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Author Topic: Nuclear fusion  (Read 7457 times)

Kanil

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Re: Nuclear fusion
« Reply #15 on: June 17, 2009, 03:42:09 am »

Hot fusion is way more fun than cold fusion.
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Yah, it sounds like minecraft with content, you have obviously missed the point, people dont like content, they like different coloured blocks.
Seems to work fine with my copy. As soon as I loaded the human caravan came by and the world burst into fire.

A_Fey_Dwarf

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Re: Nuclear fusion
« Reply #16 on: June 17, 2009, 03:51:23 am »

In fission reactions meltdowns occur due to the cooling system failing. The nuclear reaction releases so much heat that it can melt the protection surrounding it, melt the earth beneath it and keep going down until the energy from the chain reaction is used up. Usually this happens when it hits a large body (ie aquifer) of water resulting in massive amounts of steam. This steam is what does the initial damage to the surrounding environment. Assuming with hot fusion, the energy/temperature given off is far far greater, we don't have any cooling systems powerful enough to contain the initial fusion chain reaction. That I assume is what ein is talking about. It's not that it is dangerous and unpredictable when used, it is that a fusion reaction can't possible be contained in any sort of nuclear power station design we currently have.
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Jetman123

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Re: Nuclear fusion
« Reply #17 on: June 17, 2009, 04:03:43 am »

To understand fusion you have to understand fission.

Regular nuclear power is provided by fissile materials such as uranium. When struck by a high energy particle, this happens:



Basically when a neutron strikes a uranium nucleus, this causes the nucleus to split into it's component parts: protons, neutrons, and electrons. The protons and neutrons dissipate, whereas the neutrons continue on to strike other uranium nuclei, causing further reactions. This is a nuclear fission chain reaction.

Why is this useful for creating power? Because every time you split a uranium atom, a bit of heat and light is produced (mostly heat). When you have hundreds upon thousands upon hundreds of thousands of uranium nuclei splitting, you can produce a pretty damn good amount of power. This is transferred into a water pipe running through the system which turns the water into steam, which is under high pressure, and is then used to drive a turbine which drives an electric generator, producing power.

If you have enough uranium and strike it with a neutron, then one atom will split, producing more neutrons, which will then make it's neighbors split, who will make THEIR neighbors split... This is why it is referred to as a chain reaction, as one atom splitting will send a wave of splitting atoms across the whole material until there are no uranium atoms left.

A nuclear bomb uses this principle to build up a massive amount of heat and pressure from a completely uncontrolled nuclear chain reaction inside a heavy metal casing, until said casing ruptures and detonates.

In a regular nuclear reactor, the reactor itself would become so hot it would melt through it's own containment and into the ground (a "meltdown"), not explode. It's functionally impossible for a nuclear reactor to become an atom bomb.

A runaway fissile reaction is dangerous, but there are multiple methods to control it, the main one being control rods. These are inserted into the fissile material to slow down or even stop the reaction, and are used to prevent it from becoming a runaway one. If handled improperly, however, as it was at Chernobyl, a meltdown situation could occur. Chernobyl was mainly an issue with the reaction containment rupturing along with the coolant towers, releasing radioactive material over a wide area. It wasn't a nuclear blast, it was a meltdown.

Now, I've covered fission, so why is that important? Well, fusion is the same deal, except instead of splitting the atom, we're joining two atoms together.

http://upload.wikimedia.org/wikipedia/commons/3/3b/Deuterium-tritium_fusion.svg

You can do this in a variety of ways, but the most economical is probably the method pictured above - a fusion of two different hydrogen isotopes, deuterium and tritium (hydrogen-2 and hydrogen-3, respectively) to create a stable element, helium-4. This produces one extra neutron and a small amount of heat and light.

Why is this so important? Well, a number of reasons.

1. Each individual fusion reaction produces about quadruple (IIRC) the energy of a single fusion reaction. This means you can get four times the power with fusion.
2. There is no possibility of a runaway fusion reaction, for reasons I am going to cover in a moment.
3. It produces helium-4, which to my knowledge is not unstable, will not decay, and is not considered nuclear waste.
4. No pollution whatsoever, as helium-4 is not a greenhouse gas.
5. Highly economical. The only materials you need once the reactor is built are deuterium and tritum, both of which are easy to get one's hands on (the oceans are FULL of hydrogen)
6. The only radiation it produces is alpha radiation (which is, in actual fact, a helium-4 molecule moving at a high rate of speed) which is so weak it can be easily stopped by a piece of paper.

Why is there no possibility of a runaway fusion reaction?

Because fusion reactions are not chain reactions.

Splitting a uranium atom will cause all of it's neighbors to split. However, fusing deuterium and tritium will not cause other deuterium and tritium to fuse. This means you don't need control rods or mechanisms of any sort - you just have to turn off the device, and the reactions will stop themselves, without any need for additional input. It's not a chain reaction, thus, it can't meltdown unless somebody leans on the "ON" switch for a few hours.

If it's so good and clean and simple, why are we not using it already?

Because... well, as one researcher put it "We're going to put the sun in a box. However, we don't know how to build the box."

Basically the problem is this. It takes a LOT of energy to force deuterium and tritium to fuse. The best way to do this is to smash them into each other as hard as possible (think a particle accelerator). However, doing just one collision will not cut it. You need to smash a huge amount of them together all at once and then find some way to keep doing it over and over and over and use the resultant heat for power generation.

The good news? Deuterium and tritium can be accelerated, and then controlled, by magnetic fields. This means that we already know the principles that will allow us to make the box.

The bad news? A fusion reactor takes a LOOONG time to build, and is very expensive. And we're still not sure which of the many methods proposed will give us the most benefit, so we have to build them all to see which one works the best.

The main reason we don't know how to make the box is, well, we don't know which of these will give us the best bang for our buck or even cost effectiveness (as in we need to produce enough power for the thing to be worthwhile). There are all sorts of proposed designs that nobody has ever tested:



The Tokamak, a russion design that is basically a large particle accelerator arranged in a torus (doughnut) shape? (This one seems like the most likely)

http://upload.wikimedia.org/wikipedia/commons/2/2b/NOVA_laser.jpg (It's a URL as it's a large image)

Instead of magnetic confinement, could we use lasers?



Or hell, maybe we could use this old thing from the 1960s. Who knows? Not me.

« Last Edit: June 17, 2009, 04:25:29 am by Jetman123 »
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Rilder

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Re: Nuclear fusion
« Reply #18 on: June 17, 2009, 04:12:42 am »

We already have fusion reactors we just don't get enough energy out of them to make them worth while.
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Jetman123

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Re: Nuclear fusion
« Reply #19 on: June 17, 2009, 04:20:40 am »

We already have fusion reactors we just don't get enough energy out of them to make them worth while.

Right, which is the main problem here: Which one of those designs would actually be worthwhile to spend millions of dollars on?
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Grek

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Re: Nuclear fusion
« Reply #20 on: June 17, 2009, 04:31:17 am »

Helium-4 is just regular helium like you find in balloons and little kids suck to make their voices sound like mickey mouse.
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Ampersand

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Re: Nuclear fusion
« Reply #21 on: June 17, 2009, 04:57:36 am »

There's currently a european project to build a fusion reactor. It's going to be massive. And probably not worth while. It was planned before the recession, of course.
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Jetman123

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Re: Nuclear fusion
« Reply #22 on: June 17, 2009, 05:03:40 am »

Helium-4 is just regular helium like you find in balloons and little kids suck to make their voices sound like mickey mouse.

Not neccessarily, helium 3 and helium 4 are both stable. However when travelling at high speeds it's known as alpha radiation.
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Nilocy

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Re: Nuclear fusion
« Reply #23 on: June 17, 2009, 05:10:50 am »

Well, what really interesting is that fusion power works, we know this cause at least every major wester power has got an experimental running somewhere. America is doing theres with lasers, we have ours with the magnets and so do the south koreans. I think russians trying to build one (dont hold me to that). Anyhoo, the biggest problem they have is getting MOAR fuel into the reaction to keep it going, cause y'know its hard to put some fuel into a device thats as hot as teh sun and as cold as deep space. I think the record is like 20 seconds of constant activation. So yeah, you lot come up with a way of getting constant fuel into the chamber to make it worthwhile and you'll make billions.

My suggestion is just have a line of dwaves to throw buckets of water into it.
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Areyar

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Re: Nuclear fusion
« Reply #24 on: June 17, 2009, 05:28:17 am »

It doesn't even have to be that cold.
It would still be fine if it was as hot as the surface of the sun.
Tungsten can withstand those temperatures.
It's just that normally, it would be as hot as the core of the sun.
I seem to recall that the surface of the sun is theoretically hotter than the inside (inside photons cannot escape and are contained in atoms)...this may just apply to the upper layers though. Pressure is the key force at the core I guess, pressure ~ friction ~ heat.

I still hold hopes for [hot]fusion, it is inherently possible, but not soon. (as in the last 30 years it is still expected to become viable during the next 30 years ;) .) Cold fusion is still a magic trick though. Maybe nanotechnology could bring atoms together in small enough quntities to be cool and still extract energy from it. If successfull, it will be less like a nuclear reactor and more like a bioreactor, using catalysts to perform a process without the extremes required for unmediated reactions. Don't expect any type of fusion to be in time to avert climate change though.
Funny thing about nano/bio/fusion tech: they continue to fail to deliver the promises of sciFi, don't get discouraged though: these are end product/goals, in the meantime a phletora of sidetracks and offshoot technologies benefit all of us right now. As in games with reasearch: fusion tech requires tech A B C and D, before we get those, fusion is but a dream. (I nremember a game that did this most satisfactory: you'd research a basic tech, but had no controll over what minor techs came available to you or in what order, ultimately you'd aquire cold fusion or whatever, but only after obtaining several moderately usefull techs. Could have been Ascendency...or maybe Space Empires or Stars! ? oh whatever.)
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Ampersand

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Re: Nuclear fusion
« Reply #25 on: June 17, 2009, 05:33:45 am »

Thing is, we already have a giant ball of white hot plasma in the sky to draw energy from. The amount of unharnessed power bathed on the earth by the sun every day is simply absurd.
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Areyar

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Re: Nuclear fusion
« Reply #26 on: June 17, 2009, 05:52:12 am »

The problem is not energy, but how to harness/extract it and then how to transfer it without major losses.
Energy taken from the sun by 'powersats' would have to be converted to highenergy microwave and beamed down. A fine concept in theory and a constant annoyance that none have been launched yet. Maybe a sat would degrade too fast to be cost effective? More likely it is being vetoed because the beam from a 'sat could be potentially used as a 'space lasor' [/dr evil].
Certainly heat exchangers could be converted to power generators?
(I'm no expert on these technical matters)

Once beamed here, it is again in our very leaky powergrid.
If usable(!) superconductors are ever invented/discovered, they would be better employed in powerdistribution than in any type of powerplant.
With a superconducting powergrid, we could generate sufficient energy from renewable resources.
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sneakey pete

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Re: Nuclear fusion
« Reply #27 on: June 17, 2009, 07:01:03 am »

Why are you talking about launching shit into space? who mentioned it? there's plenty of space here on earth ;)

Especially now that we're starting to produce second generation panels.
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Jetman123

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Re: Nuclear fusion
« Reply #28 on: June 17, 2009, 08:07:14 am »

Why are you talking about launching shit into space? who mentioned it? there's plenty of space here on earth ;)

Especially now that we're starting to produce second generation panels.

Albedo.

The Earth gets about 1% of the sun's total radiance. More than 50% of that is reflected by the atmosphere. As a result, you actually get waaaay more power if you have a sattelite up in orbit to collect solar energy and beam it down.
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Areyar

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Re: Nuclear fusion
« Reply #29 on: June 17, 2009, 08:28:38 am »

yep. Plus a dual purpose of a bunch of 'sats can be that of solarshield. To dampen globalwarming a bit.
nothing todo with nuclear power though, except by proxy of solarfurnace. :)
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