# New Tokamak D Mode Success - Fusion is Almost Here

• B
Mentor

## Main Question or Discussion Point

https://arstechnica.com/science/201...he-d-in-tokamak-get-unexpectedly-good-result/

In the world of fusion physics, two letters say it all: ‘L’ and ‘H’. All the cool kids play with the H-mode, which is hot and fiery and is our best prospect for achieving useable fusion energy. The L-mode, which is neither hot nor fiery, has been largely abandoned. But by changing the shape of the L-mode, researchers have been able to get unexpectedly high pressures. High enough for fusion? Maybe.
I wonder if it'll fit into a Tesla and then we can remake the Back to the Future with a Tesla movie.

Auto-Didact and Drakkith

## Answers and Replies

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Borg
Gold Member
Just 20 more years?

bhobba, Klystron, Chestermiller and 2 others
LURCH
I remain steadfast in my belief that fusion reactors will become a reality in 20 years. (From some point in time).

jasonRF, Chestermiller, Wrichik Basu and 1 other person
phinds
Gold Member
2019 Award
I remain steadfast in my belief that fusion reactors will become a reality in 20 years. (From some point in time).
I think you mean from ANY given point in time.

jasonRF
Nugatory
Mentor
In 1973, when I was in high school, a classmate bet me that fusion power was no more than 20 years away.... We grabbed two scraps of paper, wrote down the terms (if in 1993 a commercial fusion power plant was in operation anywhere in the world, I'd send him a money order for $20, and vice versa), signed them, and waited. I found my piece of paper around the turn of the century, didn't bother dunning him for the twenty bucks although I'm sure that he would have paid if I had. bhobba sophiecentaur Science Advisor Gold Member That 20 years figure for fusion is like the 40~year figure for the length of life of our oil supplies. But the oil availability idea has been supplanted by the climate disaster prediction. Now the onus is on us. (Pun intended) LURCH Science Advisor I spoke out with great scepticism earlier, but I actually do find this news pretty exciting (thanks @jedishrfu for sharing this news). It sounds like a step in the right direction, anyway. mfb Mentor It is an interesting result, but it is unclear how much it will help. It is too late to change the ITER geometry - while it might be able to test this it won't have an optimized geometry for it. If this changed plasma geometry works really well it might be something for DEMO. I don't see how it would speed up that timeline, however. Might make DEMO smaller, cheaper, and therefore a bit faster maybe. In 1973, when I was in high school, a classmate bet me that fusion power was no more than 20 years away.... We grabbed two scraps of paper, wrote down the terms (if in 1993 a commercial fusion power plant was in operation anywhere in the world, I'd send him a money order for$20, and vice versa), signed them, and waited. I found my piece of paper around the turn of the century, didn't bother dunning him for the twenty bucks although I'm sure that he would have paid if I had.
20 years of funding...
We can't expect miracles if the funding is cut.

Mentor
What often happens is a poor implementation succeeds enough to be considered a breakthrough, investors flock to it and a better design comes out in the competition to commercialize it or everyone loses their shirt. So far we have a lot of shirts for sale.

Paul Colby and sophiecentaur
I have great respect for the physicists and engineers trying to crack fusion, it is a tough nut, but I do wonder whether we'll need it by the time it comes online.

Renewable energy costs are plummeting and that's killing nuclear fission reactors, both running and planned. Flow batteries with decades of cycle time and no degradation are likely to be the go-to method for grid scale storage (along with pumped hydro, though that has geographical constraints), and these are technologies that can be quickly deployed without needing a small army of expensive experts to maintain.

But given the complexity, a working fusion reactor is likely to be expensive, both to build and to run, and the markets won't fund many halo projects unless they are taxpayer subsidized...and taxpayers seem to be getting sick of such things.

Then there is the radioactive waste, which Joe and Joanne Public aren't generally aware of. Sure, ITER calls it "short lived" as if we shouldn't worry about it, but that's 50 - 100 years! I can't readily find figures for how much waste is generated per tokamak - if anyone knows, please chime in - but any radioactive waste is going to be bad PR. Plus, it adds to the overall cost.

So, I'm skeptical that fusion will ever go mainstream, no matter the shape of the container.

mfb
Mentor
By the time fusion reactors are running we might want them for spacecraft or on other celestial objects where renewables are not always feasible. Or maybe our demand increases so much that renewables just can't keep up.
Sure, ITER calls it "short lived" as if we shouldn't worry about it, but that's 50 - 100 years!
The chemical waste involved in making wind turbines and photovoltaics will stay dangerous forever. A much smaller amount of waste that gets relatively harmless in 100 years sounds amazing compared to that.
I never understood how people can present any lifetime as downside. Like... isn't it great that the waste gets less problematic over time?

bhobba and LURCH
By the time fusion reactors are running we might want them for spacecraft
That's possibly a good use case, but we're investing a lot of money of taxpayer money, let alone shareholder money, for an edge case. Right now we're struggling to get stuff into LEO safely and cheaply, fusion powered anything is the least of the issues.

Or maybe our demand increases so much that renewables just can't keep up.
Global energy consumption is expected to increase, but supposedly peak sometime in the next few decades. So unless fusion comes along sooner than later, it's too late to help out much.

A much smaller amount of waste that gets relatively harmless in 100 years sounds amazing compared to that.
I was wondering much waste a fusion reactor would generate, so appreciate your insights, because I wasn't sure. I'm expecting 1GW reactors will be common, so what amount of waste will they create annually?

mfb
Mentor
That's possibly a good use case, but we're investing a lot of money of taxpayer money, let alone shareholder money, for an edge case. Right now we're struggling to get stuff into LEO safely and cheaply, fusion powered anything is the least of the issues.
I mentioned them as one possible future application, I don't say it is the only one.
Compared to the hundreds of billions solar power gets the fusion funding is very small.
Getting stuff to LEO safely and much cheaper than today will come, funded by private companies, but let's stick to fusion here.
Global energy consumption is expected to increase, but supposedly peak sometime in the next few decades.
Where does that estimate come from?
I was wondering much waste a fusion reactor would generate, so appreciate your insights, because I wasn't sure. I'm expecting 1GW reactors will be common, so what amount of waste will they create annually?
Radioactive waste, annually: Nearly nothing. The only radioactive material that is moved around is tritium - that is fuel, not waste. Some short-living waste will come from handling tritium but the main waste product will be the activated reactor wall after the reactor is shut down (or after the wall is exchanged, if necessary). Suitable reactor wall materials are still being studied, how long they last, how active they will get and for how long will depend on that.

I mentioned them as one possible future application, I don't say it is the only one.
Not wanting to seem disagreeable, but if you posit only one use case, then that's all I can comment on. And I agree that fusion funding is pretty meager in the scheme of things, but if it's to obtain power generation for a potential that may never eventuate, that's not good use of funds.

Where does that estimate come from?
It's from DNV GL's Energy Transition Outlook. Could be wrong, but the point is that the assumption that energy is going to transition to a sharp increase may not be correct. Certainly, other studies have shown that RE can provide high 90%'s of the energy we need, and that's just using today's tech. And RE is being built right now, working, on time, on budget, with no experimental facilities needed. The UK just ran a week without using any coal powered electricity generation, and with ITER not expecting first fusion until 2025, my thought that fusion won't be needed by the time fusion is here seems likely.

Suitable reactor wall materials are still being studied, how long they last, how active they will get and for how long will depend on that.
So, we don't actually know how much nuclear waste is going to be produced but you're OK using handwavium to dismiss this? You might be right...but you might be wrong, so my question stands. Does anybody have any indication of how much radioactive waste material is likely to be produced by a working fusion reactor?

mfb
Mentor
And I agree that fusion funding is pretty meager in the scheme of things, but if it's to obtain power generation for a potential that may never eventuate, that's not good use of funds.
But we don't know if we want fusion in the future - we don't know how much it will cost. Figuring that out is the goal of the research. With the same argument you could have argued against funding of solar power or wind in the past - where it was unclear how much they would cost later on.
It's from DNV GL's Energy Transition Outlook.
I'm skeptical about the prediction that energy will both be cheaper and used less than others predict... but anyway, that is the total energy demand. Electricity demand is still rising a lot in 2050 in their model and capacity additions rise to 4 times the current value in their model.
The UK just ran a week without using any coal powered electricity generation
Yes, because they get 40% from gas, 20% from nuclear power and 10% from oil. Don't get me wrong, getting rid of coal is amazing, but the week without coal is not coming from renewables.
So, we don't actually know how much nuclear waste is going to be produced but you're OK using handwavium to dismiss this? You might be right...but you might be wrong, so my question stands. Does anybody have any indication of how much radioactive waste material is likely to be produced by a working fusion reactor?
Much less than a fission reactor but we don't have exact numbers yet and it is impossible to compress this to one or two numbers anyway.

sophiecentaur
Gold Member
but the week without coal is not coming from renewables.
It's coming from coal burned elsewhere (imports from the East). The Tories are trying to get credit for cooking the books.

Buzz Bloom
Gold Member
Right now we're struggling to get stuff into LEO safely and cheaply
Hi Tghu:

I tried to find the meaning of "LEO" at
but none of the definitions there were helpful. Would you please spell out what the acronym stands for?

Regards,
Buzz

Hi @Buzz Bloom,

regards:

I tried to find the meaning of "LEO" at
Yes, 'low Earth orbit' is the acronym. Sorry, I assumed knowledge from the context, my bad.

For @mfb, I absolutely want us to crack the fusion problem, irrespective of the use case. But I strongly object to any assertion that the radioactive waste can be dismissed. As you noted, "we don't have exact numbers yet", so no what basis can anyone decide it's going to be OK?

I'd actually hoped that an expert in nuclear physics might be able to - or already had - estimate the extent of the problem from first principles. There was a way older fusion thread that indicated the reactor wall materials would be degraded very quickly, and if that's likely, and those materials are radioactive even for a 'short lived' period (aka 50 - 100 years) then we're likely to have a serious waste problem if fusion is globally adopted.

Sadly, reactor economics - fusion or fission - may never stack up against RE. RE scales from domestic to grid capacity, offers a decentralized energy system that is resilent, is cheap enough that impoverished communities can adopt it, plugs into Li-ion and flow batteries for storage already, has low maintenance costs, esp. if it's PV, and you can shift the electrons around geographically when the sun aint shining and the wind aint blowing in any particular location if that's a desired configuration.

It's coming from coal burned elsewhere (imports from the East). The Tories are trying to get credit for cooking the books.
That's not what I've seen, it's all domestic generation, not imported electricity. We're are the figures for that nugget?

mfb
Mentor
For @mfb, I absolutely want us to crack the fusion problem, irrespective of the use case. But I strongly object to any assertion that the radioactive waste can be dismissed. As you noted, "we don't have exact numbers yet", so no what basis can anyone decide it's going to be OK?
No one dismisses it. Every estimate tells us that it should be a relatively minor issue. How much waste of which type exactly is still under study.
Similarly: I don't know the exact risk of getting into a car accident if I drive to another city - but I can still decide that it is an acceptable risk, I don't need to estimate the risk with three significant figures for that.

sophiecentaur
Gold Member
Similarly: I don't know the exact risk of getting into a car accident if I drive to another city - but I can still decide that it is an acceptable risk, I don't need to estimate the risk with three significant figures for that.
But could be one of Donald Rumsfelt's 'unknown unknowns' so it shouldn't just be dismissed perhaps. Statistics have to be treated properly. "Ten times the risk" sounds significant until you are told that the present risk is 1/100000 per lifetime.
I guess the main 'unknown' risk would be the unforeseen production of some nasty isotope with a long lifetime. Presumably 'they' have done the combinatorial analysis and decided that nothing significant can be produced if the structure has no heavy elements to start with.

mfb
Mentor
"Ten times the risk" sounds significant until you are told that the present risk is 1/100000 per lifetime.
That's the point, being off by a factor 10 won't change the conclusion, you don't need 1% accuracy.
Presumably 'they' have done the combinatorial analysis and decided that nothing significant can be produced if the structure has no heavy elements to start with.
Completely avoiding them is unlikely to work, but there are elements that behave nicely. It is likely that there will be some long-living waste, but if the quantity is small that is acceptable.

sophiecentaur
Every estimate tells us that it should be a relatively minor issue
Thanks @mfb, that's the detail I'm looking for. According to what seems to be a well formulated fusion process explanation by Tom Murphy, "All told, the radioactive toll from a D-T fusion reactor may be comparable to that of a fission reactor, though with shorter half-life."

Does that sound reasonable based on your knowledge?

mfb
Mentor
I think that estimate is too simplified.

Most of the problematic radioactive waste from fission power plants comes from long-living fission products and the fuel accumulating neutrons to form transuranium elements. Both of these do not occur at all in fusion power plants. Activated material in the reactor is a pretty minor part of the problematic waste.

Not every neutron that is absorbed somewhere will lead to something radioactive to deal with. Consider sodium, one of the elements that might be used to transport away the heat: It is all Na-23. If it absorbs a neutron it becomes Na-24, which decays to Mg-24 with a half life of 15 hours. Mg-24 is stable. It can absorb a neutron and become Mg-25, which is stable again. It can absorb another neutron and become Mg-26, which is still stable. If it absorbs another neutron it becomes radioactive - with a half-life of just 9 minutes it decays to Al-27, which is stable again. If we let it absorb yet another neutron (number 5) we get Al-28 which decays to Si-28 with a half life of 2 minutes. Si-28 is - you guessed it - stable. So are Si-29 and Si-30. Si-31 has a half life of 2.5 hours and decays to the stable P-31.

You can just keep irradiating sodium and aluminium, and silicon is quite nice as well (natural silicon is mainly Si-28) - the longest-living nuclide has a half-life of less than a day, it will be gone completely in something like two weeks.
P-32 is the first nuclide in the chain that has a longer half-life but 14 days is still very comfortable. It is also used in medicine, if it is produced it might be interesting to isolate it.

Fusion reactors will have a much higher neutron flux than fission reactors, material choices to reduce activation matter more.

Steelwolf
Fusion reactors will have a much higher neutron flux than fission reactors, material choices to reduce activation matter more.
Thanks @mfb, I've been working to get a handle on the scope of the issue, because if fusion does work - and the economics stack up - we'll have many more of these than fission plants. I also note that a hydrogen-boron reaction would be radioactive waste free, though as with all fusion approaches, the kinks still need to be worked through!

mfb
Mentor
The side-discussion about coal in the UK and total CO2 emissions has been moved to a separate thread.

Tghu Verd