Tsunami in Pacific
- Thread starter A.J.
- Start date
Incredible before-and-after satellite photos here:
Satellite Photos - Japan Before and After Tsunami - Interactive Feature - NYTimes.com
Move the slider in the center of each image to the left and right to get a full view of before and after....
Satellite Photos - Japan Before and After Tsunami - Interactive Feature - NYTimes.com
Move the slider in the center of each image to the left and right to get a full view of before and after....
David Morton
Lifetime Supporter
This terrible disaster seems to worsen with every passing hour. More and more reports and photos of incredible devastation. Will nuclear power sources and projects ever recover from the terrible press they are getting at the moment? Irrespective of how much radiation is being released and how safe or unsafe it is, and the fact it is so much lower than Chernobyl and Three Mile Island, the damage, it seems, is done.
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This has, of course, put nuclear power generation very much behind the 8 ball. It now has to fight to recover respectability in light of these explosions. Reading between the lines, meltdown does not appear imminent.
Can we hope that the engineers are able to learn, and convince the authorities that they can build earthquake proof (as well as everyotherthing proof) reactors for the future. Strikes me that the Japanese reactors have stood up amazingly well to the 9 on the Richter scale they have experienced.
This will be used by the opponents of nuclear energy , but if the world is serious about reducing CO2 emissions, nuclear is the only way to go.
Clive
Can we hope that the engineers are able to learn, and convince the authorities that they can build earthquake proof (as well as everyotherthing proof) reactors for the future. Strikes me that the Japanese reactors have stood up amazingly well to the 9 on the Richter scale they have experienced.
This will be used by the opponents of nuclear energy , but if the world is serious about reducing CO2 emissions, nuclear is the only way to go.
Clive
David Morton
Lifetime Supporter
Point really well made Clive but , and I confess, alas, it really strengthens the green lobby for wind and wave power. They may be a blot on the landscape but what happens when a windmill melts down, or a water turbine overheats ? Tidal power may be a major player in the future. For example - Jersey in the Channel Islands has a 30ft + rise and fall twice a day every day.
Jim Craik
Lifetime Supporter
Guys,
The news out of Japan is just heart breaking. It will be some time before the full extent of the loss of life and damage is revealed.
Just when it appeared that the US was ready for new offshore drilling and new Nuclear power plants the events of the last few years have shown just how problematic this type of activity can be.
The nuclear lobby may well be done and the "drill baby drill" folks also face an up hill battle.
Such a shame.
The news out of Japan is just heart breaking. It will be some time before the full extent of the loss of life and damage is revealed.
Just when it appeared that the US was ready for new offshore drilling and new Nuclear power plants the events of the last few years have shown just how problematic this type of activity can be.
The nuclear lobby may well be done and the "drill baby drill" folks also face an up hill battle.
Such a shame.
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I think you expressed that concern very well Clive, the Japanese power stations survived remarkably well intact after one of the strongest earthquakes ever recorded - the automatic shut down facilities functioned as they were intended to do, it seems that the wheels fell off at the back-up power supply stage and I'm sure lessons will be drawn from this experience.
My personal hope is that the nuclear power option will not be shelved as a result of sensationalist style reporting and much Fear, Uncertainty and Doubt that will be spread by the anti-nuclear power lobby. At our present stage of development and given the urgency of additional energy sources, nuclear is really the best option - I'm not saying the only but it does provide plentiful energy relatively quickly. This is regardless of the question about CO2, we need more energy.
The news from Japan this evening is rather more encouraging as far as the nuclear problems are concerned, hopefully they will be able to get on top of it very soon. Fukushima power stations are well and truly fuku-ed now though as a result of the use of sea water as emergency coolant in addition to the explosion issue, they were pretty old though.
I found this really good summary of reactor conditions at this link
Japan's Nuclear Situation - be a bit worried - The Something Awful Forums
UPDATE: 8:00AM GMT, March 15th: The situation at reactors #2 and #4 continues to develop. Reactors #1 and #3 are still considered stable, reactor #2 is being filled with water again, and the fire at reactor #4 is out. This FAQ has undergone extensive revision in light of new events.
In addition, this FAQ is not going to be updated quite as often due to the personal needs of the author. Large events will be covered, but please check the last-updated time (currently in GMT for an international audience) for an idea of how recent the news will be. Items relating to scientific facts should remain useful regardless.
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This thread is intended to move the various discussions about nuclear power, the safety of Japan's nuclear reactors, and related issues out of the general thread about the disaster in Japan. Nuclear talk has overwhelmed the discussion in that thread, along with people coming in asking for information about whether it's going to be another Chernobyl.
But first, a FAQ (updated at 8:00AM GMT, March 15th):
What in the hell is going on here?
In the aftermath of the recent earthquake and tsunami in Japan, two nuclear power stations on the east coast of Japan have been experiencing problems. They are the Fukushima Daiichi ("daiichi" means "number one") and Fukushima Daini ("number two") sites, operated by the Tokyo Electric Power Company (or TEPCO). Site one has six reactors, and site two has four. The problematic reactors are #1, #2, #3 and (in a different way) #4 at site one. Reactors one through three are the oldest of the ten and were due to be decommissioned this year.
In short, the earthquake combined with the tsunami have impaired the cooling systems at these reactors, which has made it difficult for TEPCO to shut them down completely. Reactors #1 and #3 are now considered safe after crew flooded the reactors with sea water. Reactor #2 is undergoing the sea water injection process but has experienced multiple complications. Reactors four through six were shut down for inspection before the earthquake occurred and are all in cold shutdown; however, the building that houses #4 experienced a fire unrelated to the reactor core.
The four reactors at site two did not have their systems impaired and have shut down normally.
There has been an evacuation in a radius of 20km around site one, and 10km around site two. Due to recent events, the Prime Minister of Japan has asked people between 20km and 30km of site one to remain indoors for the time being.
Where are you getting this information?
This FAQ is based on information taken from primary sources: press conferences by the Japanese government and TEPCO as shown on Japanese television, TEPCO press releases, independent documentation about the type of reactor, and statements by the Japanese Nuclear Safety Commission, the Japanese Nuclear and Industry Safety Agency, and the International Atomic Energy Agency.
Can this cause a nuclear explosion?
No. It is physically impossible for a nuclear power station to explode like a nuclear weapon.
Nuclear bombs work by causing a supercritical fission reaction in a very small space in an unbelievably small amount of time. They do this by using precisely-designed explosive charges to combine multiple subcritical masses of nuclear material so quickly that they bypass the critical stage and go directly to supercritical, and with enough force that the resulting supercritical mass cannot melt or blow itself apart before all of the material is fissioned. This requires extremely precise engineering, which is why building nuclear bombs is not a simple process regardless of how simple the basic idea is.
Current nuclear power plants are designed around subcritical masses of radioactive material, which are manipulated into achieving limited supercriticality for sustained fission through the use of neutron moderators. The heat from this fission is used to convert water to steam, which drives electric generator turbines. (This is a drastic simplification.) They are not capable of exploding like a bomb; if a reactor's nuclear core underwent an uncontrolled supercritical reaction, the energy produced would melt the nuclear fuel instead of exploding, which is what the makers of nuclear bombs have to try very hard to prevent.
Making a nuclear bomb is very difficult, and it is completely impossible for a nuclear reactor to accidentally become a bomb. Secondary systems, like cooling or turbines, can explode due to pressure and stress problems, but these are not nuclear explosions.
Is this a meltdown?
Technically, yes, but not in the way that most people think.
The term "meltdown" is not used within the nuclear industry, because it is insufficiently specific. The popular image of a meltdown is when a nuclear reactor's fuel core goes out of control and melts its way out of the containment facility. This has not happened, although the likelihood of his happening in the future is difficult to determine at this time.
What has happened in reactor #1 and #3 is a "partial fuel melt". This means that the fuel core has suffered damage from heat but the containment vessels are intact and no fuel has escaped containment. Core #2 is suspected to have experienced minor damage. Confinement on reactor #2 is holding but still at risk, although water levels are rising and pumping is continuing.
How did this happen? Aren't there safety systems?
When the earthquakes in Japan occurred on March 11th, all ten reactor cores "scrammed", which means that their control rods were inserted automatically. This shut down the active fission process, and the cores have remained shut down since then.
The problem is that even a scrammed reactor core generates "decay heat", which requires cooling. Under normal conditions, the cores require active cooling for a few days to over a week before they enter a "cold shutdown" state. When the tsunami arrived shortly after the earthquake, it damaged the external power generators that the sites used to power their cooling systems. This meant that while the cores were shut down, they were still boiling off the water used as coolant because they had not yet achieved cold shutdown.
This caused two further problems. First, the steam caused pressure to build up within the containment vessel. Second, once the water level subsided, parts of the fuel rods were exposed to the air inside the containment vessel, causing the heat to build up more quickly, leading to core damage from the heat.
What's this about fuel rods being exposed to the air?
When the coolant levels inside the reactor get low enough, the tops of the fuel rods will be exposed to the air inside the containment vessel. They have not been exposed to the external atmosphere and the containment vessels are all currently intact. When news reports describe "fuel rods exposed to air", this is what they mean.
What are they doing about it? What was this about explosions?
From the very beginning, TEPCO has had the option to flood the reactor chambers with boron-enriched sea water, which would replace the normal cooling systems and allow the reactors to perform their normal cooldown. Unfortunately, this also destroys the reactors permanently due to the corrosive nature of sea water and other factors. Doing so would cost TEPCO and Japanese taxpayers billions of dollars, even though these reactors were due to be decommissioned shortly. More importantly, it would make those reactors unavailable for generating electricity during a nationwide disaster. The sea water method is a "last resort" in this sense, but it has always been an option.
To avoid this, TEPCO first took steps to bring the cooling systems back online and to reduce the pressure on the inside of the containment vessel. This involved bringing in external portable generators, repairing damaged systems, venting steam and gases from inside the containment vessel, and other tasks. These methods worked for reactor #2 at site one, prior to complications; reactors four through six were shut down before for inspection before the earthquake hit. However, reactors #1 and #3 did not respond properly to these attempts, and it was decided to flood reactor #1 and later #3 with sea water.
One of the byproducts of reactors like the ones at Fukushima is hydrogen. Normally this gas is vented and burned slowly. More hydrogen gas than usual may have been generated due to damage to the fuel cores in reactors #1 and #3. Due to the nature of the accident, the vented hydrogen gas was not properly burned as it was released. This led to a build up of hydrogen gas inside the reactor #1 building, but outside the containment vessel.
During the flooding of reactor #1 with sea water, this gas ignited, causing the top of the largely cosmetic external shell to be blown off. This shell was made of sheet metal on a steel frame and did not require a great deal of force to be destroyed. The reactor itself was not damaged in this explosion, and there were only four minor injuries. This was a conventional chemical reaction and not a nuclear explosion.
You see what happened in this photo. Note that other than losing the sheet metal covering on the top, the reactor building is intact. No containment breach occurred, and eventually the water level in reactor #1 was declared "stable", with the fuel rods not exposed to air, and it continued towards cold shutdown.
At about 2:30AM GMT on March 14th, a similar explosion occurred at the reactor #3 building. This explosion was not unexpected, as TEPCO had warned that one might occur. It was been announced that the containment vessel was not breached and that the sea water process was continuing. Eventually it was declared "stable" like reactor #1 was.
Around 7:30AM GMT on March 14th, it was announced that the explosion at reactor #3 had damaged the already limping cooling systems of reactor #2. The sea water treatment given to reactors #1 and #1 began to be applied to #2.
At around 9PM GMT on March 15th, something unknown happened inside the suppression pool in reactor #2, causing a loud noise and the pressure levels within the pool to drop. Exactly what happened is unknown, but the water levels and pressure within the containment vessel itself are unchanged. Unnecessary crew have been evacuated as a precaution, according to official procedures. They are continuing to pump sea water into reactor #2, reportedly with some success. Reports have described the fuel rods as being partially exposed to air (see above) but with a rising water level. It is unknown what the long-term effect of the suppression pool event will be, as its primary use is during power generation through the turbines.
What about the fire?
Reactor #4 was in cold shutdown and was not originally considered at risk. However, shortly after the suppression pool incident at #2, it was revealed that reactor #4's building had caught fire some time previously. The exact cause of this is unknown, but the primary suspect is the explosion at the building of reactor #3. This fire has since been extinguished.
Reports indicate that the fire in reactor #4's building may have affected the storage pool containing spent fuel rods. This may be related to a sudden spike in radioactivity about the site (see below).
Is there radiation leakage?
That is a question with a complicated answer. To cover this properly we need to talk about how radiation is measured.
There are several ways of measuring radiation exposure. In this case, we are going to be using the "Gray" (or Gy) and the "Sievert" (or Sv). For the purposes of this article, they are equivalent. The radiation outside the problematic Fukushima reactors is currently being measured in micro-Svs per hour; the "μ" prefix in "μSv" is "micro", or one-millionth of an Sv.
Here is a chart showing the effects of various radiation poisoning levels. For comparison, there is also a chart of normal radiation exposure levels from things like medical x-rays and airline flights. Radiation exposure does not become an immediate health risk until around 1Sv. Radiation exposure is cumulative, if there is not a substantial period of time between exposures.
Containment on the live reactors has not, at this time, been breached. There is, as far as we know, no leaks of live reactor fuel or anything similar. This does not mean that there is not high-than-normal raditation levels around Fukushima site one, for several reasons.
One reason that the radiation levels immediately outside the plant are higher than usual was due to the deliberate release of radioactive steam. These levels go up during venting, into the 700 to 1500 microSv per hour range and then very quickly decrease to almost normal background levels, as the radioactive material in this steam has a very short half-life. This venting is done to reduce pressure inside the reactor containment vessels.
There have also been very minor releases of radioactive reactor byproducts like iodine and cesium along with the steam. This material is less radioactive than the typical output of coal power plants and has very short half-lives. It is significant mainly as an indicator of the state of the reactor cores, as radioactive iodine and cesium are a sign that there there has been core damage.
However, roughly simultaneously with the suppression pool event at reactor #2 and the fire at reactor #4's building, an alarming spike in radiation measurements occurred. This has since decreased, but for a short period of time the radiation levels at site one were dangerously high, in the 400 milli-seivert per hour range close to the reactor #4 building.
These levels did not last for more than a few minutes, and they have since dropped down to less dangerous levels. The last available reading at the site gate shows 489.8μSv/hr and dropping at 7:30PM GMT on the 15th. It is not currently known precisely what caused this spike, although the fire at the spent fuel rod pool at reactor #4's building is a strong suspect.
Is Tokyo in danger?
Currently, measured radiation levels are slightly higher than normal in many areas of Japan at the moment, including parts of Tokyo. However, they are still down in single- or double-digit microSv per hour levels, far below any danger.
This does not mean that future events might not change this. Events such as a spent fuel rod fire (see below) could cause more widespread problems, depending on the severity of the incident.
Is a "China Syndrome" meltdown possible?
Strictly speaking, no, any fuel melt situation at Fukushima will be limited, because the fuel is physically incapable of having a runaway fission reaction. This is due to their light water reactor design.
In a light water reactor, water is used as both a coolant for the fuel core and as a "neutron moderator". What a neutron moderator does is very technical (you can watch a lecture which includes this information here), but in short, when the neutron moderator is removed, the fission reaction will stop.
An LWR design limits the damage caused by a meltdown, because if all of the coolant is boiled away, the fission reaction will not keep going, because the coolant is also the moderator. The core will then only generate decay heat, which while dangerous and strong enough to melt the core, is not nearly as dangerous as an active fission reaction.
The containment vessel at Fukushima should be strong enough to resist breaching even during a decay heat meltdown. The amount of energy that could be produced by decay heat is easily calculated, and it is possible to design a container that will resist it. If it is not, and the core melts its way through the bottom of the vessel, it will end up in a large concrete barrier below the reactor. It is nearly impossible that a fuel melt caused by decay heat would penetrate this barrier. A containment vessel failure like this would result in a massive cleanup job but no leakage of nuclear material into the outside environment.
A worst case scenario regarding the cores is a containment vessel failure combined with an uncontrolled release of radioactive steam. This would cause a localized and temporary increase in radioactivity similar to what is already present (see below) but would not result in actual nuclear fuel leakage or widespread contamination. It is this possibility that lead to the evacuations.
It appeas that the fuel rod cooling problem has been largely but not completely solved through the flooding of the chambers with boron-enriched sea water. Reactors #1 and #3 have stable water levels and are therefore considered a low risk for further core melting. Reactor #2 continued to have problems, and it has only been announced recently that water flow has been re-restablished and that the fuel core is being covered again.
I read that there's a plume of radioactive material heading across the Pacific.
In its current state, the steam blowing east from Japan across the pacific is less dangerous than living in Denver for a year. If it makes it across the ocean, it will be almost undetectable by the time it arrives, and completely harmless as the dangerous material in the steam will have decayed by then.
The United States aircraft carrier Ronald Reagan passed through this plume and suffered no long-term effects. The material was removed with soap and water and the ship is now considered contamination-free.
Future incidents may generate more dangerous plumes, but it remains unlikely that anything dangerous could cross the Pacific and remain so. The accident at Chernobyl generated tremendous amounts of airborne radioactive material, and it was unable to travel more than 1500 miles, less than half the distance to the United States.
Do we need to worry about site two?
The four reactors at site two did not have their external power damaged by the tsunami, and are therefore operating normally, albeit in a post-scram shutdown state. They have not required any venting, and reactors #1, #2, and #3 are already in full cold shutdown.
Can this end up like Chernobyl?
No, it cannot. for several reasons.
•Chernobyl used graphite as a neutron moderator and water as a coolant. For complicated reasons, this meant that as the coolant heated up and converted to steam, the fission reaction intensified, converting even more water to steam, leading to a feedback effect. The Fukushima reactors use water as both the coolant and the neutron moderator, which means that as the water heats up and converts to steam, the reaction slows down instead. (The effect of the conversion of water coolant to steam on the performance of a nuclear reactor is known as the "void coefficient", and can be either positive or negative.)
•Chernobyl was designed so that as the nuclear fuel heated up, the fission reaction intensified, heating the core even further, causing another feedback effect. In the Fukushima reactors, the fission reaction slows down as the fuel heats up. (The effect of heating of the nuclear fuel on the performance of a nuclear reactor is known as the "temperature coefficient", and can also be positive or negative.)
•Chernobyl's graphite moderator was flammable, and when the reactor exploded, the radioactive graphite burned and ended up in the atmosphere. The Fukushima reactors use water as a neutron moderator, which is obviously not flammable.
Note that while Chernobyl used light water as a coolant (as distinct from heavy water), it was not a "light water reactor". The term LWR refers strictly to reactors that use light water for both cooling and neutron moderation.
The closest thing that could happen to a Chernobyl-like incident is if the spent fuel rods at the site caught fire and continued to burn. This could create large amounts of radioactive smoke, which would be more dangerous that the vented steam because it would contain nuclear material with much longer lives. So far, this appears to have been averted, but the possibility remains.
The news said this was the worst nuclear power accident since Chernobyl, though.
That's not saying much, considering the competition. The IAEA rates nuclear events on a scale where level four is "Accident with Local Consequences"; the Fukushima situation is the only class five event involving an actual power station since Chernobyl in 1986, which makes it easy to be the "worst".
This is a serious accident, but so far it is no Chernobyl. There have been no deaths, no loss of reactor containment, and no release of long-lived radioactive material.
Is this like Three Mile Island?
There are similarities. So far, the radiactive material released into the environment is greater than that at TMI, but like TMI there have been no deaths. Also like TMI, regardless of the final result of this incident, the PR damage to the nuclear power industry will have been tremendous.
How do we know the Japanese government and TEPCO aren't lying?
When Chernobyl occurred, the Soviet government attempted to keep it quiet. They failed, in part because the nuclear material and radiation detection equipment at reactors adn universtities in other countries detected it. It is extremely difficult to keep these sort of accidents a secret.
The United States aircraft carrier Ronald Reagan is nuclear-powered, and therefore has all of the same detection equipment that a land-based reactor would have. It is currently offshore of Japan, and it has detected nothing to contradict the official statements from the Japanese government and TEPCO.
However, the fire at reactor #4's building was not reported for several hours. This has led many people both in Japan and abroad to question the accuracy of TEPCO's reporting to the government and news. In addition, the presence of spent fuel rods in reactor #4's building after a major disaster is disquieting, as one would normally expect that dangerous material would have been moved to safe storage at the first opportunity.
Faith in TEPCO's ability to handle the situation has been shaken, but they would be unable to hide any events resulting in the release of radioactive material. They know this and it seems unlikely that they would try.
Given the candor of the Japanese government given these events so far, including the Prime Minister's open admission of severe problems at Fukushima site one in conjunction with a plea to keep calm, it seems unlikely that they would deliberately lie about any future developments. Time will tell.
How can I keep up with developments?
Some outlets in the western media have been very bad about reporting this event, due to a combination of sensationalist reporting, ignorance, speculation, and the use of inexact or unexplained terminology. In many cases, the same network or newspaper will carry both solid reporting and sensationalism. There is no single reliable source.
Much of the information in this FAQ was taken from live press conferences and news reports, but the live translations provided by the western networks are not very reliable and unless you speak Japanese they are probably not going to he helpful.
The press releases at the TEPCO site were previously considered to be trustworthy, but recent events have added a level of doubt. In addition, this site is often unresponsive due to the immense traffic it is receiving.
Other organizations providing accurate news in English, although not necessarily in a timely manner, include the International Atomic Energy Agency, the The Japanese Nuclear and Industry Safety Agency, and the Japanese Prime Minister's office.
A twitter account run by the NE Asia Bureau Chief for Voice of America has proven to be useful.
Where can I find more information about these issues?
Reading:
•The Japanese Nuclear and Industry Safety Agency
•the Japanese Nuclear Safety Commission - nothing useful in English, sadly
•Tokyo Electric Power Company site with some press releases in English - currently hard to reach due to traffic
•Press conferences from Prime Minister's office - not all have been translated
•The International Atomic Energy Agency is providing regular announcements
•Timeline and data sheets for the incident by the Nuclear Energy Institute - the NEI is a policy organization for the American nuclear industry so their analyses may be biased
•Wikipedia on light water reactors and nuclear weapon design
•The United States Nuclear Regulatory Commission's Boiling Water Reactor (BWR) Systems manual - the Fukushima reactors are BWRs, a subset of LWRs
•More about BWRs
Video:
•"Physics for Future Presidents" lecture ten, on nuclear weapons and nuclear reactors - if you watch anything related to this event, watch this one
•Footage of the hydrogen explosion at reactor #1
Photos:
•before and after satellite photos of Fukushima site one
Japan's Nuclear Situation - be a bit worried - The Something Awful Forums
UPDATE: 8:00AM GMT, March 15th: The situation at reactors #2 and #4 continues to develop. Reactors #1 and #3 are still considered stable, reactor #2 is being filled with water again, and the fire at reactor #4 is out. This FAQ has undergone extensive revision in light of new events.
In addition, this FAQ is not going to be updated quite as often due to the personal needs of the author. Large events will be covered, but please check the last-updated time (currently in GMT for an international audience) for an idea of how recent the news will be. Items relating to scientific facts should remain useful regardless.
--
This thread is intended to move the various discussions about nuclear power, the safety of Japan's nuclear reactors, and related issues out of the general thread about the disaster in Japan. Nuclear talk has overwhelmed the discussion in that thread, along with people coming in asking for information about whether it's going to be another Chernobyl.
But first, a FAQ (updated at 8:00AM GMT, March 15th):
What in the hell is going on here?
In the aftermath of the recent earthquake and tsunami in Japan, two nuclear power stations on the east coast of Japan have been experiencing problems. They are the Fukushima Daiichi ("daiichi" means "number one") and Fukushima Daini ("number two") sites, operated by the Tokyo Electric Power Company (or TEPCO). Site one has six reactors, and site two has four. The problematic reactors are #1, #2, #3 and (in a different way) #4 at site one. Reactors one through three are the oldest of the ten and were due to be decommissioned this year.
In short, the earthquake combined with the tsunami have impaired the cooling systems at these reactors, which has made it difficult for TEPCO to shut them down completely. Reactors #1 and #3 are now considered safe after crew flooded the reactors with sea water. Reactor #2 is undergoing the sea water injection process but has experienced multiple complications. Reactors four through six were shut down for inspection before the earthquake occurred and are all in cold shutdown; however, the building that houses #4 experienced a fire unrelated to the reactor core.
The four reactors at site two did not have their systems impaired and have shut down normally.
There has been an evacuation in a radius of 20km around site one, and 10km around site two. Due to recent events, the Prime Minister of Japan has asked people between 20km and 30km of site one to remain indoors for the time being.
Where are you getting this information?
This FAQ is based on information taken from primary sources: press conferences by the Japanese government and TEPCO as shown on Japanese television, TEPCO press releases, independent documentation about the type of reactor, and statements by the Japanese Nuclear Safety Commission, the Japanese Nuclear and Industry Safety Agency, and the International Atomic Energy Agency.
Can this cause a nuclear explosion?
No. It is physically impossible for a nuclear power station to explode like a nuclear weapon.
Nuclear bombs work by causing a supercritical fission reaction in a very small space in an unbelievably small amount of time. They do this by using precisely-designed explosive charges to combine multiple subcritical masses of nuclear material so quickly that they bypass the critical stage and go directly to supercritical, and with enough force that the resulting supercritical mass cannot melt or blow itself apart before all of the material is fissioned. This requires extremely precise engineering, which is why building nuclear bombs is not a simple process regardless of how simple the basic idea is.
Current nuclear power plants are designed around subcritical masses of radioactive material, which are manipulated into achieving limited supercriticality for sustained fission through the use of neutron moderators. The heat from this fission is used to convert water to steam, which drives electric generator turbines. (This is a drastic simplification.) They are not capable of exploding like a bomb; if a reactor's nuclear core underwent an uncontrolled supercritical reaction, the energy produced would melt the nuclear fuel instead of exploding, which is what the makers of nuclear bombs have to try very hard to prevent.
Making a nuclear bomb is very difficult, and it is completely impossible for a nuclear reactor to accidentally become a bomb. Secondary systems, like cooling or turbines, can explode due to pressure and stress problems, but these are not nuclear explosions.
Is this a meltdown?
Technically, yes, but not in the way that most people think.
The term "meltdown" is not used within the nuclear industry, because it is insufficiently specific. The popular image of a meltdown is when a nuclear reactor's fuel core goes out of control and melts its way out of the containment facility. This has not happened, although the likelihood of his happening in the future is difficult to determine at this time.
What has happened in reactor #1 and #3 is a "partial fuel melt". This means that the fuel core has suffered damage from heat but the containment vessels are intact and no fuel has escaped containment. Core #2 is suspected to have experienced minor damage. Confinement on reactor #2 is holding but still at risk, although water levels are rising and pumping is continuing.
How did this happen? Aren't there safety systems?
When the earthquakes in Japan occurred on March 11th, all ten reactor cores "scrammed", which means that their control rods were inserted automatically. This shut down the active fission process, and the cores have remained shut down since then.
The problem is that even a scrammed reactor core generates "decay heat", which requires cooling. Under normal conditions, the cores require active cooling for a few days to over a week before they enter a "cold shutdown" state. When the tsunami arrived shortly after the earthquake, it damaged the external power generators that the sites used to power their cooling systems. This meant that while the cores were shut down, they were still boiling off the water used as coolant because they had not yet achieved cold shutdown.
This caused two further problems. First, the steam caused pressure to build up within the containment vessel. Second, once the water level subsided, parts of the fuel rods were exposed to the air inside the containment vessel, causing the heat to build up more quickly, leading to core damage from the heat.
What's this about fuel rods being exposed to the air?
When the coolant levels inside the reactor get low enough, the tops of the fuel rods will be exposed to the air inside the containment vessel. They have not been exposed to the external atmosphere and the containment vessels are all currently intact. When news reports describe "fuel rods exposed to air", this is what they mean.
What are they doing about it? What was this about explosions?
From the very beginning, TEPCO has had the option to flood the reactor chambers with boron-enriched sea water, which would replace the normal cooling systems and allow the reactors to perform their normal cooldown. Unfortunately, this also destroys the reactors permanently due to the corrosive nature of sea water and other factors. Doing so would cost TEPCO and Japanese taxpayers billions of dollars, even though these reactors were due to be decommissioned shortly. More importantly, it would make those reactors unavailable for generating electricity during a nationwide disaster. The sea water method is a "last resort" in this sense, but it has always been an option.
To avoid this, TEPCO first took steps to bring the cooling systems back online and to reduce the pressure on the inside of the containment vessel. This involved bringing in external portable generators, repairing damaged systems, venting steam and gases from inside the containment vessel, and other tasks. These methods worked for reactor #2 at site one, prior to complications; reactors four through six were shut down before for inspection before the earthquake hit. However, reactors #1 and #3 did not respond properly to these attempts, and it was decided to flood reactor #1 and later #3 with sea water.
One of the byproducts of reactors like the ones at Fukushima is hydrogen. Normally this gas is vented and burned slowly. More hydrogen gas than usual may have been generated due to damage to the fuel cores in reactors #1 and #3. Due to the nature of the accident, the vented hydrogen gas was not properly burned as it was released. This led to a build up of hydrogen gas inside the reactor #1 building, but outside the containment vessel.
During the flooding of reactor #1 with sea water, this gas ignited, causing the top of the largely cosmetic external shell to be blown off. This shell was made of sheet metal on a steel frame and did not require a great deal of force to be destroyed. The reactor itself was not damaged in this explosion, and there were only four minor injuries. This was a conventional chemical reaction and not a nuclear explosion.
You see what happened in this photo. Note that other than losing the sheet metal covering on the top, the reactor building is intact. No containment breach occurred, and eventually the water level in reactor #1 was declared "stable", with the fuel rods not exposed to air, and it continued towards cold shutdown.
At about 2:30AM GMT on March 14th, a similar explosion occurred at the reactor #3 building. This explosion was not unexpected, as TEPCO had warned that one might occur. It was been announced that the containment vessel was not breached and that the sea water process was continuing. Eventually it was declared "stable" like reactor #1 was.
Around 7:30AM GMT on March 14th, it was announced that the explosion at reactor #3 had damaged the already limping cooling systems of reactor #2. The sea water treatment given to reactors #1 and #1 began to be applied to #2.
At around 9PM GMT on March 15th, something unknown happened inside the suppression pool in reactor #2, causing a loud noise and the pressure levels within the pool to drop. Exactly what happened is unknown, but the water levels and pressure within the containment vessel itself are unchanged. Unnecessary crew have been evacuated as a precaution, according to official procedures. They are continuing to pump sea water into reactor #2, reportedly with some success. Reports have described the fuel rods as being partially exposed to air (see above) but with a rising water level. It is unknown what the long-term effect of the suppression pool event will be, as its primary use is during power generation through the turbines.
What about the fire?
Reactor #4 was in cold shutdown and was not originally considered at risk. However, shortly after the suppression pool incident at #2, it was revealed that reactor #4's building had caught fire some time previously. The exact cause of this is unknown, but the primary suspect is the explosion at the building of reactor #3. This fire has since been extinguished.
Reports indicate that the fire in reactor #4's building may have affected the storage pool containing spent fuel rods. This may be related to a sudden spike in radioactivity about the site (see below).
Is there radiation leakage?
That is a question with a complicated answer. To cover this properly we need to talk about how radiation is measured.
There are several ways of measuring radiation exposure. In this case, we are going to be using the "Gray" (or Gy) and the "Sievert" (or Sv). For the purposes of this article, they are equivalent. The radiation outside the problematic Fukushima reactors is currently being measured in micro-Svs per hour; the "μ" prefix in "μSv" is "micro", or one-millionth of an Sv.
Here is a chart showing the effects of various radiation poisoning levels. For comparison, there is also a chart of normal radiation exposure levels from things like medical x-rays and airline flights. Radiation exposure does not become an immediate health risk until around 1Sv. Radiation exposure is cumulative, if there is not a substantial period of time between exposures.
Containment on the live reactors has not, at this time, been breached. There is, as far as we know, no leaks of live reactor fuel or anything similar. This does not mean that there is not high-than-normal raditation levels around Fukushima site one, for several reasons.
One reason that the radiation levels immediately outside the plant are higher than usual was due to the deliberate release of radioactive steam. These levels go up during venting, into the 700 to 1500 microSv per hour range and then very quickly decrease to almost normal background levels, as the radioactive material in this steam has a very short half-life. This venting is done to reduce pressure inside the reactor containment vessels.
There have also been very minor releases of radioactive reactor byproducts like iodine and cesium along with the steam. This material is less radioactive than the typical output of coal power plants and has very short half-lives. It is significant mainly as an indicator of the state of the reactor cores, as radioactive iodine and cesium are a sign that there there has been core damage.
However, roughly simultaneously with the suppression pool event at reactor #2 and the fire at reactor #4's building, an alarming spike in radiation measurements occurred. This has since decreased, but for a short period of time the radiation levels at site one were dangerously high, in the 400 milli-seivert per hour range close to the reactor #4 building.
These levels did not last for more than a few minutes, and they have since dropped down to less dangerous levels. The last available reading at the site gate shows 489.8μSv/hr and dropping at 7:30PM GMT on the 15th. It is not currently known precisely what caused this spike, although the fire at the spent fuel rod pool at reactor #4's building is a strong suspect.
Is Tokyo in danger?
Currently, measured radiation levels are slightly higher than normal in many areas of Japan at the moment, including parts of Tokyo. However, they are still down in single- or double-digit microSv per hour levels, far below any danger.
This does not mean that future events might not change this. Events such as a spent fuel rod fire (see below) could cause more widespread problems, depending on the severity of the incident.
Is a "China Syndrome" meltdown possible?
Strictly speaking, no, any fuel melt situation at Fukushima will be limited, because the fuel is physically incapable of having a runaway fission reaction. This is due to their light water reactor design.
In a light water reactor, water is used as both a coolant for the fuel core and as a "neutron moderator". What a neutron moderator does is very technical (you can watch a lecture which includes this information here), but in short, when the neutron moderator is removed, the fission reaction will stop.
An LWR design limits the damage caused by a meltdown, because if all of the coolant is boiled away, the fission reaction will not keep going, because the coolant is also the moderator. The core will then only generate decay heat, which while dangerous and strong enough to melt the core, is not nearly as dangerous as an active fission reaction.
The containment vessel at Fukushima should be strong enough to resist breaching even during a decay heat meltdown. The amount of energy that could be produced by decay heat is easily calculated, and it is possible to design a container that will resist it. If it is not, and the core melts its way through the bottom of the vessel, it will end up in a large concrete barrier below the reactor. It is nearly impossible that a fuel melt caused by decay heat would penetrate this barrier. A containment vessel failure like this would result in a massive cleanup job but no leakage of nuclear material into the outside environment.
A worst case scenario regarding the cores is a containment vessel failure combined with an uncontrolled release of radioactive steam. This would cause a localized and temporary increase in radioactivity similar to what is already present (see below) but would not result in actual nuclear fuel leakage or widespread contamination. It is this possibility that lead to the evacuations.
It appeas that the fuel rod cooling problem has been largely but not completely solved through the flooding of the chambers with boron-enriched sea water. Reactors #1 and #3 have stable water levels and are therefore considered a low risk for further core melting. Reactor #2 continued to have problems, and it has only been announced recently that water flow has been re-restablished and that the fuel core is being covered again.
I read that there's a plume of radioactive material heading across the Pacific.
In its current state, the steam blowing east from Japan across the pacific is less dangerous than living in Denver for a year. If it makes it across the ocean, it will be almost undetectable by the time it arrives, and completely harmless as the dangerous material in the steam will have decayed by then.
The United States aircraft carrier Ronald Reagan passed through this plume and suffered no long-term effects. The material was removed with soap and water and the ship is now considered contamination-free.
Future incidents may generate more dangerous plumes, but it remains unlikely that anything dangerous could cross the Pacific and remain so. The accident at Chernobyl generated tremendous amounts of airborne radioactive material, and it was unable to travel more than 1500 miles, less than half the distance to the United States.
Do we need to worry about site two?
The four reactors at site two did not have their external power damaged by the tsunami, and are therefore operating normally, albeit in a post-scram shutdown state. They have not required any venting, and reactors #1, #2, and #3 are already in full cold shutdown.
Can this end up like Chernobyl?
No, it cannot. for several reasons.
•Chernobyl used graphite as a neutron moderator and water as a coolant. For complicated reasons, this meant that as the coolant heated up and converted to steam, the fission reaction intensified, converting even more water to steam, leading to a feedback effect. The Fukushima reactors use water as both the coolant and the neutron moderator, which means that as the water heats up and converts to steam, the reaction slows down instead. (The effect of the conversion of water coolant to steam on the performance of a nuclear reactor is known as the "void coefficient", and can be either positive or negative.)
•Chernobyl was designed so that as the nuclear fuel heated up, the fission reaction intensified, heating the core even further, causing another feedback effect. In the Fukushima reactors, the fission reaction slows down as the fuel heats up. (The effect of heating of the nuclear fuel on the performance of a nuclear reactor is known as the "temperature coefficient", and can also be positive or negative.)
•Chernobyl's graphite moderator was flammable, and when the reactor exploded, the radioactive graphite burned and ended up in the atmosphere. The Fukushima reactors use water as a neutron moderator, which is obviously not flammable.
Note that while Chernobyl used light water as a coolant (as distinct from heavy water), it was not a "light water reactor". The term LWR refers strictly to reactors that use light water for both cooling and neutron moderation.
The closest thing that could happen to a Chernobyl-like incident is if the spent fuel rods at the site caught fire and continued to burn. This could create large amounts of radioactive smoke, which would be more dangerous that the vented steam because it would contain nuclear material with much longer lives. So far, this appears to have been averted, but the possibility remains.
The news said this was the worst nuclear power accident since Chernobyl, though.
That's not saying much, considering the competition. The IAEA rates nuclear events on a scale where level four is "Accident with Local Consequences"; the Fukushima situation is the only class five event involving an actual power station since Chernobyl in 1986, which makes it easy to be the "worst".
This is a serious accident, but so far it is no Chernobyl. There have been no deaths, no loss of reactor containment, and no release of long-lived radioactive material.
Is this like Three Mile Island?
There are similarities. So far, the radiactive material released into the environment is greater than that at TMI, but like TMI there have been no deaths. Also like TMI, regardless of the final result of this incident, the PR damage to the nuclear power industry will have been tremendous.
How do we know the Japanese government and TEPCO aren't lying?
When Chernobyl occurred, the Soviet government attempted to keep it quiet. They failed, in part because the nuclear material and radiation detection equipment at reactors adn universtities in other countries detected it. It is extremely difficult to keep these sort of accidents a secret.
The United States aircraft carrier Ronald Reagan is nuclear-powered, and therefore has all of the same detection equipment that a land-based reactor would have. It is currently offshore of Japan, and it has detected nothing to contradict the official statements from the Japanese government and TEPCO.
However, the fire at reactor #4's building was not reported for several hours. This has led many people both in Japan and abroad to question the accuracy of TEPCO's reporting to the government and news. In addition, the presence of spent fuel rods in reactor #4's building after a major disaster is disquieting, as one would normally expect that dangerous material would have been moved to safe storage at the first opportunity.
Faith in TEPCO's ability to handle the situation has been shaken, but they would be unable to hide any events resulting in the release of radioactive material. They know this and it seems unlikely that they would try.
Given the candor of the Japanese government given these events so far, including the Prime Minister's open admission of severe problems at Fukushima site one in conjunction with a plea to keep calm, it seems unlikely that they would deliberately lie about any future developments. Time will tell.
How can I keep up with developments?
Some outlets in the western media have been very bad about reporting this event, due to a combination of sensationalist reporting, ignorance, speculation, and the use of inexact or unexplained terminology. In many cases, the same network or newspaper will carry both solid reporting and sensationalism. There is no single reliable source.
Much of the information in this FAQ was taken from live press conferences and news reports, but the live translations provided by the western networks are not very reliable and unless you speak Japanese they are probably not going to he helpful.
The press releases at the TEPCO site were previously considered to be trustworthy, but recent events have added a level of doubt. In addition, this site is often unresponsive due to the immense traffic it is receiving.
Other organizations providing accurate news in English, although not necessarily in a timely manner, include the International Atomic Energy Agency, the The Japanese Nuclear and Industry Safety Agency, and the Japanese Prime Minister's office.
A twitter account run by the NE Asia Bureau Chief for Voice of America has proven to be useful.
Where can I find more information about these issues?
Reading:
•The Japanese Nuclear and Industry Safety Agency
•the Japanese Nuclear Safety Commission - nothing useful in English, sadly
•Tokyo Electric Power Company site with some press releases in English - currently hard to reach due to traffic
•Press conferences from Prime Minister's office - not all have been translated
•The International Atomic Energy Agency is providing regular announcements
•Timeline and data sheets for the incident by the Nuclear Energy Institute - the NEI is a policy organization for the American nuclear industry so their analyses may be biased
•Wikipedia on light water reactors and nuclear weapon design
•The United States Nuclear Regulatory Commission's Boiling Water Reactor (BWR) Systems manual - the Fukushima reactors are BWRs, a subset of LWRs
•More about BWRs
Video:
•"Physics for Future Presidents" lecture ten, on nuclear weapons and nuclear reactors - if you watch anything related to this event, watch this one
•Footage of the hydrogen explosion at reactor #1
Photos:
•before and after satellite photos of Fukushima site one
David Morton
Lifetime Supporter
Overnight Japan has asked the US Military for help with their Nuclear power plants and withdrawn their workers. Now they are dumping water from helicopters. The T.V. experts here WERE still saying it will be OK last night but now conceding the is a wide range of diverse issues and problems facing the authorities and engineers.
I think the experts have been gathered from "So you want to be on a show?"
ie they know very little and are guessing.
I think the experts have been gathered from "So you want to be on a show?"
ie they know very little and are guessing.
Pete McCluskey.
Lifetime Supporter
I'm hoping the press are exaggerating the risks, it is very hard to get a factual account with a World press that lives for ratings and where headlines like JAPAN FACES NUCLEAR HOLOCOST, MELTDOWN IMMINENT,
get higher ratings and sell more newspapers than, RADIATION THREAT VERY SMALL.
I see that workers have been let back into the area and am sure that would not happen if the radiation was life threatening.
Having said that I agree that the cause for nuclear power faces a huge set back, despite the fact that given the magnitude of the quake the the plants survived remarkably well.
get higher ratings and sell more newspapers than, RADIATION THREAT VERY SMALL.
I see that workers have been let back into the area and am sure that would not happen if the radiation was life threatening.
Having said that I agree that the cause for nuclear power faces a huge set back, despite the fact that given the magnitude of the quake the the plants survived remarkably well.
David Morton
Lifetime Supporter
Differing story here Pete, Sky news are saying workers are being withdrawn, More fire broke out in one of the buildings in the power station, Australian embassy, along with many other countries now, advising citizens to get out, Japanese Emperor appearing on TV, food and shelter shortages, long queues for every commodity, 20 KM total exclusion zone, Chinook dropping water - Sea water? (won't sit that well with stainless steel which is widely used in Nuclear Power Plants ) and a growing mistrust worldwide of any mention of Nuclear Power Stations.
It really sounds disastrous and in need of maximum help from the rest of the world.
It really sounds disastrous and in need of maximum help from the rest of the world.
Story is that the backup diesel generators that keep the pumps running for the water in the containment vessel were washed out to sea when the wave hit. Lots of talk here due to the fact there are two nuclear generating stations on either side of me. Darlington and Pickering. We have two systems of backup diesels and battery, should run the pumps for a week. Don't think they would run well after being submerged in 30FT of salt water.
Dave
Dave
Pete McCluskey.
Lifetime Supporter
Yes Tom, a remarkable difference in culture and attitude.
Indeed!!