Fuel cells:electricity or hydrogen powered

[bobbobwhite]

The new Honda fuel cell car is out and I am confused. There are now gas cars, electric cars, hybrids, and now hydrogen-to-electricity(fuel cell) cars. I always thought that fuel cell tech was basically filters that produced combustible H from H2O, and after combustion rejoined the combustion products with the oxygen molecules to form water as the waste product. I thought that the only major difference in the concept of an H engine and a gas engine was the fuel used, along with a smaller and specificly reformed engine for H due to the per volume power difference between gas and H.

The Honda vehicle makes what is an electric car fueled by hydrogen that is bought at a pump, just like we now do with gas. That seems to be a step back or at most a bridge to actual vehicle self-contained, fuel cell production of H. And, isn't stopping to fill up what we are trying to make obsolete? How does H to electricity as propellant constitute an improved answer over burning vehicle self-produced hydrogen in a form of combustion engine? Is not the waste product the same water and no CO2?

And, aren't we still trying to bring mainstream what was discovered way back in 1837...making propellant power out of water?

Informed answers would be appreciated.

 

[LURCH]

I think you may have been confused between fuel-cell technology and hydrogen burning technology. Fuel-cells put hydrogen in proximety with oxygen, with a conducting membrane in between. As the hydrogen passes through the membrane to get to the oxygen, only the hydrogen nuclius can go straight through; the electron gets caught in the conducting membrane and has to take "the long way around" to get through the membrane. Along the way, this electron is used to do work.

This is very different from hydrogen combustion, which simply put hydrogen in proximity to oxygen, and then throws in a match. The resulting explosion is used the same way exploding gasoline is used in most of today's vehicles.

The advantage of hydrogen combustion is that it is a simple internal combustion system and work some principles nearly identical to those used in vehicles today. The technology is very familiar.

The advantage of the fuel-cell is that it is a far more efficient reaction. I don't know the exact ratio, but the same amount of hydrogen and oxygen in a fuel-cell vehicle will propel that vehicle many times farther than it would with an internal combustion engine.

The idea behind both of these technologies is not to "do away with" pulling up to a pump to refuel your car. The idea is to do it with petroleum fuel, or other forms of fossil fuel.

 

[bobbobwhite]

I guess what we will have is an electric car

Thanks for your response. So, what it seems we will have then with fuel cell tech as an end product is a car powered by an electric motor which itself is powered by the product of the fuel cell, which is H. If an electric car is the most efficient use of H, then perhaps the ultimate vehicle power solution can be considered done, or maybe not? Will all power sources found still power the same electric motor for propulsion? Maybe that's the weak link. Comments?

In your opinion, is an electric car fueled by hydrogen considered to be the best end solution to vehicle propulsion and no emissions, or is there even a more efficient way of using H or even common H2O as a power source as has been rumored for many decades if not centuries? Or, even another form of use of magnetism, which is the primary concept in the operation of electric motors. Seems it will be hard to get away from electric motors.

Thank you again. Or any informed person who wishes to respond.

 

[jambaugh]

... In your opinion, is an electric car fueled by hydrogen considered to be the best end solution to vehicle propulsion and no emissions, or is there even a more efficient way of using H or even common H2O as a power source as has been rumored for many decades if not centuries? Or, even another form of use of magnetism, which is the primary concept in the operation of electric motors. Seems it will be hard to get away from electric motors.

Thank you again. Or any informed person who wishes to respond.

You still seem a bit confused with regard to source of energy. The fuel cell takes the chemical energy from the hydrogen and converts it to electrical energy which turns the electric motor.

H2 is a power source but H20 is not it is rather the waste product from burning H2 (either in an engine or using a fuel cell). Magnetism in and of itself isn't a source of energy but a mechanism for converting electrical energy to mechanical energy as in the typical motor.

Let me clarify a fuel cell further. Let's make a simple battery. Stick a strip of zinc in a water based electrolyte and also a pencil lead (carbon electrode) and wire each to an electric motor. The zinc will oxidize (the oxygen in the water of the electrolyte) producing electricity which turns the motor.

Note that the energy from this battery came originally from the process of refining that zinc (probably reduction with carbon from coal or oil). So even if you're using a battery you're burning fossil fuel in a sense.

Now consider one of those new Zinc-Air batteries. The oxygen used to oxidize the zinc comes from the air and not the electrolyte. (It has the advantage that you don't need to carry the weight of that oxygen as water and you get more energy per weight.)

Now consider a hydrogen fuel cell. It is just like the Zinc-Air battery except that it uses Hydrogen and not Zinc. But here's the problem. The be$t way to get hydrogen is from fossil fuels... specifically it is usually produced from natural gas. However if we can build more nuclear power plants (and/or wind and/or solar and/or crack the fusion power problem) and/or if the price of fossil fuel goes up high enough then the price of non-fossil fuel electricity would be low enough where electrolyzing water to get hydrogen would be cheaper than getting it from fossil fuels.

(A lot of "if"s here but also a lot of "or" so its worthwhile exploring each and all.)

But hydrogen may not be the best way to store electricity. There are other types of fuel cells possible [See final note below] and there is also the regular ole rechargeable battery.

I personally think that new battery tech will likely be the solution to automotive energy storage.

What hydrogen fuel does for us right now is help local emissions problems like in the LA basin where the exhaust gets trapped. But we are a long way yet from independence from fossil fuels even if everyone drove electric or hydrogen fuel cell cars tomorrow. At best these along with hybrids provide means of more efficiently using the original fuel.

One final note: I recently ran across mention of the Liquid Tin Anode Solid Oxide Fuel Cell (LTA-SOFC) which can burn almost "anything".
http://www.celltechpower.com/technology.htm"
It isn't likely to be used in cars anytime soon but potentially it could replace the steam turbine power plants and indeed allow people to electrify their house off of piped gas or fuel oil or even lawn trimmings. Its high temp and size probably won't let it be practical for personal automobiles but I could see it used on trains or maybe eventually in larger trucks.

The key idea is that tin oxide is reduced by the fuel and the tin is then oxidized in the solid electrolyte fuel cell. Its pretty neat IMNSHO!

 

[mtworkowski@o]

Very generous explanation. Thank you. Candu reactors? Low grade uranium. Nothing even close to weapons grade. Used all over the world. Good track record. What then?

 

[russ_watters]

Just to highlight the main points there:

-Fuel cells that run on hydrogen extracted from water are just batteries.
-Fuel cells that run on hydrogen extracted from methane (or methane itself) are fossil fuel burners.
-Heat engines (engines that use the heat of combustion to drive the car) can only be around 40% efficient.
-Electric motors run around 95% efficient.
-Batteries are upwards of 90% efficient.
-Fuel cells are 50-80% efficient.

So the bottom line is that at the car, by far the best way to power the wheels is with an electric motor. The best way to power the electric motor is also still an open question (batteries or fuel cells?). And we must remember that if the goal here is to get off fossil fuel, we need an overhaul of our electric power generation systems. They need to be entirely non-fossil fuel. Right now, the US gets roughly 70% of its electricity from fossil fuels.

 

[mtworkowski@o]

Russ,
As I see it, nuclear is the way to go. but the Canadian nuclear , CANDU , is much better than the ones we're building. My problem with nuclear is that I don't trust people to run them safely. People have that attitude about being sloppy. I don't know what it is. It's human nature to screw up. They'll do almost anything for money. our credo has to change, I guess. I know my credo sucks.
I like the idea of using intermediate steps to get away from fossil fuel. Off the shelf technology. We should get our ideas from the countries that are really suffering with the energy crisis. Sorry my dog is barking. out.

 

[mtworkowski@o]

Oh, Russ,
Excellent post. Focused me right up. Thanks.

 

[mgb_phys]

Candu reactors? Low grade uranium. Nothing even close to weapons grade.

In fact one great use for Candus is to burn weapons grade U and even Pu that is left over form weapons programs. It's the safest way to dispose of it.

 

[mtworkowski@o]

Is there a reason that we're not building them here? Also if Iran was constrained to use CANDUs, they wouldn't have to get any real % of 235. What's the deal.

 

[mgb_phys]

Candu do produce waste which contains Pu, you can process this to extract the Pu.

 

[russ_watters]

Is there a reason that we're not building them here?

Politics.

 

[vanesch]

In fact one great use for Candus is to burn weapons grade U and even Pu that is left over form weapons programs. It's the safest way to dispose of it.

CANDU reactors have nothing special about this. A CANDU reactor is a moderated (thermal, not fast) reactor using heavy water, meaning one can use natural uranium if one wants to (was the original motivation), but one actually uses slightly enriched uranium to use the fuel more efficiently. A LWR (light water reactor) needs slightly enriched uranium, because it can't work on natural uranium. Both can work on plutonium, but both use it badly.

Turning weapon-grade uranium into something safer is extremely easy: remix it with depleted uranium (it was separated from) and make, to your liking, again natural uranium or slightly enriched uranium - smartest move is the last of course, you can use it in any type of thermal reactor.

Best way of using weapon grade plutonium... mix it again with depleted uranium, to make MOX fuel - however, this stuff can be separated again using chemistry. Eventually, mix it with reactor-grade plutonium, to decrease its weapon-usability (although all plutonium apart from Pu-238 is weapon-usable, the easiest is Pu-239 in high purity, which is called weapon-grade).

Most efficient way to use plutonium and depleted uranium: use it in a fast sodium reactor. You win a hundred-fold in fuel efficiency. However, these research programs have had a lot of stupid political opposition in the last decades, which means we're not ready yet to build a large park of fast reactors.

Concerning proliferation, in fact a LWR is better than a CANDU, because a CANDU is build in such a way that one can continuously refuel it, which makes it suitable as a plutonium production reactor if you want to use it that way. With a LWR reactor, that's way harder, as you have to open up the pressure vessel each time. So you will get out reactor-grade plutonium instead of weapon-grade plutonium. Warning: also reactor grade plutonium can be used for a weapon, but it is more difficult. This is if the reactor is in a sensitive place, where it could be misused. A reactor in a safe place is not an issue (you don't sneak in some uranium for plutonium production without anyone knowing at the plant).

 

[vanesch]

Is there a reason that we're not building them here? Also if Iran was constrained to use CANDUs, they wouldn't have to get any real % of 235. What's the deal.

The Iran issue is different. But we're getting way off topic here.
These are the elements: As Iran is a signatory of the Non-Proliferation-Treaty, it obtained the unalienable right to use all kinds of peaceful nuclear technology, including enrichment and fuel reprocessing. The counter side is that Iran has to declare all nuclear activities to the IAEA and not have a military nuclear program. Iran has been found faulty with its declarations to the IAEA in the past, and there is strong suspicion that they want a military nuclear program.

The safest way to handle Iran would be (but there's no legal basis for that) to require them to use LWR, and sell them the low-enriched uranium fuel, and take back the spend fuel. As such, they would have nuclear power, and not have any suspicious technology (the bookkeeping can be done on the fuel). Of course, that would make Iran dependent on other nations to sell them their fuel, but it would be the only way to be sure that they don't use the civil nuclear power for military purposes. That wouldn't stop them of course from having a separate military program, hidden from the rest of the world.

If Iran had CANDU's, it could use it to produce plutonium, and as it could work on natural uranium, the bookkeeping would be more difficult (who says that there hasn't been used more natural uranium than they say ?). LWR are safer in that respect: they need LEU (lightly enriched uranium), they can't easily be refueled and one can do more easily the bookkeeping of the fuel elements that way.

 

[mtworkowski@o]

VANESCH,
Thank you for the response. I understand what you're saying. From a purely scientific point of view, is a CANDU a better machine than LWR?

 

[shamrock5585]

we do need to switch to nuclear energy as our source power plants... atleast until we can harness the energy of fusion technology. people are far too affraid of nuclear power because of incidents in the past... Everything is dangerous unless it is respected... we must regulate everything. Natural gas used to be very dangerous as well because people did not respect it enough or know enough about it... now that we know much more about nuclear technology we can regulate how it is handled and make it much safer.

 

[mgb_phys]

From a purely scientific point of view, is a CANDU a better machine than LWR?

It's less thermally efficient, it runs at a lower temperature, and recovers less of the energy from the fuel - although the fuel is reused in a fuel cycle and it can efficently burn used LWR fuel. The core is larger so it's expensive to build and the heavy water isn't cheap, but you don't need an enrichment plant. It's also proven a very safe and conservative design.

Probably the biggest advantage is that it's relatively simple and easy to build, especially because you don't need a huge pressure vessel. It looks like the capacity of the one plant in the world to produce reactor pressure vessel forgings is going to be a limit for other designs.

 

[mtworkowski@o]

It looks like the capacity of the one plant in the world to produce reactor pressure vessel forgings is going to be a limit for other designs.[/QUOTE]

What plant? What other designs? Other designs instead of what? Explain, please.

 

[vanesch]

VANESCH,
Thank you for the response. I understand what you're saying. From a purely scientific point of view, is a CANDU a better machine than LWR?

I wouldn't say so, although a CANDU reactor has certain advantages but also some problems.
I would add a few comments to mgb_phys' post.
Concerning thermal efficiency, I'm surprised: I thought that the CANDU outlet temperature was about 310 degrees, as is that of a PWR.

The main original advantage of a CANDU was the fact that it could run on natural uranium, but the problem is that you can *hardly* have any burnup with natural uranium: from the moment that you deplete it a bit, you loose criticality. Hence now CANDU's run on LEU, just like LWR. Of course, thanks to the heavy water, they can run down the fuel more than can a LWR, so I guess that with LEU they have a slightly higher fuel efficiency than a LWR.

The main disadvantage is the heavy water. It is not only costly, it is also tritium-producing. So the primary water is much more active than the primary water of a LWR. Now, if there's a market for the tritium, that can be an advantage of course.

Concerning safety, it is sure a safe design - although I don't know how it compares to say, an EPR. The CANDU reactor is by now a pretty old design after all.

 

[mtworkowski@o]

You know, the way I think sometimes we don't need to be testing new reactor designs in the field, if you know what I mean. We need safe energy now. Other countries have been using them for years without problems. I'd say jump into the pool and ramp up the knowledge curve. Opinions?

 

[mgb_phys]

From the NEI report to congress March 2008.
"The ultra-heavy forgings for reactor pressure vessels and steam generators constitute the most significant chokepoint. Japan Steel Works (JSW) is currently the only company worldwide with the capacity to make ultra-large forgings"
There is also a problem hiring high quality welders - especially since they are also in big demand in the oil industry.

I thought the point of an AGR was to run at much higher temperature than a LWR and i thought Candu ran at even lower temperature - but I don't have any personal experience.
As vanesch said Candu was built to run on raw uranium but it doesn't extract as much of the energy as more enriched fuel reactors - the used fuel still has more available fissile material in it. It does have a big advantage that it can burn waste from other reactors that is too depleted for them to use. I don't know if it is economic to run only Candu or wether the best scheme is to run leu and use a few Candus to use their waste.

The problem with most of the reactor designs at least in the USA/UK was that the first ones (50s,60s) were really aimed at weapons (either Pu/H3 generation or research) then in the 80s there was a whole spray of different new designs so that each station was basically a research project. And since the regulatory process and approval to build them took a decade they were all obsolete before construction began.
Only France seems to have taken the path of building standard desgns aimed at reliable power production and it is now probably the front runner in building the UKs new stations.

 

[mtworkowski@o]

That is a shocking wake up call. We can't make the castings? This was a great post. I have to look into this. Thank you very much!

 

[mgb_phys]

That is a shocking wake up call. We can't make the castings?

Why would a private company keep the plant capacity to make something that they might get some orders in 20years time?
We subsidise aircraft makers and shipyards to preserve capabilites for defence applications - but heavy industry must have forgot to lobby the politicians to the same extent.

 

[vanesch]

I can be wrong - maybe they outsource this - but I thought that the French Framatome was also capable of making pressure vessels (from the Areva group).

 

[mgb_phys]

Areva are the other big makers but they are probably pretty comitted building France's stations.
Of course that was the original design idea of the Candu - Canada didn't have anyone to build large pressure vessels so invented a reacotr without one!

 

[vanesch]

The problem with most of the reactor designs at least in the USA/UK was that the first ones (50s,60s) were really aimed at weapons (either Pu/H3 generation or research) then in the 80s there was a whole spray of different new designs so that each station was basically a research project. And since the regulatory process and approval to build them took a decade they were all obsolete before construction began.
Only France seems to have taken the path of building standard desgns aimed at reliable power production and it is now probably the front runner in building the UKs new stations.

This is very true. I heard the joke that the US has one kind of cheese, and 100 types of reactors, while the French have 100 kinds of cheese, and one type of reactor

Maybe the reason is also that France had only one state utility (EDF), while different utilities in the US all wanted *their* development.

That said, I think that one will have to enter a new phase of research and development, especially on the side of the fast reactors - while still running on the experience of LWR and other established designs for a few decades. One shouldn't go too fast with it: fast reactors are a whole different world than thermal reactors. The principles are known, but from knowing the principles and having had a few prototypes to a safe and reliable park of power reactors is still a step that needs to be carefully taken, or one might bitterly regret it.
Really really too bad this research and development was halted for stupid political reasons.

As to the point of lost knowhow and so on, I think the main difficulty will be the welders. Welding the stainless steel skin on the inside of the construction steel of the vessel is a delicate procedure and I don't know if there are still a lot of people around that know how to do this.

 

[bobbobwhite]

This talk about nuclear energy...I read a science article that stated if the world builds many reactors for total necessary energy supply and then, due to global warming elements already/subsequently released, humans are eradicated and thus not around to control all those reactors, the world would then be rapidly stripped of life due to overheating of the reactors and the resulting total melt downs which would release massive radiation, and the living natural world as it was for billions of years would end, and possibly another Mars would be the result.

Is that end consequence, if probable or even possible, enough to control man from building these Earth doomsday machines and looking for an earth-friendly solution instead? Isn't fusion the best of all ways to go? There is a better way if we look for it, or does man only care about the Earth when he is on it? Like the idiotic, human egocentric statement..."if a tree falls in the forest and no one is around to hear it, does it make a sound?" I cannot think of anything ever said that is less caring or more stupid and selfish than that.

Bad life philosophy in the minds of power leads to bad life consequences for every living thing, always, every time.

Nuclear reactors sadly remind me of the tale Michael More told in one of his movies about the murdering capitalist who negotiated the best price for the rope used to hang him. What is really gained if all is lost?

 

[vanesch]

This talk about nuclear energy...I read a science article that stated if the world builds many reactors for total necessary energy supply and then, due to global warming elements already/subsequently released, humans are eradicated and thus not around to control all those reactors, the world would then be rapidly stripped of life due to overheating of the reactors and the resulting total melt downs which would release massive radiation, and the living natural world as it was for billions of years would end, and possibly another Mars would be the result.

The only thing that is wrong in your statement is "science" article, because even if we have a thousand Chernobyls, life will absolutely not be eradicated. In fact, the ecological niche around Chernobyl is thriving, due to less human intervention.

http://news.bbc.co.uk/2/hi/europe/4923342.stm

But second, even shut down power plants left unattended will NOT turn into a Chernobyl.

The reason why animals are less disturbed than humans by radiation is that they are insensitive to fear mongering.

That said, honestly, if humans disappear, what duty do they have to "preserve the Earth after them" ? In other words, if they have to risk their own well-being (and even their extinction) just for the hypothetical well-being of whatever will evolve after that, would that be an intelligent move ? Should we take the risk of sacrificing humanity just for the sake of the giant ants that will come ?

Is that end consequence, if probable or even possible, enough to control man from building these Earth doomsday machines and looking for an earth-friendly solution instead? Isn't fusion the best of all ways to go? There is a better way if we look for it, or does man only care about the Earth when he is on it?

My answer to that would be: duh, of course! What would Earth mean to humans without humans ?

In fact, the most life-threatening agent on Earth is humanity. So taking your logic to the extreme, the best chance for (non-human) life to continue to exist on Earth is to eradicate immediately all humans. Indeed, man has shown time after time to be able to destroy habitats, and he's getting smarter and smarter and more powerful. Even if he would become wiser today, there's no guarantee that he will not take up his bad habits in the future. So, just as we should close down all nuclear reactors, as they might harm the giant ants in the future, we should kill all humans before it is too late. That can be done by developing a narrowly targeted contagious and deadly pathogen, which doesn't affect others, but which kills humans (and maybe a few monkeys) in days. So, according to you, should we hurry up to develop this and eradicate humanity, for the sake of the giant ants ?

As to fusion, wind, solar, etc... all these are nice technologies, and should of course be looked into. But at the end of the day, we will have to use a technology that really works, and most of these technologies are, as someone wrote it, "unobtainium". We simply don't have the technology, in the next twenty years, to replace all fossil fuel burning by fusion (because it doesn't exist yet), or solar and wind, because the installations are as of now too big, too expensive, and too unreliable. The only technology we KNOW how to make right now, and which CAN make a difference, is nuclear. That shouldn't stop you from looking into promising alternatives in the future, but if you really have to make sure that everybody gets enough electricity in a reliable way, there's no real choice.

Planning to have 70% electricity production of a country by wind and solar 20 years from now is an inexecutable plan. Planning to have 70% electricity production of a country by nuclear in 20 years has been done by France.

 

[bobbobwhite]

All you say is just your opinion

not fact. You say it won't, but you don't know a whit about whether 500-1000-20,000 or whatever number we "smart" humans deem the right amount of nuclear reactors would not ruin the Earth if melted down. Science says it will. You say no. I trust science more so science wins, you lose.

Also, your ridiculous example of "giant ants" are certainly not the only things on the Earth besides humans that could live on after a global nuclear meltdown...think "underground'. Here is a truth for you...humans are such a tiny fraction of the Earth's total biomass as to be nearly a non-entity and totally unnecessary for anything relative to Earth's energy recyling needs. The Earth would not even notice, in its recycling of the sun's energy, if we humans were here on Earth or not. Termites alone(!) have over 20,000 times the biomass of all humans on Earth and there are thousands of other insect species almost as numerous, such as ants. But, all that is very old news to bio-science. Maybe you should study that for a while to learn what may really happen, and not just opine on the matter as if that were the truth. The truth is, no one knows for absolute sure, not even science.

And, from your writing, you seem to be one of the growing number of human-centric, ultra-selfish hubrists who thinks the Earth is only important as it relates to the humans on it? My god, man, you need to get a cosmic heart and a universal philosophy for something other than yourself, and even maybe get a bit of religion? Humans are such a tiny part of anything alive as to be universally inconsequential except to our own selfish, resource squandering selves.

Yes, of course, as with you my life is very important to me, but I am thankfully a cosmic idealist who would relinquish it in a second if I could trade my puny being for the promise of an unspoiled Earth just as it was millions of years ago before the plague of humanity, not that this is possible and, yes, I admit it is easy for me to say as I won't get the chance to prove it. But, I would do it in a heartbeat, as that is how much human Earth damage has affected me.

And, I'd also it trade for just one space trip outside our universe to see what is really "there". That would be one life fully lived, trust me on that.

 

[vanesch]

not fact. You say it won't, but you don't know a whit about whether 500-1000-20,000 or whatever number we "smart" humans deem the right amount of nuclear reactors would not ruin the Earth if melted down. Science says it will. You say no. I trust science more so science wins, you lose.

It isn't sufficient to say "science says" just for this to be so. Show me a peer-reviewed scientific publication in which it is shown (as you claim) that 1) 1000 reactors, when shut down, will melt down and 2) that such meltdowns will exterminate life on earth. THAT is what it means: "science says": to show a publication for it.

The BBC article I quoted shows that the very worst kind of fuel dispersal which we witnessed at Chernobyl (it can't get worse) doesn't seem to ultimately destroy the ecosystem in the 30 km range around it - on the contrary ! The fear of radiation has chased away the humans, and this absence is much more advantageous to the ecosystem than the very slight disadvantage of having a somewhat higher background radiation.

Now, that's a 30 km radius, which corresponds to ~3000 square km.
The Earth's land surface is 150 000 000 square km (see http://en.wikipedia.org/wiki/Earth ). That means that if 1000 reactors would undergo a Chernobyl disaster (which they won't), this would at most affect 3 000 000 square km, or about 2% of Earth's land surface, and all that would then turn into an ecosystem as observed around Chernobyl. Not directly something that is comparable to a "total extinction of life on earth".

So any 'scientific' claim that 1000 reactors will extinct life as we know it on earth, will have to explain how we get around these numbers.

Also, your ridiculous example of "giant ants" are certainly not the only things on the Earth besides humans that could live on after a global nuclear meltdown...think "underground'. Here is a truth for you...humans are such a tiny fraction of the Earth's total biomass as to be nearly a non-entity and totally unnecessary for anything relative to Earth's energy recyling needs. The Earth would not even notice, in its recycling of the sun's energy, if we humans were here on Earth or not.

What´s your point in comparing human biomass to the rest ?

Termites alone(!) have over 20,000 times the biomass of all humans on Earth and there are thousands of other insect species almost as numerous, such as ants. But, all that is very old news to bio-science. Maybe you should study that for a while to learn what may really happen, and not just opine on the matter as if that were the truth. The truth is, no one knows for absolute sure, not even science.

Plankton has even a bigger biomass. So ? Although you are right that one cannot know with absolute truth anything in fact, the scientific approach is to build upon what we know to what we can expect. What we know is that the worst possible imaginable accident that could happen to a power plant is the Chernobyl accident, which is not a meltdown, but an uncontrolled power excursion in an unprotected reactor, followed by a fire that last for several days because it was a graphite reactor. A meltdown in a modern power plant is a way way less problematic event. So we can very safely state that Chernobyl is an extremely conservative upper limit to what can happen to a power plant. The reason is that we have no other "reasonable" upper limit, as the next one in the row, a genuine meltdown at Three Miles Island, was a non-event where nothing really happened outside of the reactor building. The point is important, because the power excursion, the fire and the carbon, as well as the absence of confinement building, made for a much larger spread of radioactive materials in the atmosphere than could reasonably be expected at a modern power plant. So, again, taking Chernobyl as a model is a very very severe overestimate of the real consequences of a power reactor.

So 1000 reactors can AT MOST be 1000 Chernobyl accidents, and the numbers above show that this is by far not able to exterminate life on earth. What more can science do ?

So how can one claim a scientific basis for the opposite claim ? I could just as well say that science has shown that if we build to much windmills we would cause a global storm that would blow away all life from earth, and if you have a counter argument, well, science does contradict you, and even if it didn't we can't be sure ever.

And, from your writing, you seem to be one of the growing number of human-centric, ultra-selfish hubrists who thinks the Earth is only important as it relates to the humans on it? My god, man, you need to get a cosmic heart and a universal philosophy for something other than yourself, and even maybe get a bit of religion? Humans are such a tiny part of anything alive as to be universally inconsequential except to our own selfish, resource squandering selves.

Indeed, I do not give a damn for Earth without humans on it. The reason of the importance of Earth is that it is the current support for humanity. The day that humanity can be independent of earth, Earth doesn´t matter much anymore (except maybe as a kind of museum).

But I repeat my question to you: if you deem "biomass" more important than humanity, and, as you say yourself, for Gaia, it doesn't matter much about this single species of humans, which can at most harm her, why aren't you then for a quick, targeted and total extermination of humanity ? (or maybe you are ? )

Yes, of course, as with you my life is very important to me, but I am thankfully a cosmic idealist who would relinquish it in a second if I could trade my puny being for the promise of an unspoiled Earth just as it was millions of years ago before the plague of humanity, not that this is possible and, yes, I admit it is easy for me to say as I won't get the chance to prove it. But, I would do it in a heartbeat, as that is how much human Earth damage has affected me.
And, I'd also it trade for just one space trip outside our universe to see what is really "there". That would be one life fully lived, trust me on that.

"A space trip outside of our universe" ...