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Three days after a catastrophic earthquake and tsunami hit Japan, the situation at the Fukushima Dai-ichi nuclear complex has turned into the biggest uncertainty of the crisis. Recovering from the seismic event will take tens of billions of dollars and years of work — but if the nuclear situation goes the wrong way, that would add dramatically to the disaster's cost.
How did all this happen, and how could it end? Different folks have different answers, depending on how they feel about nuclear power. Here's a roundup of the best answers I've been able to put together — accompanied by an invitation to add your own sources and perspectives as comments below:
Has there been a nuclear meltdown?
Authorities say partial meltdowns have probably occurred at three of the Fukushima Dai-ichi plants.
To understand what a "partial meltdown" means, we need to discuss how the reactors are constructed. Under normal conditions, the plants produce power by sustaining a controlled nuclear reaction inside a pressure vessel. Chain reactions in the nuclear core's uranium-filled fuel rods heat up water, generating steam that turns turbines to generate electricity. That steam is circulated through a cooling system and returned to the pressure vessel as water to keep the cycle going. The uranium oxide fuel is contained inside sheaths of zirconium metal that can withstand temperatures of 2,200 degrees Fahrenheit (1,200 degrees Celsius).
Control rods can be inserted between the fuel rods to shut down the main chain reaction in the uranium. But the water-circulating cooling system is needed as well to bring the temperature down while the radioactive decay subsides.
isotype.com / Reuters / Source: Deutsches Atomforum
The problem is that the power for the cooling system was cut off when the earthquake hit. Then the backup diesel generators were knocked out of commission by the tsunami. Backup batteries could keep the cooling system going for only about eight hours more. The plant's operator tried to bring in mobile generators to restore power, but the connections reportedly didn't match up.
Meanwhile, residual heat from radioactive decay continued to build up, and water continued to turn to steam. Eventually, the fuel rods became exposed. The temperatures apparently reached the melting point for the fuel rods' zirconium sheaths. That can result in uranium oxide fuel falling to the bottom of the pressure vessel — which is what some experts mean when they talk about a partial meltdown. Other experts, however, would reserve that term for a situation in which the nuclear fuel makes its way out of the pressure vessel but stays within a steel-and-concrete containment shell that surrounds the reactor.
Is that why radioactive material escaped?
At the three Fukushima Dai-ichi reactors that are apparently experiencing partial meltdowns, the nuclear fuel is still contained within the pressure vessel. The radioactive material is not coming from the core itself. At reactors No. 1 and No. 3, the material is contained in steam that has been released from the vessels. Plant operators opened the steam valves to reduce the risk of a high-pressure explosion inside the vessels — in effect, letting off steam to keep the lid from blowing off a pressure cooker. The steam contains radioactive cesium-137 and iodine-131, which are byproducts of the uranium reaction. The authorities said the radioactivity in that steam is still below regulatory limits and should not pose any health risk.
Despite those reassurances, authorities ordered an evacuation of the area within a 12-mile (20-kilometer) radius of the Fukushima Dai-ichi plant, and have distributed stable iodine to evacuation centers as a precaution. If people are exposed to significant amounts of radioactive debris, taking doses of iodine can prevent the uptake of radioactive iodine and reduce the risk of thyroid cancer.
Right now the radioactive plume is blowing out to sea, which means it's not wafting over Japanese population centers. It is wafting over the Pacific, however, and the U.S. Navy found that air crew members from the aircraft carrier USS Ronald Reagan were exposed to low-level contamination. The Navy says the crew members were decontaminated with soap and water, and all U.S. ships have been moved out of the downwind direction. Apparently, no harm was done.
Nevertheless, the contamination incident was worrisome to nuclear physicist Frank von Hippel, a former Clinton administration official who is now co-director of Princeton University's Program on Science and Global Security.
"I was surprised how high the radiation levels are," von Hippel told me.
So what's being done?
Plant operators have been pumping cool seawater into the pressure vessels to replace the water that's being lost as steam, in an effort to keep the fuel rods from heating up further. They've added boric acid to the seawater, because boron suppresses the nuclear reaction and could accelerate the cooldown. Authorities were reluctant to turn to this strategy because the seawater is so corrosive that it ruins the reactors for future power generation. But that's better than having the meltdown progress to an even worse stage.
What about these hydrogen explosions?
When the seawater hits the hot zirconium rods and uranium fuel, some of it is broken down into hydrogen and oxygen gas. Venting the steam allowed that hydrogen and oxygen to escape and build up between the pressure vessel and an outer structure that protects the reactor from the elements. At reactors No. 1 and No. 3, the hydrogen ignited, blowing the roof off the outer structure in each case. However, the pressure vessel and the steel containment shell remained intact. It's important to note that the hydrogen blast was not the result of any sort of atomic or "H-bomb" explosion, but was a purely chemical reaction.
Is the situation getting worse?
Yes. Authorities say another blast has been heard at reactor No. 2 at the Fukushima Dai-ichi plant. Details are sketchy, but the plant's owner, Tokyo Electric Power Co., said the explosion occurred near the reactor's suppression pool, a water reservoir that's part of the cooling system. A government spokesman said the pool was damaged, and there was concern that the No. 2 containment shell may have been breached. "A leak of nuclear material is feared," The Associated Press quoted Shinji Kinjo, a spokesman for Japan's nuclear safety agency, as saying.
Kinjo said radiation levels rose from 73 microsieverts before the blast to 11,900 microsieverts (11.9 millisieverts) three hours afterward. To put that figure in perspective, the U.S. Nuclear Regulatory Commission says that occupational exposure for adults working with radioactive material must be limited to 50 millisieverts per year.
In a nationally televised statement, Japanese Prime Minister Naoto Kan said "the level seems very high, and there is still a very high risk of more radiation coming out." Kan told people living within 19 miles (30 kilometers) of the Fukushima Dai-ichi complex to stay indoors to avoid radiation sickness.
AP also quoted Chief Cabinet Secretary Yukio Edano as saying that a fourth reactor at the complex was on fire and that more radiation had been released. "Now we are talking about levels that can damage human health. These are readings taken near the area where we believe the releases are happening. Far away, the levels should be lower," Edano said. Later, AP reported that the fire at reactor No. 4 was extinguished.
What about the nuclear fuel stored at the site?
The spent fuel rods at the Fukushima facility are stored in pools of water above the reactor. Plant operators have signaled that water levels were falling at reactor No. 1's storage pool, suggesting that the cooling system is failing. "It's on a slower fuse," von Hippel said, "but on the order of a week or so, it could boil down to the level of fuel."
What's the best-case scenario?
The seawater gambit keeps temperatures inside the pressure vessels under control for the next few days. During that time, the residual heat of radioactive decay dissipates, and operators no longer need to release steam from the vessels. Eventually, electrical power is restored to the cooling system, and each vessel's core can be removed.
What's the worst-case scenario?
Authorities can't cool down the cores, and temperatures rise to the point that the uranium fuel melts into a mess on the bottom of the pressure vessel. The concrete-and-steel containment floor beneath the vessel has been built to contain a full core meltdown — but experts can't completely rule out the possibility of a breach that causes the highly radioactive material to escape into the environment.
Right now, the situation at Fukushima Dai-ichi is analogous to the Three Mile Island incident of 1979, which involved a partial core meltdown and a release of radioactive gases — but no breach in the reactor vessel. "It's at least as bad as Three Mile Island," von Hippel said. But if the nuclear fuel breaks out of the vessel, the situation could turn into something more like the 1986 Chernobyl nuclear accident in Ukraine, which sparked fatal cases of radiation sickness and spread contamination across a wide swath of Europe.
How long will this go on?
Even under the best-case scenario, it will take years to clean up the mess. "When you're dealing with spent fuel, you don't put it in cool, dry casks until three years after the reaction has stopped," von Hippel said.
More explanations of the nuclear situation:
- Radiation health risk remains low, experts say
- BoingBoing: Inside the 'black box' of nuclear power
- Brave New Climate: Fukushima accident explained
- Scientific American: Beware the fear of nuclear ... FEAR!
- The Great Beyond at Nature: Anatomy of a meltdown
- Cosmic Log archive on the earthquake and tsunami
Princeton physicist Frank von Hippel answers your questions about the nuclear situation in Japan during an online chat at 4:30 p.m. ET Tuesday, March 15. Click here to submit your questions in advance and participate in the chat.
Have you found some particularly good explanations for what's going on, or are there some burning questions yet to be addressed? I've purposely stayed away from discussing the potential health risks in depth, because my colleague JoNel Aleccia is handling that important angle. But if you'd like to shed more light (rather than heat) on the situation at Fukushima or Japan's other stricken reactors, please feel free to add your comments below.
Join the Cosmic Log community by clicking the "like" button on our Facebook page or by following msnbc.com science editor Alan Boyle as b0yle on Twitter. To learn more about Alan Boyle's book on Pluto and the search for planets, check out the website for "The Case for Pluto."
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Are you watching it from space no shame Obama? Usually if a world leader does not want to be called the joke of humanity as people cheer as he gets put down by a jury of his peers, it would be exclusively his or her problem. Not with this little animal. To bad, huh?
Knowing that people younger and better than me were sent to their death by Shameful George for no reason is what kept me alive but something of this scale and magnitude kind of shakes any personality back into reality and hopefully they will be living meaningful lives again as soon as possible. May they all rest in peace.
after the 3rd explosion, is this still a level 4 on the INES scale ?
Ooops, a dirty mouse, double post.
Just out at 9:26 central time. It is now leaking dangerous levels of radiation. So what does this mean? Has the container breached? It sounds to me that they have an uncontrolled reaction going on and the reactor is not in a cool down phase as being said here. Either the control rods did not insert fully and immediately or they got too hot and melted and now they are back into an uncontrolled reaction.
If an uncontrolled reaction do they attempt to continue to cool or just let it go and cover it with concrete and hope for the best?
Check my post on the previous page. This IS worst case........
I have a question being a plumber wouldnt pouring water on the reactor or core be like pouring freezing water into a glass that just came out of dishwasher causing it to fracture and crack?
I find it incomprehensible that no one thought through the possibility of what could potentially happen if an earthquake AND a tsunami occurred together. This is Japan, an Island that is constantly experiencing seismic events and that has in place a sophisticated tsunami warning system. The Japanese people KNOW that earthquakes and tsunamis occur together. When the truth eventually comes out, it is likely to reveal that the crisis was precipitated by the malfeasance on the part of someone taking unwarranted 'cost saving' shortcuts as in the case of the BP disaster in the Gulf of Mexico last summer.
I heard one report (sorry, no link -- it was secondhand) that in the process of approving the site, they looked back a thousand years (historically and geologically) at tsunami records and decided that the location had not been significantly impacted. Of course, there's always that pesky 1001-year tsunami cycle.
Seriously though, this is near the very edge of the top plate at the subduction zone of the Pacific plate. Pardon my layman's take on plate tectonics and fluid dynamics, but isn't that exactly where we are likely to find the top plate's edge being pulled down like a springboard at a sumo wrestler's high-dive competition? And when that edge releases and springs back, it seems like it would push a lot of water straight up toward the surface. Asteroid collisions aside, is there any better formula for making a tsunami?
As you point out, it seems like that might have occurred to somebody in Japan.
I'm curious about the seawater being injected into the cores. Is that water all turning into steam? Does that water get recycled out, and isn't it highly radioactive after travelling through the core?
Throwing salt water on the reactor is like throwing gas onto a fire.
Salt water ions very easily splits water molecules, H2O, in a current at a lower temperature than pure H2O, into its elementary hydrogen and oxygen particles. Salt water is a much better conductor of electricity than plain old water, in fact pure water doesn't conduct electricity, most water isn't pure water just add some other molecules and water becomes a conductor. Therefore the buildup of hydrogen in the containment building is mostly caused by them trying to cool the radiation down with salt water. The fuel rods would have to get over 2500 C to split pure water molecules into hydrogen and oxygen, with salt water the temperature can be much lower...
I think I understand Gary's point and had the same curiosity. You'd think with steam still being created it would be enough to turn the turbine and generate some juice for the pumps. As the steam dissipates with the cooling of the core the turbines would grind to a halt. May be easier said than done, I'm no nuclear or any other scientist or engineer but to me it would make sense...
It's now FOUR days after the tsunami and things are getting worse at the nuclear plant. It sounds like there is no plan to fix things and everyone is just guessing on what can be done to fix it.
Thanks for this excellent explanatory report, Alan. Keep up the good work. You really are the best. A couple of questions, though, from your old editor, about the movement of radioactive clouds. How quickly can large amounts of released radiation move through the air? Is the movement dependent on the wind? Does the radiation dissipate or maintain its strength as it moves? What estimates are there for how long a catastrophic release of radiation in Japan would reach Hawaii or the continental United States.
As you watch,listen or read the news you would expect to see mushroom clouds at any time. This is just what the environmentalist and anti nuclear energy proponents want inorder to stop the US from building nuclear power stations. Nuclear power stations are not nuclear bombs and will not be causing any nuclear explosions. While a nuclear meltdown is not what is wanted it is not all gloom and doom.
This is just awesome science reporting. Thank you so much for the information, which clarified so much for me. I am heartsick for the Japanese people.
What's happening at nuclear plants is they are only good as their designs and location location location!
In America, we have far too many on the coasts and near fault lines.
That's principally due to the USGS underplaying the risks in almost every case they provide 'proof' of lower than expected risks so that they get the nuclear plant they want to play their video games online while laughing at the people who know better!
DO NOT TRUST THE USGS!
All I know is, this nuclear mess gives Japanese film directors an entirely fresh take on the Godzilla movies. Next summer's big blockbuster will star a giant, glowing, mutant creature that was born just miles off the apocalyptic coast of northern Japan. For two hours the creature will run around Japan stomping on all of the nation's nuclear power stations.
Is $10 billion dollars (as alwaysaskmom says is the proposed estimated cost) cheap? How much energy could be generated is that same amount were spent on alternative energy sources? Suppose the cost is $15 billion? What about the cost of decommissioning the nuclear plant - another $1 billion, $2 billion, $5 billion?
I guess the question is, leaving the issue of safety aside, which energy generation technology truly provides the most value for the total money spent?
I actually study radioactive materials and their uses, but am still a graduate student, for the sake of full disclosure. To answer your (and others) question, the cost of one meltdown every 20 years (thats assuming all future plants are as prone to accident as these extremely old models, which isn't remotely the case) is still quite small when distributed over all the operating nuclear plants. Since I have some academic experience with green energy, I'll try and explain why no-one who wants to seriously address the energy crisis is pursing for wind an solar...
The real problem with wind and solar power is that they don't provide stable power generation. We can control a nuclear reaction, a coal fire, and a hydroelectric dam. Solar and wind are both slaves to the weather and the day/night cycle. The long and short of it is even in places rich in wind and/or sun (Arizona, for example), assuming we had some magical inexpensive highly efficient solar panels (we don't), we still need a way to store the energy produced during the day for use at off hours and on cloudy days. Currently, there is no way for us to do that. Modern batteries aren't capable of it, let alone cheap enough. Even if the technology to do it were discovered tomorrow it would take many years to test and commercialize it, and frankly even hoping for a solution that quickly is pretty pie-in-the-sky.
*Disclaimer* Wind is somewhat better than solar, as there are areas (like off the coast of some European countries, for example) where there is pretty steady wind. These areas are the exception, not the rule. Most places in the US can't use the European model for green energy, for many reasons I will let you look up on your own. And even in Europe, the stable base power is still supplied by nuclear and coal, which can ramp up generation if needed. *End Disclaimer*
Oh, and since most major urban centers aren't near places rich in "green energy," you would have to find a way to move solar/wind power from the places it can be produced to the places it is needed (thousands of miles). If you aren't familiar with electricity, you might not realize that the line loss over even a fraction of that distance would be immense. Its the reason we build coal/nuclear plants relatively close to urban areas even though nobody wants them there... we have to. Really the only way we could pull it off would be with mass producible high-temperature superconductors, which is a very wishful thinking technology (you might as well cross your fingers and hope for viable fusion power, which we've only been trying at for sixty years...). It isn't going to happen in this generation. Which means you will still need coal or nuclear plants for most cities.
I'll also put in the side note that the cost of producing solar panels is immense, and they willdegrade. Odds are the cost of manufacturing and disposing of them are many orders of magnitude higher than you realize. Not to mention any current battery technology is very environmentally unfriendly. And theres the fact that large scale solar and wind farms, if scaled to the sizes we actually need, have been shown in models to have a reasonable chance of altering the climate in the areas they are located (wind would probably just alter storm trajectories somewhat, but large solar arrays reflecting tons of sunlight could do all kinds of crazy stuff...).
And even though this is already long, one more comment. The real issue here is that these are very old reactors, and should certainly be replaced. The ones here in the US I believe are permitted for 40 year operating lives. Do you know what is happening? Most have applied for, and been approved for, another 40 year operating cycle. Well beyond what they were meant for. I have been in several for various reasons, and nothing unnerves me more than the memories of the late 60's era control panels sprawled NASA-style (think the Apollo landing footage) across thecontrol rooms. "Why not retire them" you ask? Because we need the power, and regulations have strangled the ability to construct new coal and nuclear plants to replace them. We could build new nuclear facilities that are orders of magnitude more safe and efficient, but the permitting process and public backlash makes it nearly impossible to find investors. After all, who wants to invest in a nuclear plant when the investment will take two decades (from the start of the impact studies and court battles to the reactor coming online), with the very real possibility you could lose all your money at the whim of a changing congress? I'm not against regulation, but we have to take the uncertainty out of this. Either we aren't going to build nuclear, in which case we need to start building a heck of a lot of coal plants, or we arebuilding nuclear and should set that commitment in stone. The current "stall nuclear and coal and hope green energy just works itself out" plan is just making things worse in the long run.
Some of us are still uncomfortable with the concept of "temporary" storage pools for material that is dangerous for 10,000 years. We need to adequately address the issue of storage of radioactive waste. And I don't mean by blaming environmenatlists.... the dirty little secret that the nuclear industry dosen't want out is that properly and safely dealing with radioactive waste radically alters the cost/benefit calculation for nuclear energy. The annoying little problem is that these costs are every bit as real as the cost of concrete or nuclear fuel. We also, obviously, need to factor in the cost of assuring that our current nuclear plants are adequately designed for all potential earthquakes, floods, sinkholes, etc. that might be possible over, say, a 10,000 year horizon. All the blame for holding up nuclear energy in this country cannot just be casually tossed at "environmentalists". Proponents of nuclear energy have a history of attempting to hide costs and ignoring risks.
@worksinphysics - thanks for the thoughtful reply. My understanding of solar generated power (admittedly, essentially none) is that solar cells don't require a so called "sunny day", but function well, although less efficiently, even when it is cloudy. That is, they just need light to generate power, not direct sunlight. Any clarification you could provide would be appreciated.
You're points about the lifecycle of solar cells being limited at this time is well taken. If a commitment were made to solar cells as a significant component of a multi-faceted approach to energy, I wonder if the technology improvements would catch up with the problems with the current designs.
Finally, are there any developments solar technology toward having rooftop systems that are more reliable and, importantly, panels able to be easily swapped out for replacements rather than having to replace entire systems?
If as much money and scientific development is directed to solar power as has been directed to nuclear power, would the technological barriers to efficient and practical use of solar (ok, and wind as well) start to fall?
The schematic is incorrect.
Lines 6&7 carry superheated radioactive water under extreme pressure, they actually go through a heat exchanger to produce steam to run the turbine that turns the generator.
But it doesn't matter anymore... they have blown 3 cores and the 4th is on the way. There is so much radioactivity, no man could survive to try to work in that area, all have evacuated. Nobody is manning the pumps, or anything else. All information coming from this incident has been false from the outset, allowing time to place troops to manage civil unrest.
When three reactors are running away, (Melting down,) there is no accident. It is a total failure of engineering that the diesel generators were not installed high enough off the ground to protect them from tsunami. They were on the coast, for Bettys sake, people. They were in an earthquake zone. You know, a place where tsunami is a real threat. We know that nuclear power can be rendered safe but not with gamblers doing the engineering. I see stupid engineering all the time, and the arrogant folks that do the engineering can't be spoken to. They are usually so full of themselves that accusations of faulty work is like a battle line drawn. They would rather attack the messenger than fix the monster they have created. I like the Chineese solution. You screw up designing something in China that upsets the economy and they shoot you.
Don't shoot the engineers.... you can bet some engineers were arguing for a high level of protection against tsunamis. It was the politicians who chose the lower cost engineering option, and it was the people who put those politicians in the position to decide who are most at fault.
Someone asked earlier about the effect of an open reactor vessel...How high is the pressure inside the reactor vessel and how much does it raise the cooling water's boiling point? I believe I read somewhere that if the water gets to hot or boils, it can create gas pockets that further impede fuel rod cooling.
Did Japan ask GE [General Electric] to build these plants, or did G.E. build these out of the kindness of their hearts in return for bombing the japanese back to the stone age $(sorry , that should have been a ? mark)
The plant's operator tried to bring in mobile generators to restore power, but the connections reportedly didn't match up.......
Either this is false information made by a desk jockey that never turned a screwdriver or an outright lie. Any 2nd year electrical apprentice could rewire this in less than 30 minutes and have the pumps up and running. You cut the plug off, open the electrical panel to the pump and make a direct connection. Even if these are huge generators with wire as thick as your thumb it is still possible.
You're thinking like an American. In a situation like this, forget doing it per code or rulebook or whatever. You cut and splice what you need to and use the rulebook to sit on while you do it. It's the cowboy way.
The Japanese approach to problem solving is sometimes restrained by trying to think inside the box the point that nobody comes up with anything else. The culture teaches that breaking the rules is just not done, so people never practice it.
It seems to me that this would be especially true for engineers on something like a nuclear power plant who have probably been told their whole careers to just do what is in the manual books and only what is approved by the kancho (boss) -or else.
Alan .. Thanks for a basic overview as to what happened and is happening without all of the political and journalistic flowering that cloud the issue. The article has led to a wonderful discussion without the political bs.
The only question I have related to the article is worse casing the situation with a Chernobyl reference. The reactor styles are extremely different and the support structures are very different (these reactors have properly designed containment structures), so this style of reactor (unless construction was faulty and mis-information about the design provided) worse case would not even be nearly as bad as a Chernobyl outcome. ie. Firefighters would not be truck and ladder hosing down the core with a fully open containment vessel spreading uncontrolled radiation for miles. Perhaps another article on differences between Chernobyl and the Japanese reactors???
Again, wonderful job.. kudos!
Dr Mike
If these nuclear reactors would happen to have a full meltdown how far would these radioactive chemicals spread & at what rate?
Depends upon which isotopes, their half-lifes, wind direction, and other variables. For the most part, people outside the plant (especially, if they are outside of the evacuaton zones) will receive little, if any, harmful dose. Low doses (ie. a few milirem here or there) will not do bodily harm. Best case though, is for people nearby to watch for plume direction ... it's possible that people 5 miles away in one direction may receive no dose, while others, 20 miles away in the other direction, may receive dose. Depends on the plume direction (wind) and if the isotope has - or hasn't - decayed yet.
Overall, good informational article followed by intellectual (mostly unbiased) comments.
Based on info from Japan, it does not appear a worst-case-scenario will occur. The plant & operators have done a remarkable job staving off such a catastrophe so far. However, it is unfortunate that the dissimination of information has not been more forthright (partly due to Japanese culture). I think it may take weeks, or months, to really know exactly how the situation was handled and what lessons learned will come from this. Hopefully the NRC won't overreact / over-regulate as a result of this.
Who could have ever anticipated an earthquake in Japan? And then a tsunami, that's probably never happened before. It's no wonder they did not anticipate a loss of power due to these highly unlikely events.
What are we, a bunch of idiots?
The Japanese did anticipate earthquakes & tsunamis ... I guess having the 4th largest quake/ tsunami combo in recorded history makes them ill-prepared?!?
Maybe they should try making a plant that will survive a natural disaster that annihilates their country ... would that suffice?
As bad as the situation is over there, it seems the magnitude of such concurrent disasters is the problem. However, a nuke plant closer to the epicenter than those in Fukushima was able to shut down safely. This supports that the design basis - although based on lower magnitude quakes & tsunami - could actually shoulder a greater impact. The engineers were not totally in the wrong. Japan was just hit with something much greater than expected.