Posts by nemecystt 17 publicly visible posts • joined 13 Jul 2021
Oh, and the issues with high energy neutrons aren't just activation of reactor vessel materials. There's also blistering and embrittlement of materials over time. Besides the structural elements, Helion will have to replace their electromagnetic coils fairly frequently. They are very close to the reactor "core" and they are taking quite high forces. Their conductivity will start to suffer first and then, ultimately, their structural integrity too.
Regarding your other question about production of 3He, there are 3 sources.
Fusion of Deuterium with itself has 2 outcomes of equal probability: Tritium and a proton, or 3He and a neutron. So they can use their reactor design, if it really works, with DD fuel and then refine / separate the outputs. This is likely to be a net negative power reactor, so the secondary D-3He reactor that follows not only has to break even on its own, but also make up for that pre-processing loss.
They can sell the Tritium to other fusion companies, or sit on it and wait for it to slowly decay into 3He (12 year half-life). That's the second way to source 3He. They could procure Tritium (difficult and super expensive) and wait for it to decay. Tritium is currently produced in very small amounts in specially prepared fission reactors and is proposed to be self-generated / recycled in some future fusion reactors not of the Helion design. Both of these require 6Li and neutrons.
There's more 3He on the Moon than on Earth (or at least we think it will be more easily procured there). However the efficiency of mining the Moon for resources to use back on Earth is rather questionable, not to mention many, many decades away. This is the only source which does not require machinery to endure a high neutron flux. Just cosmic rays...
The trouble is scaling renewables and storage to cover everything including transport and industrial heat, not just domestic 'leccy just wont cut it without killing the planet with mining. There has to be a mix of carbon-free sources, some of which are immediately despatchable and can also be 24-7. Then there's the issue of bringing the third world and others up to the living standards us lucky few enjoy. Some kind of nuclear has to be in that mix. I don't see any alternative, besides perhaps space based solar, but that's another huge can of worms and isn't secure.
Unfortunately, that's not how two plasmoids rammed together and magnetically confined behave. Think of it more like a bunch of angry bees and a bunch of angry wasps in a small chamber. Bees will collide with bees as much as bees collide with wasps. They're whizzing all over the place, bouncing off each other and steered by magnetic fields. It is not a one-shot head-on collision at all.
With respect, have you researched Helion's process using sources of info other than Helion?
The 3He production from D-D is neutronic.
Further, D-D side reactions (neutronic) are unavoidable in any 3He-D bult plasma/plasmoid at 100 million Kelvin. Just look at the respective fusion cross-sections.
There is even the possibility of residual Tritium (you'll not evacuate it all between pulses), formed in the D-D side reactions then giving you some D-T fusion too. This means more neutrons, and higher energy ones at that.
The process is not aneutronic. D-D side reactions are unavoidable at the energies needed to get the D-3He reaction to work.
The 3He production process is also not aneutronic.
Problems.
Big problems with regulation and longevity.
However, unlike other approaches, the temperature issue is lessened. They are doing small scale repeated pulses. That should be easier to manage.
Oppenheimer and others had concerns that the nuclear *fission* bombs might cause a propagating chain *fusion* reaction (of hydrogen and nitrogen in the atmosphere and hydrogen in the oceans). Oppenheimer tasked Hans Bethe and others to calculate if this was actually possible. They concluded it was not. Indeed no A-bomb or H-bomb ever ignited the atmosphere.
If it was that easy, without confinement, we would have had fusion power stations decades ago.
The plasma in a tokamak is really not very dense. There are just a few grams of deuterium and tritium in there at any one time. Magnetic confinement is required to try to keep the plasma from melting or vaporising tiny holes in the first wall of the vacuum vessel, and to try to squeeze the plasma more tightly to increase the fusion rate. It is not necessary to prevent a chain reaction. Controlled fusion very rapidly fizzles if the conditions drift even slightly away from optimum.
You really don't need to worry about a Tokamak, or similar, turning into a nuclear bomb.
Do you have any reliable sources / references for this thermodynamics defying trick that you allude to regarding cavitation? There have been a lot of "woo" / fraudulent claims in that sphere over the years. Although there are (flawed) patents going back to the 70s claiming to be able to use it to enable fusion break even, I don't think I have seen anything convincing about cavitation in and of itself being an energy source, merely an energy concentrator or possible route to more efficient steam generation. Thanks in advance.
The sonoluminescence from the cavitation elicited by the pistol shrimp does indeed include the creation of a plasma, and fusion would not be absolutely out of the question, but the probability would be vanishingly low for even one fusion event, given the "triple product" we could infer from the conditions and the "fuel" species present.
Nevertheless, the pistol shrimp is the inspiration for First Light Fusion in Oxford. Their approach is all about focusing and amplifying shockwaves initiated by a physical projectile.
No disrespect, but if you knew what you were looking for then your google-fu needs a workout. Google search did used to be much more powerful and targetable than it is now, sadly, but you can still reduce the greediness of its matching by using quotation marks. Search for "Sail" "Stanford", for example.
In terms of fusion fuel, sure: less mass than you would need fission fuel for the same output. If you were fusing Deuterium and Tritium and had a closed loop Tritium cycle via a Lithium breeding blanket, you could stockpile enough Deuterium and Lithium and your Tritium seed load.
With a "solid first wall" reactor vessel you are probably going to have to do some maintenance well before 5 years though. There are some liquid first wall ideas out there like First Light and General Fusion which, if they can be made to work, would massively extend your maintenance intervals.
But I am not sure why the need for a sealed, set-and-forget fusion reactor. The materials and radiation levels involved are nowhere near as monster evil bogeyman as in fission reactors, and the nuclear proliferation issue is pretty much non-existent too.
We're straying further off the topic of the article now though.
The issue of SMRs creating 30 times the waste of a gigawatt scale power station is, perhaps, ameliorated by two future factors:
1) some gen 4 fission reactor proposals can be run from the waste from these SMRs and older plants. Overall the amount of net waste at the end goes down
2) fission may only be a relatively short-lived "bridge" now until the boffins get fusion to work properly and at commercial scale
Public and private investment is pouring into Fission both large scale and small modular on both sides of the Atlantic, but especially in the US. Similar can be said for fusion research.
I don't think we have a flotilla of energy Theranoses about to run aground out there. Investors are a little more scrutinising these days and while many startups may be chasing pipe-dreams, a few will eventually succeed.
The jokes about cow farts fall rather flat(ulent). Methane doesn't come out of the back end. It's a bovine burp thing, people. Plus, by itself, methane is odourless. Which is why they need the fancy IR satellite thingummy and not just a horde of roaming noses. Sorry to have caused such a stink.
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