Latest posts by Nancy Thorner (see all)
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According to a February 12 article in USA Today by Wendy Kock titled “Quest for pollution-free fusion energy takes major step”:
The decades-long quest to develop a pollution-free energy source via nuclear fusion — the power source of the sun and other stars — has taken what scientists say is a major step forward.
The article cites a study by the National Ignition Facility (NIF) at the government funded U.S. Department of Energy’s Lawrence Livermore National Laboratory in which a lab experiment produced more energy out of fusion than was put into the fuel that sparked the reaction. What followed in the article was an admission that the lab results fell short of what is considered the “holygrail of fusion: ignition — the point at which more energy is produced than was used throughout the process.”
A day later, February 13, the quest to develop nuclear fusion was questioned by James Conca, a Forbes.com contributor, in his article, “Do We Really Need Nuclear Fusion for Power”:
Why build a fission reactor to make tritium via neutron capture on deuterium to make the fuel for a fusion reactor, when you could just use the fission reactor to make the energy ion the first place?
Ed Ingold remembers his father-in-law saying there is enough uranium above ground, much of it stored in Oak Ridge, Tennessee, where he worked, to power 1,000 reactors of 1,000 MW each. To put that in perspective, each of those reactors would have twice the output of all the windmills in the US.
So-called “fast” reactors refer to the harnessing of high energy (fast) neutrons to “burn” naturally occurring uranium 238. Unfortunately, the Fast Breeder Reactor Project at Oak Ridge National Laboratories (ORNL) was halted by the renowned “nucular [sic] engineer,” President Jimmy Carter, and the scientists involved were re-tasked to harnessing the limitless power of coal. The other “nuclear” problem, spent fuel disposal, can be credited to another famous Navy veteran, President Richard Nixon, who halted development of fuel reprocessing. We aren’t burying nuclear ashes. To the contrary, only about 5 percent of nuclear fuel is consumed before fission products accumulate, absorbing neutrons, until the fission reaction cannot be sustained.
Fusion reactors don’t burn “limitless” fuel, vis-à-vis hydrogen, like the sun. They burn relatively rare isotopes of hydrogen – deuterium and tritium. Deuterium constitutes only 0.016 percent of naturally occurring hydrogen, as found in water. The separation process consumes huge amounts of electricity and a vast supply of water. A 200 MW power station, dedicated to producing deuterium, would yield about twelve liters of “heavy water” (D2O) a year. Tritium does not occur naturally (12 year half-life), but is made in fission reactors. As the good professor points out in the linked article, you can make tritium on the fly by irradiating lithium with fast neutrons. Incidentally, that’s how it works in a hydrogen bomb, packed with (among other things) solid lithium deuteride. One downside is that 99 percent of the world’s lithium is found in the mountains of Peru and China, and most of what we import goes into batteries.
There also some questions about the “limitless” energy available from fusion reactions. The project hailed in the Forbes article uses a D+T reaction, which yields helium and a fast neutron. About 80 percent of the energy of this reaction is imparted to the neutron. The tritium (T) comes from neutron bombardment of lithium, which is endothermic (consumes energy).
The net result is 99 percent of the energy is in the form of fast neutrons. Since neutrons don’t interact well with materials, only about 30 percent of this energy can be converted into heat for turbines, and replacing the heat needed to sustain the fusion reaction. The by-products of the fusion reactions are not radioactive (other than tritium, which is difficult to contain), but the neutrons render everything they contact radioactive. In short, instead of burying spent fuel, you bury the reactor, once the materials of its construction are transmuted until they are not structurally sound.
It’s also puzzling why it’s claimed that this experiment produced more energy than it consumed. The brief (7 billionths of a second) reaction released about 9,400 joules of energy due to the fusion reaction, above that used to heat the reactants. To achieve this, approximately 1.8 trillion joules of energy was imparted by a bank of X-Ray lasers, which occupy a 10 story building with a footprint of over an acre. It’s like an inveterate gambler who brags about $500 of winnings, after laying down $5,000 on the ponies during the season — or Congress, where spending less than you wished is called savings.
There’s nothing wrong with the science, and it’s important to continue. For the foreseeable future, we should recognize that the most important gains are in the form of knowledge and technology, rather than a viable source of electricity. How few men stepped on the moon, but who doesn’t benefit from the technology which came out of the Apollo project? Who hasn’t worn or used something made of Teflon, used a computer, watched a program broadcast by satellites, or handled a cell phone? Someday there will be a Scottie who knows just what to do with a dilithium crystal or two.