Fusion Reactors
The Sun A Natural Fusion Reactor Here we go again, trying to build an efficient fusion reactor. What is the attraction to scientists of creating a fusion reactor? I guess we could look at it this way. Scientists know that there is an awful lot of energy coming from the sun that falls onto the earth. If we could harness enough of its efficiently, there would be no need for any other power source, but we can’t right now. We do feel however, that we might be able to imitate the processes of the sun here on earth. A fusion reactor is basically a miniature sun that we are taking energy from. We are able to do this now, but we need to be able to get more energy out of this reactor than we put into it and there lies the rub. So far we have not been very successful at this, but with each new reactor we seem to be getting more efficient. A fusion reactor relies on super hot plasma. This plasma is so hot that it can actually be hotter than the sun. We are talking about plasma that would be as hot as 200 million degrees. Obviously we don’t have any containers that can hold anything this hot, so how do we plan on containing it? This is done with massive magnets that hold the plasma in place. The plasma comes from a hydrogen isotope that can be found in the world’s oceans and is very plentiful. This type of reactor would be the answer to the world’s power problems and suddenly power would become a cheap commodity, if of course it is not price controlled by big companies, or governments. The way a basic fusion reactor works is that hydrogen atoms are heated to tens of millions of degrees, they collide and create helium which releases energy. The energy is changed to steam and the steam drives generators that produce electricity. Prior to the plans for a new more efficient fusion generator, the European Torus, known as JET, produced a peak output of 65% of the power that was put into it, making it completely useless for the efficient generation of electricity.
ITER is a fusion reactor that was announced in 2005. It was stated that it is being built with the plan that it will put out several times more power than it will need to take in. The next generation of an ITER type fusion reactor will be called DEMO. So why is hydrogen the fuel of choice for these fusion reactors? The reason for this is that hydrogen atoms have the smallest nuclear charge and need less heat to overcome the repulsion to each other. Helium has one of the lowest masses, so it makes a good byproduct. Different isotopes can be used that have a helium byproduct. No matter what is used, it seems that we have at least thousands of years worth of it. Looking at this from another point of view, we have enough fuel to get us to the point where we will have the technology to use direct sunlight someday, to supply the world's needs.
Tokamak The U.S. began its work on fusion reactors in 1951. It was thought that a commercial fusion plant would have been perfected long before now. The early work was code named Project Matterhorn. These early attempts faced containment issues. It was not easy trying to figure out how to contain plasma that was hotter than the sun. The first thermonuclear fusion reaction was created in the Soviet Union, at the Kurchatov Institute in Moscow. The Soviets developed the first *tokamak. The machines that are being developed today, that are expected to put out more energy than they take in, are all based on the tokamak. Even an efficient fusion reactor is not a bed of roses. There are problems that we will have to overcome, such as the machines getting brittle from all the neutron flux. Lets face it, all these atoms bouncing around can not be good for materials, so there has to be a way found that will allow us to swap out parts, without having to replace the entire reactor. People were so sure that we would be getting our electricity from fusion reactors today, that a pamphlet was put out in the 1970s by General Atomic that stated that "Several commercial fusion reactors are expected to be online by the year 2000." This just goes to show you what can happen when you try and predict the future. Scientists have decided that another way to accomplish fusion is with lasers. This was thought of in the 1960s, but we didn’t have lasers powerful enough to accomplish this, As the years went by, lasers became more and more powerful. These lasers still were not powerful enough for this task, but then something happened. In the 1980s lasers experienced a large jump in power, power that would be sufficient to accomplish fusion. It is beginning to look like the laser approach to fusion energy will be even more practical than the magnetic containment approach and be even more efficient. Additionally it is much easier to maintain a laser driven system than a magnetic containment one. Unlike today’s nuclear fission reactors, fusion reactors are not capable of producing a catastrophic accident that would produce a major release of radioactivity into the environment. That makes fusion power far safer than fission power. If you are wondering why, the answer is easy to explain. When a fusion reactor has a problem, it stays hot for days, so hot that it could melt fuel rods, even when the reactor is stopped. A fusion reactor, because of the way it is built, would cool rapidly when off, thus avoiding any catastrophe. About the worst type of accident that could happen to a fusion reactor, is a local release of radioactivity and injury to staff, but there is no chance of a runaway chain reaction. Will we finally succeed in building an efficient fusion reactor? We have been working on the project for about 60 years so far and we seem to be getting very close. It I were a betting man, I would say that we will see one in the next 20 years or less. *Wikipedia definition of tokamak - A tokamak is a machine producing a toroidal magnetic field for confining a plasma which is characterized by azimuthal (rotational) symmetry and the use of a plasma-borne electric current to generate the helical component of the magnetic field necessary for stable equilibrium. |
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