Comment by acidburnNSA | Hacker News Reader

Comment by acidburnNSA | Hacker News Reader

Here's a fun and almost forgotten fact. In the early 1960s, the US government built a prototype nuclear reactor that was cooled with liquid metal sodium but had graphite moderators to slow the neutrons down. This reactor could start up with very low enriched uranium (as opposed to sodium cooled fast-neutron reactors which need quite high enrichments to start up) and make superheated steam at the exact same conditions as a coal plant.

Well the local utility just SW of Lincoln Nebraska needed the power one way or the other, and didn't know if the new type of reactor was going to work or not. So they decided to build an equivalent power coal plant on the other side of the turbo-generator building! The idea was that when the nuclear reactor was in an outage, the coal plant could spin the turbine. Two plants, one turbine-generator! Wild.

So anyway the nuclear plant did have a few troubles. The vendor, Atomics International, had them figured out and was planning to fix, but the utility declined it's option to purchase the plant in the end. Today, a grassy outline of a nuclear reactor can be seen right next to the still-operating coal plant down in Hallam, NE.

Honestly it was an awesome reactor concept and I want to see it brought back. I visited this site a few months ago and got a little tour. Very fun.

https://whatisnuclear.com/reactor_history.html#the-hallam-so...

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

Google maps view of the outline: https://www.google.com/maps/place/Hallam,+NE+68368/@40.55864...

This is entirely off topic, but scrolling around the map you linked, it looks like massive portions of Nebraska and surrounds are gridded by roads. Is this true? I'm an Australian, never been to the US, but is that common? I can't imagine that kind of project here.

EDIT: Massive portions of the US! I find this mindblowing.

I find this fascinating! Do you mind if I ask what you found surprising, exactly? Is it more that those fairly sparsely populated areas have so many roads, or is it more that the inland areas are populated at all? For what it's worth, quite a few people live in the plains states in the US. Not many relative to the real population centers in the country, but I think perhaps significantly more than the inland areas of Australia.

Primarily the sheer number and scale of roads, yes. I’ve done a lot of driving inland in Aus, and even where there is a lot of arable land it is not nearly so neatly or densely carved up, generally just hectares of paddocks/farmland with fire and access trails and fences.

I’m utterly awed at the scale of infrastructure that must’ve been involved in building those thousands of kilometres of roads, let alone maintaining them (I imagine they aren’t particularly “maintained”, but all the same).

As an American who has traveled abroad, I can assure the vast majority of our roads are "maintained" only in the sense that they are passable roads. There really are no standards that are adhered to. It's common where I live to find potholes that would destroy the front suspension of any car attempting to traverse them.

But they could be maintained, if people wanted...

They absolutely cannot. Not in their entirety. The sheer number of roads necessary to be maintained will require more labor and material than we can afford at that scale.

Additionally, many of them criss-cross private land. And some segments of the US population is pretty particular about keeping people of their land. Yeah, hard to do in the mid-west and plains, but that doesn't stop them putting up threatening signs all over.

Car's aren't nearly as fragile as people make them out to be.

You might be surprised how well maintained they are. We (I am from the US) spend a lot of money on infrastructure for cars and trucks. This trades off to some extent against rail infrastructure, though freight rail is more robust than commuter / passenger rail.

It's all carved up for farming. This was the norm in my home state (Iowa). They're all gravel roads mind you, so not ideal driving if you don't live there. You kick up dust the whole way.

Note that each grid square is 1 mile by 1 mile. Long history of that, it is an interesting historical rabbit hole.

An interesting historical note is that across much of the west, each of those mile square sections was divided up into 16 pieces at 40-acres, which IIRC was the smallest unit of land you could purchase from the federal government.

You'll still find a lot of old homestead remnants across the west -- I used to climb through a few of them on a ranch I spent time at as a kid.

See:

- https://en.wikipedia.org/wiki/Section_(United_States_land_su...

- https://en.wikipedia.org/wiki/Public_Land_Survey_System

- https://en.wikipedia.org/wiki/Land_Ordinance_of_1785

Also, if you look closely, many of the boundaries are just dirt path, not maintained road. And some don't have roads - it just appears that way from above because one crop/field ends and another starts.

But, yeah, the amount of roads, even just basic gravel or dirt double-track, is pretty amazing. I knew some of it existed, but didn't quite realize it spanned the entire middle third of the US until just now.

Thanks for pointing this out! I'm also an Australian, and my mind is similarly blown. I grew up in Sydney, and whenever I would fly into Melbourne it was always a point of interest to compare the aerial view of Sydney's sprawling mess of streets with Melbourne CBD's clean, and logical grid layout.

People sometimes forget that the middle of the US was populated by millions of immigrants from Northern and Central Europe. Lots of those towns you're looking at were German-speaking towns up until WWI. There are still tons of Norwegian and Swedish cities and towns out there. All of those immigrants were given plots of land to farm, and developed communities accordingly. The Homestead Act was the way that millions made a new life for themselves in the new world.

If you want to have even more fun, most of those roads have Street View.

I would imagine that the middle of the US would look a lot like the middle of Australia if it wasn’t good farm land.

There's a slow-rolling crisis as many local governments find they can't afford to maintain (much less rebuild) so many roads. Many are being downgraded to gravel.

Ohio is the U.S. State with the highest road density, IIRC.

Similar to sodium cooled reactors, there are also lead or lead-bismuth cooled reactors, which have had one real life deployment ( onboard the Soviet Alfa class submarines), with its own advantages and disadvantages, and there are proposals to develop new versions.

There's so much interesting nuclear-related tech and concepts we haven't fully explored because of nuclear FUD ( much of which would be solved by the new tech).

Thanks, I had no idea lead-bismuth reactors existed. It seems the large number of unstable lead isotopes and their long decay chain would assure a long cooldown requirement before any maintenance could be done in the reactor compartment/primary coolant system. Not only that, but this stuff would present a huge disposal problem. https://en.wikipedia.org/wiki/Isotopes_of_lead

It seems the Alfa class was decommissioned for scrapping, though one was refitted with a pressurized water reactor for a while. https://en.wikipedia.org/wiki/Alfa-class_submarine#Decommiss...

An interesting issue with this design is that if the Pb-Bi coolant ever solidified, the reactor control rods became frozen in place.

MSR Thorium reactors are the holy grail clean fuel for India and China.

Very interestingly, this is a 1974(!!) program plan to resume development of MSR from the US ORNL MSR team

https://www.osti.gov/biblio/4227904

CANDU reactors (Canadian) use non-enriched/naturally occurring uranium (0.72% u-235) by using heavy water as a moderator. Not sure why you'd use anything but them if you were starting a nuclear program from scratch.

Heavy water reactors have their drawbacks. Heavy water is expensive, which offsets the cost of uranium enrichment. The lower energy density of un-enriched uranium means more frequent refueling. They also produce more waste.

And this is why it was made in Canada, cheap electricity and uranium all around to make heavy water and fuel those reactors.

are industrial quantities of heavy water "made" or just extracted/isolated?

You still create the waste either way, either as depleted uranium or as spent fuel.

Depleted uranium means “uranium that is even less radioactive than naturally occurring uranium”. You don’t want to eat it, or atomize it and blast it out into the environment, but it’s actually a useful material. It’s sometimes used as a radiation shield for X-ray equipment.

Not quite as wild, but there was a similar thing in Sweden 50 years ago, where an oil burner was retrofitted to the cancelled nuclear power plant at Marviken: https://en.wikipedia.org/wiki/R4_nuclear_reactor . The reactor, which was more or less completed but never loaded with nuclear fuel, was used for various experiments related to reactor safety.

Lol, wild seeing Hallam, NE on a post on HN about nuclear reactors. Drive by this place often, will stop and look at it now. Thanks

Yeah the Sheldon station is right by that Monolith project. Fun to drive by for sure.

Sodium cooled reactors with graphite moderator have not become common for some reasons. There are some issues like sodium burns in contact with air, as does hot graphite. Potential positive coefficient (unstable) states. But the pressure in the piping could be low, compared to water/steam, so maybe cost could be low and power density high.

I think a lot of these plans to retrofit coal plants with nukes are quite overoptimistic. I'm ambivalent since they could be used as reasons to prop up coal plants longer. "See, we should invest in, and get some subsidy for a new steam turbine in our coal plant so it can be used with the graphite-sodium nuke that's going to replace the boiler in 15 years". But on the other hand, we need all potential, even unlikely solutions to replace coal burning.

> sodium burns in contact with air

Is that so? I think you are confusing air with water here. In contact with air, sodium oxidizes quickly, but it does not burn spontaneously.

search: 'sodium leak at nuclear reactor' @DDG : <https://html.duckduckgo.com/html?q='sodium leak at nuclear r...>

Good idea.

"At 19:47 high temperature liquid sodium coolant at one of the three secondary heat exchangers started leaking through a broken thermometer sheath ... on the piping and it ignited on contact with air."

https://onlineethics.org/cases/case-1-fire-sodium-coolant-le...

That's a good catch. For some reason I was thinking of room-temperature sodium, but of course the liquid sodium from sodium cooled nuclear reactors is hot, and apparently burns in contact with the air.

If you read more closely though the article you linked to, you'll see that the complaint there was not the fire in particular (which caused some damage, but no radioactive leaks), but the claim of the plant operators that the plant was "absolutely safe", and the attempt of a cover-up. In other words, the safety of this plant was judged not in comparison with the safety of a conventional water-cooled reactor, but in comparison with an absurd goal of "absolute safety".

When people hear the sodium can cause fire when in contact with the air, they immediately remember the spectacular explosions of sodium in contact with water. Then they assume a sodium cooled reactor is a beast that only a madman would contemplate.

In reality, sodium cooled reactors are not any worse than water-cooled reactors. All reactors present various challenges, and some of the challenges faced by sodium cooled reactors will be higher, and some lower than those facing water-cooled reactors.

But sodium cooled reactors have an absolutely tremendous advantage: most of the fissile material they use as fuel (be it Uranium or Plutonium) does undergo fission and creates fission products, as opposed to actinides. Bottom line: the nuclear waste from sodium cooled reactors (and all types of fast neutron reactors) is much, much more manageable than the nuclear waste of conventional nuclear reactors.

If you use a steam turbines, the sodium would be potentially in contact with water easily, on different sides of the wall in the heat exchanger with a lot of surface area etc. I wonder if you used a CO2 turbine instead...

(circa:1957) The Sodium Reactor Experiment : https://en.wikipedia.org/wiki/Sodium_Reactor_Experiment

Sodium-Cooled Fast Reactor : https://en.wikipedia.org/wiki/Sodium-cooled_fast_reactor

Bill Gates’ nuclear play uses liquid sodium

Yes. That is the more traditional fast neutron version. We have 450 reactor years of experience w those.

How do you measure those years? Experience of designers and engineering? Or years of reactors in operation?

years of reactors in operation

Thanks for the explanation.

Considering our very recent understanding of sodium Coulombic explosions[0], using liquid sodium for... anything requires an enormous amount of care[1].

  [0] https://www.youtube.com/watch?v=8PEVmflpUCo
  [1] https://www.youtube.com/watch?v=rAYW9n8i-C4

Yea and there’s a reason they stopped. It’s unmaintainable. How will you replace a section of cooling pipe with molten or solid sodium in it?

> liquid metal sodium

> graphite moderators

Nope.

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