Now that fusion power in the form of a tokamak is a bust, and civil fusion power in the form of laser-induced fusion is also a bust, could we power a city using a good old-fashioned H-bomb? Set it off in a large underground cavern filled with liquid and use the resulting hot liquid to power a turbine until it cools. Then set off another one in the same place.

I’m pretty sure that using a 1-kT A-bomb in this way is within current materials and safety specifications, but am far from sure about a 1-MT H-bomb.

Checking web – https://www.reddit.com/r/AskHistorians/comments/4lflb1/what_was_the_smallest_hbomb_ever_produced/

“There is not as big a divide between atomic bombs and hydrogen bombs as you might think. At the low end, a small amount of deuterium and tritium (isotopes of hydrogen) are added in the hollow centre of the fission package. This releases neutrons when compressed by the explosion. These neutrons interact with the plutonium or uranium to increase the fission yield. This allows a smaller amount of Pu or U to be used, reducing the size, weight and cost of the bomb. An example is the WE177A, which weighed 600lb and would typically be carried by a fighter (although in practice RAF planes never carried live weapons other than on bomb tests). The WE.177C weighed 1000lb, delivered 190kt, and was also delivered by strike fighters.”

“Staged nuclear weapons add more hydrogen in a secondary stage outside the core. It is possible to get most of the yield from fusion, but in practice they usually use the neutrons to increase fission yield. These are larger.”

“They have had low-yield boosted nuclear devices since 1951 with the RDS-2 / Joe 2 test, which gave 38kt.”

So to summarise that, H-bombs can be as small as 38kT. And the original question then becomes – how big a H-bomb could be completely contained within a large underground cavern lined with concrete and filled with a heavy liquid such as bromoform or sodium polytungstate solution?

mollwollfumble said:

Now that fusion power in the form of a tokamak is a bust, and civil fusion power in the form of laser-induced fusion is also a bust, could we power a city using a good old-fashioned H-bomb? Set it off in a large underground cavern filled with liquid and use the resulting hot liquid to power a turbine until it cools. Then set off another one in the same place.

I’m pretty sure that using a 1-kT A-bomb in this way is within current materials and safety specifications, but am far from sure about a 1-MT H-bomb.

Checking web – https://www.reddit.com/r/AskHistorians/comments/4lflb1/what_was_the_smallest_hbomb_ever_produced/

“There is not as big a divide between atomic bombs and hydrogen bombs as you might think. At the low end, a small amount of deuterium and tritium (isotopes of hydrogen) are added in the hollow centre of the fission package. This releases neutrons when compressed by the explosion. These neutrons interact with the plutonium or uranium to increase the fission yield. This allows a smaller amount of Pu or U to be used, reducing the size, weight and cost of the bomb. An example is the WE177A, which weighed 600lb and would typically be carried by a fighter (although in practice RAF planes never carried live weapons other than on bomb tests). The WE.177C weighed 1000lb, delivered 190kt, and was also delivered by strike fighters.”

“Staged nuclear weapons add more hydrogen in a secondary stage outside the core. It is possible to get most of the yield from fusion, but in practice they usually use the neutrons to increase fission yield. These are larger.”

“They have had low-yield boosted nuclear devices since 1951 with the RDS-2 / Joe 2 test, which gave 38kt.”

So to summarise that, H-bombs can be as small as 38kT. And the original question then becomes – how big a H-bomb could be completely contained within a large underground cavern lined with concrete and filled with a heavy liquid such as bromoform or sodium polytungstate solution?

Underground test depths.

Plumbob Rainier, 1.7 kT, depth 283 m – fully contained.
Amchitka Milrow, 1 to 1.2 MT, depth 1,220 m – fully contained but created a dome 5 m high and 6 km wide, which is unsatisfactory.
Amchitka Cannikin, 5 MT, depth 1,860 m – fully contained but created a dome 6 m high which subsided into a lake, which is unsatisfactory.

This table ought to be useful. Note that going from 1 kT to 1 MT is only a factor of ten in radius.

So let’s take our radius to be edge of unstrained zone – 1 km for 1 kT and 10 km for 1 MT. Hmm, that’s big. Too big.
OK. Let’s take our radius to be edge of cracked zone – 120 m for 1 kT and 1.2 km for 1 MT. Hmm, that’s small. Too small?
250 m radius is about the biggest natural cavern, but that’s filled with air which makes it intrinsically weaker.

Perhaps we could install energy dissipating devices in the cavern, such as a concrete mesh (like armour blocks for seawalls) that turns kinetic energy first into turbulence and then into heat.

Note that average temperature rise becomes independent of bomb yield, because cavern volume is proportional to yield. 1 kT is 4.184 × 10 ¹² joules. 120 m radius is 7 × 10 ⁶ metres cubed.

Oh, slight problem, temperature rise is only 0.14 °C. Independent of bomb yield. That’s too small for efficient conversion of heat to mechanical work.
Back to the drawing board.

mollwollfumble said:

Now that fusion power in the form of a tokamak is a bust, and civil fusion power in the form of laser-induced fusion is also a bust, could we power a city using a good old-fashioned H-bomb?

You mean they are not 10 years away any more?

When did that happen?

> Oh, slight problem, temperature rise is only 0.14 °C. Independent of bomb yield. That’s too small for efficient conversion of heat to mechanical work. Back to the drawing board.

Tentative solution, fill the space around the H-bomb with beer.

Well, not actually beer but a liquid of the type “wet foam”, a bubbly liquid. The gas will (temporarily) absorb the pressure. Scattering off the 1000:1 density ratio surfaces will remove the shock wave. The two liquids will convert kinetic energy to heat via turbulence. And unlike solids the processes are all completely reversible.

Picture showing “wet foam” at the bottom.

Bubbly liquid.

For a 1 kT bomb, reducing the radius from 120 m to 40 m would increase the temperature from 0.14 °C to 4 °C. Reducing it to 12 m would increase the temperature from 0.14 °C to 140 °C.

This BOE calculation does not look right. The melting point of rock varies from 600 °C to 1200 °C. If I set the 4 m melt cavity minimum radius to 1200 °C then 600 °C would correspond to a radius of just 5 m, not 12 metres. 140 °C at 12 metres would be 3800 °C at 4 m rather than 1200 °C. OK, so the measurements quoted in the table above for the radius of the melt zone are wildly inaccurate rather than plain wrong.

So if the foam absorbs the kinetic and pressure energy well enough then a 1 kiloton bomb in a 12 m radius cavity full of “beer” and a 1 megaton bomb in a 120 m radius cavity full of “beer” would be just about right. These cavity sizes would be easy to create and maintain.

mollwollfumble said:

> Oh, slight problem, temperature rise is only 0.14 °C. Independent of bomb yield. That’s too small for efficient conversion of heat to mechanical work. Back to the drawing board.

Tentative solution, fill the space around the H-bomb with beer.

The “Feedback” page at the back of New Scientist is getting a bit repetitive these days.

You ought to volunteer to revive Daedalus.

https://www.gizmodo.com.au/2013/04/the-bomb-proof-miracle-materials-that-will-make-the-future-safer/

Multiple sheets of Zetix may help, too, and the walls could be of explosion-resistant concrete.

“Zetix is a fabric so strong it will resist multiple car bomb blasts without breaking. It absorbs and disperses the energy from explosions thanks to an inner structure built around the principle of auxetics: objects that actually get fatter the more you stretch them. A quirk of physics means the fabric contains pores which open when they experience impact — allowing blast air to pass through, but stopping solid debris at the same time. The result is a material which can dissipate the energies of multiple blasts”

The through-flow from Zetix would create turbulence to convert the damaging kinetic energy into useful heat.

The Rev Dodgson said:

mollwollfumble said:

Now that fusion power in the form of a tokamak is a bust, and civil fusion power in the form of laser-induced fusion is also a bust, could we power a city using a good old-fashioned H-bomb?

You mean they are not 10 years away any more?

When did that happen?

It was tacit in the design of the Joint European Torus (JET) in 1975. There has been no serious attempt at JET to approach break-even-point. Instead, JET has been and is used to study instabilities called “edge modes” and to investigate wall materials that are less damaged by the impact of ions.

Even the definition of break-even-point was changed to reflect this attitude. Break-even-point now means producing enough neutrons to turn uranium into plutonium for use in fission reactors.

As for inertial confinement fusion using lasers, this was never intended for civilian use. And “Experiments during the 1970s and ’80s demonstrated that the efficiency of these devices was much lower than expected”.

So the “just around the corner” possibility for tokamaks and laser induced fusion really died in the mid 1970s. This conclusion just never got widely publicised, and I’ve only recently accepted it myself.

The Rev Dodgson said:

mollwollfumble said:

> Oh, slight problem, temperature rise is only 0.14 °C. Independent of bomb yield. That’s too small for efficient conversion of heat to mechanical work. Back to the drawing board.

Tentative solution, fill the space around the H-bomb with beer.

The “Feedback” page at the back of New Scientist is getting a bit repetitive these days.

You ought to volunteer to revive Daedalus.

I have a huge respect for Daedalus and its creator David Jones. I remember several columns quite clearly. Daedalus was a better inventor than I will ever be. Just as the thread was shutting down, David Jones came up with a pair of fake perpetual motion machines, challenging all visitors to determine how they worked – nobody was able to get the correct solution.

I, too, missed the memo about tokamaks being a bust. I was under the impression that the ITER project was still going ahead.

You do wonder if it was thought fusion power would be easy as fission power (relatively speaking) and then it was realised just hard it is and technology took many decades to even get to the point to just create experimental reactors and commercial reactors may never be viable or technology is still decades away from creating them.

The Rev Dodgson said:

mollwollfumble said:

> Oh, slight problem, temperature rise is only 0.14 °C. Independent of bomb yield. That’s too small for efficient conversion of heat to mechanical work. Back to the drawing board.

Tentative solution, fill the space around the H-bomb with beer.

The “Feedback” page at the back of New Scientist is getting a bit repetitive these days.

You ought to volunteer to revive Daedalus.

:)

Loved that column in Nature.

David Edward Hugh Jones (20 April 1938 – 19 July 2017) was a British chemist and author, under the pen name Daedalus, the fictional inventor for DREADCO. Jones’ columns as Daedalus were published for 38 years, starting weekly in 1964 in New Scientist. He then moved on to the journal Nature, and continued to publish until 2002.

https://en.wikipedia.org/wiki/David_E._H._Jones

dv said:

I, too, missed the memo about tokamaks being a bust. I was under the impression that the ITER project was still going ahead.

It is. I haven’t looked at the specs for it yet.

The specs look much better than I expected. Anyone want to place bets?
https://www.iter.org/factsfigures

“ITER has been designed for high fusion power gain. For 50 MW of power injected into the Tokamak via the systems that heat the plasma it will produce 500 MW of fusion power for periods of 400 to 600 seconds.”

The Rev Dodgson said:

mollwollfumble said:

Now that fusion power in the form of a tokamak is a bust, and civil fusion power in the form of laser-induced fusion is also a bust, could we power a city using a good old-fashioned H-bomb?

You mean they are not 10 years away any more?

When did that happen?

mollwollfumble said:

dv said:

I, too, missed the memo about tokamaks being a bust. I was under the impression that the ITER project was still going ahead.

It is. I haven’t looked at the specs for it yet.

The specs look much better than I expected. Anyone want to place bets?
https://www.iter.org/factsfigures

“ITER has been designed for high fusion power gain. For 50 MW of power injected into the Tokamak via the systems that heat the plasma it will produce 500 MW of fusion power for periods of 400 to 600 seconds.”

ITER won’t be releasing any energy onto the grid. The earliest possible date for that is 2033, with planned fusion reactor https://en.wikipedia.org/wiki/DEMOnstration_Power_Station

Anyone taking bets?

I just realised something.
The temperature at the core of a nuclear bomb (A-bomb or H-bomb) is 28 to 83 million degrees C.
The temperature in the JET and ITER tokamaks is 150 million degrees C.

That makes the H-bomb safer than the tokamak. Perhaps.

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

Now that fusion power in the form of a tokamak is a bust, and civil fusion power in the form of laser-induced fusion is also a bust, could we power a city using a good old-fashioned H-bomb?

You mean they are not 10 years away any more?

When did that happen?

mollwollfumble said:

dv said:

I, too, missed the memo about tokamaks being a bust. I was under the impression that the ITER project was still going ahead.

It is. I haven’t looked at the specs for it yet.

The specs look much better than I expected. Anyone want to place bets?
https://www.iter.org/factsfigures

“ITER has been designed for high fusion power gain. For 50 MW of power injected into the Tokamak via the systems that heat the plasma it will produce 500 MW of fusion power for periods of 400 to 600 seconds.”

ITER won’t be releasing any energy onto the grid. The earliest possible date for that is 2033, with planned fusion reactor https://en.wikipedia.org/wiki/DEMOnstration_Power_Station

Anyone taking bets?

I just realised something.
The temperature at the core of a nuclear bomb (A-bomb or H-bomb) is 28 to 83 million degrees C.
The temperature in the JET and ITER tokamaks is 150 million degrees C.

That makes the H-bomb safer than the tokamak. Perhaps.

You can;t get a runaway effect can you, doesn’t it shut down if anything fails or fuel isn’t added

mollwollfumble said:

Anyone taking bets?

I bet that renewables continue to get cheaper and the drive for new power sources kind of fades off…

dv said:

mollwollfumble said:

Anyone taking bets?

I bet that renewables continue to get cheaper and the drive for new power sources kind of fades off…

A decent bet but … warning: devil’s advocate mode engaged.

What’s a renewable? Perhaps we need to split renewables into four groups: ancient, modern, never-never and dying.

Ancient renewables include hydro and geothermal.
Modern renewables include wind farm and solar electric.
Dying renewables include solar thermal and wave.
Never-never renewables include tidal, burning sewage, microalgae.

The only renewable that is going to get both wider use and cheaper is solar electric. And that’s mainly because lithium is a non-renewable.

You know wind power is kind of ancient too…

Re lithium, probably a silly question, but does it get used in the process of making power, or like some metals can it be recycled back into batteries again?

AwesomeO said:

Re lithium, probably a silly question, but does it get used in the process of making power, or like some metals can it be recycled back into batteries again?

Gets recycled.

dv said:

AwesomeO said:

Re lithium, probably a silly question, but does it get used in the process of making power, or like some metals can it be recycled back into batteries again?

Gets recycled.

Well that’s good news for the future, and I guess with its value, it’s probably mostly going to get recycled once electric cars really kickoff.

mollwollfumble said:

dv said:

mollwollfumble said:

Anyone taking bets?

I bet that renewables continue to get cheaper and the drive for new power sources kind of fades off…

A decent bet but … warning: devil’s advocate mode engaged.

What’s a renewable? Perhaps we need to split renewables into four groups: ancient, modern, never-never and dying.

Ancient renewables include hydro and geothermal.
Modern renewables include wind farm and solar electric.
Dying renewables include solar thermal and wave.
Never-never renewables include tidal, burning sewage, microalgae.

The only renewable that is going to get both wider use and cheaper is solar electric. And that’s mainly because lithium is a non-renewable.

What’s wrong with those in the “never-never” category

Cymek said:

You can’t get a runaway effect can you, doesn’t it shut down if anything fails or fuel isn’t added?

An H-bomb shuts down quickly if fuel isn’t added, too.

dv said:

You know wind power is kind of ancient too…

Windmills are, wind-pumped water is. But both of those are in the “dying” category.

AwesomeO said:

Re lithium, probably a silly question, but does it get used in the process of making power, or like some metals can it be recycled back into batteries again?

Could get recycled – usually isn’t.

Even with recycling and recharging of batteries, you can still get more power out of lithium used in a fusion power plant.

party_pants said:

mollwollfumble said:

Never-never renewables include tidal, burning sewage, microalgae.

What’s wrong with those in the “never-never” category

Tidal is never-never because our coastlines and coastal lakes are more valuable for other purposes.

Burning sewage is never-never because of the energy required for evaporation of water.

Microalgae is never-never because it requires excessive quantities of almost-fresh water, because you have to feed it fats in order to get biodiesel out, and because it can’t absorb carbon from polluted water so is no use in bioremediation.

Fusion would be useful off world say on the moon were you could use Helium 3 to fuel it.

We’ve had fusion power before, well sort of, the big bang is the result of a previous species in another universe becoming developed enough to start a fusion reaction that got away on them.

Peak Warming Man said:

We’ve had fusion power before, well sort of, the big bang is the result of a previous species in another universe becoming developed enough to start a fusion reaction that got away on them.

I wonder if you could destroy your local space time, supernovas don’t do it so probably not

Cymek said:

Peak Warming Man said:

We’ve had fusion power before, well sort of, the big bang is the result of a previous species in another universe becoming developed enough to start a fusion reaction that got away on them.

I wonder if you could destroy your local space time, supernovas don’t do it so probably not

If you can destroy your local space-time, there would be nothing to observer the event, should it happen, so absence of observational evidence is not evidence that it cannot happen.

I think PWM is probably right.

Or possibly right.

Not totally impossible anyway.

Cymek said:

Fusion would be useful off world say on the moon were you could use Helium 3 to fuel it.

That’s a darn good idea. What would you do with all that power?

mollwollfumble said:

Cymek said:

Fusion would be useful off world say on the moon were you could use Helium 3 to fuel it.

That’s a darn good idea. What would you do with all that power?

Powering bases and/or settlements, industry, well into the future I imagine

mollwollfumble said:

Cymek said:

Fusion would be useful off world say on the moon were you could use Helium 3 to fuel it.

That’s a darn good idea. What would you do with all that power?

Build a magnetic rail gun to launch pods of it back to Earth.

• What would you do with all that power?

Shake and Bake…

party_pants said:

mollwollfumble said:

Cymek said:

Fusion would be useful off world say on the moon were you could use Helium 3 to fuel it.

That’s a darn good idea. What would you do with all that power?

Build a magnetic rail gun to launch pods of it back to Earth.

I was wondering if you get send it back to Earth

furious said:

• What would you do with all that power?

Shake and Bake…

We make those by the way, Weyland Yutani

Yes. Good idea.

That way it wouldn’t matter if the fusion power is dircotinuous. Just time the events to match launch windows.

party_pants said:

mollwollfumble said:

Cymek said:

Fusion would be useful off world say on the moon were you could use Helium 3 to fuel it.

That’s a darn good idea. What would you do with all that power?

Build a magnetic rail gun to launch pods of it back to Earth.

Would that work from Mars too?

• That way it wouldn’t matter if the fusion power is dircotinuous. Just time the events to match launch windows.

Use gigantic thrusters to move the moon, variously, closer and further away from the earth and the resultant effect on the tides would make for super tidal power…

mollwollfumble said:

party_pants said:

mollwollfumble said:

That’s a darn good idea. What would you do with all that power?

Build a magnetic rail gun to launch pods of it back to Earth.

Would that work from Mars too?

I must confess I have not done the calculations.