View Full Version : Fusion Power and the Big Boom

06-07-2001, 10:37 AM
Pretty simple question here:

Let's say the experiemnts I'm conducting with my hommeade Spheromak in my bathtub are successful and I am able to produce lots and lots of electricity using fusion. I build a power plant outside sunny Memphis and sit back and let the cash roll in. But Murphy's Law catches up with me and I have a failure of magnetic containment at my new power plant. What happens? Does the reaction become uncontrolled and flatten most of the Memphis suburbs? Or does the containment vessel simply melt and leave me with an expensive cleanup bill?

And let's not limit our discussion to the Spheromak design. Would the Tokamaks turn into a thermonuclear bomb under the right circumstances? Is there any way any of the current fusion design proposals could get out of control and go Dr. Strangelove on us?

06-07-2001, 11:47 AM
My WAG...

It'd certainly flatten your bathroom, your house and probably a few other nearby houses as well but I think Memphis as a whole would be ok.

Explosions and the attendant pressure wave that does most of the damage are caused by a LOT of energy being released over a very SHORT period of time. A nuclear reactor isn't working under the same principles. It's keeping a controlled amount of energy running at a constant rate. I don't think the energy in an equivalent timespan is anywhere near what you see in a thermonuclear device.

So, you get a relatively little BOOM and then a meltdown and an unholy mess.

Presumably one could equate a fusion Tokomak to a regular fission reactor and those don't seem to explode in the same fashion as an A-bomb does (as evidenced by Chernobyl...blew the top off the reactor house and made a mess but no mile wide crater).

Caveat: I don't know if it is fair to draw an analogy between fusion and fission reactors but it sounds reasonable.

As far as the Spheromak goes the reactor uses some fundamental principles of nature to cause the hydrogen plasma to essentially generate its own magnetic field. The stronger the fusion reaction the naturally stronger the containment field becomes. Whether this makes the reactor inherently safe (*cough* like the Titanic was 'unsinkable) or whether it is safer than a Tokomak design I don't know.

06-07-2001, 01:20 PM
This is mostly WAG too, but to expand a bit on Whack-a-Mole's post. . .

The magnetic field in a fusion reactor is there to provide a "bottle" to keep the plasma in. To do fusion, you need a hot/high-pressure plasma, which you can't exactly keep in a Mason jar--the jar would melt. Or blow up. Or whatever. Even if you could make a jar with the physical strength to contain the plasma, the plasma would cool due to contact with the jar, making it too cool to fuse.

The above I'm pretty confident about. What follows is pure wag.

If you lost your containment field, your number-one problem would not be runaway fusion--the fusion would cease as the super-hot plasma expanded. And the rapidly-expanding super-hot plasma would be your problem.

First of all, it would melt lots of stuff. First to go would be the walls of your vacuum chamber. I doubt that would slow it down much. Kiss your bathtub good-bye. Much of the air will be ionized and turn to plasma as well--not as hot as the original plasma, of course, but hot enough to ruin your day. It'll robably set your house on fire, at the very least.

Second, super-hot plasmas are made of fast-moving charged particles and high energy photons--radiation, in other words. I'm not sure how fast the little particles would be going (how "hard" the radiation would be), and what would be in the mix--lots of beta (electrons) and gamma (photons), certainly, probably a good share of alpha (helium nuclei) as well. Plus a lot of protons flying around, but I'm not sure how dangerous those buggers are--they aren't as ionizing as the other types of radiation, but they use proton rays in cancer therapy, so it can't be very good for ya.

I eagerly await an answer from a real physicist.

Saint Zero
06-07-2001, 02:01 PM
Fusion derives its power from fusing hydrogen particles together. Thus the need for massive magnets and lazers and the like.

If your bathtub Tokamak, Spheromak, or even the new NSTX loses magnetic integrity, you might lose the bathtub. You see, the one main thing keeping fusion from being easy to produce is the fact that turblence cools the reaction. The magnets and lazers keep the pressure up, and thus the turblence down.* Without that, the plasma will cool down in short order. If you dump a ton of hydogen into the mix, it'll cool down and stop because your magnetic field won't be able to pressurize it quick enough to maintain the heat needed.

*Physics was a while back: IANAHEP. (I am not a High Energy Physicist