Liquid Lithium to Contain Fusion Reactors

nigelc writes: "ABCNews.com reports on Liquid Metal walls for a fusion reactor, and how it may solve some of the temperature problems. Probably only of scientific interest to most of us, unless you're into some serious overclocking.""

Comments

Hooboy, Better Think Twice About This...

[cybrpnk]

I used to work in Oak Ridge in the nuclear program years ago and those guys LOVE to consider using liquid metals to cool things. Back in the 1970s it was the the Clinch River Breeder Reactor, which was gonna turn plentiful inert (U-238) uranium into vast quantities of power-packed plutonium in a machine cooled with liquid sodium. Wow - CRBR never got built.

Logically, a layperson would consider a liquid metal to be a very dangerous material to have around, but if you've already got pounds and pounds of plutonium you are juggling around, sodium doesn't seem so nasty anymore. They would still be talking about using sodium if it weren't so darn reactive - read corrosive. That's where our friend lithium comes in - less reactive, less corrosive. Ha.

There aren't any electric generator turbines that run on liquid lithium pressure so there's gonna be a lithium-to-water-to-steam heat exchanger loop in there somewhere in a functional fusion powerplant. Lithium is gonna come in contact with water somehow, by accident (or design) and make hydrogen gas which is not only explosive, but turns into radioactive tritium when bombarded by the neutrons put out by ANY reactor - fission or fusion.

Playing around with explosive hydrogen gas near a reactor is often done deliberately and may be a hidden agenda here. Don't kid yourself - America needs tritium. It is a prime ingredient in nuclear weapons and however much of it you've got, you've only got half that much 12 years later. This means unless you replenish your tritium stockpile you loose half of your nuclear weapons arsenal every 12 years. So far this hasn't been a problem because we are retiring nukes rapidly after winning the Cold War and we are scavinging tritium for our online weapons from the ones we retire. Sooner or later the US will run out of recycled tritium.

We used to make tritium at Savannah River Nuclear Plant but that was closed for environmental reasons years ago. Now the US is going to refurbish that old reactor and start it back up. Sooner or later we're gonna have to switch over to something else besides World War II factories like Savannah River. When that happens, and it's a fusion reactor with a lithium core, remember that there's something else in going on with that liquid metal coolant...

This is science journalism?

[Spamalamadingdong]

The article states:

and then direct a torrent of neutrons to collide head-on.

No fusion reactor does any such thing. Collisions of neutrons with neutrons do not figure in any reactor currently contemplated, fusion or fission; the only collisions are between neutrons and nuclei, or between nuclei themselves. So why is a science-illiterate writing an article about the cutting edge of fusion research, and why should we give the slightest bit of credence to either an author or a news outlet which would let something like this go out without proper fact-checking?

And think again, without paranoia

[Spamalamadingdong]

Logically, a layperson would consider a liquid metal to be a very dangerous material to have around...

Like solder? It can burn you, you know. But so can a great many solid materials and vapors (even water). You do have the toxicity of lead-based solders, but they're toxic even when they're in solid form.

Lithium is gonna come in contact with water somehow, by accident (or design) and make hydrogen gas [gcsechemistry.co.uk] which is not only explosive, but turns into radioactive tritium when bombarded by the neutrons put out by ANY reactor - fission or fusion.

The lithium will breed tritium under neutron bombardment whether water is involved or not; the production of hydrogen is a chemical reaction caused by the decomposition of water, the production of tritium is a nuclear reaction caused by the neutron-induced fission of lithium-6 into helium-4 and hydrogen-3.

Lithium is a lot less active (and thus corrosive) than sodium, but it's not suitable as a coolant for fission reactors because it has this pesky tendency to capture neutrons. In a fusion reactor which needs tritium anyway, this is an advantage.

Playing around with explosive hydrogen gas near a reactor is often done deliberately and may be a hidden agenda here.

Just FYI, people play around with "explosive hydrogen gas" for lots of reasons in lots of places. You'll find people playing with hydrogen in every plant which manufactures vegetable shortening from oil, because hydrogenating the oil is part of the process to allow it to solidify at room temperature. Ditto every plant which manufactures nitrogen fertilizers (which starts with fixation via the Haber process, N2 + 3 H2 -> 2 NH3).

A little more information and a little less paranoia would serve you well.

Re:And think again, without paranoia

[cybrpnk]

Well, I agree I oversimplified some things to make for a short and understandable post, but I assure you that I've got the "little more information" at hand as well. Everything I said was a verifiable fact, although I agree that my introduction of the tritium topic in the post by referring to neutron irradiation of hydrogen gas instead of fission of lithium was somewhat misleading, tho true...

I know a little about the nuclear uses of lithium. In Oak Ridge I worked on the team that documented the pollution that occurred in the program there in the 1950s when Lithium 6 was separated from Lithium 7 and purified to use as fusion fuel in hydrogen bombs. There was a step where the Lithium 6 was dissolved in liquid mercury to purify it and later recovered by reacting it with nitric acid. Over 7 million pounds of mercury were dumped into Bear Creek, then the Clinch River, then the Tennessee River, then the Ohio River and ultimately the Mississippi by lithium processing in Oak Ridge. My point remains, and it's not paranoia, that there are unintended consequences that come with the use of major technologies like this. The public would do well to keep this in mind...if only they were smart enought to, as you correctly allude to in your other post here.

I've got a permanent burn mark above my right knee where I dropped a blob of solder on bare skin and I'm still using it routinely at work and at home in building my Beowulf cluster, etc, so I assure you I'm not afraid of technology for technology's sake. The fact remains that a reactive liquid alkali metal at 600 degrees C is inherently much more dangerous than non-reactive tin and lead at 250 degrees C. Fusion powerplants of the future will almost certainly use a lithium-water heat exchanger as I stated (and you did not deny) and it's almost a certainty that THESE THINGS LEAK at times and such a leak will probably cause LOTS of hydrogen gas to form. Hydrogen gas explosions were serious steps in both Three Mile Island and Chernobyl accidents and have the potential to be one in a lithium cooled fusion reactor accident as well. Such a reactor probably wouldn't contaminate miles of countryside but the loss of the investment in the reactor would be devastating, as well as public confidence in the supposed "safety" of fusion reactors over fission ones. Such a public relations disaster doesn't occur at vegetable shortening of fertilizer plants even when they have explosions there (and they do) because those are "low-tech" kinds of plants in the public eye and they are more conditioned to think of them as "risky". Things like reactors and space shuttles are held, perhaps unfairly, to a higher standard.

Again, you post proves my point when you note correctly that sodium doesn't absorb neutrons like lithium does. It's easier in explaining it to the public to say sodium is "more corrosive" which is true. But the very fact a fusion reactor group would pick lithium instead of sodium for the coolant shows that somewhere along the line, neutron absorption and tritium production is important...the "hidden agenda" that is neither paranoia on my part or even hinted at in the ABC article.

Re:And think again, without paranoia

[sigwinch]

Fusion powerplants of the future will almost certainly use a lithium-water heat exchanger as I stated (and you did not deny) and it's almost a certainty that THESE THINGS LEAK at times and such a leak will probably cause LOTS of hydrogen gas to form.

If it turns out to be a major safety problem they can use a three-stage heat exchanger, with a less-reactive metal or a noble gas as the middle stage.

Your obsession with hydrogen is misguided anyway. The reaction is

alkali metal + H2O --> alkali oxide + H2 + heat

The problem is that the hydrogen is liberated rapidly, making the system explode from overpressure, which causes an overpressure wave (explosion) and blows chunks of hot nasty stuff everywhere. Afterwards the hydrogen might burn a little in the air, or even cause a gas explosion, but that's minor compared to the explosion of the piping and pressure vessels. If the reaction liberated nitrogen it would be just as bad.

My point remains, and it's not paranoia, that there are unintended consequences that come with the use of major technologies like this.

There are very few, if any, unintended consequences in any industrial operation. The bad things you are talking about are predictable and manageable. The only unknown is the will to proprely address them.

Hydrogen gas explosions were serious steps in both Three Mile Island and Chernobyl accidents and have the potential to be one in a lithium cooled fusion reactor accident as well.

Yeah, but those were fission reactors, which have to be as strong as possible because fission ash is so dangerous. The high strength of their pressure vessels and pipes means that more pressure can build up, producing a more spectacular explosion. A fusion reactor is vastly less radioactive, and its systems can be made deliberately weak so that they explode at a lower pressure, causing less damage.

Such a public relations disaster doesn't occur at vegetable shortening of fertilizer plants even when they have explosions there (and they do) because those are "low-tech" kinds of plants in the public eye and they are more conditioned to think of them as "risky".

I suspect you strongly underestimate the political fallout from uncontrolled energy releases at chemical plants, and overestimate panic from 'nookyular radiation'.

But the very fact a fusion reactor group would pick lithium instead of sodium for the coolant shows that somewhere along the line, neutron absorption and tritium production is important...the "hidden agenda" that is neither paranoia on my part or even hinted at in the ABC article.

1) There is no "hidden agenda". The fusion reactors will probably burn a deuterium-tritium mixture. If they didn't breed tritium, you'd need accelerators or fission reactors to get the tritium. If they make their own tritium, you can feed them with deuterium from tap water and lithium, both of which are fairly plentiful and innocuous.

2) Tritium for boosting plutonium bombs? Big deal. Any nation that can afford plutonium and ICBMs can afford tritium no matter how it's made.

This isn't the first concept to use lithium thusly

[Spamalamadingdong]

One of the first concepts for the use of lithium as a renewable "first wall" involved chambers which contained a vortex flow more or less like a toilet bowl. Pellets of D-T would be dropped into the center of the vortex and triggered with laser pulses; the flowing lithium would absorb the energy of the resulting micro-explosion and renew itself in time for the next pulse. The lithium would also carry away the heat. This concept was discarded when it was found that laser fusion required implosion of material to far higher densities than could be obtained with a single incoming beam, and the necessary symmetric system of incoming beams prohibited the use of a lithium vortex.

This concept appears to use lithium as the "first wall". I'm not sure exactly what the first wall has to absorb, besides the heat conducted to it from plasma leakage (plasmas do leak, they are subject to all kinds of instabilities) and soft X-rays. I do know that if you had a symmetric torus you could rotate the magnets to "pump" the liquid metal along the wall using eddy-currents, but I expect that this would be far more expensive and difficult than what they're planning. You can't have two different magnetic fields; you have one field, which is the sum of all the fields induced by all the current-carrying elements in the reactor, plus whatever the Earth decides to give you (which is probably not significant on this scale). You could have a multi-pole magnetic field at the surface which would fall off rapidly toward the center (not unlike the focussing magnets used in a synchrotron) but I'm not sure what effect this would have on either the metal wall or the plasma (and unlike synchrotrons, I don't know any tokamak experts I could ask).

Re:Lets try a little logic here

[TheBoquaz]

If you get nothing else out of this, know that neutron absorbtion and tritium production are GOOD, not sneaky, nor nefarious. They are things we are trying to accomplish so that this will be a commercially viable technology.

From working at General Atomics in San Diego, I know that the "wall problem" is one of the few last hurdles that fusion programs will have to clear before they produce a commercial grade reactor.

So... what will this wall need to do?
First, it's there in part to seal in the vacuum chamber, but there are many ways of doing that.
Second... well, there are a LOT of things the wall has to do, but one of the most difficult, and important is that it HAS to absorb neutrons.

You point out that lithium absorbs neutrons all over the place, and that makes you suspicious. The reason they want to use lithium in liquid walls is because it absorbs neutrons! In fact, it would be nice if it absorbed MORE neutrons. They want to use lithium in solid walls, but it melts too quickly, hence, liquid walls.

We don't want those things just flying around everywhere, I would rather create some tritium than irradiate my office (and if you can feed it back into the reactor... remember tritium is FUEL for fusion plants!)

I'm sure that the engineers who will eventually design a lithium, liquid metal wall reactor will have no idea what to do with all this spare fuel they are generating. What a problem! Better just go sell it to the government, because we don't want any more fuel in our reactor.

Why Li and Na?

[DumbSwede]

I am pro fusion, but not a fusion pro. I am confused why such reactive metals must be used for the jacket, Tin and Lead have low melting temperatures, even lower if mixed as an alloy. Not sure how reactive Gallium is, or whether Mercury would had a high enough boiling point, but there are dozens of metals, potentially infinite alloys, what huge advantage does sodium and lithium have for this proposed use? Also, do Lithium and Sodium have large magnetic properties, or do all metals react to a strong enough magnetic field? Yes I know most metals are nowhere near as magnetic as iron and nickel, but are there any completely magnetically inert? Does the liquid jacket have to be a metal? While the plasma is very hot, what will be the surface temperature of the surrounding jacket? It is my understanding that the magnetic confinement should confine most of the extreme heat, with the liquid jacket extracting thermal energy at a controlled rate for use.

Re:Why Li and Na?

[cybrpnk]

A pound of lithium or sodium will absorb a LOT more heat than a pound of solder, so by using reactive alkali metals you have a lot less stuff to pump around than if you used something else as a coolant. Pumping a lot less stuff means a simpler system, and that's always good.

Also, the key reason (which isn't even mentioned in the ABC article) for using lithium is that when lithium is hit by the fusion reactor's neutrons, it will change into radioactive tritium gas, which is a rare fuel the fusion reactor needs to keep going. So you start the reactor with a little bit of tritium you got someplace else, then use the reactor's own neutrons to convert common metal (lithium) into the rare fuel you need to keep it going. No other metal - sodium, lead or tin included - will do this, only lithium.

You are the smartest person in this whole thread, pal - instead of showing your ingnorance by stubbornly defending a particular position with facts (me included), you openly admit the things you don't know and ask intelligent questions to make yourself more knowledgable. Do not ever lose this open mind you have - it is much more rare than tritium gas.