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...

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.

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.