- The end product of Deuterium + Tritium is regular, stable Helium, making waste disposal both safe, and cheap
- The input of the process, heavy water, while not safe, is way less dangerous than thorium or uranium
- The whole process is no way involved with nuclear weapons, making security concerns much less relevant
- Since the process produces magnetically charged plasma, steam turbines are not necessary, a solution of directly harvesting energy with electromagnets was proposed.
Direct harvesting is not possible with the fusion reactions we are currently working on. The products are electrically neutral, so the only way to harvest the energy is as heat.
Helium-3 fusion produces charged particles, which it might be possible to directly harvest as electricity. The He3 fusion reaction has a high activation energy, which is currently unachievable, and there is no Helium-3 on Earth. We'd have to get it from space, somehow. (The movie "Moon" was set on a Helium-3 mining outpost on the Moon.)
Conveniently, pure deuterium fusion (D-D) is easier than D-He3 fusion, and the output of D-D fusion is half He3, and half tritium which decays to He3 with a 12-year half-life. So if we can get net power from He3, we can make He3 from deuterium and generate energy in the process.
D-D fusion does produce neutrons but they're much lower energy than D-T neutrons. Fusion startup Helion is working on a hybrid D-D/D-He3 reactor, saying the combination will produce only 6% of its energy as neutron radiation, low enough so they can do direct conversion.
They've built half a dozen reactors, and now they're working on a seventh that they'll use for a net power attempt around 2025. They recently had a fundraising round led by Sam Altman, and raised $500M with another $1.7 billion of commitments based on milestones.
There is no usefully available Helium-3 on the moon, either. The only practical source known is decay of tritium, which must itself be synthesized by nuclear reaction, and is, for military use.
Another choice is fusion of ordinary hydrogen, usually labeled "p" for the proton, with boron, B, thus "pB". But that is even harder to achieve. Still, it is being worked on.
There is no route to commercially viable fusion extracting heat from Tokamak reactors, as any such reactor would need to be enormously bigger and much more expensive to operate than the same-rated fission reactor, which is not today competitive, and gets less so all the time.
Some people hope that something can be learned from Tokamak work that might be applicable to potentially practical designs, but the money is all going to Tokamak, while the others mostly go begging.
(Note that you can drink a lot of pure heavy water without worrying about any health impact. I still wouldn't recommend it, but bad things would be unlikely to happen by accident.)
> You could consume a single glass of heavy water without suffering any major ill effects, however, should you drink any appreciable volume of it, you might begin to feel dizzy. That's because the density difference between regular water and heavy water would alter the density of the fluid in your inner ear
> magic heavy chemical water with different nuclear properties...
That seems a bit dismissive. I would naively assume that there have been exactly zero studies to see if there are any problems with babies drinking heavy water, beyond some LD50 extrapolation.
Another big one is the default-to-safety nature of fusion vs. fission. With fission, if things go wrong, the nuclear process often speeds up and can run out of control. With fusion, generally when things go wrong temperatures dissipate and the fusion process halts naturally.
The amount of helium will be much lesser than what you think it is. If we produce all the energy in the world using fusion, it will create less helium per day than a tank used by kids helium balloon shop.
> If one ton of deuterium were to be consumed through the fusion reaction with tritium, the energy released would be 8.4 × 10^20 joules[1]
That's 0.84 exajoule(233 TWh) per kilo of deuterium or 0.42 exajoule(117 TWh) per kg of helium produced. World energy consumption is 1.6 exajoule per day[2] so less than 4 kg helium will be removed per day if energy extraction is perfect or few 10s of kg assuming imperfection
Your energy estimate is off, but also ~10kg of helium is ~56 cubic meters or ~2,000 cubic feet that’s several large helium tanks which run around 291 cubic feet as that’s a serious pain to move around without a hand truck.
Actual fuel fuel estimate: “a 1000 MW coal-fired power plant requires 2.7 million tonnes of coal per year, a fusion plant of the kind envisioned for the second half of this century will only require 250 kilos of fuel per year, half of it deuterium, half of it tritium.” https://www.iter.org/sci/FusionFuels
“Global electricity consumption in 2019 was 22,848 terawatt-hour”
22,848 * 1000 / 365 / 24 = 2608 different 1GW reactors each producing 250kg of helium per year. So 652,000 kg/year if all the worlds electricity was made from fusion or ~3,650,000 cubic meters or ~130,000,000 cubic feet of helium.
PS: Efficiency numbers could wildly change those estimates, but that’s the rough ballpark for electricity let alone stuff like transportation or home heating etc.
You are talking if helium is stored in atmospheric pressure. It is generally sold compressed like all other gas. Search google for 10kg helium tank. In my area it is available for $30.
That’s the weight of the tank not the helium inside it. They should advertise it as filling ~30 helium balloons. Which obviously weigh far less than 10kg or they wouldn’t float.
The ~300 cubic foot tanks are 9 inches in diameter, 55 inches tall, with about 130 pounds and contain about 1.5kg of helium.
Missing, arguably the most important factor: It is not a runaway reaction. You don't need a giant pool of water with functioning pumps to mitigate a disaster. There are some newer designs that are self-regulating but surprised to see this is not at the top of the list.
It's not possible to have a runaway reaction in a light water reactor either. The major incidents (TMI and Fukushima) happened as the reactor cooled down. It's just that the power output of the decay heat is enough to cause problems.
Heavy water is not a radiological hazard, but it's toxic [1]. I doubt there have been definitive experiments on humans (for obvious reasons). I wouldn't try substituting it for ordinary water.
It is toxic when you ingest >20% of your body weight. Let's just say that that sort of thing won't happen by accident.
(And to point out the obvious, every other liquid apart from drinking water is more toxic when you ingest literal bucketfuls, including harmless household liquids like vinegar, shampoo, ethanol, olive oil.)
I think I heard on a podcast the other day that a 10ft x 10ft tank of heavy water would produce the same amount of energy the entire world consumes in a year (or some crazy stat like that).
> - Since the process produces magnetically charged plasma, steam turbines are not necessary, a solution of directly harvesting energy with electromagnets was proposed.
But wouldn't that require aneutronic fusion to be viable? I had thought that the prevalence of neutron radiation otherwise would have made directly tapping the plasma for electricity impractical.
Yes. But mostly aneutronic fusion is possible, in principle.
"Side reactions" produce neutrons and gamma rays, and fusion products can get involved in side reactions too, also producing neutrons and gamma rays. If you can keep recirculating the desired reactants, filtering out the products and side products, those reactions can be kept to a low level.
- The end product of Deuterium + Tritium is regular, stable Helium, making waste disposal both safe, and cheap
- The input of the process, heavy water, while not safe, is way less dangerous than thorium or uranium
- The whole process is no way involved with nuclear weapons, making security concerns much less relevant
- Since the process produces magnetically charged plasma, steam turbines are not necessary, a solution of directly harvesting energy with electromagnets was proposed.