# Nuclear Hot Air Turbine



## Mike Donoghue (Nov 29, 2017)

Hey, all!

A friend of mine just sent me a link to a website that discusses a fascinating way of generating power from a nuclear reactor. I thought it'd be worthwhile to share with the community here.

Basically how it works is that a constant stream of gaseous helium is blown through the reactor to carry heat away from it in a single, closed loop. The helium then passes through a heat exchanger where it transfers its heat to a separate, isolated stream of air. That air is driven by an air compressor, which draws in atmospheric air from outside the plant and blows it through the heat exchanger at high pressure, becoming hot as a result. That hot compressed air then passes through a gas turbine, where it expands and turns the turbine, which then turns an electric generator.

Here is the link: https://nereusblog.wordpress.com/2017/08/11/the-nuclear-gas-turbine-htr-gt-the-nereus-engine/

Apparently it is/was an idea from a group of engineers in the Netherlands.

What I find neat is the relative simplicity, which is a major advantage in any technology. Gas turbines and diesel engines are a very common way of generating electricity when solar panels or wind turbines aren't operating, but they all use oil or methane (natural gas) for fuel. But if there could be a nuclear alternative to hydrocarbon-fueled gas turbines, then, holy cow, that'd be a game changer!

I'm interested in hearing peoples' thoughts on this.


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## Brian G Turner (Nov 29, 2017)

I'm not sure this is actually simplified, especially when you're directly exposing air to potentially radioactive material. Sounds like an invitation to contamination to me. 

I'm also confused as to why it's thought that it's carbon-based fuels that are expected to take the slack when renewables aren't working, when we plainly have existing nuclear reactors to do that job.

Also, the amount of money we through into nuclear power is ridiculous - here's a recent BBC report on Hinckley C, which estimates £18 billion to build and £30 billion in subsidies. That's a total of £48 billion - if on target - and at no point factors in the cost of reprocessing and clean-up: Hinkley will 'hit the poorest hardest'


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## J Riff (Nov 29, 2017)

Yes, and - this is the device the Aliens focus on - the 'primary heat exchangers"... isn't it??  An invitation to disaster. *


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## Dave (Nov 29, 2017)

I don't like the sound of the highly kinetic idea of the helium gas when associated with the radioactivity either. Far too much more can go wrong, more catastrophically, than can in a conventional nuclear reactor (which is already a very simple idea of heating water (usually) to drive a steam turbine.) I see how this idea might make it suitable for putting into vehicles, but I think safety considerations will quickly negate that.


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## Foxbat (Nov 29, 2017)

There's a reason why UK AGRs don't use Helium and are filled with Carbon Dioxide instead. Helium is far too expensive and getting rarer everyday.

Also, superheated steam is far more efficient than hot air and tends to carry much less oxygen than air (lessening the chances of corrosion and leakage) - which is why heat exchangers in a reactor are used to heat water into steam(which then drive the turbine) rather than air.

Edit: Something to consider when thinking of using Helium  https://phys.org/news/2010-08-world-helium-nobel-prize-winner.html


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## Dave (Nov 29, 2017)

All those people who say we have no reason to go to space so we shouldn't bother, you know they will be the first ones asking why we haven't started helium mining on other planets yet.


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## Venusian Broon (Nov 29, 2017)

Dave said:


> I don't like the sound of the highly kinetic idea of the helium gas when associated with the radioactivity either.



erm, currently all nuclear reactor designs have the core surrounded in _something, _whether that's carbon control rods or something else to control the fission process. And some designs actually use the water the transfers heat from the core directly as steam to push the turbine (other more cautious designs separate out that water and transfer the energy to anther steam/water loop so that core water is in a 'closed loop')

But Helium is an inert gas and the question is, does the heat transfer process, transfer radioactivity also? My guess is that, 'technically', it does not (I'd guess that there may be some sort of contamination from imperfections in materials in the core bleeding into the gas). If this inner core system ruptured that would therefore release a lot of hot helium (that would easily bee-line to escape the earth's gravitational pull into space.) Hopefully then there would be a safely mechanism that would shut down the reactor - those control rods again no doubt.

Water close to the core can sometimes be a very bad thing - although we regularly bath highly radioactive materials in water as this allows us to control the heat transfer - as there can be occasions where a big build up in temperature could build up masses of steam, and if there's no where for it to go and then an explosion....well that's how we got Chernobyl. Hot Helium gas would get over some of those concerns.

However, I agree with Foxbat re: the expense and other factors.



Dave said:


> All those people who say we have no reason to go to space so we shouldn't bother, you know they will be the first ones asking why we haven't started helium mining on other planets yet.



Or why people are playing with helium in the form of party balloons.

However as Helium gets ever more expensive and useful then the technology to extract the low levels of it they you always find in natural gas sites will no doubt step up. Much cheaper than trying to mine the moon. Still.


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## Dave (Nov 29, 2017)

Venusian Broon said:


> ...some designs actually use the water the transfers heat from the core directly as steam to push the turbine (other more cautious designs separate out that water and transfer the energy to anther steam/water loop so that core water is in a 'closed loop')


Those with the water around the rods are the more usual designs, yes? So, there is liquid around the rods not gas, and those closed systems with heat transfer mean that it is unlikely to boil dry unless people deliberately break the system, as you say. But if you think having hot gas is safer than liquid water (an extremely efficient liquid conductor of heat) then I may be wrong. I accept the inert gas will produce less corrosion though.


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## Foxbat (Nov 29, 2017)

There's always some confusion about radioactive materials in a reactor. They mainly fall into two categories 1) Fission Products and 2) Activation Products.

Fission products are what is created by the fission process. These are usually heavier  isotopes  like Americium 241, Plutonium239, Caesium 137, etc. (although you do get Tritium...an isotope of Hydrogen as a tertiary fission product as well). Normally, these are contained within the fuel cladding and don't see the light of day unless there is a rupture of the clad (what is known as a 'burst can').

Activation Products are created when the structure surrounding the core becomes activated (usually through interaction with neutrons. These include Cobalt 60, Argon 41 (due to gas impurities...normally the presence of air), Chrome 51, Iron 55 etc. 

Most of the problems encountered are from Activation Products (both Argon 41 and Cobalt60 are high gamma emitters and most problematic to the workforce in AGRs with their high volume of steel internally). 

Most structures tend to be made of steel or similar so it wouldn't matter whether you had a straight-forward reactor known today or a Helium/hot air design, the structure at some point would be subject to neutron flux and would produce activation products. To counter this, you'd probably need some kind of biological shield (14 feet thick of pre-stressed concrete with a cooling system works).


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## Foxbat (Nov 29, 2017)

Dave said:


> Those with the water around the rods are the more usual designs, yes? So, there is liquid around the rods not gas, and those with heat transfer mean that it is unlikely to boil dry unless people deliberately break the system, as you say. But if you think having hot gas is safer than liquid water (an extremely efficient liquid conductor of heat) then I may be wrong. I accept the inert gas will produce less corrosion though.


UK Advanced Gas Cooled Reactors use CO2. Pressurised water or Boiling Water reactors use water dosed with Boron for control of neutron flux. The reason for pressurised water is to prevent water flashing off to steam and leaving the core exposed. Boiling water tend to work at lower temperatures.


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## Mirannan (Nov 29, 2017)

Hmmm... I do get the point about helium being impractical as a coolant because the supply is running out, and there is another problem; like hydrogen, helium is slippery stuff; it diffuses out through minute pores remarkably quickly. However, other gases are just as inert and much more common; the best example is probably argon, which is just as inert as helium and is much more common and easier to purify - it's around 0.9% of the atmosphere and has a reasonable boiling point.

Incidentally, induced radioactivity is not only a problem for fission reactors. Should a fusion power tokamak ever be built, it will have an even worse problem with this because all the possible reactions produce vast numbers of high-energy neutrons. DPF or maybe Polywell fusion would not have this problem.


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## Mike Donoghue (Nov 29, 2017)

Brian G Turner said:


> I'm not sure this is actually simplified, especially when you're directly exposing air to potentially radioactive material. Sounds like an invitation to contamination to me.
> 
> I'm also confused as to why it's thought that it's carbon-based fuels that are expected to take the slack when renewables aren't working, when we plainly have existing nuclear reactors to do that job.
> 
> Also, the amount of money we through into nuclear power is ridiculous - here's a recent BBC report on Hinckley C, which estimates £18 billion to build and £30 billion in subsidies. That's a total of £48 billion - if on target - and at no point factors in the cost of reprocessing and clean-up: Hinkley will 'hit the poorest hardest'



Hey, Brian;

One of the key advantages of Helium is that it is noncorrosive, even inside the core, and is practically transparent to neutrons, so it won't become radioactive from neutron (capture) activation. As for the air, it is isolated from the helium by the pipes inside the heat exchanger.

You're right that there are nuclear power plants that _can_ back up wind and solar, but here's the rub; changes in wind or cloud cover can lead to sudden drops in power that need to be addressed within minutes. The magnox and water-based of reactors (such as Hinkley) of the UK cannot, or otherwise have a difficult time ramping up their power fast enough to back up wind and solar. Gas turbines and diesel engines can go from cold to near full power in minutes. Such back up plants will often idle in anticipation of wind and solars' power falls, using up fuel very inefficiently as a result.

The economics of Hinkley are a mess, although not out of malice or corrupt government. The selling point of Hinkley was to have a power plant that could guarantee a certain price of electricity over a matter of _decades_, hence why it is so large at today's prices; the number crunching takes into account that costs across the entire economy will rise over the lifetime of the plant, which is a valid assumption, but it is still an _assumption_. High-end, ultra efficient coal plants can be very expensive, too, and can reasonably guarantee a stable price of electricity over decades, but coal still has a gigantic waste stream and has to be imported. Whether or not Hinkley turns out to be a white elephant, I have no idea, but it has a myriad of advantages over fossil-fueled plants and wind and solar can't provide the reliable power. It is sad it is so expensive, though.

Also with Hinkley is the fact that current nuclear power plants the world over are outgrowths of decades old, complicated and inefficient technology and are hobbled by overly restrictive rules, but that's another story.


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## Mike Donoghue (Dec 3, 2017)

Foxbat said:


> There's a reason why UK AGRs don't use Helium and are filled with Carbon Dioxide instead. Helium is far too expensive and getting rarer everyday.
> 
> Also, superheated steam is far more efficient than hot air and tends to carry much less oxygen than air (lessening the chances of corrosion and leakage) - which is why heat exchangers in a reactor are used to heat water into steam(which then drive the turbine) rather than air.
> 
> Edit: Something to consider when thinking of using Helium  https://phys.org/news/2010-08-world-helium-nobel-prize-winner.html



I say this with respect and sincerity that you are wrong about the price and availability of helium being a showstopper for helium cooled reactors. I have had this exact conversation numerous times with others and I am happy to explain once more:

There is an astronomical difference between a substance's RESERVES and its RESOURCES. A _reserve_ has several sub-definitions, but as a whole, it means how much of the material is recoverable at current market prices, give or take a bit, or may be feasibly recoverable in the future. A _resource_ is how much of the material exists at all in nature, regardless of economic feasibility. In Helium's case, it is constantly being created inside and on the surface of the Earth from the radioactive decay chains of Uranium and Thorium. Each atom of Uranium will result in ~8 helium nuclei from alpha decay, and each atom of Thorium will result in ~6 helium nuclei at the end of their decay chains. There is on the order of 13x10^16 kilograms of Uranium and 480x10^16 kilograms of Thorium in the Earth. Applying their specific activities to those figures results in _at least_ 2.1x10^26 helium nuclei per second. That is 30 tons per day directly from the Uranium and Thorium atoms. Factoring in their daughter products (let's say the average is 7) and you end up with _210 tons per day._ That's over 1 million cubic meters per day of naturally occurring helium. World helium consumption is 80 million cubic meters per year. The Earth is creating over 365 million cubic meters per year. Some of that ends up confined in rocks; some of it, in concentrated pockets, ends up migrating to the surface by tectonic action. This is relevant to gas-cooled reactors because they do not use _anywhere near _as much helium as MRIs, balloons, and other industrial processes.

Since the core of a gas-cooled reactor does not need the helium to be liquefied, like with an MRI, it doesn't need a large mass of gas. Take a 6 meter high by 3 meter wide cylinder as the core of a gas-cooled reactor. It is pressurized to 4 MPa. Fill that reactor will spherical fuel balls and the empty volume inside the core ends up being only ~31 cubic meters (after applying sphere packing). Multiplying by, say, 4 for the piping and heat exchanger and you only need ~150 cubic feet of helium for a medium sized gas-cooled reactor. At _most_, losses throughout the system would be 10% a year of the complete inventory. Currently, the USGS reports the price of Helium to be ~$4 USD per cubic meter at near atmospheric pressure. That's decimal dust in terms of consumption and cost.

I am able to sleep easy at night knowing that humanity's relationship with helium for gas-cooled reactors is bright.

sources: Radiogenic Heat
http://hpschapters.org/northcarolina/NSDS/thorium.pdf
http://hpschapters.org/northcarolina/NSDS/uranium.pdf


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## Foxbat (Dec 3, 2017)

Yes. You're right. I was wrong about the price. But that price, it should be noted, has nothing to do with market forces or resource availability and more to do with an ad-hoc pricing formula related to this bill: Text of H.R. 3008 (104th): Helium Privatization Act of 1996 (Reported by Senate Committee version) - GovTrack.us

The Helium Privatisation Act is generally seen as a mess that has depleted Helium stocks through under-pricing and squandering of resource. The low price has also made it unattractive for private operators to take up the slack in Helium production and it was estimated back in 2012 that the US reserves may be exhausted by 2020. 

The Helium Stewardship Act of 2013 tries to repair the damage done and has gone sopme way to address the problem but, in many analysts opinions, does not go far enough and that usage is still outstripping production/storage/refining.
H.R.527 - 113th Congress (2013-2014): Helium Stewardship Act of 2013


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