On April 26, 1986, two powerful explosions tore through Unit 4 of the Chernobyl nuclear power plant, flipping the reactor's giant 2,000-ton concrete lid into the air like a coin. White-hot chunks of the nuclear core rained down on adjacent buildings, setting fires and peppering the ground outside. Remnants of the core burned for 10 days, churning a thick plume of radioactive isotopes equivalent to 400 Hiroshima bombs high into the atmosphere.
1. "WHAT DOES THAT TELL YOU ABOUT SAFETY?"
Although Chernobyl contaminated half the planet with fallout, memory of the disaster had almost faded into obscurity when a tsunami swamped Japan's Fukushima Daiichi power plant last year. At the time, many observers resurrected the specter of Chernobyl as a reassuring example of what wasn't happening at Fukushima—a nuclear meltdown. We know now, though, that three of Fukushima's reactors did melt down, spewing radioactive contamination over parts of Japan and into the sea.
Twenty-five years separate Chernobyl from Fukushima, but the occurrence of nuclear meltdowns is more frequent than this span suggests. The nuclear power industry measures safety trends in "reactor-years." One reactor-year is equivalent to one nuclear reactor generating electricity for one year. The Nuclear Regulatory Commission's safety goal for U.S. reactors is one incident in every 10,000 reactor-years. Thomas Cochran, a physicist and consultant for the Natural Resources Defense Council, calculates that the world's fleet of light-water power reactors has racked up 11,500 reactor-years and counts five "partial core melt" accidents ("nuclear meltdown" is a term of art with no well-defined meaning) thus far worldwide. He credits Fukushima with three partial core melts. Three Mile Island and Greifswald, a plant in the former East Germany, account for the other two. (Chernobyl is not on the list because it was an old Soviet design used in only a handful of nuclear power plants in operation today.) "Historically, that means 1 percent of light-water reactors have had a partial core melt," Cochran says. "One percent is a lot higher than one in every 10,000 reactor-years. What does that tell you about safety?"
In fact, the global rate is about five times the baseline goal of U.S. regulators. If the rate of partial core melts holds true for the 353 light-water reactors currently operating, we can expect a nuclear meltdown to occur every six years on average. From a historical perspective, Chernobyl isn't just a curious artifact of the Cold War; it is one of the first events in a growing trend, and we are only now beginning to understand how to cope with its fallout.
2. "A HOUSE OF CARDS"
While Japanese emergency workers fought to stabilize Fukushima's overheated reactors, Ukrainian construction crews half a world away began an important new phase in Chernobyl's protracted cleanup, bulldozing the contaminated soil around the steel-and-concrete tomb that encloses the scorched wreckage of Unit 4's reactor building. The Shelter, as the tomb is known in Ukraine, was designed to last 15 years. More then a decade after that deadline, it still looms above the complex like a medieval fortress.
"It's a house of cards," said Eric Schmieman, a senior technical adviser for the Shelter Implementation Plan, the organization charged with maintaining the Shelter. Schmieman was standing outside SIP's office building, located several hundred yards from the Shelter. He explained how Soviet engineers cobbled it together in just six months. The north wall is a stack of debris-filled concrete forms. The south wall consists of steel panels propped against girders. The steel plates that make up the roof are affixed by gravity alone. "They didn't have a guy up there saying, 'Move it another foot,' " Schmieman said. "It was all done by crane."
Some 480,000 cubic yards of concrete and 7,300 tons of steel went into the Shelter, and it is held in place mostly by friction and luck. When Soviet workers finished building the Shelter, it was riddled with holes the size of picture windows. Leaking water corroded the steel support beams. A large crack was buckling the west wall. Birds flew in and out, spreading radioactive contamination. Ukraine inherited the crumbling Shelter after the Soviet Union broke up. By then it had become even more dangerously unstable, and Ukraine didn't have the money or expertise to repair it.
The G7 nations agreed to fund a complete rehab of the Shelter in 1997. They chartered SIP to oversee dozens of projects: plugging holes in its walls, replacing its roof, stabilizing its west wall and ventilation stack, installing monitoring equipment, and so on. In essence, the Shelter had to be fixed up in order for it to be safely torn down. The costliest project to date, and the last in SIP's mandate, is the New Safe Confinement, a $1.3-billion arch that will, if all goes well, completely seal off the Shelter from the environment. Schmieman, the principal member of the arch's conceptual design team, has tackled complex engineering problems all over the world. But the arch, he said, is by far the most challenging project he's ever worked on. Everything about the arch—its size, its purpose and the hazardous conditions under which it's being built—is unprecedented. Now he grinned. "This is kind of like what working on the pyramids must have been for engineers back in Egyptian times."
The July 2012 issue of Popular Science arrived yesterday, and I read the previous articles about "Climate Change" and "The Battle." When I came upon the "Chernobyl Now" article, I noted the radiation dose unit, "rem." This took me back to the days and weeks after Japan's "311" earthquake and tsunami natural disasters that led to the Fukushima nightmares. NHK World reports referred to "micro- and milli-sieverts," which were unfamiliar to me. Wikipedia soon cleared up what these readings meant in "rem" and "rad" equivalents. "Gray" (Gy) refers to "rad," though it became clear that a 1 Sievert (Sv) = 100 rem reading was bad news. As for long term low level radiation levels, anything approaching 5-10 mSv was high enough to keep people from returning to homes in the area. Since these are SI/Metric system measures, I don't expect to read about them outside of scientific literature. Still, a foreign visitor to the Tohoku region should be aware that Sieverts, milli- or micro- matter. I live in Hawaii, so before approaching that drifting mass of Tohoku region trash, a radiation detector that reads out in Sieverts may come in handy.
As of the UNSCEAR 2008 report, the remaining legacy of Chernobyl is 0.002 mSv/yr in global average exposure (a figure which was 0.04 mSv per person averaged over the entire populace of the Northern Hemisphere in the year of the accident in 1986, although higher among the most affected local populations and recovery workers). Natural background radiation (such as radon from uranium and cosmic rays and much else) averages 2.4 mSv/yr globally but frequently varies between 1 mSv/yr and 13 mSv/yr depending on a person's location as determined by UNSCEAR.
(Each 1 mSv is 0.1 rem, thus 100 mrem).
The effects of low-dose radiation are not just a mystery. Actually, for example, since the United Kingdom averages 2 mSv/yr compared to 7 mSv/yr natural radiation in Finland, we know, if tiny fractions of a mSv exposure caused vast numbers of extra deaths like the anti-nuclear environmental activist group referenced in this article tries to claim, there would be far more extra deaths seen in Finland compared to the U.K. Instead, Finland has actually lower cancer mortality (even if age-adjusted) and greater life expectancy than the U.K., in thus the opposite of proving much harm from even as high as a 50 mSv/decade (5 rem per decade) difference. Of course, there are other differences between the countries affecting cancer and life expectancy totally unrelated to radiation, but the preceding provides still an upper limit.
Radiation exposure from the nuclear fuel cycle and normal nuclear power operation is 0.0002 mSv/yr on average to the public, not much compared to the 1 to 13 mSv typical natural radiation variation by location. After Germany's Green Party went after nuclear power there, the net result in practice now is they are resulting to building many more coal power plants (for baseload power, even with all their solar power efforts). I don't know off the top of my head figures for German coal power plants in particular, but, over 1937-2040, global coal combustion is estimated to release 2.9 million tons cumulatively of uranium and thorium radioisotopes, from burning 637 billion tons of coal worldwide. You actually can get more radiation exposure living by a coal power plant, as implied at:
On nuclear power topics and radiation in general, some meaningful quantification is everything. For example, most people have been told countless times of how radioactive waste disposal is a top threat and problem including some manmade radioisotopes having half-lives of millions of years. They have usually never even heard a decently partially specific numerical picture, like how the following is the case:
"Since the fraction of a radioisotope's atoms decaying per unit of time is inversely proportional to its half-life, the relative radioactivity of a quantity of buried human radioactive waste would diminish over time compared to natural radioisotopes (such as the decay chains of 120 trillion tons of thorium and 40 trillion tons of uranium which are at relatively trace concentrations of parts per million each over the crust's 3 * 10^19 ton mass).[*][**][***] For instance, over a timeframe of thousands of years, after the most active short half-life radioisotopes decayed, burying U.S. nuclear waste would increase the radioactivity in the top 2000 feet of rock and soil in the United States (10 million km^2) by ≈ 1 part in 10 million over the cumulative amount of natural radioisotopes in such a volume, although the vicinity of the site would have a far higher concentration of artificial radioisotopes underground than such an average.[****]"
I've enjoyed Popular Science articles on other topics in the past, but, coming in now, I'm somewhat surprised that Popular Science has articles with what I would consider a bias against nuclear power. Even for purely business perspective considerations, I bet much of the customer base is relatively technophilic.
"Equivalent to 400 Hiroshima bombs" is misleading at best, as actually the nuclear bomb killed utterly predominantly from the blast, etc. plus the radiation pulse from the explosion itself, not nearly so much from the fallout. A device of a few kilotons has literally hundreds of times less fallout than later devices never used in war of up to megatons fissile (plus fusion) yield, although even the latter is commonly overrated in public perception of lasting radiation as under energy constraints limited in space and time like the rule of sevens (see nuclear weapons FAQ online if really interested).
Three Mile Island killed nobody and highlighted the value of the containment domes universal amongst Western reactors.
* Sevior M. (2006). "Considerations for nuclear power in Australia" (PDF). International Journal of Environmental Studies 63 (6): 859–872. DOI:10.1080/00207230601047255.
** Thorium Resources In Rare Earth Elements
*** American Geophysical Union, Fall Meeting 2007, abstract #V33A-1161. Mass and Composition of the Continental Crust
**** Interdisciplinary Science Reviews 23:193-203;1998. Dr. Bernard L. Cohen, University of Pittsburgh. Perspectives on the High Level Waste Disposal Problem
I appreciate all the additional information you provide and the associated links. PoPSCi often just plagiarizes someone elses article on the internet, changes a few words and call it their own. They rarely get their own hands dirty and do investigative journalism. But I do appreciate they do provide a one stop for a variety of scientific, gadget journalism.
It interesting to note from the above article, of the picture and even the option to enlarge it. I did choose to enlarge it and then later with my computer more so. I found a great many display and controlling panels have been removed from the old picture. My guess the removal of them was not for the technology, but to remove evidence of where controlling circuits were last left and indicators too. By removing enough panels, we loose evidence of a history of what went wrong... Of course, I am just negatively guessing too.
There is a lot of information lacking here so I will try to go through it step by step. The first thing people should about safety is that the legal limit for public dose in the US is 0.1 rem from a man-made nuclear source. The occupational dose is 5 rem year. These numbers and other useful information can be found online through the Nuclear Regulatory Committee in the 10CRF20; for other information you will have to look around the website. These limits are set well below what is considered a dangerous amount of radiation exposure.
Now as for the article it seems to imply that nuclear power is unsafe in the US and even Japan which is an invalid assertion. Here is why. In the US the one major accident, three-mile island, that occurred, occurred early on and in response to that accident safety protocol has been modified to prevent such events and similar events in the future. In addition three-mile island, though it suffered a partial core melt, did not leave any lasting effect on the environment. The only thing of note that happened in three-mile island was a release of Iodine 131 which diluted to non-lethal levels in the air and subsequently decayed. As a testament to the fact that three-mile island was not a catastrophic disaster, the Three-mile Island facility is still open; the steam plumes can still be seen rising from the cooling towers on a drive I83.Three mile island is an old design and an old plant and the US is currently building new plants (4units) in Vogtle GA and Summer SC. These new builds are new designs with increased safety and better safety features which should amplify the US nuclear industry's already exemplary safety record. No one in the US public has ever been reported to die due to a nuclear accident.
As for Chernobyl ... Chernobyl was a completely avoidable scenario that was caused not by the design of the reactor but intentional misuse. Fukushima on the other hand was caused by an unforeseen combination of disaster coupled with a lack of readiness to deal with such an extreme disaster. What really caused three of six units at Fukushima to melt down was the complete loss of power. After the earthquake hit all six plants shut down and were safe despite the fact that nuclear plants until that point were only rated for a magnitude 8 earthquake, no the magnitude 9 that occurred. The plants then lost power to the grid and were forced to use diesel generators to keep critical equipment, mainly cooling pumps, online to maintain plant stability. After the plants were in stable shut down the tsunami hit and wiped out the diesel generators cutting off all power. It was at this point that with no power, the emergency cooling pumps were unable to keep the core cool and other measures were needed to supplement. It was the unreadiness for such an unpredictable disaster and culture of conformity that then led a period of inaction that resulted in the melt-downs. It should also be noted that the plants that suffered the worst damage were older and scheduled to be shut down within a few months of when the disaster occured. The other three newer plants survived the disaster well.
In the US we do not have such problems; we are prepared to deal with extreme problems quickly, even ones we cannot predict. This may seem absurd, and question how you can be prepared for a disaster you cannot predict, but the answer is relatively simple. In the US we have protocols in place that allow us to respond to the needs of the plant under any circumstance. These protocols are also being reviewed with utilities and updated in wake of Fukushima. What these protocols mean is that if something goes wrong with the plant we can respond to that need if necessary regardless of the disaster. For instance if a plant loses power we can assure that the power is returned to the plant quickly so that it may restart the cooling pumps before compromising damage is done to the core. This type of response readiness is part of the American Nuclear culture. We have a culture that responds immediately and does not need to follow a bureaucratic chain to implement life-saving measures in response to a disaster. In addition to this there is a large knowledge base in nuclear safety and the ability to call on expertise quickly. In fact even for a university research reactor, which are in general melt proof, a senior staff member must be able to be called in and arrive within 15 minutes for the core to even be allowed to operate. We can all be assured that due to the safety culture which exists heavily in the US nuclear industry that we do not need to fear a nuclear disaster. Even in our one great disaster the public and environment was kept safe as we could expect for any potential future disaster.
The US has some of the oldest reactors running in the world. Many should have been shutdown, except no replacement could be built. They are not safe by todays standards. Japan did suffer a sort of unexpected disaster but that is what a disaster is, unexpected. Any reactor in the world can suffer this fate.
The loss of life still needs to be determined. Cities that produce nuclear fuel have tremendously high rates of cancer. Workers in mines and transportation die or will die as a secondary result of their occupation. No one is safe from nuclear products, every bit adds up. There is no safe amount.
Saying that nukes are safer or not than a coal or propane plant is also hard to measure.
The safest thing to say is it is easy to save energy than to create it.
Those are also the BARE MINIMUM requirements. In my experience (atleast for reactors in research labs), we had further limits above and beyond what the NRC required. If NRC says we could operate with an SRO on 15 minute call, we had our limits set so that the SRO had to inside the building. It went that way for nearly every regulatory requirement on down the list.
Great points all around. POPSCI is fairly transparent in their dislike for nuclear power. It's unfortunate that the context needs to come from commentors.
and this is why we should be using LFTR. they can't melt down because they are not control overload reactions... they produce far less radioactive waste which becomes safe after a hundred years instead of tens of thousands of years... they produce way more energy... they use a common element... they can't be weaponized... and can be made much much smaller and cheaper.
Jefro, would you please name one American city that produces nuclear fuel that has abnormally high cancer rates?
And Jefro, please also inform us as to the number of fatalities due to nuclear energy in the United States. How does that number stack up against coal, gas, wind, etc.?
You can throw all the stats you want around but the truth about nuclear power that all plants have in common...is the inability of humans to foresee every possible outcome and scenario.
All the meltdowns involved the human incapacity to foresee the future and no amount of number throwing will change that.
Nuclear power is dangerous and coal is dangerous. I don't like either one, but it's easier to combat and clean up a coal disaster than a nuclear one. If you want to argue it isn't, you're fooling yourself.
Most nuclear and coal plants in the US are unnecessary. We have more than enough landmass to use CSP and PV solar energy especially with the improvement of molten salt storage systems and pumped water systems that use gravity for nightime power needs.
I'm not against LFTR. But the reason it can't melt down because it already is molten, with the fission products circulating in the coolant. It is as if a meltdown has already occurred. How is this safer than, say, a liquid metal-cooled reactor with solid fuel that contains the fission products?
phoenixamaranth, the truth is in the statistics. If it were easier to clean up a coal disaster, why have we not prevented the deaths of tens of thousands of Americans every year for the last 50 years or so? (See the American Lung Association report.) During that same period, exactly zero members of the public have been killed by nuclear energy, including the old plants that Jefro is worried about. We all want nuclear to be safer, but the claim that it is not safe enough while the alternatives are far worse does not hold water.
I agree. In my experience as well, limits for individual groups are often set to a higher standard than that required by the NRC. My university research reactor for instance operates far below the limits of its legal operating window; so much so that the legal operating power would need to be multiplied about five fold before new pumps would be need to keep within our DNBR limit. However, as far as I can tell this is not unusual for university reactors. Thanks for drawing attention to the often missed fact that in the nuclear industry we strive to exceed the bare minimum that is required of us.
I recently had the pleasure of listening to a representative of the NRC give a talk about its response to Fukushima and the lessons brought back to the US. One of the things she pointed out, and is corroborated by history, is that in the US we will never keep a plant online if there is a serious and factually based concern about its safety. An example of this is the Maine Yankee which was decommissioned in 1996 due to cost and concerns about its safety.
As these old plants age you can expect to see them be decommissioned. This is not a bad thing. However, new plants must be built to replace them because a single nuclear plant on average accounts for about 0.2% of the nation powers and in many states can account for much more. The Trojan plant for instance, before it was decommissioned in 1993, accounted for 12% of all Oregon's electricity (1100MW). This is a huge amount of power and is difficult to supplement with other sources. As a point of reference the typical US coal plant outputs 50-300MW and the typical US solar plant outputs 5-100MW. So short of building a mega-coal plant or mega-solar plant, you would need many plants to replace nuclear. Due to the capacity factor on solar the number of plants you would need to replace a single 1000MW nuclear plant would cost somewhere on the order of $14billion and would take up an area half the size of Washington DC; and this is based on solar thermal which is cheaper and more efficient. To put that in perspective a single new 1000MW nuclear plant only cost somewhere between $5-$11billion and displace a couple of acres while protecting local natural wildlife for usually at least a couple square miles (due in part to NIMBY and security).
As far as your safety concerns go; there really is no way to say this nicely, you are just wrong. In fact there is actually a theory with some factual basis that some amount of radiation is good for you and will reduce your risk of cancer, but we will return to cancer later. You are right that an unexpected disaster is unexpected, but the effects of an unexpected scenario are not. As an analogy we will consider an unexpected disaster while you are driving. Suppose you are driving through Kansas and a rhinoceros t-bones your car from the side of the road. This is a completely unexpected event as rhinoceros are not native to Kansas, but is one that could happen if for instance a rhino escaped from a zoo. I also guarantee the common US sedan is not rated for rhino strikes. Now what is not unexpected is what will happen to your car. Your car will most likely roll; but you will be protected by your car's frame which is tested against rolling. You will also be protected by your seatbelt and airbag which are tested and rated to keep you safe. Now because of these features we can conclude that your car is safe even in unexpected scenarios because the designers took into consideration the physics of how are car responds to different forces. A nuclear plant is no different. Just because we cannot predict a magnitude 9 earthquake, or some other disaster, does not mean we cannot be ready to deal with the situation. We can in fact deal with it because we know the physics of how a reactor works. There are realistically only a finite number of outcomes for a reactor in a disaster even though there might be a seemingly infinite number of disasters. Because of this plans can be formulated, and reactors can be designed such that in the event of the unexpected operators and task forces can respond and keep the reactor stable until the core is cool and the risk of meltdown has subsided. As a testament this claim just look around the US. There have been no meltdowns in 33 years, even thought there have been plenty of disasters (Hurricanes, tornadoes, earthquakes, floods, equipment failure, ect.). As a great example the recent earthquake originating in Virginia, a state in which an earthquake of that magnitude is completely unexpected, caused a nuclear plant near the epicenter to trip or automatically shutdown. I don't remember hearing any headlines about a meltdown or a leak or a release of deadly gas. I do however, remember hearing a headline that said the earthquake hit but the nuclear plant shut down safely.
Now for you cancer concern, people in cities get cancer reasons not related to nuclear power. Your facts about increased cancer rate due to nuclear fuel in cities that produce nuclear fuel are just wrong. In fact Wilmington NC is home to GE's nuclear fuel fabrication facility -one of only a handful fabrication facilities owned by various companies in the US- and the cancer risk locally is among the lowest in the entire state of NC. The reason why people in more populated cities with a nuclear fabrication lab are getting cancer is because they live in a city. While living in a city you are likely to be exposed to smog, car exhaust, cigarette smoke, and a number of other pollutants all of which are known to cause cancer. Unless you physically go into a nuclear fuel fabrication facility and enter a room that requires a hazmat suit or respirator without wearing one, you are not going to get cancer. Even the people who work there do not need to worry about getting a significant increase in the probability of getting cancer because over their career they might get at worst a 1-5% increased likelihood of getting cancer at some point later in their life, which means when they are maybe older than 50. Now this seems large until you actually compare it to their risk of getting cancer in the first place which the dwarfs that number. And then on top of that only a few employees might reach that 1-5% number.
There is just no evidence to back up your claims that nuclear is unsafe and is killing people. The numbers on public deaths due to commercial nuclear power in the US is none. You take more of a risk driving your car or using a power tool than you do living near a nuclear power plant. The US nuclear operational safety record is quite impressive and in many ways unmatched by almost any other industry. For anyone who is outside the nuclear community I can assure you that safety is held to the highest level in the operations of our facilities. In fact safety precedes all other considerations and is always our limiting factor on how much power we can produce.
in a LFTR what is molten is sodium mixed with thorium. if the system isn't forced to stay operational then the system uses natural laws of physics to stop where as current tech have to be controlled at all time to prevent overload that leads to a melt down. And in this case a melt down is NOT the same as molten sodium.
A metal-fueled sodium cooled reactor (SFR) also uses the natural laws of physics to stop the chain reaction and to remove decay heat, with no operator action. In this case, the fission products are still retained in the undamaged solid fuel elements. I believe that in an LFTR, the molten salt fuel/coolant mixture is circulating inside the primary system. So the SFR retains an additional barrier between the fission products and the environment. This was demonstrated by Argonne National Laboratory in the EBR-II Shutdown Heat Removal Tests in 1986. So I do not see any reason to claim that an LFTR is safer than a SFR. I am not arguing that the LFTR is unsafe, but I am arguing that the SFR's inherent safety has been decisively demonstrated.
I do not doubt the SFR's inherent safety.
The argument here should not be about which is safer, but which is a better choice.
The SFR is using a solid fuel, whereas the LFTR uses a liquid fuel. I believe you to be very knowledgeable on this already so I won't try to impress upon you the significance of this difference.
Edit: actually, for the benefit of others who may not be aware of this I will list some points on the difference.
a) Liquid fuels 'burn' more efficiently i.e. MUCH less waste
b) Solid fuels need to be manufactured to a high degree of accuracy, with low tolerances to be safe and efficient i.e. high fuel element manufacturing cost. While it would be a gross oversimplification to say a LFTR is "Fill 'er up!" style cheap, it's a pretty good analogy.
c) Liquid fueled reactors can be 'throttled' meaning power output can be controlled to suit high/low demand periods. Have you tried throttling a solid-fuel rocket? :)
d) A LFTR can be shut-down and RESTARTED almost instantly. A Solid Fueled reactor of ANY kind, not just SFR takes forever in comparison. In terms of safety, I doubt I need to impress upon anyone the massive advantage this brings.
e) One of the MOST important elements to consider is that LFTR uses THORIUM. Which is leaps, bounds and pirouettes more abundant than uranium et al. Hence you deal with resource concentration problems (e.g. middle east) since EVERYONE has Thorium (Although the most cheaply extractable sources are still in certain places)
There are many MANY more points I can bring up, but I did not mean this to bash the SFR, just to inform the differences and why I still consider LFTR to be a superior choice.
While there are some advantages to LFTR, there are many down sides as well. The safety is not well understood as they have not been operated for a time reasonably long enough to determine what the real safety pitfalls actually are. Here are a few comments on the comments presented above.
To comment (a), there in reality is the same amount of fission product waste from any type of reactor; but you are correct in that high level Actinide waste will be reduced. In addition noble metal build-up in piping adds a refueling cost as at some point the pipes must cleaned or replaced. This also adds a restrictive uncertainty for safety as the roughness factor of the piping must be well known to calculate a safe operating window without being overly restrictive.
To comment (b), liquid fuel is not that easy it must be kept hot or it will freeze and leaking is a much bigger problem especially when the fuel is easily oxidized. This is a difficult problem to overcome and requires that effective design measures keep the liquid fuel from coming in contact with the water coolant.
To comment (c), solid fueled reactors are known to be 'load following' meaning they automatically throttle to match demand. All two or more loop reactors are capable of doing this, it is not a unique feature to LFTR.
To comment (d), while this might be true, LFTR will not even start up unless the lithium in the FLiBe contains low Li-6 content, as Li-6 is a neutron poison.
To comment (e), although thorium is very abundant a thorium reactor requires high enrichments of U235 in order to make a good breeder to ensure a closed fuel cycle. Thorium does not fission but may be transformed into U233 which does fission. A low uranium enrichment thorium reactor will not necessarily be able to produce enough U233 to replace the U235 burned resulting in a need for more U235. U235 is not as abundant as uranium (composing only about 0.7% of natural uranium).
A issue that was missed is that LFTR have issues incorporating delayed neutrons which decreases the neutron lifetime and makes changes in criticality occur much more rapidly. As a point of reference a reactor running on prompt neutrons must react a couple of orders of magnitude faster than a reactor that has delayed neutrons. The reason this is an issue is it puts limitations on the operating window. A LFTR may not operate in conditions in which the certainty of the control system to respond in time is low. Another issue missed is the nuclear data problems associated with reactor grade graphite. The uncertainty in the mathematical description of how graphite moderates neutrons is still high; however, this particular issue is being overcome. Graphite additionally does not hold up particularly well to intense radiation and the moderation of neutrons by graphite can change drastically over the core lifetime. This change must be accounted for in the design for criticality safety. If the positive reactivity coefficient for the graphite becomes more positive with radiation damage the core operating limits must be designed around this. If it becomes less positive the core must have higher fluid flow in the secondary loop to provide the same power or a burnable poison is needed which can be decreased with core life.
Interest in LFTR using FLiBe is coming around again, and this is not a bad thing; but while LFTR overcomes some problems with traditional reactors it presents a whole new set of equally challenging problems. The point of this post is to shine a light of realism over an idealistic view. In the end economics, operational certainties, and safety will always determine whether a reactor is built. I think it would be interesting to see LFTR one day but an enormous amount of work and research needs to be done before we see these plants as part of the nuclear mix. LFTR technology is about 40 years behind its solid fueled cousin and is much less understood. Research however, will be stalled on the part of the industry however, due to the development of SMR (small modular reactors), AP1000's, ESBWR, ABWR and VHTR (very high temperature reactors). These five reactor designs will be the focus of the next couple of decades. Any research into LFTR will have to be funded through private donors to individuals foolhardy enough to undertake the challenge.
I used to really enjoy reading Popular Science articles and being able to get fairly unbiased views of most science and technology related issues. However, in the recent years it is clear that there is a strong bias towards "green" issues. For example the most recent article on Climate Change or this article on Nuclear Power Plants. I never thought that Popular Science would give into the bandwagon hype and throw away its scientific background. It's a good thing there are readers like engineer238 and tenb who are well informed and have at least taken the time to educate themselves on the issue. At least we can learn something from their educated discussions about this issue.