Fusion Reactor accident

I am in no way a nuclear engineer, but it is possible (I think) for the reactor's output to exceed it's operational capacity, that would create a tremendous amount of heat, and could result in an explosion in the reactor core, much like what happened with Chernobyl.

They're Spiders... ON FIRE!!!!!!

right now, the reason that fusion isn't really viable is because you get less energy out than you put in. So one isn't going to go 'runaway' the way fission can for certain of the older designs.

To make fusion go, however, requires temperatures high enough to create a plasma (separating electrons from electron shells. We're talking like a million (?) degrees C. So seems to me that could be explosive if mishandled, although it isn't really the fusion that is causing it. In fact, containment of that plasma is one of the thornier technical problems involved with designing a fusion reactor.

In theory, the reaction would become self-sustaining, but that hasn't ever been achieved. Am I making sense or is this too geek-speak. I'm not a pro, btw, though I've looked into the basics, so I could be making mistakes...

One thing to note (you didn't ask about this, but just to be clear) - a fusion reactor explosion would not result in the release of radioactive material like Chernobyl did. Certainly, tritium (H3) (a source, not a waste product) is radioactive, but not to near the degree as fission waste products - it is not bioaccumulative, for one. The principle waste of fusion is Helium. Non-radioactive. The pieces of the shattered plant would be radioactive as well, but that isn't the same as clouds of sr90 blanketing the terrain.

Hope all that helps.

If you're talking about a hydrogen fusion reactor like ITER, you won't get a spectacular city-leveling kaboom like we saw in Chain Reaction, but there are dozens of contingencies that could disable the reactor for a spell.

Part of the reason we're running the ITER experiments now is that it's a much safer engine than common fission reactors.

How far into the future is your setting? Mine's far enough that I'm using strange matter reactors (based on the Strange Matter Hypothesis) which are highly efficient fuel-wise, but the strange matter needs to be contained in a magnetic bottle, or it starts reacting with anything it touches. The stuff will consume an entire planet, left alone for enough time (making China Syndrome look tame), but is quite useful for starship reactors, where the core can be ejected into space in an emergency.

Frequent haunts (San Francisco)
Cafè Enchantè, Geary @ 26th Ave.
Coffee Bean @ Market, 3rd & 4th streets next to Four Seasons
Peets, Fillmore @ Sacramento
Peets, Van Ness @ Bush
Peets, Mission @ 3rd Street
On The Corner Cafè, Divisadero @ Oak St.

sorry, deleted double post hiccup. Connection problems. Moderator feel free to delete.

Simple answer is: it won't.

A poorly-designed fission reactor can fail in really bad ways because you have a huge pile of fuel with a reaction that can become self-sustaining until you have many tons of molten uranium on your hands, but a fusion reactor requires external inputs to keep the reaction going. A typical fusion reactor would contain a fraction of a gram of fuel at a temperature millions of degrees, held in place by magnetic fields and surrounded by many tons of metal: so if there was a problem in the reactor the gas would just expand, hit the walls and heat them up by a few degrees.

Hmm. That was a handwavy explanation. If you don't fill up a steam locomotive with enough water on a long trip, eventually the water remaining inside the pressure vessel is superheated* and the steam above can't contain it. It suddenly all vaporises, resulting in an explosion in the reactor core, just as much like what happened with Chernobyl. Well, uh...

(That is true, by the way. It has happened. Don't put a beer keg on a bonfire.) The point I'm trying to make is that explosions can happen for a lot of different physics reasons and you should be wary of just limping them together with "like what happened with Chernobyl" without a real understanding of the processes involved.

* In this context, superheated doesn't just mean "very very hot", it means a liquid under pressure at a temperature above its normal boiling point. Release the pressure and it all turns into steam very, very quickly: an explosion. Firemen call it bleve, boiling liquid expanding vapor explosion.

That was exactly what I have come up with before I have time to read your reply. I just needed a confirmation that overpowering the fusion reactor can cause it to explode but of course, I'm not talking about Chernobyl-size explosion, just a small explosion that is enough to destroyed a room, Hmm, an explosion that devastated the whole city, it could make an interesting sub plot.

Always do your best but never ever think that you are the best cause then, you would stop improving

Hard to figure out how to make a magnetically contained fusion reaction explode. Nuclear reactors existed naturally because all you need is a high enough concentration of enriched fuel, and using a water moderated reactor was apparently not obvious to the Russians.

Pressure increases linearly with temperature, while radiative dissipation increases with the fourth power. So for a fusion reactor to explode, rather than have some freak accident involving ultrapowerful magnets, you would need to have the pressure break the containment before quenching or cracking the magnets from the heat, which doesn't seem possible. The natural state of hydrogen gas is not to fuse - and similarly, CANDU reactors use unenriched fuel for much the same reason.

Thing is with a CANDU reactor you can at least have steam (and naturally, vent it appropriately). With fusion you have... a few grams of deuterium.

The most common misconception about the speed of light

A fusion reactor basically has one major problem, keeping the high temperature contents from destroying the containment. This is especially problematic with magnetic systems, as magnets get weaker when heated up. A secondary one is the decay of the containment vessel due to the bombardment of interior with high energy particles. However neither is likely to make the reactor explode as at worst the most that will happen is all of the contents escaping due to containment. However this should be noted as pretty bad anyway, as the plasma within is insanely hot. This will destroy everything nearby (remember this stuff is the same temperature as the heart of the sun.). Also it's under a very high pressure (again core of the sun levels) so it's going to be quite a plume (the reactor would probably rupture like an over-shook drinks can). This'd still be a disaster, but you're probably looking at building/ block level destruction than a nuclear blast.

A better idea might me to look at its fuel. Fusion reactors need a constant supply of hydrogen to run, which is famously explosive. In addition, fusion reactors need cooling for their magnets. Add their exotic coolants to a nearby stash of hydrogen and thrown in a well aimed leak and you could be looking at one heck of a bang.

I add all words used here to my word count. Yes, even the ones in the procrastination threads.

"A fusion reactor basically has one major problem, keeping the high temperature contents from destroying the containment."

No, the major problem with a fusion reactor is keeping the gas hot enough and dense enough to fuse: any failure causes a tiny amount of very hot gas to hit the containment vessel, which will typically have a mass a million or more times greater than the amount of fuel inside.

If you're talking about a super-advanced reactor which doesn't use a heavy containment vessel then you're right, it's likely to melt through and release a tiny amount of radioactive gas into the atmosphere, but in the near future you're talking about thousands of tons of metal vs a fraction of a gram of hot gas. Not a big deal.

I asked about this myself a few years ago while visiting one of the prototype research reactors and the guy who was showing us around pointed out that there simply isn't enough energy in the fuel to cause any significant damage to the reactor.

chernobyl didn't explode.

~Jesse James Akins

Yeah, but only because a lot of brave people gave their lives to prevent a blast that could have leveled Moscow.

There’s a whole new universe waiting for you: http://www.vastdistances.wordpress.com

There is one thing that hasn't been considered here and that is energy density. When I started designing the fusion reactors for the Arcturian spaceships I wanted to use the H->He reaction as there is plenty of hydrogen around for them to burn, collecting deuterium or tritium was too fiddly. However the problem is that hot hydrogen only fuses very slowly, you need a lot of it to get a significant power output.

To run a standard Arcturian ship you need 144 megawatts of power.

I realised that this would mean (serious handwaving here) having say a kilogram of material at fusion temperatures inside the reactor.

The containment problem is left as an exercise for the reader.

However this means that a plasma rupture or leak could cause a lot of damage. Captain Keefe, ACSF, takes up the story:

"We think he thinks he's some hold over Eva," said Keefe. "You'll have to sort that out between you. I think it's obvious what he's trying to do, he wants to see if his weapon will bring down an eighty-footer. He had it all set up the first time, but Jane was cautious and changed landing sites. Then he realised how fast an eighty-footer is, and concocted a plan to make one hold still, only Jane was too sharp for him."

"If damaging a ship was all-" began Eva, but Keefe turned on her.

"Listen, and listen well. An eighty-footer carries a hundred-and-forty-four megawatt fusion reactor. It's bloody difficult to rupture one, but if Duncan had managed it, it'd have vented plasma at about ten million degrees, and left a crater the size of a strikeball field. Somewhere in that crater would be a thin layer of carbon, which would be the remains of your own mother and daughter. You aren't playing games any more, you've sold out to the sort of person who'd make that happen, so that he could test his weapon, and very soon real people are going to be dying because of it. Do I make myself clear?"

Actually, it did in that the runaway reaction flash-boiled the surrounding water, blasting the 2200 lb steel and concrete lid off and destroying most of the superstructure above the reactor vessel. While a runaway reaction to the same extent as Hiroshima was unlikely due to the configuration of the fuel rods, it certainly was more powerful than most explosive ordinance.

A working fusion reactor would involve large quantities of hot steam, and would likely be dependent on liquid-cooled superconducting magnets. Either of which could level a building if handled improperly.

Actually, I have a rough idea for a steamless design for mine. The magnetic bottle is effectively the stator of an alternator and the plasma the rotor. It was the only way I could think of designing a rector that would give enough power but be no larger than a file cabinet.