Natrium 'advanced nuclear' power plant wins Wyoming permit

1/15/2025 at 9:23:19 PM

> That application was submitted in March 2024 and is on track for approval in December 2026

Next time you complain that waiting for a code review approval till next week is excruciatingly long, think about these turnaround times.

Also this is why we can't quickly build many reactors to ramp up electric generation for millions of new electric cars, etc.

by nine_k

1/15/2025 at 10:42:53 PM

The grid connection backlog is about 6 years, so this is considerably quicker than for a renewable energy project that requires a new grid interconnect.

by bryanlarsen

1/16/2025 at 2:40:08 AM

That is actually VERY fast for anything related to nuclear reactors.

by UltraSane

1/16/2025 at 1:11:40 AM

You probably don't want a nuclear reactor (of all things) to be built in sprints of two weeks, according to the tenets of Agile.

by thrance

1/16/2025 at 2:26:30 AM

Okay, we had a partial meltdown in prod, and released some radioactive iodine-131, so that goes on the sad face side of of the retro board.

But on the good side, we _didn't_ have a hydrogen explosion due to some late-night troubleshooting, great work Carl!

But we learned a lot, our alerts were confusing, and our metrics didn't surface coolant level or the relief valve that was stuck open.

So next sprint, let's focus on monitoring and cross-team knowledge transfer! 3 points, right?

by EdwardDiego

1/16/2025 at 2:34:57 AM

While true, this has nearly nothing to do with building (still to happen) or planning (has to be finished before the approval process). It is a 2 year paperwork delay and making sure the NIMBYs have all the time they might need to get organised.

by roenxi

1/16/2025 at 2:53:54 PM

> Also this is why we can't quickly build many reactors to ramp up electric generation for millions of new electric cars, etc.

"We" here means any country on the planet. Nuclear plants are simply inherently more complicated and more risky to build that the alternatives. Even China, who often rightly, gets criticized for pushing through individual rights on such projects can't build them quickly.

Look at the shape of these curves [1], nuclear is flatlining while renewables are accelerating at incredible speed.

[1]:https://cleantechnica.com/2023/02/06/renewables-in-china-tre...

by _aavaa_

1/16/2025 at 5:57:27 AM

The time to review reactor design should be long, given that something going wrong with a leak of any kind could have widespread effects for generations.

by IOT_Apprentice

1/15/2025 at 10:56:44 PM

> why we can't quickly build many reactors

No. The reason is that they have not been price competitive with renewables.

And so there isn't the volume of approvals that gives regulators experience which in turn reduces approval times.

Commercial solar takes months to approve by comparison.

by threeseed

1/16/2025 at 3:06:04 AM

The reason nuclear isn't price competitive with renewables—or anything, really—is because of the amount of safety regulation and lack of experience building plants. Both of these emerged, at least in part, from decades of protests from well-meaning people with a laughable misunderstanding of how radiation works. So, you get people saying "don't build nuclear, it's unsafe!" and then you demonstrate that it's as safe as any energy technology in existence, so those people say "okay fine... don't build nuclear, it's expensive!" when they are the reason it's expensive. Meanwhile, we managed to create an irreparable 1.3C rise in global temperatures while waiting for solar, wind, and battery to catch up to where we could have been 70 years ago.

by karaterobot

1/16/2025 at 2:10:32 PM

There needs to be generalized a term for NIMBYs for resisting various solutions to a number of issues because this pattern in liberal democracies around the planet isn’t exactly helping anyone make progress on the more core issues these folks seem to also be interested in.

by devonkim

1/15/2025 at 11:29:17 PM

Once they’ve approved this reactor, build more of the same.

by TheSpiceIsLife

1/15/2025 at 11:34:11 PM

That's a decision for the markets.

And right now renewables continue to get better and cheaper so it will be hard for nuclear to get much traction.

by threeseed

1/16/2025 at 2:57:57 PM

> That's a decision for the markets.

Says who? This is an opinion, not a fact.

All of the newer SMR companies are pitching their design as costly at start, but then cheaper because of mass production. Well the entire gaggle of companies won't all be able to mass produce their SMRs in the numbers required to get the scale down since there isn't the appetite for it.

by _aavaa_

1/15/2025 at 11:06:08 PM

Last I checked solar without batteries is roughly the same price per Kw as nuclear. There’s a huge difference in capability though because nuclear is 24/7 peak availability which solar can’t do and if you start building batteries the price increases substantially.

I agree on regulatory experience but that comes more from panic over nuclear proliferation rather than any economic reason. Whether or not you view that as a legitimate concern is open to debate.

by vlovich123

1/15/2025 at 11:09:28 PM

For anyone arguing about this, please first look at https://www.cis.org.au/commentary/opinion/nuclear-vs-renewab...

The primary cost of running solar plants is no longer the panels themselves (ie if they drop to 0 the $/KW wouldn’t change a whole lot).

by vlovich123

1/16/2025 at 11:26:30 AM

That's a Liberal Party think-tank supporting a hypocritical and ill-thought-out Liberal policy.

Maybe people should read something from the actual domain experts instead? The latest CSIRO report specifically responded to the claims made about extending the time period.

> CSIRO said accounting for a 60-year life reduced the costs of nuclear by about 9% compared with calculating over 30 years, but found other technologies such as solar and wind saw similar cost reductions of about 7% under the same approach.

You yourself seem a bit confused about facts after using these sources.

1. Nuclear is not anywhere near the same price as solar. (I'm hoping you typo'd and were really trying to make the much saner but still wrong claim that renewables plus storage has costs comparable to nuclear which this document tries to claim)

2. It's not just the panel costs that have dropped, the delivered cost of solar energy has been falling. It dropped 12% in 2023 alone. This has lots of causes, like the safe and predictable success of solar allowing for lower interest rates and cheaper panels allowing for other assumptions to be rethought (e.g. ditch trackers that used to maximise output per panel and use the money and space saved to buy more panels).

by ZeroGravitas

1/16/2025 at 5:38:15 AM

> nuclear is 24/7 peak availability

Well, nuclear is 24/7 base load. Nuclear can't peak that well. Also, when nuclear goes offline it does so for days.

by cryptonector

1/15/2025 at 11:13:52 PM

> Last I checked solar without batteries is roughly the same price per Kw as nuclear.

You didn't check, you decided to cook the presentation of the facts.

Indeed, solar is not available 24/7. But it's not individual installations which need 24/7 availability, it's the grid as a whole; plus, energy use during the day and night differs, so even the grid as a whole doesn't need the same generation capacity 24/7. And - the grid has many different energy sources (i.e. not just solar and nuclear), some renewable and some non-renewable, which aren't daylight-only.

Which is to say there is plenty of room for solar installations irrespective of energy storage solutions. And indeed, those installations are taking place, and they are rather cheap.

by einpoklum

1/16/2025 at 11:58:30 PM

> Indeed, solar is not available 24/7. But it's not individual installations which need 24/7 availability, it's the grid as a whole; plus, energy use during the day and night differs, so even the grid as a whole doesn't need the same generation capacity 24/7

The peak to trough is ~30% reduction if I recall correctly. It’s different but not massively so. And long distance energy transport is insanely expensive. It’s being done but mainly to stabilize the grid rather than arbitrage. And your entire solar capacity in the US goes offline for ~12+ hours. That’s a lot of energy you’re going to have to supplant in other ways regardless of long distance.

> And indeed, those installations are taking place, and they are rather cheap.

Because the cost of storage and the destabilization of the grid it causes the provider are treated as externalities.

by vlovich123

1/16/2025 at 1:38:34 AM

> Last I checked solar without batteries is roughly the same price per Kw as nuclear

When your basic assumption is that an entire industry is doing something dumb, it’s probably wrong. If nuclear was actually that cheap electric companies would constantly be proposing new projects, but it’s not.

> 24/7 peak availability

The industry abandoned nuclear because electricity demand stopped increasing decades ago. It simply isn’t cost competitive when facing both significant curtailment and the need for backup generation for the multiple weeks to months downtime nuclear power plants have semi annually.

That’s the core issue nuclear needs both 24/7 demand, and the grid to also be perfectly fine when it goes away for months. That only possible when it makes up ~30% of supply which is roughly where it’s been for decades.

Now having not built nuclear for decades once off projects are constantly wildly over budget and behind schedule. Solar + batteries is currently beating even optimistic estimates for nuclear just about anywhere, let alone current boondoggle pricing.

by Retric

1/16/2025 at 11:55:37 PM

> When your basic assumption is that an entire industry is doing something dumb, it’s probably wrong. If nuclear was actually that cheap electric companies would constantly be proposing new projects, but it’s not.

The industry is doing the right thing but the reason it’s not choosing nuclear is because regulatory burdens make project success and prices highly variable and uncertain, not to mention a shift in political winds kills your project. The reason isn’t purely a price thing.

> The industry abandoned nuclear because electricity demand stopped increasing decades ago

There’s no way this is true considering that crypto and AI have started to push significant power demands.

> Now having not built nuclear for decades once off projects are constantly wildly over budget and behind schedule. Solar + batteries is currently beating even optimistic estimates for nuclear just about anywhere, let alone current boondoggle pricing.

That’s a choice we get to make. China is building their nuclear muscle because they realize it’s required for baseload for solar, way cheaper than batteries, and the only way you’re going to be able to charge all these EVs.

by vlovich123

1/17/2025 at 3:53:25 AM

> There’s no way this is true considering that crypto and AI have started to push significant power demands.

I was describing what happened when we stopped building nuclear power plants, not what’s happening now or in the near future.

From 1.7TWh in 1975 to 3.1TWh in 1995 is an 82% increase in demand in just 20 years, but the next 20 years only takes us to 3.9TWh in 2015 a 26% increase. That had massive knock on effects in terms of power plant construction, move forward to 2023 demand is only at 4TWh less than a 3% increase. https://www.statista.com/statistics/201794/us-electricity-co...

The point of that was simply context.

> The reason isn’t purely a price thing.

All that risk ultimately just equates to a cost, if nuclear was wildly profitable to operate nobody would care about those risks but it’s at best barely breaking even when nothing goes wrong.

Also, costs rose not because of regulations in a vacuum. 3 mile island happened because of a lack of maintenance, you don’t solve that problem without spending more money on maintenance. And so it goes for a huge range of issues like foreign material in cooling ponds. Suddenly there’s all this effort when working around cooling ponds to avoid a multi million dollar issue and that’s not free, but there’s no free lunch where you can avoid the expense and not also be cautious.

Thus nuclear power was always expensive, the costs where initially just hidden as risk and escalating maintenance costs.

by Retric

1/16/2025 at 1:52:53 AM

>Last I checked solar without batteries is roughly the same price per Kw as nuclear

Checked where? Lazard says it is one fifth of the price.

>There’s a huge difference in capability though because nuclear is 24/7 peak availability which solar can’t do

Not 24/7. They have to be turned off for maintenance and when that happens e.g. France burns an awful lot of gas.

Pair solar with wind and storage and it's still cheaper than raw, nuclear power and would be even if matching storage were 4x the cost.

by pydry

1/16/2025 at 11:59:46 PM

> Not 24/7. They have to be turned off for maintenance and when that happens e.g. France burns an awful lot of gas.

Pretty sure >90% of France’s energy consumption is completely green. Renewable grids wish they could boast these kinds of numbers.

by vlovich123

1/16/2025 at 2:43:33 AM

A key metric that controls the cost is just how much storage do we want? 4 hours? 1 day? 1 week?

by UltraSane

1/16/2025 at 8:24:53 AM

https://reneweconomy.com.au/a-near-100-per-cent-renewables-g...

by pydry

1/16/2025 at 5:22:10 PM

Very interesting. But having no dispatchable power generation other than 5 hours of storage runs a real risk of local or national outages during rare prolonged wind and solar shortfalls.

by UltraSane

1/16/2025 at 9:51:34 PM

On the sunniest windiest days when wind and solar is massively overproducing we can synthesize natural gas or hydrogen. That can be used to fill in the gaps for the last 1-3% of energy.

The rountrip efficiency of this is shit (~40% compared to 90% for pumped storage or batteries) but the important thing is it's cheap to store a lot of it for a long time and straightforward to use a lot of it all at once during those rare dark, windless spells. For natgas we even already have the infrastructure.

What's really startling is the cost of producing a kwh from stored syngas/hydrogen generated from solar and wind is similar to the cost of getting a kwh from a nuclear power plant.

So, worst case storage + solar + wind ~= average case nuclear power.

by pydry

1/15/2025 at 11:22:47 PM

Indeed so. Renewables had about 15 years of breakneck-pace progress and massive production with huge economies of scale, which I cannot say about nuclear reactors.

But even if nukes were somehow very cheap to build, the review process due to high safety requirements and a lack of a standardized reusable reactor design would make the process slow. To become cost-competitive, nuclear reactors need to be mass-produced, using a proven design that needs little review. The French sort of achieved that, with two mass-produced types of reactors.

Renewables as baseload are still problematic though. Solar cells and even wind turbines are not expensive, but the batteries are very expensive, and are a huge fire hazard. It would be interesting to estimate how much would a kWh cost from a nuclear power station, and from an equal-power LiFePO4 battery installation with the capacity of, say, 3 days worth of the rated max power. Batteries can be replaced gradually, but would need to be replaced much sooner.

[Update:]

If we take a modest nuclear generation unit producing 300 MW of electric power, I'd like to compare it with a battery that can store 300 MW * 3 days of energy from renewable sources. It's 21.6 GWh. With LiFePO4 typical bulk price of $100 per kWh, the upfront cost in batteries alone would be $2.16 billion. It's still lower than nuclear reactor equipment, but very much in the same ballpark.

by nine_k

1/16/2025 at 2:34:32 AM

> but the batteries are very expensive, and are a huge fire hazard

Have you seen how the fire risk petroleum presents? It's crazy.

by EdwardDiego

1/15/2025 at 11:59:37 PM

> but very much in the same ballpark

You need to factor in waste disposal and decommissioning costs for nuclear.

And if you are concerned with the fire risks of batteries you may want to think about the impact of serious events with a nuclear reactor. In almost all cases they end up being quite expensive.

by threeseed

1/16/2025 at 2:33:11 AM

Not like there's a history of steam explosions or hydrogen formation in historical nuclear reactor incidents.

by EdwardDiego

1/15/2025 at 8:26:28 PM

This is a fast reactor. That is, a reactor in which the neutrons, instead of being moderated down to thermal energies, remain at high energy.

The fission cross section for such energetic neutrons is much lower than for thermal neutrons. Therefore, there has to be a much greater density of fissionable material in the reactor core.

The lack of a moderator also means rearrangement of the core in an accident is potentially much more dangerous. If the fuel itself rearranges to become more compact, say by melting and flowing, the reactivity could increase. This is not possible in (say) a light water reactor, where such a rearrangement would reduce reactivity.

The nightmare scenario for any fast reactor, warned about by Edward Teller in 1967, is a rearrangement that causes the core to become supercritical on prompt neutrons alone (that is, on only the neutrons released promptly at the moment of fission, not on those + the delayed neutrons emitted by some fission products as they decay). A fast prompt supercritical configuration could potentially explode with great violence, greater than Chernobyl. An atomic bomb is a prompt fast supercritical system.

I will want to see how the NRC does or does not license their design, a process that has just started. I will not be surprised if their approach ends up being unlicensable in the US because safety cannot be assured by analysis under accident conditions.

by pfdietz

1/16/2025 at 1:06:27 AM

It's not quite like that.

> An atomic bomb is a prompt fast supercritical system.

Yes, it is, but more precisely it is a fast hypercritical system. The difference is this: in a supercritical system the ratio of neutrons in a new generation vs the old generation (generally denoted by k) is higher than one. For example 1.001 qualifies as supercritical. In a hypercritical configuration, k is higher than 2. In nature things generally evolve in a continuous way. To get to 2 you need to first get to 1 and 1.001, for example. For a bomb, it is very important to get to 2 extremely quickly, so that the assembly does not start the chain reaction while k is 1.001, or 1.1. To do that, you use either a gun or high explosives, to quickly reassemble a subcritical configuration into a hypercritical one, before a stray neutron has a chance to start a barely supercritical reaction (also known as a "fizzle").

With a reactor, there's no way to get an atomic bomb effect, because you go through the point of k=1.001. When you get there, there are plenty of neutrons around that this results in a "fizzle". Heat is produced and the core dilates and the ratio becomes low again. This results in "prompt excursions", each one lasting less than one second, each one some sort of a "bomb fizzle". These excursions are annoying, but they are not Hiroshima.

> I will not be surprised if their approach ends up being unlicensable in the US because safety cannot be assured by analysis under accident conditions.

What you are saying is a Catch-22. NRC can't approve a new design because it doesn't know how it performs under accident conditions, but then you can't know how something performs under accident conditions if you don't build it, and you don't build it if NRC does not approve it.

The fact is, Russia has been operating the BN-800 sodium-cooled fast reactor for 10 years [1], and the smaller BN-600 for 45 years. So sodium-cooled fast reactors can work, and Russia likes them enough that it plans to build a bigger version, BN-1200. They don't explode. You could say "not yet", and sure thing, this means that the NRC needs to work hard to cover all the bases. But this is not impossible.

[1] https://en.wikipedia.org/wiki/BN-800_reactor

by credit_guy

1/16/2025 at 4:12:48 AM

You are assuming that as the core starts to expand, it doesn't expand in a way that increases k (for example, suppose liquid sodium is violently expelled from collapsing coolant channels; this could increase k). Can this be assured? Because if not, the yield could become very large. Granted, this doesn't seem likely, but can you assure it's impossible, in any possible accident, and any possible geometry of fuel and voids?

> What you are saying is a Catch-22. NRC can't approve a new design because it doesn't know how it performs under accident conditions, but then you can't know how something performs under accident conditions if you don't build it, and you don't build it if NRC does not approve it.

Even if you build it, and even if there is an accident, you don't know how it behaves under accident conditions. You just know how it behaved in that particular accident.

It might be easier for developers if we could build thousands a fast reactors and let some of them explode to get some statistics on what works, but that's not how the NRC is arranged, and even that would not ensure all the catastrophic risk had been retired.

by pfdietz

1/16/2025 at 12:30:45 PM

Here's some of the software Terrapower wrote in order to model the neutron economy of the Natrium reactor [1]. Such software has been written ever since the early days of the atomic era.

Nuclear engineers know how k behaves, they don't need to make assumptions. Here's a 101 on reactivity feedback effects by the NRC [2].

The US has built all sorts of nuclear reactors, sodium-cooled included. Even one that was sodium cooled and used molten (hot) plutonium as fuel [3].

The experience with prompt criticality excursions is (for the better or worse) extensive [4].

The NRC absolutely has the ability (and duty) to analyze all possible accident conditions for this reactor. This is the page it maintains for Natrium [5]. They have already received and reviewed thousands of documents for it. We would not be at the point that they allow the building to start if they think there's a slight chance the reactor would be "unlicenseable".

[1] https://terrapower.github.io/armi/

[2] https://www.nrc.gov/docs/ml1214/ml12142a130.pdf

[3] https://www.osti.gov/biblio/4206527

[4] https://en.wikipedia.org/wiki/Prompt_criticality#List_of_acc...

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

by credit_guy

1/16/2025 at 3:35:40 PM

The NRC has no duty whatsoever to analyze accident conditions. The NRC requires the licensee to do the analysis; the NRC just has to evaluate whether they did it properly and sufficiently.

I do wonder how you think all possible accident conditions could be evaluated. All possible geometries of melted fuel? The possibilities are vast, indeed exponentially vast.

Edward Teller in his 1967 comment expressed skepticism that the consequences of a serious accident in a fast breeder could be evaluated (yes, I know Natrium is not quite this configuration, uranium having a considerably higher bare core critical mass, but it's similar):

"For the fast breeder to work in its steady-state breeding condition you probably need something like half a ton of plutonium. In order that it should work economically in a sufficiently big power-producing unit, it probably needs quite a bit 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 can 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 a plutonium reactor, a couple of tons of plutonium can melt. I don't think anybody can foresee where one or two or five percent of this plutonium will find itself and how it will get mixed with some other material. A small fraction of the original charge can become a great hazard."

by pfdietz

1/17/2025 at 2:11:01 AM

So your line of argument goes something like this: "->Do you concede that there are disaster scenarios that you didn't think of? ->Yes, I'm not God to know everything, I concede that. ->Well, QED, a fast reactor is unlicenseable." Case closed, right?

But the problem with this argument is that it can be applied to anything. In particular, if you really follow this argument, we should shut down all the current operating reactors, because, you know, there might be disaster scenarios that we didn't consider.

I hear you, I hear you. This argument only applies specifically to fast reactors, because this is what Dr. Teller said in 1967. But why did Teller say that?

In 1961 a nuclear reactor that the US Army commissioned with the stated intent to be virtually idiot proof, went boom. It became prompt critical. What happened was one of the most (if not the most) life-beats-fiction events in the history of nuclear reactors. It appears one of the operators decided to commit suicide by pulling a control rod as fast as he could [1]. Of course, since the guy died in the following half a second, we'll never know his true motives.

Another thing is that Teller was profoundly anti-communist. In 1957 another mind-bending accident happened in the Soviet Union, [2]. It had to do with plutonium, it went something like this: the Soviet Union was producing lots of plutonium to build bombs. Plutonium is extracted by chemical separation from spent uranium. After the separation, various steps are taken to increase the concentration, and eventually to purify the plutonium metal, but some chemical tailings that contained plutonium in low concentration remained. They were dumped in large underground tank. The solution contained ammonium nitrate, but it was mostly water. Water is a good moderator, so there's a good chance the solution would from time to time undergo prompt criticality excursions. Nothing major, no explosion happened. Yet. But because of the periodic heating, the water evaporated, and in time the ammonium nitrate became more concentrated, and it became a huge amount of (chemical) explosive. At some point this ammonium nitrate decided to go boom, like it happened in Beirut in 2020. The explosion was totally non-nuclear, but it put in the atmosphere a huge dirt cloud full of plutonium and other radioactive nasty stuff. The Soviet Union kept this a secret for many, many decades. But some people in the West learned some tidbits about this, and Teller, obsessed as he was with the Soviet Union, might have been one of the guys in the know. Plus, Teller (the father of the hydrogen bomb) had access to the highest level of top secret information in the US in regards to nuclear things. If anyone in the US knew anything about the Kyshtym, then Teller knew that too.

But why did Teller say that about fast reactors and not thermal reactors? Because that was the context. He was asked to testify if the US should build a sodium-cooled fast reactor. And he said it's a bad idea. If you know anything about Teller, is he said everything with a supreme confidence. Everything was very black and white for him, and he always knew with utmost certainty what was black and what was white. He thought for example that we should use hydrogen bombs to dig canals. Or that we should put anti-ballistic-missile thingies orbit that would zap the incoming missiles with a beam of X-rays produced by a nuclear bomb explosion [3]. This is not a joke.

Ok. Let's leave Dr. Teller aside for now. Are sodium-cooled reactors too risky to build. Well, patently not, considering that Russia is operating 2 right now and plans to build more. But let's say you are not happy with this. Will there be a point where you would concede that the experience the world has with building and operating such reactors is sufficient for the NRC to start granting such licenses? If not, what makes fast reactors any different that pressurized water reactors?

And by the way, the Natrium reactor is not designed to burn plutonium. It is not designed to be a breeder reactor. And the issue about prompt neutrons is actually less of a problem for such a reactor: U-238 has the highest ratio of delayed neutrons to prompt neutrons of any fissionable isotope and for fast reactors a larger proportion of fission events involve U-238 compared to thermal reactors [4].

[1] https://en.wikipedia.org/wiki/SL-1

[2] https://en.wikipedia.org/wiki/Kyshtym_disaster

[3] https://en.wikipedia.org/wiki/Project_Excalibur

[4] https://www.nuclear-power.com/nuclear-power/fission/prompt-n...

by credit_guy

1/15/2025 at 8:57:22 PM

reddit had a nice list of the pros and cons: https://www.reddit.com/r/NuclearPower/comments/17k0wcc/natri...

I understand the risks around sodium, but the "passive natural circulation cooling" I don't understand. Is it more feasible with this design and why?

" Pros:

    high temperature means we can use process-heat which is a much more efficient use of heat.

    fast spectrum neutrons means we can burn importantly troublesome parts of nuclear waste.

    fast spectrum is also better for breeding new fuel, significantly increasing how much energy we can extract from uranium/thorium.

    passive natural circulation cooling is much more feasible.

Cons:

    fast spectrum is a little more complicated to control.

    fast reactors require high enrichment.

    inspection of the plant is very difficult with liquid metal.

    high temperature liquid metal doesn't play nicely with metal pipes.

    sodium burns in air and is explosive with water.

    we simply do not have nearly as much experience with sodium as we do water and that really cannot be understated.
"

by manvillej

1/15/2025 at 9:27:55 PM

I suppose that "passive natural circulation cooling" means that plain convection of the coolant(s) is sufficient to cool the reactor, without involving pumps which could fail. Convection can't fail as long as there is coolant and no significant obstacles.

by nine_k

1/16/2025 at 2:51:04 AM

Russia has been operating a sodium-cooled fast reactor for 45 years.

by UltraSane

1/15/2025 at 8:44:16 PM

Based on your comment it sounds unreasonable to select this design. It must have some reason to exist?

by thecopy

1/15/2025 at 9:00:45 PM

Fast reactors do have some attractive features. They have better neutron economy and work better with plutonium. They can achieve breeding ratios comfortably above 1 with the U-Pu system. They produce less actinide waste since the chance of neutron capture not causing fission is lower, and can more effectively destroy actinide waste. Sodium-cooled fast reactors will operate at higher temperature than LWRs, enabling the salt thermal storage scheme they propose to use.

In large reactors, these features have not been enough to compensate for the disadvantages and sodium-cooled reactors have not been successful, coming in more expensive than light water reactors for a given power output. France, which had been developing fast reactors, has recently mothballed the effort with no plan to restart before 2050.

by pfdietz

1/16/2025 at 2:54:01 AM

Russia has two of them, one 800MW and one 600MW, and plan to build a 1.2GW version.

by UltraSane

1/16/2025 at 4:01:03 AM

Even the Russians admit their LWRs are cheaper.

by pfdietz

1/15/2025 at 9:07:56 PM

The main advantages of using a fast reactor are less nuclear waste and more energy for a given fuel input.

by aidenn0

1/15/2025 at 9:28:56 PM

Even burning some of the "nuclear waste" which is just nuclear fuel than needs refining.

by nine_k

1/16/2025 at 2:52:14 AM

It can make more fuel than it uses. It needs enriched uranium at startup but then can convert regular uranium and/or thorium to usable fuel.

by UltraSane

1/15/2025 at 9:22:55 PM

> If the fuel itself rearranges to become more compact, say by melting and flowing, the reactivity could increase.

Wouldn't you just design the shape of the reactor so that if it got too hot for any reason, the shape it would melt into would result in a less compact geometry that would slow down rather than speed up the reaction?

by AnthonyMouse

1/15/2025 at 9:31:01 PM

How do you do that in a way that's amenable to conclusive analytic demonstration? For example, how do you prevent melted fuel from flowing into the cooling channels that go through the core?

About the only approach I'd be comfortable with would be dissolving the fuel in molten salt (probably chloride salt). This is not Natrium's approach.

Melting of fuel is not a theoretical problem -- it has actually happened at two fast reactors in the US (EBR-1 and Fermi-1, the latter the reactor in the hyperbolically titled book "We Almost Lost Detroit"). No explosions occurred, but it's very troubling the fuel melted at all. The NRC will surely insist on analysis of the consequences of partial fuel melting accidents.

by pfdietz

1/15/2025 at 10:10:57 PM

To begin with you might start with a geometry which by design is already close to maximally compact, so that a geometry change would tend to go in one direction.

> For example, how do you prevent melted fuel from flowing into the cooling channels that go through the core?

Expect that to happen and use a geometry that doesn't cause the reaction to increase in speed if it does, e.g. because fuel flowing into the cooling channels would make the fuel less rather than more compact.

by AnthonyMouse

1/15/2025 at 10:29:45 PM

Slightly hesitant to jump in since pfdietz definitely knows more about this than I do... but...

Cooling typically means things like maximizing surface area, minimizing the thickness of the object being cool, etc.

Maximum neutron density presumably happens in a sphere, which is coincidentally the shape that minimizes surface area.

The whole point of a nuclear reactor is that it heats up, and you can convert that heat into useful fuel. Presumably that means you need to carry quite a lot of heat away per volume. Presumably that means putting the fuel into a spherical shape really doesn't work that well.

by gpm

1/15/2025 at 11:02:39 PM

To cool something, you need a material which is a decent conductor of heat. The reaction materials are mostly uranium, plutonium and thorium, which are metals. They conduct heat pretty well all on their own.

by AnthonyMouse

1/15/2025 at 11:27:41 PM

Metal fuels also melt at considerably lower temperature than oxide fuels.

Uranium oxide melts at 2865 C; uranium metal at 1132 C, plutonium metal at just 639 C. In contact with iron, plutonium forms a eutectic with a melting point of just 410 C, below the melting point of zinc. There was a crazy reactor at Los Alamos, LAMPRE, that used molten eutectic Pu-Fe in tantalum tubes as the fuel.

by pfdietz

1/16/2025 at 6:09:39 AM

1132 C shouldn't be an infeasibly low temperature when the reactor is only expected to heat the coolant to 300-350 C. Meanwhile thorium metal is 1750 C.

Or use uranium carbide. High melting point with still decent thermal conductivity.

by AnthonyMouse

1/15/2025 at 10:27:12 PM

Why would fuel melting be possible? The way I'd show it is by having the increased Doppler broadening and thermal conductivity and lots of headroom make that sort of accident impossible.

by wbl

1/15/2025 at 11:02:25 PM

Presumably, those operating EBR-1 and Fermi-1 (and SRE in California, which also melted down) didn't think those would melt either. The issue is showing by analysis such an occurrence is not possible. It's not incumbent on anyone to show it is possible, it's incumbent on the prospective licensee to show it isn't.

by pfdietz

1/17/2025 at 11:51:34 AM

I'm quite ambivalent about nuclear power. On the one hand it's been proven that nuclear power isn't the answer to the energy transition question (https://sppga.ubc.ca/nuclear-is-not-the-solution/) - on the other hand - it makes up waaay more of my current carbon free energy.

For southern states, or states that get a lot of solar power, they shouldn't have nukes.

For areas that have plenty of wind, they shouldn't have nukes.

For areas with lots of people, they shouldn't have nukes.

Areas of seismic activity, they shouldn't have nukes.

Research needs to be done on how to lower the cost of interconnect and installation of solar power... like billions of dollars of research rivaling nuke research.

by lucidguppy

1/16/2025 at 2:46:07 AM

It truly baffles me how humanity has the technology for a nuclear reactor that can actually CREATE MORE FUEL THAN IT USES and no one wants to use it.

by UltraSane

1/16/2025 at 3:19:08 AM

That whole "create more fuel than it uses" thing means there are proliferation implications.

by NewJazz

1/16/2025 at 4:22:50 AM

Yeah, the breeder reactions are good because they can burn long lasting isotopes, generating short half life and more easily disposable materials, but they also make more of the risky isotopes (those with low critical mass that are more easily/chemically separable). Thorium is quite a bit better about that (not perfect), but it's even less well understood for actual reactor design and production.

by kurthr

1/16/2025 at 7:30:11 AM

Not in the US.

by flanked-evergl

1/16/2025 at 4:31:23 PM

There are still proliferation concerns for nuclear-armed states.

Have you heard of non state actors? Would be a shame if US built a breeder reactor in each state and oath keepers or whoever got a hold of one.

by NewJazz

1/16/2025 at 5:16:16 PM

That is not a reasonable reason not to make them.

by UltraSane

1/17/2025 at 12:20:31 AM

OK, but you have to pay for adequate security.

by NewJazz

1/15/2025 at 10:09:56 PM

Did we cannibalize some of our nuclear warheads, in order to get the enriched uranium?

https://wyofile.com/fate-of-natrium-nuclear-plant-may-depend...

by nobodyandproud

1/15/2025 at 10:34:44 PM

Apparently yes, accoriding to [CNN].

"In the current stockpile, the average duration since a warhead was manufactured or refurbished is roughly 28 years." [DoE]. I suppose some of the aging warheads will be reprocessed as fuel.

[CNN]: https://www.cnn.com/2024/09/09/climate/nuclear-warheads-hale...

[DoE]: https://www.energy.gov/nnsa/us-nuclear-weapons-stockpile

(Previous version of this comment was incorrect.)

by nine_k

1/16/2025 at 5:33:08 PM

Thanks. It looks like it meant to be short-term but nonetheless.

by nobodyandproud

1/16/2025 at 10:25:51 AM

Is this old news or are there two big celebrations recently about being allowed to build the "non-nuclear" bits of a nuclear plant?

Following nuclear news would be absolutely tragic if I didn't think it was all a pointless diversion from the real work being done. As such their lack of progress leaves me a bit more ambivalent.

by ZeroGravitas

1/16/2025 at 12:34:37 AM

Liquid sodium certainly is a choice. Very few non-experimental liquid sodium reactors out there.

by denkmoon

1/16/2025 at 2:45:17 AM

It has a huge advantage of being able to operate at 850C at much lower pressures so you don't need 30cm thick steel

by UltraSane

1/16/2025 at 4:00:36 AM

Low pressure, but you sure don't want air in there

by pwarner

1/16/2025 at 4:37:08 AM

any idea why the Natrium class wasn't designed to be a breeder reactor?

dont know much about the subject but this will have more or less the same runway as gasoline

by gunian

1/15/2025 at 8:24:05 PM

> That application was submitted in March 2024 and is on track for approval in December 2026

Huh? Is this something where there's multiple incremental steps in the process, and that date is just the final approval stamp, or does it actually just take more than 1.5 years?

by smaddox

1/15/2025 at 9:25:11 PM

I'm generally pretty open to the idea that the NRC is bad and needs to be reformed, but a year and a half doesn't seem that unreasonable? Especially for a new reactor design.

by simplicio

1/15/2025 at 8:52:48 PM

I'm pretty sure this is extremely fast for the nuclear industry.

by daedrdev

1/15/2025 at 8:43:09 PM

It's always fun seeing someone jump into NRC discourse for the first time.

by bpodgursky

1/15/2025 at 9:30:43 PM

I hope this involves a lot of much faster feedback / modification cycles, and the process ends when all the feedback has been addressed.

by nine_k

1/15/2025 at 8:56:20 PM

Feds

by myheartisinohio