500MW from half a gram of hydrogen: The hunt for fusion power heats up

http://www.extremetech.com/extreme/123837-500mw-from-half-a-gram-of-hydrogen-the-hunt-for-fusion-power-heats-up

by ukdm • 14 years ago

22 44 14 years ago

ntoshev• 14 years ago

They probably mean MW/h ...

pieter• 14 years ago

ITER won't produce any stable power at all, so they most likely mean something like "A single run of ITER will consume about half a gram of hydrogen while having a peak output of 500MW (for a few seconds).

mrsebastian2• 14 years ago

Yeah, the plan for ITER is to produce 500MW over 1,000 seconds, with an input power of 50MW (and 0.5 grams of deuterium-tritium fuel).

The current record is, like, 10 seconds and no one has broken even on input/output power...

Edit: Ah, actually the current record is less than 1 second: http://en.wikipedia.org/wiki/ITER#Background

DanWaterworth• 14 years ago

I thought that, but I now think it means in a single run, using just half a gram of hydrogen, the peak output power is 500MW, it would be helpful if it also mentioned how much usable energy was generated too.

mrsebastian2• 14 years ago

I don't think anyone knows how much 'usable' energy ITER will generate (plus, ITER won't be a power plant -- the heat produced will actually be thrown away -- so I guess we won't ever know.)

tocomment10• 14 years ago

Fusion idea that I've always had. Why can't we scale up a something like a car engine's piston and cylinder to be 1000's of times bigger and explode hydrogen bombs in it to move the piston up and down?

I know it sounds kind of absurd to think about but it seems like it would work to me. Can anyone explain why it wouldn't work? Is it just a cost issue?

rbarooah2• 14 years ago

What use would this have?

tocomment10• 14 years ago

Generate energy, use the piston to drive a giant generator.

GiraffeNecktie2• 14 years ago

Sounds great except for the absurdly impractical parts (i.e. exploding hydrogen bombs to move a giant piston). Where would you propose expelling the radioactive gases after the first stroke of the engine?

tocomment10• 14 years ago

Good point about the radioactive gas. I wonder if there is some way to mitigate that?

tocomment10• 14 years ago

Funny this was down voted on the same day we have this article on the front page: Bill Gates: We need crazy energy entrepreneurs

Perhaps we're part of the problem? We should discuss radical energy ideas, teach others what wouldn't work, and how to change them, not poo poo them.

dbcooper3• 14 years ago

No. Even "crazy" entrepreneurs need to have some familiarity with their business ...

huxley3• 14 years ago

Only for some definitions of crazy. Bill Gates isn't using pyramid power to cure malaria, is he?

silon3• 14 years ago

See project Orion.

dbcooper3• 14 years ago

The coulomb barrier (electromagnetic force derived) for hydrogen nuclei is not overcome until a temperature of about 120 million kelvin. Obviously, no metallic materials can operate at this temperature.

Controlled magnetic fields are required to contain a plasma above the coulomb limit.

tocomment10• 14 years ago

See my other comment above. Let me know what you think.

arethuza• 14 years ago

One idea that was actually investigated was to explode atomic bombs underground and use the heat released to produce steam that could be user to generate power. The Project Gnome test used a relatively small bomb (3.1kt) which created a 20m wide cavity - which people eventually entered (!):

http://en.wikipedia.org/wiki/Project_Gnome

http://www.wipp.energy.gov/science/ug_lab/gnome/gnome.htm

mseebach• 14 years ago

I think that combustion engines are mainly good for their scalability in terms of output: You can make a combustion engine go from cold to pulling a tractor trailer up a mountain in seconds. For sustained loads (electricity generation), the steam pressure and turbines setup is much more efficient.

huxley3• 14 years ago

Are there actually any materials which could withstand repeated contained hydrogen bomb explosions in the same manner as a piston? No point having a 1000x sized piston you only use 2 or 3 times.

alphaBetaGamma• 14 years ago

Nuclear fusion needs high temperature (so that the hydrogen nuclei have enough energy to get close together). "High" means ~10 million kelvin, several orders of magnitude higher than the fusion/evaporation point of any material.

So your giant piston will melt and evaporate long long long before you get fusion.

tocomment10• 14 years ago

I'm talking a really giant piston and cylinder so that the piston and cylinder walls are far enough away from the blast that they don't experience destructive levels of heat. (You'd explode the bomb in the middle of the cylinder (during freefall))

aqme283• 14 years ago

Despite their name, hydrogen bombs are primarily uranium fission bombs[1].

What you've described is just another kind of fissile nuclear reactor, though surely far less stable and likely far less efficient.

The other problem is that materials weaken and swell (as in gain actual volume) when bombarded with radiation. It would be pretty difficult to make a piston that changes shape throughout its life.

[1] http://en.wikipedia.org/wiki/Teller%E2%80%93Ulam_design

tocomment10• 14 years ago

So it's not possible to trigger large scale fusion from a fission based trigger?

tgflynn4• 14 years ago

If I understand what you're suggesting I think it addresses only the aspect of how to convert the energy released by fusion reactions into useful work (ie. mechanical or electrical energy). This is not actually the difficult part of building a practical fusion reactor.

Even if your design could work you need a way to produce pure fusion explosions. There is currently no sufficiently energy efficient way of doing this. Thermonuclear bombs require a fission explosion to trigger them (in fact I believe most produce more energy from fission than from fusion).

The laser based inertial confinement schemes actually are designed to produce tiny pure fusion explosions. If such a system could be built that produced more fusion energy than the driving lasers consume there would be many ways to convert that energy into electrical energy (photovoltaics, steam generators/turbines, etc.). I suspect an internal combustion engine would not be the most practical of these methods from an engineering point of view.

tocomment10• 14 years ago

> (in fact I believe most produce more energy from fission than from fusion).

If this is true, then that puts a kink in my design. I assumed the vast majority of energy output was from fusion. (why else would they build them?)

I mainly suggest my design because it seems so difficult to trigger fusion without fission using current technology.

bradleyland3• 14 years ago

Lots of great answers here, but only a couple really get down to brass tacks.

TGFlynn answers the question of why we can't use fusion bombs: "Thermonuclear bombs require a fission explosion to trigger them (in fact I believe most produce more energy from fission than from fusion)." So in short, even setting off "fusion" bombs produces lots of bad byproducts.

The other part of your question is, "why not a big piston and cylinder?" Car engines are heat engines as well. They convert heat in to kinetic energy (motion). The problem is that they're relatively inefficient when compared to the typical means of heat/motion conversion used in a power plant. They're also far more complex and require more maintenance than other, simpler designs.

The design of a car engine has advantages that suit it well to use in an automobile. Namely that it's power output is easily variable. You don't need peak horsepower when sitting at a stoplight, so you throttle the engine back and generate far less power. This requirement is almost nonexistent in power plants. There is some variability, but you're dealing with average power consumption from thousands of households. The rate of increase/decrease is much, much slower than you find in an automobile.

Because of this, power plants use heat engines that might require a lot of energy to get started, but are more efficient once operating. Steam generators coupled with turbines are most common. The heat is used to boil water, which creates steam, which is used to drive some type of turbine. Turbines are wildly efficient if they're designed properly. The primary inefficiency in a steam/turbine power plant is startup and shutdown, but plant operators try to minimize this impact by employing operation strategies that distribute load in a way that can scale up and down minimally.

So, why not use a large piston in cylinder design? Because it's less efficient, more complex, requires more maintenance, and requires more materials to construct.

bradleyland3• 14 years ago

There's a greater lesson in all this discussion. Great ideas can be stifled by the limitations of knowledge. That is to say, if you "know" that an idea cannot work, you may not explore it. However, if you know nothing about the principles that limit a field, you can't even begin to postulate solutions, because you can't see that an idea is as absurd as putting the cart in front of the horse.

zerostar07• 14 years ago

Looks like those sun gamma rays haven't been following their diet.

GiraffeNecktie2• 14 years ago

I'm not sure why we're still pursuing the incrediblly difficult and expensive route of fusion when thorium is simple, safe, inexpensive and incredibly abundant.

JumpCrisscross• 14 years ago

Because the fusion route is cheaper and more abundant not to mention more powerful. It's not an either or.

torstesu• 14 years ago

I completely agree, especially since Norway has large reserves of the stuff. One challenge though, is that uranium is also abundantly available and still much cheaper to mine than thorium. Another challenge is that it is not the fuel which drives the cost, as in conventional power plants; it is the capital cost concerned with building the reactors themselves. Therefore, a thorium-fueled reactor has to be considerably cheaper to build than a uranium-fueled reactor and it is easy to pose the question if this will ever be true. There has to be some serious subsidizing to incentivize commercial development, adaption and investment.

DanBC• 14 years ago

People are scared of "Nuclear" - mention uranium and many people will panic.

There's the problem of allowing some countries to have a Uranium energy programme which gives them access to the beginnings of nuclear weapons technology.

drucken• 14 years ago

1. Thorium is a natural by-product, in fact it is in the waste slurry, from rare earth mineral mining.

2. Tiny amounts are required relative to uranium for electricity production. We have already mined in the West more than we will need for a hundred years, if we had production Molten Salt Reactors today.

3. It is far more electrically efficient than uranium.

So, there is no comparison purely based on which is the better fuel for fission. Thorium wins by multiple factors if not magnitude across many aspects, including fission waste prodcuts.

However, that said, the trust cost of fission is, as you mentioned, the upfront cost of the nuclear reactors. Since this quasi-government industry has seen little innovation in practice for 70+ years, conventional nuclear power plants have remained enormous capital sinks and risky endeavours.

There is now some serious research going into MSRs (including thorium) and other nuclear tech. But it is mainly being led by China, excluding sidetracking efforts like the Travelling Wave Reactors of Bill Gates et. al, who need as much energy as they can get.

aqme283• 14 years ago

This article talks about tokamaks like they're the only magnetic confinement technology out there. Things like stellarators and dipoles have been gaining a lot of ground lately and could one day overtake tokamaks as the standard magnetic confinement tech.

http://en.wikipedia.org/wiki/Wendelstein_7-X http://en.wikipedia.org/wiki/Levitated_dipole

500MW from half a gram of hydrogen: The hunt for fusion power heats up

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