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Thread: [Fukushima, power stations, nuclear scare]

  1. #1
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    [Fukushima, power stations, nuclear scare]

    http://www.cbc.ca/news/world/story/2...r-reactor.html

    Reactors at the two power stations are struggling to maintain forced cooling and control pressure within the reactors. Controlled venting of primary coolant steam is needed to keep things together. Everyone is getting in a tizzy about it.

    Obviously, states of emergency have been declared and evacuations are underway, but that's par for the course when it comes to the ultra precautionary attitude to all things nukyular.

    Since it takes an electron microscope to image my respect for journalists, I don't know what to go on.

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    Someone (geonuc?) posted this link in the Babbling thread on the earthquake. It reads a bit more factual and and quite a bit less sensational.

    World Nuclear News: Massive earthquake hits Japan

    ETA: yes, it was geonuc.
    Last edited by slang; 2011-Mar-12 at 01:29 AM. Reason: url fixed, thanks Rhaedas
    ____________
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    That's the only good info I've seen on the reactors. At least it has more than the mainstream "oh nooos" crap.

    The link needs to be fixed a bit. Take out the asterisk.

    Any idea on why the generators kicked off after only an hour in the one reactor?

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    I'm interested in knowing more about these releases. Some controlled venting of primary coolant steam was being done to control reactor pressure. There are also reports of "leaks". Are these "leaks" actually idiot journalists getting confused about the controlled venting or are there genuine uncontrolled releases going on?

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    Another decent source
    Union of Concerned Scientists:
    Nuclear Crisis in Japan: What We Know
    The boiling water reactors at Fukushima are protected by a Reactor Core Isolation Cooling (RCIC) system, which can operate without AC power because it is steam-driven and therefore does not require electric pumps. However, it does require DC power from batteries for its valves and controls to function.

    If battery power is depleted before AC power is restored, however, the RCIC will stop supplying water to the core and the water level in the reactor core could drop. If it drops far enough, the core would overheat and the fuel would become damaged. Ultimately, a meltdown could occur: the core could become so hot that it forms a molten mass that melts through the steel reactor vessel. This would release a large amount of radioactivity from the vessel into the containment building that surrounds the vessel.

  6. #6
    I'm very scared. How likely of a risk is this? Should we start panicking? I'm not trying to be sensationalist but I can't help it right now.

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    Quote Originally Posted by Chombie View Post
    I'm very scared. How likely of a risk is this? Should we start panicking? I'm not trying to be sensationalist but I can't help it right now.
    If you live within a couple of miles of the nuclear plant there might conceivably be some risk. If you live in another country there is probably no risk at all. If you do feel the need to worry, worry over the workers who are now working in (for them!) dangerous environment: they are very worried about the fate of one crane operator whose vital signs can't be detected.

    See todays article from World Nuclear News, updated a few minutes ago. To add to what Squink posted:

    Even now, the primary focus of work at the site remains to connect enough portable power modules to fully replace the diesels and enable the full operation of cooling systems.
    Squink's article suggests that because people have been evacuated there is risk of a serious accident, but other sources say that the evacuation was to reduce any risk from venting contaminated steam.
    ____________
    "Dumb all over, a little ugly on the side." -- Frank Zappa
    "Your right to hold an opinion is not being contested. Your expectation that it be taken seriously is." -- Jason Thompson
    "This is really very simple, but unfortunately it's very complicated." -- publius

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    For those reading this thread and not following the other or have not seen it on TV or elsewhere it looks like one of the reactor containment buildings just suffered a very large steam explosion and collapse. It looks like the reactor vessel let go.

    Yeah, this is about as bad as it can get. Maybe the explosion blew the fuel assembly apart so that it can't melt down.
    Et tu BAUT? Quantum mutatus ab illo.

  9. #9
    Just supposing that the reactor vessel failed and there is radioactive steam spewing out, how far away do you have to be to be relatively safe? The big population centers of Chiba and Tokyo are like 200-300 km away. Is that a relatively safe distance, or not?
    As above, so below

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    'If' there is a catastrophic venting and leakage of radioactive material and steam... then knowing the wind direction and moving yourself so as not to be within the area of radioactive fallout. You can be assured that every effort is being made to lessen the risks as best as can be.... Moving away from the 'danger area' might be a thoughtful step... If this was to happen and has...
    No better equipped nation to cope than Japan...

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    It seems there is no confirmed information on what happened there. This is a problem because in the absence of information, the media will just make up whatever they want.

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    Quote Originally Posted by Glom View Post
    It seems there is no confirmed information on what happened there. This is a problem because in the absence of information, the media will just make up whatever they want.
    I've done some reading on the Wikipedia, so I'm an expert now... not really, but from reading about Boiling Water Reactor safety systems and failure modes, the explosion that you can see on the video shouldn't have happened. According to the articles, BWRs are the ones with the big square containment buildings, as seen in the video. They are big and square because they don't just contain the reactor (a bigger reactor than in a Pressurized Water Reactor), but also the primary coolant loop and turbine that is slightly radioactive too. Inside this is the Dry-well and the Wet-well. which serves as a safety feature for cooling pressure transients in the reactor.

    So, maybe it was the wet-well that have a steam explosion. Or maybe it was a hydrogen explosion, as steam and zirconium alloys can create hydrogen as the Zr oxydizes, and the catalytic recombiners might not have functioned to prevent a deflagration (which presupposes structural issues caused by a melt-down in progress). Or maybe it was a steam explosion caused in the turbine and coolant loops independently of the reactor.

    Either way, the containment building that might have had 1.2 to 2.4m thick walls of prestressed reinforced contrete, has been reduced to rubble so that its inner steel skeleton is visible.
    Et tu BAUT? Quantum mutatus ab illo.

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    From the thread in Babbling:

    Quote Originally Posted by HenrikOlsen View Post
    Unfortunately, the http://www.world-nuclear-news.org/ site, which is likely one of the few places to go to for reliable, not filtered through the holes in a journalists knowledge, information, is down from overload.

    If you can get through it looks like the story is here http://www.world-nuclear-news.org/RS...s_1203111.html
    Here is the article, I assume it's ok to duplicate it here to lessen the load on their servers..

    Battle to stabilise earthquake reactors
    12 March 2011
    UPDATE 6: 10.15 am GMT

    Attention is focused on the Fukushima Daiichi and Daini nuclear power plants as Japan struggles to cope in the aftermath of its worst earthquake in recorded history. An explosion has been seen at the site.

    Three of Fukushima Daiichi's six reactors were in operation when yesterday's quake hit, at which point they shut down automatically and commenced removal of residual heat with the help of emergency diesel generators. These suddenly stopped about an hour later, and this has been put down to tsunami flooding by the International Atomic Energy Agency (IAEA).

    The loss of the diesels led the plant owners Tokyo Electric Power Company (Tepco) to immediately notify the government of a technical emergency situation, which allows officials to take additional precautionary measures.

    Even now, the primary focus of work at the site remains to connect enough portable power modules to fully replace the diesels and enable the full operation of cooling systems.

    Pressure and releases

    Without enough power for cooling systems, decay heat from the reactor cores of units 1, 2 and 3 has gradually reduced coolant water levels through evaporation. The consequent increase in pressure in the coolant circuit can be managed via pressure release valves. However, this leads to an increase in pressure within the reactor building containment. Tepco has said that the pressure within the containment of Fukushima Daiichi 1 has reached around 840 kPa, compared to reference levels of 400 kPa.

    The company has decided to manage this "for those units that cannot confirm certain levels of water injection" by means of a controlled release of air and water vapour to the atmosphere. Because this water has been through the reactor core, this would inevitably mean a certain release of radiation. The IAEA said this would be filtered to retain radiation within the containment. Tepco has confirmed it was in the process of relieving pressure at unit 1 while preparing to do the same for units 2 and 3

    Explosion

    Television cameras trained on the plant caputured a dramatic explosion surrounding unit 1 at around 6pm. Amid a visible pressure release and a cloud of dust it was not possible to know the extent of the damage. The external building structure does not act as the containment, which is an airtight engineered boundary within. The status of the containment is not yet known.

    Monitoring of Fukushima Daiichi 1 had previously shown an increase in radiation levels detected emerging from the plant via routes such as the exhaust stack and the discharge canal.

    Over the last several hours evacuation orders for local residents have been incrementally increased and now cover people living within ten kilometres of the power plant.

    Raised temperatures

    Meanwhile at adjacent Fukushima Daini, where four reactors have been shut down safely since the earthquake hit, Tepco has notified government of another emergency status.

    Unit 1's reactor core isolation cooling system had been operating normally, and this was later supplemented by a separate make-up water condensate system. However, the latter was lost at 5.32am local time when its suppression chamber reached 100C. This led Tepco to notify government of another technical emergency situation.

    Tepco has announced it has decided to prepare for controlled releases to ease pressure in the containments of all four units at Fukushima Daini.

    A three kilometre evacuation is in progress, with residents in a zone out to ten kilometres given notice of potential expansion.

    Workers

    A seriously injured worker was trapped within unit 1 in the crane operating console of the exhaust stack. Breathing and a pulse could not be confirmed, Tepco said as it considered a rescue. At unit 3 one worker is known to have received a radiation dose of 106 mSv.

    Researched and written

    by World Nuclear News

    Fukushima Daiichi
    Unit 1
    - 439 MWe BWR, 1971
    - Automatically shut down
    - Water level decreasing
    - Pressure release implemented
    - Explosion observed with unknown
    effect
    Unit 2
    - 760 MWe BWR, 1974
    - Automatically shut down
    - Water level lower but steady
    - Preparations for pressure release
    Unit 3
    - 760 MWe BWR, 1976
    - Automatically shut down
    - Preparations for pressure release
    Unit 4
    - 760 MWe BWR, 1978
    - Shut for periodic inspection

    Unit 5
    - 760 MWe BWR, 1978

    - Shut for periodic inspection
    Unit 6
    - 1067 MWe BWR, 1979
    - Shut for periodic inspection

    Fukushima Daini
    Unit 1
    - 1067 MWe BWR, 1982
    - Automatically shut down
    - Offsite power available
    - Water level stable
    - Preparations for pressure release
    Unit 2
    - 1067 MWe BWR, 1984
    - Automatically shut down
    - Offsite power available
    - Water level stable
    - Preparations for pressure release
    Unit 3
    - 1067 MWe BWR, 1985
    - Automatically shut down
    - Offsite power available
    - Water level stable
    - Preparations for pressure release
    Unit 4
    - 1067 MWe BWR, 1987
    - Automatically shut down
    - Offsite power available
    - Water level stable
    - Preparations for pressure release
    ____________
    "Dumb all over, a little ugly on the side." -- Frank Zappa
    "Your right to hold an opinion is not being contested. Your expectation that it be taken seriously is." -- Jason Thompson
    "This is really very simple, but unfortunately it's very complicated." -- publius

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    Quote Originally Posted by Jens View Post
    Just supposing that the reactor vessel failed and there is radioactive steam spewing out, how far away do you have to be to be relatively safe? The big population centers of Chiba and Tokyo are like 200-300 km away. Is that a relatively safe distance, or not?
    The reactor vessel is the metal receptacle which holds the core: http://en.wikipedia.org/wiki/Reactor_vessel

    Around the vessel is the containment, which is reinforced concrete several-feet-thick. Note that is *not* the square structures you see in photographs.

    Around the containment are the square exterior buildings. You cannot see the containment at the Japanese plants, as it's inside the square building. That building is of more conventional construction so it's easily possible it could fail and the containment stay intact.

    To answer your immediate question, if the reactor vessel failed, the containment would hopefully limit the problem. Note Cherynoble did not have a containment.

    So far there's no indication the containment failed at the Japanese plant. However it appears the building surrounding the containment was damaged, which is serious.

    Prevailing winds are west to east, and the reactors are on the Japanese east coast. This would tend to somewhat mitigate the risk to population centers to the south.

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    Well it's nukyular, therefore its scary.
    Some farmacies are running out of iodine pills, in Finland... Which wasnt exactly close to Japan last time i checked the map. Not sure if the 2m shift made it closer tho.

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    I'm now hearing that the explosion of a secondary containment building was in fact the explosion in a switchyard.

  17. #17
    Quote Originally Posted by joema View Post
    So far there's no indication the containment failed at the Japanese plant. However it appears the building surrounding the containment was damaged, which is serious.
    Thanks. I'm not absolutely sure, but it seems that what may have happened is that a valve was opened to relieve the pressure, and the explosion might have been from that. It seems that the situation may be under control there, which is good to hear.
    As above, so below

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    Quote Originally Posted by slang View Post
    From the thread in Babbling:

    Here is the article, I assume it's ok to duplicate it here to lessen the load on their servers..

    Battle to stabilise earthquake reactors
    12 March 2011
    UPDATE 6: 10.15 am GMT
    ...
    Three of Fukushima Daiichi's six reactors were in operation when yesterday's quake hit, at which point they shut down automatically and commenced removal of residual heat with the help of emergency diesel generators. These suddenly stopped about an hour later, and this has been put down to tsunami flooding by the International Atomic Energy Agency (IAEA).
    The loss of the diesels led the plant owners Tokyo Electric Power Company (Tepco) to immediately notify the government of a technical emergency situation, which allows officials to take additional precautionary measures.
    Even now, the primary focus of work at the site remains to connect enough portable power modules to fully replace the diesels and enable the full operation of cooling systems.

    ...
    If the main problem is just getting enough portable power there then there are portable gas turbine generators capable of putting out 10's of megawatts. You could also use the power from a nuclear aircraft carrier at a power range of 200 megawatts, though there might concern about bringing it off shore in a zone subject to tsunamis.


    Bob Clark

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    Quote Originally Posted by slang View Post
    ETA: yes, it was geonuc.
    I live to serve.

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    I'm getting really annoyed (again) by the use of non-precise terminology by the news media. I don't expect them to be nuclear engineers, but it sure seems they intentionally 'dumb down' what they hear from experts and it just doesn't work.

    I just heard someone report that there is "three times the normal heating" inside the reactor. What does that mean? Three times the temperature? I doubt it, because it would be a molten pile of slag. Three times the heat flux? That doesn't make sense because what is normal - the reactor is designed for considerably more power than it's now putting out.

    I'm sure the reporter was told 'something' was three times normal or three times what would be expected, but because he dumbed down the terminology, I have no idea what.

    I'm annoyed.

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    The BBC just had an "expert" "speculating" that containment at Fukushima 1 has been breached (and the government are down playing the seriousness). I am very skeptical of that but it does sound as if it is, at least potentially, quite serious. The evacuation zone has been expanded to 20km.

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    A message for anyone out there who might have second thoughts on atomic power.

    Tonight we are to run our clocks behind 1 hour (Spring up, fall back).

    It is also advised that we change our batteries in smoke detectors. Ever wonder how they work?

    They have, according to wiki, "about 37 kBq or 1 Ci of radioactive element americium-241 (241Am), corresponding to about 0.3 g of the isotope." Now I guess you could take one apart, place the element in your tighty-whities, and in 20 years you might get cancer.

    If you don't have that smoke detector, you can die in **minutes** from a carbon containing gas. Same with AGW and the atom's role in reducing those other carbon gas emissions.

    I myself would much rather have been at the Fukushima power plants than here: http://en.wikipedia.org/wiki/Cosmo_Oil_Company

    At Cosmo, the problem was THERMAL radiation that is instantly deadly. Same as with what your household detectors prevent. And the thing is, had those oil storage tanks contained bio-diesel or methanol--other than the flames being a different color--the result is the same, an inferno like the Texas City Disaster of 1947 and later. And we all should be wary of growing our fuel. It is not the drill head, but the plow that marks Gaia the most. And Lovelock, who postulated the Gaia theory with Margulis, advocates atomic power these days.

    People simply need to understand risks and get a better handle on fault trees. Chernobyl was an example of bad design--not an indictment of nuclear power itself in my estimation. Three Mile Island was an example of a problem with meatware, what with "ambiguous control room indicators" and poor user interface, although the real problem there, as now, was plumbing.

    Pipes (their joins and fittings especially) are often the first thing to go in an earthquake. In a hydrocarbon plant of any stripe, the disaster is instant. In Japan, were I to hazard a guess, all that was needed were seismic-resistant fittings, and maybe a protable fire truck/pumper truck with some mobile tankers that could drive up a hill, wait out a tsunami, then come back down if generators failed. They should have been uphill with a launch pad type gravity feel deluge system even, as an additional back-up. At least here, they had time, which is something you don't have with combustable sources of power housed in what are essentially eggshells.

    You might say the real problem was a lack of flexibility. The rock failed. It is not teflon or rubber, so rock shatters when loads are forced upon them. They break and you have a temblor. At plants it is lack of flexibility in fittings that cause instand fires and (later) coolant problems, same as when your radiator springs a leak. And, lastly, is political inflexibility--that of anti-nukes who would exploit such a tragedy--in much the same way an AGW denier would mock the failure of OCO and the Glory mission failures, using that to curtail other earth science missions, or to block such "things called volcano monitoring" as Bobby Jindal would have done out of ignorance. But that issue, and the brillant article at arstechnica on bias, have been discussed at responsible sites like this one before.

    Water is the ultimate in flexibility--it is fluid. As Spike tells Rocco in the Bebop episode "Waltz for Venus," his "fighting ability comes not from excessive strength, but fluid motion."
    http://cowboybebop.wikia.com/wiki/Waltz_For_Venus

    We saw with the seismic sea waves that were more than great waves in a harbor, that water, while pliable, can indeed come as a torrent, what with tsunami best described as flash floods from the ocean.

    We as human beings need to be as water. Protean, capable of changing our thoughts--then nothing will halt our reach for the stars.

    It is when we are inflexible, stilted--that's when things break.

    News blurbs:

    http://www.msnbc.msn.com/id/42044156...fic/?gt1=43001
    http://en.wikipedia.org/wiki/Japan_earthquake_2011

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    Quote Originally Posted by publiusr View Post
    People simply need to understand risks and get a better handle on fault trees. Chernobyl was an example of bad design--not an indictment of nuclear power itself in my estimation. Three Mile Island was an example of a problem with meatware, what with "ambiguous control room indicators" and poor user interface, although the real problem there, as now, was plumbing.
    Pipes (their joins and fittings especially) are often the first thing to go in an earthquake. In a hydrocarbon plant of any stripe, the disaster is instant. In Japan, were I to hazard a guess, all that was needed were seismic-resistant fittings, and maybe a protable fire truck/pumper truck with some mobile tankers that could drive up a hill, wait out a tsunami, then come back down if generators failed. They should have been uphill with a launch pad type gravity feel deluge system even, as an additional back-up. At least here, they had time, which is something you don't have with combustable sources of power housed in what are essentially eggshells.
    Seems to me what you are saying is that Fukushima is also an example of bad design.

    Bob Clark

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    You are always going to have a problem with fittings. Pipes themselves are a bit flexible, but the joins are often the problems. Perhaps seismic resistant design cues taken from quick release launch tower umbilicals can be used in both atomic power plant retrofits and petrolium storage tank farms both.

    This is the pay-off in having the interests of a generalist, btw. So many problems in science and technology emerge from a lack of intellectual cross pollination and sloppiness. But that's a meatware issue again.

    Something else to consider. We have to do something with fissile material. Right now, this material is surrounded by high explosives, and sitting atop solid rockets that ATK bashers seem to hate so much. OK, so what would be a good design to contain fissile material? Take it out of warheads atop ICBMs, place neutron moderation rods it it, and cover with water.

    You have just built 90% of an atomic power plant.

    Just add a turbine, back ups and fittings that flex/shut off quickly like umbilical attachments do, and you're done.

    Now I imagine a turbine can "walk" so you have to have a firm foundation for them. I remember pictures about a strange Titan II motor accident, where the nozzle seemed to have been sawed off and thrown a distance from an engine test. A Titan II in flight yields, but a test stand/battleship as they are called are quite rigid. From Ed Kyle:

    This reminds me of an engine failure on a Titan 2
    (N-4) that occured during a ground abort launch
    attempt on June 27, 1962. According to David
    Stumpf's "Titan II", a combustion instability
    problem during engine start acted like an
    "ultrasonic saw", cleanly cutting off the thrust
    chamber just below the fuel torus. The thrust
    chamber was ejected from the flame deflector and
    came to rest several hundred feet from the launch
    pad.

    http://sci.tech-archive.net/Archive/.../msg00434.html

    My guess is that the earthquake shook loose the attachment points in a less violent way than that nozzle failure. The coolant vented out. Radiator leak on a big scale.

    So the problem is how to attach things that give (pipes) to items that need to be firmly rooted in a foundation. I think some of the umbilical tower umbilical line tech might solve all this once and for all.

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    They've decided the reactor isn't worth saving any more so are going to kill it. The problem will be resolved, but the reactor will be a write-off.

  26. #26
    Quote Originally Posted by Glom View Post
    They've decided the reactor isn't worth saving any more so are going to kill it. The problem will be resolved, but the reactor will be a write-off.
    What is this kill process like?

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    One thing that really cheesed me off in the coverage; an independent nuclear consultant complained that people always overstate the symptoms of radiation poisoning, which leads to authority figures understating the risks, to avoid mass panic. Now I may be a superstitious prole, but from what I've read of the symptoms of acute radiation sickness, I'd sooner get Ebola. So are the public wrong to view radiation sickness as a fate worse than death?

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    Quote Originally Posted by Glom View Post
    They've decided the reactor isn't worth saving any more so are going to kill it.
    How do they do that?
    I may have many faults, but being wrong ain't one of them. - Jimmy Hoffa

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    Quote Originally Posted by Glom View Post
    They've decided the reactor isn't worth saving any more so are going to kill it. The problem will be resolved, but the reactor will be a write-off.
    Thanks for that. I had heard they planned to flood the reactor with seawater but didn't make the connection that would mean scrapping the plant:

    Q&A: Explosion at Fukushima nuclear plant.
    By Sylvia Pfeifer in London
    Published: March 12 2011 18:10 | Last updated: March 12 2011 18:10
    Why are they now flooding the reactors with seawater?
    Nuclear energy experts on Saturday said the decision to flood the core of one of the reactors at the Fukushima Daiichi facility with seawater is a clear sign the authorities had decided to write it off and that it would never be operational again.
    http://www.ft.com/cms/s/0/81f3133c-4...#axzz1GQ2dbGyT


    Bob Clark

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    Quote Originally Posted by Extravoice View Post
    How do they do that?
    Sea water and boric acid, if I got it right...

    Copying from World Nuclear News (since they already had a meltdown of their own, on the webserver), only what seems to have changed from this morning:

    Explosion

    Television cameras trained on the plant captured a dramatic explosion surrounding unit 1 at around 6pm. Amid a visible pressure release and a cloud of dust it was not possible to know the extent of the damage. The external building structure does not act as the containment, which is an airtight engineered boundary within.

    Chief cabinet secretary Yukio Edano appeared on television to clarify that the explosion had damaged the walls and roof of the reactor building but had not compromised the containment.

    Monitoring of Fukushima Daiichi 1 had previously shown an increase in radiation levels detected emerging from the plant via routes such as the exhaust stack and the discharge canal. Tepco have said that the amount of radioactive material such as iodine it is detecting have been increasing. The amount of radiation at the site boundary now exceeds a regulatory limit triggering another set of emergency precautions. It also meant the incident has been rated at Level 4 on the International Nuclear Event Scale (INES) - an 'accident with local consequences'.

    To protect the public from potential health effects of radioactive isotopes of iodine that could potentially be released, authorities are preparing to distribute tablets of non-radioactive potassium-iodide. This is quickly taken up by the body and its presence prevents the take-up of iodine should people be exposed to it.

    Over the last several hours evacuation orders for local residents have been incrementally increased and now cover people living within 20 kilometres of the power plant.

    Seawater injection

    The injection of seawater into the building started at 8.20pm and this is planned to be followed by addition of boric acid, which is used to inhibit nuclear reactions. Tepco had to put the operation on hold for a time when another tsunami was predicted, but work recommenced after the all-clear.

    Raised temperatures

    Meanwhile at adjacent Fukushima Daini, where four reactors have been shut down safely since the earthquake hit, Tepco has notified government of another emergency status.

    Unit 1's reactor core isolation cooling system had been operating normally, and this was later supplemented by a separate make-up water condensate system. However, the latter was lost at 5.32am local time when its suppression chamber reached 100C. This led Tepco to notify government of another technical emergency situation.

    Tepco has announced it has decided to prepare for controlled releases to ease pressure in the containments of all four units at Fukushima Daini.

    A three kilometre evacuation is in progress, with residents in a zone out to ten kilometres given notice of potential expansion.

    Workers

    A seriously injured worker was trapped within Fukushima Daiichi unit 1 in the crane operating console of the exhaust stack and is now confirmed to have died. Four workers were injured by the explosion at the same reactor and have been taken to hospital. A contractor was found unconscious and taken to hospital.

    Two workers of a 'cooperative firm' were injured, said Tepco; one with a broken bone.

    At Fukushima Daiini unit 3 one worker received a radiation dose of 106 mSv. This is comparable to levels deemed acceptable in emergency situations by some national nuclear safety regulators.

    The whereabout of two Tepco workers remains unknown.

    Researched and written
    by World Nuclear News
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