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The truth is I didn't say Brown said that. I said "Brown thinks we have to share the blame because we export uranium to Japan". I doubt if there are any Greens who don't share this view. What is your angle?
Japan's turn
- Thread starter Sean K
- Start date
The truth is I didn't say Brown said that. I said "Brown thinks we have to share the blame because we export uranium to Japan". I doubt if there are any Greens who don't share this view. What is your angle?
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Great posts Agent M ..
In my opinion this is very bad situation..
I am out of all uranium stocks and into potash..
In my opinion this is very bad situation..
I am out of all uranium stocks and into potash..
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Would a 'thorium' powered reactor not have the current difficulties that Japan is experiencing now?
Sean K
Moderator
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Understandably uranium stocks pounded. Short term knee jerk imo. Pending how bad the fall out actually is... Do coal stocks crash every time there's a coal mine accident? Did gold crash when the Beaconsfield mine collapsed? Hmm, maybe a bit different situations. The nuclear fallout can cause quite a bit more damage can't it.
Looks like deaths are going to go into the 10s of thousands.
That family complaining the Aust Govt isn't doing enough about their missing family member is a bit tough. What else could we do?
Looks like deaths are going to go into the 10s of thousands.
That family complaining the Aust Govt isn't doing enough about their missing family member is a bit tough. What else could we do?
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I'd imagine they'll bounce back.
The coverage the situation at the plant is recieving is ridiculous.
Youl'd think another Chernoble was on the cards, when it's an impossibility.
No disaster here apart from that other one.
Yeah, that one.
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Spooly 74
I think the situation with the disintegrating nuclear power plants is far more dangerous than perhaps some members might realise. The Guardian offers quite a detailed insight into what is a rapidly deteriorating situation.
http://www.guardian.co.uk/world/2011/mar/14/japan-nuclear-fukushima-third-reactor
On an ongoing basis the effect of the loss of so much generating capacity on the Japanese economy looks bleak. There is talk of ongoing rolling power cuts. Not sure how this would affect many industrial and commercial operations. How do you keep a manufacturing plant going when power is cut for 2-3 hours ? What about offices and high rise buildings?. It's one thing to have rolling power cuts in struggling third world economies which often don't/can't have sophisticated manufacturing/commercial activities. That is not Japan.
And what about the Toyoko Electric and Power company? As far as I can see it is a dead man walking. I just cannot see how it can economically recover from this catastrophe. So which pension funds etc are going to take the massive loss? And how long can they continue to operate and in particular attempt to secure the power stations with drastically reduced power sales income and no future prospects? What will the financial fallout look like ? And at what stage will the company management cut their losses and walk away ?
Unfortunately this incident is highlighting what has always been the Achilles heel of nuclear power. While in theory the risk of a break down might be small the consequences will be absolutely catastrophic. We can be talking about poisoning thousand of square Klms for many hundreds of years That is a lot worse than simply the localised problems of a coal mine accident or a breakdown in a conventional power station. I think there is very good reason to reassess the rewards and risks of nuclear power.
And there is also one final point quite devastating point. If one of the reactors finally bursts in Japan it will inevitably trigger off the other reactors on the same site. Bit like one explosion in a munitions factory.
___________________________________________________________________________
Finally. If the Japanese economy does start to fail under the pressure of a disintegrating power supply, uncontrollable breakdowns in nuclear power stations and the consequences of the earthquake /tsunami what will be the effects on the rest of the world economy ?
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the japanese have decided its best to not display any radiation figures in the near vicinity, so everything is "under survey" ,, meaning its now censored!!
in light of the fact the number 2 reactor has just had an explosion inside the plant and its pressure dropped in the reactor itself, its evident the number 2 reactor has breached
radioactive material is now leaving the reactor and into the surrounding environment. it can be released into the ocean or can go into the atmosphere in the form of steam..
information is a repost from another forum
As a reference, based on background radiation measurements in the lower atmosphere at different altitudes above sea level up to 1100 m and over the land were made at a temperate latitude (40 °) in the Thessaloniki region, North Greece, before and after the Chernobyl accident (26 April 1986), using a portable γ-ray scintillation detector and a Cutie-pie survey meter with an ionization chamber, the average value of the total background radiation at ground level was 87 nGy h-1 (10.0 μR h-1, 25 cps), i.e. 60% from terrestrial radiation, 55 nGy h-1 (6.3 μR h-1, 15 cps) and 40% from cosmic radiation, 32 nGy h-1 (3.7 μR h-1, 10 cps), before the Chernobyl accident, while, after it, the total background radiation was doubled, due to the long-lived radioactive fallout suspended in the atmosphere and or deposited onto the ground.
in light of the fact the number 2 reactor has just had an explosion inside the plant and its pressure dropped in the reactor itself, its evident the number 2 reactor has breached
radioactive material is now leaving the reactor and into the surrounding environment. it can be released into the ocean or can go into the atmosphere in the form of steam..
information is a repost from another forum
As a reference, based on background radiation measurements in the lower atmosphere at different altitudes above sea level up to 1100 m and over the land were made at a temperate latitude (40 °) in the Thessaloniki region, North Greece, before and after the Chernobyl accident (26 April 1986), using a portable γ-ray scintillation detector and a Cutie-pie survey meter with an ionization chamber, the average value of the total background radiation at ground level was 87 nGy h-1 (10.0 μR h-1, 25 cps), i.e. 60% from terrestrial radiation, 55 nGy h-1 (6.3 μR h-1, 15 cps) and 40% from cosmic radiation, 32 nGy h-1 (3.7 μR h-1, 10 cps), before the Chernobyl accident, while, after it, the total background radiation was doubled, due to the long-lived radioactive fallout suspended in the atmosphere and or deposited onto the ground.
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The Age has an excellent article which explains the ongoing nature of the problem with the disintegrating nuclear power plants.
Just for a start it seems like the 200,000 people who had to evacuate from their homes won't be getting back for months if they have to keep venting radioactive steam.
http://www.theage.com.au/environment/a-growing-nuclear-dread-20110314-1bueo.html
Just for a start it seems like the 200,000 people who had to evacuate from their homes won't be getting back for months if they have to keep venting radioactive steam.
http://www.theage.com.au/environment/a-growing-nuclear-dread-20110314-1bueo.html
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That's hardly a detailed insight.
Agreed, maintaining power supply will be a big challenge.
Could just mean it's as described, Under Survey.
Below are some censored results.
18,000cpm is 300Bq which is equivalent to a fraction of our bodies naturally occuring radioactive material.
From the Age article
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Spooly my comments were made with regard to the unfolding nature of the breakdown of the nuclear reactors. Unfortunately this is now happening with confirmation that there has been a breach of at least one of the reactors containment vessels and a fire in another reactor.
In that sense there would be no comparison between the relatively limited escape of radioactivity in the last 24-48 hours and the amounts that could be vented in the near future.
I would have thought that simply logic would take anyone to the same conclusion. A catastrophic collapse of one reactor would almost certainly cause such damage in the immediate area it would have to compromise the other units. And remember every unit is currently unable to cool itself with the nuclear cores getting hotter and hotter.
In that sense there would be no comparison between the relatively limited escape of radioactivity in the last 24-48 hours and the amounts that could be vented in the near future.
I would have thought that simply logic would take anyone to the same conclusion. A catastrophic collapse of one reactor would almost certainly cause such damage in the immediate area it would have to compromise the other units. And remember every unit is currently unable to cool itself with the nuclear cores getting hotter and hotter.
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spooly74
you sound like your sceptical..
the whole place is going up in flames, and is being raised to the ground.. there is nothing that can be done,,
radioactive material is now spewing into the air
the disaster can lead to many many deaths from radiation poisoning
the situation is as bad as one could make it.. 3 reactors are basically critical, one burning, and one is full of MOX.. plutonium is in the fuel rods..
this is 100% a catastrophic emergency and disaster..
you sound like your sceptical..
the whole place is going up in flames, and is being raised to the ground.. there is nothing that can be done,,
radioactive material is now spewing into the air
the disaster can lead to many many deaths from radiation poisoning
the situation is as bad as one could make it.. 3 reactors are basically critical, one burning, and one is full of MOX.. plutonium is in the fuel rods..
this is 100% a catastrophic emergency and disaster..
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As you say, this is unfolding. We don't know what could happen yet.
The situation could get worse. High levels (8 times background radiation) were reported at the gates of a plant, but dropped minutes later, indicating some form of breach.
I'm not trying to play this down, just put it in perspective atm.
Some good news: All Fukushima No.2 plant reactors safely halted
I would have thought that simply logic would take anyone to the same conclusion. A catastrophic collapse of one reactor would almost certainly cause such damage in the immediate area it would have to compromise the other units. And remember every unit is currently unable to cool itself with the nuclear cores getting hotter and hotter.
That's not a realistic scenario. These aren't Russian reactors, or bombs.
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Latest I heard is it was still a level 4 on the INES scale.
Might have changed?
The scale is logarithmic.
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That really means, "Get the F*** Out of there if you haven't already. You'll glow the dark soon."
IFocus
You are arguing with a Galah
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It will be really heavy with the explosions they would have lost most of their instrumentation and with that the means of any sort of remote control over the process measurements, control valves etc.
It will inhibit them seeing WTF is really happening which is one possible reason for the lack of information on the status of the reactors simply because they wont know.
Also the warnings sound like to me that a deteriorating situation is expected.
It will inhibit them seeing WTF is really happening which is one possible reason for the lack of information on the status of the reactors simply because they wont know.
Also the warnings sound like to me that a deteriorating situation is expected.
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Yep.
I just saw an interview on the ABC with a English physics professor (who is on the board of the English Nuclear Oversight Committee) that said all of these Nuclear Power stations have back-up control rooms for these types of situations. However, if most of the instruments were blown off with these 2 explosions, it won't help much.
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Very strongly agreed.
Nothing that happens at a coal, oil, gas, hydro or other non-nuclear power station has this scale of impact. You won't be hearing of a 30km evacuation zone around a coal-fired plant anytime soon that's for sure.
Looking at the overall situation, I'm no expert on nuclear reactors but it seems to be a classic case of a bad situation that slowly but surely keeps getting worse. It's gone from a "safe shutdown" to "issues" to "releasing pressure" to "elevated levels of radiation but still safe" to the point where huge numbers of people now seem to be at health risk directly as a result of this plant.
The point at which this is the non-event that nuclear supporters keep harping on about has passed. Human health and the environment is now actually at real risk.
I have never been keen on nuclear power, always regarding it as the power source to be used only where coal, gas, hydro etc isn't available. Sadly, once again we seem to be learning the hard way about the reality that nothing man does is 100% guaranteed to be safe.
True, luckily last news are that situation improves.
Possibly others will learn how to do things better.
To me (outside bystander) it looks that there were not enough levels of emergency contingencies.
Pumps failed, OK, why didn't they have 2 more pump systems, or 3, or some other non pump one?
Possibly vacuum chambers to take up compressed steam?
Possibly plant was too powerful for safe containment should things go wrong.
I know economy of scale is important and few hundred MW is better than fraction of that, but maybe more smaller plants bit wider spaced would be better?
Possibly others will learn how to do things better.
To me (outside bystander) it looks that there were not enough levels of emergency contingencies.
Pumps failed, OK, why didn't they have 2 more pump systems, or 3, or some other non pump one?
Possibly vacuum chambers to take up compressed steam?
Possibly plant was too powerful for safe containment should things go wrong.
I know economy of scale is important and few hundred MW is better than fraction of that, but maybe more smaller plants bit wider spaced would be better?
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i guess there is concern on the latest fire in reactor number 4
also the government evoking article 15 on the various divisions and instrumentalities and government departments themselves.. news black out now..
this article may be of interest..
VERY INTERESTIN?G: Japan's Nuclear Situation
Written by Dr Josef Oehmen, research scientist at MIT:
I am writing this text (Mar 12) to give you some peace of mind regarding some of the troubles in Japan , that is the safety of Japan 's nuclear reactors. Up front, the situation is serious, but under control. And this text is long! But you will know more about nuclear power plants after reading it than all journalists on this planet put together.
There was and will *not* be any significant release of radioactivity.
By "significant" I mean a level of radiation of more than what you would receive on - say - a long distance flight, or drinking a glass of beer that comes from certain areas with high levels of natural background radiation.
I have been reading every news release on the incident since the earthquake. There has not been one single (!) report that was accurate and free of errors (and part of that problem is also a weakness in the Japanese crisis communication). By "not free of errors" I do not refer to tendentious anti-nuclear journalism - that is quite normal these days. By "not free of errors" I mean blatant errors regarding physics and natural law, as well as gross misinterpretation of facts, due to an obvious lack of fundamental and basic understanding of the way nuclear reactors are build and operated. I have read a 3 page report on CNN where every single paragraph contained an error.
We will have to cover some fundamentals, before we get into what is going on.
Construction of the Fukushima nuclear power plants
The plants at Fukushima are so called Boiling Water Reactors, or BWR for short. Boiling Water Reactors are similar to a pressure cooker. The nuclear fuel heats water, the water boils and creates steam, the steam then drives turbines that create the electricity, and the steam is then cooled and condensed back to water, and the water send back to be heated by the nuclear fuel. The pressure cooker operates at about 250 ?C.
The nuclear fuel is uranium oxide. Uranium oxide is a ceramic with a very high melting point of about 3000 ?C. The fuel is manufactured in pellets (think little cylinders the size of Lego bricks). Those pieces are then put into a long tube made of Zircaloy with a melting point of 2200 ?C, and sealed tight. The assembly is called a fuel rod. These fuel rods are then put together to form larger packages, and a number of these packages are then put into the reactor. All these packages together are referred to as "the core".
The Zircaloy casing is the first containment. It separates the radioactive fuel from the rest of the world.
The core is then placed in the "pressure vessels". That is the pressure cooker we talked about before. The pressure vessels is the second containment. This is one sturdy piece of a pot, designed to safely contain the core for temperatures several hundred ?C. That covers the scenarios where cooling can be restored at some point.
The entire "hardware" of the nuclear reactor - the pressure vessel and all pipes, pumps, coolant (water) reserves, are then encased in the third containment. The third containment is a hermetically (air tight) sealed, very thick bubble of the strongest steel and concrete. The third containment is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown. For that purpose, a large and thick concrete basin is cast under the pressure vessel (the second containment), all inside the third containment. This is the so-called "core catcher". If the core melts and the pressure vessel bursts (and eventually melts), it will catch the molten fuel and everything else. It is typically built in such a way that the nuclear fuel will be spread out, so it can cool down.
This third containment is then surrounded by the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. (this is the part that was damaged in the explosion, but more to that later).
Fundamentals of nuclear reactions
The uranium fuel generates heat by nuclear fission. Big uranium atoms are split into smaller atoms. That generates heat plus neutrons (one of the particles that forms an atom). When the neutron hits another uranium atom, that splits, generating more neutrons and so on. That is called the nuclear chain reaction.
Now, just packing a lot of fuel rods next to each other would quickly lead to overheating and after about 45 minutes to a melting of the fuel rods. It is worth mentioning at this point that the nuclear fuel in a reactor can *never* cause a nuclear explosion the type of a nuclear bomb. Building a nuclear bomb is actually quite difficult (ask Iran ). In Chernobyl , the explosion was caused by excessive pressure buildup, hydrogen explosion and rupture of all containments, propelling molten core material into the environment (a "dirty bomb"). Why that did not and will not happen in Japan , further below.
In order to control the nuclear chain reaction, the reactor operators use so-called "control rods". The control rods absorb the neutrons and kill the chain reaction instantaneously. A nuclear reactor is built in such a way, that when operating normally, you take out all the control rods. The coolant water then takes away the heat (and converts it into steam and electricity) at the same rate as the core produces it. And you have a lot of leeway around the standard operating point of 250?C.
The challenge is that after inserting the rods and stopping the chain reaction, the core still keeps producing heat. The uranium "stopped" the chain reaction. But a number of intermediate radioactive elements are created by the uranium during its fission process, most notably Cesium and Iodine isotopes, i.e. radioactive versions of these elements that will eventually split up into smaller atoms and not be radioactive anymore. Those elements keep decaying and producing heat. Because they are not regenerated any longer from the uranium (the uranium stopped decaying after the control rods were put in), they get less and less, and so the core cools down over a matter of days, until those intermediate radioactive elements are used up.
This residual heat is causing the headaches right now.
So the first "type" of radioactive material is the uranium in the fuel rods, plus the intermediate radioactive elements that the uranium splits into, also inside the fuel rod (Cesium and Iodine).
There is a second type of radioactive material created, outside the fuel rods. The big main difference up front: Those radioactive materials have a very short half-life, that means that they decay very fast and split into non-radioactive materials. By fast I mean seconds. So if these radioactive materials are released into the environment, yes, radioactivity was released, but no, it is not dangerous, at all. Why? By the time you spelled "R-A-D-I-O-N-U-C-L-I-D-E", they will be harmless, because they will have split up into non radioactive elements. Those radioactive elements are N-16, the radioactive isotope (or version) of nitrogen (air). The others are noble gases such as Argon. But where do they come from? When the uranium splits, it generates a neutron (see above). Most of these neutrons will hit other uranium atoms and keep the nuclear chain reaction going. But some will leave the fuel rod and hit the water molecules, or the air that is in the water. Then, a non-radioactive element can "capture" the neutron. It becomes radioactive. As described above, it will quickly (seconds) get rid again of the neutron to return to its former beautiful self.
This second "type" of radiation is very important when we talk about the radioactivity being released into the environment later on.
What happened at Fukushima
I will try to summarize the main facts. The earthquake that hit Japan was 5 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 5 times, not 0.7). So the first hooray for Japanese engineering, everything held up.
When the earthquake hit with 8.9, the nuclear reactors all went into automatic shutdown. Within seconds after the earthquake started, the control rods had been inserted into the core and nuclear chain reaction of the uranium stopped. Now, the cooling system has to carry away the residual heat. The residual heat load is about 3% of the heat load under normal operating conditions.
The earthquake destroyed the external power supply of the nuclear reactor. That is one of the most serious accidents for a nuclear power plant, and accordingly, a "plant black out" receives a lot of attention when designing backup systems. The power is needed to keep the coolant pumps working. Since the power plant had been shut down, it cannot produce any electricity by itself any more.
http://ansnuclearcafe.org/2011/03/11/media-updates-on-nuclear-power-stations-in-japan/
also the government evoking article 15 on the various divisions and instrumentalities and government departments themselves.. news black out now..
this article may be of interest..
VERY INTERESTIN?G: Japan's Nuclear Situation
Written by Dr Josef Oehmen, research scientist at MIT:
I am writing this text (Mar 12) to give you some peace of mind regarding some of the troubles in Japan , that is the safety of Japan 's nuclear reactors. Up front, the situation is serious, but under control. And this text is long! But you will know more about nuclear power plants after reading it than all journalists on this planet put together.
There was and will *not* be any significant release of radioactivity.
By "significant" I mean a level of radiation of more than what you would receive on - say - a long distance flight, or drinking a glass of beer that comes from certain areas with high levels of natural background radiation.
I have been reading every news release on the incident since the earthquake. There has not been one single (!) report that was accurate and free of errors (and part of that problem is also a weakness in the Japanese crisis communication). By "not free of errors" I do not refer to tendentious anti-nuclear journalism - that is quite normal these days. By "not free of errors" I mean blatant errors regarding physics and natural law, as well as gross misinterpretation of facts, due to an obvious lack of fundamental and basic understanding of the way nuclear reactors are build and operated. I have read a 3 page report on CNN where every single paragraph contained an error.
We will have to cover some fundamentals, before we get into what is going on.
Construction of the Fukushima nuclear power plants
The plants at Fukushima are so called Boiling Water Reactors, or BWR for short. Boiling Water Reactors are similar to a pressure cooker. The nuclear fuel heats water, the water boils and creates steam, the steam then drives turbines that create the electricity, and the steam is then cooled and condensed back to water, and the water send back to be heated by the nuclear fuel. The pressure cooker operates at about 250 ?C.
The nuclear fuel is uranium oxide. Uranium oxide is a ceramic with a very high melting point of about 3000 ?C. The fuel is manufactured in pellets (think little cylinders the size of Lego bricks). Those pieces are then put into a long tube made of Zircaloy with a melting point of 2200 ?C, and sealed tight. The assembly is called a fuel rod. These fuel rods are then put together to form larger packages, and a number of these packages are then put into the reactor. All these packages together are referred to as "the core".
The Zircaloy casing is the first containment. It separates the radioactive fuel from the rest of the world.
The core is then placed in the "pressure vessels". That is the pressure cooker we talked about before. The pressure vessels is the second containment. This is one sturdy piece of a pot, designed to safely contain the core for temperatures several hundred ?C. That covers the scenarios where cooling can be restored at some point.
The entire "hardware" of the nuclear reactor - the pressure vessel and all pipes, pumps, coolant (water) reserves, are then encased in the third containment. The third containment is a hermetically (air tight) sealed, very thick bubble of the strongest steel and concrete. The third containment is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown. For that purpose, a large and thick concrete basin is cast under the pressure vessel (the second containment), all inside the third containment. This is the so-called "core catcher". If the core melts and the pressure vessel bursts (and eventually melts), it will catch the molten fuel and everything else. It is typically built in such a way that the nuclear fuel will be spread out, so it can cool down.
This third containment is then surrounded by the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. (this is the part that was damaged in the explosion, but more to that later).
Fundamentals of nuclear reactions
The uranium fuel generates heat by nuclear fission. Big uranium atoms are split into smaller atoms. That generates heat plus neutrons (one of the particles that forms an atom). When the neutron hits another uranium atom, that splits, generating more neutrons and so on. That is called the nuclear chain reaction.
Now, just packing a lot of fuel rods next to each other would quickly lead to overheating and after about 45 minutes to a melting of the fuel rods. It is worth mentioning at this point that the nuclear fuel in a reactor can *never* cause a nuclear explosion the type of a nuclear bomb. Building a nuclear bomb is actually quite difficult (ask Iran ). In Chernobyl , the explosion was caused by excessive pressure buildup, hydrogen explosion and rupture of all containments, propelling molten core material into the environment (a "dirty bomb"). Why that did not and will not happen in Japan , further below.
In order to control the nuclear chain reaction, the reactor operators use so-called "control rods". The control rods absorb the neutrons and kill the chain reaction instantaneously. A nuclear reactor is built in such a way, that when operating normally, you take out all the control rods. The coolant water then takes away the heat (and converts it into steam and electricity) at the same rate as the core produces it. And you have a lot of leeway around the standard operating point of 250?C.
The challenge is that after inserting the rods and stopping the chain reaction, the core still keeps producing heat. The uranium "stopped" the chain reaction. But a number of intermediate radioactive elements are created by the uranium during its fission process, most notably Cesium and Iodine isotopes, i.e. radioactive versions of these elements that will eventually split up into smaller atoms and not be radioactive anymore. Those elements keep decaying and producing heat. Because they are not regenerated any longer from the uranium (the uranium stopped decaying after the control rods were put in), they get less and less, and so the core cools down over a matter of days, until those intermediate radioactive elements are used up.
This residual heat is causing the headaches right now.
So the first "type" of radioactive material is the uranium in the fuel rods, plus the intermediate radioactive elements that the uranium splits into, also inside the fuel rod (Cesium and Iodine).
There is a second type of radioactive material created, outside the fuel rods. The big main difference up front: Those radioactive materials have a very short half-life, that means that they decay very fast and split into non-radioactive materials. By fast I mean seconds. So if these radioactive materials are released into the environment, yes, radioactivity was released, but no, it is not dangerous, at all. Why? By the time you spelled "R-A-D-I-O-N-U-C-L-I-D-E", they will be harmless, because they will have split up into non radioactive elements. Those radioactive elements are N-16, the radioactive isotope (or version) of nitrogen (air). The others are noble gases such as Argon. But where do they come from? When the uranium splits, it generates a neutron (see above). Most of these neutrons will hit other uranium atoms and keep the nuclear chain reaction going. But some will leave the fuel rod and hit the water molecules, or the air that is in the water. Then, a non-radioactive element can "capture" the neutron. It becomes radioactive. As described above, it will quickly (seconds) get rid again of the neutron to return to its former beautiful self.
This second "type" of radiation is very important when we talk about the radioactivity being released into the environment later on.
What happened at Fukushima
I will try to summarize the main facts. The earthquake that hit Japan was 5 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 5 times, not 0.7). So the first hooray for Japanese engineering, everything held up.
When the earthquake hit with 8.9, the nuclear reactors all went into automatic shutdown. Within seconds after the earthquake started, the control rods had been inserted into the core and nuclear chain reaction of the uranium stopped. Now, the cooling system has to carry away the residual heat. The residual heat load is about 3% of the heat load under normal operating conditions.
The earthquake destroyed the external power supply of the nuclear reactor. That is one of the most serious accidents for a nuclear power plant, and accordingly, a "plant black out" receives a lot of attention when designing backup systems. The power is needed to keep the coolant pumps working. Since the power plant had been shut down, it cannot produce any electricity by itself any more.
http://ansnuclearcafe.org/2011/03/11/media-updates-on-nuclear-power-stations-in-japan/
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Things were going well for an hour. One set of multiple sets of emergency Diesel power generators kicked in and provided the electricity that was needed. Then the Tsunami came, much bigger than people had expected when building the power plant (see above, factor 7). The tsunami took out all multiple sets of backup Diesel generators.
When designing a nuclear power plant, engineers follow a philosophy called "Defense of Depth". That means that you first build everything to withstand the worst catastrophe you can imagine, and then design the plant in such a way that it can still handle one system failure (that you thought could never happen) after the other. A tsunami taking out all backup power in one swift strike is such a scenario. The last line of defense is putting everything into the third containment (see above), that will keep everything, whatever the mess, control rods in our out, core molten or not, inside the reactor.
When the diesel generators were gone, the reactor operators switched to emergency battery power. The batteries were designed as one of the backups to the backups, to provide power for cooling the core for 8 hours. And they did.
Within the 8 hours, another power source had to be found and connected to the power plant. The power grid was down due to the earthquake. The diesel generators were destroyed by the tsunami. So mobile diesel generators were trucked in.
This is where things started to go seriously wrong. The external power generators could not be connected to the power plant (the plugs did not fit). So after the batteries ran out, the residual heat could not be carried away any more.
At this point the plant operators begin to follow emergency procedures that are in place for a "loss of cooling event". It is again a step along the "Depth of Defense" lines. The power to the cooling systems should never have failed completely, but it did, so they "retreat" to the next line of defense. All of this, however shocking it seems to us, is part of the day-to-day training you go through as an operator, right through to managing a core meltdown.
It was at this stage that people started to talk about core meltdown. Because at the end of the day, if cooling cannot be restored, the core will eventually melt (after hours or days), and the last line of defense, the core catcher and third containment, would come into play.
But the goal at this stage was to manage the core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (our pressure cooker) remain intact and operational for as long as possible, to give the engineers time to fix the cooling systems.
Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Which one failed when or did not fail is not clear at this point in time.
So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200?C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has 11 pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was about 550?C.
This is when the reports about "radiation leakage" starting coming in. I believe I explained above why venting the steam is theoretically the same as releasing radiation into the environment, but why it was and is not dangerous. The radioactive nitrogen as well as the noble gases do not pose a threat to human health.
At some stage during this venting, the explosion occurred. The explosion took place outside of the third containment (our "last line of defense"), and the reactor building. Remember that the reactor building has no function in keeping the radioactivity contained. It is not entirely clear yet what has happened, but this is the likely scenario: The operators decided to vent the steam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in the steam more time to subside). The problem is that at the high temperatures that the core had reached at this stage, water molecules can "disassociate" into oxygen and hydrogen - an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel (because it was badly designed and not managed properly by the operators) that lead to the explosion of Chernobyl . This was never a risk at Fukushima . The problem of hydrogen-oxygen formation is one of the biggies when you design a power plant (if you are not Soviet, that is), so the reactor is build and operated in a way it cannot happen inside the containment. It happened outside, which was not intended but a possible scenario and OK, because it did not pose a risk for the containment.
So the pressure was under control, as steam was vented. Now, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts will reach the critical temperature of 2200 ?C after about 45 minutes. This is when the first containment, the Zircaloy tube, would fail.
And this started to happen. The cooling could not be restored before there was some (very limited, but still) damage to the casing of some of the fuel. The nuclear material itself was still intact, but the surrounding Zircaloy shell had started melting. What happened now is that some of the byproducts of the uranium decay - radioactive Cesium and Iodine - started to mix with the steam. The big problem, uranium, was still under control, because the uranium oxide rods were good until 3000 ?C. It is confirmed that a very small amount of Cesium and Iodine was measured in the steam that was released into the atmosphere.
It seems this was the "go signal" for a major plan B. The small amounts of Cesium that were measured told the operators that the first containment on one of the rods somewhere was about to give. The Plan A had been to restore one of the regular cooling systems to the core. Why that failed is unclear. One plausible explanation is that the tsunami also took away / polluted all the clean water needed for the regular cooling systems.
The water used in the cooling system is very clean, demineralized (like distilled) water. The reason to use pure water is the above mentioned activation by the neutrons from the Uranium: Pure water does not get activated much, so stays practically radioactive-free. Dirt or salt in the water will absorb the neutrons quicker, becoming more radioactive. This has no effect whatsoever on the core - it does not care what it is cooled by. But it makes life more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water.
http://ansnuclearcafe.org/2011/03/11/media-updates-on-nuclear-power-stations-in-japan/
When designing a nuclear power plant, engineers follow a philosophy called "Defense of Depth". That means that you first build everything to withstand the worst catastrophe you can imagine, and then design the plant in such a way that it can still handle one system failure (that you thought could never happen) after the other. A tsunami taking out all backup power in one swift strike is such a scenario. The last line of defense is putting everything into the third containment (see above), that will keep everything, whatever the mess, control rods in our out, core molten or not, inside the reactor.
When the diesel generators were gone, the reactor operators switched to emergency battery power. The batteries were designed as one of the backups to the backups, to provide power for cooling the core for 8 hours. And they did.
Within the 8 hours, another power source had to be found and connected to the power plant. The power grid was down due to the earthquake. The diesel generators were destroyed by the tsunami. So mobile diesel generators were trucked in.
This is where things started to go seriously wrong. The external power generators could not be connected to the power plant (the plugs did not fit). So after the batteries ran out, the residual heat could not be carried away any more.
At this point the plant operators begin to follow emergency procedures that are in place for a "loss of cooling event". It is again a step along the "Depth of Defense" lines. The power to the cooling systems should never have failed completely, but it did, so they "retreat" to the next line of defense. All of this, however shocking it seems to us, is part of the day-to-day training you go through as an operator, right through to managing a core meltdown.
It was at this stage that people started to talk about core meltdown. Because at the end of the day, if cooling cannot be restored, the core will eventually melt (after hours or days), and the last line of defense, the core catcher and third containment, would come into play.
But the goal at this stage was to manage the core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (our pressure cooker) remain intact and operational for as long as possible, to give the engineers time to fix the cooling systems.
Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Which one failed when or did not fail is not clear at this point in time.
So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200?C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has 11 pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was about 550?C.
This is when the reports about "radiation leakage" starting coming in. I believe I explained above why venting the steam is theoretically the same as releasing radiation into the environment, but why it was and is not dangerous. The radioactive nitrogen as well as the noble gases do not pose a threat to human health.
At some stage during this venting, the explosion occurred. The explosion took place outside of the third containment (our "last line of defense"), and the reactor building. Remember that the reactor building has no function in keeping the radioactivity contained. It is not entirely clear yet what has happened, but this is the likely scenario: The operators decided to vent the steam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in the steam more time to subside). The problem is that at the high temperatures that the core had reached at this stage, water molecules can "disassociate" into oxygen and hydrogen - an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel (because it was badly designed and not managed properly by the operators) that lead to the explosion of Chernobyl . This was never a risk at Fukushima . The problem of hydrogen-oxygen formation is one of the biggies when you design a power plant (if you are not Soviet, that is), so the reactor is build and operated in a way it cannot happen inside the containment. It happened outside, which was not intended but a possible scenario and OK, because it did not pose a risk for the containment.
So the pressure was under control, as steam was vented. Now, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts will reach the critical temperature of 2200 ?C after about 45 minutes. This is when the first containment, the Zircaloy tube, would fail.
And this started to happen. The cooling could not be restored before there was some (very limited, but still) damage to the casing of some of the fuel. The nuclear material itself was still intact, but the surrounding Zircaloy shell had started melting. What happened now is that some of the byproducts of the uranium decay - radioactive Cesium and Iodine - started to mix with the steam. The big problem, uranium, was still under control, because the uranium oxide rods were good until 3000 ?C. It is confirmed that a very small amount of Cesium and Iodine was measured in the steam that was released into the atmosphere.
It seems this was the "go signal" for a major plan B. The small amounts of Cesium that were measured told the operators that the first containment on one of the rods somewhere was about to give. The Plan A had been to restore one of the regular cooling systems to the core. Why that failed is unclear. One plausible explanation is that the tsunami also took away / polluted all the clean water needed for the regular cooling systems.
The water used in the cooling system is very clean, demineralized (like distilled) water. The reason to use pure water is the above mentioned activation by the neutrons from the Uranium: Pure water does not get activated much, so stays practically radioactive-free. Dirt or salt in the water will absorb the neutrons quicker, becoming more radioactive. This has no effect whatsoever on the core - it does not care what it is cooled by. But it makes life more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water.
http://ansnuclearcafe.org/2011/03/11/media-updates-on-nuclear-power-stations-in-japan/
