Lockheed Says they have a Fusion Energy Breakthrough

[bpwoods]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Ok, lets say it actually does work, on an industrial scale, and the consumers can pay. That is, their nett incomes are sufficient after they have paid for their necessaries. Then what? One really does have to wonder. I suppose the majority* can "amuse ourselves to death ..." - whilst the privileged few actually get a take-home wage packet. Sounds fun!

* You mean: "Where does their income come from?" Yep!

[ASH]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Fusion power is not quite as clean as many folks envision. The intense neutron flux generated by fusion can cause structural damage to metals (in particular) and can also create induced radioactivity in other materials. We won't be getting off scott free from nuclear waste if we finally get fusion going.

The sun is not so "clean" when you don't have a few miles of atmosphere protecting you from it.

That's a good point. The deuterium-tritium fusion reaction (²H + ³H --> ⁴He + n) is the easiest to run, and it spits out energetic neutrons. My understanding is that since the tritium fuel is itself radioactive, with a short half-life, it has to be manufactured. One way of doing this would be to include a blanket of lithium in the reactor's shielding, since neutron irradiation of lithium is one of the standard ways to "breed" tritium (similar to how breeder reactors manufacture plutonium from uranium). So ideally, the neutron flux from the reaction could be exploited to generate fuel for the reaction. But you're right -- the structural materials of the reactor are also going to get irradiated over time, ultimately weakening and becoming radioactive themselves. However, I think it's fair to say that the amount of radioactive waste produced would be limited to the reactor structure itself, whereas a conventional fission plant produces a steady stream of radioactive waste from its spent fuel elements.

While checking my facts, I ran across an interesting reference to an alternate fuel that would be much harder to get going, but which won't spit out neutrons. Apparently the late Robert Bussard advocated fusing normal hydrogen with boron-11. The reaction, ¹H+¹¹B --> 3 ⁴He, runs off of the most abundant naturally-occurring isotopes of both elements and doesn't generate neutrons (except by some side reactions which run at very low rates). The downside is that the reaction requires like 10x the temperature and 500x the quality of plasma confinement to run, and the energy density of the fuel is ~2500x lower than deuterium-tritium fusion. So given how hard it is to make deuterium-tritium go, this isn't a realistic alternative. But it is interesting trivia.

Also... fun trivia about the sun. The sun has much better "confinement" than a terrestrial fusion reactor, but no access to refined heavy hydrogen fuels, so it (mainly) runs a different fusion reaction than the ones we talk about in connection to fusion power. The proton-proton fusion chain is a multi-step process that makes neutrons from protons through the inverse beta-decay process:

¹H+¹H --> ²H+e⁺+ν (the proton turns into a neutron and emits an antimatter electron plus a neutrino)
²H+¹H --> ³He
³He+³He --> ⁴He+2 ¹H (86% of the time)
or
³He+⁴He --> ⁷Be
⁷Be+e^- --> ⁷Li+ν (a proton absorbs an electron, turns into a neutron, and emits a neutrino)
⁷Li+¹H --> 2 ⁴He (14% of the time)

Interestingly, although these reactions do produce gamma-rays, they're actually "clean" with respect to production of free neutrons. Also, free neutrons have a half-life of about 10 minutes, so any neutrons emitted by the sun would decay into protons and electrons long before they reached earth's atmosphere (assuming they travel at the same speed as the solar wind... which seems fine for a hypothetical).

[astonas]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Thanks, ASH, good information!

Did your reading happen to turn up the reasons why Alpha- and Gamma-emitting reactions weren't pursued for power? Gamma clearly has some concerns, but I'd expect Alpha particle damage to be comparatively manageable.

[radon]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Thanks, ASH, good information!

Did your reading happen to turn up the reasons why Alpha- and Gamma-emitting reactions weren't pursued for power? Gamma clearly has some concerns, but I'd expect Alpha particle damage to be comparatively manageable.

Alpha particles could be desirable. They can be used to produce a high voltage current directly.

[ASH]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Thanks, ASH, good information!

Did your reading happen to turn up the reasons why Alpha- and Gamma-emitting reactions weren't pursued for power? Gamma clearly has some concerns, but I'd expect Alpha particle damage to be comparatively manageable.

Thanks.

Since this normally occurs in a plasma and the helium nuclei would be stripped of their electrons, when I wrote ⁴He that really meant "alpha particle". So deuterium-tritium fusion and deuterium-deuterium fusion both produce energetic alpha particles plus neutrons. Also, there's a minor deuterium-tritium fusion side chain that results in emission of a 16.7 MeV gamma-ray instead of the neutron. (Immediately after fusion, ⁵He is produced in an excited nuclear state; it normally decays into ⁴He + n, but sometimes the excited ⁵He nucleus just relaxes to its ground state by emission of a gamma-ray.) In the sun's proton-proton reaction, the positron which is emitted when the proton changes to a neutron eventually meets up with an electron and they annihilate into a pair of gamma-rays. The crazy ¹¹B reaction releases three alpha particles per fusion.

Practical research has focused on deuterium-tritium fusion (because it is easiest and has the highest energy density of the easier fuels) and deuterium-deuterium (because it's almost as easy, tritium is expensive to come by, and the neutrons released by the reaction apparently present less of a radiation hazard due to their lower energy). I think other possible reactions haven't been pursued because the difficulty of achieving fusion increases steeply with atomic number. The Coulomb barrier height goes up with the number of protons. Also, as a rule of thumb, the change in nuclear binding energy per unit mass of stable reactants becomes less attractive the closer you get to the most tightly bound isotope (⁶²Ni). So I think other reactions haven't been pursued for power because they seem unattainable or less efficient.

[astonas]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Practical research has focused on deuterium-tritium fusion (because it is easiest and has the highest energy density of the easier fuels) and deuterium-deuterium (because it's almost as easy, tritium is expensive to come by, and the neutrons released by the reaction apparently present less of a radiation hazard due to their lower energy). I think other possible reactions haven't been pursued because the difficulty of achieving fusion increases steeply with atomic number. The Coulomb barrier height goes up with the number of protons. Also, as a rule of thumb, the change in nuclear binding energy per unit mass of stable reactants becomes less attractive the closer you get to the most tightly bound isotope (⁶²Ni). So I think other reactions haven't been pursued for power because they seem unattainable or less efficient.

Thanks, that makes more sense to me now.

I was thinking in terms of collision cross-sections (which seem much more favorable), and let that distract me from the more elemental (no pun intended) issue of barrier height.

[ASH]

Re: Lockheed Says they have a Fusion Energy Breakthrough

I came across one other interesting factoid concerning fusion and neutrons:

The two common fuels used in fusion power experiments, deuterium-tritium and deuterium-deuterium, both release neutrons when they fuse. In the D-T reaction you get 17.6 MeV of energy out per fusion, split between the kinetic energy of the ⁴He alpha particle (3.5 MeV) and the neutron (14.1 MeV). The two main branches of the D-D reaction occur with equal probability, releasing either a 1.01 MeV ³H ion plus a 3.02 MeV proton or a 0.82 MeV ³He ion plus a 2.45 MeV neutron. So you get 1 neutron from the D-T reaction per 17.6 MeV of energy out, and 1 neutron per 7.3 MeV of energy out from the D-D reaction. If you use the elementary charge to convert from MeV to Joules, you find that this is 1 neutron per 2.92 pJ for D-T or per 1.17 pJ for D-D.¹ This ends up being one of the bases of skepticism about cold fusion. Most of those "palladium in a beaker" type experiments load the palladium lattice with deuterium, and the general claim is that packing deuterium atoms into the palladium somehow catalyzes D-D fusion. However, given that 1 neutron per 1.17 pJ equates to about 855 billion neutrons per second for 1 Watt of fusion power, experiments that report heat rises consistent with Watts of power generation have to explain where trillions of neutrons are going. In particular, an LD₅₀ dose of radiation is about 4.5 Sieverts, and for 2.5-MeV neutrons (the energy emitted by D-D fusion) 1 Sievert's worth of exposure corresponds to an accumulated fluence of 2.9 billion neutrons per square centimeter. Thus, if your tabletop cold fusion experiment is really fusing deuterium, one meter from an unshielded reaction, the flux would be 6.8 million neutrons per square centimeter per second for every Watt of fusion power generated. It would take a half hour to accumulate a lethal dose generating 1 W of fusion power from the D-D reaction. As implausible as it is that something about palladium would lower the potential energy barrier to D-D fusion (implausible because deuterium nuclei are closer together in a D₂ molecule than they are when packed into palladium, and D₂ doesn't spontaneously fuse), it's even less plausible that loading deuterium into palladium somehow influences nuclear reaction rates, energetics and branching ratios. Generally speaking, the stuff you do at the scale of chemical bonds doesn't significantly perturb nuclear states; it's the wrong distance and energy scale. So even if the palladium is somehow catalyzing D-D fusion, it's practically inconceivable that it would significantly change what D-D fusion entails, and the fact cold fusion researchers generating Watts of power from glass beakers aren't dying in droves of acute radiation poisoning is suspicious.

¹Footnote: For the branch of D-D fusion that produces a ³H tritium ion and a proton, the tritium is very likely to fuse with deuterium if it encounters any, giving you the higher-energy neutron than comes from the D-T reaction. Thus, in experiments where the reaction products are confined and mix with the reactants, D-D fusion inevitably gives you some D-T fusion as well, along with the higher-energy neutron.

[ASH]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Thanks, that makes more sense to me now.

I was thinking in terms of collision cross-sections (which seem much more favorable), and let that distract me from the more elemental (no pun intended) issue of barrier height.

Yeah -- I can see that. If they were neutral particles, then being bigger would seem to help. (The Coulomb barrier issue is one of several reasons that e-cat guy's claims aren't remotely credible: fusing deuterons to ⁵⁸Ni or ⁶⁰Ni is vastly harder than fusing two deuterons together.)

I dug into it a little more, and learned there's yet another reason why high-Z elements make bad hot fusion fuels: the sharing of kinetic energy with the electrons in the plasma. Not only is the Coulomb barrier higher for high-Z fuels, but unless you somehow remove all the electrons from the plasma, everything tends to thermalize such that on average, electron-ion collisions neither add to nor subtract from the kinetic energy of either particle in the plasma. If you're trying to make the ions go fast so they'll slam into each other and fuse, and you're having a tough time as it is heating up the ions, having them share their energy with the electrons in the plasma ends up being a drag. For higher-Z elements, you get multiple electrons in the plasma per ion, and speeding up the ions by heating the plasma becomes less and less efficient the more non-fusing particles there are in the plasma per ion.

[astonas]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Yeah -- I can see that. If they were neutral particles, then being bigger would seem to help. (The Coulomb barrier issue is one of several reasons that e-cat guy's claims aren't remotely credible: fusing deuterons to ⁵⁸Ni or ⁶⁰Ni is vastly harder than fusing two deuterons together.)

I dug into it a little more, and learned there's yet another reason why high-Z elements make bad hot fusion fuels: the sharing of kinetic energy with the electrons in the plasma. Not only is the Coulomb barrier higher for high-Z fuels, but unless you somehow remove all the electrons from the plasma, everything tends to thermalize such that on average, electron-ion collisions neither add to nor subtract from the kinetic energy of either particle in the plasma. If you're trying to make the ions go fast so they'll slam into each other and fuse, and you're having a tough time as it is heating up the ions, having them share their energy with the electrons in the plasma ends up being a drag. For higher-Z elements, you get multiple electrons in the plasma per ion, and speeding up the ions by heating the plasma becomes less and less efficient the more non-fusing particles there are in the plasma per ion.

That part I did happen to remember from my plasma engineering class long ago, hence my focus on He2+ over some of the higher-Z fuels you were mentioning.

And of course I agree with you that 58Ni is just silly, and doubly so for cold fusion.

[astonas]

Re: Lockheed Says they have a Fusion Energy Breakthrough

As implausible as it is that something about palladium would lower the potential energy barrier to D-D fusion (implausible because deuterium nuclei are closer together in a D₂ molecule than they are when packed into palladium, and D₂ doesn't spontaneously fuse), it's even less plausible that loading deuterium into palladium somehow influences nuclear reaction rates, energetics and branching ratios. Generally speaking, the stuff you do at the scale of chemical bonds doesn't significantly perturb nuclear states; it's the wrong distance and energy scale.

You're in good company. This was the logic of Seaborg's most vehement argument that cold fusion could never be fit for anything but out-of-hand dismissal, back when Fleishman and Pons first claimed it.

Nothing that's come up in field theory since his death (that I've heard of) has even hinted at any reason to rethink that argument. I'm looking forward to seeing what EJ's expert says; just this objection alone seems to be pretty unassailable, and it'll be interesting to see a proposed mechanism that claims to overcome it.

[jk]

Re: Lockheed Says they have a Fusion Energy Breakthrough

i loved reading this conversation, which i could dimly follow only at the conceptual level. it's terrific having guys like you around to elevate our technical conversations, in the same manner that grg55 elevates our understanding of the energy markets. thanks.

[astonas]

Re: Lockheed Says they have a Fusion Energy Breakthrough

i loved reading this conversation, which i could dimly follow only at the conceptual level. it's terrific having guys like you around to elevate our technical conversations, in the same manner that grg55 elevates our understanding of the energy markets. thanks.

Thanks! I've gotten a lot form your own expertise over the years as well!

And in case it's not clear, I'll just mention that on this topic, the casual reader should definitely regard ASH's information as both more current, and more deeply researched, than mine. I'm serving mostly as the foil on this one.

(We all have to take our turns in that role, to have an informative site.)

[Polish_Silver]

Re: Lockheed Says they have a Fusion Energy Breakthrough

Fusion power is not quite as clean as many folks envision. The intense neutron flux generated by fusion can cause structural damage to metals (in particular) and can also create induced radioactivity in other materials. We won't be getting off scott free from nuclear waste if we finally get fusion going.

The sun is not so "clean" when you don't have a few miles of atmosphere protecting you from it.

I agree with that, especially since there is not yet any practical fusion reactor. So how can anyone place an upper limit on the waste it might produce.