia has very slightly higher Volumetric Energy desnity than H2, but it has an extremely lower Gravimetric (mass) energy density.[1] The difference has significant implications for the intended application.

1. https://commons.wikimedia.org/wiki/File:Energy_density.svg

Hmm... I don't think that takes into account the weight of the tankage.

700 bar tanks aren't light, especially not ones that can resist hydrogen embrittlement.

The best metric is %-wt of hydrogen. Compressed hydrogen tanks go from 4.5-7% hydrogen by weight. I've read state-of-the-art vessels can get as high as 10%. Liquid ammonia is 17% hydrogen by weight, so as long as the tanks don't erode this too much, you're still doing better than compressed H2.

LH2 tanks may be very lightweight. Given good insulation, that is much preferred, particularly for aviation.

Right, for large aircraft LH2 might be the way to go. General aviation is more likely to be looking at pressurized H2 due to boil-off.

LH2 will not be practical for most small aircraft, although "business jets" will probably take it up.

Most of the rest will continue to rely on gasoline or propane. Eventually it will be cheaper to synthesize this from atmospheric CO2 than to mine it.

Right, boil-off is a problem for general aviation, so compressed H2 is the hydrogen option there, which is less attractive.

Although, Universal Hydrogen[0] has a wild idea: "... the development of a state-of-the-art uncooled liquid hydrogen storage system that will be able to store liquid hydrogen without venting for over two days. This storage life will be achieved through the use of a specially insulated dual- walled aluminium capsule that allows the pressure inside to build up without exhausting the boil-off."

Yikes.

[0] https://hydrogen.aero/career-list/?gh_jid=4150445004

I think it's generally understood that densities are per unit volume, and if you want to refer to gravimetric density, you would talk about the 'specific energy.' [0]

That said, you make a good point. The energy density advantage isn't huge when comparing to liquid H2, although it's more significant vs compressed H2.

[0] https://en.wikipedia.org/wiki/Specific_energy