[ttfkam]

I love how green hydrogen is assumed to become abundant and trivially easy to retrofit into existing infrastructure but fast neutron reactors are automatically considered infeasible by comparison.

Or that by far the easiest way to produce massive amounts hydrogen without emitting carbon into the atmosphere is… wait for it… nuclear power.

[ben_w]

> Or that by far the easiest way to produce massive amounts hydrogen without emitting carbon into the atmosphere is… wait for it… nuclear power.

No, that isn't the easiest way.

The easiest — not best, easiest — way to produce massive amounts of hydrogen is whatever your electrical power source is plus some low corrosion rods in a river.

If you want the cheapest, well, in most cases PV is the cheapest source of electricity — there's variance, sometimes it's wind.

Nuclear is so expensive that it's the same range of prices as PV plus batteries. And when you're using the electricity to make hydrogen, with the hydrogen as the storage system, batteries are redundant.

[ttfkam]

Since PV needs batteries to be grid-useful (duck curve and all that), it's perfectly reasonable to have both.

And no, hydrogen as the storage system doesn't make batteries redundant. Law of conservation of energy. You are talking about using electricity to split water molecules, presumably more electricity to compress and store the collected hydrogen, and then you have the losses associated with converting back to electricity in a fuel cell or conversion to mechanical energy through combustion.

A square meter of PV provides a theoretical maximum of ~1KW at 100%. Even the experimental perovskite cells only get 45% of that. 450W/m^2. Whereas nuclear is measured in gigawatts per reactor with multiple reactors per plant.

Then a storm hits. Far less sunlight. Then something like hail hits. Damage to panels. Then there's the issue of security if someone wanted to cripple the grid.

Nuclear is 24/7, rain or shine, wind or no, impervious to even hurricanes, and already has a robust security and logistics apparatus around it.

I have PV panels on my home. I love the idea of decentralized power. But the hydrogen economy is pretty theoretical at this point. Hard to store for any length of time, comparatively low combustion energy, low energy density overall, etc. It may happen, but "may" is a bad bet for long term national policy. I'd rather push more toward electrified high speed trains than hydrogen.

[ben_w]

> Since PV needs batteries to be grid-useful (duck curve and all that), it's perfectly reasonable to have both.

Needs storage*, what that storage is depends on other factors.

(* there's a "well technically" for just a grid, in that China makes enough aluminium they could build an actually useful global power grid with negligible resistance, but it doesn't matter in practice)

As it happens, I agree with one crucial part of your final paragraph — hydrogen is hard to store for any length of time (not sure you're right about comparatively low combustion energy but that doesn't matter, low energy density overall is accurate but I don't think matters).

I favour batteries for that because battery cars beat hydrogen cars, and the storage requirements for a power grid are smaller than the requirements for transport, so we can just use the big (and expanding) pile of existing factories to do this.

But hydrogen has other uses than power, and where it's an emergency extra storage system you don't necessarily need a huge efficiency. That said, because one of the main other uses of hydrogen is to make ammonia, I expect emergency backup power to be something which burns ammonia rather than hydrogen gas — not only is it much more stable and much easier to store, it's something you'd be stockpiling anyway because fertiliser isn't applied all year around anyway.

But you could do hydrogen, if you wanted. And some people probably will, because of this sort of thing.

> A square meter of PV provides a theoretical maximum of ~1KW at 100%. Even the experimental perovskite cells only get 45% of that. 450W/m^2. Whereas nuclear is measured in gigawatts per reactor with multiple reactors per plant.

This is completely irrelevant for countries that aren't tiny islands or independent cities.

Even then, and even with lower 20% efficient cells, and also adding in the capacity factor of 10% that's slightly worse than the current global average, Vatican City* has the capacity for 11.1 kW/capita: https://www.wolframalpha.com/input?i=0.5km%5E2+*+1kW%2Fm%5E2...

They are of course not going to tile their architecture in PV — there's a reason I wrote "that aren't … independent cities" — but this is a sense of scale.

(* Number 7 on the Wikipedia "List of countries and dependencies by population density": https://en.wikipedia.org/wiki/List_of_countries_and_dependen...)

> Then a storm hits. Far less sunlight.

That's what the storage is for

> Then something like hail hits. Damage to panels.

Panels are as strong as you want them to be for the weather you get locally. If you need bullet-proof (FSVO), you can put them behind a bullet-proof screen.

> Then there's the issue of security if someone wanted to cripple the grid.

The grid isn't the source; if you want to cripple a grid, doesn't matter if the source is nuclear, PV, coal, or hamster wheels.

> Nuclear is 24/7, rain or shine, wind or no, impervious to even hurricanes, and already has a robust security and logistics apparatus around it.

Really isn't 24/7, it's 70-80%: https://en.wikipedia.org/wiki/File:Worldwide_Nuclear_Power_C...

And mis-estimating the environmental risks is exactly what went wrong with Fukushima.

[ttfkam]

> And mis-estimating the environmental risks is exactly what went wrong with Fukushima.

It took a massive earthquake and tsunami to cause this, and the number of deaths/injuries due to the power plant is a rounding error compared to the earthquake and tsunami. Fukushima actually did most things right with the notable exception of not putting the backup generators on the roof. Had they put the generators on the roof, neither of us would have ever known the name "Fukushima".

When evaluating the Fukushima exclusion zone, compare it to the Exxon Valdez oil spill of 1989. In that case, we still haven't cleaned up all the oil, and up to 450 miles from the initial spill. By comparison you want to transition to ammonia as a fuel source, which you correctly note is easier to store long term than molecular hydrogen and far more energy dense. Sounds like a good deal since molecular nitrogen is incredibly abundant as well.

Now I want you to imagine there's an ammonia spill in the magnitude of Exxon Valdez. Long term, the ammonia would almost certainly dissipate faster than crude oil, but the immediate acute toxicity would be far worse. You're killing basically all sea life in the area, the fumes would take out most birds and even quite a few people. If the spill were on land, it could severely compromise the ability to grow crops in the region for a long time. And that's not in the face of a massive earthquake and tsunami, but inattentiveness on the part of a single ship's crew.

The point being that large scale energy production and storage will NEVER be fuzzy and completely safe. The most common metric is deaths per unit of electricity. If a power source is small, even one death can be unforgivable. For massive amounts of power, statistics matter.

https://ourworldindata.org/safest-sources-of-energy

Note that the nuclear stats include both Chernobyl and Fukushima. This is notable since Chernobyl was a worst case scenario with a flawed design that has never existed in Western commercial reactors precisely because it was so unacceptably dangerous: no containment vessel, graphite moderation, graphite fuel rod tips, lack of education for its staff, a culture of secrecy, etc.

In the meantime, nuclear has provided obscenely large amounts of electricity since its inception. I'm all for expanding solar and wind, but folks really need to understand the real enemy is fossil fuels: coal, oil, natural gas, etc. The single largest threat to our survival as a species isn't a multi-kilometer exclusion zone but a CO2-laden atmosphere that makes the entire equatorial zone uninhabitable, and that's precisely what we're looking at within a century.

The faster we can move off carbon-based fuels by any means necessary, the better. That includes nuclear. Excluding nuclear from the conversation out of hand is lunacy.

[natmaka]

Hydrogen is already used in many industrial processes (~1e8 metric tons/year), including turbo-alternators, while there is not a single ready-to-be-built model of industrial breeder reactor.

[ttfkam]

Not only was a design ready to be built, it was built. Went online 39 years ago. Produced 1.2GWe at peak. Not only produced power on its own but reprocessed spent fuel from other nuclear reactors.

Decommissioned 28 years ago. Because it didn't work? No. Because it wasn't safe? No. Because it wasn't reliable? No, it had a 95% availability rate.

It was taken out of service due to political pressure and legal maneuvering, not technical reasons.

https://en.wikipedia.org/wiki/Superph%C3%A9nix

[natmaka]

Facts: Superphénix was a prototype. It didn't reach its goal (reaching the industrial stage). Not a single model of breeder reactor reached it. Mentioning its high availability rate neglects planned shutdowns (planning enough of them improves it). Its load factor in 1996 (just before its shutdown), more relevant, was 0.31, thus well below the minimum viable for an industrial reactor. Some people consider the project to be a success, but no expert or its operator has ever said so (they proclaimed their confidence in their ability to achieve industrial operation by an unspecified date), and its successor, named "ASTRID", launched 12 years later, which was supposed to design and build a reactor for €5 billion, spent more than €700 million on studies alone before being put on hold, so "it worked, but everything has to be redesigned...".

[pfdietz]

Yes, hydrogen is clearly a much easier technology to make work than fast reactors. Why is this even a question? For example, fast reactors have the issue that in an accident, if fuel melts and rearranges, one can have potentially have a configuration that is prompt supercritical on fast neutrons. This is functionally an atomic bomb.

Also, even in a Fallout Future where everything is nuclear powered, hydrogen is still needed! Some 6% of today's global natural gas consumption goes to making hydrogen, and a good chunk of that is for ammonia synthesis, which is necessary to feed eight billion people.

[PaulHoule]

The main hang ups for fast reactors in the US are: (1) our regulators are less sanguine about occupational safety for plutonium workers then the French and Russians (carcinogenic Pu nanoparticles —- the high energy ball mill can make sand deadly, just think what it can do for Pu) and (2) fear of nuclear proliferation if the “plutonium economy” expands. There is also (3) the economics will never be attractive with a steam turbine and all the heat exchangers that entails, but a power set like

https://www.swri.org/markets/energy-environment/power-genera...

could fit in the employee break room of the turbine house of an LWR and could make it competitive. It’s a big if though.

[ttfkam]

"Functionally an atomic bomb"?

Why do you speak on topics you obviously know so little about? Where did you get this nonsense?

Fast neutron designs aren't without their challenges, but causing an atomic explosion is not on that list. Hydrogen explosions? Possible. Steam explosions? Possible.

Atomic explosions? Not even theoretically can you get enough U-235 to clump together to do that without cancelling known basic laws of physics.

To build a bomb, you need a purity of 90%+ U-235. Nuclear power plants have what? 2%? 3%? Might even go as high as 5%? Might as well expect a pack of bubble gum to spontaneously explode.

[PaulHoule]

The more detailed simulations have gotten the less bad a meltdown looks in a fast reactors. Usually some of the molten core flows away and no more critical mass. If it goes over critical there can be some energy release but over time it looks less and less and not a problem to contain.

Sodium has its problems (burns in carbon dioxide!) but the chemistry is favorable for a meltdown because the most dangerous fission products are iodine and cesium. The former reacts with the sodium to make a salt that dissolves in the sodium, the second alloys with the sodium. Either way they stay put and don’t go into the environment.

[pfdietz]

The problem is you need to ensure it's not bad in any possible configuration from an accident. This is hard to do. Will the energy release at criticality drive the material into an even more critical configuration? Such "autocatalytic" systems were considered for bomb design, but weren't chosen because of the large amounts of plutonium needed. But a fast reactor might have the plutonium of hundreds of atomic bombs.

Edward Teller famously warned about this is a nuclear industry trade publication in 1967.

The only fast reactors I'd trust would be ones with fuel dissolved in molten salt; it's hard to see how that could become concentrated in an accident that doesn't boil the salt. But such reactors have their own problems, in particular exposure of reactor structures to intense fast neutron fluxes (not as bad as in fusion reactors, but worse than LWRs.)

[ttfkam]

Increasing the heat past a certain threshold reduces the nuclear reactivity. Read up on "passive safety".

Teller may have warned about this in 1967, but nuclear technology hasn't been stagnant since 1967. Folks read his stuff and designed systems specifically to fail safe, not run away. Stop fear mongering based upon a 60-year-old supposition. Stop assuming everyone working in the nuclear industry is an idiot that hasn't thought about safety.

[pfdietz]

> Increasing the heat past a certain threshold reduces the nuclear reactivity. Read up on "passive safety".

The safety arguments for fast reactors are typically that a serious scenario will not occur, for example that fuel won't melt, not that if it does occur the results won't be bad. Do you trust that sort of argument? I don't.