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Thursday, March 12, 2009

Nuclear Physics 101 (in progress)

Hydrogen Fuel
Biodiesel Fuel
Canada's Green Party
Batteries and Supercapacitors

Nuclear Physics 101
Nuclear Paradigm Shift
Can Auto Dealers Go Green
Wind and Other Energy Alternatives

The Obama team needs a primer on Nuclear Physics. And so do most people who care about the future and want to do something about the damage being done to our planet. The four generations of Nuclear Energy development and the latest rediscovered fertile to fissionable Molten Salt Reactor (MSR) design which for lack of a better word I'll refer to as THOR. I really mean Liquid Fluoride Thorium Reactor (LFTR). But that's a mouthful and the catalyst is Thorium so lets call it THOR coming from the name for the God of lightning.

Since it is 60 years old in concept it's hard to think of it as fourth generation reactor design but it is being classified as such along side of the souped up Light Water Reactors (LWR) and upgrades of the traditional reactor designs that produce so much more dangerous nuclear waste.

The nuclear industry keeps boasting about it's safety record since Chernobyl and relatively harmless Three Mile Island incident. What is conveniently unspoken is that they still need to store significant amounts of radioactive fuel. So what else is new? Actually THOR or LFTR is what's new to most of us and very different from the traditional view of nuclear reactors.
It's the alchemists dream, turning iron into gold, living forever, an abundant energy source a dream at least in terms of nuclear energy.

Nuclear Physics 101
(without gluons, quarks, leptons, fermions, hadrons, bosons and antineutrinos.)

The only naturally occurring source of nuclear fuel is Uranium. Thorium is not a fuel, technically, but later I'll explain the Thorium Cycle which produces fuel. We'll come back to this. Uranium is found in trace amounts and needs processing to be as pure as possible. The ability to create man made Isotopes of radioactive elements is partly what is keeping the nuclear industry alive. And although very expensive to build Nuclear Reactors are still the most efficient electricity producers ever.

Nuclear energy is not new it's just new to humans. They started to understand it about 100 years ago. But nuclear energy was around when the first stars were born and the big bang occurred. In fact, have you ever wondered how the center of the earth stays hot and keeps molten lava flowing. It is the presence of thorium and uranium changing from one state to another perpetually releasing energy and heat that causes the melting rock.

Let's look at it's chemistry. Transuranic elements are the elements that are heavier than Uranium (element 93) and more unstable than the lighter elements and no longer exist naturally. Over the earths history they all decayed or converted to other substances then vanished. An unstable element is called "radioactive" however everything is radioactive to some degree. The elements that decay the fastest and have a significant level of decay are called "radioactive" and they have a short half-life and are often the most toxic.

Uranium is getting scarce and has been expensive to process. The industry has come up with some creative ways to produce fissile Uranium including breeder reactors and the dismantling of nuclear bombs to use the Uranium for fuel. Plutonium is very familiar to us and is generally man made by using nuclear fission. Because these elements are unstable they will convert to stable or unstable isotopes meaning they will have an atomic weight more or less near the natural weight plus or minus a few neutrons. For instance 238U is the normal atomic weight of Uranium but they have some 235U and 234U mixed with it. Just trace amounts can weaken Uranium's fissile ability so Uranium is processed by chemical means either into its useful concentrated 235U or into depleted Uranium-238 which is useless for energy but used in weapons ammunition. So a fissile element is able to convert to a new element and in the process releases energy. Note:E=mC2 the famous Einstein formula which explains where the energy comes from in a nuclear reaction. What happens when observing the binding forces in order of the smallest atomic weights to the largest the atoms actually reverses their ability to bind and these atoms are described as too large. So the ideal binding elements are, no surprise, iron and nickel. But really the study of the elements properties are the key. The elements instability are caused by their size.
It's actually the opposite in gravitational forces of large bodies. The larger the object the greater the density.

Radium (element 88) was the first synthetically recreated radioactive element back in 1936. Now various isotopes of Uranium and Plutonium are the most used in Nuclear Power plants. The atomic number indicates the number of protons in an element. Fission is dependent upon the unstable elements being able to absorb the uncharged unstable neutrons. Actinides (now called Actinoids) are all radioactive and are typically created during fission in nuclear reactions. Their order starts at a lower atomic weight (89-103) than Transuranics (93-118) however they also include some of the transuranics (93-103).
Thorium has 90 protons and is element 90. In it's natural state it has an equal number of
protons and electrons.

Neutrons are uncharged and unstable. This unstable state therefore can be harmful but also very useful. Here's where the clever idea came from to manipulate the isotopes.
If you think of the nucleus as a big ball of protons and neutrons and the forces that bind them together as having a limited range of say... the diameter of an iron or nickel atom... what happens when you have a really big atom like uranium where the protons at the north pole are beyond the attraction range of the protons at the south pole?
Now the electromagnetic forces with their long range can start to cancel out some of the overall binding energy since the protons hate each other electromagnetically.
Now imagine this ball like a drop of liquid, suspended in space. Then a neutron comes along and makes it wobble... wibble... and at some point, the nucleus elongates and you have enough protons outside that short range from each other. The strong nuclear force starts to isolate to binding these two future twins and the electromagnetic force between these two hemispheres is the only force remaining.... PING... fission. The smaller pieces added together require a lot less energy to stay together because more of the protons are in range of each other. The leftover energy is that ping that sent them flying away from each other. The kinetic energy (plus the lesser gamma and neutron energies) of the 2 fission fragments flying away from each other is equal to the "mass defect" between U-235 and FP1 + FP2 (Fission Product 1 + Fission Product 2). As it turns out, all the parts put together in the original uranium atom have a higher mass than the pieces after fission. The mass difference got turned into an energy of approximately 200 MeV (pronounced mega-electron volts). Of this energy, 168 MeV is the kinetic energy of the FP1 and FP2 running away from each other, an average of 2.43 neutrons are emitted with a kinetic energy of ~2 MeV each, and a ~30 MeV gamma.

This curve is one way of expressing how all the stuff of the world behaves according to the size of it's nucleus (Uranium at 235 is really proud of it's nucleus) and compares that nucleus size to how strong each nucleon (neutrons and protons) is glued together. When we fission a heavy nucleus, we are really just taking energy that was stored as mass from when some star went kablooey a kazillion years ago and pushed a bunch of elements together very tightly, all kinds of heavy stuff was made. Since the short range nuclear force can only hold such a big atom together, all we ever find is Uranium since it's pretty stable. Who knows, maybe that Uranium atom was something really big at first but decayed to where it is now. If it wasn't for the kablooey, we wouldn't see atoms much bigger than nickel or maybe cobalt.

The Thorium Cycle
This is a process which starts as Thorium then converts to Protactinium-233 and then decays after 27 days to become Uranium 233.
Molten salt melts at higher temperature than pressurized water and it is safer in reactors because it does not require high pressures that Light Water Reactors and CANDU reactors need so that the water remains in a liquid state. Fluoride salt has some very stable qualities. Fluoride is the salt of choice for THOR LFTR's (undecided but I'm tempted to use THOR instead of LFTR's but that might defeat our cause) ... ... to be continued