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New design could finally help to bring fusion power closer to reality

phys.org

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Re: New design could finally help to bring fusion power closer to reality

#31

Post by mapt »

ZenoArrow wrote: post #17
iaw wrote: post #12

The big problem with controlled fusion, as I understand it, isn't creating a net energy positive fusion reactor like this article implies. The physics is already there, we just need the engineering to catch-up. The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, i…

> "The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, it's also challenging because materials don't handle neutron bombardment well." Isn't that problem solved with aneutronic fusion? https://en.wikipedia.org/wiki/Aneutronic_fusion Of course we should focus on ge…

The problem is, low neutron fusion reaction cycles require a very high pressure/temperature/plasma density to reach peak reactivity, substantially higher than D+T and D+D fusion.

If we do eventually progress to aneutronic fusion test reactors, we will first have to get neutron-emitting fusion reactions working to the level of substantial net power generation, even if a given test reactor only lasts a few months before neutron irradiation becomes unmanageable.

Re: New design could finally help to bring fusion power closer to reality

#32

Post by bane »

iaw wrote: post #12

The big problem with controlled fusion, as I understand it, isn't creating a net energy positive fusion reactor like this article implies. The physics is already there, we just need the engineering to catch-up. The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, i…

Not a nuclear physicist, so this is my armchair layman's "why don't they just..." analysis.

But doesn't nuclear fission work off of neutron bombardment? Why not build a hybrid reactor where the "shield" undergoes fission while the core is generating fusion and perhaps they can produce a useful amount of power, perhaps with the fission "shielding" powering the magnets or some such?

Re: New design could finally help to bring fusion power closer to reality

#34

Post by idlewords »

bane wrote: post #32
iaw wrote: post #12

The big problem with controlled fusion, as I understand it, isn't creating a net energy positive fusion reactor like this article implies. The physics is already there, we just need the engineering to catch-up. The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, i…

Not a nuclear physicist, so this is my armchair layman's "why don't they just..." analysis. But doesn't nuclear fission work off of neutron bombardment? Why not build a hybrid reactor where the "shield" undergoes fission while the core is generating fusion and perhaps they can produce a useful amount of power, perhaps with the fission "shielding" powering the magnets or some such?

What would be the advantage of a hybrid like that over a straight-up fission reactor?

Re: New design could finally help to bring fusion power closer to reality

#35

Post by InclinedPlane »

iaw wrote: post #12

The big problem with controlled fusion, as I understand it, isn't creating a net energy positive fusion reactor like this article implies. The physics is already there, we just need the engineering to catch-up. The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, i…

Embrittlement and neutron activation are already well understood and perfectly tractable problems, since they affect the fission power industry to the same degree. That comes down to the materials you use to construct your reactor.

There are thre main problems, only one is entirely engineering the other are on the border of engineering and physics. The most pressing problem is one of plasma containment lifetime. The longer you can contain a plasma the more feasible it is to operate a fusion reactor as a power source. Right now that time is measured in seconds. An equally important problem is plasma temperature, the higher the plasma temperature the higher the fusion rate, and the farther beyond break-even the fusion reactions will be. ITER is "designed" for containment times of up to a thousand seconds, about 15 minutes, though in reality it is likely to fall far short of that. And even that is a far cry from what would make fusion power production feasible engineering wise. As it happens, tokamaks are not necessarily particularly well suited to long containment times, but there hasn't been sufficient funding to thoroughly research all of the most promising designs (such as stellarators, gas-dynamic mirror fusion, spheromaks, etc.). It seems extraordinarily unlikely that the first and most easily constructed plasma confinement system would be the most capable one as well.

The main purely engineering hurdle is cost effectiveness. Which is about being able to construct a plasma containment and heating system and all of the other components of a fusion reactor (some straightforward, some not) within a reasonable cost, not multiple billions of dollars for a single 1 GW plant. There breakthroughs in superconducting wire and so forth can have an enormous impact on the economic viability of fusion power, so it's a hugely important step.

Re: New design could finally help to bring fusion power closer to reality

#36

Post by dosshell »

mikeash wrote: post #8
DennisP wrote: post #3

Meanwhile, MIT's fusion program is likely to be shut down soon. Their Alcator C-Mod has the strongest magnetic field of any tokamak in the world, and made a serious breakthrough in tokamak physics several years ago. I had a chance to visit a couple years ago. A grad student showed us a metal tie, about a meter long, and said they'd calculated that two of them could hold down the Space Shuttle during launch. To hold t…

I had to run the numbers on that Space Shuttle thing, just to see. The Space Shuttle weighed about 4.5 million pounds at launch, and had a thrust-to-weight ratio of 1.5, meaning there was about 2.25 million pounds of net upward force on it. So each of those metal ties was capable of carrying a bit over a million pounds of load. Neat.

And in Si units about: 500 000 kg (453 592.37)

Re: New design could finally help to bring fusion power closer to reality

#37

Post by regularfry »

iaw wrote: post #12

The big problem with controlled fusion, as I understand it, isn't creating a net energy positive fusion reactor like this article implies. The physics is already there, we just need the engineering to catch-up. The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, i…

There's also the problem of getting rid of the ash. Conventional tokamaks have divertors at the base (and sometimes the top) to get the spent plasma out of the chamber. These plates inevitably come into contact with the plasma, and we just don't have the materials to withstand that yet. We're not unimaginably far off, but it's unsolved. To add to the fun, some of the more promising materials have the rather entertaining property of being explosive under standard conditions...

Re: New design could finally help to bring fusion power closer to reality

#38

Post by gizmo686 »

dosshell wrote: post #36
mikeash wrote: post #8

Earlier quoted context omitted.

I had to run the numbers on that Space Shuttle thing, just to see. The Space Shuttle weighed about 4.5 million pounds at launch, and had a thrust-to-weight ratio of 1.5, meaning there was about 2.25 million pounds of net upward force on it. So each of those metal ties was capable of carrying a bit over a million pounds of load. Neat.

And in Si units about: 500 000 kg (453 592.37)

kg is a unit of mass.The Si unit of force is the Newton.

Re: New design could finally help to bring fusion power closer to reality

#39

Post by louithethrid »

iaw wrote: post #12

The big problem with controlled fusion, as I understand it, isn't creating a net energy positive fusion reactor like this article implies. The physics is already there, we just need the engineering to catch-up. The challenge is the materials that compose the reactor become brittle and highly radioactive far faster than usable. Controlled fusion as an energy source isn't just challenging because fusion is difficult, i…

Regarding brittleness - TRIZ suggested to build a reactor vessel that is replaceable in parts - or to use a shield substance that takes the damage instead. Not an machine engineer though.
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