15 ms·
Too little, too late. The traditional fission industry is being killed by high CAPEX and nothing about the current tokamak based designs suggests they will be a
by manholio 5y ago
Too little, too late. The traditional fission industry is being killed by high CAPEX and nothing about the current tokamak based designs suggests they will be any cheaper to build for a given power rating:
- They need large, highly advanced cryocooled superconducting magnets in very close proximity to a hundred million degree plasma. This only makes economic sense in massive, and expensive plants.
- They are a very strong source of fast neutrons useful to transmute cheap depleted uranium into plutonium, so carry massive proliferation risks, need close regulatory scrutiny and will require mounts of paperwork to operate, thus exceptionally inflexible to improvements and rapid iteration. Just like the current fission crop.
- Aneutronic fusion is a currently a purely theoretical concept, in the last 70 years nobody has been able to contain even the much cooler D-T plasma for economically viable durations and temperatures.
- The structure of the reactor becomes radiologically active and cleanup operations must be considered. Highly penetrating neutron radiation means some radiation will escape regardless of containment, requiring a radiological exclusion zone. No Mr. Fusion in your car, sorry.
- They operate and must breed sensitive nuclear materials - Tritium, a well known component of boosted thermonuclear weapons. The limited efficiency of tritium production from lithium-6 might require obtaining some from fission reactors to top up the fuel cycle and keep fusion reactors operating.
So when you draw the line, a life time of magnetic containment research has produced a speculative design that even if it were to work, which it doesn't, would be, in the best case scenario, comparable to existing fission designs that are being phased out for cost and risk issues.
A PhD money pit with zero chance of ever building anything useful. I know it, you know it, I'm ready for the proverbial downvote protecting one's paycheck from their own knowledge.
- Izikiel43 5y agoCheck Sparc before all that stuff, iter is outdated but there are alternatives being worked on.
- manholio 5y agoWhen SPARC ignites, 5 years from now, and when it achieves long burns at Q=10, after a good few more years, then I will redact the "nobody has been able to contain D-T plasma for economically viable durations and temperatures" part. The rest of the points will probably remain true decades into the future, though.
- gameshot911 5y agoThis is a really nice, well-informed post. Out of curiosity, why do you prefer to post it under a throwaway account?
- manholio 5y agoIt's a real account, see my very first post on it for details. Sorry, to disappoint, nothing up my sleeve.
- willis936 5y ago>The limited efficiency of tritium production from lithium-6 might require obtaining some from fission reactors to top up the fuel cycle and keep fusion reactors operating. Citation needed.
- manholio 5y agoSince nobody has yet demonstrated tritium breeding, a citation is actually not needed. There exist purely theoretical models where neutron multiplication is used so that the single fast neutron generated in a D+T reaction can breed more than a single tritium atom when it hits li-6 (which would be clearly insufficient to have a self fueling rector). It's all a complex mess of absorption cross sections and neutron spectra, dependent on lithium blanket geometries, coolant and structural material parasitic interactions. The tritium breeding efficiency today sits at exactly 0% and until that changes, concerns that it may never reach the required 110% are at least somewhat warranted.
- willis936 5y agoFrom the talks I've been to the targeted performance of blankets is 120% and simulations predict this should be possible without prohibitively thick blankets. ITER's TBM will be doing important work to test theory. It isn't clear to me that external sources of tritium will be necessary. Between Li-6 fission and Be neutron multiplication there is theoretically plenty of neutrons to go around even though they aren't easy to capture. Viability of blanket breeding hasn't been demonstrated to work yet, but my original point is that it hasn't been demonstrated to not work. I see now the "might" in your statement.
- manholio 5y agoSure, by the "it hasn't been demonstrated to not work" standard the whole field should generate cheap electricity tomorrow. Just that it's so unimaginably, fiendishly hard to make it work, perhaps the most challenging technical problem in history. It might never work, for interesting values of never. My point was that fueling is in itself a very difficult and complex problem that has yet to be solved, far from the "it runs on seawater" popular tropes.