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 Post subject: A better coolant!
PostPosted: Sep 25, 2010 6:18 pm 
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A better coolant!

When Barry Brook and Tom Blees were invited to visit Per Peterson’s laboratory at the Nuclear Engineering Department of UC Berkeley they found that Per’s research focuses on development of a high-temperature reactor with an incredibly high power density.

Why? In short, it’s all about the money.

In Europe or North America, one the most frequently cited criticism of nuclear energy involves economics. High materials and construction costs for Advanced Light Water Reactors (ALWRs) are a road block to their deployment,
Decreasing the cost of new nuclear construction is a winning strategy today.

Per’s argument — and a quite persuasive one — is that if the costs of advanced reactors can be brought way down, below that of pressurized and boiling water reactors (PWRs and BWRs), then their scaled-up deployment is highly likely.
Per’s aim is to develop really compact nuclear units with very high power densities. In a nutshell, very high power densities mean very low costs.

Small is cost effective. Small means less volume for the hot cell, smaller containment, less cost for the coolant, less structural material for the reactor as a whole, less volume and weight for the building, smaller springs for earth quake mitigation. Small is easier to build and even may make factory manufacturing possible for a very powerful unit.

Small means rigid, you can deploy it in the arctic, the desert, and the jungle where the oil shale and sand are.

The large size and associated high cost is one reason that utilities and the oil companies have not embraced the PBMR. Utilities want economies of scale. Oil companies want something they can deploy in the boondocks and in a refinery.

Ideally, they want large power output in a small package.

The primary aim of the nuclear designer is to develop a really compact nuclear unit with very high power densities, based on mostly well-understood technology that is deployable on the compressed time-scale as compared to current reactors.

What does high power density really mean? It means high operating temperatures and a high outlet temperature. High temperatures also mean increased thermodynamic efficiency in power generation. High temperatures also mean efficient hydrogen production and effective process heat for industrial applications.

But something is wrong. The PBMR can achieve an output temperature of 950C and the PB-AHTR is good for only 704C.

So what is the problem? Using molten salt reactor coolant restricts the material used in the core to a low temperature nickel alloy. Because of this, there is a ceiling placed on the temperature of the core. This is a tradeoff that is counterproductive to the main goal of the PB-AHTR and low cost nuclear power, in general.

I therefore ask why not use Gallium liquid metal coolant. Gallium is the other fusion coolant that many fusionairs favor over lithium.

Gallium is much less chemically reactive than lithium or other alkali metals; it is non toxic, it melts at a lower temperature than other light metals, and is less costly than pure alkali metals. Pure Gallium is not a harmful substance for humans to touch. It has been handled many times only for the simple pleasure of watching it melt by the heat emitted from a human hand.

Unlike Lithium-7, it does not need to be enriched. It has a very low neutron cross section, and is about the same as lithium 7 to my eye.

Gallium is a metal (atomic weight 69.72) with a very low melting point (29.9C) and a high boiling point (2005C). The density of Gallium is approximately 6 g/cm3 at 33°C. Gallium is electrically conductive and also paramagnetic.

No core, piping, heat exchanger pre heating is required. Gallium behaves like water at room temperature.

This means that pipe stresses from elevated temperature operation and the danger of “freeze-plugging” a pipe section are also avoided.

The vapor pressure is quite low, essentially zero at 20°C.

The chemical reactivity and toxicity of Gallium and were investigated by literature search predict possible Gallium reactions when spilling in air at 20°C. The results predicted that low levels of oxides would form. The reaction rate at 20°C is not expected to proceed to the extent that significant quantities of Ga2O3 are produced from Gallium.

Gallium has no or minor chemistry with hydrogen, deuterium, and tritium; and has very modest retention of atomic deuterium.

Gallium is stable with many metals and does not readily attack ceramics.

Gallium has good negative void characteristics since it expands uniformly with increasing temperatures. In fact it is used in some high temperature thermometers.

Gallium is corrosive. Group VIII metals are soluble is Gallium. These include Iron, Cobalt, Nickel, Rhodium, Palladium, Osmium, Iridium, and Platinum. Gallium is corrosive to aluminum.

But Gallium is combatable with my favorite high temperature structural materials: tungsten, molybdenum, carbon, and silicon carbide.

Smither has stated that the surface tension of Gallium is much higher than that of water. Due to high surface tension, Gallium is stated to be “immune” to the presence of small cracks in piping, or channels in an imperfect seal, which would result in a serious leak if water were the cooling fluid.

Gallium has 24 isotopes whose half-lives are known, with mass numbers 61 to 84. Of these, two are stable: Ga69 and Ga71 with natural abundances of 60.1% and 39.9% respectively.

Gallium can be made very pure and is available with a contamination level of 1 part in 10^^10.

Cost, pure: $220 per 100g but I have seen costs quoted as low as $.25 per gram.

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 Post subject: Re: A better coolant!
PostPosted: Sep 25, 2010 6:52 pm 
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Axil wrote:
A better coolant!

When Barry Brook and Tom Blees were invited to visit Per Peterson’s laboratory at the Nuclear Engineering Department of UC Berkeley they found that Per’s research focuses on development of a high-temperature reactor with an incredibly high power density.

Why? In short, it’s all about the money.

In Europe or North America, one the most frequently cited criticism of nuclear energy involves economics. High materials and construction costs for Advanced Light Water Reactors (ALWRs) are a road block to their deployment,
Decreasing the cost of new nuclear construction is a winning strategy today.

Per’s argument — and a quite persuasive one — is that if the costs of advanced reactors can be brought way down, below that of pressurized and boiling water reactors (PWRs and BWRs), then their scaled-up deployment is highly likely.
Per’s aim is to develop really compact nuclear units with very high power densities. In a nutshell, very high power densities mean very low costs.

Small is cost effective. Small means less volume for the hot cell, smaller containment, less cost for the coolant, less structural material for the reactor as a whole, less volume and weight for the building, smaller springs for earth quake mitigation. Small is easier to build and even may make factory manufacturing possible for a very powerful unit.

Small means rigid, you can deploy it in the arctic, the desert, and the jungle where the oil shale and sand are.

The large size and associated high cost is one reason that utilities and the oil companies have not embraced the PBMR. Utilities want economies of scale. Oil companies want something they can deploy in the boondocks and in a refinery.

Ideally, they want large power output in a small package.

The primary aim of the nuclear designer is to develop a really compact nuclear unit with very high power densities, based on mostly well-understood technology that is deployable on the compressed time-scale as compared to current reactors.

What does high power density really mean? It means high operating temperatures and a high outlet temperature. High temperatures also mean increased thermodynamic efficiency in power generation. High temperatures also mean efficient hydrogen production and effective process heat for industrial applications.

But something is wrong. The PBMR can achieve an output temperature of 950C and the PB-AHTR is good for only 704C.

So what is the problem? Using molten salt reactor coolant restricts the material used in the core to a low temperature nickel alloy. Because of this, there is a ceiling placed on the temperature of the core. This is a tradeoff that is counterproductive to the main goal of the PB-AHTR and low cost nuclear power, in general.

I therefore ask why not use Gallium liquid metal coolant. Gallium is the other fusion coolant that many fusionairs favor over lithium.

Gallium is much less chemically reactive than lithium or other alkali metals; it is non toxic, it melts at a lower temperature than other light metals, and is less costly than pure alkali metals. Pure Gallium is not a harmful substance for humans to touch. It has been handled many times only for the simple pleasure of watching it melt by the heat emitted from a human hand.

Unlike Lithium-7, it does not need to be enriched. It has a very low neutron cross section, and is about the same as lithium 7 to my eye.

Gallium is a metal (atomic weight 69.72) with a very low melting point (29.9C) and a high boiling point (2005C). The density of Gallium is approximately 6 g/cm3 at 33°C. Gallium is electrically conductive and also paramagnetic.

No core, piping, heat exchanger pre heating is required. Gallium behaves like water at room temperature.

This means that pipe stresses from elevated temperature operation and the danger of “freeze-plugging” a pipe section are also avoided.

The vapor pressure is quite low, essentially zero at 20°C.

The chemical reactivity and toxicity of Gallium and were investigated by literature search predict possible Gallium reactions when spilling in air at 20°C. The results predicted that low levels of oxides would form. The reaction rate at 20°C is not expected to proceed to the extent that significant quantities of Ga2O3 are produced from Gallium.

Gallium has no or minor chemistry with hydrogen, deuterium, and tritium; and has very modest retention of atomic deuterium.

Gallium is stable with many metals and does not readily attack ceramics.

Gallium has good negative void characteristics since it expands uniformly with increasing temperatures. In fact it is used in some high temperature thermometers.

Gallium is corrosive. Group VIII metals are soluble is Gallium. These include Iron, Cobalt, Nickel, Rhodium, Palladium, Osmium, Iridium, and Platinum. Gallium is corrosive to aluminum.

But Gallium is combatable with my favorite high temperature structural materials: tungsten, molybdenum, carbon, and silicon carbide.

Smither has stated that the surface tension of Gallium is much higher than that of water. Due to high surface tension, Gallium is stated to be “immune” to the presence of small cracks in piping, or channels in an imperfect seal, which would result in a serious leak if water were the cooling fluid.

Gallium has 24 isotopes whose half-lives are known, with mass numbers 61 to 84. Of these, two are stable: Ga69 and Ga71 with natural abundances of 60.1% and 39.9% respectively.

Gallium can be made very pure and is available with a contamination level of 1 part in 10^^10.

Cost, pure: $220 per 100g but I have seen costs quoted as low as $.25 per gram.


Doesn't it expand on freezing?

"Combatable" is what we don't want. Compatible is good.

(How fire can be domesticated)


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 Post subject: Re: A better coolant!
PostPosted: Sep 25, 2010 7:22 pm 
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Axil wrote:
A better coolant!
Quote:
But something is wrong. The PBMR can achieve an output temperature of 950C and the PB-AHTR is good for only 704C.

You need a major heat source. The temperature of the heat source helps some but it isn't dramatic. PB-AHTR is dramatically smaller than PBMR for the same heat output.
Quote:
I therefore ask why not use Gallium liquid metal coolant. It has a very low neutron cross section, and is about the same as lithium 7 to my eye.

I don't know your source but looking at Sigma I see 100x larger cross-section for slower neutrons, 1000x for faster ones and a big resonance region.

The other property required is that uranium and thorium form a solution with it rather than a mixture. We need to be certain that the uranium won't form clumps anywhere. Do you know how uranium will react with this?
Quote:
The vapor pressure is quite low, essentially zero at 20°C.

What is the vapor pressure at 700C?


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 Post subject: Re: A better coolant!
PostPosted: Sep 25, 2010 7:41 pm 
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Lars wrote:
What is the vapor pressure at 700C?
Wikipedia says 1 Pa (0.0075 mmHg) at 1037C. Also mentioned is an alloy with plutonium, and a tendency to cause severe embrittlement of metal structures - and it does expand on freezing.


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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 12:34 am 
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Quote:
I don't know your source but looking at Sigma I see 100x larger cross-section for slower neutrons, 1000x for faster ones and a big resonance region.


Upon closer examination, you are correct. But as a tradeoff, is this poorer neutron performance worth 1300C degrees of operating temperature headroom? Remember, in the PB-AHTR the moderation is done by the TRISO fuel itself.

In a loca, the reactor temperature goes beyond 1600C. What happens to the nickel alloy then?

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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 1:31 am 
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Quote:
The other property required is that uranium and thorium form a solution with it rather than a mixture. We need to be certain that the uranium won't form clumps anywhere. Do you know how uranium will react with this?


Quote:
The liquidus of the uranium gallium system has been determined by Jaffee. In addition, evidence of two compounds has been reported. Maskrey and Frost reported UGa3, while Dempster reported UGa2. Because work in the United Kingdom tends to support the presence of the second compound, it is included with the other data to give a tentative diagram.

Judging from the liquidus and a reported melting point of about 1300 C for UGa3, it seems likely that UGa3 melts congruently to some lower temperature. The compound UGa2, if present, may be stable. There appears to be a eutectic at the high-uranium end of the system where a dip in the liquidus occurs
.
The melting point of gallium was virtually unaffected by small additions of uranium. On the other hand, it was reported from the United Kingdom that a eutectic occurs at 14 a/o uranium and about 28 C.

Jaffee found little solubility of uranium in solid gallium.

Jaffee's method for determining the liquidus was rather simple; he determined solubility by feeling with a stirring rod to determine whether uranium was present in the bottom of a crucible of gallium. In spite of the simplicity of his method, the resulting data connect nicely with filtration data obtained by Hayes and Wilkinson for temperatures of 700 and 500 C at the gallium end of the system.

The solid solubility of gallium in uranium is reported to be very low.


The diagram just shows that uranium and gallium (1 to 100%) will liquefy and combine if the temperature (1150C to 1300C) is right.

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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 3:14 am 
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The exotic coolants like Gallium may face another problem, that of poor availability. I have searched the web and the best I found is a eutectic of two common industrial metals, Aluminium and Magnesium. Compositions with 33-65.9% Mg have melting point in the region of 450°C. Operating temperatures of British AGR and fast breeders are in the region of 600°C and it can be a good coolant at this temperature and improve the thermal efficiency from around 30% of water or heavy water cooled reactors to 40%. It also has a low absorption cross-section compared to sodium besides less fire risk and could be used for thermal spectrum too. It also has a good thermal conductivity. I have forwarded a suggestion to the Indian BARC.


Last edited by jagdish on Sep 26, 2010 12:09 pm, edited 1 time in total.

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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 3:45 am 
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Axil wrote:
...

Gallium is much less chemically reactive than lithium or other alkali metals; it is non toxic, it melts at a lower temperature than other light metals, and is less costly than pure alkali metals. Pure Gallium is not a harmful substance for humans to touch. It has been handled many times only for the simple pleasure of watching it melt by the heat emitted from a human hand.


Alkali metals are not expensive because they are scarce. Gallium, on the other hand, has very limited supplies.

Large increases in demand will cause alkali metal prices to drop and Gallium prices to skyrocket.


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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 5:30 am 
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The solar people aren't going to like your competition, Axil.

:lol:


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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 12:28 pm 
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Quote:
Alkali metals are not expensive because they are scarce. Gallium, on the other hand, has very limited supplies.

Large increases in demand will cause alkali metal prices to drop and Gallium prices to skyrocket.





AVAILABILITY OF INDIUM AND GALLIUM … SEPTEMBER 2009





Quote:
Gallium Mining and Extraction Process Overview


Similar to indium, gallium is a minor metal with no primary mining activity. Gallium is extracted from bauxite as part of the bauxite-alumina refining flow that most commonly utilizes the Bayer liquor process.

By all accounts, gallium-containing bauxite is plentiful in the earth’s crust and is widely distributed both geographically and politically. Similar to indium, this contributes to the stability of the supply of gallium feedstocks.

More interesting, only a small portion (less than ten percent) of the potentially available gallium in the bauxite is actually extracted. Hence, the existing flow of bauxite processing offers tremendous capacity increases. Historically, the low extraction volume was limited more by the relatively small demand and economics of relatively low prices. For all practical purposes, gallium output is limited only by facilities investment and capacities.

As a conclusion, gallium is plentiful.

GaAs wafers used for ICs in wireless devices consume the majority of gallium today. LED devices represent the second largest consumer of gallium followed by solar, batteries, alloys, and other minor applications.

The reclaimed gallium from the GaAs wafer production is a significant part of the gallium reclaim and refining process.

Any near-term supply and demand shortfall will only be due to the time required to bring facilities on-line.

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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 1:00 pm 
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Reference:

http://en.wikipedia.org/wiki/Plutonium- ... te_note-13

Quote:
Also mentioned is an alloy with plutonium


Plutonium-gallium alloy (Pu-Ga) is an alloy of plutonium and gallium, used in nuclear weapon pits - the component of a nuclear weapon where the fission chain reaction is started.

The preferred alloy is 3.0-3.5 mol.% (0.8-1.0 wt.%) gallium. This alloy was developed during the Manhattan Project.

My take is that the neutron performance of gallium can’t be that bad if this (Pu-Ga) alloy can go critical.

See Plutonium-gallium phase diagram below.


Attachments:
Plutonium-Gallium phase diagram.jpg
Plutonium-Gallium phase diagram.jpg [ 295.81 KiB | Viewed 3127 times ]

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Last edited by Axil on Sep 27, 2010 12:33 am, edited 1 time in total.
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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 2:21 pm 
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Quote:
Also mentioned is an alloy with plutonium, and a tendency to cause severe embrittlement of metal structures


The primary reference that I have found for brittleness in metals is related to aluminum as gallium infiltrates and settles into the aluminum crystal grain boundaries.

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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 4:03 pm 
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Pebble Bed Failure... Another Feeble-Headed Nuke Drops Dead ...By HARVEY WASSERMAN

Quote:
As Michael Mariotte of the Nuclear Information & Resource Service puts it:

"The Pebble Bed has failed for the same reason all the other new reactor designs ultimately will fail: they are too expensive compared to the competition. Renewables and energy efficiency are cheap and getting cheaper; nuclear is expensive and getting more so."

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 Post subject: Re: A better coolant!
PostPosted: Sep 26, 2010 6:17 pm 
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Wasserman wrote:
... breeder reactors, which would magically create new fuel from used fuel.
Magic, thats how nuclear physics works!


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 Post subject: Re: A better coolant!
PostPosted: Sep 28, 2010 12:55 am 
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Quote:
I don't know your source but looking at Sigma I see 100x larger cross-section for slower neutrons, 1000x for faster ones and a big resonance region.


It looks to me like the inelastic neutron cross section of both lithium7 and Ga71 stop before the thermal range is reached.

Both the elastic and the total neutron cross section cross sections of Ga71 look to be only a few barns more than those for Li7 in the thermal range.

But the (n,y) gamma production cross section is 100X more for Ga71 than for Li7.

Does that not mean that Ga71 is producing gamma radiation from the energy it gets from the neutrons whereas L17 is doing something else to dissipate the neutron energy? Transmutation maybe? What Li7 is doing, I just don’t know.

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