The environmental impacts of fusion power.

[Sorcerer]

I was reading about a "new" fusion reactor design called the stellarator

http://news.sciencemag.org/physics/2015/10/feature-bizarre-reactor-might-save-nuclear-fusion

 

And I began to consider possible environmental impacts of using fusion as earth's primary power source.

 

At first I wondered, since deuterium would need to be extracted from sea water if this reduction in water would effect us majorly. But research led me to find that fusion requires very little fuel, the ocean is roughly only 1/4000th deuterium, and that at 1995 levels of energy use it would take 160 billion years to use up.

 

However I couldn't find the answer to the related questions:

 

How much free oxygen would several hundred years of use add to the atmosphere?

What would be the environmental effects of increased atmospheric oxygen?

At what level/time frame would it become problematic?

Would sequestering the oxygen be relatively simple?

 

I recall it hypothesised that in the past there have been higher levels of oxygen and giant insects are evidence of this.

 

Would increases in oxygen lead to increases in consumer metabolism and would this mean more carbon locked up in biomass?

 

Would more oxygen increase forest fires?

 

Would more oxygen mean metal goods would corrode faster?

 

(I wasn't sure where to put this, it's physics because it's fusion, it's chemistry because it's atmospheric chemistry and it's biology and earth science too. Move it or leave it as you see fit. Thanks admin.)

[John Cuthber]

In very broad terms nuclear reactions are about a million times more energetic than chemical ones. So, to get a given amount of energy, you need roughly a million times fewer atoms to fuse than you would need to burn if you were getting that energy from a chemical reaction like a fire.

Burning fossil fuels does remove oxygen from the air- but the cumulative effect over the centuries has been small. It is of the order of the hundred parts per million or so of CO2 that has been added.

Since the concentration in air is about 21% the loss of 100 PPM is practically immeasurable.

 

The production of "spare" Oxygen from splitting water and fusing the deuterium would be about a million times smaller.

It's not a problem.

[Sorcerer]

In very broad terms nuclear reactions are about a million times more energetic than chemical ones. So, to get a given amount of energy, you need roughly a million times fewer atoms to fuse than you would need to burn if you were getting that energy from a chemical reaction like a fire.

Burning fossil fuels does remove oxygen from the air- but the cumulative effect over the centuries has been small. It is of the order of the hundred parts per million or so of CO2 that has been added.

Since the concentration in air is about 21% the loss of 100 PPM is practically immeasurable.

 

The production of "spare" Oxygen from splitting water and fusing the deuterium would be about a million times smaller.

It's not a problem.

By that reasoning it would be equivalent after 1 million years, no?

 

Assuming use of fusion for a billion years the problem would be 1000 times worse.

 

Do we ignore the issue because the time scale for it to eventuate seems incomparably large in relation to our own lifetimes?

Edited October 24, 2015 by Sorcerer

[John Cuthber]

By that reasoning it would be equivalent after 1 million years, no?

 

Assuming use of fusion for a billion years the problem would be 1000 times worse.

 

Do we ignore the issue because the time scale for it to eventuate seems incomparably large in relation to our own lifetimes?

OK, for a start, it has taken centuries of industrialisation to produce the changes- even if we assume it's all in the last hundred years that means we have a hundred million years before the effect is as big as the (practically immeasurable) drop in oxygen level.

 

In a hundred million years we will have evolved to roughly the same extent that we have since the dawn of the mammals.

If the effect caries on for another ten billion years it will be unimportant compared to the fact that the sun will have gone out.

 

The reason I ignore it is nothing to do with the lifetime of a human, it's a log time compared to the lifetime of a species and even a star.

 

Did you realise that when you posted?

[Sorcerer]

OK, for a start, it has taken centuries of industrialisation to produce the changes- even if we assume it's all in the last hundred years that means we have a hundred million years before the effect is as big as the (practically immeasurable) drop in oxygen level.

 

In a hundred million years we will have evolved to roughly the same extent that we have since the dawn of the mammals.

If the effect caries on for another ten billion years it will be unimportant compared to the fact that the sun will have gone out.

 

The reason I ignore it is nothing to do with the lifetime of a human, it's a log time compared to the lifetime of a species and even a star.

 

Did you realise that when you posted?

Good point. Just to clarify it's an increase in oxygen, I realise you most likely made a typo there.

 

Yes certainly it would afford us and other life time to adapt to the gradual increase but we would be knowingly and willingly influencing this environmental selective pressure. There are a myriad of possible scenarios which could result, could we be certain that we would be happy with every one?

 

You also make an assumption that our energy use will remain at present levels, wouldn't it be, even with advances in efficiency, more likely to increase. Wouldn't the temptation to use more energy due to false a perception the consequences would be negligible encourage us to use as much as possible.

 

If we increased the rate of water conversion to helium and oxygen to now match CO2 increase except over 250k years not 1 million. Could we reasonably assume life would easily adapt then?

Edited October 24, 2015 by Sorcerer

[John Cuthber]

The point remains; the increase in oxygen due to fusion will be about a million times smaller than the drop due to getting the equivalent energy from fossil fuels.

What we really need to do is stop wasting energy and to focus on renewables.

[Sorcerer]

Burning fossil fuels does remove oxygen from the air- but the cumulative effect over the centuries has been small.

 

The production of "spare" Oxygen from splitting water and fusing the deuterium would be about a million times smaller.

It's not a problem.

The difference between a chemical reaction removing oxygen and a fusion reaction removing the reactive partner of oxygen, is that a chemical reaction can cycle with earth's geology, eventually, since the system (excepting radioactive decay and diffusion into space/input via comets/meteorites and space dust) is balanced, the original state of the system can return. Converting hydrogen, which would otherwise be bound to oxygen, into helium means that the chemical balance of the earth is altered. Without removal of the added helium and the addition of hydrogen from an exo planetary source the system will irrevocably be altered.

 

I'm not saying it's not worth it, but I am wondering what effects this might possibly have.

The point remains; the increase in oxygen due to fusion will be about a million times smaller than the drop due to getting the equivalent energy from fossil fuels.

What we really need to do is stop wasting energy and to focus on renewables.

I agree, but fusion technically isn't renewable. And may be a long way off, or never achieved.

 

Whereas there is a massive fusion reactor all ready to go about 1 AU away, it might not be completely renewable either, but it will last longer than the habitable future lifetime of earth.

[MigL]

Just to be clear, you can also fuse Hydrogen just like the Sun does, although it is a lot more difficult than starting off with Deuterium.

So technically it could be renewable ( just capture one comet and you're good for another million years ).

 

And in case you still haven't grasped John's replies...

If we fuse all the Deuterium in the Earth's oceans to produce power equivalent to the total present world usage, for the next billion years, the Oxygen levels will not increase to the levels of most Las Vegas casinos or Michael Jackson's sleeping/hyperbaric chamber.

I.E. within 'normal' limits

[swansont]

Fusing two deuterium nuclei yields just under 24 MeV of energy. Getting a Joule of energy requires 2.6 x 10^11 interactions, freeing up that many oxygen atoms from water. Divide by two, since atmospheric oxygen is diatomic. So ~4.5 x 10^12 Joules are released per mole of gaseous oxygen produced (IOW, fusion produces a lot of energy). That's 32 grams of oxygen. Let's do this a million times per second, producing 4.5 Exawatts (edit; that's 10^18) of power. In a year, we produce a trillion kilograms of oxygen. The mass of the atmosphere is ~5 x 10^18 kg, and less than a quarter of that is oxygen. So the oxygen increases by around a part in a million per year. Minuscule.

 

For a point of reference, how does this this Megamole per second of oxygen release compare? The average person produces of order a kilogram of CO2 every day. 44000 kg in a Megamole, so removing that oxygen from the air each second requires 44000 x 86400 = 3.8 billion people just breathing. IOW, we've increased our removal of this much oxygen from the atmosphere over the last several decades as our population went from ~3 billion to ~7 billion people. We're not suffocating.

[Sorcerer]

 

For a point of reference, how does this this Megamole per second of oxygen release compare? The average person produces of order a kilogram of CO2 every day. 44000 kg in a Megamole, so removing that oxygen from the air each second requires 44000 x 86400 = 3.8 billion people just breathing. IOW, we've increased our removal of this much oxygen from the atmosphere over the last several decades as our population went from ~3 billion to ~7 billion people. We're not suffocating.

I must point out that the O2 and CO2 cycle with regards to human food consumption and respiration is self balanced. Oxygen consumed by us is needed to metabolise sugar, that sugar was produced by a plant which excreted oxygen. So although our population increased, so too did the intensity of our agriculture. The mutual balance of both negate any net effect long term.

 

Taking hydrogen and turning it to helium however has no natural cycle to balance, we remove a naturally reductive agent H from the system and are left with the intert He and the now imbalanced half oxygen.

 

However I accept that the oxygen increase will most likely be insignificant and over such an extended period that the biosphere will have time to adapt and humanity will have time to find a contingency for any unforseen complication.

Edited October 25, 2015 by Sorcerer

[Klaynos]

He escapes the atmosphere if not contained, so also not a problem.

[swansont]

I must point out that the O2 and CO2 cycle with regards to human food consumption and respiration is self balanced. Oxygen consumed by us is needed to metabolise sugar, that sugar was produced by a plant which excreted oxygen. So although our population increased, so too did the intensity of our agriculture. The mutual balance of both negate any net effect long term.

 

There's nothing that actually requires the balance to be there. We could plant more crops than would balance that, or fewer. We deforest lands without balance. We existed for a long time before we had agriculture, as did a much larger biomass of oxygen breathers.

[Sorcerer]

 

There's nothing that actually requires the balance to be there. We could plant more crops than would balance that, or fewer. We deforest lands without balance. We existed for a long time before we had agriculture, as did a much larger biomass of oxygen breathers.

I was just pointing out that there's a direct link between consumer and producer. To simplify lets take sugar. That sugar required CO2 to produce and the producer excreted O2. The consumer requires O2 to burn the sugar and excretes CO2. That process there is balanced stoiciometrically. Since a consumer is the second part of the cycle there is no possible way for it to consume more oxygen than was produced.

 

Any other Geo engineering hasn't occurred, except the burning of fossil fuels and deforestation. Which is CO2. Unfortunately we aren't planting more to balance that out. We barely have the room to feed ourselves and maintain the ecosystems that's the planets life support.

Edited October 25, 2015 by Sorcerer

[swansont]

I was just pointing out that there's a direct link between consumer and producer. To simplify lets take sugar. That sugar required CO2 to produce and the producer excreted O2. The consumer requires O2 to burn the sugar and excretes CO2. That process there is balanced stoiciometrically. Since a consumer is the second part of the cycle there is no possible way for it to consume more oxygen than was produced.

Any other Geo engineering hasn't occurred, except the burning of fossil fuels and deforestation. Which is CO2. Unfortunately we aren't planting more to balance that out. We barely have the room to feed ourselves and maintain the ecosystems that's the planets life support.

But that's a false balance. The two processes are independent. A plant grows regardless of whether there's an animal around to breathe the oxygen it gives off.

 

I'm not sure what you mean by geo engineering. Man was not involved in the fluctuating values of various atmospheric gases for the vast bulk of earth's history.

[Sorcerer]

He escapes the atmosphere if not contained, so also not a problem.

I'm not worried about He at all in fact we need He and are running low on it.

But that's a false balance. The two processes are independent. A plant grows regardless of whether there's an animal around to breathe the oxygen it gives off.

 

I'm not sure what you mean by geo engineering. Man was not involved in the fluctuating values of various atmospheric gases for the vast bulk of earth's history.

OK we need to go back a bit, you alluded that excess oxygen produced by fusion could be mopped up by an increase in human population.

 

I pointed out that an increase in human population must be in conjunction with an increase in food production.

 

An increase in food production = increase in oxygen production.

 

Therefore an increase in population cannot balance the excess oxygen.

[MigL]

And we're saying there will be NO 'unforeseen complications' from the trivial increase in oxygen.

[swansont]

I'm not worried about He at all in fact we need He and are running low on it.

 

OK we need to go back a bit, you alluded that excess oxygen produced by fusion could be mopped up by an increase in human population.

I pointed out that an increase in human population must be in conjunction with an increase in food production.

An increase in food production = increase in oxygen production.

Therefore an increase in population cannot balance the excess oxygen.

I provided numbers for context. Your "balance" assertion lacks any numbers at all. You plant crops, but there used to be vegetation there, which was replaced by the crops, so is there more oxygen? If there is, is the matching 1:1? Go ahead and make your case, but a bald assertion just doesn't fly.

[Sorcerer]

To put it very simply.

 

Photosynthesis can be reduced to the equation 6CO₂ + 6H₂0 + energy --------------------> C₆H₁₂0₆ + 6O₂

And respiration can be reduced to C₆H₁₂0₆ + 6O₂ --------------------> 6CO₂ + 6H₂0 + energy

 

In order for animal biomass to absorb oxygen from the atmosphere it must therefore have sugar, during the production of sugar an equal ammount of oxygen had previously already been excreted. Therefore there is no net loss of oxygen in the system.

 

 

And we're saying there will be NO 'unforeseen complications' from the trivial increase in oxygen.

 

I've already agreed with this.

 

However I accept that the oxygen increase will most likely be insignificant and over such an extended period that the biosphere will have time to adapt and humanity will have time to find a contingency for any unforseen complication.

[swansont]

To put it very simply.

 

Photosynthesis can be reduced to the equation 6CO₂ + 6H₂0 + energy --------------------> C₆H₁₂0₆ + 6O₂

And respiration can be reduced to C₆H₁₂0₆ + 6O₂ --------------------> 6CO₂ + 6H₂0 + energy

 

 

That assumes one photosynthesis reaction per respiration reaction. You haven't shown that this would be the case. How much biomass is required to balance a human, and how much is planted to feed humans?

[Sorcerer]

It's shows that for sugar to exist to be respired that oxygen has already been produced.

 

The unit is a unit of glucose. Which is the biochemical fuel for metabolism.

 

All biomass (except chemotrophs), including plant biomass, must burn glucose.

[swansont]

It's shows that for sugar to exist to be respired that oxygen has already been produced.

 

The unit is a unit of glucose. Which is the biochemical fuel for metabolism.

 

All biomass (except chemotrophs), including plant biomass, must burn glucose.

 

None of which address my point. If a human's respiration were offset by e.g. 100 plants (some "standard" plant we could reference anything to) so that the production was balanced, there is nothing that keeps farmers from planting 120 plants for each person. Or that eating these 100 plants is the nutritional requirement of a person, since the nutritional value of different foodstuffs is not the same — not all of a plant is edible, for example. So it's entirely possible that food-wise, a human only needs 80 plants, or needs 150. In both situations, there is no balance of CO2 and O2. You've made no argument of this sort at all.

[Sensei]

A plant grows regardless of whether there's an animal around to breathe the oxygen it gives off.

That's not quite true.

If there will be no CO₂ in atmosphere, plants won't be able to grow.. And spread gens for the next generation.

 

Animals are active CO₂ producers.

Absence (extinction f.e.) would impact plants as well, as they would lose source of food (CO₂ from atmosphere).

 

Without animals, plants would have to rely on natural CO₂ sources like Vulcan eruptions, or fire. Quite not reliable sources, as they're pretty random.

Extinction of animals would lead to mass extinction of plants, in few thousands or millions years, not able to grow anymore without CO₂.

Edited October 27, 2015 by Sensei

[John Cuthber]

Sensie,

What do you think happens to dead plants if they are not eaten?

[swansont]

That's not quite true.

If there will be no CO₂ in atmosphere, plants won't be able to grow.. And spread gens for the next generation.

 

Animals are active CO₂ producers.

Absence (extinction f.e.) would impact plants as well, as they would lose source of food (CO₂ from atmosphere).

 

Without animals, plants would have to rely on natural CO₂ sources like Vulcan eruptions, or fire. Quite not reliable sources, as they're pretty random.

Extinction of animals would lead to mass extinction of plants, in few thousands or millions years, not able to grow anymore without CO₂.

 

That's light-years away from the context in which I made the statement.

[Ophiolite]

I would have participated in the thread earlier, but I have been debating how many angels you can get on a pinhead on another forum.