[Mefustae]

The Hindenburg disaster ruined the concept of airships as anything other than a niche for most things. Ironic cause more people survived than died and the passengers who did die were all killed by jumping/falling out of the ship as it crashed. Those who stayed inside all survived.

Even then it wasn't because of the hydrogen that made it go up, it was the paint.

Well, to be fair, the hydrogen didn't exactly slow the process. Unless the Mythbusters were wrong, at any rate. Are you saying the Mythbusters were wrong? If you are, I don't think you truly appreciate what you're saying. Sir, would you like to step outside?

[Shade]

The Hindenburg disaster ruined the concept of airships as anything other than a niche for most things. Ironic cause more people survived than died and the passengers who did die were all killed by jumping/falling out of the ship as it crashed. Those who stayed inside all survived.

Indeed. Airships are inherently safe - Even if punctured, they don't go pop, they just leak very, very slowly. You could empty an ammo belt from a chaingun into one and it might not even notice until several hours later when the helium pressure started to drop noticably, and from that point they'd still have hours to do something about it before it became a real problem. And due to helium being an inert gas, they don't exactly burn very well either, and, even if they did, since you'd be under the thing instead of above you're still mostly safe from the fire and heat, so you can just wait until you're on the ground and then get out.

But ah well, perhaps some day people will come to their senses and realize there's a difference between a flawed early 1900s design and the stuff that would be built today. At least, I hope so. Because I've always had a love for huge airships and I'd dearly like to see them return in some form so I can experience them first hand

Even then it wasn't because of the hydrogen that made it go up, it was the paint.

That's one theory. As far as I know it has never been proven one way or another. But as Mefustae says, the presence of hydrogen certainly wouldn't have helped matters, so it's a fair bet to say that had it been using helium, the burn would have taken longer.

[Flaser]

Actually, you're all correct. There are several different possible fuels for fusion power. Helium-3 is one of the better ones as it doesn't result in any radioactivity itself (although side products from its fusion might do).

Not entirely correct either.

Even in a He-3, De reaction you can't avoid spontaneous De-De reactions which do produce a nominal amount of neutrons. (The proposed "good side" of a He-3 reaction is that it produces less neutrons which require heavy shielding, instead producing protons which can be contained with a magnetic field).

Moreover all fusion reactions produce massive amounts of radiation. That's where all the excess energy goes. Hence why the internal parts of the reactor are massively irradiated. The reason why it's a lot better than a fission reactor is, that these are merely contaminated parts, and you don't have to deal with massive amounts of used radioactive fuel.

[Flipside]

The thing about Hydrogen is that it is lighter than air, hence why it is used for balloons. The thing about the Hindenburg was that the balloon was above the passenger compartment and heat rises.

That's why most of the Hindenburg victims were those who jumped.

Edit: Of course, had it happened 2 miles over the Atlantic, it would have been a different story, in some ironic way, it's almost lucky that when it did catch, it wasn't that far off the ground.

[karajorma]

Not entirely correct either.

Even in a He-3, De reaction you can't avoid spontaneous De-De reactions which do produce a nominal amount of neutrons. (The proposed "good side" of a He-3 reaction is that it produces less neutrons which require heavy shielding, instead producing protons which can be contained with a magnetic field).

Moreover all fusion reactions produce massive amounts of radiation. That's where all the excess energy goes. Hence why the internal parts of the reactor are massively irradiated. The reason why it's a lot better than a fission reactor is, that these are merely contaminated parts, and you don't have to deal with massive amounts of used radioactive fuel.

That's kinda what I said. The fusion of ³He doesn't itself result in radioactivity but it's products/side reactions might do.

So since ³He + ²H and ³He +³He reactions don't produce neutrons themselves it makes ³He a better fuel. Especially in the second case where you're only pumping in ³He and can only get side reactions once you've built up some waste products.

[perihelion]

There's no "might do" about it.  That is what does happen.  It has been experimentally established.

I also don't think relying on the Helium-3 / Deuterium reaction is a practical solution because it doesn't really address the problem.  When you are talking about reactions that are only sustained for a couple microseconds, fine, starting off with a primary reaction that produces no high-energy neutrons might make sense.  There's hardly enough time for the daughter reactions to kick in.  But, I don't know anyone daft enough to suggest that microsecond fusion "pulses" are a viable way to produce power.  They are great for studying fusion and plasma behavior in a lab environment, but a sustained reaction is what is needed for a practical power source.

What we really need is some way of directly addressing the high-energy neutron problem, because I see no way to side-step it.  In any steady-state reaction, regardless of your initial fuel, you are going to end up having the reactions with the highest cross-sections take dominance in a very short period of time.  That means you are going to get a lot of high-energy neutrons, period.  Better shielding is theoretically possible, but that still doesn't address the fundamental problem that those neutrons are carrying huge amounts of energy out of the system.  That's energy we need to capture.  Ideally, not just capture but keep within the reaction itself so it can be self-sustaining.  None of the current approaches are capable of achieving this.

Unless someone figures out a way to reflect neutrons or persuade the plasma itself to absorb more of them, I cannot see fusion except as a very interesting (and expensive) science project.

[karajorma]

Wouldn't a fuel that resulted in less high energy neutrons be better then? It might not eliminate the problem but just reducing the problem would surely make it a better choice, right?

[Flaser]

Not entirely correct either.

Even in a He-3, De reaction you can't avoid spontaneous De-De reactions which do produce a nominal amount of neutrons. (The proposed "good side" of a He-3 reaction is that it produces less neutrons which require heavy shielding, instead producing protons which can be contained with a magnetic field).

Moreover all fusion reactions produce massive amounts of radiation. That's where all the excess energy goes. Hence why the internal parts of the reactor are massively irradiated. The reason why it's a lot better than a fission reactor is, that these are merely contaminated parts, and you don't have to deal with massive amounts of used radioactive fuel.

That's kinda what I said. The fusion of ³He doesn't itself result in radioactivity but it's products/side reactions might do.

So since ³He + ²H and ³He +³He reactions don't produce neutrons themselves it makes ³He a better fuel. Especially in the second case where you're only pumping in ³He and can only get side reactions once you've built up some waste products.

It DOES result in radioactivity: plain old "gamma radiation" regardless what you use as fusion fuel.

[perihelion]

Wouldn't a fuel that resulted in less high energy neutrons be better then? It might not eliminate the problem but just reducing the problem would surely make it a better choice, right?

I don't think the high cost of obtaining helium-3 and tritium are going to be overcome by the minimal benefit they provide in the long run.  The neutron flux is still pretty high.  It does not take long at all for the daughter reactions to start kicking off neutrons.  How long depends on how you design your reaction, but we're talking seconds at best.  Probably scant fractions of a second.

On the other hand, using a fuel with an initially low neutron emission rate may make it easier to get the reaction started.  Kind of like priming a gasoline engine?  That mode of heat loss would be minimized even if only for short time.  But in a steady-state reaction I don't think you'd see much difference unless you plan to exhaust most of your fuel unburned such that the fuel doesn't spend enough time at high temperature / density for the daughter reactions to do much damage...

...don't burn all the fuel... that is an idea I'd never considered before.  hmm.  You know, that might actually work.

[redsniper]

* redsniper patents the idea before perihelion.

[perihelion]

   Is there any precedent for using online forums as evidence of prior art?

[karajorma]

...don't burn all the fuel... that is an idea I'd never considered before.  hmm.  You know, that might actually work.

Given the fact that helium is basically inert and hydrogen isn't it probably wouldn't be that hard to scrub off the hydrogen either. The main issue would be cooling the exhaust before scrubbing and then reheating the fuel afterwards. But maybe you could use that as part of the power generation step.

[Kosh]

http://www.hydrogennow.org/Facts/Safety-1.htm

1. The bags of hydrogen that provided the lifting force for the Hindenburg were NOT the main contributor to the fire. The surface of the ship was coated with a combination of dark iron oxide and reflective aluminum paint. These components are extremely flammable and burn at a tremendously energetic rate once ignited. The skin of the airship was ignited by electrical discharge from the clouds while docking during an electrical storm. This reaction has been proven chemically for years, and was demonstrated with actual remnants of the Hindenburg sixty years later, which burned as vigorously as on the day of the disaster.
2. The hydrogen burned quickly, safely, above the occupants. When the escaping hydrogen was ignited by the burning skin of the airship, it burned far above the airship, and was completely consumed within 60 seconds of the ignition. During this period of time, the airship descended to the ground from the 150-foot docking tower

'nuff said.

[karajorma]

Wikipedia gives both arguments.

Those who believe hydrogen was the initial fuel discount arguments for the incendiary paint theory as not credible. They point out that cellulose acetate butyrate (CAB) varnish is rated within the plastics industry as combustible but nonflammable. That is, it will burn when placed in a fire but is not readily ignited by itself. In fact, it is considered to be self-extinguishing. That many pieces of the Hindenburg's skin survived despite such a fierce fire is cited as proof. In his experiment, Addison Bain used a high-energy ignition source (a spark) to make it burn.

Fe2O3 + 2Al → Al2O3 + 2Fe (aluminum and iron oxide reaction)

They point to pictures that show the fire burning along straight lines coinciding with the boundaries of gas cells. This suggests that the fire was not burning along the skin, which was continuous. Crew members stationed in the stern reported actually seeing the cells burning.

[Flipside]

To be honest, a site advocating Hydrogen would probably try to stress the fact it wasn't hydrogen that caused the Hindenburg, since the Hindenburg is one of the first images that come to mind when people mention Hydrogen balloons.

Personally, I'm not convinced, I've put hydrogen in a test tube an performed a 'pop test', to suggest that stuff doesn't contribute to a fire is kind of like saying that 3 weeks of snow are completely unrelated to loud noises, therefore snow does not contribute to avalanches.

[Dark RevenantX]

Oh the humanity!

[Ashrak]

talking about fusion when is the ITER TOKAMAK reactor suposed to go online?

[Mefustae]

talking about fusion when is the ITER TOKAMAK reactor suposed to go online?

Don't hold your breath.

Construction of the ITER complex is planned to begin in 2008, while assembly of the tokamak itself is scheduled to begin in the year 2011.

[Ashrak]

so the whole mayan calendar world exploding is just right at the time of the reactor going online awesome

[perihelion]

Given the fact that helium is basically inert and hydrogen isn't it probably wouldn't be that hard to scrub off the hydrogen either. The main issue would be cooling the exhaust before scrubbing and then reheating the fuel afterwards. But maybe you could use that as part of the power generation step.

The problem is getting new fuel in and old fuel out of the reaction stream without causing a disruption.  Regardless of how much of the fuel you burn before you exhaust it, this is extremely difficult.  Dealing with the exhausted gases once they are out of the reaction stream is trivial compared to getting them out in the first place.  Some of the stellarator designs seem to have a better shot at this than any other concept I've seen so far.