Progress toward developing nuclear fusion into a practical source of energy was in the news again recently. Present nuclear power comes from fission, splitting the atoms of a certain isotope of uranium. But nuclear power, as we have it now, had a downside. It creates wastes that will remain dangerously radioactive for centuries, and it is vulnerable to meltdowns and other accidents. It also requires the scarce and expensive 235 isotope of uranium or man-made plutonium for fuel.
The highest-profile nuclear disasters have been Three Mile Island, in Pennsylvania, Chernobyl, in Ukraine, and Fukushima, in Japan. The Fukushima disaster was caused by a tsunami. "The China Syndrome" was a 1979 movie about the meltdown of a nuclear reactor. The movie was so-called because the super-hot reactor core might burn it's way right through the earth and emerge in China.
Getting nuclear power from fusion, rather than this messy fission process, will supposedly do away with all that. Fusion means combining atoms together, rather than splitting them apart, and is the process that takes place in stars including the sun. Both processes release energy, fusion far more, and any material can theoretically be used in the fusion process. The fusion process produces no dangerous radioactive wastes.
Part of the problem with nuclear energy is that it's early proponents made too many promises. Energy would be so inexpensive that we wouldn't even bother metering it. When that never became reality it made nuclear power look like somewhat of a failure, even though it really isn't.
But here we go again with the development of fusion. Pretty soon we will live in a fusion wonderland. All of the energy that we could possibly need will be produced cleanly and efficiently. Along with electric vehicles this will save the environment, and we will all live happily ever after.
The trouble is that we will be dealing with temperatures and energies that we have never dealt with before. That is the great challenge of fusion, how to contain the process. We are replicating the process that goes on in the center of the sun and no material on earth can withstand it. Before combining into larger atoms the original atoms first come apart into a state of matter called plasma. The approach is to suspend the process in a magnetic field. The most common device for accomplishing this is called a Tokamak.
When the first nuclear bomb was detonated, in New Mexico in 1945, no one knew exactly what was going to happen simply because there had never been a known nuclear explosion on earth before. Some people were worried that it might cause the atmosphere to ignite. But the test went as planned and nothing of the kind happened.
But today we keep reading reports that we are getting closer to making nuclear fusion, as opposed to fission, into a practical source of energy, and I think we should take another look at this concern.
Nuclear fusion is what forms all elements, other than the hydrogen and helium and traces of lithium that formed in the Big Bang. Atoms are usually kept separate from one another because the negative electric charges of their outermost electrons mutually repel. But when enough matter is brought together by it's common gravity the pressure at the center of the mass is enough to overcome this mutual repulsion and crunch smaller atoms together into larger ones.
All mass contains a certain amount of internal energy, known as the Mass-Energy Equivalence. But when atoms are crunched together like this the new larger atom contains less internal energy than the smaller atoms that formed it. This excess energy is released as radiation. The volume of mass that has enough force, by it's mutual gravity, to crunch smaller atoms into larger ones is known as a star, and the release of the excess energy is why stars shine. The energy released adds to the heat inside the star and it is this tremendous heat and pressure that continues the fusion process. Our sun is presently at the stage of fusing four hydrogen atoms into one helium atom, but it contains heavier elements because it is a second-generation star.
Fusion is the crunching of small atoms into larger ones, usually by the tremendous heat and pressure in the centers of stars. The opposite process is fission, the splitting of large atoms usually by high-speed neutrons. Both processes release energy, but fusion releases far more energy per mass.
All of the nuclear energy that we use at the present time is from fission, the splitting of either the 235 isotope of uranium or plutonium. Efforts have been going on for a long time to get energy from fusion. We can fuse smaller atoms together into larger ones, one way is by using lasers, but, as of this writing, no one has yet made fusion into a net source of energy, meaning that we get more energy out of the process than we put into it. However the latest news is that we are making definite progress in that direction.
Fusion is what makes so-called "thermonuclear" weapons so much more powerful than an ordinary atomic bomb. A thermonuclear weapon is also known as a hydrogen bomb. In such a bomb an ordinary atomic bomb acts as a mere detonator, bringing about the heat and pressure needed to start the fusion process.
The easiest atoms to fuse, those requiring the least energy, is the hydrogen isotope know as deuterium. Ordinary hydrogen is the simplest and lightest atom. An ordinary hydrogen atom is just one electron in orbit around one proton. But there is an isotope of hydrogen, deuterium, which has a neutron, as well as the proton, in the nucleus.
When atoms are fused together heavier atoms typically have a higher neutron-to-proton ratio in the nucleus. A neutron is formed by crunching an electron into a proton, the process known as K-capture. Deuterium is the easiest to fuse because, unlike ordinary hydrogen, it has a neutron already there.
A molecule of water is two atoms of hydrogen and one of oxygen, the familiar H2O. If the hydrogen atoms are deuterium, with the neutron in the nucleus, it is about 10% heavier than ordinary water, and known as "heavy water". Heavy water is useful in nuclear processes because, as a moderator it won't absorb neutrons because it's hydrogen atoms already have neutrons, and, as fusion material because it's hydrogen atoms have neutrons already there.
Within a thermonuclear weapon, or hydrogen bomb, an ordinary atomic bomb, based on the fission (splitting) by high-speed neutrons of either plutonium or the 235 isotope of uranium, acts as the mere detonator to provide the heat and pressure to get the fusion process going, which may use heavy water as a fusion material. In a typical design the extremely high-energy X-rays from the initial explosion will be enclosed by a radiation case so that they will bring about the fusion in the split second before the entire bomb is blasted apart. The radiation case can itself be made of fissile material, uranium, to add to the explosive yield.
With that background let's go back to the concern, in 1945, that the first nuclear test might cause the atmosphere to ignite.
Most of the air around us consists of nitrogen and oxygen. The atoms of nitrogen and oxygen are diatomic, meaning usually two atoms of nitrogen together as well as two atoms of oxygen. If such a diatomic molecule of oxygen has a carbon atom attached it forms carbon dioxide. There is also water vapor in the air. Air is thus a mixture, rather than a chemical compound, there is no such thing as a molecule of air.
(Note-My theory is that it is these diatomic molecules of nitrogen and oxygen in the air that result in circular storms, such as hurricanes, tornadoes, cyclones and. typhoons. If the molecules spin, and the spin of the long axis gets coordinated with other molecules, the result will be a circular storm. Of the air just consisted of single atoms there would be no circular storms. The same principle applies to water molecules linking by hydrogen bonding. If not for this there would be no eddies or whirlpools in water).
Here is the danger of atmospheric ignition. Now that we are reportedly getting closer to making nuclear fusion a practical source of energy, which involves tremendously high temperatures and energies, what if we reached a point where there was so much energy in such a confined space that it caused the diatomic molecules of oxygen and nitrogen in the air to start fusing into a single atom?
If we fused two atoms of nitrogen together we would get an atom of silicon. If we fused two atoms of oxygen together we would get an atom of sulfur. But remember the reason stars shine. After fusion the new larger atom contains less internal energy than the atoms that were crunched together to form it. That energy must be released. What if that energy caused two more oxygen or nitrogen atoms to fuse, and that excess energy was released, and the process continued?
The atmosphere would literally ignite.
If an atomic bomb is detonated on sand, the tremendous heat and pressure may fuse the sand into glass. But that is just chemical fusion, combining atoms into molecules without affecting the nucleus of the atom. Nuclear fusion, as takes place in stars, is actually combining atoms to make completely different atoms.
Ordinary ignition, such as burning fuel, is just chemical ignition. Molecular bonds between atoms contain energy, and breaking the bonds releases that energy. If the molecular bonds in a material release more energy than it takes to break the bonds, that material will burn. What I am referring to here is a similar concept, but the far greater energy being both released and required by nuclear fusion.
It is not so much the actual amount of energy being released, a vast amount of energy is released already by nuclear tests and reactors and even by lightning, it is rather energy density, confining the energy to a very limited area as does the radiation case in a thermonuclear weapon.
I consider this as the fusion version of a reactor meltdown but, unless it could be stopped, would destroy life on earth. I am not saying that this is going to happen, just that we should give it some thought. It doesn't just apply to the air, but also to the earth and the water of the sea. It wouldn't go any further than iron, because the ordinary fusion process only goes as far as iron, but fusion ignition could theoretically turn everything on earth into iron.
No comments:
Post a Comment