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Fusion Power: The Burning Issue
ITER core. This huge cost difference is unlikely to be dramatically reduced by further development for the following reasons:
- Net fusion power from tokamak plasmas requires a very large plasma volume with an expensive structure surrounding it;
- DT fusion produces high-energy (fast) neutrons, which require large volumes of materials to capture neutron energy and slow down neutrons for easy capture;
- The tokamak is inherently a huge, hollow torus while a fission reactor core is a comparatively small, right circular cylinder; and
- In general, the more materials in a piece of equipment, the more expensive it will be.
It Gets Worse
Because of the inherently high neutron fluxes associated with DT fusion, large amounts of radioactivity will be generated in the blanket region, and the blanket structure will rapidly suffer major radiation damage. That damage will necessitate replacement every few years. 1 Blanket replacement would represent an incredible challenge because access to the inside of the tokamak donut would be dramatically restricted by huge superconducting magnets, which surround the plasma chamber and blanket. Because of the high induced radioactivity inherent to DT fusion, blanket replacement would have to be carried out by robots. Their tasks would include cutting the blanket structure into pieces, removing those pieces to a safe area for compression to minimum volumes, then inserting new blanket elements, connecting related plumbing, and making hundreds of meters of vacuum-tight welds capable of withstanding high temperatures and repeated thermal cycling.
If the blanket region in a fusion power reactor were made of stainless steel, as in ITER, then that fusion reactor would generate on the order of 10 times the radioactive waste of a fission reactor. 2 If ferritic steel were used instead, the induced radioactivity is projected to be a roughly comparable fission in terms of curies/watts, but the volume would be much greater. 5 Since all such operations would present significant safety concerns, a high level of regulation surely would be required based on those factors alone.
Fusion technologists properly point out that radioactivity induced in fusion is less noxious than fission products, and their point is well taken. Still, it remains to be seen how the public would react to the production, handling, shipment, and storage of huge quantities of fusion radioactive waste. Parenthetically, the consumption of fuel in DT fusion would be volumetrically trivial, but the consumption of structural materials would be enormous; in effect, DT tokamak power reactors could almost be characterized as "fueled" by structural materials.
So, how does all of this add up? First, the physics of DT tokamak fusion would make it inherently much more expensive than fission power. Second, because high levels of radioactive waste would be generated in DT tokamak fusion, high levels of safety and regulation would almost certainly be required. Third, it is not at all clear how the public would react to these inherent characteristics, but it is likely that reactions would be negative because of related high electricity costs and various safety concerns.
All of this stands against a background of fusion being touted as low cost, clean, and