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Nuclear Power Primer

Posted By: LarryC

Nuclear Power Primer - 07/16/06 05:19 AM

Power Plant Coal, Oil and Nuclear

Start with a pile of fuel. Get it all hot and bothered. Add water. Make steam. Turbine goes roundy round. Alternator goes roundy round. 'lectricity makes light bulb shine bright.

Life is good.

How do we make nuclear fuel hot and bothered?

Start off with a big honkin' atom. Lets say Uranium. All Uranium atoms have 92 protons in their nucleus. Thats what makes it Uranium. If it had 2 protons in its nucleus, it would be Helium. Anyway, along with the 92 protons, U also has around 140 some odd neutrons. The different number of neutrons is what gives us the different isotopes (U235, U238, U812 [Linked Image], etc.)

Now we all remember that like charged particles don't want to be around each other. Well, in order for the 92 protons to be nestled up nice and tight next to each other in this nucleus, something has to be holding these protons together. That something is called the Nuclear force. A physical analogy would be compressing a spring and keeping it compressed with a piece of safety wire. Cut the wire and all that energy is going to come out. Nuclear fission is the same way. Fission or split the nucleus and the energy that was used to hold the pieces together gets released.
No new bits and pieces are made, they just get rearranged.

Example: Start off with 1 U238 atom. This means we have 92 protons and 146 neutrons. We will ignore the electrons for right now. For some reason, it decides to split up, and it breaks up into a big chunk, a little chunk, and some crumbs. We end up with Dy161, K66, and 2 He4 and 3 neutrons. And, everybody is now moving away from where we started. We did not make any new matter and we did not destroy any matter, we just released some energy and rearranged things a bit.

Now the Dy161 is probably not happy with the way it is and will probably spit out some He4 (alpha particles) or neutrons to get to a more stable configuration. Same with the K66. Eventually everybody settles down.

When everybody is moving about, that is heat. Collect the heat, add water, and we have got steam.

What causes a nucleus to split or spit out stuff? Either it wants to, or more often, something hit it. A big clunky nucleus is not very stable. Add a neutron that is zipping along and runs into the nucleus, and that nucleus may just go to pieces. If neutrons from that fission bangs into another nucleus, and then more and more fissions happen, that's a Chain Reaction. If the chain reaction is under control, it is called a nuclear reactor. If it is not under control, then it is called a nuclear bomb.

Now, most of the zipping around particles don't hit a susceptable nucleus. And the ones that do manage to hit a nucleus, most of them don't trigger a fission either. Thats why the nuclear fuel has to be enriched with the right kind of U and it has to be arranged in the right physical configuration, and then they add all sorts of stuff to make sure it gets consumed in the right sequence, and doesn't get too hot and all those engineering types of things.


[This message has been edited by LarryC (edited 07-16-2006).]
Posted By: LarryC

Re: Nuclear Power Primer - 07/16/06 05:33 AM

Power Plant Design

Nuclear fuel gets hot. We use water to take the heat away. The two basic designs are Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR).

BWR plants uses the water that cools the fuel to make steam. This steam drives the turbines directly. They are cheaper to build and more thermally efficient, but the steam plant is now slightly radioactive and more difficult to work on.

PWR plants keep the water that cools the fuel seperate from the water that makes the steam to drive the turbines. This adds to the initial cost but steam plant maintenance costs should be cheaper. Also thermal efficiency goes down slightly because you have another heat exchanger and fluid loop.

There are other flavors of power plants that use hi pressure gasses for heat transfer and earlier versions that used liquid Sodium.

Different designs came about because of different needs.

Posted By: renosteinke

Re: Nuclear Power Primer - 07/16/06 02:30 PM

Nuclear power does have it's uses. Here's a pair that are often overlooked.

Say you live in a rural area that is in danger of development. Simply by placing a large sign, saying "Future Site of China Syndrome Nuclear Power Plant," you pretty much guarantee your rural peace for decades to come.

Or, if you installed treadmills around what looked like a nuclear plant, you would be able to have the protestors generate your power instead, as they marched about!
Posted By: Kenbo

Re: Nuclear Power Primer - 08/09/06 02:48 PM

Ok got that.

So how does nuclear fusion work then?
Am I right to think this is the opposite from fission ?
Posted By: C-H

Re: Nuclear Power Primer - 08/09/06 03:30 PM

Fusion is the opposite of fission: Instead of splitting atoms, you smash the together. Instead of very heavy atoms, you use very light atoms: Hydrogen. Not the ususal hydrogen (except in the case of the sun and the stars) but instead hydrogen with one or two extra neutrons. You make one helium atom out of two hydrogen atoms and get a neutron left over along with a lot of heat.

[Linked Image]

[This message has been edited by C-H (edited 08-09-2006).]
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