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RE: Nuclear fusion - 7/24/2008 12:54:36 AM
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Method
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quote:
ORIGINAL: Bettawrekonize
I think you're missing the point here. The energy doesn't primarily come from the heat (though I did mention it does produce a lot of heat), the energy primarily comes from the pressure. The 2.6 MJ/kg is the amount of heat energy that it produces. The amount of energy it produces total is way more than that.
It's been a while since college chem so I could be getting this wrong. According to Boyle's Law heat and pressure are one in the same. The kinetic energy of the gas is what produces both the pressure and the heat. Also, the reaction is controlled by pressure. The higher the pressure the less O2 is released. Therefore, the energy of the reaction determines the pressure that it can produce.
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http://peswiki.com/index.php/Directory:Hydrogen_Peroxide_as_Fuel
So, it releases almost the same amount of energy as hydrogen, energy that can be used.
Someone else will have to look it up, but I find it interesting that the Space Shuttle reduces hydrogen for it's propulsion. It has an liquid oxygen tank and a hydrogen tank. If H2O2 were just as viable I would think that they would use that. Perhaps they prefer the stability of liquid oxygen over hydrogen peroxide or the redox reaction is more powerful than the catalytic conversion of hydrogen peroxide. Don't know.
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RE: Nuclear fusion - 7/24/2008 12:58:11 AM
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Bettawrekonize
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BTW, I found this interesting
China Automakers Showcase Fuel-Saving Cars
Too bad it doesn't mention miles per gallon (I've tried looking elsewhere and couldn't find it).
Most of the criticisms I've read on the subject (other than safety of course) focus on the amount of energy put into producing hydrogen peroxide. For example.
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This is a completely useless quest. To use hydrogen peroxide as a fuel (monopropellant), you are essentially decomposing it into water and oxygen. You will get back no more than the enrgy you put in to make the peroxide out of water in the first place! And where are you going to get the energy to do that from?
http://www.physicsforums.com/showthread.php?t=148146
The fuel efficiency criticisms that Embeded seemed to have made up don't seem to be mentioned anywhere else.
I also read these posts.
http://cr4.globalspec.com/thread/21702/Hydrogen-Peroxide-Injection-Systems-for-Engines
The question then becomes, can we produce this stuff (say, in some specialized lab) and use it more efficiently (ie: with less pollution at a lower cost) than something else (gasoline)? Or will the cost of production + consumption combine amount to more costs and more pollution than something else.
< Message edited by Bettawrekonize -- 7/24/2008 3:05:48 AM >
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RE: Nuclear fusion - 7/24/2008 1:02:56 AM
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Bettawrekonize
Posts: 1460
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quote:
ORIGINAL: Method
It's been a while since college chem so I could be getting this wrong. According to Boyle's Law heat and pressure are one in the same. The kinetic energy of the gas is what produces both the pressure and the heat. Also, the reaction is controlled by pressure. The higher the pressure the less O2 is released. Therefore, the energy of the reaction determines the pressure that it can produce.
According to Boyle's law (with a constant temperature k), "For a fixed amount of gas kept at a fixed temperature, P and V are inversely proportional (while one increases, the other decreases)."
http://en.wikipedia.org/wiki/Boyle%27s_law
Basically, if you have f (f as in fixed) units of gas in volume V at temperature k (constant). As volume increases, pressure decreases. As volume decreases, pressure increases.
You're probably thinking of Charles law or something.
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At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature (in Kelvin) increases or decreases.
http://en.wikipedia.org/wiki/Charles%27_law
But in the case of Hydrogen peroxide, the increased pressure is not only from increasing the heat of a gas (perhaps that's where you and embedded seem confused). It's from releasing oxygen from a liquid (the separation of oxygen from water).
< Message edited by Bettawrekonize -- 7/24/2008 1:30:26 AM >
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RE: Nuclear fusion - 7/24/2008 1:07:41 AM
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Bettawrekonize
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quote:
ORIGINAL: Method
Someone else will have to look it up, but I find it interesting that the Space Shuttle reduces hydrogen for it's propulsion. It has an liquid oxygen tank and a hydrogen tank. If H2O2 were just as viable I would think that they would use that. Perhaps they prefer the stability of liquid oxygen over hydrogen peroxide or the redox reaction is more powerful than the catalytic conversion of hydrogen peroxide. Don't know.
I already read all about that, but I don't want to get into a huge discussion about that right now (since it's more off topic and I already steered this thing off topic enough).
More on that here
Land Me On The Moon ... Softly: Apollo's LLRV.
I think they use something else now (I read other sites on it and I can't remember, but I think they found something that's somehow better for what they need)?
http://www.peroxidepropulsion.com/article/2
< Message edited by Bettawrekonize -- 7/24/2008 2:39:05 AM >
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RE: Nuclear fusion - 7/24/2008 1:58:11 AM
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Bettawrekonize
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quote:
ORIGINAL: Embedded
Also... "half the energy density" means it has less energy per unit mass than gasoline.
I know what half the energy density means.
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I also found it to be less... but much less than half... more like a thirteenth. That link does not support your claim.
The energy density is about half that of gasoline (according to the site I linked to).
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Aluminum was chosen originally because it is an abundant natural resource and is readily available from recycled sources, says Rusek, who estimates that the cells are at least 20 times higher in energy density than a standard lead-acid car battery.
"That means a 20-kilogram lead-acid battery would put out the same amount of energy as a one-kilogram hydrogen peroxide fuel cell," he says, noting that other metals, such as lithium alloys, might also work in hydrogen peroxide fuel cells.
http://www.sdearthtimes.com/et0100/et0100s16.html
< Message edited by Bettawrekonize -- 7/24/2008 3:30:32 AM >
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RE: Nuclear fusion - 7/24/2008 3:27:35 AM
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Bettawrekonize
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Uhm... weird how, according to wikipedia, it says 2.7 MJ/kg as a monopropellant but gasoline has 46.9. MJ/kg. Weird how this didn't come up in the other message boards I read through (or I probably missed it since I only skimmed through them). Thanks Embedded.
http://en.wikipedia.org/wiki/Energy_density
I guess it does seem like the website I linked to (saying it has half the energy density as gasoline) misinformed me. I'll have to read more about it when I have more time. Thanks again.
< Message edited by Bettawrekonize -- 7/24/2008 3:34:29 AM >
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RE: Nuclear fusion - 7/24/2008 5:43:50 AM
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ianz
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quote:
ORIGINAL: Bettawrekonize
Uhm... weird how, according to wikipedia, it says 2.7 MJ/kg as a monopropellant but gasoline has 46.9. MJ/kg. Weird how this didn't come up in the other message boards I read through (or I probably missed it since I only skimmed through them). Thanks Embedded.
http://en.wikipedia.org/wiki/Energy_density
I guess it does seem like the website I linked to (saying it has half the energy density as gasoline) misinformed me. I'll have to read more about it when I have more time. Thanks again.
Hey just a bouquet to you for your reaction to the various posts on this topic. A great example for all of us.
Regards, Ian
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RE: Nuclear fusion - 7/25/2008 1:02:29 PM
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Method
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quote:
ORIGINAL: Embedded
Fusion research has been going on in the US for about 50 years. Billions have been spent and billions more will be spent. The potential payoff is so great that, I think, it is worth it.
I agree. The fact of the matter is that we have already produced fusion reactions that produce more energy than what we put into them. We call them thermonuclear warheads. We can do it with a hammer (metaphorically), but can we produce positive energy output with violin. I think we can, but it is going to have to be an international effort.
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I think that ultimately we are going to have to go to fission and then, hopefully, fusion reactors. It is a shame that they are so potentially deadly. Both produce a lot of radioactive waste. Fusion should produce less than fission though.
I agree. Fission is where we should be putting capital instead of coal plants. We should also be putting money into research that looks at sizing down nuclear plants. Right now it takes serious capital to build a nuclear power plant but if we can shrink them down smaller companies can get into the mix. I was watching a show recently that talked about pebble bed reactors. They use softball sized graphite balls embedded with uranium to fuel the reaction. Supposedly the waste is much easier to deal with, the reaction is not as tempermental, and the reactors can be much smaller. I'm no expert, but this certainly sounds like a good idea from the standpoint of a layperson.
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RE: Nuclear fusion - 7/25/2008 4:46:45 PM
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Rasico
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This may be a very stupid question, but the waste produced by nuclear fission has to go somewhere right? Why not put it on the moon or somewhere out in deep space where it won't risk being attracted back to earth? I'm sure someone has thought of that so there must be a reason why it's not viable yet.
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RE: Nuclear fusion - 7/25/2008 5:05:24 PM
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essentialsaltes
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quote:
ORIGINAL: Rasico
This may be a very stupid question, but the waste produced by nuclear fission has to go somewhere right? Why not put it on the moon or somewhere out in deep space where it won't risk being attracted back to earth? I'm sure someone has thought of that so there must be a reason why it's not viable yet.
The main problem is that it's ridiculously expensive to do so. It costs about $20,000 per kilogram to get something into a geosynchronous orbit, much less out to the moon.
Or to turn it around, it probably costs more energy to get rid of the waste that way than we got out of the nuclear fuel in the first place.
_____________________________
"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: Nuclear fusion - 7/25/2008 6:58:23 PM
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Method
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quote:
ORIGINAL: Rasico
This may be a very stupid question, but the waste produced by nuclear fission has to go somewhere right? Why not put it on the moon or somewhere out in deep space where it won't risk being attracted back to earth? I'm sure someone has thought of that so there must be a reason why it's not viable yet.
Some have suggested putting the waste in large acrylic cubes and sinking them into the ocean. I think this has been done with great success.
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RE: Nuclear fusion - 7/26/2008 3:36:18 PM
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Fireborn
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Maybe I'm missing something...
As I was aware, the only radioactive waste produced by nuclear fusion was from the production of the fuel, not the process itself, since it involves light nuclei instead of heavy (i.e., radioactive) nuclei.
Am I wrong?
Also, I posted earlier, but didn't hear any responses - what about tidal turbine generators similar to wind generators, now being put in rivers and oceans? The density of water is much higher than air, and can generate a lot more energy than air generators, and are more predictable.
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RE: Nuclear fusion - 7/26/2008 3:46:04 PM
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DanJames
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quote:
ORIGINAL: Method
quote:
ORIGINAL: Rasico
This may be a very stupid question, but the waste produced by nuclear fission has to go somewhere right? Why not put it on the moon or somewhere out in deep space where it won't risk being attracted back to earth? I'm sure someone has thought of that so there must be a reason why it's not viable yet.
Some have suggested putting the waste in large acrylic cubes and sinking them into the ocean. I think this has been done with great success.
Right. We have plenty of really good ways to safely get rid of waste. I think putting the waste on the moon would be a lot like burying it in a wildlife reserve. Why sully the moon? Not only that, but if the rocket sending the waste into space were to fail, we would have nuclear waste peppering the land over its flight path... which I hear is never a swell situation.
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RE: Nuclear fusion - 7/27/2008 7:31:53 AM
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Real_Solitude
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quote:
ORIGINAL: essentialsaltes
I think I was playing within the bounds of the OP's "in the forseeable future". I think current mass-produced panels have a conversion efficiency of only about 10-15%, so that would mean we'd have to pave nearer 0.1% of the earth (or 0.3% of the land surface). That's a small fraction, but still a huge area, something like 5 million square kilometers. Looked at another way, the total solar power currently generated is less than 0.1% of the global demand, so we need to increase the current installation by a factor of 1000. Producers are certainly cranking up production, but it'll take some time to get there.
Hmm, hopefully it's still within the foreseeable future.
If there's a Moore's law for solar, and I don't know if there is, we could see feasible solar within 20 years.
_____________________________
"Instead of feeling alone in a group its better to have real solitude all by yourself."
~Faye Valentine
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RE: Nuclear fusion - 7/29/2008 4:05:47 PM
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Embedded
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quote:
ORIGINAL: Bettawrekonize
quote:
ORIGINAL: Embedded
You might want to read: this page on safety and other properties (linked from PESWiki). They also mention on that page that 90% H2O2 yields only 2.6 MJ/kg (even worse than I calculated).
I think you're missing the point here. The energy doesn't primarily come from the heat (though I did mention it does produce a lot of heat), the energy primarily comes from the pressure. The 2.6 MJ/kg is the amount of heat energy that it produces. The amount of energy it produces total is way more than that.
Beta, you need to learn some thermodynamics terms and understand what they mean. Heat IS Energy. Energy has many forms and names (chemical, electrical, mechanical, potential, nuclear, kinetic, thermal, AND heat) Energy is almost allways expressed in units of Joules in Physics (aka work).
1 Joule = one kilogram accelerated at one meter per second squared for the distance of one meter. If you lift one kilogram of mass one meter off the floor you have done 9.8 Joules of work. Some of that work is now stored in the mass as potential energy by nature of its position. A Joule is part if the ISU Physics units because it is based on meters, kilograms and seconds (MKS).
Another unit of energy is the calorie. It is used often in Thermodynamics and Chemistry(though they more often use the Joule.)
I Calorie = the amount of heat required to raise one gram of liquid water by one degree Celsius. So to raise the temperature of one liter (1 kilogram) of water from room temperature (20C) to boiling (100C) would require eighty thousand calories or 80kcal just to get it to the boiling point. BUT in order to actually boil away the water would require even more heat. Often that is called the heat of vaporization. To actually boil away teh water (convert the liquid to vapor) requires an additional 542,180 calories. One gram of water is one cubic centimeter of water in volume. Since the calorie is based on centimeters, grams and seconds it is often called a CGS system unit.
There are other units which mean the same thing. Another CGS unit is the "erg" (almost never used any more). Another ISU/MKS unit is the kilowatt-hour which is often seen on your utility bill. Yet another one used in Nuclear and Particle Physics is the electro-volt or eV. A very common unit in the US is the BTU or British Thermal Unit. The British rarely use that unit anymore.
In any case...
Joules == A*BTUs == B*calories == C*kilowatt-hours == D*ergs ==E*electron-volts
and so on. Where A, B, C, D, and E are conversion constants. The type of unit used is by convention in the particular discipline and can be handy for other calculations within the scope of a particular problem. I prefer to use Joules most of the time but I will use whatever is most convenient, depending on the problem.
Yet one more (and there are probably some I forgot) unit of energy you may see quite often is the milliamp-hour (mAh) which is usually used for rating the energy capacity for batteries. It leaves out a required unit (the voltage) but that is just the voltage of the battery. So a 6-volt battery of, say, 100mAh has the same amount of energy stored in it as a 12-volt battery of the same rating. But the 6-volt battery will deliver it over a period of time that is twice as long as the 12-volts.
So when a chemist talks about the "heat of reaction" they are talking about the amount of energy that is produced by that reaction. Some of the energy may be used to produce a voltage and current flow, as in a battery, some of it will warm up the battery. "Heat" in the energy sense of the word does not always mean a rise (or drop) in temperature.
Again, this is all basic high school chemistry and physics. If you haven't had a class in those subjects or have forgotten the terms and what they mean then I suggest you read up on it or take a course in it at your college or at a local community college. The reason I say this is because there is MUCH more to the subject than I can possibly explain here and as a responsible citizen who has to make informed decisions on public (and private) energy policies and products you really should have at least a basic understanding of the subject.
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Actually, it does not burn, it decomposes, with a release of tremendous energy, close to the energy per mole of H2.
http://peswiki.com/index.php/Directory:Hydrogen_Peroxide_as_Fuel
So, it releases almost the same amount of energy as hydrogen, energy that can be used. More interesting questions are, how much energy is required to produce it and where will that energy come from? How much does it cost to produce?
Very good questions. You have the right idea!
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I hope you understand the role of catalysts. It is not "used up" in a reaction.
Of course. That's the whole point. You mix H2O2 with a catalyst and you can use the same catalyst over and over to keep on producing more energy from more H2O2.
Excellent.
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RE: Nuclear fusion - 7/29/2008 4:15:31 PM
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Embedded
Posts: 57
Joined: 4/11/2005
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quote:
ORIGINAL: Bettawrekonize
Most of the criticisms I've read on the subject (other than safety of course) focus on the amount of energy put into producing hydrogen peroxide. For example.
quote:
This is a completely useless quest. To use hydrogen peroxide as a fuel (monopropellant), you are essentially decomposing it into water and oxygen. You will get back no more than the enrgy you put in to make the peroxide out of water in the first place! And where are you going to get the energy to do that from?
http://www.physicsforums.com/showthread.php?t=148146
The fuel efficiency criticisms that Embeded seemed to have made up don't seem to be mentioned anywhere else.
Ahem... I didn't make those criticisms up. But, again... you are asking the right questions.
quote:
I also read these posts.
http://cr4.globalspec.com/thread/21702/Hydrogen-Peroxide-Injection-Systems-for-Engines
The question then becomes, can we produce this stuff (say, in some specialized lab) and use it more efficiently (ie: with less pollution at a lower cost) than something else (gasoline)? Or will the cost of production + consumption combine amount to more costs and more pollution than something else.
Good questions!
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RE: Nuclear fusion - 7/29/2008 4:26:35 PM
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Embedded
Posts: 57
Joined: 4/11/2005
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quote:
ORIGINAL: Bettawrekonize
Uhm... weird how, according to wikipedia, it says 2.7 MJ/kg as a monopropellant but gasoline has 46.9. MJ/kg. Weird how this didn't come up in the other message boards I read through (or I probably missed it since I only skimmed through them). Thanks Embedded.
http://en.wikipedia.org/wiki/Energy_density
I guess it does seem like the website I linked to (saying it has half the energy density as gasoline) misinformed me. I'll have to read more about it when I have more time. Thanks again.
You are very very welcome.
I really do hope you (and everyone else for that matter)learns more about thermodynamics in general and energy in particular. Without the practical knowledge your mind will always be a soft punching bag for every scam-artist, charlatan, and snake-oil salesman that comes along. As energy sources get tighter we will see a LOT more scams bombarding us from all directions.
You are certainly asking the right questions and you appear to be understanding the answers. It is a life long process... keep it up.
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RE: Nuclear fusion - 7/29/2008 4:33:22 PM
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Embedded
Posts: 57
Joined: 4/11/2005
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Method,
The 'pebble bed reactors' are a neat idea. I think we a;ready know how to make small scale reactors. We have a whole bunch installed in submarines and aircraft carriers. Not sure if the USN is allowed to share the knowhow though.
There are some valid criticisms of the PBRs on the wikipedia site. I have one that wasn't mentioned there though. Most countries aer pretty nervous about security of nuclear materials (You should see the red-tape I have to wade through for small amounts in our lab). Making lots of smaller reactors would, I think, be more difficult to make secure against attack or theft.
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RE: Nuclear fusion - 7/29/2008 4:44:47 PM
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Method
Posts: 1162
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quote:
ORIGINAL: Embedded
Method,
The 'pebble bed reactors' are a neat idea. I think we a;ready know how to make small scale reactors. We have a whole bunch installed in submarines and aircraft carriers. Not sure if the USN is allowed to share the knowhow though.
There are some valid criticisms of the PBRs on the wikipedia site.
There is no such thing as a completely safe nuclear reactor, but I think these concerns can be easily overcome. The main criticism seems to be the graphite itself. It can combust in the presence of O2 releasing the radioactive fuel in the smoke. This seems like it would be easy to contain, but who knows.
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I have one that wasn't mentioned there though. Most countries aer pretty nervous about security of nuclear materials (You should see the red-tape I have to wade through for small amounts in our lab). Making lots of smaller reactors would, I think, be more difficult to make secure against attack or theft.
I work in a lab that uses radioactive materials as well. We only have about 1 mCurie of P32 at anyone time and various amounts of tritium. You couldn't even kill a single person with the amounts we have, and yet we have to jump through so many hoops that it is almost not worth it. I think this is partly why so many biotech companies are starting to push chemiluminescent, fluorescent, etc. based assays. The problem is that the isotope based assays are usually much more sensitive, but oh well.
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