alt.hn

3/4/2026 at 9:56:20 PM

NRC issues first commercial reactor construction approval in 10 years [pdf]

 https://www.nrc.gov/sites/default/files/cdn/doc-collection-news/2026/26-028.pdf

by Anon84

3/4/2026 at 10:56:13 PM

The Kemmerer Unit 1 project... would be used to demonstrate the TerraPower and General Electric-Hitachi Natrium sodium fast reactor technology. [0]

https://en.wikipedia.org/wiki/Sodium-cooled_fast_reactor

[0] https://www.nrc.gov/reactors/new-reactors/advanced/who-were-...

by WorkerBee28474

3/5/2026 at 3:16:00 AM

Nice, I like the sodium fast reactor concept. Produces less waste, can be passively cooled when shut down, and doesn't run pressurized so reactor vessel can be thinner.

Sodium leaks can be nasty, but they can be dealt with.

by SoftTalker

3/5/2026 at 5:56:37 AM

Are there any nuclear alternatives that don't include strapping low grade bombs to the reactor core (PRW/BWR: water separation -> hydrogen + oxygen -> boom, like happened @ Fukushima) or using coolants that instantly start violently combusting when exposed to air or moisture (sodium)?

I love the promise of nuclear energy, and I understand that every single engineering decision has tradeoffs, but these tradeoffs just seem so bad? Are there really no better options?

by jacobn

3/5/2026 at 7:17:07 AM

There have been some sodium cooled designs that have used a closed cycle gas turbine using nitrogen as the working fluid for the secondary circuit, in order to avoid any issues with sodium-water reactions with a traditional steam Rankine secondary circuit.

There are also fast reactor designs using lead as the coolant rather than sodium. These are interesting, but less mature than sodium cooling. Sodium is better from a cooling and pumping perspective though.

by jabl

3/5/2026 at 10:37:46 AM

Lead-bismuth eutectic.

A eutectic is an alloy that has a lower melting point than any of its components.

Lead-bismuth eutectic or LBE is a eutectic alloy of lead (44.5 at%) and bismuth (55.5 at%) used as a coolant in some nuclear reactors, and is a proposed coolant for the lead-cooled fast reactor, part of the Generation IV reactor initiative. It has a melting point of 123.5 °C/254.3 °F (pure lead melts at 327 °C/621 °F, pure bismuth at 271 °C/520 °F) and a boiling point of 1,670 °C/3,038 °F.

https://en.wikipedia.org/wiki/Lead-bismuth_eutectic

by nandomrumber

3/5/2026 at 2:54:42 PM

Bismuth leads to the production of polonium, which is extraordinarily dangerous.

by pfdietz

3/5/2026 at 12:25:34 PM

Yes, some lead cooled reactor designs have used LBE, others pure lead. Though AFAIU so far the only lead cooled reactors that have actually been built and operated in production have used LBE. There is a pure lead cooled reactor under construction that should be started up in a few years if the current schedule holds.

by jabl

3/5/2026 at 7:18:14 AM

The improvement is more on the fuel cladding for classic pwr or pebble bed reactors... But even without all this, nuclear is one of the safest sources of power on the planet, because we made it so

by Moldoteck

3/5/2026 at 6:24:06 AM

The AGRs are advanced reactors that use an inert coolant, CO2. In fact they have been designed to cool down quicker than any credible loss of coolant. And have been in service since the 70s, with some slated to go on until 2030.

by chickenbig

3/5/2026 at 6:22:04 AM

I mean the LWR fleet has proven to be incredibly safe by any objective measure with deaths per TWhr as good or better than wind/solar. The very incident you mentioned had a direct death count of 0 or 1 depending on who you ask. Industrial shit blows up all the time, you just don't hear about it because it's normal and accepted.

What needs to improve about nuclear is our ability to deliver it on time and on budget. Safety is already more than adequate.

by evilos

3/5/2026 at 7:13:07 AM

That is never going to happen until we are building more of a consistent design. I think every LWR is use today is a custom bespoke piece of equipment.

by wombatpm

3/5/2026 at 3:11:26 PM

Yes, standardizing on a handful of designs will help immensely, as well as building two or more reactors on one site to share the overhead costs between units.

For example, building out more AP-1000s is really a no brainer. The first-of-a-kind is always expensive and the AP-1000 was especially so due to many factors. We bore that cost and now we should reap the benefits of Nth of a kind builds.

by evilos

3/5/2026 at 6:22:02 AM

I was also curious. Claude answers: https://claude.ai/share/244fc2f5-1c4d-4e52-b316-e9cc34c8b98b I would be interested in a real expert's critique/commentary of this answer.

I like the pebble-bed design because it seems the most intrinsically safe of the three.

by fwipsy

3/5/2026 at 8:19:37 AM

Pebble beds are very safe but also very fuel inefficient.

by user____name

3/5/2026 at 12:00:37 PM

>I love the promise of nuclear energy

Nuclear today isn't that much different from steam engine - the fundamentals make it a technology of the past clearly losing to the today's tech, in this case to the massive solar/wind accompanied by the battery storage.

Nuclear will work in space, as it is the only tech feasible beyond the Mars orbit.

May be, may be the fundamentals will be sufficiently, to make it feasible on Earth, different for thorium MSRs and hopefully for fusion (my favorite is fusion driven thorium reactor - no need for fusion breakeven and relatively safe as turning off the fusion, the source of neutrons, stops thorium fission)

by trhway

3/5/2026 at 1:54:54 PM

Thorium is inefficient. And its related to steam in that steam converts to heat and power. Differentiates considerably on the front end.

Nuclear solar and wind are all natural complements. This stupid this or that argument only empowers old oil and gas tech looking to hold on to the future.

by boringg

3/5/2026 at 3:22:33 PM

Steam usage is a wonderful invention. It's certainly not a technology of the past. Nuclear will work anywhere you don't want to have oversized transmission network and where weather conditions aren't stellar, unless ren are combined with another firm source like gas/coal/geothermal/hydro

by Moldoteck

3/5/2026 at 7:49:19 AM

China has a liquid uranium in the vein of the lftr design allegedly operating.

That I believe is the safest design, but I'm not a nuclear engineer.

by AtlasBarfed

3/5/2026 at 1:04:13 AM

Their hoped-for completion date is "2031". Anyone want to hazard a guess about what their actual completion date for this plant will be?

by rgmerk

3/5/2026 at 1:23:59 AM

Presumably it’ll end up like the NuScale one, raise a few billion for design and prototyping and then every 6 months or so increase the target wholesale price by 50% until it makes no sense at all economically to begin primary construction. They’ll reverse IPO along the way and manipulate the stock enough to get insiders paid out while the carcass of a company trundles along.

by mikeyouse

3/5/2026 at 2:03:18 AM

No. They have Bill Gates as a founder. Bill Gates understands that nuclear is a long game.

> They’ll reverse IPO along the way and manipulate the stock enough to get insiders paid out while the carcass of a company trundles along.

I'm not sure what "reverse IPO" means, maybe you mean they'll be acquired by a SPAC, like NuScale was. I doubt it. Bill Gates founded Terrapower in 2008, he is not looking for a quick buck.

by credit_guy

3/5/2026 at 5:08:25 PM

Reverse IPO is a way for scammy companies to go public by being acquired by an already public penny stock - precursor to the later SPAC shell games to do the same. Basically all of these companies do it (NuScale, Oklo, Terrestrial Energy, etc) so I’m just waiting for TerraPower to do the same.

I hope you’re right and they stay focused on actual engineering instead of financial engineering but many of Gates’ other investments haven’t been so fortunate and went down the latter path. The billions of dollars in taxpayer funds and constantly shifting tech and demo projects gives me a lot of pause though. (MSR! TWR! Fast Reactor! Fujian! Hebei! Idaho! Hanford! Wyoming! UK!)

by mikeyouse

3/5/2026 at 1:29:18 AM

In theory, at least, they have finished their design, had it reviewed by the NRC, and had it approved, so there should be no significant design changes.

But that also applies for the current generation of reactors and nobody can build them to schedule or budget in the USA or Europe.

by rgmerk

3/5/2026 at 2:02:22 AM

Yep. NuScale received design certification as well and still ended up with multiple huge revisions. It’s not easy to build any nuclear, much less a FOAK reactor.

But when that fails, you can just siphon up taxpayer money via your connections to the ruling cabal.

https://www.thedailybeast.com/tiny-trump-linked-firm-in-line...

by mikeyouse

3/5/2026 at 1:47:56 AM

> so there should be no significant design changes

The NRC frequently changes requirements for reactors while they're under construction. The NRC does not waive the right to demand changes merely due to prior design approval. This is a novel (for the US) design, so there will be unanticipated changes as the project progresses.

Russia has been operating two sodium cooled fast reactors for decades. The BN-600 and BN-800 are both operating today. The early history of the BN-600 was... interesting, suffering (at least) 14 sodium fires due to leaks. This "Natrium" design is similar; a sodium pool with two sodium loops. They are taking on the additional challenge of storing a massive quantity of molten salt. It's going to take a lot of effort by many steely eyed missile people to make this happen.

Trump issued an EO in 2025 that's supposed to make the NRC more circumspect about requiring changes of approved designs. Then there is all the pull Gates has. Wyoming is no hotbed of anti-nuclear activism. So that's all to TerraPower's favor. But TerraPower will need to fully utilize all the tailwind it can find to make this work.

by topspin

3/5/2026 at 7:45:31 AM

To reference Admiral Rickover's 'Paper Reactor' memo [1], TerraPower is now going to commence transforming their paper design into a practical reactor. Historically, this does not usually prove successful.

1. https://whatisnuclear.com/rickover.html

by GolfPopper

3/5/2026 at 1:05:52 AM

No, but I'm certain the polymarket gamblers do.

by willis936

3/5/2026 at 1:26:11 AM

I did have the same thought, had a quick look (I'm not a polymarket user) and couldn't find a market relating to this project.

Put it this way, if it's in commercial operation by 2031 I'll eat my hat.

by rgmerk

3/5/2026 at 1:48:28 AM

If the DOW needs fissile material, then you might be impressed at how fast things are done. The obstacles are mostly discretionary.

by GorbachevyChase

3/5/2026 at 11:39:05 AM

Never.

Come April, all the production and construction capacity will be commandeered for the war machine.

by TheSpiceIsLife

3/5/2026 at 3:14:51 AM

China have 28 nukes under construction right now, and have built more in the last 30 years than the rest of the world combined.

Even with all that experience and expertise, their questionable environmental policies and questionable worker rights, it still takes them SEVEN years to build a single nuke.

The claim that anyone else can do it faster with zero recent experience isn’t only laughable, it’s downright fraud.

by testing22321

3/5/2026 at 7:22:55 AM

it takes about 5y for latest units. And their env/worker policies are not that questionable in this regard. Heck, Japan did finish it's first ABWR FOAK in under 4y so China is in fact slow here. The question is rather why China bans inland expansion

China and Russia are about on par in build times now. Korea is next with APR, Barakah having about 8y/unit, W-house and EDF are the slowest for many reasons

by Moldoteck

3/5/2026 at 4:23:37 AM

The Chinese CAP1400s took 5 years and that's a new design to them. The first NPP was built in 1951 (ish) and took 18 months from blackboard to grid interconnection. Some designs take longer, others are shorter. Some parts of Vogal were rebuilt 3x times due to the federal government changing the design requirements multiple times during construction. Another challenge is that NPPs are built rarely enough that its hard to be a supplier to the nuclear industry so many parts are custom built per project. That doesn't have to be the case. The idea there is a hard limit of 7 years, sorry...that just isn't so.

by hunterpayne

3/5/2026 at 2:49:37 PM

> 5 years

Be careful with these figures. I understand they start the clock later than the west does.

by pfdietz

3/5/2026 at 3:26:49 PM

Do they? Did japan start the clock later too with it's first ABWR?

by Moldoteck

3/5/2026 at 5:03:54 PM

We weren't talking about Japan.

by pfdietz

3/5/2026 at 8:13:25 PM

We were talking about timelines. Chinese timelines are faster than western but slower than Japanese. So maybe you can expand your thought about how China is counting years differently

by Moldoteck

3/5/2026 at 4:27:31 AM

Wow, that's A lot. Even though there's diminishing returns with more workers, they'd probably build them faster if they weren't scaling out so much concurrently, right?

Seems like we could match a 7 year clip at a much smaller scale. We'll be forced to at some point, but we need to overhaul the regulatory mess and fix the grid first. Hopefully that happens long before battalions of Chinese drones and droids take over the world.

by webXL

3/5/2026 at 12:01:57 PM

flip "2" and "3" in that year

by bdangubic

3/4/2026 at 11:19:31 PM

And the verbiage that many will glance over yet will have the greatest future impacts for all alive is: "...includes an energy storage system..."

Todays U.S. meeting "Roundtable on Ratepayer Protection Pledge" with the U.S. President himself leading that meeting garnished commitments from Big Tech as it relates to energy. In time Big Tech Energy divisions will be thing and some citizens will be paying their utilities bill to them.

by bokohut

3/5/2026 at 1:49:54 AM

In Texas and Massachusetts you can actually pick your power provider while paying the natural monopoly for the wires. In time I hope we all can do this.

by conradev

3/5/2026 at 2:31:00 AM

This is how it works in NYC, but the wires are almost twice as expensive as the power. (If you add taxes and the numerous weird fees, the total bill is a solid 3x the cost of the power.) It's really all about the grid maintenance and management these days.

by ploxiln

3/5/2026 at 10:20:55 AM

To be fair: grid buildout is quite expensive.

A comparison: the giant Dogger Bank offshore wind farm project (multi-GW) cost somewhere in the $10bn range. On the other hand, Germany calculates with >$100bn for grid buildout within the next decade (https://www.netzentwicklungsplan.de/sites/default/files/2023...).

Also, having customers that rely on your grid but buy very little of your power is simply unappealing for operators, so I would assume that their pricing tries to disincentivise as much as possible (=> "they gonna overcharge you for the grid connection").

by myrmidon

3/5/2026 at 11:01:18 AM

The not-so-hidden costs of collecting extremely diffuse wind / solar is the elephant in the room 10x bill for the supporting grid infrastructure.

Nuclear advocates, like myself, claim drop in replacement nuclear power reactors at existing coal / gas sites would largely obviate this.

Even adding new nuclear power reactors at greenfield sites would constitute a significantly reduced grid build cost, as the power is highly concentrated.

And nuclear is so say that nuclear power reactors employees are routine exposed to less radiation at work than they are at home in their kitchen with granite bench tops.

YIMBY.

by TheSpiceIsLife

3/5/2026 at 12:45:42 PM

I can see that argument applying to wind, but for solar its the opposite because that is really easy to get closer to consumers than a conventional plant ever could be (i.e. on the rooftop).

At this point, I don't believe in a nuclear renaissance, because it seems to me that nuclear power got left behind too far; catching up in cost metrics is already hard enough, but matching growth rates (in "installed TWh/a" of wind/solar) seems virtually impossible by now. The only remaining holdouts (China, US, France, ...) are basically doing it as a hedge and/or to keep/obtain related engineering capabilities (and at the very least an easy path toward weapon-grade material).

It is clear to me that no one "actually believes" in nuclear power (by stating clearly: we are solve gonna current and future energy problems by mainly relying on freshly built nuclear power), so I can only see its relevance dwindling (I'd argue that China comes closest, but even they are much more in the hedging/securing capabilities category than anything else).

by myrmidon

3/5/2026 at 3:01:00 AM

We do this for gas. IMHO you end up paying monopoly rates for the pipes and then stupid game prices for the gas. Maybe the savvy consumer comes out ahead but seems like a net negative to me.

by treis

3/5/2026 at 5:49:26 AM

It's not monopoly rates, it's actual utility rates. The only problem here is if the utility is allowed to make a profit. Gas pipes, electric lines and internet connections are like roads in today's society. Can't really live without them.

So assuming the pipe maintenance is done at cost, with no money not being spent on the network. What would your better net positive solution even look like?

by hvb2

3/5/2026 at 7:39:05 AM

People can live without gas pipes. One of the big tasks at the moment is planning to stop people building new gas pipes that won't be used enough to justify the price and how to phase out the existing gas pipes so the pricing doesn't enter a "death spiral" as people start leaving the network, leaving the government to bail it out.

by ZeroGravitas

3/5/2026 at 11:05:40 AM

I’m all for burning less gas, it’s too important a resource to simply burn for heat.

But we need to build the nuclear reactors first.

In the mean time, no: people can’t just freeze in the dark.

by TheSpiceIsLife

3/5/2026 at 12:55:48 PM

Heat pump exists. I’d rather burn gas in the (mostly existing) gas plants than put more gas pipes into the ground.

by realityking

3/5/2026 at 7:04:28 PM

Heat pumps don’t solve switching away from gas.

by TheSpiceIsLife

3/5/2026 at 10:22:16 PM

If you don't put in heat pumps, nuclear reactors are one of the more expensive ways to heat a home.

If you do put in heat pumps, nuclear reactors are still one of the more expensive ways to heat a home, but you need a third as many of them as compared to the no-heat-pumps case, if you insist on heating only with nuclear power.

Nuclear power is really only important if you also want spicy atoms, because it's by far the cheapest source of spicy atoms. Annoyingly, this is now a thing a lot of countries have a solid reason to want.

by ben_w

3/5/2026 at 7:35:55 AM

Heh, wouldnt NYC be best case scenario for a grid? It has high density, large number consumer base etc?

If only they could sort the underground cabling...

by samarthr1

3/5/2026 at 5:08:13 AM

We do that in Northern California as well. There are only a couple of options though.

by sgc

3/4/2026 at 11:31:45 PM

There are large solar power stations on the grid in California owned by tech firms so you may indeed already be paying, indirectly, Apple for energy.

by jeffbee

3/5/2026 at 12:23:08 PM

Who wants to bet this will be (1) economically viable to operate (2) delivered on time (3) delivered within the stated budget?

by jacquesm

3/5/2026 at 2:05:37 PM

I will never, ever understand the HN obsession with presenting nukes as a practical and economically viable technology.

Wind and solar prices are still dropping hard, battery and storage tech is evolving fast, but - let's build monsters that consistently overrun time and budget, and run on fuel that can only be obtained from some of the least stable countries on the planet.

by TheOtherHobbes

3/5/2026 at 3:25:10 PM

Didn't know canada and Australia are least stable countries on the planet or that US doesn't have own uranium deposits.

Neither did I know regions like Germany (or EU as a whole) can get by on ren alone looking at winter capacity factor data

by Moldoteck

3/5/2026 at 6:07:10 PM

The EU still haven't sanctioned the Russian nuclear industry despite 19 sanction packages.

Four years into the war we've almost completely cut out all other parts of the Russian economy. Except the nuclear indutry. We're just too dependent.

by ViewTrick1002

3/5/2026 at 8:14:52 PM

Mostly because many countries still have VVER reactors.

It'll happen anyway. Orano and Urenco are expanding while Framatome and Westinghouse learned to manufacture VVER fuel elements

by Moldoteck

3/5/2026 at 9:17:21 PM

Again trying to deflect.

It is France that is tied to the hip of the Russian nuclear industry, and keeps blocking the sanctions.

While continuing to move forward with partnerships with Rosatom and relying on Russian reprocessing for the fuel supply chain .

by ViewTrick1002

3/5/2026 at 2:15:26 PM

Grids need reliability. Battery tech is not close to providing long enough durations to fulfill load with just renewables. I would much rather have nukes than natural gas filling that role.

by klysm

3/5/2026 at 2:19:55 PM

This is roughly 1980. We are now in 2025. Battery tech has been increasing massively and besides that we now have HVDC tech which can transport very large amounts of energy from end of the country to another without significant losses. The whole 'baseline power' argument is getting really long in the tooth, it is mostly a matter of dogma at this point. It's not 'nukes' or 'natural gas', it's 'what is the best possible mix for this current moment in time.

The problem with nuclear power is that it is so expensive to be on standby that you need to buy their output even when you don't need it. So energy market pricing tends to be dominated by the least effective sources rather than by the most effective sources. If nuclear plants were left to fend for themselves they'd be out of business in a year. More so if you consider the cost of decommissioning.

by jacquesm

3/5/2026 at 2:25:36 PM

I think storage (transport of energy in time) will beat transmission (transport in space) for users not constrained by population density.

by pfdietz

3/5/2026 at 2:52:56 PM

Well, the race is definitely on. But another couple of years of reduced costs for solar and wind deployments and it may well be that nuclear projects underway will end up being cancelled before construction is complete.

by jacquesm

3/5/2026 at 2:30:03 PM

One really nice thing about nuclear is that the fuel is highly portable. Small reactors next to datacenters take away a lot of complexity; transport, grid connectivity, etc. Plus they're already being built in industrial-ish areas.

by vessenes

3/5/2026 at 2:23:06 PM

Very long duration storage in my opinion is going to be thermal.

Standard Thermal's approach seems very simple and promises to deliver 365/24/7 heat (ultimately sourced from PV) at 600 C for cost competitive with Henry Hub natural gas. It's difficult to see how nuclear competes with that.

by pfdietz

3/5/2026 at 2:59:20 PM

There is a very interesting tech using superconducting loops to store power. I think that that will be the 'battery of the future' but it is going to take a while before that sort of thing is safe enough (and cheap enough) for things like vehicles. But for stationary short term 'ride through' situations it has already been deployed, and also for stabilization of the grid in the presence of fast fluctuating loads or generators.

by jacquesm

3/5/2026 at 3:10:42 PM

Superconducting storage is inherently short term, as the capex per unit of energy storage capacity is rather high. I doubt it's competitive with batteries even for diurnal storage. It might have niche uses, for example smoothing demand (on time scale of hours, not days) from intermittent high power users like electric arc furnaces.

by pfdietz

3/5/2026 at 3:36:41 PM

Batteries work fine right now. Much better than nuclear plants that will take another decade to build. There's probably a few dozens twh of batteries being deployed in between. They retain their charge quite long too.

It's more an economical tradeoff than a technical one. But mostly, people doing off grid setups manage fine in some parts of the world. Winter months are challenging at higher latitudes. But there are also wind turbines and cables as alternatives. Cables allow you to import/export power from further south or further west or east. It's one of those things that might be a lot easier than building a lot of new nuclear power plants.

The issue with gas (aside from emissions) is that gas turbines are a bit hard to get. The lead time for getting new ones is pretty terrible and companies making them aren't exactly eager to make risky investments in extra production capacity for turbines that may or may not be needed in a 5-10 years. And once you manage to get them, you have to supply them with gas; which is expensive. Gas prices fluctuate a lot.

If you look at this through an economic lens, the next ten years will see:

- Hundreds of GW of solar deployed. Every year. Still growing. Probably quite a few TW of capacity added. - A bit less wind turbines but still quite a lot. The US seems to have some irrational anti wind mill sentiment currently. But that might change. Huge potential there for upgrading old ones too. And offshore wind obviously. - > 3 twh of battery produced for use in transport, grid, and domestic storage. - Some new gas plants coming online here and there. But not a lot. Gas usage will grow but renewables will out grow it. - Probably growing number of GW of cables and long distance cables. Possibly even cross Atlantic. - Lost of coal plants being decommissioned (just too expensive). Offsetting most of the gw added by gas. - A sprinkling of nuclear plants coming online. Mostly in Asia. If it's not approved yet, there's no way in hell many will come online before 2036 in the US/EU. A few GW per year.

The big picture here is that if you need a lot of power, you want low cost and feasibility. Gas is feasible. If you can get the turbines. But it's not cheap. If you want cheap, you mainly need to decide on the number of gw of panels you can afford to buy. And where to put them. Or wind. But the point is it's very feasible and quick to execute once you decide on a budget. Battery is not cheap (but still dropping in price year over year). And you may not actually need infinite buffers. You can fall back to gas when needed but as little as you can get away with (because $$).

Any AI/data centers still in business in ten years will probably be competing on energy cost. That's likely not going to be gas or nuclear mostly.

by jillesvangurp

3/5/2026 at 2:27:47 PM

So, allow me to say a few things:

Nuclear is about replacing baseload - currently coal basically

Small nuclear agrees you with about "monsters"

Storage at this scale is also not easy

SNR definitely pencil out in today's energy regime.

by vessenes

3/5/2026 at 6:09:17 PM

Storage at that scale already exists in for example California.

EDF in France is now crying that renewables are cratering the earning potential of their nuclear fleet, and increasing maintenance costs due to having to adapt.

In e.g. Australia coal plants are forced to become peakers, or be decommissioned.

We need firming for when the 10 year winter hits. Not an inflexible "baseload" plant producing enormously subsidized electricity when renewables and storage already flood the grid. Which is far above 90% of the time.

by ViewTrick1002

3/5/2026 at 7:04:37 PM

> presenting nukes as a practical and economically viable technology.

The practicality and economic viability are entirely under our control. We made them impractical and uneconomical here, while they are practical and economical in France and China.

by naasking

3/5/2026 at 1:59:49 PM

Prediction market?

by smallnix

3/5/2026 at 2:41:33 PM

Fast reactors have an extremely serious potential failure mode.

In a thermal reactor, reactivity is maintained by a carefully designed lattice of fuel elements and moderator. Disrupt this lattice and reactivity goes down. Thermal neutrons are also highly absorbed by certain neutron poisons with resonances that enable neutron capture at low energy; these can be added to shut down any potential reaction.

Fast reactors aren't like that. If fuel rearranges (for example, by melting and flowing into coolant channels) reactivity can increase. A fasts reactor will have ~100 times the "bare core" critical mass of fissionable material in it, so there's plenty of room for serious rearrangement to bring fission material into a prompt fast supercritical configuration.

That by itself could give you an explosion. But if the explosion then compresses some other part of the system beyond supercriticality, one could get an even more serious explosion. The possibility with something with a yield in the kiloton range can't easily be ruled out. This would be far worse than Chernobyl.

The fast reactor concepts I've seen deal with this by saying "our design can't ever melt down". Color me skeptical on that, and defense in depth says you don't believe such claims when failure could be so catastrophic. Even if regulators can be convinced (or be made to say they are convinced), the first experience that indicates the assumption wasn't true will lead to all reactors of that design being permanently shut down. This would be a serious financial risk to anyone thinking of building them.

If I were dead set on a fast reactor I'd look at something like a fast MSR (chloride salt) where such rearrangement could be ruled out.

by pfdietz

3/5/2026 at 4:17:11 PM

Not sure about this argument, do you have any references?

In a LWR, if the coolant/moderator boils away, sure, the reactivity goes down. But there is plenty enough decay heat left to melt all the fuel that can then flow into a puddle of suitable geometry and go boom. Hypothetically speaking, at least.

I suppose in practice most LWR's use lightly enriched fuel so it's very hard to get enough material close enough together to make it critical, let alone supercritical, without a moderator of some sort. Of course, plenty of research reactors, naval reactors etc. have operated with very highly enriched fuel (90+%?), but even these have AFAIU so far managed without accidentally turning themselves into nuclear bombs.

Seems most contemporary civilian fast reactor designs are designed to operate with HALEU fuel, where the limit is (somewhat arbitrarily) set at 20%. A lot higher enrichment than your typical LWR, but still much lower than you see in weapons, and you still need quite a lot of it before it can go boom.

by jabl

3/5/2026 at 4:41:39 PM

It's straightforward. Consider what would happen (for example) if all the fuel in a reactor is compressed into a more compact configuration.

In a thermal reactor, there's no problem, as there's now no moderator. There was massive rearrangement and compaction of melted fuel at the TMI accident, but criticality was not going to be a serious issue for the fundamental reasons I gave above.

In a fast reactor? It can only become more reactive. Anything else there was only absorbing neutrons, not helping, and the geometric change reduces neutron leakage.

Edward Teller somewhat famously warned about the issue in 1967, in a trade magazine named "Nuclear News":

“For the fast breeder to work in its steady state breeding condition, you probably need half a ton of plutonium. In order that it should work economically in a sufficiently big power producing unit, it probably needs more than one ton of plutonium. I do not like the hazard involved. I suggested that nuclear reactors are a blessing because they are clean. They are clean as long as they function as planned, but if they malfunction in a massive manner, which can happen in principle, they can release enough fission products to kill a tremendous number of people.

… But if you put together two tons of plutonium in a breeder, one tenth of one percent of this material could become critical. I have listened to hundreds of analyses of what course a nuclear accident could take. Although I believe it is possible to analyze the immediate consequences of an accident, I do not believe it is possible to analyze and foresee the secondary consequences. In an accident involving plutonium, a couple of tons of plutonium can melt. I don’t think anyone can foresee where one or two or five percent of this plutonium will find itself and how it will get mixed with other material. A small fraction of the original charge can become a great hazard."

(Natrium is not a breeder but the same argument holds.)

That no fast reactors have yet exploded is of course no great argument. How many fast reactors have been built, particularly large ones? Not many. And we've already seen a commercial fast reactor suffer fuel melting (Fermi 1).

by pfdietz

3/5/2026 at 4:00:09 PM

They originally were going to build their first plant using this technology starting in 2018 in China, but that got killed by the first Trump administration.

by tzs

3/4/2026 at 10:43:42 PM

This is huge, historic even.

by josefritzishere

3/5/2026 at 3:09:34 AM

How is this fundamentally different from Nuscale approval? Like Nuscale this is also brand new design, sodium fast reactor, that hasn't been commercially deployed and is likely to run into usual ballooning budgets and western nuclear construction roadblocks/delays

by mayama

3/5/2026 at 2:26:38 PM

Nuscale wasn't a sodium fast reactor. Perhaps you phrased that poorly? Nuscale is a PWR.

by pfdietz

3/5/2026 at 3:44:03 AM

If there’s more than one approval a decade maybe the odds will be higher it won’t be a bloated mess.

by dmix

3/5/2026 at 5:32:08 AM

Or you just have two bloated messes

by croes

3/5/2026 at 6:24:52 AM

They're already building this one. Nuscale didn't break ground AFAIK.

by evilos

3/5/2026 at 3:52:12 AM

You know what would be even bigger? Building perfectly safe and fine AP 1000s that already exist many times today and can be built whenever you want to.

0 under construction in the US

by dopa42365

3/5/2026 at 6:52:28 AM

Westinghouse plans 10 AP-1000 reactors in the USA

https://www.world-nuclear-news.org/articles/westinghouse-pla...

Yes, it would be better if they had already started, but the ship is turning.

by mpweiher

3/5/2026 at 7:00:27 AM

It is not. The right wing is instead waking up to reality. Apparently they like extremely cheap distributed electricity. Who could have guessed that.

Why MAGA suddenly loves solar power

The Trump-led attack on solar eases as the right reckons with its crucial role in powering AI and keeping utility bills in check.

https://www.washingtonpost.com/business/2026/03/02/katie-mil...

by ViewTrick1002

3/5/2026 at 2:28:35 PM

Solar also means all those data center jobs (and, really, many general industrial jobs) flow out to low population density red areas.

by pfdietz

3/5/2026 at 6:30:10 AM

True but additional context: Wikipedia says that two came online in 2023 and 2024, and two more are partially constructed, seeking additional funding to continue. Lots more internationally.

by fwipsy

3/5/2026 at 10:57:07 AM

The two that came online in 2023 and 2024 are hardly a success story if you look at their history.

by muldvarp

3/5/2026 at 1:50:21 AM

Maybe. There is a long road from "approved" to "operational".

by amanaplanacanal

3/5/2026 at 1:11:22 AM

Great, hopefully the ship is turning around slowly. I have been hearing from pro-carbon "environmentalists" for 30 years that "we should have built nuclear 20 years ago but doing so now would be pointless". Meanwhile we may have just reached peak-coal today if we are lucky. Well past time to stop listening to anything those grifting charlatans have to say.

by stinkbeetle

3/5/2026 at 3:16:31 AM

> Well past time to stop listening to anything those grifting charlatans have to say.

Are you describing the "just build nukes" party here?

Cause we've been waiting a while for this nuke solution to actually ship but every example is far more expensive all while the nuke lovers block solar and wind for the same reasons.

by tacticus

3/5/2026 at 3:51:41 AM

There is no for-profit companies that are in it to save the planet, despite what the brochures say. Unfortunately for non-carbon power companies, their main competition is each other rather then fossil fuel sources.

by Shitty-kitty

3/5/2026 at 5:21:24 AM

No.

by stinkbeetle

3/5/2026 at 1:53:26 AM

They got what they wanted. They are still successfully killing solar and wind projects.

I'll be surprised if this project actually gets built, though.

by amanaplanacanal

3/5/2026 at 3:16:00 AM

I don't think killing solar and wind projects is what the greens do. The problems with solar and wind are entirely due to the laws of physics. They get large advantages in the energy markets in most places. They have been very effective in preventing nuclear though which ironically does so much real world damage to their cause that all the rest of what they do is a drop in the bucket.

by hunterpayne

3/5/2026 at 10:06:24 AM

Sorry, I was talking about the fake environmentalists being funded by the fossil fuel industry. And the fossil fuel industry is still successfully killing solar and wind projects in the US.

by amanaplanacanal

3/5/2026 at 5:36:08 AM

Our problem isn’t energy production, it’s storage.

Nuclear power plants aren’t flexible enough for sudden changes in energy consumption.

by croes

3/5/2026 at 6:28:19 AM

France seems to work. They have plenty of nuclear power that is flexible. And you can have other forms of consumption flexibility; otherwise wind and solar are really in trouble.

by chickenbig

3/5/2026 at 6:54:46 AM

France uses their own and their neighbors fossil capacity to manage nuclear inflexibility.

When a cold spell hits France exports turn to imports.

Now EDF is crying about renewables lowering nuclear earning potential and increasing maintenance costs.

The problem is that they are up against economic incentives. Why should a company or person with solar and storage buy grid based nuclear power? They don’t.

Why should they not sell their excess to their neighbors? They do.

https://www.bloomberg.com/news/articles/2026-02-16/edf-warns...

by ViewTrick1002

3/5/2026 at 8:05:56 AM

No it doesn't. You can see it https://www.services-rte.com/en/view-data-published-by-rte/g...

French nuclear is more flexible than coal by design and as flexible as many older gas plants with ALFC system. They can reach up to 0.5%/second modulation (proved by Philipsburg) if the situation requires but it's rarely the case if you have a fleet. It's still not as fast as BWR's that can reach 1%/second but german coal is the slowest load follower and still meets min requirements imposed by the grid.

"When a cold spell hits France exports turn to imports." - was true in the past, a bit, but afaik this and last winter France was net exporting a ton. And with FLA3 reaching full capacity this year it'll be even less of a problem. It's not like they have a problem now, they are the largest net exporter on the continent and it's unlikely to change soon.

"Now EDF is crying about renewables lowering nuclear earning potential and increasing maintenance costs." - yes, because ren generation is acting like a parasitic source without proper BESS deployments - they eat into firm power profits without providing firm power benefits.

"Why should a company or person with solar and storage buy grid based nuclear power? They don’t." - because in many places of the world solar+bess are not sufficient. It's also the reason why Microsoft signed a contract for TMI way above market prices instead of building a fully offgrid ren solution

EDF is selling power to neighbors and makes money from it. It also is modulating it's npp a lot, which will maybe change when AC's will be more widely deployed and EV's will expand. It also is trying to schedule most maintenance works in summer, during lowest demand periods

by Moldoteck

3/5/2026 at 11:24:06 AM

Which are paragraph after paragraph agreeing that nuclear power is inflexible, can’t meet a true grid load on its own without flexibility and that renewables craters the earning potential of both existing and new built reactors.

As EDF will be able to sell fewer and fewer hours at a profit we will likely see them crying for handouts to even maintain the existing plants. Let alone new builds requiring 18-24 cent/kWh average prices to cover the costs.

by ViewTrick1002

3/5/2026 at 11:33:11 AM

Who is agreeing that nuclear is inflexible? RTE real generation data is a direct proof it's false.

EDF needs no handouts for maintenance of their reactors. But I'm eager to see their profits evolution in 2026 H1 after arenh got ditched. There will be some govt loans for EPR2, but the amount is rather tiny if we compare to say German EEG fund.

by Moldoteck

3/5/2026 at 1:52:20 PM

The proposed subsidies for the EPR2 program is 11 cents kWh and interest free loans. Sum freely, but you end up towards 20 cents kWh.

Why always the German comparison? Who even brought up Germany Can’t the nuclear handouts stand on their own?

The EEG costs are quickly going down as expensive early projects are losing their subsidies.

Renewables and storage are built in massive amounts all over the world without subsidies.

Why this completely one sided focus on absolutely massive handouts for the electricity sector, which is already solved by renewables and storage for the 99% of the cases when we still need to decarbonize industry, agriculture, construction, aviation, maritime shipping etc?

It makes absolutely and sounds like a solution looking for a problem, with a bunch of people who can’t let go attached to it.

It is the fax machine of the internet age. It is time to let go.

by ViewTrick1002

3/5/2026 at 3:10:10 PM

Yes, epr2 will get some state loans and cfds, if approved by EC. I brought up Germany because it's a famous example of lots of subsidies going into transition/deployment

EEG costs are projected to rise per EWI because even though most expensive contracts are being over, it's paid more frequently. It's projected nr will reach 23bn/y.

"which is already solved by renewables and storage for the 99% of the cases" - it's not solved by far in Europe unless you add something on top, eg. Gas firming.

It's interesting to say nuclear is a fax machine in the internet age when nuclear is our youngest invention to extract energy while solar/wind/hydro are much older. Such arguments make no sense whatsoever

by Moldoteck

3/5/2026 at 7:11:25 AM

France is part of the EU power grid and flexibility comes from that not from nuclear power plants. And the government had to rise the subsidies for nuclear energy to prevent higher rises of the energy prices. The costs for the consumers still raised.

And their power plants were in trouble in the last hot summer because the rivers were too hot to be used for cooling. Won‘t be the last time. And that will be a big problem when people turn on their AC in a heat wave but the power plants can’t power up because they don’t have enough cool water.

And that was before drone wars were a thing.

People react nervously when unknown drones fly around airports and power plants.

And didn’t we learn from the internet that centralization is a bad thing? Nuclear power plants are exactly that.

Imagine a grid where every consumer is also a producer who can satisfy their energy needs at least partially for themselves even without the grid. Try to blackout that.

by croes

3/5/2026 at 7:55:52 AM

"France is part of the EU power grid and flexibility comes from that not from nuclear power plants." - blatant lie. You can see in generation data they are flexing a lot in the summer. https://www.services-rte.com/en/view-data-published-by-rte/g...

"And their power plants were in trouble in the last hot summer" - blatant lie. Cooling was fine, it's env protection law to avoid damaging the fauna(read - to not boil fish). Yet, it affects about 0.02% of annual generation and valid almost exclusively to NPP without cooling towers. Yet in those exact periods EDF was net exporting about 14GW to neighbors, again, data is public. French nukes can handle ppl's AC's just well, probably EDF even hopes for that to modulate their npp less and get more $

Why people always spread such nonsense without even checking the facts? Like https://www.vie-publique.fr/files/rapport/pdf/288726.pdf

"And didn’t we learn from the internet that centralization is a bad thing? Nuclear power plants are exactly that." France has a combination of centralized and decentralized power - npp's are distributed around the country but each can generate a lot of power. Even more distribution and you start paying a ton for transmission lines and maintenance. That's the reason Germany started subsidizing them from this year, with about 6bn/y. Full decentralization is not a feature and you still can't achieve it since transmission system is centralized, prime example being recent cascade blackout in Spain.

"Imagine a grid where every consumer is also a producer who can satisfy their energy needs at least partially for themselves even without the grid. Try to blackout that." - that'll mean having to need a fully parallel grid for firming. Besides, a lot of home solar are grid followers - if there's a blackout, it'll shut down too unless you have a special invertor+bess which many dont have (yet)

"And that was before drone wars were a thing." - a drone would do nothing to a NPP. Even an airplane impact can be tolerated depending how new is the NPP.

by Moldoteck

3/5/2026 at 9:04:14 AM

> Cooling was fine, it's env protection law to avoid damaging the fauna(read - to not boil fish)

You do understand what the point of environmental protection is?

If you kill the flora and fauna you are not environment friendly.

by croes

3/5/2026 at 10:09:10 AM

Yes, i understand it very well

The problem is you framed it as

1- not being able to cool reactors physically, which is false

2- being a major deal, when it affects only 0.2% of generation per year, during a period when EDF is net exporting about 14GW to the neighbors

3- being an unfixable issue, which is again false. The problem exista for reactors without cooling towers. EDF can fix it by building them. But there's no financial incentive here. Where would EDF sell extra power when export is already maximized in that same timeframe and market prices in summer are low?

by Moldoteck

3/5/2026 at 1:05:24 PM

> because the rivers were too hot to be used for cooling.

Where does it say physically?

> being a major deal, when it affects only 0.2% of generation per year

Interesting choice of time period. Energy problems are rarely viewed from a yearly perspective.

> being an unfixable issue, which is again false.

Who said unfixable? It’s a current problem and any change needs time and money.

That time and money can be used for decentralization.

Drones will get cheaper and cheaper and more capable and many nuclear power plants aren’t built for that threat

by croes

3/5/2026 at 1:18:51 PM

Now you are being mean, or are engaging in discussions to spread misinformation

"And their power plants were in trouble in the last hot summer because the rivers were too hot to be used for cooling" - this does imply that cooling was not possible. You said nothing about the fact it's just a legal limit. Nor did you specify what/how many NPP exactly got modulated. Is "their" supposed to mean all? A bunch?

"And that will be a big problem when people turn on their AC in a heat wave but the power plants can’t power up because they don’t have enough cool water." - this implies it's both a major problem during heatwaves and/or that it's unfixable, both being false.

"> being a major deal, when it affects only 0.2% of generation per year

Interesting choice of time period. Energy problems are rarely viewed from a yearly perspective." - did you omit on purpose LITERALLY the following text "during a period when EDF is net exporting about 14GW to the neighbors" ? France is largest net exporter on the continent both yearly and in summer in particular. You are free to inspect energy charts data.

"That time and money can be used for decentralization." - french generation is already sufficiently decentralized. They can decentealize even more by building more plants across the country.

"Drones will get cheaper and cheaper and more capable and many nuclear power plants aren’t built for that threat" - nuclear plants are built or upgraded to withstand airplane impacts, a drone would barely scratch the outer reinforced concrete.

All your statements are either made on purpose to mislead (especially considering how you dismiss your own statements or omit crucial parts of text quoting me) or you are communicating your thoughts in a very unoptimal way...

by Moldoteck

3/5/2026 at 7:26:44 AM

Nuclear power is one of the most flexible sources of power, especially PWR's with ALFC or even more so - BWR's You can actually see how France is flexing in the summer on RTE website

by Moldoteck

3/5/2026 at 7:49:24 AM

France's nuclear operators have been claiming this for years. But recently started claiming that wind and solar are bad because they force nuclear to flex which is too expensive.

> Electricite de France SA said growing solar and wind generation was increasing equipment wear and maintenance costs at its nuclear reactors, which are forced to reduce output when power demand is insufficient.

https://www.bloomberg.com/news/articles/2026-02-16/edf-warns...

by ZeroGravitas

3/5/2026 at 8:09:44 AM

"France's nuclear operators have been claiming this for years. But recently started claiming that wind and solar are bad because they force nuclear to flex which is too expensive." - one doesnt disprove the other.

French nuclear is extremely flexible https://www.services-rte.com/en/view-data-published-by-rte/g... but it doesn't mean it's free. Solar and wind without proper bess to support them are creating problems for other generators, acting as grid parasites without offering proper firm generation

by Moldoteck

3/5/2026 at 2:31:27 PM

The flexibility claim was always the same lie: that what mattered was technical flexibility, when economic flexibility wasn't there.

by pfdietz

3/5/2026 at 3:12:51 PM

That's false too. Most of the arguments from antinuclear activists in this direction are about physical capacity of modulating too slow, which was false. Regardless, EDF is modulating now mostly due to economic reasons. Above 50-60% capacity factor you'll be fine, beyond that it'll be problematic with any asset, at which point you'll need to ask yourself if you love gas or you let nuclear run for some minimal CF or if you mandate each NPP to build a bess buffer to absorb capacity when needed

by Moldoteck

3/5/2026 at 6:25:17 AM

The storage problem is home-made, because our problem is intermittent renewables that can't produce on-demand.

With consistent producers like nuclear there is no storage problem.

And of course the Natrium plant has the buffer so it can ramp grid output up and down while maintaining the reactor at consistent power levels.

by mpweiher

3/5/2026 at 6:58:22 AM

> With consistent producers like nuclear there is no storage problem.

This tells me you’ve never looked at a demand curve. In for example California the demand swings from 18 GW to 50 GW over the day and seasons.

The problem has always been economical. And this solution is looking like a bandaid to get taxpayer handouts.

Why store expensive nuclear electricity rather than extremely cheap renewable electricity?

by ViewTrick1002

3/5/2026 at 10:33:03 AM

> This tells me you’ve never looked at a demand curve. In for example California the demand swings from 18 GW to 50 GW over the day

Have you been looking at "net demand" curves? Total demand variation is not too large over the day. The wind/solar production enormously increases the magnitude of remaining demand difference over the day.

https://www.caiso.com/todays-outlook

> and seasons.

Nobody is talking about batteries to deal with demand swings between seasons though. Capacity has to accommodate whether it's nuclear or fossil or battery or renewable. The issue is day to day variation. And it does not matter how much wind/solar capacity you have, you can't supply demand without storage. That is untrue of other generation types.

Other generation might use batteries to take the edge of peaks, but that would only be done if it made total cost cheaper. That's not the case for renewables. If there were no other generation then they would have to use storage, so it's always going to make them more expensive.

by stinkbeetle

3/5/2026 at 11:41:51 AM

The net demand curve varies 30 GW over the period you posted?

It goes 7 GW negative.

The problem with nuclear power is that about all costs are fixed. It costs 18-24 cents/kWh when running at 100% for 40 years excluding backup, transmission, final waste disposal and taxes.

Now remove any earning potential from large portions of the day coming from renewables and storage and the economics simply does not pan a out.

by ViewTrick1002

3/5/2026 at 3:30:16 PM

Are you sure with the numbers? Maybe for failed projects like Vogtle it may be true but otherwise, the cost is about 4.7ct/kwh everything included looking at swiss open data. And Goesgen didn't run at 100% CF all these years.

by Moldoteck

3/5/2026 at 5:26:08 PM

Same costs for HPC, FV3, Polish AP1000s and EPR2s as well.

I don't see the relevance comparing with a plant that start construction over half a century ago?

by ViewTrick1002

3/5/2026 at 8:12:18 PM

Do you want to compare maybe with barakah which was not a foak and didn't have the supply chain issues like with epr/ap1000?

by Moldoteck

3/5/2026 at 9:21:55 PM

You mean middle eastern labor and design that doesn’t fly with western regulations?

Sounds applicable!

Let’s first acknowledge that KHNP pulled out of all western projects except the Czech one after their settlement with Westinghouse. They don’t exist as an option.

Then let’s look at the Czech subsidies. They aren’t materially different compared to any other modern western nuclear construction.

They’ve shaved a few billion from the headline number but the project is still pure cost plus putting all construction and financial risk on the governments tab.

by ViewTrick1002

3/5/2026 at 7:05:26 AM

Nuclear power plants and the electric networks have a big problem when power consumption has sudden big changes, like this

https://www.wsj.com/business/energy-oil/a-new-threat-to-powe...

Storage would mean just to reroute the energy to storage, otherwise you need to lower the power plant‘s output what doesn’t happen fast in nuclear power plants

by croes

3/5/2026 at 6:22:49 AM

Construction for the non-nuclear parts started a while ago and is proceeding.

https://www.world-nuclear-news.org/articles/terrapower-break...

by mpweiher

3/5/2026 at 7:53:08 AM

The non-nuclear bit is the key there. Site construction is not the challenge. Turning a theoretical reactor design into a working reactor design is.

As far as I can tell, in its 20 years of existence, TerraPower has not built a reactor. nor had one of its designs built by someone else.

by GolfPopper

3/5/2026 at 9:41:23 PM

This is the first one.

Before you build the first one, you haven't built one.

Are you saying first things can never be built?

by mpweiher

3/5/2026 at 10:56:35 PM

If I go around bragging about my awesome self-built home design for years, and then buy, clear and level a plot of land, while it is a necessary step, it is also largely irrelevant to my ability to actually build the house, much less the quality of the finished building.

by GolfPopper

3/5/2026 at 2:05:33 AM

[dead]

by 111111011

3/5/2026 at 12:38:00 AM

[flagged]

by burnt-resistor

3/5/2026 at 1:14:04 AM

> pedo Bill Gates

Huh? You’re going to need a citation to throw those kind of accusations around. A serial philanderer? Absolutely. But all indications are he was interested in adult women, not even young women. I think the Russian call girls that Epstein set him up with were in their 30s?

by tw04

3/5/2026 at 12:45:52 AM

What are the substantive safety or environmental objections to the project that TerraPower is bypassing by allegedly bribing the government?

by eli_gottlieb

3/5/2026 at 1:13:51 AM

I don't know. I guess we'll find out the hard way.

by jfengel