ACCORDING to US nuclear expert, Mark Mervine, the Fukushima Daiichi nuclear power plant withstood the earthquake but the tsunami destroyed its backup power which is necessary for cooling the reactor. The situation is critical. Furthermore, there are another five reactors at that site that were in commercial operation.
Following is an extract from an interview recorded by Mr Mervine’s daughter, Eveyln.
Q: I guess the big question that everyone has today is, has the explosion or any of the damage, I guess there hasn’t been a lot of damage to the plant, it’s just overheating, do you think any of this is causing nuclear leakage and if so, is that a big problem?
A: So, I‘ve actually looked at the before and after picture from the explosion that’s available on the news and, in my opinion, they have an extremely serious situation at this nuclear power plant. So, my speculation is they were venting the steam in order to try and cool the reactor, unfortunately, without power they don’t have a lot of their normal instrumentation that they would have.
Q: So they can’t monitor things to the same degree –
A: They don’t even have their backup power, I mean they basically have the bare minimum of instrumentation provided by whatever battery power they have left. My guess is, and it was reported in the news that they had a hydrogen explosion, so they obviously had hydrogen and other gases that were generated, that built up to an explosive level and if you look at the photos the entire building surrounding the reactor, the only thing left of it is the steel frame, the whole building has collapsed. That would normally be called the auxiliary building, and that building actually does house a lot of the emergency systems for the reactor. So I think we have a very very serious situation at this power plant where the entire auxiliary building has been destroyed.
According to reports, the containment is intact, so if there has been any release of radioactivity, it has been very minor, to this point, but they have got to find a way to get some electricity, and cool that reactor. And the last report I saw said that there plan was to use seawater. So obviously, they’re going to get some temporary pumps, they’re going to use seawater, mixed with boron. Boron is a substance that will absorb neutrons, very similar to borax that you could go buy to wash your clothes with, that will keep the reactor from going critical again when they add the cold seawater. Even though the control rods have been fully inserted, when you add cold water, cold water is denser than warm water, and it can cause the neutrons that are still bouncing around the reactor to moderate, to a speed at which, (so moderate means slow down), they could strike the fuel and cause a fission.
We obviously don’t want any more fission because that generates more heat and we certainly don’t want the reactor to go critical because that generates a lot of heat. And, critical is not the bad word that you see in the news, where you say “Oh, reactor’s going critical!”; when it operates, it’s normally critical; all critical means is it has a self sustaining reaction, which is what you need to operate. What we wouldn’t want it to do is to go to a terminology called super-critical, that would be really bad. But in any event, when you add the cold water and you don’t add the boron, then you have the potential of causing the fission level to go up in the reactor and more heat to be generated, which you don’t want to do. This is beyond the last resort, to do this, at a nuclear plant.
Q: To use sea water to cool it –
A: I think they’re basically down to their last option here.
Q: So what do you think is the best case scenario for this plant, and added to that question, what is the worst case scenario?
A: I think the best case is that the military get the generators on-site with some emergency pumps and they’re able to rig up a cooling system to cool that reactor, to keep it cool, and they’ll have to cool it for several days before it gets to the point where the heat is decayed off. Obviously the plant is destroyed, and I’m sure it will have to be decommissioned. The question is how much additional damage is there at the site, because, there’s actually six nuclear reactors at that same site and two more that were planned or are under construction.
Q: I see, so this is just one that’s been failing.
A: This is just one of six reactors at that site that were in commercial operation.
Q: Oh that’s scary, so that there could be trouble with the other ones.
A: The question is, as a result of this explosion – has any damage occurred in any of the other, adjacent, reactors and also what is the situation of the additional reactors?
Q: Right, if they don’t cool them, it seems like this same thing could happen to them.
And also from the same interview…
And, that plant was automatically shut down, when the earthquake occurred, and for about the first hour, they were running on their diesel generator. Once a plant shuts down, it has two ways to get electricity, one is from the grid, and another is from emergency diesel generators that they have on site. In this case, because of the magnitude of the earthquake, the grid basically went dark, so they were operating on their diesel generators and everything was functioning as it should be. But then, based on news reports, about an hour after the earthquake and the shutdown, the tsunami hit, and flooded the plant, where the diesel generators were, and that caused them to lose their diesel generator power and reduced them to their emergency battery backup power only.
Q: And that wasn’t quite enough to have the cooling capability that they needed?
A: The emergency backup on the batteries gives them, you know, very very limited capabilities, so they were having a very difficult time keeping the plant cool.
Q: Do they sort of have to go to a smaller cooling system, smaller pumps and that sort of thing, that can be run off of their battery?
A: I don’t know the specifics of that plant and what they might have done in Japan. Obviously, Japan being in an earthquake zone probably had additional requirements for the plant that we wouldn’t have to have in other places around the world. But, in any event, based on news reports, they did have some type of cooling capability using their battery power, the problem of course is, the batteries are only good for a few hours.
Q: Yeah, the news reports said that the Japanese military was actually trying to get in replacement batteries to cool the plant, I’m sure they’ve continued that effort but I haven’t heard any update on that in the news.
A: So, the reports that I saw on the news said exactly that, they were trying to supply the plant with additional batteries and a portable diesel generator.
Q: Right, I hope they’re successful soon. So how are nuclear power plants in general built to withstand earthquakes and tsunamis? You may not know about this, since you work on power plants that are in more tectonically stable regions, but are there some specific requirements for natural disasters?
A: There are, and depending on what the worst case scenario would be anticipated for an earthquake, their requirements are different. So probably the best example I could give is, I once participated in an inspection of the Trojan nuclear power plant which was in Oregon. That plant has been shut down now, but compared to the plants that I had worked in Wisconsin and in Vermont they had a lot more requirements on them for earthquake protection. So the way you do that, there is a lot more supports for all the equipment, all kinds of hydraulic dampeners which allow the equipment to move back and forth without breaking. I know in Japan they have a requirement that all the plants have to be built on bedrock, so, they actually have to go down to bedrock in order to begin to build the supports of the plant. So, yeah, there’s numerous precautions that are taken and, like I said, there were probably additional backup system requirements that were required by the Japanese government, for those plants, being in an earthquake zone.
Q: Yeah but this was just such an enormous earthquake, I mean, I don’t think they’re released the official report yet, but this is probably in top five biggest earthquakes so even if they prepared for the absolute worst, this is something that really stressed all of their systems and backups, I imagine.
A: Well, I think really the key here was not so much the earthquake. By all reports, the plants functioned exactly as they were supposed to do in the earthquake, they shut down automatically, when the grid was lost their diesel generators started, and everything was fine. What really put us in the situation we’re in now is the tsunami as a result of the earthquake, but not the earthquake itself.
Read more here: http://skepchick.org/2011/03/a-conversation-with-my-dad-a-nuclear-engineer-about-the-fukushima-daiichi-nuclear-power-plant-disaster-in-japan/
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Well, either way it’s wrecked- and dangerous. I wonder how safe the next nuke they build at Fukushima will be? Mind you, they probably need a quake on the scale of this one or Sendai 1931, or the Great Kanto quake of the early twenties, but with some real half wittedness they might still be able to create a new Chernobyl, the next time ’round.
It seems like reactor No. 2 is leaking as they resume seawater injections and this is preventing to seawater from fully covering the rods.
One thing we can be sure of though, regardless of the outcome and how disaster proof this 40 yo plant and any modern replacement may be, it will generate bulk nuclear bed wetters for generations to come.
I’ve pasted this comment on Climate Conv Group today http://www.climateconversation.wordshine.co.nz/2011/03/nuclear-reactor-blast-impossible-meltdown-no-sweat/
update from my previous link http://bravenewclimate.com/2011/03/15/fukushima-15-march-summary/
Unit 2: This is now of most concern, and the situation continues to change quickly. Here is the key information to hand (I will update as new data emerges).
Loud noises were heard at Fukushima Daiichi 2 at 6.10am this morning. A major component beneath the reactor is confirmed to be damaged. Evacuation to 20 kilometres is being completed, while a fire on site has now been put out.
Confirmation of loud sounds at unit 2 this morning came from the Nuclear and Industrial Safety Agency (NISA). It noted that “the suppression chamber may be damaged.” It is not clear that the sounds were explosions.
The pressure in the pool was seen to decrease from three atmospheres to one atmosphere after the noise, suggesting possible damage. Radiation levels on the edge of the plant compound briefly spiked at 8217 microsieverts per hour but later fell to about a third that.
A close watch is being kept on the radiation levels to ascertain the status of containment. As a precaution Tokyo Electric Power Company has evacuated all non-essential personnel from the unit. The company’s engineers continue to pump seawater into the reactor pressure vessel in an effort to cool it.
Evacuation ordered
Prime minister Naoto Kan has requested that evacuation from 20 kilometer radius is completed and those between 20-30 kilometers should stay indoors. He said his advice related to the overall picture of safety developments at Fukushima Daiichi, rather than those at any individual reactor unit.
Shortly afterwards Noriyuki Shikata said radiation levels near the reactors had reached levels that would affect human health. It is thought that the fire had been the major source of radiation.
Prime minister Naoto Kan has requested that everyone withdraw from a 30 kilometer evacuation zone around the nuclear power plant and that people that stay within remain indoors. He said his advice related to the overall picture of safety developments at Fukushima Daiichi, rather than those at any individual reactor unit.
Regarding radiation levels: It is very important to distinguish between doses from the venting of noble-gas fission products, which rapidly dissipate and cause no long-term contamination or ingestion hazard, and aerosols of other fission products including cesium and iodine.
From NEI:
Yukio Edano, Japan’s Chief Cabinet Secretary, during a live press conference at 10 p.m. EDT, said there is a fire at Fukushima Daiichi 4 that is accompanied by high levels of radiation between Units 3 and 4 at the site. The fire began burning at Unit 4 at around 6 a.m. Japan time on March 14 and is still burning. Fire fighters are responding to the fire. The reactor does not have fuel in the reactor, but there is spent fuel in the reactor (pool) and Edano said that he assumes radioactive substances are being released. “The substances are coming out from the No. 4 reactor and we are making the utmost effort to put out the first and also cool down the No. 4 reactor (pool).”
Edano said that a blast was heard this morning at Unit 2 at about 6:30 a.m. A hole was observed in the number 2 reactor and he said there is very little possibility that an explosion will occur at Unit 2.
“The part of the suppression chamber seems to have caused the blast,” Edano said. A small amount of radioactive substance seems to have been released to the outside.
TEPCO workers continue to pump sea water at 1, 2 and 3 reactors. “The biggest problem is how to maintain the cooling and how to contain the fire at No. 4.” At 10:22 a.m. Japan time, the radiation level between units 2 and 3 were as high as 40 rem per hour. “We are talking about levels that can impact human health.” Edano said.
Of the 800 staff that remained at the power plant, all but 50 who are directly involved in pumping water into the reactor have been evacuated.
More updates to the above as the fog of uncertainty begins to clear…
———————————
Finally, a telling comment from a friend of mine in the US nuclear research community:
The lesson so far: Japan suffered an earthquake and tsunami of unprecedented proportion that has caused unbelievable damage to every part of their infrastructure, and death of very large numbers of people. The media have chosen to report the damage to a nuclear plant which was, and still is, unlikely to harm anyone. We won’t know for sure, of course, until the last measure to assure cooling is put in place, but that’s the likely outcome. You’d never know it from the parade of interested anti-nuclear activists identified as “nuclear experts” on TV.
From the early morning Saturday nuclear activists were on TV labelling this ‘the third worst nuclear accident ever’. This was no accident, this was damage caused by truly one of the worst of earthquakes and tsunamis ever. (The reported sweeping away of four entire trains, including a bullet train which apparently disappeared without a trace, was not labelled “the third worst train accident ever.”) An example of the reporting: A fellow from one of the universities, and I didn’t note which one, obviously an engineer and a knowlegable one, was asked a question and began to explain quite sensibly what was likely. He was cut off after about a minute, maybe less, and an anti-nuke, very glib, and very poorly informed, was brought on. With ponderous solemnity, he then made one outrageous and incorrect statement after another. He was so good at it they held him over for another segment
The second lesson is to the engineers: We all know that the water reactor has one principal characteristic when it shuts down that has to be looked after. It must have water to flow around the fuel rods and be able to inject it into the reactor if some is lost by a sticking relief valve or from any other cause – for this, it must have backup power to power the pumps and injection systems.
The designers apparently could not imagine a tsunami of these proportions and the backup power — remember, the plants themselves produce power, power is brought in by multiple outside power lines, there are banks of diesels to produce backup power, and finally, banks of batteries to back that up, all were disabled. There’s still a lot the operators can do, did and are doing. But reactors were damaged and may not have needed to be even by this unthinkable earthquake if they had designed the backup power systems to be impregnable, not an impossible thing for an engineer to do. So we have damage that probably could have been avoided, and reporting of almost stunning inaccuracy and ignorance.Still, the odds are that no one will be hurt from radioactivity — a few workers from falling or in the hydrogen explosions, but tiny on the scale of the damage and killing around it.
It seems pathetic that Russia should be the only reported adult in this — they’re quoted as saying “Of course our nuclear program is not going to be affected by an earthquake in Japan.” Japan has earthquakes.
That’s the end of the quote – from a personal level this is the worst natural disaster that I remember in my lifetime; commiserations to all our Japanese friends and I’m looking for a site where I can donate
the best site I’ve found to keep up to date is http://bravenewclimate.com/2011/03/15/fukushima-15-march-summary/
updates are available on links to the right
and for overall background
http://www.climateconversation.wordshine.co.nz/2011/03/nuclear-reactor-blast-impossible-meltdown-no-sweat/
“Defense of Depth”
http://www.businessinsider.com/japan-reactors-pose-no-risk-2011-3-1
http://mitnse.com/
You Can STOP WORRYING ABOUT A RADIATION DISASTER IN JAPAN — Here’s Why
written by Dr. Josef Oehmen, a research scientist at MIT.
I repeat, there was and will not be any significant release of radioactivity from the damaged Japanese reactors.
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.
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. 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), which is filled with graphite, 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 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 “moderator rods”. The moderator 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 moderator 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 moderator 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 Xenon. 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 7 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 7 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 moderator 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.
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, moderator 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.
But Plan A had failed – cooling systems down or additional clean water unavailable – so Plan B came into effect. This is what it looks like happened: In order to prevent a core meltdown, the operators started to use sea water to cool the core. I am not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us. The point is that the nuclear fuel has now been cooled down. Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced now.
The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure. Also, boric acid has been added to the seawater. Boric acid is “liquid control rod”. Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core.
The plant came close to a core meltdown. Here is the worst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the water steam to avoid pressure buildup. The third containment would then have been completely sealed to allow the core meltdown to happen without releasing radioactive material. After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor, and all radioactive particles to settle on a surface inside the containment. The cooling system would have been restored eventually, and the molten core cooled to a manageable temperature. The containment would have been cleaned up on the inside. Then a messy job of removing the molten core from the containment would have begun, packing the (now solid again) fuel bit by bit into transportation containers to be shipped to processing plants. Depending on the damage, the block of the plant would then either be repaired or dismantled.
paul walter’s comment is vintage Unleashed hysteria; is there one natural catastrophe where the greenies/lefties don’t come out caterwauling about AGW being proved; they are doing it about the Earthquake and the nuclear situation is grist for the mill; some salient facts:
1 There are 55 operating nukes in Japan; the 6 plants at Fukushima are the oldest, the worst sited, were due to be decomissioned next week and are of the notorious General Electric
Mark I reactor type; they are a superseded reactor which nonethe less still withstood the worst Japanese Earthquake but not the Tsunami.
2 Despite it being compromised the Fukushima complex is nothing like Chernobyl or even 3 mile which were completely different and worse reactors.
3 All the remaining 49 reactors survived the Earthquake.
4 Modern generation and thorium reactors have no such cooling down requirements.
5 10’s of thousands of people are dead and the ghoulish, green driven media focuses on the nuclear leakage.
6 A bit of perspective from janama:
“Whilst everyone concentrates on the possibility of nuclear fall out from the Fukushima plant the fact that a hydro dam in the Fukushima Prefecture has burst and flooded towns and destroyed houses, and presumably people, seems to have gone unnoticed and unreported except for a slight mention in the ABC news online.
In 1975 the Banqiao Dam burst due to an earthquake.
From Wikipedia
“According to the Hydrology Department of Henan Province,[5] in the province, approximately 26,000 people died from flooding and another 145,000 died during subsequent epidemics and famine. In addition, about 5,960,000 buildings collapsed, and 11 million residents were affected.”
Cohenite’s comment doesn’t help.
I suppose it was the Greens fault there was an earthquake, let a system failure with the badly sited reactors. Let’s remember there has been a big push lately to revive nuclear and major efforts to extoll its alleged vitues. Nonetheless, do I object to nuclear, per se?
No, anymore than I’m against reckless deep water drilling of the sort attempted by BP in the Carribean, that gave rise to the Morning Horizon disaster.
No.
But there’d have to be exponentially more forward planning, transperancy and accountability based on science rather than the imperatives of big business cutting corners, before it’d win me over again.
“2 Despite it being compromised the Fukushima complex is nothing like Chernobyl or even 3 mile which were completely different and worse reactors”,
3 Mile was a Light Water Reactor, and water loss stops the nuclear chain reaction dead in its tracks. It’s the residual heat that remains the problem.
Chernobyl was a graphite moderated reactor, with coolant water, but is thermally unstable when the coolant is removed. Increasing core temperature actually accelerates the nuclear chain reaction, while the same coolant in the LWR type kills it.
Doesn’t help what paul? Goto Barry Brook’s site:
http://bravenewclimate.com/2011/03/13/fukushima-simple-explanation/
Read what Brooks has to say and then say something sensible when you are more reasonably informed.
The Japanese nuclear events are a real tragedy. I’ve worked in the US nuclear industry for 25 years. My novel “Rad Decision” culminates in an event very similar to the Japanese tragedy. (Same reactor type, same initial problem – a station blackout with scram.) The book is an excellent source of perspective for the lay person — as I’ve been hearing from readers. It is available free online at the moment at http://RadDecision.blogspot.com . (No adverts, nobody makes money off this site.) Reader reviews are in the homepage comments.
Let’s not forget, it was the fledgling environmental movement in the 1960s which encouraged the Japanese to go nuclear and give up their belching coal fired power stations.
Interesting threads and comments at
http://diggingintheclay.wordpress.com/2011/03/14/fukushima-reactor-3-blast-looks-serious/#comments
e.g. boballab says:
March 15, 2011 at 3:32 pm
and
http://chiefio.wordpress.com/2011/03/12/japan-nuke-plant-explosion/
A quote from boballab, talking about Japanese integrity.
‘Turns out in the shallow bays and such the wave got well over 40 ft in height in the simulation, just like what really happened since it went over 10 meter walls. Now what was the last wave height the MSM reported 25ft? Again would an academic that did a report for the US or UK governments admit to the media they screwed up? Not a chance, again it would be no comment followed by the PR hacks and lawyers.’
this is a bit o/t but there is a nice article in American Thinker http://www.americanthinker.com/2011/03/why_the_japanese_arent_looting.html
Why The Japanese Aren’t Looting
(last para)
Perhaps more successfully than any other people of the world, the Japanese have evolved a social system capable of ensuring order and good behavior. The vast reservoir of social strength brought Japan through the devastation of World War II, compared to which even the massive problems currently afflicting it, are relatively small. Japan has sustained a major blow, but its robust social order will endure, and ultimately thrive.
I must say that everything you read on this matter is pure speculation. Even experienced Nuclear people do not know what is going on as the Japanese aren’t telling anyone.
I’m just going to sit this one out until we have more definitive information and I’ll try to ignore the sensationalist headlines in the press and ABC.
“Why The Japanese Aren’t Looting?”
val – if you were on a metro train in Tokyo and accidentally left your wallet on the seat all you need do is wait for the train to come around again and your wallet will still be there. The Japanese have developed a culture that does not steal.
Jen – Alan Jones speaks to Craig Knowles, the new chairman of the Murray Darling Basin Authority.
http://podcasts.mrn.com.au.s3.amazonaws.com/alanjones/20110316-aj2-craigknowles.mp3
John, thanks for that info; the Aust Red Cross have launched an appeal
Japan and Pacific Disaster Appeal
http://www.redcross.org.au/default.asp
you can donate by Paypal or phone
or more directly to the Japanese Red Cross http://www.google.com/crisisresponse/japanquake2011.html
(the latter seems to limit donations to 50,000 yen – about $100)
It’s such a huge disaster
The most disturbing thing is the reaction of the media. Let us take a completely over the top fear. Let us assume by some miracle this becomes an uncontained nuclear explosion.
It would be a tragic event that greatly affects Japan no where else. In the past the british exploded nuclear bombs in South Australia in the open air it did not affect us. There is no need our stock market to tank. There is no need for us to buy iodine. There no need to interview every alarmist that can be found.
If Jennifer won’t mind my taking some space with this comment, I’d like to mention the fire in the Number 4 Reactor.
You’ll probably see images taken from a helicopter showing what looks to be dramatic footage, and then you’ll hear the worst possible case scenarios about it.
This fire is in the Number 4 reactor, and be aware that this reactor was shut down and cold at the time of the Tsunami for maintenance and possibly refuelling.
The concrete structure for this reactor was breached during one of the Hydrogen explosions from the other on site reactors, and this is where the fire probably started at a later time.
The fire is in and around the ‘spent rods’ pool, and that needs some explanation.
When the oxide exists in the ground as yellowcake, it already has an ‘enrichment’ (for want of a better word) level of 0.7%.
The ore is mined and goes through 5 separate processes before it is ready to be used as fuel in the reactor of a power plant.
150,000 tonnes of rock and ore will go through those 5 processes to yield 24 Tonnes of ‘fuel’ which is around the total amount for a typical reactor refuel.
At the end of those 5 stages it is at an enrichment level of 3 to 5%, most typically 3%.
This needs to be stressed here as enrichment for weaponisation takes it to around 98% enrichment, and requires numerous further processes, so it’s not just a matter of ‘holding down the button’ during the enrichment process to keep going to that 98%.
The end product is turned into a powder in one of those processes, and this powder is then ceramicised into tiny pellets. These pellets are then inserted into a rod, about the thickness of a biro, only longer. The rods are different lengths, depending upon the reactor type, BWR and its derivatives, or PWR.
The rods are arranged in bundles and there are different amounts of rods in the bundles for PWR and BWR type reactors.
These bundles of rods are then inserted into the reactor in numbers of bundles.
Judicious use of the rods in those bundles will see the bundle lasting up to 3 years and a typical reactor is refuelled after 18 months.
Those rods full of pellets sustain the reaction over that time, and the enrichment level is depleted over time.
When that rod reaches an enrichment level of around 1% or slightly lower, the rod is not really viable for continuation of use as fuel for the reaction.
The bundles or even the separate rods that have reached that low level of enrichment, are then removed from the pile, and kept inside the reactor in their own pool of cooling water for a further time, usually around three years, and over that time, the enrichment level depletes to around 0.7%
Sound familiar?
That’s the same level of enrichment as the original ore in the ground.
The rods or the bundles are then removed to a dry storage site.
This fire in and around this ‘spent rods’ pool is still serious but in no way anywhere on the scale as an exposing of the pile, which may (or even may not) have happened in those other reactors.
It might be said here that if the plant was closed down, then it was probably for a refuel, and those rods and bundles would have been removed from the pile and placed into that storage pond, and they would have still had significant inherent heat in them, hence this fire, which looks to have been extinguished.
So, when you see dramatic footage and hear all sorts of disaster scenarios, be aware that again, this is in the main uninformed comment from some people whose job it is to make the worst case scenario.
I am by no means an expert, but if you have even the most basic information in the first place, it adds context to what is being talked about.
I know I sometimes use a lot of space to say very little, but information like this cannot be explained in an 8 second sound bite.
Tony.
Tony thank you for that; I am following the nuclear situation in Japan but only because I am concerned for Japan rather than any personal concern
As for keeping in touch with what’s happening in regard to the nuclear situation in Japan I keep in touch through the bravenewclimate link I have posted before
I’ve found in Aust the media are about 12 hours behind
One thing the media does do is show the world images and I’m hopeful through those that more people will be inclined to donate to the Japanese disaster
I’ve put the links above
Yes, we might denigrate the media but because of it the rest of the world is aware of the extent of the disaster even though different media put different slants on it
So accept facts and not opinion – good policy
AND the facts make this the worst natural disaster that I remember in my lifetime
Professor Dr. Barry Brook has a further UPDATE at the following link, dated 16th March, today.
http://bravenewclimate.com/2011/03/16/fukushima-16-march-summary/
Tony
“AND the facts make this the worst natural disaster that I remember in my lifetime”
Well Val, like me you probably weren’t told about this either, 170,000 killed in 1975 and it was a renewable energy scheme to boot:
http://en.wikipedia.org/wiki/Banqiao_Dam
Val,
re. the no looting in Japan,
It’s quite amazing to see vending machines;sometimes rows of them selling all manner of stuff; just out in the open on the streets, not one of them vandalised or broken into.
During the rainy season in smaller towns you might see an umbrella-stand under one of the street verandas containing some brollies you might like to borrow on the understanding you will return it later!
Different mentality altogether.
thanks spangled and Mack for the comments; Mack we in Aust would benefit from the Japanese ‘neighbourhood’ approach
and spangled while I accept what you say I was talking about ‘natural’ disasters –
A bit of encouraging news out of Fukushima Dai-ichi:
So it appears that they are planning another venting of unit 2 and after the radiation subsides subsequent to that event they will get the mains connected to the stricken units.
Once they get power, they can top off the spent fuel pools and begin normal circulation of water in the reactors.
Paul Walter,
now that you have done the usual and thrown out a buzz word:
“…but with some real half wittedness they might still be able to create a new Chernobyl, the next time ’round.”
Would you please present us with some serious research showing just how catastrophic the destruction of the Chernobyl reactor really was?? I believe you will find there is amazingly little human or natural damage done by this accident. Not that I would want to have been in the are at the time, but, give us a quantification of how bad it really was.
As with nuclear winter and so much else I grew up with it turns out that apparently Chernobyl and the effects of radiation in general are quite overhyped!! fits amazingly well with all the rest of the enviro whacko hypersensitivity.
Sorry, I couldn’t resist a bit of gallows humor.
For part of the time that I was a student at Humboldt State University, I had a housemate who was an avid angler. One day, he told me that warm-water outlet of the then-operational nuclear power plant at nearby Eureka, California was a great place to catch perch. My response?
Tom, I hope that you enjoy your nuclear fishin. 🙂