D Tibbets wrote:I disagree about water steam and helium steam dangers. One will cook you and the other will freeze you. The explosive overpressure may be similar, and the shrapnel danger would be similar.
What is important is the scale of the contained pressure and the volume. The LHC was a small accident which as you point out, with small volume and modest B field. A Tokamak like ITER may have magnets with hundreds of times larger volumes and at least several times as much strength/ unit of volume. Take the explosive damage that occurred at the LHC and multiply it by ~ 1000 or more. And as I pointed out earlier, consider the hot liquid lithium blanket (this may make a pretty good explosive by itself- dispersed in a cloud by a quenching explosion, it may make an excellent fuel air explosive. Add to that nearby large water steam plumbing...
I don't know what kind of liquid helium sequestration the LHC had between magnets, apparently there was some, otherwise I suspect up to all of the magnets would have failed rather than 1-~12 that were destroyed or damaged. Or perhaps there was enough time for the more distant magnets to be shut down by safety mechanisms and the current was drained before the helium drained out and the magnets had a chance to quench.
The LHe2 has enough energy stored in it to pack a mean punch. The important energy storage is because of the temperature differential
between the liquid helium and the outside world.
Think of it like you're standing on a mountain. Lots of potential energy, but you're not moving. Unless you jump off a cliff, because that means there's a gap you can bridge and gain energy from it. Just make sure you bring your parachute.
Now if the liquid helium lines in the ITER facility were to fail somehow, there's enough bad things that can happen. Remember, not just the coolant lines are at a few Kelvin, but also the superconducting magnets.
Suppose there was some damage caused to the field magnets, causing a near instant quench. The quench area would heat up rapidly under the influence of Kiloamps of current, melting the superconducting coils and rupturing the LHe2 conduits inside.
Now the fun starts to build up. The coils are either in contact with the vacuum vessel directly or through the liquid lithium blanket. Very cold LHe2 coming in contact with very hot liquid lithium (or in case of Polywell, even direct plasma contact), means the liquid helium would flash evaporate into gaseous helium -- FAST. Not only that, but it would expand at a high rate, probably causing some part of the vacuum vessel to rupture.
This in turn would suck in outside air (because it's a vacuum chamber) and start to implode, probably not particularly fast because once a disaster of this magnitude hits the facility, vacuum pumping would have stopped already.
The whole situation starts to go downhill once you realize the helium explosion would scatter the liquid lithium blanket airborne over some distance, as D. Tibbets pointed out. Lithium + Air = bad news, burning very fast and intensely.
The steam plumbing would make the situation even more complicated, because lithium and water aren't very good friends. Especially not when mixed together in gaseous form in a cloud, which would add to the yield of the explosion even more. And cause some VERY nasty acid deposits in the direct vicinity. Imagine a laptop battery the size of a warehouse blowing up.... you don't want to be underneath that.
Now if it were regular lithium there would be less of a problem, but don't forget, if ITER is a running facility, this would be highly irradiated
lithium, scattered across the countryside, in a burning fireball. Which means a release of radioactive fallout across miles.... starts to sound like Tsjernobyl, to be honest.
The whole thing complicates even more if the lithium blanket is also being used for tritium fuel breeding, which would make the radiation hazard even more acute. The half-life of lithium isotopes spread over the country would be a lot more manageable than the release of heavier radioactive isotopes like in fission reactors, but there's also the toxicity of airborne LiO2 dust to deal with...
I wonder what kind of safety measures the ITER crew has in mind to combat any catastrophic scenarios.
Because we can.