Could Fusion Power Consume the Earth's Oceans?

[fenderzilla]

Not a conspiracy theorist or naysayer or anything, just a slightly concerned nerd hoping to be filled in on the science. So fusion power sounds really cool - it's clean, efficient energy that runs on hydrogen. That hydrogen would be obtained from the earth's oceans. I'm just wondering, how much water are we talking here? water is already becoming more valuable as the world's population increases. Suppose if we were to replace every single power generator in the world with fusion reactors. all the power in the world. just from fusion. how much water would that consume annually? would we see an effect on the earth's oceans?

also, since we'd electrolyze the water to get the hydrogen out of it, that would release a lot of oxygen. what effect would that have on the atmosphere, relating or not to global warming?

[SargeRho]

It'll take thousands or millions of years before it'll have any effect.

[Kryten]

The kind of fusion reactors that are being worked on now don't use just any hydrogen-they need the relatively rare isotope hydrogen-2, AKA deuterium (also tritium, but that's produced in a different way). Even if all of the deuterium in the ocean was taken out, that'd total about a tenth of one percent of the hydrogen, and thus water.

[Lohan2008]

Hydrogen-2 (deuterium) can be made by nuclear bombardment, so it take power to make it or (0.015% or 150 ppm) typical of ocean water. Not very efficient.

The most common method of producing tritium is by bombarding a natural isotope of lithium, lithium-6, with neutrons in a nuclear reactor.

{Wikipedia}

Edited October 12, 2014 by Lohan2008

[TheGatesofLogic]

Hydrogen-2 (deuterium) can be made by nuclear bombardment, so it take power to make it or (0.015% or 150 ppm) typical of ocean water. Not efficient.

Not efficient compared to what? heavy water factories have been around since before world war two, all that is necessary to convert heavy water into pure deuterium is electrolysis, which is very simple. by comparison you have to mine out coal which takes significantly more energy per ton of coal mined than the per equivalent energy velue of hydrogen being purified.

[cantab]

The main fusion reaction being worked on is deuterium-tritium fusion. Deuterium is found naturally and as mentioned makes up less than 1% of the hydrogen in water. Tritium is manufactured in nuclear reactors.

Proton-proton fusion, using normal hydrogen, isn't under consideration because the reaction results in a diproton which almost always splits up again, only rarely beta decaying to deuterium.

But even if it was, annual world energy use is on the order of 10¹⁸ Joules. That entire energy demand could be met by a single ton of hydrogen, so 10 tons of ocean water. The world's oceans contain a billion billion tons of water.

Maybe one day we'll (f)use it all up, but by that point Earth will be a likeness of Coruscant and humanity will be an interplanetary if not interstellar civilization.

And what's valuable is fresh water. Seawater is not scarce for any non-landlocked country, but isn't very useful (can't drink it, can't water crops with it) and it's expensive to desalinate it.

[jwenting]

Not efficient compared to what? heavy water factories have been around since before world war two, all that is necessary to convert heavy water into pure deuterium is electrolysis, which is very simple. by comparison you have to mine out coal which takes significantly more energy per ton of coal mined than the per equivalent energy velue of hydrogen being purified.

compared to filtering out the little deuterium that is in the water anyway...

[Kerbart]

Asimov wrote a short story about that. He did the math to show that no, even if you tried, you couldn't. That didn't stop politicians from using this "fact" and then the tables got turned on them.

[magnemoe]

The main fusion reaction being worked on is deuterium-tritium fusion. Deuterium is found naturally and as mentioned makes up less than 1% of the hydrogen in water. Tritium is manufactured in nuclear reactors.

Proton-proton fusion, using normal hydrogen, isn't under consideration because the reaction results in a diproton which almost always splits up again, only rarely beta decaying to deuterium.

But even if it was, annual world energy use is on the order of 10¹⁸ Joules. That entire energy demand could be met by a single ton of hydrogen, so 10 tons of ocean water. The world's oceans contain a billion billion tons of water.

Maybe one day we'll (f)use it all up, but by that point Earth will be a likeness of Coruscant and humanity will be an interplanetary if not interstellar civilization.

And what's valuable is fresh water. Seawater is not scarce for any non-landlocked country, but isn't very useful (can't drink it, can't water crops with it) and it's expensive to desalinate it.

Yes, note that energy consume will go up, however its limits because of heat, not global warming but just that you use so much energy you heat the earth, this start to get an problem if we use far more than 100 times as much energy as today. At this point you will have to move some energy intensive industry off earth and it makes no sense to use hydrogen from earth.

Say 1000 ton hydrogen/ year or 10.000 ton water maximum.

Loss of hydrogen for other reasons is an far larger problem, if you make hydrogen for fuel or for industrial use you get leaks and spill, much of that hydrogen will escape earth.

[TheGatesofLogic]

compared to filtering out the little deuterium that is in the water anyway...

yeah... the math for that doesn't add up though. Filtering the deuterium out really isn't that energy intensive compared to the energy output from a fusion reactor. It's a similar case to the purification of fission fuel, which is typically low-enriched, and requires considerable centrifuging to separate the isotopes of uranium into usable quantities.

[Nuke]

The kind of fusion reactors that are being worked on now don't use just any hydrogen-they need the relatively rare isotope hydrogen-2, AKA deuterium (also tritium, but that's produced in a different way). Even if all of the deuterium in the ocean was taken out, that'd total about a tenth of one percent of the hydrogen, and thus water.

there is also p-b11 which would use the normal hydrogen, but i think we would run out of boron first.

he3? hows that moonbase coming?

Edited October 13, 2014 by Nuke

[Kryten]

there is also p-b11 which would use the normal hydrogen, but i think we would run out of boron first.

P-B11 certainly isn't near-term tech, the issues with power density in particularly make it far harder than D-T.

he3? hows that moonbase coming?

He³ isn't really that much more common on the moon than on earth, and it's cheaper to manufacture it (by producing tritium and letting it decay) than to extract even now.

Edited October 13, 2014 by Kryten

[NASAFanboy]

Fusion power will consume the oceans the day solar power finished the energy of the sun. Green energy is almost just crap - eventually, our fusion plants will run the ocean dry and our solar plants will run the sun dry. Do we want to live in a world without oceans or a sun?

this is satire

[fenderzilla]

Okay cool, i wasn't really that worried to begin with anyway. Fusion is the way to go!

[Javster]

I don't get the argument over hydrogen-2 and deuterium and stuff.

You can just get hydrogen from electrolysing water, right?

[magnemoe]

I don't get the argument over hydrogen-2 and deuterium and stuff.

You can just get hydrogen from electrolysing water, right?

Deuterium is hydrogen with one proton and one neutron. Most hydrogen is just a proton. if its together with oxygen you get heavy water.

And yes you get hydrogen by electrolysing water or breaking down natural gas.

[Hannu]

I don't get the argument over hydrogen-2 and deuterium and stuff.

You can just get hydrogen from electrolysing water, right?

Normal hydrogen is so called H-1, which have only one proton in nucleus. Reaction of two protons happens through weak interaction and it is extremely improbable. It is important in light star's energy production in so called proton-proton-cycle, but it has never detected in laboratory. It is extremely weak even in Sun's core. In spite of hydrogen is at tremendous 15 million K temperature and insane pressure in Sun's core, it produces much less power per mass or volume unit than a human body and that reaction was completely useless in energy industry even we could produce such a conditions artificially.

Technically interesting fusion reactions are deuterium-deuterium, deuterium-tritium and deuterium-He3 -reactions. Deuterium is rare isotope of hydrogen, which have neutron and proton. In nature one of 6000 hydrogen atoms is deuterium. Tritium is radioactive hydrogen isotope which can be produced artificially and it is even more sensitive to fusion than deuterium. He3 is light helium atom, which produce less neutrons when fused with deuterium. Neutrons can damage structures of reactor and make materials radioactive. However, He have larger electric charge and is therefore much more difficult to achieve fusion at all. Even easiest reactions are extremely difficult due to high electric potential energy barrier between nuclei. That needs overinsane temperatures (tokamaks have achieved fusion but not net energy production), combined insane temperatures and pressures (hydrogen bombs, no problem is too bad to mankind if it helps to kill others) or exotic muon catalysis (fusions happens but producing of muons takes much more energy).

[Grimfilth]

Okay cool, i wasn't really that worried to begin with anyway. Fusion is the way to go!

Yeah it is, but there's still enough uranium, gas and coal for the next couple of decades. And just like cars, why would any power supply company want to invest in something which robs them of their own income? But, NIF is doing great and ITER should be the last pilot plant. Just in time before we run out of uranium ore.

[TheGatesofLogic]

Yeah it is, but there's still enough uranium, gas and coal for the next couple of decades. And just like cars, why would any power supply company want to invest in something which robs them of their own income? But, NIF is doing great and ITER should be the last pilot plant. Just in time before we run out of uranium ore.

Uranium is hardly scarce... If we converted all energy production on the planet to Gen III LWR reactors we would be able to sustain an exponentially increasing energy demand for the next 50 years purely on the stockpile of uranium and fuel derivatives we have now. Not to mention the vast potential thorium holds for new reactor designs.

[-Velocity-]

Asimov wrote a short story about that. He did the math to show that no, even if you tried, you couldn't. That didn't stop politicians from using this "fact" and then the tables got turned on them.

Actually, in the story they weren't using water for nuclear fusion, they were using it as the propellant in their nuclear thermal rocket engines. Which uses a lot more than fusion would- and still they would never run out.