Small Modular Nuke Plant Proposed, This Time for Fusion
Despite frequent hopes to the contrary, Mr. Fusion still lives firmly in the realm of science fiction. The two primary methods of obtaining fusion—inertial confinement and tokamaks—date from the 1950s. While they've been refined and improved, we're still a long way off from generating power with it.
But the rest of the research world hasn't stood still, and developments in other areas of research have been gradually reshaping the fusion landscape. Now, researchers from MIT are claiming that high-temperature superconductors can produce magnetic fields that would allow a compact, modular fusion reactor. Because of its modular designs, researchers could easily swap out parts to try new configurations. Oh yeah—they also calculate it should work as a power plant as well.
The team is calling the new tokamak design ARC, for affordable, robust, compact. In fusion research, most of those terms are relative. Compact still allows a fusion chamber that's about four meters tall, making for a building-sized facility. "Affordable" in fusion allows for a cost estimate that runs in the neighborhood of $5.6 billion. The vast majority of that cost comes from the superconducting wiring, which is estimated to run at $4.6 billion. Mind you, that much money would buy you 5730 kilometers of superconducting wiring. A few of these reactors would probably float the superconductor manufacturing industry out of its infancy.
(The authors estimate that the REBCO ribbons would have a usable lifespan of about nine years in the radiation-heavy environment of the reactor. But so little is known about the response of this material to radiation that this is little more than an educated guess.)
Rather than metal, the wiring would be rare-earth barium-copper-oxide superconducting tape, or REBCO. (The formula for this material is (RE)Ba2Cu3O7-x, where RE is a rare-earth element, often Yttrium.) In a draft paper, REBCO wiring has been reported to produce magnetic fields over 35 Tesla; the ARC design only needs 20T fields. Even so, "The total stored magnetic energy in the [magnetic] coil system is approximately 18 GJ."
While REBCO can remain superconducting up to 80K, the authors plan on cooling the magnets to 20K. So, the design has a bit of headroom should things not work out quite as hoped for. And that's probably a good thing, given that lots of things about the plant haven't been tested yet. These include the shape of the containment field that holds the plasma in place and the method of transferring energy in to the plasma itself. All of this relies on things most of the fusion field is excited about, but they still need to be validated through experimentation.
Another major untested material will be a mixture of molten salts of lithium fluoride and beryllium fluoride. This will completely surround the fusion chamber, and serve multiple purposes. For one, it will transfer heat out, something that will be essential if this thing is ever used to generate power. It also acts as a shield for other components, absorbing some of the stray neutrons produced by the fusion reaction. And, because it's a liquid, the salt doesn't suffer from the structural decay seen in metal shielding.
Finally, some of those neutrons will induce atomic rearrangements that will result in tritium production. Tritium is a heavy, short-lived isotope of hydrogen, and acts as fuel in the fusion reaction. So, the ability to produce more of it is essential for keeping the reactor sustainable; the authors write about making sure "they do not jeopardize the world tritium inventory."
Read more here:
http://arstechnica.com/science/2015/08/small-modular-nuke-plant-proposed-this-time-for-fusion/