2 ms·
> Now, the mass of the support structure scales as volume X B ^2 No it does not, just as an example the fusion blanket is a constant thickness for a given leve
by Retric 2y ago
> Now, the mass of the support structure scales as volume X B ^2
No it does not, just as an example the fusion blanket is a constant thickness for a given level of neutron flux per m2 and sub linear scaling as flux increases. Same deal with your cooling loop etc.
You’re making several other mistakes, but because at a fundamental level the costs relationships are more complex than what you’re modeling.
Consider despite being a novel experimental design and having a huge research staff etc, Vogtle Electric Generating Plant still cost more than ITER to build. Sure the scale is an order of magnitude smaller, but fission has been around for a half century at this point is seemingly much simpler and you’d assume there was a great number of efficiency gains to be had. https://en.wikipedia.org/wiki/Vogtle_Electric_Generating_Plant https://en.wikipedia.org/wiki/Vogtle_Electric_Generating_Pla...
- pfdietz 2y agoYes, it does. This follows from the fact that structural mass is proportional to stored magnetic energy, just as the mass of a pressure vessel is proportional to volume x pressure (for materials of a given strength). Viewed another way: if we double B, we quadruple the forces on each segment of conductor, and therefore must quadruple the strength of the supports. I explicitly said "support structure", the structure that is resisting the force of the magnets. There are other parts that scale more slowly, but I don't need to show that all components scale poorly to show that overall there are diseconomies of scale. Note that this is NOT like in a fission reactor. In a fission reactor, everything scales just about linearly with power.
- Retric 2y ago> I don't need to show that all components scale poorly to show that overall there are diseconomies of scale. Yes you do. If A represents 0.001% of the cost then increasing it by 20x doesn’t matter and the support structure is cheap. Same deal with a fission reactor there’s several diseconomies of scale for example around the length of control rods passive cooling after an accident etc, most of them just don’t matter much.
- pfdietz 2y agoVery well. I will simply note that 2/3rds of the mass of ARC is the support structure for the magnets. And the rest of the mass includes the blanket.
- Retric 2y agoNow just look up how expensive steel is per kg vs superconductors or lithium and … ahh yea weight is a poor predictor of cost.
- pfdietz 2y agoYou do realize that almost all the mass of a PWR reactor is steel, right? The steel pressure vessel, steel supports for the fuel bundles. So the argument you are making there is that the mass discrepancy between fusion reactors and PWRs grossly understates the difference in cost.
- Retric 2y agoYour point? The cost of the reactor is just a fraction of the total cost of a fission power plant.
- reaperman 2y agoIn a separate line of inquiry, this is what I’ve been thinking about wrt fusion lately. Even if the “fusion” part were free, how much would the electricity cost just based on the steam generator turbine part? (More generally, the sum of all the non-fusion parts of a fusion power plant) Further, if electricity from a fusion plant were effectively free (like it didnt need turbines or something) what would large-scale desalination cost even if it did use truly free energy? This is what I’d be excited for from fusion power, because potable water scarcity is a huge upcoming/ongoing problem in some developing nations with very large populations.
- 2y ago