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Liquid Salt Nuclear Reactors

Envisage
Posts: 3,646
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3/4/2015 8:01:06 AM
Posted: 1 year ago
This post is going to be a dump of what I think about this subject with no structured coherency... but hopefully it might interest some.

Our existing solid-fuel nuclear reactors currently run into a plethora of problems:

1. They need to be constantly cooled/temperature controlled and balanced to prevent overheating and inevitable meltdown.

Turning off a nuclear reactor simply isn't enough, since the decay products give off heat, enough heat to melt the fuel rods and jepoardise the casing, which is essentially what has happened in Chernobyl, and Fukashima.

2. They are inefficient, only 1% of the fuel in the solid fuel rods is ever consumed, this is due to the build up of neutron poisons, such as Xenon, Krypton, Samarium, etc. Which require defuelling and reprocessing to remove.

3. Solid ceramic fuel rods are currently required, of which suffer structural integrity issues when radon, hydrogen and helium are released from decay products. Gasses escaping from solids cause fissures and cracks.

4. Pressurised water coolant is required, but because water boils at a meagre 100C, it needs to be pressurised to operate at the temperature that the reactor operates at (with water temperatures exceeding 300C). The pressures used are on the order of 200 ATM, roughly the same pressure as an industrial gas cylinder, except with hot radioative material beating down upon it on one side of the wall, and highly pressurised water on the other. A single structural failure of crack in this system will suddently have super-critical water suddenly open to the hot interior of the reactor... boom!

5. Build-up of transuranics, leading to wasted fuel and long-lived nuclear waste (~30,000 year cooldown time).

http://en.wikipedia.org...

While most attention is focussed on nuclear fusion to solve these problems, a much simpler solution is on the horizon, with reactors in India and China making significant progress. Liquid fuel reactors essentially solve all these problems with pressurised solid fuel reactors. They have inherent safety built-in, since the liquid salt is already molten, and chemically stable, thus it's impossible for it to have a meltdown in the same manner solid fuel reactors have.

Moreover, most radiation poisons either boil off as gasses (Xenon, Krypton), or they plate out as solids, no longer able to interfere with the reactions. An especially promising variant are reactors based on Thorium, a far more abundant element than Uranium, and even more abundant than Uranium-235, which is considerably rarer than gold, and requires expensive enriching processes to make viable.

Thorium reactors are fertile nuclear fuels, in that they breed fissile material. 232-Thorium absorbs a neutron and converts to 233-U, which is fissile, and reacts in much the same way 235-U does. Unlike U-235, which is only 0.72% abundance of Uranium and requires expensive centrifuging to achieve viable concentrations (there is a reason why making a nuclear bomb isn't all that easy, and why the US gets edgy over Iran possessing centrifuges, since that allows converting rather useless natural uranium into the good stuff.). 232-T is 100% abundance of thorium, however, and hence requires no enriching, and consequently a much lower fuel cost. Not to mention thorium is largely a byproduct of heavy/precious metal mining.

Another big advantage of Thorium is that it's much more difficult for nuclear weapons to proliferate form it, since the reactors simply do not produce much plutonium, and the plutonium it does produce is mostly of the 238-Pu variety, which is useless for fission, but very useful for space exploration (for use in radioisotope thermoelectric generators, such as the one the Curiosity rover has, which allows it to function with no solar panels on Mars), and the reactor itself constantly consumes bred fuel, it never has a large stockpile of fissile material in the mixture (unlike solid fuel reactors, which must have all of it's fissile material in one place) which means it also chews through the transuranics which form the long-lived waste that is so problematic with solid fuel reactors. The decay products are only harmful for ~300 years, much fewer than the 30,000 the transuranics are.

http://en.wikipedia.org...

/brainfart
RuvDraba
Posts: 6,033
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3/4/2015 2:17:15 PM
Posted: 1 year ago
Thanks indeed for these brainfarts, Envisage.

My country of Australia has significant interest in exporting Thorium, since we have such big reserves of it (alongside Uranium) and since it's generally considered weapon-unfriendly.

Have you got any visibility of the issues in using it? Given the abundance and the benefits, it seems to me that the lag on adoption has been surprisingly long. Is that a general suspicion of fission power, or are there technical or other issues?
Sosoconfused
Posts: 237
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3/4/2015 2:18:50 PM
Posted: 1 year ago
At 3/4/2015 8:01:06 AM, Envisage wrote:
This post is going to be a dump of what I think about this subject with no structured coherency... but hopefully it might interest some.

Our existing solid-fuel nuclear reactors currently run into a plethora of problems:

1. They need to be constantly cooled/temperature controlled and balanced to prevent overheating and inevitable meltdown.

Turning off a nuclear reactor simply isn't enough, since the decay products give off heat, enough heat to melt the fuel rods and jepoardise the casing, which is essentially what has happened in Chernobyl, and Fukashima.

2. They are inefficient, only 1% of the fuel in the solid fuel rods is ever consumed, this is due to the build up of neutron poisons, such as Xenon, Krypton, Samarium, etc. Which require defuelling and reprocessing to remove.

3. Solid ceramic fuel rods are currently required, of which suffer structural integrity issues when radon, hydrogen and helium are released from decay products. Gasses escaping from solids cause fissures and cracks.

4. Pressurised water coolant is required, but because water boils at a meagre 100C, it needs to be pressurised to operate at the temperature that the reactor operates at (with water temperatures exceeding 300C). The pressures used are on the order of 200 ATM, roughly the same pressure as an industrial gas cylinder, except with hot radioative material beating down upon it on one side of the wall, and highly pressurised water on the other. A single structural failure of crack in this system will suddently have super-critical water suddenly open to the hot interior of the reactor... boom!

5. Build-up of transuranics, leading to wasted fuel and long-lived nuclear waste (~30,000 year cooldown time).

http://en.wikipedia.org...

While most attention is focussed on nuclear fusion to solve these problems, a much simpler solution is on the horizon, with reactors in India and China making significant progress. Liquid fuel reactors essentially solve all these problems with pressurised solid fuel reactors. They have inherent safety built-in, since the liquid salt is already molten, and chemically stable, thus it's impossible for it to have a meltdown in the same manner solid fuel reactors have.

Moreover, most radiation poisons either boil off as gasses (Xenon, Krypton), or they plate out as solids, no longer able to interfere with the reactions. An especially promising variant are reactors based on Thorium, a far more abundant element than Uranium, and even more abundant than Uranium-235, which is considerably rarer than gold, and requires expensive enriching processes to make viable.

Thorium reactors are fertile nuclear fuels, in that they breed fissile material. 232-Thorium absorbs a neutron and converts to 233-U, which is fissile, and reacts in much the same way 235-U does. Unlike U-235, which is only 0.72% abundance of Uranium and requires expensive centrifuging to achieve viable concentrations (there is a reason why making a nuclear bomb isn't all that easy, and why the US gets edgy over Iran possessing centrifuges, since that allows converting rather useless natural uranium into the good stuff.). 232-T is 100% abundance of thorium, however, and hence requires no enriching, and consequently a much lower fuel cost. Not to mention thorium is largely a byproduct of heavy/precious metal mining.

Another big advantage of Thorium is that it's much more difficult for nuclear weapons to proliferate form it, since the reactors simply do not produce much plutonium, and the plutonium it does produce is mostly of the 238-Pu variety, which is useless for fission, but very useful for space exploration (for use in radioisotope thermoelectric generators, such as the one the Curiosity rover has, which allows it to function with no solar panels on Mars), and the reactor itself constantly consumes bred fuel, it never has a large stockpile of fissile material in the mixture (unlike solid fuel reactors, which must have all of it's fissile material in one place) which means it also chews through the transuranics which form the long-lived waste that is so problematic with solid fuel reactors. The decay products are only harmful for ~300 years, much fewer than the 30,000 the transuranics are.

http://en.wikipedia.org...

/brainfart

These are indeed interesting. It solves a lot of problems and doesn't have to deal with the low energy density problem that wind/solar has to deal with. It is also more likely to be ready sooner than fusion. However, I see this having a public opinion problem. After the Fukushima incident nuclear power will have a significant uphill battle in the western world as far as public opinion goes. China has the advantage of not being subject to public opinion the same way that the west is. So perhaps with them leading, the west will rethink their moratorium on nuclear power in favor of this type of technology when they see it working in China.
Envisage
Posts: 3,646
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3/4/2015 2:27:39 PM
Posted: 1 year ago
At 3/4/2015 2:17:15 PM, RuvDraba wrote:
Thanks indeed for these brainfarts, Envisage.

My country of Australia has significant interest in exporting Thorium, since we have such big reserves of it (alongside Uranium) and since it's generally considered weapon-unfriendly.

Have you got any visibility of the issues in using it? Given the abundance and the benefits, it seems to me that the lag on adoption has been surprisingly long. Is that a general suspicion of fission power, or are there technical or other issues?

It's been mothballed technology for a plethora of reasons (virtually none of them technological, but rather in their application). I have researched both sides, so I will do a brainfart of a negative response to this shortly. Yes, there are some technological hurdles to jump to make it large-scale, but we already had experimental reactors working and cooking just fine in the past, when it was researched for the purposes of developing a nuclear powered plane (no, really).

Long story short, Heavy Water Reactors won out, but the political and economical landscape has changes a lot since then.
RuvDraba
Posts: 6,033
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3/4/2015 2:36:22 PM
Posted: 1 year ago
At 3/4/2015 2:27:39 PM, Envisage wrote:

It's been mothballed technology for a plethora of reasons (virtually none of them technological, but rather in their application). I have researched both sides, so I will do a brainfart of a negative response to this shortly. Yes, there are some technological hurdles to jump to make it large-scale, but we already had experimental reactors working and cooking just fine in the past, when it was researched for the purposes of developing a nuclear powered plane (no, really).

This will be fascinating. I look forward to it. :)

Long story short, Heavy Water Reactors won out, but the political and economical landscape has changes a lot since then.

A key factor is sometimes whether extant industries will invest in new technologies rather than defending existing barriers to entry. Democratic governments can be loathe to invest in competition to existing campaign funding. :)
Iredia
Posts: 1,608
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3/4/2015 3:01:49 PM
Posted: 1 year ago
Great post ! But why hasn't the technology been deployed yet despite its advantages ?
Porn babes be distracting me. Dudes be stealing me stuff. I'm all about the cash from now. I'm not playing Jesus anymore.