Fusion is not Fission
Fission and Fusion are both Nuclear Energy. When people discuss nuclear power, they are usually referring to nuclear fission. This is because we have many nuclear power plants that use fission, but no one has been able to build a working fusion plant yet. The biggest practical difference between the two is that fusion reactions don’t have the problem of “chain reactions” and “melt-downs”.
- The Difference Between Fission and Fusion
- Nuclear Fission - Splitting Atoms
- Fusion Alternative
The Difference between Fission and Fusion
The main difference between fission and fusion is that in fission, a large nucleus is split apart into smaller ones, and in fusion, two nuclei are combined (fused) into a larger one. (With Hydrogen-Boron fusion, the hydrogen fuses to the boron-11, temporarily creating an unstable isomer of carbon-12 which immediately breaks apart into three Helium nuclei. Some have said this makes it a fission reaction, but it’s not, as explained in this faq). Both processes release vast quantities of energy. (See simple animation of fission, and an explanation of deuterium-tritium fusion).
It takes less energy to split two atoms with fission than it does to fuse two atoms, which is why fission reactors were developed first, and why fusion reactors have not been developed yet. Despite this, the promise of fusion has always been greater than that of fission.
Nuclear Fission - Splitting Atoms
HOW FISSION WORKS: In a commercial nuclear power plant, a sufficiently large quantity of fuel material (usually enriched uranium) is accumulated in a reactor pile such that a “chain reaction” occurs, in which the neutrons emitted by a single fission reaction are captured by another nucleus to trigger another reaction, and so on. This solcomhouse.com link explains the basics of nuclear fission and has some good schematic illustrations of nuclear power plants. [Here’s one of a pressurized water reactor.]
ENERGY EFFICIENCY: When nuclear reactors were first designed, the promise was that energy was going to be so cheap it would no longer be worth metering. In practice, however, the costs of operating a nuclear power plant are very high and result in high energy prices.
These costs are not related to fuel. If we were measuring energy efficiency as the simple output of energy based on fuel mass put into the equation, fission has much more energy efficiency than oil (but is still 3 to 4 times less than fusion energy. In fusion, the amount of mass transformed into energy is much greater than in fission, as smaller particles fuse together to create the energy).
The inefficiency comes into play when you consider that the nuclear fuel creates heat. This heat is used to boil water which produces steam. The steam turns a turbine to generate electricity. This transformation of heat energy into electric energy is cumbersome and expensive (Note: many current models of fusion energy also have the same heat to electricity inefficiency built into the design. The beauty of the Plasma Focus Device championed by this website is that it proposes to generate electricity directly, thus reducing powerplant cost and complexity).
A second source of cost/inefficiency is that once the nuclear fuel is used up, it must be disposed of, and at the end of its life, a nuclear power plant needs to be decomissioned. Cleanup and storage of nuclear waste is very expensive because the waste is radioactive (see below).
And finally, security issues add to the cost of nuclear energy (see security).
RADIOACTIVITY: Current nuclear reactors use uranium or plutonium fission to produce electricity. Uranium and plutonium are both radioactive. During the fission process, there are many ways a radioactive atom can split apart so the two smaller atoms, called reaction products, will be from a set of various elements. But these elements all have one thing in common. They are all radioactive.
The fission process is designed to split a nucleus apart into two smaller atoms and some high energy neutrons. These neutrons slam into whatever is in their path. This creates heat which in a nuclear power plant is used to boil water to run a steam powered generator. However, heat is not the only thing neutrons produce. A neutron can enter the nucleus of a non-radioactive atom and make it radioactive.
So fission power plants have three problems with radioactivity:
* The fuel is radioactive.
* The reaction byproducts are radioactive.
* The high energy neutrons can take ordinary materials in the reactor building and make them radioactive.
These materials are radioctive for a long time, hundreds of thousands of years. Nuclear fuel waste disposal is a complicated problem as you will see in this link on Nuclear Waste Storage.
Fun Nuclear waste link: Yucca Mountain Youth Zone.
And here is a site that feels the danger is overstated, especially if the industry uses “nuclear fuel recycling” to reduce the volume of waste.
Whatever your stand is on the nuclear waste issue, the debate takes place in the context of a limited fuel resources scenario. The pro-nuclear authors like to ask “what happens when the oil eventually runs out?” (The Canadian Nuclear Association Website has a plethora of speeches along this line such as the keynote presentation by Murray Elston entitled “CERI 2004 Electricity Conference - Nuclear Energy: An Essential Part of the Energy Mix Monday, December 06, 2004.” The pro-nuclear crowd also like to point out the clean air benefits of nuclear in articles like: “Finland Must Build Sixth Nuclear Power Station To Reach Kyoto Goals”)
This presumes that we have no other option but to rely on nuclear fission and deal with the divisive political problems of radioactive waste. Luckily, fusion looms on the horizon, and this debate will soon be moot.
SECURITY ISSUES: It’s true that some nuclear- fuel-recycling enthusiasts feel that the dangers of radioactive waste are overrated. Nevertheless, the US adopted a moratorium on nuclear fuel recycling in 1977 in order to reduce potential nuclear proliferation among non-nuclear nations. The recycled plutonium, apparently, can be used to make bombs. This is one reason why the US is reluctant to allow countries such as Iran to pursue nuclear energy programs.
The Focus Fusion Alternative
What many people don’t know is that there is an alternative called focus fusion power which is fundamentally different than the nuclear power in use today. It is truly a clean and safe alternative to fossil fuels and nuclear fission. Instead of splitting atoms, a fusion power plant takes small atoms such as hydrogen and fuses them together to make bigger atoms. This produces much less radioactive waste, and if the right atoms are chosen it produces none at all.
We know that fusion is possible. It is the energy source that powers the sun. It has also been demonstrated in laboratories on earth, but no commercially viable fusion power plant has yet been developed.
One reason for this is that fusion does not happen spontaneously like fission. For fusion to occur the atoms must be confined in a magnetic field and raised to temperatures of 100 million Kelvin or more.
This takes a lot of electricity, and the trick is getting out more electricity than you put in.
However, this has a serendipitous safety advantage. Fusion reactors cannot sustain a chain reaction so they can never melt down like fission reactors. Simply turn off the power and the fusion stops.
While fusion holds great promise, conventional approaches to fusion still have a lot of drawbacks. Please read this comparison of conventional fusion vs. focus fusion to see the difference.