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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

#21

Post by iaw »

adeledeweylopez wrote: post #14
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…

It seems like they address this issue as well: "Another key advantage is that most of the solid blanket materials used to surround the fusion chamber in such reactors are replaced by a liquid material that can easily be circulated and replaced, eliminating the need for costly replacement procedures as the materials degrade over time. "It's an extremely harsh environment for [solid] materials," Whyte says, so replacin…

It's been half a decade since I studied anything fusion related but IIRC regardless of using a liquid blanket you still have to have the machinery (powerful microwaves, particle injectors, etc) and the inner wall present.

Liquid breeder blankets are definitely the way to go but I don't think they are the full solution. (They are super neat because you can use them to make more fuel for fusion through neutron capture, so not only do you reduce radioactivity but you also reuse the energy in a useful fashion)

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

#22

Post by ethbro »

throwaway_yy2Di wrote: post #13

Here's the paper (no paywall): http://arxiv.org/abs/1409.3540 Interesting that the liquid blanket is the same as in the molten-salt thorium reactors (lithium beryllium fluoride (FLiBe)).

Iananp, but wouldn't that be for the same reasons? E.g. in both case you're trying to absorb energetic neutrons?

(Upon research: https://en.wikipedia.org/wiki/FLiBe#Coolant) Apparently it has properties that make it both a great coolant & a neutron moderator. Neat!

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

#23

Post by iaw »

throwaway_yy2Di wrote: post #19
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…

According to their paper [0], the entire vaccum vessel is considered disposable and might survive only a few months. (It's also explicitly an experimental reactor meant to study neutron radiation damage, so they're hardly claiming it's a practical commercial design. But I think you're right, that the problem is basically unsolved). This allows the vacuum vessel to be replaced quickly, mitigating first wall survivabil…

Thanks for pointing that out. I don't think I conveyed myself well in my original post, this is a fantastic development but I feel like the article didn't emphasize that the development is really about moving towards the material science that we need. It felt like the article sensationalized the energy output per unit size and didn't focus enough on the material science challenges of the problem (as well as how much this will aide in their solution).

The authors clearly recognize this, I just wish the public understood it better.

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

#24

Post by iaw »

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…

I can honestly say I'd never heard of that before you posted your link. I don't know enough to form a valid opinion here.

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

#25

Post by throwaway_yy2Di »

iaw wrote: post #23
throwaway_yy2Di wrote: post #19

Earlier quoted context omitted.

According to their paper [0], the entire vaccum vessel is considered disposable and might survive only a few months. (It's also explicitly an experimental reactor meant to study neutron radiation damage, so they're hardly claiming it's a practical commercial design. But I think you're right, that the problem is basically unsolved). This allows the vacuum vessel to be replaced quickly, mitigating first wall survivabil…

Thanks for pointing that out. I don't think I conveyed myself well in my original post, this is a fantastic development but I feel like the article didn't emphasize that the development is really about moving towards the material science that we need. It felt like the article sensationalized the energy output per unit size and didn't focus enough on the material science challenges of the problem (as well as how much…

The article was written by MIT's public-relations office, so interpret that as you like.

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

#26

Post by iaw »

azernik wrote: post #20
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…

One thing mentioned in the article was another advance in this design, where some of the materials that deal with the most intense neutron bombardment are replaced by a liquid that can be pumped out and circulated. Presumably there's still a containment vessel for this liquid that is a maintenance pain, but they do seem to be working on the problem.

The liquid blanket technology is nothing new or unusual and, from what I recall, seems to be generally agreed as the way to go. You are exactly correct about the containment vessel, and there is also the raw machinery needed to maintain the containment field and the reaction. I think the lifespan for these things is on an upper bound of 3 years, and I can't remember if that is at power plant or experimentation scale (experimental reactors run way less frequently and create less radiation than a power plant would).

It's an interesting problem to me because fusion is largely solved and well understood from the physics perspective (which is what most people consider the challenging esoteric part), the remaining challenge is a much more 'mundane' task of developing economic methods to create the needed materials.

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

#27

Post by throwaway_yy2Di »

ethbro wrote: post #22
throwaway_yy2Di wrote: post #13

Here's the paper (no paywall): http://arxiv.org/abs/1409.3540 Interesting that the liquid blanket is the same as in the molten-salt thorium reactors (lithium beryllium fluoride (FLiBe)).

Iananp, but wouldn't that be for the same reasons? E.g. in both case you're trying to absorb energetic neutrons? (Upon research: https://en.wikipedia.org/wiki/FLiBe#Coolant ) Apparently it has properties that make it both a great coolant & a neutron moderator. Neat!

They actually have nearly opposite goals. The fusion blanket is supposed to transmute lithium to tritium [0] (create more fusion fuel), so it has capture as many neutrons as possible. The fission-reactor coolant is supposed to be transparent -- to capture as few neutrons as possible. Both of them need isotopic separation of lithium to be practical. But in opposite directions. ARC's FLiBe needs to be Li-6 enriched, and MSR needs to be Li-6 depleted.

The MSRE fuel used 99.993% Li-7 (your link), and the ARC blanket is 90% Li-6 (arXiv paper).

[0] https://www.iter.org/mach/tritiumbreeding

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

#28

Post by api »

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…

This strikes me as the general problem with nuclear power: it works so well -- in a sense -- that it tears apart the fabric of matter itself, making its components, fuels, wastes, etc. absolute hell to handle. It's tough to use matter to contain matter-decomposition machines.

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

#29

Post by derwildemomo »

iaw wrote: post #24
ZenoArrow wrote: post #17

Earlier quoted context omitted.

> "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…

I can honestly say I'd never heard of that before you posted your link. I don't know enough to form a valid opinion here.

"I don't know enough to form a valid opinion here.".

Beautiful. This is pretty much the last thing I ever expected to read on the interweb.

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

#30

Post by aqme28 »

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…

There are also reactions with fewer overall neutrons such as D-D fusion, which one of my professors was a large proponent of.
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