HebaruSan

Brainstorming: Fusion power via counterweight

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While mowing the lawn my mind strayed as it often does to power generation and megaprojects. With ITER-style fusion power still decades away from practicality, I wondered about ways to exploit a more established method of fusion: the hydrogen bomb. The problem is how to convert a big impulse of energy into steady day to day flow for residential and commercial use. The Orion drive concept used a "pusher plate" to absorb energy from a nuclear blast for propulsion. Could something similar work for power?

temp-profile-1.pngDig a tall shaft into the ground. Put a hydrogen bomb at the bottom, and a massive counterweight on top of it. Detonate the bomb to raise the counterweight, converting the energy of the explosion to gravitational potential energy. Slowly lower it and extract energy to the grid via standard means (cranes/pulleys/turbines, etc.). Repeat with a new bomb each time the counterweight gets to the bottom. A few web searches gave me some scratch numbers for ballparking:

Typical energy from a hydrogen bomb:  2.09 × 1014 J   (58055 Mwh)

Mass of heaviest object ever lifted on land:  23178000 kg  (227376180 N)

Assuming no losses to friction/drag/etc., height that bomb would lift that object: 

   (2.09 × 1014 J) / (227376180 N) = 919 km

So best/worst case scenario, we'd need a vertical shaft 919 km deep. Some further web searches suggest that the temperature at that depth is around 2000° C and the rock may be molten.

So that's the baseline for this idea. Not very practical; obviously smaller bombs or bigger counterweights would reduce the needed depth, and frictional losses throughout the system would reduce both the power output and the maximum height of the counterweight.

Any other ideas for charging your phone with an H bomb?

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Well it turns out most hydrogen thermonuclear bombs get more than half of their yield from fission - the uranium tamper.

So even this is basically fission power and we already have fission reactors.

Thermonuclear bombs that have a higher percentage of their yield from fusion do exist but they have lower yields than a more conventional thermonuclear bomb for a given size.

We could use something other than gravitational potential. Maybe some kind of spring. If it follows Hooke’s law then the energy stored would be a function of the displacement squared, so maybe that could work. Would be a ridiculous spring though.

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55 minutes ago, Bill Phil said:

Maybe some kind of spring. If it follows Hooke’s law then the energy stored would be a function of the displacement squared, so maybe that could work. Would be a ridiculous spring though.

That has the advantage of working in any direction; you could surround the bomb with 6 pusher plates, each with its own ridiculous spring going up/down/left/right/forward/back.

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55 minutes ago, Bill Phil said:

 

Thermonuclear bombs that have a higher percentage of their yield from fusion do exist but they have lower yields than a more conventional thermonuclear bomb for a given size.

 

I get the impression that small and lightweight are not the primary concerns.

Maybe detonate the device inside a salt cavern and then run a heat engine off the molten salt.  

 

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13 minutes ago, farmerben said:

I get the impression that small and lightweight are not the primary concerns.

Maybe detonate the device inside a salt cavern and then run a heat engine off the molten salt.  

 

Yeah but it lowers the total energy output to use a non-fissile tamper.

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The size of a mountain, and down through the mantle... That would be some piston!  Like any piston, it would need some working fluid to be moved by the energy of the blast and not just... melt. Maybe pressurized Hydrogen would be appropriate? It would be a great gatherer of neutrons, and has a low enough viscosity to really accelerate our mountain!

Rather than just relying on height to store energy we might be able to save vertical space in our piston by turning it into a solenoid generator. If the mountain we're pushing were a giant magnet and the tube's walls were filled with alternating wire coils, we could generate electricity while the mountain was still on the rise using Lenz's law. It would become the world's largest generator! I'd need to think about it a while to make a real estimate, but it's fairly normal for the forces involved to be 10-100x greater than gravity, so our piston may only need to pierce the crust and not fully the mantle :D .

 

 

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Maybe using fluid instead of a fixed counter weight? Like, just fill up the tube with water, then it goes all geyser, then it flows back through multiple channels with generators which are closed when ready to fire again. 

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1 hour ago, Cunjo Carl said:

Rather than just relying on height to store energy we might be able to save vertical space in our piston by turning it into a solenoid generator. If the mountain we're pushing were a giant magnet and the tube's walls were filled with alternating wire coils, we could generate electricity while the mountain was still on the rise using Lenz's law. It would become the world's largest generator! I'd need to think about it a while to make a real estimate, but it's fairly normal for the forces involved to be 10-100x greater than gravity, so our piston may only need to pierce the crust and not fully the mantle :D .

I think I don't know enough about solenoid generators; how would this deal with storing the energy and converting it to a small steady flow over time?

27 minutes ago, Katten said:

Maybe using fluid instead of a fixed counter weight? Like, just fill up the tube with water, then it goes all geyser, then it flows back through multiple channels with generators which are closed when ready to fire again. 

Nice, I like how that ties into current efforts to store surpluses from wind and solar by pumping water uphill of hydroelectric plants.

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Posted (edited)

i thought about using a massive lead walled chamber with the nuke in the center. the chamber would be well insulated from heat loss (asbestos?) and evacuated of air before the detonation (the size of the chamber should accommodate the bomb vapor). the idea is that the nuke would melt the lead which would collect in a basin, a heat exchanger would go to a boiler that would feed turbines to generate power (the usual power plant setup). when the lead gets close to its solidification temperature it would be pumped out to recoat the chamber walls to reset for the next shot (probably just spraying it on the walls). the problem is the shot frequency probably wouldn't be very high. think of it more as a nuke charged thermal battery. im not sure how you would go about the buildup of fission products, so all the re-priming and maintenance would have to be done robotically. being in a lead walled chamber would keep much of the radioactivity contained. this structure would probably also be built deep underground for containment purposes.

brownie points if you can create the fusion explosion without a fission primary. of course if that tech ever got out everyone would have nukes. also there are probably better material choices.

Edited by Nuke

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20 minutes ago, HebaruSan said:

I think I don't know enough about solenoid generators; how would this deal with storing the energy and converting it to a small steady flow over time?

They wouldn't store energy very well, but would provide a 'good' way to convert the thermal energy of the nuke into useable electrical energy. (speaking relatively of course, most of this is just brainstorming for the fun! Given the size scales involved it would be hard to make work IRL) Once this electrical power is made, it would need to be stored in batteries or similar, which would be pretty prohibitive come to think of it. What other ways could we store that sort of energy though... I see now why you wanted the Mm piston.

Perhaps rather than a mountain, if we used the energy of the nuke to push water. Ah, @Katten just suggested this. It has some real advantages for storing silly amounts of energy! Just putting some numbers on paper, the Hoover Dam in the States can store (very roughly):

Energy = m*g*h
7.6*10^16J = (35.2km^3 * (10^3 m/km)^3 * 1000kg/m^3) * 9.8 m/s^2 * 220m
... relative to the 10^14J of the nuke.

So maybe instead we should do something like the Hoover dam but backwards. We could find a suitably deep fjord, dam off the entrance, nuke the water out of the inside and then gather energy by letting the water flow back in from the ocean! I'm sure nothing could go wrong... :blink:

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Make a pool on top. Push the water up, filling the pool.
Make it cold to force the water condesation. Use high mountains with cold tops.
Let the tropopause help you, it will keep the fountain below 9-17 km, so right above your mountains.

The tropopause is at 9 km in the polar regions, 17 at the equator.

1. Do we have some islands with snowy peaks? Does any forum user live there or they are uninhabited?

2. Himalayas. They are high and cold. And wide, it's also important for the water collection.
Some wide and deep well should be excaved between them.

3. Antarctica. Ellsworth Mountains are the highest place, up to 5 km. The tropopause is even closer to the peaks than in Himalayas. 9 - 5 = 4 while 17 -9 = 8.
Maybe even better place like Himalayas. Make Antarctica warm again!

 

And the well should be enough deep.

Spoiler

 

 

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10 hours ago, Bill Phil said:

Well it turns out most hydrogen thermonuclear bombs get more than half of their yield from fission - the uranium tamper.

So even this is basically fission power and we already have fission reactors.

Thermonuclear bombs that have a higher percentage of their yield from fusion do exist but they have lower yields than a more conventional thermonuclear bomb for a given size.

https://en.wikipedia.org/wiki/Tsar_Bomba#Genesis

 

Quote

The initial three-stage design (coded A620EN, not tested) was capable of yielding approximately 100 Mt (420 PJ) through fast fission, 3,000 times the size of the Hiroshima and Nagasaki bombs,[21] but it was thought that it would have caused too much nuclear fallout, and the aircraft delivering the bomb would not have had enough time to escape the explosion. To limit the amount of fallout, the third stage and possibly the second stage had a lead tamper instead of a uranium-238 fusion tamper (which greatly amplifies the reaction by fissioning uranium atoms with fast neutrons from the fusion reaction). This eliminated fast fission by the fusion-stage neutrons so that approximately 97% of the total yield resulted from thermonuclear fusion alone (as such, it was one of the "cleanest" nuclear bombs ever created, generating a very low amount of fallout relative to its yield).[22] There was a strong incentive for this modification since most of the fallout from a test of the bomb would likely have descended on populated Soviet territory.

Many bombs that use Fusion are simply Fusion boosted fission weapons:

https://en.wikipedia.org/wiki/Boosted_fission_weapon

That use fusion to boost the nuetron flux and cause more efficient fissioning of the fissile material. Early fission bombs were very inefficient: only a small fraction of the U235 underwent fission before the assembly came apart (before it blew itself apart and the chain reaction stopped). So for compact weapons, they were looking for ways to get as much of the fission fuel to split in the tiny fraction of a second that it achieves criticality.

Still, As the Tsar bomba shows... you can have your bomb be close to a pure fusion weapon if you desire.

 

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8 hours ago, KerikBalm said:

https://en.wikipedia.org/wiki/Tsar_Bomba#Genesis

 

Many bombs that use Fusion are simply Fusion boosted fission weapons:

https://en.wikipedia.org/wiki/Boosted_fission_weapon

That use fusion to boost the nuetron flux and cause more efficient fissioning of the fissile material. Early fission bombs were very inefficient: only a small fraction of the U235 underwent fission before the assembly came apart (before it blew itself apart and the chain reaction stopped). So for compact weapons, they were looking for ways to get as much of the fission fuel to split in the tiny fraction of a second that it achieves criticality.

Still, As the Tsar bomba shows... you can have your bomb be close to a pure fusion weapon if you desire.

 

I didn’t say you couldn’t.

Just that you would have to sacrifice energy on a per bomb basis. 

I think some of the estimates for the Tsar Bomba with a uranium tamper were around 100 megatons, double the lead tamper yield.

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1 hour ago, Bill Phil said:

I didn’t say you couldn’t.

Just that you would have to sacrifice energy on a per bomb basis. 

I think some of the estimates for the Tsar Bomba with a uranium tamper were around 100 megatons, double the lead tamper yield.

You initially responded to the idea with:

"So even this is basically fission power and we already have fission reactors." and that is what I take issue with. Considering that we have an example of a bomb that was 97% fusion energy, it is clear that bombs as a source of fusion energy are possible. You also said

"Well it turns out most hydrogen thermonuclear bombs get more than half of their yield from fission - the uranium tamper.

...

Thermonuclear bombs that have a higher percentage of their yield from fusion do exist but they have lower yields"

And while nothing you said was unambiguously false,  it was very misleading.

If I may, here's how I'd rephrase your first post so that I take no issue with it, it wouldn't be misleading, and it would respond to the OP's idea:

Quote

It turns out most hydrogen thermonuclear bombs get more than half of their yield from fission - the uranium tamper.

So we'd have to be careful about the bomb design if we want to call this "fusion" power, and not another form of basically fission power.

Thermonuclear bombs that have a yield of 97% of their energy from fusion have been tested, but most weapon designs optimized for size and with no concern about fallout have a "3rd stage" fission tamper to boost yield and result in a ratio closer to 50:50 Fusion:Fission power.

 

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Pure fission and boosted fission weapons are obsolete, virtually all modern nuclear weapons are Teller-Ulam design. A non-fissionable tamper (typically lead) leaves most of the energy yield from the fusion and significantly reduces fallout, which would be desirable if you want to reuse a system - or simply if fissionable materials (typically natural or depleted uranium) are in short supply. And as the Tsar Bomba test showed, a lead-tampered weapon can still be very powerful.

As far as harnessing that power goes, I don't think OP's idea of using the pressure mechanically is on to much. It would require a lot of massive and complex machinery, and would greatly increase the chance of a radioactivity release. More promising is to use the heat, as was mentioned above and as studied by a 1970s project.

https://en.wikipedia.org/wiki/Project_PACER

A drawback is the need for your fusion fuel to be in the form of precision-engineered nuclear bombs, which will be much more expensive than a bulk deuterium-tritium mix. Once the military surplus runs out (assuming you use it, which may be an issue as it's not low-radioactivity lead-tampered weapons), it's unlikely to be cost-effective.

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15 minutes ago, cantab said:

Once the military surplus runs out (assuming you use it, which may be an issue as it's not low-radioactivity lead-tampered weapons), it's unlikely to be cost-effective.

Say, a leader of a small tropical country has bought several nukes just on the occasion of army sales.
So, by using these nukes he can provide his country with cheap energy for several years.

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Slightly off topic, but if we're talking about building a giant tube and detonating a bomb inside, why not build a giant nuclear cannon to get things into orbit? You have an Orion style pusher plate at the bottom of your payload, you detonate a nuke behind you that vaporises part of the pusher plate and smacks it out of the tube at horrendously high accelerations. Something similar has happened by accident before and the steel cap was propelled to 66km/s, and that was without optimisation and a relatively small 300t bomb. If you want to lower the accelerations so you can carry more delicate payloads, you could perhaps flood the chamber with sea water that, when vaporised, could act as something of a "mass beam" to push your payload into space without it's own propellant. Of course, you'd have to angle the launch tube to get enough horizontal velocity and the payload would still need it's own engines to get into orbit, so maybe this makes more sense as a weapon instead. Or maybe it doesn't make any sense at all.

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Posted (edited)

All I can say is that I wouldn't be happy in case one of these had an accident nearby

Edited by Aperture Science

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If you're going to dig a 900km hole you might as well use geothermal energy at that point. As the first plot showed you're already well into the mantle, and temperatures down there are going to be quite toasty.

Rather than using a weight in a shaft to generate power, it would be quite useful as an energy battery. Lots of renewable sources are non-constant (e.g. solar, wind), and could use surplus to lift the weight up the shaft to store energy. When direct energy is not available, lower the weight and extract energy, probably using a highly geared pulleys to spin generators.

An example of this kinetic energy battery appears in the Neal Stephenson novel Anathem, where a series of descending weights are used to power a clock for hundreds of years (they had some weird priorities). 

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38 minutes ago, natsirt721 said:

 

If you're going to dig a 900km hole

 

How much energy would this take? 

@HebaruSan, how wide is this hole? Is 1m^2 big enough for the bomb?

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22 hours ago, Nightside said:

How much energy would this take? 

@HebaruSan, how wide is this hole? Is 1m^2 big enough for the bomb?

Let's say 1 m^2 hole, 900,000m deep. Total volume 900,000 m3, density of rock is about 3000 kg/m^3, so total mass is 2.7e9 kg. But wait, we only have to lift the first meter of rock 1 meter, and the second meter only needs to go 2 meters. Time for calculus!

Let dh be a differential height with units meters.  Gravitational energy is mass * height * gravity. mass = dh * area * density, or 3000 kg/m * dh.  Integrate from 0 to 900,000 f=(3000 kg/m * 9.81 m/s * h m)dh and we get...

1.19e16 J

Of course, this is pure gravitational potential energy of the core sample - actual energy costs are going to be much higher due to mechanical inefficiencies.

p.s someone check this math, I haven't solved an applied integration problem in a while.  The units check out, but that doesn't mean it's correct.

 

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On 6/18/2019 at 12:23 PM, Aperture Science said:

All I can say is that I wouldn't be happy in case one of these had an accident nearby

The whole thing already is that. :D

Also low yield compared to fission reactors. It's ok as a thought experiment, nothing more.

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Posted (edited)
On ‎6‎/‎16‎/‎2019 at 3:17 PM, HebaruSan said:

While mowing the lawn my mind strayed as it often does to power generation and megaprojects. With ITER-style fusion power still decades away from practicality, I wondered about ways to exploit a more established method of fusion: the hydrogen bomb. The problem is how to convert a big impulse of energy into steady day to day flow for residential and commercial use. The Orion drive concept used a "pusher plate" to absorb energy from a nuclear blast for propulsion. Could something similar work for power?



temp-profile-1.pngDig a tall shaft into the ground. Put a hydrogen bomb at the bottom, and a massive counterweight on top of it. Detonate the bomb to raise the counterweight, converting the energy of the explosion to gravitational potential energy. Slowly lower it and extract energy to the grid via standard means (cranes/pulleys/turbines, etc.). Repeat with a new bomb each time the counterweight gets to the bottom. A few web searches gave me some scratch numbers for ballparking:

Typical energy from a hydrogen bomb:  2.09 × 1014 J   (58055 Mwh)



Mass of heaviest object ever lifted on land:  23178000 kg  (227376180 N)

Assuming no losses to friction/drag/etc., height that bomb would lift that object: 

   (2.09 × 1014 J) / (227376180 N) = 919 km

So best/worst case scenario, we'd need a vertical shaft 919 km deep. Some further web searches suggest that the temperature at that depth is around 2000° C and the rock may be molten.

So that's the baseline for this idea. Not very practical; obviously smaller bombs or bigger counterweights would reduce the needed depth, and frictional losses throughout the system would reduce both the power output and the maximum height of the counterweight.

Any other ideas for charging your phone with an H bomb?

Earthquakes?

On ‎6‎/‎19‎/‎2019 at 8:49 PM, natsirt721 said:

If you're going to dig a 900km hole you might as well use geothermal energy at that point. As the first plot showed you're already well into the mantle, and temperatures down there are going to be quite toasty.

Rather than using a weight in a shaft to generate power, it would be quite useful as an energy battery. Lots of renewable sources are non-constant (e.g. solar, wind), and could use surplus to lift the weight up the shaft to store energy. When direct energy is not available, lower the weight and extract energy, probably using a highly geared pulleys to spin generators.

An example of this kinetic energy battery appears in the Neal Stephenson novel Anathem, where a series of descending weights are used to power a clock for hundreds of years (they had some weird priorities). 

Or just use Geothermal energy and not bother with the solar and wind. If your digging a 900 km shaft economically solar and wind is a side show all that heat would be enough to boil tonnes of water. According to heb's graph you would not even need to go beyond the lithosphere to heat up water. If you went a littile bit deeper to where it is 1000 *C (the asthenosphere according to the graph. To ensure a quick boil you can dig a side cavern where you heat up the water and take the steam to power turbines. Then take the water and put it down a slide with a water turbine spinning the system even faster as it is falling via gravity back into the heating area. Global Warming solved and hundreds if not thousands of megawatts of energy. The question is the cost of digging such a hole and cavern also it would need to be autonomous because humans could not be down their and if a earthquake/rock collapse happened those workers would be unreachable. It could be controlled from the surface.

As a note that graph assuming im looking at it right seems off. If you measure it each section is about the same length and the asthenosphere seems to begin at 100 meters. But Wikipedia says otherwise. https://en.wikipedia.org/wiki/Asthenosphere

Also this seems rather preposterous given other attempts at drilling such holes. I doubt it would be economically worth it unless hundreds of thousands of megawatts could be generated from one plant. Since it is so far beneath the surface is would be safe from some smaller asteroids and EMPs I think so it has some Planetary Defense value because if their is ever another disastrous solar flare then our actual power source is safe. 

https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

Edited by Cheif Operations Director
More info

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Posted (edited)

Look at the heat budget of earth

https://en.wikipedia.org/wiki/Earth's_internal_heat_budget

It 47 +- 2 terawatts that is (one terawatt is 1 trillion watts) If we harnessed even 1% of that or 470,000,000,000 watts (470 billion gigawatts if I did my math right) we would have a ton of extra power Some the RMBK-1000 reactor produced 1 gigawatt and 4 of the,provided 10% of Ukraine's power if I remember correctly(do not quote me on that)  

Edited by Cheif Operations Director
I think 1 million is = to 1 billion for some reason :)

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