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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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Hi, Folks
There is no way for air to get into the pressurized nuclear reactor vessel.
What actually happens is that when the fuel rods become uncovered with no flow they heat up from the decay heat. Eventually the temperature reaches a point where the Zirconium metal surrouding the nuclear fuel reacts with the steam. It causes ZrO2 and H2. The H2 (hydrogen) will go out when the release steam to control the pressure in the reactor.
It is that released H2 that caused the explosions...when it mixed with air outside the reactor. Still no air in the reactor.
The ractor fuel would have to heat up another 2000 degrees to actually have melting of the ceramic uranium dioxide.
LARRY ........please consult with the other two nuclear experts Curly and Moe
An up-date for March 14, 2011
The latest explosion was heard at 6:10 a.m. local time on Tuesday. A top Japanese official said the fuel rods in all three of the most troubled nuclear reactors appeared to be melting.
(CBS/AP) SOMA, Japan - A Japanese spokesman says a fourth reactor at a quake-damaged nuclear plant is on fire following an earlier explosion, and radiation is now spewing from it. The radiation level is now elevated to a point that may damage health, the spokesman said.
The fire has now been extenguished but radiation leaking from the #3 reactor is increasing.
Making matters worse, the wind over the radiation-leaking nuclear plant in northern Japan will blow inland from the northeast and later from the east on Tuesday, the Japan Meteorological Agency said, according to Reuters. The radiation will now be spreading via wind and rain inland onto Japan itself.
Officials just south of Fukushima reported up to 100 times the normal levels of radiation Tuesday morning, Kyodo News agency reported.
Kyodo reported that radiation levels nine times higher than normal were briefly detected in Kanagawa prefecture near Tokyo.
Tokyo also reported slightly elevated radiation levels, but officials said the increase was too small to threaten the 39 million people in and around the capital, about 170 miles (270 kilometers) away.
An agency spokesman, Shigekazu Omukai, says the nuclear core of the reactor was not damaged in the explosion early Tuesday. But the agency says it suspects the bottom of the container that surrounds the generator's nuclear core might have been damaged.
Another agency spokesman, Shinji Kinjo, said "a leak of nuclear material is feared."
A drop in water levels left uranium rods completely exposed Monday at the imperiled Fukushima Dai-ichi -- and although the water was restored, the rods were again exposed after a second episode. That increases the risk that radiation will spread -- and that there may eventually be a meltdown.
The IAEA said it had been informed "that the spent fuel storage pond at the Unit 4 reactor of the Fukushima Daiichi nuclear power plant is on fire and radioactivity is being released directly into the atmosphere."
It added: "Dose rates of up to 400 millisievert per hour have been reported at the site. The Japanese authorities are saying that there is a possibility that the fire was caused by a hydrogen explosion."
AC, 2 questions.... 1) how can a storage pool of water be on fire?
2) why wasn't this plant designed to withstand an earthquake and tsunami which are known to have occurred in this area?
and a bonus question: how much do we not know about the design of the nukes in the US?
I've been advocating more US nukes to address the folly of our addiction to global oil with something more cost-effective than current solar and wind. This incident once again raises the question of how deeply has the nuclear industry been lying to us and puts extreme doubt on the validity of cost estimates on nuclear power, which obviously now must include the possiblity of plants being put prematurely off-line due to earthquakes.
Somewhere along the cost/benefit curve, the advantage of oil and nuclear will shift to solar and wind whose negative environmental impacts are orders of magnitude less.
Joe,
Now I have worked at nuclear sites, but I'm on the electrical generator side.
I believe the spent fuel rods would produce hydrogen also if water levels dropped. Not sure of this, but it makes sense to me. Hydrogen of course is a fuel source for fires.
As far as question 2 goes I have a feeling the plant was designed to withstand it, the back up generation on the other hand was not designed for this. Due to the increased cost of doing maintenance on a nuke site in the US, some of the sites have moved the diesels to adjacent sites to make maintenance easier.
The average person knows very little about the design of nuclear reactor. Unfortunately too much information on the subject for the average person can be worse than being left in the dark. Take me for example, I know enough to get myself in trouble, but not enough to design or run one.
I think overall nuclear reactors are very safe and while this incident is tragic, the emphasis should be put on how can we make nuclear power safer rather than how bad nuclear power is. We can make the next generation nuclear reactors ready to with stand the issues thrown at them in the past and more, but we are limited in the modifications we can do to existing reactors. We need to allow new design reactors to be built to replace the older ones as this will increase the safety of nuclear power in the long run.
seems like in the current case the reactors themselves performed as designed... the problem was the failure of the backup generators. It's incredible that noone thought of the possibility that an earthquake and tsunami might damage the backup generators and put the nuclear plant at risk of destruction. some politician chose to save money by ignoring tsunami risk.
joe mota,
The fuel rod storage pool in unit #4 was lost its required water levels and cooling. This exposed the fuel rods and they started to burn/oxidize releasing hydrogen. The hydrogen cause a explosion which damaged the storage area and has prevented the authorities from adding additional water. The water is currently boiling as the fuel rods continue to burn/oxidize. They are currently considering the possibility of dropping additional water from helicopters, due to it being too dangerous for people to approach from the ground...
BTY - The temperature is rising in the TWO remaining undamaged reactors, due to limited cooling...
The USA has 23 nuclear reactors that are of the same General Electric design of these in Japan. They have design defects that have been known for over 30+years. The 'Containment vessel' is a weak design that will fail due to corrosion problems, they have been recommended to be decommission for decades, but MONEY rules, and they are still being operated... see http://openchannel.msnbc.msn.com/_news/2011/03/13/6256121-general-electric-designed-reactors-in-fukushima-have-23-sisters-in-us
I'm against nuclear energy due to the current storage problems and the large numbers of 'Old Style' reactors. With their numerous leaks and on-going corrosion problems.
There are currently ZERO 'Long Term' nuclear storage sites in the WORLD...
The last one in Germany was CLOSED due to flooding, because they found the radioactivity was causing the salt structure to collapse...
While you can recycle the old fuel rods. There are millions of tonnes of material from the reactor core and other parts that become radioactive during the reactors operation. They still have to be placed in storage for Hundreds of years...
The 'New Generation' of nuclear power generators solve many of these problems, except for the 'Long Term' storage... Though, IMO - They should still restrict where they are going to be built and have Robust and Redundant - SAFETY systems...
ALL types of power generation have draw-backs and SAFETY issues. But they ALL have VIABLE uses in different locations around the World...
Man just has to CHOOSE which trade-offs are worth-it in the long run...
Even if ALL of these reactors have melt-downs, the location will become unusable for DECADES and the ground-water may be effected for Hundreds of years. The Human threat beyond Japan's shores will be minimal and decrease rapidly as the distances increase...
Other than what Larry clarifies about Zirconium oxidization in 2200+ degree water, I think you explained the situation in layman's terms very well Mr. Boyle.
There may be a slight melting of the Ceramic Urainium Dioxide going on, as hot Cesium and Iodine around the facility is being detected in trace amounts.
I've revised that little section, please give it a look and see if it comes closer to the mark. When the zirconium degrades and releases the fuel, is there a danger that the fuel pellets could set off a chain reaction again?
A good question that I don't have a good answer to. I'd have to look more into the exact details of the of this particular G.E. core design (assuming they can be attained) to give you a good answer.
Generally, the more loose the pellets are, the more it should help slow down the reaction. The reaction works most efficiently when they are packed together tight in their zirconium casings. However, the shape of the core slots the casing slide into may prevent the pellets from becoming more loosely packed, even if the casings completely oxidize away.
The fuel assemblies are most likely just like the one pictured on this webpage. That isn't a good thing. If the pellets fall out of the zirconium casings and fall into a pile at the bottom of the core, the crisis gets worse.
http://theenergycollective.com/dan-yurman/49523/idaho-inks-new-spent-fuel-agreement
p.s. I've actually been inside that room out at the INL (in picture #2) that has the pool of spent fuel rods. It was very fascinating too see a lot of the stuff out there that the general public normally doesn't get to see. My gradfather who worked out there back in the 1960s, and was allowed to bring one relative with him for a special tour of the site many years ago.
Alan, the only thing I'd adjust now is removing the 'oxygen gas' part.
Once the Zirconium passes 2200F, it absorbs the oxygen atom in the water molecules, freeing the 2 hydrogen atoms to bond into an H2 molecule. The explosions were just the hydrogen gas being vented out of the core reacting with the O2 already in the air with the assistance of some kind of momentary spark or flame.
Are you all aware that it has been reported that the Reactor # 3 is fueled with MOX fuel rods containing both plutonium and uranium? It is the only reactor with the MOX fuel (mixed oxides), all the others are fueled with uranium only. Reactor # 3 is one of the cores with a previous explosion on Sunday. It is being reported that if that specific reactor is compromised and plutonium is released, then this will be on the same scale as Chernobyl.
Chernobyl experienced a massive chemical-based explosion because they used graphite (carbon) as part of their coolant system. That's what scattered the nuclear material and made it so bad. The use of plutonium only means that Strontium-90 (which can replace calcium in your body) is a potential byproduct of decay.
With a boiling point of about 1600C, it could potentially be released as a gas if there's a breach of containment resulting from what this article calls a 'full meltdown'. That'd still be bad, but not nearly as bad as Chernobyl. Chernobyl was a very high 7, this would be more like a very low 7, or maybe a high 6, depending on how much is released.
Still, nothing so far indicates the possibility of an explosive release of radioactive material. If containment is lost, it should mean there won't be any more hydrogen explosions.
BWR has negative void coefficient, so there should be no chain reaction in the absence of water.
The one thing I don't understand is why there isn't a closed loop system at the plant to provide power for the pumps.
IF the reactor is up and generating electricity why isn't some of that used for running the cooling pumps?
It doesn't make sense that you have to rely on external power for running the cooling pumps when you have a source available internally.
From what i understand, there is such a system--the problem is that the reactor isn't up and running. Part of the response to the earthquake was an automatic re-insertion of the control rods, significantly slowing the reaction, and halting power generation at the plant. All of the heat generated at this point is being generated within the individual fuel rods, and from the decay of radioactive byproducts of the previous reactions. The problem is, even a full shut-down of the reactor doesn't drop heat buildup to zero, but drops it to (I believe) less than 10% of what it would be in a fully running reactor.
When the earthquake took place, the control rods immediately fell into place and stopped the chain reaction, as I understand it. But I know what you're saying about a closed-loop system. My guess is that some of the power generated by the reactors goes into the batteries, but that lasts for only so long after shutdown.
The SECOND back-up cooling system, uses the steam pressure from the 'containmant vessel' to run a turbine that circulates the reactor water/coolant. This operates until the water level drops below certain levels. This is what has occurred, but it also gave the operators the needed time to help rectify the many other problems.
The control system of these reactors depend on electrical power, to control the valves, pumps, and control of the fuel rods. This is backed up with batteries, but they generally last only hours, not days. The operators have been swapping out these batteries, as they became discharged.
The generators of most power plants are enabled by EXTERNAL electrical power sources. This is how they sencronize the power generated with the 'power grid' itself and makes the power generators 'cheaper' to build. Unfortunatly, when the EXTERNAL electrical power is lost, the generators CAN NOT generate power on their own...
I worked with 200KVA electrical generators for decades and my father was the Electrical/Nuclear Engr. These are just a little insight.
there is certainly not power going to the batteries from the reactor.
It would seem relatively easy (or doable, given the situation) to air lift backup generators and fuel for this situation.... I don't get the "connectors don't match" --- it seems like a problem that an industrial electrian--or the manufacturer-- could solve.
K
Good basic article Mr. Boyle. I agree that if the connectors did not match up, it should have been relatively easy to air lift in the necessary components to make a match up. Given the seriousness of this emergency, I find it difficult to believe that this was not checked before the backup generator was even shipped. The proper connections should have arrived on time, even if shipped from the other side of the world. We don't have all the facts that the experts possess, but something doesn't add up if this is what really happened. I would appear they have their hands full and are doing everything they can to avoid the worse possible scenario. In situations, money is no object, but lack of all the facts are a real detriment.
I'd like to think that the "connectors don't match" is probably a lot more complicated than it sounds.
The back-up generators were already damaged by the tsunami and may have included damage to where they could have easily tied in an available portable generator.
I'd like to think it's highly unlikely that nuclear power plant operators asked for and received portable generators and then found out they didn't have the right "plug". I'd like to find it far more likely that the plant operators knew what they needed and because of the scope of the emergency found those portable generators - and still find those portable generators - unavailable.
I don't think I'd like it at all that there are no manufacturers that even make a portable generator that could have alleviated the emergency they're still experiencing.
I don't buy the "plug" story. First off, these are very large pumps moving thousands of gallons/minute. My guess is the generators involved are probably in the 3 megawatt range, maybe larger to also support other systems. That's big. You wouldn't "plug this in". It's a electric power plant, no self respecting "denki", (electrician in Japanese), would be stopped by a plug. You'd grab some cable and hardwire it in. I've been in numerous crisis management situations and you find a way. More than likely, if there were some problem with the generators, it was probably related to the output voltage or inadequate size.
My guess is that something got lost in translation. If the generators had the right output, I can assure you that they'd find a way to get it connected. Been there, done that. Most translators tend to make some silly mistakes and substitutions when faced with engineering terms. They don't understand the words. Seen it many times in engineering discussion with the Japanese.
The electric motors that turn the coolant pumps are huge. Some are almost three stories tall. It takes an incredible amount of horsepower to turn the pumps to circulate the amount of water necessary to keep the reactor cool. I once heard an old timer say 3 coolant pumps set in the river beside Three Mile Island would make the Susquehanna River flow backwards) Each reactor has 2 to 4 coolant pumps and motors. The electrical demand needed by just one motor requires three wires, each the size of a man wrist to supply enough current to power the motor. Finding a back up generator sized correctly would be nearly impossible. Companies who rebuild these motors don't keep one. They use a large transformer to convert the power on hand. This piece of equipment is the size of a tractor trailer. It has to be put on a ship to be moved. Getting one of these units to a place where there is no roads or working ports is a logistical nightmare. At best to move something large enough to do the job will take weeks by ship. The Russians have a plane large enough to move a reactor vessel. Maybe they will help.
ntdog: Our fire department couldn't match up their hoses to a series of hydrants here not too long ago. Things like that happen without proper and consistent planning.
There are very large "stationary power" generators built on large skids the size of a semi. They use these in remote mining operations, and other "off the grid" applications, as well as crisis management. These go up to around 3 megawatts. Diesel locomotives are in fact large diesel generators. Most large ships have similar large generators. It takes some skill, but a number of these can be paralleled to provide even higher total outputs. Staging and setting these up is no easy task, but it can be done surprisingly quickly with enough people and an open checkbook. One should keep in mind that this is a huge power company, they have the necessary resources and appropriate skill sets.
I had heard one report that said they were using fire engines to pump water. I'm sure this was at much lower flow rates than necessary, but it was probably better than nothing. For all we know, they may still be using these. Unfortunately, there's not enough resolution in recent aerial photos to be able to see just what they've staged.
We really don't know the specifics of how they are operating now. I had heard that not all the reactor's generators at the site were knocked out. That could mean that you might be able to use say #4 reactor's emergency power generator to supply the pumps on #1. For all we know, they may be swapping around what ever capacity they have from one reactor to another. So much depends on just how much infrastructure was destroyed. Sometimes reconfiguring existing switchgear on the grid side, can be done and then backfeed power to the "original path". Remember, these reactors are part of a large distribution system that already has parallel paths built in for normal operation. You could isolate the plant from the rest of the grid and then re-energize it locally through whatever emergency power generation you have locally. Using that approach gives you lots of switching options.
I am almost certain they have done portions of the above. Another option may be restoring and isolating portions of the grid from other power plants. This is when you throw out the original design concept and draw out the "new" supply on the back of a napkin. You focus on one thing, make the pumps run. Whatever it takes. The one potential issue I see here is that Japanese engineers, although highly educated and capable, are not very good at thinking outside the box. It's part of the cultural thing. I've seen it up close and personal. When you deal with such a crisis, you need to throw out a lot of the normal conventions, and while still using your skills, start with a clean slate using what you do have available and cobbling it together. Sometimes I've heard it called"MacGyvering".
I'm sure they've actually done some of this, but probably didn't take that route early on. These are people very committed to Standard Operating Procedure, which is a good thing normally. It can slow you down though when you need to scramble.
Unfortunately, we probably won't ever hear the details, other than through inside tracks and maybe trade journals. The normal media ignores this kind of thing because they don't understand it. How many times have you seen one of the talking heads interrupt one of the "experts" just about the time it gets interesting. If you're technically oriented, it gets pretty frustrating. Then you'll hear things like "all three reactors have exploded now", (actually heard this reported multiple times by an otherwise decent MSNBC reporter yesterday.) They will say stupid things like this because to them it's just a black box. It's the same thing as some translator saying the plugs didn't match. We're not talking about water heaters and backyard swimming pool pumps here, but those are the only kinds of things most people can relate to.
Lost is translation is accurate.
Best information is that the plants handled the above design basis earthquake with no problem. All safety equioment was operating nominally and the operators were still doing their post event walkdowns when the tsunami wave hit. The beyond desing basis tsunami wave was the start of the problems.
The tsunami wave was ~7.7 m, while the protective wall was only ~6 m. So the tsunami wave washed over the sea wall barrier. The wave then took out (among other things) the fuel tanks for the backup diesel generators, the cooling system for the backup generators, and flooded (with water, mud, and rubble) the backup generator transformer room in the basement. The backup generators themselves were still intack and operated for a few more minutes before overheating/running out of fuel.
The "connectors don't match" problem was that they needed to pump and dig out the basement; find intact, dry cells; and make connections. There are hundreds to thousands of circuts involved. The workers are also limited in the amount of time they can spend working in the area, since they are on tanked air.
The have the circuits for Unit 5 & 6 up, and are currently working on the ones for Units 1 and 2 (as of Friday evening). Ones for Units 3 and 4 will take longer.
Can we please stop using the China syndrome as an example of a meltdown. Not even getting into the whole melt through the earth hyperbole which is not worth addressing, there is really no chance whatsoever of core melt breaching primary containment. Even at Chernobyl, the core melt eventually spread and cooled (Chernobyl was a massive disaster, orders of magnitude worse than this, but the point is the the core did not melt into the soil.)
Unlike chernobyl, even this ancient GE reactor is provided with a rudimentary "core catcher" designed to at the very least, keep the molten core inside the concrete shell of containment. Thats a worst case scenario, but even that worst case is still a tiny fraction of the human impact of the explosion and graphite/uranium fire at Chernobyl.
Besides which, China's to the west of Japan. If this core melts into the earth, it'll be headed for the South Atlantic.
As for fire, if the spent-fuel containment pool goes dry, there will be a uranium fire open to the air. Which is very Chernobyl.
Yeah, in japan, it would have to be the "Argentina Syndrome"?
There are a couple of points that no one is bringing up. Steel melts at 2500 to 2700 degrees. Concrete fails at slightly less than that. It's my understanding that when fission occurs it can generate temperatures to 5000 F. And the other thing that I've heard. Reactors built in 1985 (10 to 15 years after these) were built to withstand 7.0 earthquakes.... not 9.0, nor the daily occurences of 6.0 and up after shocks.
True ... steel can melt in the 2500 to 2700 range; however, you need to consider pressure. Typically, you have water in these reactors at the saturation temp/ pressure of around 500 degress and 1000 psi. Hence, you're not dealing with normal atmospheric conditions. Likewise, these plants are not dealing with "normal" catastrophes. Design basis for these reactors were based on Probabalistic Risk Assessments using historical data. If anyone could have predicted this, they should have their name changed to Nostradomus.
All these things assume the containment vessels are intact. There was, I hesitate to remind everyone, a really big earthquake, and numerous aftershocks that would be themselves considered really big.
So the reactor and all of its parts and the containment vessel and the cooling systems could all have suffered mechanical damage (cracks, instability, shifts and settling, etc), and may continue to suffer damage from the ongoing aftershocks.
There was probably also at least some mechanical damage from the tsunami; we have plenty of footage of water mowing down houses so there was certainly some potential for force damage there, other than just flooding.
And then there is going to be damage from the explosions.
So I don't think it's safe to assume anything is going to work properly at this point.
Japan has a well known and fully documented history of earthquakes and associated tsunamis. True, this 9.0 is the biggest in recent times, but that doesn't place it beyond the realm of "predictability".
There are three credited barriers to release of radioactive material from the core of a nuclear power plant after an accident: fuel cladding, reactor vessel, and contaiment building.
Indications are that there is failures in the fuel cladding for some of the fuel in the reactors. The reactor vessels are all indicating that they are still intact (hold pressure). Primary containment in the containment buildings also seems intact (hold pressure), while the secondary containment in Units 1 & 3 appear breached. So there are at least two barriers left intact. A major release of radioactive material from the reactor cores is unlikely at this time without some additional significant change.
The spent fuel pools only have fuel cladding and water depth as barriers to radiation release in an accident. There is breached fuel and the water levels are low. So there is a chance of release of significant radioactive material. However, the amont that could be release from the spent fuel pools, even the short cooled fuel in unit 4's pool is significantly less that from a core. Expectations are that they may have some additional gaseous releases from the fuel pins over pressurizing, but it isn't likely anymore to have a massive release.
Most of the documents I've seen on these GE BWRs indicate that the storage pools are in the outer, secondary containment--the part of these buildings damaged by the hydrogen explosions.
See for instance this PDF of a TEPCO presentation, in which the pools are shown uncovered and under the blown out roof structure we've seen in the broadcast images:
This suggests that any uncovering of the rods in the storage pools is potentially dangerous indeed, and makes you wonder about what might have happened as a result of the explosions we saw. If they are usually uncovered like that, what would a hydrogen blast have done to the pool structure?
I haven't seen any mainstream reporting on this issue.
As to the control rod insertion--i.e. the scram of the reactor--I've read some speculation that the use of boron in the seawater being introduced into the reactor suggests that insertion of the rods may have been problematic or incomplete. There's some discussion of this here:
from some apparently knowledgeable commentators (along with a lot of inevitable noise.)
I'd like to read/hear/see an in depth interview with an impartial academic from outside the industry that walks through the various contingencies with the particular reactor designs involved, going beyond the ABCs of a core meltdown.
Could another big enough hydrogen explosion in the secondary containment (as I understand they are still venting hydrogen as required) cause a smaller but more Chernobyl-like event in the storage pools, if due to damage already sustained they are heating up? Could the explosions already experienced have caused a more serious radioactive release from the pools than is being discussed currently?
Very unlikely. The storage pools are built out of the same concrete as primary containment. Unmonitored the pools can begin to heat and theoretically eventually pose a threat. However, you have much much longer to deal with it. Weeks vs. hours or days.
Worst case scenario, you throw a firehose over the edge and start pumping seawater. The saltwater poses big problems in the long term but short term it's a much easier thing to deal with than the reactor itself.
That makes good sense. Are they protected from the top? Would the explosions have boiled off the water?
The main problem with the spent rod pool is that without it's cooling system, it will heat up and accelerate evaporation of the water in the pool. Even spent fuel rods need to stay fully submersed as they are highly radioactive. They won't melt, but they do emit a lot of radiation.
There is a lot of rebar reinforcement in these structures, so for the time being, we can still hope that their structural integrity hasn't been compromised.
As long as there is no recent core offload fuel in the spent fuel pool it will not melt if the water evaporates (recently offloaded fuel will melt). But, without water shielding there will be a major radiation issue for anything above the pool structure.
I'm quite the novice here -
Is the reinforcement within these structures constructed to move monolithically or are they fixed and rigid to the supporting members?
Is there some component divergence and flexibility to keep the core structure in tact during the subsequent movement during seismic events?
It's entirely possible that some of these fuel rods had just come out as #4 reactor was down for a refueling. Also, I wonder about MOX rods vs. LEU rods. As I understand it, this plant used MOX in some of it's reactors. As these contain recycled plutonium from former Russian weapons, are they somewhat more active or have higher energy capabilities? Anybody know?
I would bet that there was no cooling water circulation going on so the pool was evaporating down. It's not unlikely that recently pulled rods got exposed and caught fire. Recovering the rods with water should have solved things, but during the time the rods or casings were burning, if they were, a whole lot of relatively uncontained radiation could have escaped. Maybe that has something to do with the latest higher readings??
Seems like there are more potentially serious issues related to just where this latest explosion occurred in unit 2. Can the reactor vessel be isolated from the suppression ring?
1NewDay, I think the MOX fuel is in reactor #3.
The bird's eye aerial photo that I saw last night looking down into the heavily damaged reactor buildings has me much more concerned than before. The hydrogen explosions caused more damage than anyone had previously assumed.
I think the blast at #3 was pretty powerful. If you look though, you'll see no visible damage at #2 but #3 looks pretty mangled. At least in the photos I can find. #1 is the North-most, slightly smaller and slightly offset building. #2 had the most recent explosion, but as described, this would have actually occurred below ground level in the pressure suppression ring. Technically, I believe this is in part of the primary containment. I'm struggling with how they would get hydrogen there and then what would set it off. Seems to me that is sort of a combination sump and shock absorber for pressure changes. It would appear that it should have a water seal, keeping any gas out. I'm probably missing something, but it would almost seem to suggest that the reactor water level was extraordinarily low or that when they added the seawater, the core was so hot that it immediately flashed into steam causing pressures to rise instanteously in the reactor vessel causing a "burp" to get past the water seal and into the ring pipe.
I'm not certain, but I believe the spent fuel pools are located with the top being fairly high in the outer building structure. They probably use the same overhead crane to remove the fuel rods and then lower them into the pool. The only containment these have is the outer building which is basically just a shell not designed to contain any overpressure. What is interesting is recent reports that they are considering using helicopters to put water into the #4 spent fuel pool. This seems like you couldn't do that with the roof in place???
I would guess that the pools in #1 and #3 are open to the sky right now. I'd guess that #1 is probably intact, but would have some concerns about #3 for the simple reason that the damage looks more significant. Of course we don't know about what rods are in there and how hot they are. Likely #4 had the hottest rods because they were refueling #4 reactor. Of course all this is speculation and we're just not hearing the details.
There's a few people who have pointed to the spent fuel pools very early on as being a huge potential issue. Being that this plant has operated for 35 years or so, you might guess that there's a lot of fuel rods sitting there. You have to conclude that they may be very close to loosing the whole plant. The fity or so people remaining there are probably at a high risk of not surviving. How long they can keep the plant limping along in it's precarious position has to be in question. Core meltdown in all three active reactors is becoming more of a real possibility. The real question is if the containment will hold as designed. This is starting to look very bad.
No links permitted? Here's the link to the pdf in plan text: www.nirs.org/reactorwatch/accidents/6-1_powerpoint.pdf
And above, I meant another explosion, this time in the *primary* containment (which apparently might not be catastrophic in and of itself) causing something to happen to the pools in the secondary containment.
It would seem from the images that there isn't enough of the secondary structure left on #1 or #3 to collect gas now.
Mr. Boyle, thank you so so much for actually addressing both the best case, and worst case scenarios. This is by far the most informative article I have read in the last two days regarding this issue.
As an ex-SRO I can say that achieving criticality (a self sustaining chain reaction) is actually quite difficult. Reactor design involves achieving a specific geometric layout of fuel pellets. It would be virtually impossible for a melted reactor core to achieve criticality
I do not believe the 'worst case scenerio' has been presented. Just a question .....What would happen if the three cores go into full meltdown to the already fractured tectonic plates that may lie near this tiny topical geographic area?.....I do not know of any study that has addressed this issue, as there is no case incident worldwide that would pose such a question. This much added abnormal heat concentrated in on specific location----how hot, for how long, and how deep---- must certainly have a geologic impact!
A "full meltdown" to the tectonic plates is impossible. First, the challenge of breaching the reactor vessel. Second, the challenge of breaching the concrete and steel base of the primary containment. Third, the challenge of breaching the concrete basemat of the reactor building. Even at Chernobyl the corium did not breach concrete. It cooled as it flowed and solidified as it cooled. So we might as well postulate the REAL worst case ... a large asteroid hitting the site of all these reactors which would then result in another multiple reactor accident along with the asteroid hit. Ain't going' to happen.
I agree with Mark Groblewski, except for the "geologic impact!" of which I'm not so sure. The part I know I agree with is the fact that I've not seen the "worst case scenario" presented anywhere, really, in the mainstream. This journalist (thanks, Alan Boyle) has done a better job than most that I've read at the NY Times, LA Times, Washington Post, etc. But the article and follow-up still left out the tragic punchline I would suggest is on the minds of the people living within striking distance of various risks from this mother nature-assisted disaster. The verbal volley is entertaining, but others nearer the accident may or may not be affected by radiation for a lifetime, no? I could be mistaken because I'm an information technology geek, not a nuclear industry insider. Ask me about Intel dual-core meltdowns.
Nice try Carl-2164242, but I'm not convinced that if I don't fret over large asteroid hits then I should not fret on something with less impact, so to speak. Am I worried about getting hit by an asteroid? No. Am I worried about getting zapped by some sort of nuclear explosion from Japan? No. I suppose stranger things have happened.
A good starting point to me for a reasonable discussion on worst case scenarios would begin with the risk factors to humans (babies and pets, even!) at concentric circle distances around the damaged facility(s). How hard is that, Mr. Alan Boyle? What would the 80-years-old survivors from various radioactive-related distances from Hiroshima and Nagasaki tell us? Is that different than what think-tanks tell us? Is anyone writing here actually "on the ground?" Is there no more correlation between the radiation from an atomic bomb and from a power plant than there is from an unlikely power plant total meltdown and a considerably more unlikely asteroid hit? Can we put a glass dome over Japan like from The Simpsons Movie and be done with this annoyance?
No because radiation penetrates glass..
I'm surprised they didn't have a steam-driven Emergency feedwater pump to supply the reactor with water even if electricity was lost, that's pretty much the standard at the reactors I've worked at. Reactor boils water - some steam siphoned off to drive turbine driven pump which pumps water into the reactor, providing cooling
They do, but you need some electricity to operate the valves and whatnot that run it. When that goes you cant run it. Seems silly until you actually see how complicated these things are.
At our plants all the valves associated with our steam driven pump are DC (Battery bank) powered and located outside containment. They can be operated manually by operators in the field if needed. Even if DC power is lost and no instrumentation is available, you can still keep the core cooled - just let them run wide open
The DC battery backup only lasted about 8 hours which is why they lost cooling to the core from the steam driven pump backup after that (they lost all electric based instrumentation and control at that point).
The worst case here is most likely a HPME, or high pressure melt ejection, where liquid core material at the bottom of the reactor bottle is blasted out like a firehose by high reactor pressure due to stuck steam valve. It's very unlikely after this amount of time, but theoretically possible.
At that point, if the containment holds, its a big nasty cleanup. If containment has some failure, which it may have already, then you get some amount of nasty steam and vapor release.
Even in that situation, we're still talking tiny compared to Chernobyl and without the high temperature graphite fire that lofted core material etc into the stratosphere.
It would be bad vs Chernobyl, which was absolutely incredible catastrophic.
A zirc fire is practically impossible unless the spent fuel pool itself is damaged. There should be relatively easy access to the spent fuel pool to allow water to be pumped in even if it's sea water. I would postulate that they are monitoring the pool level closely and making plans for pumping makeup water into it. Adding sea water now would make a big mess unnecessarily if they can arrange for pure water to be added in the next couple of days ... and no complex system needed to add the water ... just a fire truck and a hose (along with the water source).
The water just needs to be free of salts, mineral impurities, and deuterium.
As long as the pool isn't leaking, they have a few days.
Are any of the Japan reactors currently in an uncontrolled reaction? I know what has been said above, but from what I've read once the control rods have melted the reactor is back into an uncontrolled state.
How is it not bad that seawater being pumped directly into the reactor (which was a closed coolant loop) then being allowed to vent directly into the atmosphere (now an open coolant loop)? Doesn't this venting contain nuclear radiation? How is it not any worse than just opening the core to the atmosphere?
How long does it take for the reactor to cool enough it doesn't need coolant if the control rods were actually inserted immediately like everybody says they were?
Relevant questions. I'll try to answer them as best as I can.
Contaminates in the seawater do produce some radioactive particles when exposed to radiation in the core. There's also hot Cesium and Iodine from the fission reaction itself. Whether that is just random atoms falling off the surface of the pellets, thereby getting caught up in the vented steam, or an indicator of some core melting is still uncertain, but more likely to be the first if the levels detected are really as low as they're reporting.
Exposing the core directly exposes the radioactive fuel rod assemblies to the atmosphere. The water and the containment vessel would no longer be keeping that radiation contained. As I understand it, water itself can't be made radioactive, but most types of mineral contaminants that can be dissolved in water can. That's why they use purified light water, or purified heavy water (deuterium) for nuclear applications.
I've heard the estimate on cool down is up to 10 days.
Tritium is an isotope of hydrogen, which allows it to readily bind to hydroxyl radicals, forming tritiated water (HTO), and to carbon atoms. Since tritium is a low energy beta emitter, it is not dangerous externally (its beta particles are unable to penetrate the skin), but it is a radiation hazard when inhaled, ingested via food or water, or absorbed through the skin. Tritium has a half life of 12.5 years.
The incident in Japan will never be like the Chernobyl incident, if it progresses to that level. The situation at Chernobyl did not progress through a phase remotely like the TMI incident. Chernobyl was a catastrophic failure of a reactor undergoing fission reaction. From my understanding, what is happening in Japan is a result of hydrogen buildup from a cooling (and non-fissioning) reactor core. The reactor cores have been fully scrammed (negligible fission reaction occurring) and the problem is resulting from non-circulating cooling water and residual reactor heat. The core is not adding additional heat/energy to the problem. Still plenty of room for stuff to go wrong but not in the same manner as Chernobyl. I'm not sure what the potential energy output of the hydrogen buildup could be, but the reactor fission output spike at Chernobyl was substantial. A hydrogen explosion could duplicate that same explosive force but then there were fires at Chernobyl and the nature of the firefighting efforts that lead to most of the deaths. Those factors likely do not exist in the designs and reaction to an explosion at the Japanese reactors.
Chernobyl exploded while running as a result of a runaway nuclear reaction. The reactor design made that a possibility. The reactor core didn't just melt down (like at TMI) and escape the reactor vessel. At least make that clear.
Some people might say the biggest uncertainties of the quake and tsunami are how many tens of thousands have died and the survivors wondering in anguish if they will see their loved ones again, and beyond that, how they will put their lives back together.
Still, this is one of the clearest and most informative articles I've seen about the reactor situation, and accompanied by some of the most sane and erudite commentary one could imagine in a public internet forum.
I'm always hearing about how "expensive" solar power is. Here in Raleigh, they're pushing to build a nuclear plant at $10 BILLION as a "preliminary estimate." Everyone knows that once they've taken away the ratepayers ability to protest, the "cost" will balloon upwards. This is just to BUILD the reactor. Gosh, I wonder what the ratepayers will pay in order to CLEAN UP this horrible mess????
So let's say it costs $20 billion to build one reactor. This cost does not include what ratepayers are already experiencing in terms of increased costs for water. You see, we have a water problem here in the southeast -- yet somehow the crazies in charge think we have enough water to build a new reactor! That reactor will chew up enough water to service a large city. Yet, little old ladies who live alone are being ticketed for watering their begonias.
For $20 billion, we could build covered parking lots over our extremely large high schools and have enough solar power panels installed to create power for entire neighborhoods. We could use solar in the best way possible, to curb peak demand. Solar would kick in during the hottest part of the day, and would eliminate spikes associated with air conditioning.
The comparison between solar and nuclear must be done properly. The cost of building a reactor (20 billion) must be compared to the cost of building a solar "plant." (i.e. the cost of purchasing and installing solar panels.) Then the cost of running nuclear (cost of uranium, cost of running plant on a day-to-day basis) must be compared with the cost of running the solar "plant" (i.e., zero, nothing, zip).
We must realize that the reason governments "favor" nuclear is simply the taxes that are paid, monthly. When solar creates energy that goes directly to the homeowner, the state has trouble "taxing" that and more importantly, the utility companies cannot gouge the homeowner. It's up to the reader to decide whether the ability of the utility company to gouge the homeowner is a bad thing.
Well....I thought this discussion was supposed to simply informational and not political...BUT....once you start discussing "taxes" and where they go...subsidies....Solar, wind, Biomass and OTEC are all emerging technologies, AND are ALL heavily subsidized currently, with tax dollars...even the COAL industry is subsidized, looking for that holy grail, "clean" coal ( what an oxymoron that is!).
All methods of energy exploration and generation have their risks: see the fires raging in Japan? Those fires were at oil and natural Gas facilities...not to mention a dam or two suffering quake damage.
All of the reactors in Japan are GE based design, built in the 70's. There are currently much better and safer designs available, surpassing all BWR and PWR reactors now in service.
How do I know? These "safe" reactors have been in use for years in submarines and aircraft carriers.
Generation IV reactors need not be based on the solid fuel models in existence today....and can be built more cheaply, without having to generate fuel to operate them.
" We have the technology"....
(Reposting since my original response ended up as comment #43)
Is $10 billion dollars (as alwaysaskmom says is the proposed estimated cost) cheap? How much energy could be generated if 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?
The debate of nuclear power vs. alternative energies is not cost driven. The issue has to do with efficiency. Yes for 10 billion you could build a LOT of solar panels and they might power a small community on a sunny day - but a 10 billion dollar nuclear plant would generate enough power to run entire counties or small states. Solar power is not a consistant source; cloud cover reduces power output as much as 75%, and then there is the issue of night. Nuclear power is far more reliable, consistant, and controllable. Despite this current tragedy nuclear power is still the safest and most environmentally friendly energy source we have discovered in terms of kWhr production. Let's learn from this and start upgrading our older facilities to make them even safer as opposed to the knee-jerk reaction of shutting down irreplaceable sources of energy our society requires. I use the word irreplaceable because to try and replace the worlds nuclear power generating facilities with any other combination of power production would certainly cause greater damage to the environment and still not meet our needs.
So how does all of this factual information bear on the decisions to be made about the future of nuclear power in America?
I remember the corporate propaganda about nuclear energy in California being safe. Yet plants like Rancho Seco and Diablo Canyon were being built in near proximity to earthquake faults. Rancho Seco was closed down due to proximity to an earthquake fault and Sacramento. Then the Diablo Canyon power plant was built in close proximity to earthquake faults, operated for over two decades and is now decommissioned. The last I heard is nuclear waste is being stored at the site.
Is Newsvine and MSNBC afraid to confront the issue that is blatantly obvious in all the Japanese news? Is Nuclear Power a wise option to chose for the future. This seems to be a decent factual information article. How about a follow up on Nuclear Power yes or no?
Now would be the best time for articles addressed to the general public about how much safer Gen-III+ and Gen-IV reactors are than the 40-year old designs in use at Fukushima Dai-ichi. Especially, new designs for thorium reactors seem to solve many problems that Gen-II reactors suffer from in operational safety, fuel cost and availability, waste management, weapons proliferation, etc.
And even so, this isn't really a failure of the GE plant design so much as it is a failure to plan for the dangers inherent in locating a power reactor on one of the most earthquake-active shorelines in the world -- in the country from which we get the word 'tsunami.'
A good place to start for the lay person:
energyfromthoriumdotcom
There are some very enthusiastic and outspoken proponents of liquid fluoride thorium reactors at that site. While the idea of using a LFTR 'now' might be a great idea, practically speaking, how long would it take for a plant to become operational, including fulfilling all NRC requirements, acquiring funding, site location and approval, getting insurance, ...? Not that a "traditional' plant would be faster, but...
Jubal...Kirk Sorenson addresses your same question in the Q&A of his Google tech talk Energy From Thorium: A Nuclear Waste Burning Liquid Salt Thorium Reactor www.youtube.com/watch?v=AZR0UKxNPh8 in minute 58.
To summarize what he said, in a "Manhattan Project" type of effort with full resources utilized and the red tape/politics be damned we could develop a prototype reactor in 2-3 years and a production model in 5 years. He estimates cost for such a project at $300-$400 million but qualifies that by saying since he works for the gov't (NASA) he realizes it could easily go into the billions.
Please....some with more knowledge, emphase that is is IN NO WAY like Chernobyl. Chernobyl was a combination of bad reactor design, operator error...The reactor was burning, and no containment, with the most important point still unsaid: Chernobyl was driven 95% by fission energy, and not by heat decay energy used in power generation....There is enough hysteria and mis information being generated regarding the scenarios.
Kudos to Mr. Boyle for not contributing to that hysteria.
Have they though about adding liquid nitrogen to the containment vessel??
Liquid nitrogen exists at LOW temperature and HIGH pressure - impossible I do believe. Google It.
Hopefully the containment floor is as good as it was at TMI. Per Jay Lehr of the Heartland Institute, TMI was rated a 5 as there the melted core existed the vessel and reached the containment floor went in 5/8 in. and it held with plenty to spare.
Even so a friend of mine tested many residents near TMI for weeks using a full body scanner after the special truck had a police escort to the site from regular tests at another plant site. All they found was two older ladies had some radon - they lived in an unfinished house buried with roof near ground level.
There may have been a spark to cause the hydrogen/oxygen explosion - TMI had a flash that released pressure - may have not been at same mixture ratios as in Japan . Why didn't they just vent more to prevent an the three explosions especially with winds out to sea.
This may sound stupid but here it goes. Have they thought about adding liquid nitrogen to the containment vessel. The temperature of the nitrogen would re-leave the pressure in the vessel. Nitrogen and hydrogen in a vessel are not explosive. If vented the mixture would be diluted and should be less explosive. Along with the liquid nitrogen on the pressure, it should help cool the core for a temporary fix?
March 14th. 2011 @ 9:16 P.M.C.T.
I worked at General Electric Nuclear Instrumentation Department Manufaturing facility in San Jose California in1970.
We designed and built complete systems for all of the power generating companies world wide.
We built the fuel control rod raising and lowering equipment with elecric motors and a HAND crank is case power was lost at the plant.
Why did it take so long to to reinsert the fuel control rods?
They did reinsert the control rods pretty quickly, based on reports from the scene. However, there's residual decay heat that apparently built up ... and needs to be carried away by the cooling system. Some of the commenters here are more knowledgeable than I am and can provide additional information. One of the commenters surmised that the control rods couldn't be fully deployed for some reason.
Well, from what I can ascertain, the site workers are being evacuated because unit #2 has lost containment in the recent explosion. (Saltwater is being fed to the reactor with no rise in water level, no drop in temperature, no rise in pressure, and there is an increase in radiation outside containment.) To make matters worse, it was the one unit of the three that were most badly damaged at the site that was running on MOX, while the other units were using standard LEU fuel rods (uranium only). MOX typically uses weapon grade plutonium (239, oxide) in a mix, generally between 12% and 25%, with uranium 235 (oxide). Plutonium is much more toxic to the human body than uranium. If reports are true, this is now a worst case scenario.
Chalk another one up to the arrogance of man. Why in the world is Japan so dependent upon nuclear electrical generation when it is so rich in geothermal assets? There's a lot more heat underground to boil water than nuclear fuel could ever generate, and the risks are minimal, not to mention so much more cost effective. I guess there is no one capable of collecting fuel costs, making it less profitable.
I'm glad I'm not stuck with the cleanup bill. The insurance company isn't because of an exclusion clause. It's going to be more expensive to make it safe (, not even talking about disassembling the site and removing it to someplace safe,) than it was to build it, upgrade it, maintain it, plus the electricity it generated, and I'm not talking anywhere near close. Shutdown, radical or routine, is the one cost that no one associated with nuclear energy wants to discuss. It makes nuclear energy incapable in the long run of being financially competitive as a generating source.
It has long been said that Japan uses so much nuclear power because "Japan has no coal, no oil, no natural gas, and no choice."
Geothermal, who knows. I've never looked into it in Japan. But It too has a mixed track record of success in Scandinavia and disasters in California, I believe it was, where they used up the local ground water and left the plant dead.
Admittedly a dead geothermal plant is not exactly a danger to anyone, compared to this problem.
I live on the Big Island Hawaii (you know the one with the volcano) and our utility HELCO produces about 20% of our electricity with a geothermal plant. Its important to note that unlike solar/wind, geothermal meets the base load demand in our grid which is an important distinction in power distribution that solar/wind proponents usually don't even realize.
I visit the Big Island on occasion and didn't know about that 20% geothermal, Pele be praised. I have seen what seems to be a small solar power generation facility south of the Kona airport. Is that a HELCO installation? Where is the geothermal plant located?
BTW, all the islands have volcanoes. In fact, they are volcanoes. ;-) I know, I know... Pu'u O'o is the only one that's not sleeping; the only one above sea level, anyway.