Hacker News Reader

Comment by rx_tx | Hacker News Reader

> The microreactor can generate 5 MW of electricity or 13 MW of heat from a 15 MW thermal core. Exhaust heat from the power conversion system can be used for district heating applications or low-temperature steam.

They are aiming 8 years planned service life, and one novel thing is the use of heatpipes (like your CPU cooler) using liquid metal as a working fluid.

They actually don't say how big it is, I guess still quite sizeable given the heat output. Definitely not a single-family home device.

View on HN

They say they envisage delivery of the whole system on four trucks.

Not single family home (unsurprisingly, the economics of very small scale nuclear are awful even ignoring the safety concerns), but night and day compared with conventional large nuclear reactors.

> I guess still quite sizeable given the heat output. Definitely not a single-family home device.

I’d think the 5MWe would be a hint. Standard residential service drop is like 40kW.

"Big" there might be referring to physical size.

I'm wondering, they say using sodium, and having tested heat pipes up to 800°C... but their schema shows sodium vapor... but sodium only boils at 900°C ??

So I guess they underpressurize these pipes ?

That would make sense, since in a traditional liquid metal reactor, the boiling of the working fluid is instead a failure mode to be avoided at all costs (since boiling dramatically increases the pressure resulting in burst pipes), especially with sodium that burns on contact with the air, explodes on contact with water, oh and also is highly radioactive at that point (for a short time).

They seem very sure of themselves, but I still wonder what kind of stresses are involved, and what does this mean for heat pipe longevity ? (and calling heat pipes with a phase changing working fluid "passive" still seems kind of wrong ?)

EDIT : The relatively small amount of sodium probably matters a lot here ?

Static vs passive cooling, I think is what you're looking for here.

Heat pipes are used in CPU coolers and work on the same principle. A small amount of liquid is in the pipe, at reduced pressure, which makes heat transfer very efficient.

I suck at chemistry, but wiki clearly discusses advantages of sodium for heat transfer in nuclear reactors: https://en.wikipedia.org/wiki/Sodium-cooled_fast_reactor (tl;dr: safety margin from the large range of temps at which sodium is liquid; doesn't like to absorb neutrons, and isotopes aren't that problematic when it does).

Yes, but they use water. (Also reduced pressure means reduced density, which should in theory make heat transfer less efficient... except when phase changes are involved !)

That reactor is a radically different design, operating at a much lower temperature, where sodium doesn't evaporate.

But the whole point of a heat pipe is that phase changes -are- involved! So, water’s fine for temperatures in a “normal” range, like a CPU, but perhaps not great for higher temperature ranges.

And then, this is a nuclear reactor. Whatever’s in the heat pipe in a reactor will be bombarded with neutrons. Water is a neutron moderator, so you wind up with heavy water in the heat pipes and not-very-nice fission products in the reactor due to slower neutrons.

I never said they should use water, I'm just wondering what kinds of stresses (including chemical ones ?) are involved here...

If you can get the heat out, no reason it couldn't be tiny. A hayabusa motorcycle engine can be tortured into producing 1MW mechanical from about 5MW thermal.

The heat engine required to meet efficiency would likely be the limit (although I think TEGs might be getting cheaper).

The main issue is unless you have a big pile of them, you need 1% of your population to be nuclear engineers and security.

My understanding is on-shore windmills cost about ~$1.5M and $50k in maintenance per year - last for 20 years - for 1MW.

I'm skeptical this can come anywhere close to that.

But if it's within an order of magnitude - it could replace old coal powerplants as they're decommissioned.

Apples & oranges: wind is an intermittent generator versus eVinci for base generation

bingo! it's crazy that people keep comparing this to wind turbines.

A problem with on-shore wind is that it is already getting hard to find more space for it in some European countries. You also can't put windmills in densely populated areas where most power is needed so you have to take energy transmission cost into account as well.

If it can be demonstrated that these reactors are safe, you could put them almost anywhere.

the number one problem with onshore wind is a capacity factor around 30% and on top of that you could have long periods with no wind at all.

Periods where wind operates below 5% capacity in Poland are really common. I've seen it once below 1%. When I write this it's 7,5% - below 10% for 14 hours already.

Nobody in the developed world will allow a nuclear reactor to be built anywhere near their house...

So, however safe these are, they'll still be relegated to 100+ miles from any big city. So the transmission costs will be similar to wind/solar.

While the operational safety sounds excellent, I am worried about what a generalization of this kind of reactor would entail. Your typical reactor is under heavy surveillance and 200 (67?) times more powerful : we are very unlikely to "lose track" of the fuel.

Let's say this becomes moderately popular and we soon have a million of them across the world (enough for about 10% of our today's energy needs)... who is going to keep track of all of them ?!

The High-Assay Low-Enriched Uranium required here is enriched between 5% and 20% compared to a conventional reactor using between 3% and 5% fuel. Because enriching from the natural 0.7% to 20% is 90% of the effort, 20% is considered to be the line separating civilian and military uses. And we're much closer to that limit with these reactors. I am baffled that this is not being even mentioned in the article, nor the pdf ? (I guess they are not particularly willing to disclose just how many of those would need to be gathered for the minimum 25 kg of 90% enriched Uranium for a bomb ?)

And as safe as these might be under normal operation, how many decades for a forgotten abandoned one, exposed to the weather, to leak ? How much and what kind of radiation release can we expect ? (Carried by water to the closest steam I assume?)

You need over 90% enriched for practical nuclear weapon use. It is not "most of the effort" to get to 20%: in fact, if you're stealing it then it's none of the effort: you don't have a centrifuge operation, so whether it's natural or 20% or 70% it is all equally useless.

The difficulty of enrichment is the plant and logistics of doing it, none of which you can steal.

I should have been more clear that I am assuming an hostile nation-state with some minimal capabilities : the biggest difficulty is probably to be able to deliver the bomb to a target once you have one, which gets even worse if you want to use it as an open threat for deterrence rather than a (frankly suicidal) surprise attack : you pretty much need an ICBM (see all the North Korean failures before they (supposedly) stole SSR-Ukrainian tech).

Difficulty of enrichment seems to be heavily proportional to time : the whole "game" around Iran's enrichment seems to be about not letting them get it high enough that they can go from weapons-useless uranium to a ready bomb in a short enough amount of time for the other countries not being able to react.

(There's also a possibility of a much smaller actor to make a dirty bomb from that mildly enriched uranium, but I have even less ideas about how likely that is.)

Uh, you can't run life saving medical equipment or refrigerator service on wind turbines. That means that all the bodies of people that die without ventilators etc, during no wind days would have no chilled morgue to sit in, and would rot

>Uh, you can't run life saving medical equipment or refrigerator service on wind turbines

Man! If only there was some device that stored energy for later use!

You gotta include it in the cost figures, though.

Wind has the distinct advantage compared to this tech in that it actually exists. I can buy a turbine tomorrow and have it online in a month or two.

Sure, but that's a different and unrelated argument to the question of theoretical cost which is what was being discussed.

Sure. This costs infinity because it doesn't exist and 100% wind based power generation would cost less than that, but more than a wind turbine by itself to include storage.

There’s such a thing as energy storage and long distance DC transmission. Why does the old “intermittent power” argument crop up every time when there’s clear engineering solutions to those problems? Next thing you know you’ll be blaming regulations on lack of new nuclear and talking about how we’re running out of lithium, both of which are false arguments as well.

It crops up because people give these absurdly misleading cost estimates for adding incremental wind power to the grid. You can’t have wind power without spending money on an equivalent amount of reliable power, and no one wants to include those required costs in their estimates. This tends to dramatically understate the actual economics of wind.

There are plenty of studies of near-100% renewable energy grids and the electricity comes out similar to long-term wholesale trends (pre-Ukraine), even taking storage/transmission into account.

Let’s see one for wind power, then. OP implies wind is an order of magnitude cheaper.

How about this one:

https://web.stanford.edu/group/efmh/jacobson/Articles/I/21-U...

With those 2 things combined into a solution, you're gambling that we will always have average good wind conditions long enough to keep the grid batteries from going empty. Sadly, under your proposed regime, as time approaches infinity the chance that the grid will run out of power approaches 100%.

If you could avoid straw-manning me about nuclear and lithium in the future that would be super cool. I've played enough factorio to know that green power and batteries are part of the best solution, but you need high energy density generation systems for fast advancement too! If we turn our backs on that tech we know works we will lose future opportunities, or at least delay them

If your local energy storage or grid isn't reliable enough, you can always have a backup diesel generator. Or hydrogen powered generator if you insist this is green. Or some solar cells on your roof. And as much fuel as your risk analysis demands. But the reality is, hospitals can rely on local emergency services for support, and it is likely more cost effective run the risk of spoilage in the rare event of a multi-day power outage than invest in local generation for your refrigeration. My guess would be local equipment failure is more of a risk than a multi-day renewable energy outage, even in latitudes where solar is useless.

> you can't run life saving medical equipment or refrigerator service on wind turbines

There are countries running on 95%+ renewable electricity right now[1]. Including wind, hydro, solar, geothermal and biomass. Humanity keeps neglecting what is already proved to work. Because politics? Coal and gas are cheaper options? Environment is not considered in the equation?

Edit: source [1]: https://en.m.wikipedia.org/wiki/List_of_countries_by_renewab...

> There are countries running on 95%+ renewable electricity right now[1].

That list ignores that countries trade electricity. If, say, Germany produces a lot of electricity by renewables it can sell the excess to France (which has lots of nuclear). If Germany is low on electricity, it can buy from is neighbors. The system as a whole is nowhere near 90%.

The one exception are probably countries that have all hydro and biomass.

You created a straw man. There are 10 countries that fit the 95%+ criteria, all of them probably have excess of production and have 0 interest in buying power. But yeah, what you say could theorically happen.

All large hospitals have emergency generators. Of course they are supposed to be for emergencies, not for dealing with regularly intermittent power. That is typically dealt with advertised in advance power shutdowns to residential areas, and in richest countries, by not sending the signal that remotely turns on your water balloon heater during cheap hours.

you can run life saving medical equipment or refrigerator service on batteries.

I think it's a standard thing for vital infrastructure to be backed by generators.

big industrial consumers can factor their own specialised requirements for storage, backup.

Current wholesale price of electricity in EU is 110-120 USD / MWh.

5 * 110 Euro * 24 hours * 365 days * 8 years planned service life = $38,533,000. If they can offer a price under 5M USD per MW they won't have problem finding buyers.

This doesn't even account for savings for businesses that can consume most of that output - they save another 20-30% on transmission fees + there are several MW of waste heat as low temperature steam that can be used directly or indirectly in many industrial processes.

Yeah dedicated units for large industry would be a huge buyer here: if you can hit the right price point, aluminium smelters in particular would be very interested customers I suspect.

This thing only outputs hot water, you need a lot more equipment and people to turn that into useful power on the grid.

Fuel costs, maintenance, and operation would be over $2M.

Normal energy prices are about half of what you quoted. It's TBD if they come back down to normal in the near future in the EU.

You're looking at $18M in revenue. This thing will probably cost more than $10M to purchase, and then you need land, a grid-tie in, and permits.

It would still work - but the numbers aren't going to look as good as wind & especially solar.

Comparing the price of unreliable energy to reliable energy is like comparing the price of a junk bond with a treasury and wondering why the latter costs so much more. It costs more because when you turn it on you get a known and reliable source of power, day or night, cloudy or sunny, windy or quiet. That's why it costs more.

I wonder what the cost of decommissioning is. That's easy to ignore just like it's easy to ignore the cost of mitigating the CO2 emissions from gas...

If they're modular then they'll be intended to run more than one. You get the land, grid tie-in, permits and staff and then... stack 4 of these instead of 1. You use the same benefits from economies of scale to have as many of these as can be safely crammed into your building and go from there.

It's a shipping container, same type of footprint and install as the tesla battery packs. They have pictures and videos if you google it.

4 trucks for the whole setup

Just imagine the ragne of those trucks running on that "battery".

Reply on news.ycombinator.com