What are the problems with biofuels

Factual Questions
41

[QUOTE=Stranger On A Train]
Cite and cite.
r
[/QUOTE]

http://www.minesandcommunities.org/Action/press861.htm
“The USA averages around 30 mining deaths per year - compared to some 8,000 in China - and its safety record has been steadily improving over the past few decades.”

That is 8,030 in just two nations. Two of the biggest coal mining nations, true.

“utdoor air pollution in the U.S. due to particulate pollution alone was estimated by the Environmental Protection Agency (EPA) in 1997 to cause at least 20,000 premature deaths each year. Other estimates place this number at 50,000 to 100,000 deaths per year.(1) Globally, about 800,000 people per year die prematurely due to outdoor air pollution, according to a 2005 study published in the Journal of Toxicology and Environmental Health.” 800,000 deaths per year from air pollution, much of it from buring coal or oil. So I was wrong- it isn;t 10’s of thousands, it’s **100’s **of thousands.

"# Air pollution from burning coal in the USA causes 24,000 deaths per year, including 2,800 from lung cancer. The number is much higher in nations with lower emissions standards.

Over the last 10 years, coal mining deaths have averaged 33 deaths per year in the USA, and more than 6,000 per year in China…Last week “hundreds” of people were burned alive when an oil pipeline caught fire. More than 1000 people have died there in the past year from similar pipeline fires. Outside of Nigeria (where it occurred) no one seems to care."

24,000 deaths per year just from coal buring just in the USA. 1000 deaths per year from oil extraction just in Nigeria.

42

[QUOTE=DrDeth]
True there was Chernobyl but Chernobyl will never happen again- that sort of plant was on itway out when it happened.
[/QUOTE]

The “it will never happen” argument always falls flat to my ears. Nobody ever thinks a disaster can happen. If they did, they would prevent it. The Titanic was supposedly “unsinkable”. It was supposedly impossible for the World Trade Center to fall down. You can look back at anything with 20/20 hindsight and say, “Oh yeah - that’s what they did wrong; we won’t do that again”. But when people start saying something will “never happen”, I take it with a grain of salt.

43

[QUOTE=Chronos]
Yes, but switchgrass is a lot cheaper to install and maintain than solar cells or mirrors and boiler towers. And that 1% is energy in a form that’s easy to store and to fill up cars with. You have to compare that efficiency with the efficiency of turning solar energy into some other practical vehicle fuel. Biodiesel may not be the best use of that acreage, but it’s not as dismal (compared to other options) as you make it out to be.
[/QUOTE]

I agree that there are good practical reasons for using biofuels in the short term (10-20 years). My point (which I didn’t quite get across) was that, in the long term, finding more effective conversions from solar to useful energy will be essential. “More effective” includes energy storage, transportability, etc. And the biofuel feedstocks can provide additional benefits beyond simply energy - soil conservation, wildlife habitat, and so on. There’s no easy answer, and I didn’t mean to imply that there was.

44

[QUOTE=lowbrass]
The “it will never happen” argument always falls flat to my ears. Nobody ever thinks a disaster can happen. If they did, they would prevent it. The Titanic was supposedly “unsinkable”. It was supposedly impossible for the World Trade Center to fall down. You can look back at anything with 20/20 hindsight and say, “Oh yeah - that’s what they did wrong; we won’t do that again”. But when people start saying something will “never happen”, I take it with a grain of salt.
[/QUOTE]

Chernobyl will never happen again just like the Hindenburg disaster will never happen again. They no longer use either technology.

45

[QUOTE=DrDeth]
Chernobyl will never happen again just like the Hindenburg disaster will never happen again. They no longer use either technology.
[/QUOTE]
Again, this is not true. There are a number of different types of graphite-moderated reactors still in operation in a variety of nations. The use of graphite-moderated designs were particularly popular with the UK Atomic Energy Authority and British Nuclear Fuels, as well as extensive use in former East Bloc nations in which many are still operated. Reactors of similar design as those at Chernobyl is still in operation in Lithuania and the Ukraine and will remain operating for the forseeable future. (One of the advantages of RMBK-type reactors and graphite moderation in general is the ability to use natural uranium or a variety of other combinations of fissible materials with minimal processing or enrichment.) The PBMR design that is under development also uses pyrolitic graphite as a moderator, though the fuel and moderator are contained within a silicon carbide shell which (in theory) should provide containment even if the fuel element overheats and liquidizes.

Saying that “it could never happen again” is paramount to sticking one’s head in the sand. There are certainly ways to make commercial nuclear fission power generation more fault tolerant and less complex, but no amount of handwaving is going to eliminate the risks and costs associated with it.

It’s also noteworthy that aside from the costs in constructing nuclear power generation facilities and all of the operational costs involving fuel processing and so forth, there’s also a massive end-of-life cost with decommisioning and remediation of the facilities. You can’t just shut them down and break it up for recycling; there is a long, expensive, and not slightly hazardous multi-year effort in making the now-deactivated facility safe. Facilities can’t be used indefinitely because structural materials in the reactor will become damaged by neutron embrittlement and corrosion/erosion from the coolant loop, which can’t be serviced or replaced due to radioactive activation. (A modular reactor like a PBMR would go a long way to minimizing this problem, but other existing designs will have limits based upon how long they can survive the harsh conditions in the reactor itself, plus obsolescence of control hardware and so forth.)

Nuclear fission is not a panacea. It is, at best, a lesser-of-two-evils choice, allowing us to transition from fossil fuels to some more minimally polluting form of energy production that is still over the horizon.

Stranger

46

[QUOTE=Stranger On A Train]
Again, this is not true. There are a number of different types of graphite-moderated reactors still in operation in a variety of nations. The use of graphite-moderated designs were particularly popular with the UK Atomic Energy Authority and British Nuclear Fuels, as well as extensive use in former East Bloc nations in which many are still operated. Reactors of similar design as those at Chernobyl is still in operation in Lithuania and the Ukraine and will remain operating for the forseeable future. (One of the advantages of RMBK-type reactors and graphite moderation in general is the ability to use natural uranium or a variety of other combinations of fissible materials with minimal processing or enrichment.) r
[/QUOTE]

Graphite moderated yes (altho rare)- Chernobyl type- no. It wasn’t just the graphite:

** The reactor had a dangerously large positive void coefficient. The void coefficient is a measurement of how the reactor responds to increased steam formation in the water coolant. Most other reactor designs produce less energy as they get hotter, because if the coolant contains steam bubbles, fewer neutrons are slowed down. Faster neutrons are less likely to split uranium atoms, so the reactor produces less power. Chernobyl’s RBMK reactor, however, used solid graphite as a neutron moderator to slow down the neutrons, and neutron-absorbing light-water to cool the core. Thus neutrons are slowed down even if steam bubbles form in the water. Furthermore, because steam absorbs neutrons much less readily than water, increasing an RBMK reactor’s temperature means that more neutrons are able to split uranium atoms, increasing the reactor’s power output. This makes the RBMK design very unstable at low power levels, and prone to suddenly produce too much energy if the temperature rises. This was counter-intuitive and unknown to the crew.

* A more significant flaw was in the design of the control rods that are inserted into the reactor to slow down the reaction. In the RBMK reactor design, the control rod end tips were made of graphite and the extenders (the end areas of the control rods above the end tips, measuring 1 metre in length) were hollow and filled with water, while the rest of the rod – the truly functional part which absorbs the neutrons and thereby halts the reaction – was made of boron carbide. With this design, when the rods are initially inserted into the reactor, the graphite ends displace some coolant. This greatly increases the rate of the fission reaction, since graphite is a more potent neutron moderator (a material that enables a nuclear reaction) and also absorbs far fewer neutrons than the boiling light water. Thus for the first few seconds of control rod activation, reactor power output is increased, rather than reduced as desired. This behavior is counter-intuitive and was not known to the reactor operators.

* The water channels run through the core vertically, meaning that the water's temperature increases as it moves up and thus creates a temperature gradient in the core. This effect is exacerbated if the top portion turns completely to steam, since the topmost part of the core is no longer being properly cooled and reactivity greatly increases. (By contrast, the CANDU reactor's water channels run through the core horizontally, with water flowing in opposite directions among adjacent channels. Hence, the core has a much more even temperature distribution.)

* To reduce costs, and because of its large size, the reactor had been constructed with only partial containment. This allowed the radioactive contaminants to escape into the atmosphere after the steam explosion burst the primary pressure vessel.

* The reactor also had been running for over one year, and was storing fission byproducts; these byproducts pushed the reactor towards disaster.

* As the reactor heated up, design flaws caused the reactor vessel to warp and break up, making further insertion of control rods impossible.

and
*Since the

Chernobyl accident, all remaining RBMKs have been retrofitted with a number of updates for safety. The largest of these updates fixes the RBMK control rod design. Previously the control rods were designed with graphite tips, which when initially inserted into the reactor sped up the reaction, instead of slowing or stopping it. This design flaw caused the first explosion of the Chernobyl accident, when the emergency button was pressed to stop the reactor. The updates are

* An increase in fuel enrichment from 2% to 2.4%. This difference improves neutron absorption, reducing the reliance on cooling water for reactor control.
* Manual control rod count increased from 30 to 45.
* 80 additional absorbers inhibit operation at low power, where the RBMK design is most dangerous.
* SCRAM (rapid shut down) sequence reduced from 18 to 12 seconds.
* Precautions against unauthorised access to emergency safety systems.

Closures

Of the 13 RBMKs built (and one is still under construction at Kursk), all three surviving reactors at the Chernobyl plant have now been closed and one of the two reactors at Ignalina in Lithuania has shut down with the second due to close by 2010. [1]*

Chernobyl was a unique accident with the quite a few human errors (which *could re-occur, but not likely as the USSR is gone) and *some half-dozen technical design errors, all of which have been fixed on the very few RBMK reactors still extant. Chernobyl will never happen again, it is impossible although certainly an accident of some other sort could happen. Nor will the Hindenburg disaster happen again, although of course a dirigible could still crash.

47

No it can’t, because it would have to get built first.

An ancillary problem with biofuels is that there are a lot of dirtbag hippie types out there doing car conversions. My cousin had a brand new VW ruined by one of these guys. It wouldn’t run on grease or diesel, and it would have cost her more to fix than just to buy another car.

48

[QUOTE=DrDeth]
Chernobyl will never happen again, it is impossible although certainly an accident of some other sort could happen.
[/QUOTE]
You keep using that word; I do not think it means what you think it means.

While the RBMK-type reactors have all been modified to alleviate the some of the design problems that led to the fire at Chernobyl #4 (though they all still lack containment domes, so another core meltdown and fire would exhaust straight to the atmosphere as Chernobyl #4 did), and no doubt there is a greater awareness of the possibility of the procedural failures that led to the excursion and subsequent fire, it is not “impossible” for a core meltdown to occur again in these or in most other types of commercial power generating reactors, and in fact there have been a number of partial meltdown events. The inherent problems with graphite moderated reactors is the potential for graphite to combust if heated to very high temperatures in the presence of oxygen, and the fact that graphite will undergo rapid structural phase transformations (see Wigner energy) which can make it prone to suddenly and unpredictably increasing the degree of moderation and thus the reaction rate. It is very difficult to extinguish such fires without worsening the situation. (Dumping water into the pile may moderate emitted neutrons, increasing the reaction rate.)

The Chernobyl incident is not the first time that such an accident has occured with a graphite moderated reactor; the most notable case is the fire at Windscale Pile #1. While the Windscale piles suffered from the then-ignorance about the issues with using solid graphite moderation and a lack of containment features in the design (and mitigated, if serendipitously, by other design selections) the fact remains that graphite-moderated reactors–which are not as rare as you believe, and in fact the graphite-moderated Advanced Gas Cooled Reactor design is the mainstay of British Energy–have some inherent risks.

Reactors that use water as a moderator can be designed to be inherently failsafe–that is, an excursion that results in excessive heat or thermal neutron production causes the reactor to passively reduce the reaction rate, whether by boiling off the moderator, changing the fuel geometry, et cetera. Some, like the CANDU reactor, meet this critiera, but most Pressurized Water Reactors and Boiling Water Reactors can become supercritical if active control systems fail or are deactivated. In fact, the reactor that suffered a Loss of Coolant Failure at Three Mile Island was a PWR type widely considered (at that time) to be one of the safest designs available. It’s fortunate that the vented coolant cloud travelled over the ocean rather than land. Og help you if you should have a LOCA in a liquid metal-cooled reactor, like the one that occured at the Santa Susana Field Laboratory SRE on a full-sized commerical reactor; the amount, extent, and duration of contamination could dwarf Chernobyl. The United States does not currently operate any liquid-metal cooled reactors, commerically or otherwise (and we’ve had some very narrow misses with ones we have operated) but France, Japan, and Russia all operate metal-cooled fast breeder reactors and intend to construct and develop more.

Before you continue on with such a gung-ho attitude about how “impossible” it is for an accident on the scale of Chernobyl to reoccur, I recommend that you read up on the history of nuclear fission reactors and the the multitude of near-misses (INES Level 3 or higher) that have occured with commerical or civilian experimental nuclear fission piles. We have in many cases been fortunate, rather than successful, at limiting the scale and effects of nuclear accidents.

Back to the question posed by the o.p. (which has already been adequately addressed, but I need to do something to excuse this abominable hijack that I’ve extended) the major problem with biofuels is one of the scale of production and attendant impact as already detailed by Public Animal No. 9. It seems unlikely that we can replace petrofuels entirely with biofuels, or at least not without some major effects, but given a current surplus in agricultural production it can, along with conservation and more efficient utilization, serve to extend existing petroleum reserves and reduce carbon emissions imbalance while using mostly existing infrastructure for distribution, and only modest modifications to existing transportation technology. Contrast that with a hydrogen-based transportation system, which will require massive changes in how it is distributed and stored and significant alterations to internal combustion engine designs. As a supplemental energy source, biofuels can provide a backup to existing fuels in a “peak oil” scenerio, giving time to develop a more ultimately viable energy production and distribution system, and with advances in biotechnology might even become a viable permanent segment in mobile energy sources that can not be effectively served by proposed petroleum replacements.

Stranger

49

[QUOTE=Chronos]

[QUOTE=Askance]
The only scalable carbon-neutral forms of energy production are solar and geo-thermal. Smaller but significant contributions can come from hydro, wind and tidal.
[/QUOTE]
This seems a very peculiar ordering. Hydro is already the cheapest power, and accounts for a significant fraction of generation. The only sense in which it’s “not scalable” is that it’s already scaled up to near its maximum: There are only so many places where it’s economical to put in a dam. But the same is true, to a much greater degree, of geothermal. To my knowledge, the only places in the US with enough geothermal activity to make energy generation practical are Yellowstone and Hawaii. Meanwhile, photovoltaics can only just barely break even after decades of operation, and non-photovoltaic solar electricity generation can never seem to get off the ground, yet you put solar as your #1 scalable non-carbon source.
[/QUOTE]
They were not ordered within the two categories.

The scalable source of geo-thermal I was thinking of is what they are calling “hot rocks”; here in Australia for instance it has turned out that a large part of the state of South Australia (50% larger than Texas) is underlain by vast areas of hot rock, and pretty much all you need to do is pump water down to it and pipe the steam up. In assuming the same would be true of significant parts of the US as the US has more geothermal activity in general. The downside is (in SA’s case) it’s a way away from the areas that need power, but on the other hand it can produce it in such prodigious quantities at such a small unit cost that efficiency is almost irrelevant.

As you say, hydro is pretty much maxed, not to mention that dams are being recognised as a bad idea all round.

I’m as certain as can be that solar power - whether distributed photo-voltaic or concentrated solar-thermal - will be economic in the near future, especially if we can spend on research even a tenth of what is spent on nuclear and “clean coal” research.

50

[QUOTE=Askance]
I’m as certain as can be that solar power - whether distributed photo-voltaic or concentrated solar-thermal - will be economic in the near future, especially if we can spend on research even a tenth of what is spent on nuclear and “clean coal” research.
[/QUOTE]

This will become true even if no technological improvements occur simply because coal and petroleum are finite and their price inevitably must rise to point of making solar the cheaper option. The only question is how long before it happens. 10 years? 100? 1,000? But as fossil fuels get more expensive, the market will create more incentive for solar power R&D. This will (supposedly, hopefully) create innovations that increase solar efficiency and thus make it cheaper. This of course will bring the tipping point in favor of solar over fossil fuels that much closer. There are huge assumptions here of course. Innovations in fossil fuel efficiency could keep it cheap for longer. And other power sources may play a big hand.

51

[QUOTE=Stranger On A Train]
Back to the question posed by the o.p. (which has already been adequately addressed, but I need to do something to excuse this abominable hijack that I’ve extended) the major problem with biofuels is one of the scale of production and attendant impact as already detailed by Public Animal No. 9. It seems unlikely that we can replace petrofuels entirely with biofuels, or at least not without some major effects, but given a current surplus in agricultural production it can, along with conservation and more efficient utilization, serve to extend existing petroleum reserves and reduce carbon emissions imbalance while using mostly existing infrastructure for distribution, and only modest modifications to existing transportation technology. Contrast that with a hydrogen-based transportation system, which will require massive changes in how it is distributed and stored and significant alterations to internal combustion engine designs. As a supplemental energy source, biofuels can provide a backup to existing fuels in a “peak oil” scenerio, giving time to develop a more ultimately viable energy production and distribution system, and with advances in biotechnology might even become a viable permanent segment in mobile energy sources that can not be effectively served by proposed petroleum replacements.

Stranger
[/QUOTE]

Well, the purpose of my post was to assume that we could completely supplant petrofuels with biofuels and then ask what the new problems would be. If you attempt to use food crops, then the problems have been discussed to death. If you use only waste products, you will not have enough feedstock. Algae might be able to scale up as necessary, but at what cost? That is what I wanted to know.

On the nuclear question, where are the PBMRs? I know that they are being developed in China and South Africa, but most of the stuff I can find on them is old. What are your thoughts on their safety vis-a-vis the Wigner energy problem? I know that they run at about four times the annealing temperature of graphite, but that is not to say that it is impossible :wink: for them to catch fire.

Thanks,
Rob

52

Quoth Askance:

OK, I’m not familiar with this “hot rock” technology, nor how prevalent suitable sites would be in the US, so I’ll concede that point for now. But I still think it’s going to be a long, long time before solar of any sort surpasses hydro. Certainly, solar technologies are going to improve, and the rate of improvement will probably increase as fossil fuels run out. But hydro has a huge head start, both in existing power capability and in price, and even with accelerated development, it’ll take a while for solar to catch up. And by that time, who knows, we may have already developed practical fusion, or somesuch.

53

[QUOTE=sweeteviljesus]
Well, the purpose of my post was to assume that we could completely supplant petrofuels with biofuels and then ask what the new problems would be. If you attempt to use food crops, then the problems have been discussed to death. If you use only waste products, you will not have enough feedstock. Algae might be able to scale up as necessary, but at what cost? That is what I wanted to know.
[/quote]
I don’t know that anybody has a true handle on the costs, or the extent that production could be scaled to, other than that existing methods of production could only be supplimental rather than a replacement. But the benefits of being able to use the existing distribution architecture and current engine designs with minimal modifications goes a long way to providing viability and justification even if the production of biofuels isn’t itself cost competitive with other energy production methods.

[QUOTE=sweeteviljesus]
On the nuclear question, where are the PBMRs? I know that they are being developed in China and South Africa, but most of the stuff I can find on them is old. What are your thoughts on their safety vis-a-vis the Wigner energy problem? I know that they run at about four times the annealing temperature of graphite, but that is not to say that it is impossible :wink: for them to catch fire.
[/QUOTE]
The United States and Great Britain have demurred from developing new reactor designs owing to the cost of funding research, public scrutiny, and political inclination away from nuclear power. Western Europe, with limited natural resources and increaing population density, has traditionally been more amenible to nuclear fission energy production, though the catastrophe at Chernobyl threw a heavy cloud over that, and a residual effect of the United States enticing or essentially forcing nations of Western Europe (Turkey, West Germany, the Neatherlands, Belgium, Itally) to allow the installation of tactical and intermediate range nuclear-armed ballstic missiles has created or at least exacerbated movements to rid European nations of nuclear technology of any sort. The peoples of the former Soviet Union and republics thereof had (or more properly, were not allowed to have) such scruples, and these nations are now heavily dependant upon existing nuclear power installations, but while one of the focuses of the PBR design is safety, the Soviets were more concerned about plutonium production and extraction for nuclear weapons, and as a result of that and the subsequent poverty and lack of ongoing research they haven’t gone into more advanced deisgns. China, on the other hand, is very interested in advancing and expanding their power generating capability, and both their burgening, cash flush economy and lack of existing, mature infrastructure allows them to go in more progressive directions. South Africa, with its desperate need for desalination capability, is in a similar place.

From a techincal standpoint, PBMR designs are highly attractive; they offer a high degree of passive safety, protective encapsulation of fuel elements and resultant waste, the ability to use a working gas which is both nearly thermodynamically ideal and functions at low pressure with essentially no corrosion issues, and offers ready modularity and expandability that can’t be done with standard “rod and pool” designs. The downsides are the size of the pile, which has to be very large because of the low energy density (though the lack of complexity in plumbing, cooling and heat exhanger systems, and handling mechanisms probably makes this a wash), and the cost and required quality control of fuel element production as opposed to existing unclad elements is much higher, possibly by an order of magnitude. This also produces substantially more depleted (but still radioactive) high level waste, which is a significant problem if you insist on transporting it to a central site like Yucca Mountain, but perhaps not so much if you use on-site expandable storage. Reprocessing would also be essentially out of the question, or at least dramatically more difficult and producing a large volume of high level waste products, so PBMR is really the best approach only for a once-through fuel cycle. The Wigner energy problem is essentially a non-issue with PBMR even if it occured; owing to the low energy density even an uncooled pile is unlikely to attain meltdown temperatures, particularly with the silicon carbide coating.

However, in general with nuclear fission power, even if you resolve all other safety issues with the reactor itself you still have issues with the processing and reprocessing or reduction/storage/disposal of waste products. Because processing and reprocessing require labor intensive procedures and use caustic substances that require vigilance and dutiful preventative maintenance, these processes are the most likely to result in accidents and release, such as occured at the Mayak processing facility that contaminated hundreds of square miles and forced the evacuation of the town of Kyshtym and surrounding areas in 1957, and is now classified as a INES Level 6 nuclear accident.

Nuclear fission offers an alternative to carbon-producing fossil fuel power production, but it has its significant drawbacks as well.

Stranger

54

[QUOTE=Stranger On A Train]
I don’t know that anybody has a true handle on the costs, or the extent that production could be scaled to, other than that existing methods of production could only be supplimental rather than a replacement. But the benefits of being able to use the existing distribution architecture and current engine designs with minimal modifications goes a long way to providing viability and justification even if the production of biofuels isn’t itself cost competitive with other energy production methods.

[/QUOTE]

I didn’t mean cost in terms of price per barrel, I meant in terms of things like increased water usage. In other words, would biofuels be sustainable?

[QUOTE=Stranger On A Train]

and the cost and required quality control of fuel element production as opposed to existing unclad elements is much higher, possibly by an order of magnitude. This also produces substantially more depleted (but still radioactive) high level waste, which is a significant problem if you insist on transporting it to a central site like Yucca Mountain, but perhaps not so much if you use on-site expandable storage. Reprocessing would also be essentially out of the question, or at least dramatically more difficult and producing a large volume of high level waste products, so PBMR is really the best approach only for a once-through fuel cycle.

However, in general with nuclear fission power, even if you resolve all other safety issues with the reactor itself you still have issues with the processing and reprocessing or reduction/storage/disposal of waste products. Because processing and reprocessing require labor intensive procedures and use caustic substances that require vigilance and dutiful preventative maintenance, these processes are the most likely to result in accidents and release, such as occured at the Mayak processing facility that contaminated hundreds of square miles and forced the evacuation of the town of Kyshtym and surrounding areas in 1957, and is now classified as a INES Level 6 nuclear accident.

Nuclear fission offers an alternative to carbon-producing fossil fuel power production, but it has its significant drawbacks as well.

Stranger
[/QUOTE]

How much does it cost to make a pebble? How many pebbles in a 1GW reactor? How long is their life?

Also, two criticisms of the PBMR are that the pebbles can crack (from the buildup of Radon?) and that the pebbles can get stuck removing them. Are these real issues? If so, can they be mitigated?

What can be done about the fuel cycle in terms of processing and dealing with spent fuel?

Thanks for your help,
Rob

55

Going back to algae, where would said algae be harvested from? Would producers of algae-based biofuels “farm” it or would it be skimmed “from the wild,” as it were? I would have significant problems with the former, as algae is a significant link in the food chain of just about every pond or lake or ocean it’s found in, though algae buildups and blooms can and do happen. I don’t know what scraping said blooms down would give you in terms of biofuel, but I get worried when we start mucking with ecosystems. I’d like to hope that no intelligent scientist would propose skimming up wild algae, but I honestly don’t know how horrible or harmless attacking an algae bloom would be. (And I’d like to think we wouldn’t go after ordinary, non-blooming ponds!) I’m usually not very good at gauging large-scale impacts, thought the idea of it makes me rather worried. If anybody has any reliable numbers/facts about the relationship between algae and pond/river/ocean ecosystems, do link me and set me aright!

Still, I have to ask where and how one would “farm” algae. True, if you’ve got standing water, you’ll have a harder time not getting algae to grow. (I’ve been around too many backyard pools not to know this.) But would there be enough algae in simple, average standing pools to make a significant harvest? Or would “algae farms” be needed? Then we could have a problem akin to having to make more space for biofuel crops, and there’s only so much crop space out there. Of course, algae could be grown in large tanks in buildings, but you’d still have to put those buildings somewhere. And again, how much algae do you need to make a suitable amount of biofuel?

56

[QUOTE=Freezair SilverEye]
Going back to algae, where would said algae be harvested from? Would producers of algae-based biofuels “farm” it or would it be skimmed “from the wild,” as it were? I would have significant problems with the former, as algae is a significant link in the food chain of just about every pond or lake or ocean it’s found in, though algae buildups and blooms can and do happen. I don’t know what scraping said blooms down would give you in terms of biofuel, but I get worried when we start mucking with ecosystems. I’d like to hope that no intelligent scientist would propose skimming up wild algae, but I honestly don’t know how horrible or harmless attacking an algae bloom would be. (And I’d like to think we wouldn’t go after ordinary, non-blooming ponds!) I’m usually not very good at gauging large-scale impacts, thought the idea of it makes me rather worried. If anybody has any reliable numbers/facts about the relationship between algae and pond/river/ocean ecosystems, do link me and set me aright!

Still, I have to ask where and how one would “farm” algae. True, if you’ve got standing water, you’ll have a harder time not getting algae to grow. (I’ve been around too many backyard pools not to know this.) But would there be enough algae in simple, average standing pools to make a significant harvest? Or would “algae farms” be needed? Then we could have a problem akin to having to make more space for biofuel crops, and there’s only so much crop space out there. Of course, algae could be grown in large tanks in buildings, but you’d still have to put those buildings somewhere. And again, how much algae do you need to make a suitable amount of biofuel?
[/QUOTE]

Most of the development work right now is taking place on “farms” – controlled environments with specific species of algae. Here’s one of the more exotic ideas.

57

[QUOTE=Chronos]
Quoth Askance:OK, I’m not familiar with this “hot rock” technology, nor how prevalent suitable sites would be in the US, so I’ll concede that point for now. But I still think it’s going to be a long, long time before solar of any sort surpasses hydro. Certainly, solar technologies are going to improve, and the rate of improvement will probably increase as fossil fuels run out. But hydro has a huge head start, both in existing power capability and in price, and even with accelerated development, it’ll take a while for solar to catch up. And by that time, who knows, we may have already developed practical fusion, or somesuch.
[/QUOTE]
Solar doesn’t have to surpass hydro; hydro is as it is and there’s nothing much we can do to improve or extend it. Solar doesn’t have to compete with it, it has to compete with the technologies it is looking to replace, primarily burning fossil fuel but also nuclear.

As for hot rocks:

Greener than wind or solar, geothermal energy gets little attention—even though, as Nick Schulz writes, it could provide 2,000 times our current power needs.

Earth continuously heats the rock deep below the surface; a new report from M.I.T. suggests harvesting that renewable energy

58

[QUOTE=sweeteviljesus]
I didn’t mean cost in terms of price per barrel, I meant in terms of things like increased water usage. In other words, would biofuels be sustainable?
[/quote]
That all depends on what (various) methods are used to produce biofuels. My SWAG on it is that, no, biofuels would not be sustainable, in the sense of replacing existing petrofuel, but that they could supplant and/or become a niche fuel for applications where other alternatives (grid mass transit, eletric battery, hydrogen fuel cell, et cetera) may not fit the bill. I suspect that biodiesel will be more expensive than the current costs of petroleum fuels, but not by an order of magnitude.

It’s interesting that you bring up water usage, because both the usage of water and thermal pollution of natural bodies of water are significant concerns that don’t receive the attention they deserve. Availability of fresh, potable water is going to become a significant environmental issue, particuarly in arid regions where the depletion of natural aquifers is increasingly significant. The availability of water for irrigation to crops for food or fuel is a serious consideration, and one that is difficult to quantify at this point.

[QUOTE=sweeteviljesus]
How much does it cost to make a pebble? How many pebbles in a 1GW reactor? How long is their life?

Also, two criticisms of the PBMR are that the pebbles can crack (from the buildup of Radon?) and that the pebbles can get stuck removing them. Are these real issues? If so, can they be mitigated?

What can be done about the fuel cycle in terms of processing and dealing with spent fuel?
[/QUOTE]
I don’t know how to answer the first set of questions. My reference text (Nuclear Reactor Engineering, Samual Glasstone, although I see there’s a new edition I need to check into) doesn’t go deeply into costs of different types of next generation systems. The lifespan of an element is probably something like 2-3 years, and because you are constantly cycling elements through the pile you can ideally get nearly optimal usage (as compared to fuel rod bundles where you have to pull the bundle before the inner elements “poison” the reactions by absorbing too many neutrons). The number of pebbles depends on several factors including size, degree of enrichment, et cetera.

Cracking is a real issue; any manufactured product will have defects, and the thermal stresses that the pellets will see will exacerbate these. I don’t have a simple answer for that other than to maintain high quality control standards and implement containment structures and protocols that limit the amount of damage or contamination a fractured element could do. I think the problem of a jammed element could be mitigated by redundantly safe design.

Issues with processing and disposal or reprocessing of spent fuel remain. With PBMR, there’s a larger volume of high level waste than other systems, and as previously mentioned, it’s not readily capable of being reprocessed. The total amount of radioactivity is about the same, however. With the PBMR concept, reprocessing is basically out of the question; the radioactive elements comprise only a small fraction of the total mass and bulk, and it would be very difficult to sort them out. On the other hand, reprocessing and enrichment are laborous, time-consuming, and potentially hazardous processes (due to procedures and volitile chemicals used) where as PBMR pebble elements can be formed of low grade enriched and even thorium, so the economics and safety of a “once-through” cycle are not as unappealing as it might seem, and the fact that, if the fuel elements are intact at the end of the use cycle, they’re already self-contained and require no processing.

I think that transporting high level wastes to a central underground repository like Yucca Mountain is more of a political “out of sight, out of mind” solution rather than a good technical one; on-site storage eliminates the (significant) hazards of interstate transportation and provides a way to measure leakage and contamination. But of course, people want a nuclear waste depot in their backyard even less than they want a nuclear power plant.

Nuclear fission power is viable, and probably unavoidable; but in the end, improving efficiency (especially in transportation, residential and commerical structures, and appliances) combined with more ultimately sustainable energy sources (solar, geothermal, wind, nuclear fusion when-and-if that is viable) should be the goal we move toward. I have to admit not having more than a passing familiarity with “hot rocks”-type geothermal, but I have some doubts about the viability, both from a cost and environmental standpoint, of drilled down to the mantle. One could readily tap into thermal differences in the ocean, too, but despite many schemes proposed, none seem to cope with the practical difficulties of profitably extracting energy while dealing with the technical problems of working in that environment. I have my doubts that geothermal energy is going to provide more than a tiny fraction of total energy requirements.

Stranger

59

Has anyone heard of using old oil wells for geothermal energy extraction? Is this the same as “hot rocks”? I read an article about it, but I don’t remember where.

Thanks,
Rob

60

Hello. new here. Maybe this fella has stumbled on to something whilst looking for a cure for cancer after his daughter was diagnosed with it. If he is for real, he just may have made a major discovery.
http://www.youtube.com/watch?v=Lud1qceKqyQ&eurl=http%3A%2F%2Fwww%2Egoogle%2Ecom%2Fsearch%3Fhl%3Den%26q%3DKanzius%252C%2B%26btnG%3DGoogle%2BSearch