A friend of mine who was trained as a physicist used to joke about a future in which each of us would carry handheld fusion reactors that plug in anywhere to provide copious amounts clean energy for our homes, automobiles, offices and factories.
The reality of fusion power, however, is one of huge scale and vast obstacles according to Daniel Jassby, a former research physicist at the Princeton Plasma Physics Lab. (All of what follows assumes that the remaining obstacles to producing net energy from fusion will be overcome. Addressing that issue would require a seperate and lengthy essay.)
Perhaps the most unexpected revelation Jassby offers runs entirely contrary to the clean image that fusion energy has in the public mind. It turns out that the most feasible designs for fusion reactors will generate large amounts of radioactivity and radioactive waste.
As Jassby explains, inside the Sun, which is powered by fusion, normal hydrogen atoms, each consisting of nuclei containing one proton, are fused together and produce helium plus energy. Here on planet Earth, fusion reactors "burn neutron-rich isotopes [that] have byproducts that are anything but harmless: Energetic neutron streams comprise 80 percent of the fusion energy output of deuterium-tritium reactions and 35 percent of deuterium-deuterium reactions." (Deuterium is a hydrogen atom consisting of one proton and one electron in its nucleus. Tritium is a radioactive form of hydrogen having one proton and two neutrons.)
Jassby details the consequences:
[T]hese neutron streams lead directly to four regrettable problems with nuclear energy [both fission and fusion]: radiation damage to structures; radioactive waste; the need for biological shielding; and the potential for the production of weapons-grade plutonium 239—thus adding to the threat of nuclear weapons proliferation, not lessening it, as fusion proponents would have it.
He explains what this means for the operation of fusion reactors:
[I]f fusion reactors are indeed feasible—as assumed here—they would share some of the other serious problems that plague fission reactors, including tritium release, daunting coolant demands, and high operating costs. There will also be additional drawbacks that are unique to fusion devices: the use of a fuel (tritium) that is not found in nature and must be replenished by the reactor itself; and unavoidable on-site power drains that drastically reduce the electric power available for sale.
So, you may be asking: Why don't scientists just use ordinary hydrogen instead of deuterium and tritium isotopes? Our attempts to re-create the Sun's power on Earth face "much lower particle densities and much more fleeting energy confinement," Jassby explains. That's why scientists use deuterium and tritium "which are 24 orders of magnitude more reactive than ordinary hydrogen." That's 1024 times more reactive and therefore 1024 times EASIER to fuse under the considerably less favorable conditions we can create here on Earth.
"This gargantuan advantage in fusion reactivity allows human-made fusion assemblies to be workable with a billion times lower particle density and a trillion times poorer energy confinement than the levels that the sun enjoys," Jassby explains.
The neutrons which are liberated in this type of fusion have to go somewhere. Over time, just like in nuclear fission plants, these neutrons damage the reactor vessel wall. One design addresses this issue by encapsulating the fusion fuel in a "one-meter thick liquid lithium sphere or cylinder." This will create tons of radioactive waste that has to be removed annually. Without this approach the vessel walls will have to be replaced periodically and then transported to waste disposals sites. Scientists are working on better reactor vessel materials.
This problem is less pronounced using just deuterium as fuel. But deuterium alone is 20 times LESS reactive than a deuterium-tritium mix making it harder to successfully create deuterium-only fusion. In addition, deuterium-only reactors make ideal breeding environments for plutonium-239, atomic bomb material that can be made by introducing uranium-238 into the reactor.
(Uranium-238 is much cheaper and far more plentiful than uranium-235—which makes up only 0.7 percent of mined uranium and which is the only naturally-occurring fissile material. Bombarding uranium-238 with neutrons is a good way to make plutonium-239, a fissionable product suitable for atomic bombs.)
To power the enormously energy-intensive process of fusion, a fusion plant will use a lot of energy just to run itself. That means scale will matter. In order to accommodate this so-called parasitic power drain AND produce enough excess electricity to sell to pay for the costs of constructing the plant and for its ongoing operation, fusion plants will have to have a capacity of at least one gigawatt (one billion watts). One gigawatt can supply electricity to 300,000 to 750,000 homes depending on how the calculation is done. And, even much larger capacity per plant will be desirable because it will decrease the percentage of power production devoted to sustaining the fusion reaction and servicing the plant infrastructure. In short, making fusion plants big will be the only way to make them economical. So much for my friend's fantasy of handheld fusion power units!
In a second article, Jassby addresses the International Thermonuclear Experimental Reactor (ITER) located in France. The project is a cooperative research venture designed to study and perfect fusion. It will not produce any electricity itself, but rather set the stage for so-called demonstration plants which could be built in the second half of this century.
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This experimental reactor has the drawbacks listed above. The timeline it offers for practical fusion makes one wonder just how useful fusion energy, if made economical, will be in addressing urgent concerns about reducing carbon emissions. Of course, there is the obvious issue of having to build such plants using existing energy sources which are mostly based on fossil fuels. And, just to operate its experiments, ITER will require 600 megawatts of power, a window into the parasitic power requirements of fusion reactors.
The fantasy of cheap, unlimited fusion power arriving soon with no serious side-effects prevents us as a society from grappling with near-term energy depletion and our ongoing dependence on fossil fuels in the accelerated manner required to prevent a major energy crisis. Hope that fusion energy will somehow solve our energy and climate problems is not a real plan. It is just another illusory and far-in-the-future technical fix offered to convince us that we don't need to alter our way of life in any substantial way to address the serious problems we face.
By Kurt Cobb via Resource Insights
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