Japan: Fukushima operator built nuclear plants to withstand only up to 7.9 quake

Documents from Tokyo Electric, the operator of the Japanese nuclear plants in crisis after Friday's devastating quake and tsunami, reveal that the company tested the Fukushima plant to withstand a quake up to magnitude 7.9. That threshold is well below the force of Friday's quake, recently upgraded to 9.0.

Snip from Wall Street Journal:

Tepco's last safety test of nuclear power plant Number 1--one that is currently in danger of meltdown--was done at a seismic magnitude the company considered the highest possible, but in fact turned out to be lower than Friday's quake. The information comes from the company's "Fukushima No. 1 and No. 2 Updated Safety Measures" documents written in Japanese in 2010 and 2009. The documents were reviewed by Dow Jones. The company said in the documents that 7.9 was the highest magnitude for which they tested the safety for their No. 1 and No. 2 nuclear power plants in Fukushima.

Thousands of evacuees from areas around Japan's Fukushima nuclear power plant were scanned for radiation exposure, though the Japanese government insists radiation levels are low. Video courtesy of Reuters

Simultaneous seismic activity along the three tectonic plates in the sea east of the plants--the epicenter of Friday's quake--wouldn't surpass 7.9, according to the company's presentation.

Japan Tries Using Seawater to Cool Damaged Reactor (WSJ)

Photo (Reuters): The damaged roof of reactor number No. 1 at the Fukushima Daiichi nuclear plant after an explosion that blew off the upper part of the structure is seen in this handout photo released by Tokyo Electric Power Company (TEPCO) in Fukushima Prefecture, northeastern Japan, March 12, 2011. Japanese authorities battling to contain rising pressure in nuclear reactors damaged by a massive earthquake were forced to release radioactive steam two plants, after evacuating tens of thousands of residents from the area. Tokyo Electric Power Co also said fuel may have been damaged by falling water levels at the Daiichi facility, one of its two nuclear power plants in Fukushima, some 240 km (150 miles) north of Tokyo. Picture taken March 12, 2011.


  1. X, a nitpick: It’s not the Richter scale anymore. It was phased out 20 years ago in favor of the moment magnitude scale. The proper way to refer to this event would be as a magnitude 9.0 quake.

  2. Just because the quake was a 9.0 at the Epicenter doesn’t mean it was that strong where the reactor was. The strength varies based on the distance from the Epicenter. Please don’t cause unnecessary panic. (Charles from Tokyo)

  3. Did I just hear someone say “Three Mile Island”?

    Time to get out that dusty old VHS videotape of “The China Syndrome”.

    1. I liked that movie, it made w Wilford Brimley a star.

      Here’s a previous Boing Boing piece about that fine actor:


      Seriously, it’s a good flick: Jane Fonda looks seventies-hot, and Jack Lemmon does his thing like the pro that he was, and Michael Douglas is forthright throughout.

      It is worth seeing , and it’s on dvd too.

      1. That was a GREAT movie. I really have a soft spot for it though; it was the very first movie my parents took me to!

  4. #
    0426: Japanese government spokesman Yukio Edano says radioactive meltdowns may have occurred in two reactors at the plant – AFP.

    0406: More on the specific dangers of Fukushima 1 plant’s reactor 3: The BBC’s Chris Hogg in Toky says the reactor is fuelled with uranium and plutonium, meaning the consequences of a meltdown are much more severe than at the other reactors.

    time checks are upto 10 minutes ago Japan time.

    This is not Chernobyl nor Three Mile Island.

  5. Did the quake itself cause any significant damage to the plants? My understanding is that the safety protocols in place worked (i.e. the reactors shut down in response to the quake), but then the coolant pumps were damaged in the subsequent tsunami, thus resulting in the present problems.

  6. This is likely going to go down to be worse than Three Mile Island but no where near the Russian/Ukraine reactor. It appears the pressure vessel was breached, and they had a melt down, and the secondary containment barrier is toast. They have nuclear byproducts (Cesium, Rebidium, Iodine) found in the atmosphere thus the used fuel is exposed to that air and releasing radioactive gas, small amounts of fuel and burnt fuel byproducts into the air.

  7. When you consider that the DAiichi-1 reactor *survived* a 9.0 magnitude scale earthquake (Thank you, Mithras), and only encountered problems when the 6 backup generators were taken offline by a 30′ tsunami, I’d say the engineers did a fine-*ss job building for a 7.9 magnitude temblor.

    It’s important to remember that Daiichi-1 reactor was due to be taken off line forever on Mar 26th of this year. Decommissioned.

    I learned today that the Spanish word for earthquake is “temblor”.

    I learned that Daiichi-1 was built in 1967, and went online in 1970.

    I learned what a BWR is, and the significant improvements that have been made since the GE3 designs were first put into productions.

    I learned that “meltdown” first entered popular vocabulary with The China Syndrome, a movie that was technologically way inaccurate, and that “meltdown” is not a technical term with a quantifiable definition.

    I learned that even if a meltdown (whatever that means) occurs at Daiichi or Daini, it won’t be like Chernobyl.

    I feel ashamed of the dingleberries who think this is karmic justice for Pearl Harbor, and ashamed that it took this series of disasters to make me go in search of information. But I am working on reducing my own ignorance.

    Good night, and peace be with Japan and the world.

  8. Japan ministers ignored safety warnings over nuclear reactors

    Seismologist Ishibashi Katsuhiko claimed that an accident was likely and that plants have ‘fundamental vulnerability’


  9. OK, maybe another dumb question, but I haven’t seen it answered anywhere yet: if partial power to run the station can be routed from the power of the steam turbines that the reactor itself is running, why is there no ability to convert this into AC power onsite for operation of controls, valves, etc. in lieu of the failed batteries and diesel generators?

    1. the backup system used batteries rather than ac generators. I think it’s a question of scale.

    2. Simply because most power plants are not designed for a “black” startup – they tend to assume that there is network power available.

      On top of this, the reactors were shutdown when the quake occured, so all that’s left is the energy from the decay heat in the core – which is enough to potentially damage the reactor, but at this point (more than a day after shutdown) is going to be less than 0.5% of the normal operating power – and that’s not enough to get the generators running.

      And even if they were given permssion to bring one of the reactors back on line, they would likely not be able to do so, since some of the decay products in the core (notably xenon-135) are highly effective neutron poisons and will have to be allowed to decay to a low level before the reactor can achieve criticality again. How long this will take depends on a wide range of factors – but it can easily be a matter of days.

    3. OK, maybe another dumb question, but I haven’t seen it answered anywhere yet: if partial power to run the station can be routed from the power of the steam turbines that the reactor itself is running, why is there no ability to convert this into AC power onsite for operation of controls, valves, etc. in lieu of the failed batteries and diesel generators?

      I wonder if there is an implied security requirement in this element of the design? Evil doers could take over the plant but it could still be shut down remotely by cutting the power.

  10. ssociated Press= TOKYO (AP) — Inside the troubled nuclear power plant, officials knew the risks were high when they decided to vent radioactive steam from a severely overheated reactor vessel. They knew a hydrogen explosion could occur, and it did. The decision still trumped the worst-case alternative — total nuclear meltdown.


  11. It’s good to know that after the nuclear plants have been devastated by a 9.0 shake they will survive the lesser aftershocks. Being that Japan is built on so many faults and nearby volcanoes, it seems so American that they would save money by not making the buildings withstand anything higher than a 7.9.
    I suppose the recent requests for building new plants in the US can withstand a 4.3. It would be too spendy to make or test them for anything stronger. Stockholders would see smaller dividends otherwise.

  12. #10, Moosedesign:

    I posed this question to a friend who has a better grasp of nuclear engineering than I do;

    It boils down to this as I understand it: The coolant pumps demand more power than the reactor is capable of generating.

    I know, I know, I find it hard to understand, too. Seems more modern plants use gravity to feed the coolant to the core rather than pumps, as well.

    Not sure how that works. I could be WAY wrong on this, too. But let’s face it, it’s all water out to sea at this point.


  13. The real issue with structural design isn’t the magnitude, but the intensity of shaking, which is measured on the Mercalli intensity scale.

    Shaking varies with distance and depth. A 7.9-magnitude quake on a near-surface fault in the immediate vicinity of the structure could easily generate shaking in the Mercalli IX-to-X range. (Mercalli uses Roman numerals to avoid confusion with magnitude.)

    The epicenter of the recent quake, despite the main shock’s magnitude of 9.0, was about 150km away from the reactor and about 24km deep – so it only produced shaking in the Mercalli VI-VII range at the reactor’s location.

    That’s far, far less than what a closer magnitude 7.9 could have produced.

    And 7.9 is a reasonable estimate for a maximum credible nearby quake from a near-surface fault. Subduction-zone quakes can be larger because the physical mechanism is different – but they will always be at some depth, and – in Japan’s case – some distance offshore.

    A structure designed to survive the shaking from a nearby 7.9 could easily survive the shaking that this quake produced at Fukushima.

    And, as previous commenters have noted, it did. It wasn’t the quake itself that precipitated the reactor crisis, it was the tsunami.

  14. @a_user: i had understood that it was that lack of available AC that was to be provided by the now dead batteries. Again, INANE (I’m not a nuclear engineer… deliberate acronym), but if the facility to convert the energy being created by the turbines into usable AC power was available then conceptually, assuming the scale was sufficient, you would have the power you needed. Further, if it is indeed a matter of scale and you are trying to increase redundancy then perhaps the ability to slave functioning power generation of the other reactors’ turbines to the troubled reactor’s controls would be an option?

    @E. Howe: “It boils down to this…” OK, I did appreciate that… This is totally outside my realm, but I do find it difficult to believe that even a single reactor’s turbines wouldn’t provide the power necessary to run the valves and controls that are apparently in need of power at the moment. The scale is probably entirely beyond me, but if a diesel generator or batteries can do it, its hard to imagine that a reactor’s turbine that presumably powers a great deal more when online wouldn’t be up to the task.

    Would be interesting to know the volume of water that is needed to cool the reaction, and in turn the number and power of the pumps (I am assuming the issue is the feedwater pumps and not those within the inerted drywall) employed for that purpose to get a better sense of scale. From the WNN’s website it does appear that Unit 1 (that experienced the explosion) is the oldest of the reactors from Fukushima Daiichi or Fukushima Daini, dating to 1971. Perhaps its age is part of the issue…

  15. BTW, it should probably be stated that all of my above is pure ignorant speculation and genuine curiosity and isn’t meant in any way to be a criticism of the engineers at the troubled facility. I have no doubt that they are doing everything that they can under horrific circumstances, with an unknown level of damage that the tsunami undoubtedly dealt and worst of all, the death and injury of a number of their co-workers working the very problem. I regret that I hadn’t mentioned that earlier…

  16. Re: Steam power to move the cooling pumps:
    Anon #24 certainly sounds like they’re making well-informed, rational points, and I’m not going to provide any beter armchair nuclear engineering.

    But, interestingly enough- based upon my minutes and minutes of research on Wikipedia last night, I read a lot of details on what happend at Chernobyl that had managed to escape my attention for the past 20 years.

    Chernobyl engineers faced the problem of “How do you cool the reactor and power the cooling pumps when you’re trying to cut all the power coming out of the reactor, and there’s no power available on the grid?”

    There were three diesel generators on site that were designed to do just that. [I suppose they would do little good if they were swamped by a tsunami.] The problem with the existing generator design is that they took 60 seconds to come online, and that was deemed too long of a time period to leave the reactor uncooled. So, an experiment was created! The question to be answered was, “Can the remaining energy of the spinning steam turbine provide enough electricity to get through the 1 minute gap?”

    The answer, as previously determined through experiments, was no. Another few variables were tweaked, and then a test was scheduled for a day in which they were going to shut down the reactor for maintenance.

    1: The power plant in Kiev sut down unexpectedly that day, so the Chernobyl plant stayed online longer than intended. The day shift operators who had been drilling on the procedures weren’t available. The night shift operators started following unfamiliar processes.

    2: At the beginning of the test, it was calculated that the power from the Generator had to be outputting 700-800MW. This was going to be enough to power the turbines for the desired test window. During the leadup to the test, the output from the Generator inadvertently fell to 30MW.
    The operators tried to get the power level back up, but essentially, the reactor was in a “cooling state”. In order to quickly get back to the desired power levels, the control rods were almost fully withdrawn, which created a slingshot effect. (Instead of being at a steady state, or cooling at 700MW, it was now racing upwards rapidly.)

    3: When the test started, there wasn’t enough energy left in the turbines to keep the coolant circulating as desired. Even after the Diesels were brought online, the reactor was boiling off the coolant, which made things get even hotter. Automated safety systems appear to have kept things mostly in check, but about a minute after the test, somebody felt the need to hit the big red “shut down the generator button.” (unknown why, as the engineers perished.) When the control rods were lowered into place to shut everything down, there was a design flaw which displaced coolant, and made things even HOTTER for awhile.

    4: At this point, bad things happened. Too much heat contributed to some control rods fracturing. This caused an inability to further stabilize the reactor, which resulted theoretical spike of power from near zero, to 550MW (as per instrumentation) and then to about 30GW. (theoretical, and about 10 times normal output.) Now, lots of heat = Lots of Steam = Expanding pressures = ruptured valves = more heat = more steam = more ruptured everything = more….

    So there’s the “dude who read it on the internet’s” synoposis of “something posted on the internet by an unknown source.” Take it with plenty of grains of salt.

    But Now realizing that the accident was created by higher-level-chain-of-command employees intentionally forcing the reactor into an unknown state, and the worker bees trying to meet these goals even when everything around them is indicating that it’s a bad idea- that explains a lot.

    [granted, the apparent 60 second coolant window during shutdown that was already deemed “unacceptable” must have been a pretty bad design flaw. But get people involved, and things hit the fan quickly.]

  17. I’d love to see the headline of this article modified to have “and it did” at the end.

    As can’t be pointed out enough, the reactor did fine with the quake. It was the tsunami that took out the generators that did it.

  18. Hi. I hope I can help clarify a bit of this for you guys. I work in a PWR nuclear power station. I’m fairly new to the industry so my knowledge is a bit limited.

    When the quake struck the plant safety systems will have auto-tripped (shutdown) the reactor, which trips the turbines.

    At this stage any steam that is still being produced is dumped (into a start up vessel) as it tends to not be of a high enough quality for the turbines- poor quality (too wet) steam can damage the turbine blades and cause it too disintegrate- which would write off the plant and be a very serious accident.

    At full power the station uses about 10% of the electricity it produces to power pumps valves lights etc. The reactor coolant pumps use a lot of this power to pump about 100,000 gallons/min through the reactor (in a PWR). After a trip a much lower coolant flow rate would be required (not sure exact level?).

    Generators produces AC power during operations.

    Emergency generators produce AC power for post-trip cooling and instrumentation etc.

    Batteries supply DC power after trip until emergency generators are online. DC power is converted to AC by an inverter to run plant.

    A meltdown is when the fuel cladding (zircaloy) heats up beyond its melting point (1850ºC ; 3362ºF) and the fuel is released into the core. This is considered a breach of the 1st boundary; the 2nd boundary is the reactor pressure vessel; the 3rd the reinforced concrete containment building. At this stage it is unconfirmed whether or not the fuel cladding has melted.

    This is the 1st close up photo I have seen of the station. It looks like the blast only blew of the building facia panels. hopefully the reinforced concrete containment building is still fully intact. It should be- these buildings are built to with stand exactly this kind of event. Reports are that the pressure vessel is still fully intact.

    The radiation levels recorded are likely just from the vented steam. Any fission products in the steam are quite possibly a result of failed fuel in the reactor (pin whole cracks in the fuel cladding from where it rubs against the support grids) which are not uncommon.

    The media have massively over hyped this event. I hope it will not effect international new build projects as quite frankly we need them. There are lots of old nuclear power stations that are nearing the end of their lives that need replacing and nuclear is the only mass generation low carbon energy available. If public opinion goes against nuclear then utility companies will build coal or gas plants which churn out millions of tonnes of CO2 / day. That will only speed up global warming.

    Please see through all the media hype and wait until all the facts are available. I think that this event will at its very worst be equivalent to TMI; a disaster, but not damaging to public health or the environment.

  19. Are you sure that the Tepco documents weren’t referring to shindo 7.9, which is the Japan Meteorological Agency’s seismic intensity scale? At Fukushima, the quake was about shindo 5.

  20. To the idiots saying this is karma for pearl harbour:

    Dropping nuclear bombs on Nagasaki and Hiroshima in response to pearl harbour wasn’t enough for you?

    Maybe you will be proud to know that the reactors that are failing in Japan are AMERICAN made GE reactors.

    The Japanese should have told the USA “no thanks, we will take the Canadian design reactor” back then.
    But, of course, Japan was still under the thumb of USA back then.
    (The Canadian “candoo” reactor design back then shuts down and goes cold if there is any failure.)

    To Americans who are sane and normal, I apologize for this post.

    America seems produce a lot of racist, fear mongering, hate spreading, ignorant jackasses that do Nothing to improve the USA’s image.

  21. so,, in a land of earthquakes… why was the reactor built at such a low quake-proof threshold ??

    why not build all power stations in japan with much higher thresholds??

    were they trying to save a quick buck by spending less on quake-proofing the most potentially dangerous objects on earth?

    Thank you TEPCO for being ‘tight’ and causing a world wide problem!

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