Thoughts on Fukushima-Daiichi

In the mid-afternoon on Friday, March 11, 2011, the seismic sensors at the Fukushima-Daiichi nuclear power plant in the Fukushima Prefecture of Japan registered the earliest indications of the largest earthquake in modern Japanese history. They executed a preprogrammed response and began to drive all of the long control rods into the three reactors that were currently operating at the site. The control rods caused each generation of fission to produce fewer neutrons and fewer fission reactions. In three minutes the reactors were making 10% of their rated power from fission; in six minutes they were making 1%, and within ten minutes nuclear fission as a source of heat had ended in the first three units at Fukushima Daiichi. It would never begin again.

Each fission reaction splits the nucleus of an atom of uranium-235 or plutonium-239 into two smaller atoms and releases a great deal of energy. The energy release from nuclear fission is roughly a million times greater per unit weight than fossil fuels, which is why nuclear fission is such a compelling long term energy source. The two “fission products” that result are highly radioactive but decay towards stability very quickly. There are about 80 different sequences of decay that fission products can follow, and roughly a quarter reach a completely non-radioactive state within a day. Within a month, about three-quarters are stable, and within a year, about 80%. But in the first few hours after a nuclear reactor shuts down these fission products are producing significant amounts of heat and, unlike fission, this heat generation can’t be turned off. It has to run its course to completion. Therefore, managing what is called “decay heat” is one of the most important aspects of operating a nuclear reactor safely. To remove the heat, today’s reactors have an abundance of safety systems, all of which have the same mission—keep removing decay heat from the nuclear fuel. As the reactors at Fukushima-Daiichi cooled down, the tsunami hit.

The tsunami destroyed the diesel generators that provide power to drive the pumps that circulate the water coolant through the reactor that removes decay heat. Without an active removal of decay heat, the reactor was adding heat to the water faster than it was taking it out, and the temperature was rising. Because this was a reactor that operated on water that was already at its boiling point, this also meant that the pressure inside the reactor was rising as well.

The reactors at Fukushima-Daiichi are called boiling-water reactors (BWRs) and were manufactured by General Electric. They have a primary and a secondary containment structure, both made from thick reinforced concrete, to protect against the release of radioactive materials. Inside the primary containment are two vessels called a “drywell” and a “wetwell.” The drywell is a large steel pressure vessel that looks like a giant upside-down pear and holds the reactor and primary pumps, and the wetwell is a large toroidal vessel that looks like a donut. The wetwell is connected to the drywell by a number of wide pipes. Both the drywell and the wetwell are surrounded by a secondary containment vessel (or shield building) also built from reinforced concrete about a meter thick. This rectangular secondary containment building is the structure that most people have seen in pictures of the reactor. At the top of the secondary containment building is a steel frame structure with “blowout” panels that holds the crane used to remove solid nuclear fuel during fueling and refueling.

The designers of the reactors at Fukushima-Daiichi had anticipated situations where pressure was rising in the core. So long as power was available, pumps would circulate hot fluid from the reactor to the wetwell where it would be condensed. Heat removal could continue indefinitely in this way. But it all relied on a power source, and power had been lost due to the tsunami’s destruction of the diesel generators.

The water in the reactor is susceptible to damage from radiation, causing it to split into its components, hydrogen and oxygen. Normally, circulation would channel the hydrogen and oxygen to a recombiner where they would be restored back to water, but in the hours after the reactors were shut down, hydrogen was accumulating and separating in the wetwell and reached a point where it was vented into the sparse steel-frame structure at the top of the reactor building. It was only a matter of time before the hydrogen reached a level where it would detonate, and one after another, the first unit, then the third unit, and finally the second unit, suffered hydrogen explosions that blew off the steel panels and left the top of the reactor building exposed. The reactor vessels remained intact as did the reinforced concrete containment buildings, but each reactor building lost its hat due to the hydrogen explosions.

Initially there was hope of saving the reactors to generate power again after the crisis had passed. But as that hope faded and the need to remove the steadily-decreasing decay heat remained, operators at Fukushima-Daiichi took measures that would cool the reactors but would ruin them for future operation, such as the decision to try to cool the reactors with seawater. It will be necessary for some time to actively cool the reactors while the decay heat continues to decrease, but within a few months it will be possible to depressurize the reactors and assess their internal states. There may have been some melting and damage to the fuel—it is not known at this time.

What is known is that this is a situation very different than Chernobyl or Three Mile Island. There was no operator error involved at Fukushima-Daiichi, and each reactor was successfully shut down within moments of detecting the quake. The situation has evolved slowly but in a manner that was not anticipated by designers who had not assumed that electrical power to run emergency pumps would be unavailable for days after the shutdown. They built an impressive array of redundant pumps and power generating equipment to preclude against this problem. Unfortunately, the tsunami destroyed these systems.

There are some characteristics of a nuclear fission reactor that will be common to every nuclear fission reactor. They will always have to contend with decay heat. They will always have to produce heat at high temperatures to generate electricity. But reactors do not have to use coolant fluids like water that must operate at high pressures in order to achieve high temperatures. Other coolant fluids like fluoride salts can operate at high temperatures yet at the same low ambient pressures as the outside. Liquid fluoride salts are impervious to radiation damage, unlike water, and don’t evolve hydrogen gas which can lead to an explosion. Conventional solid nuclear fuel like that used at Fukushima-Daiichi can melt and release radioactive materials if not cooled consistently during shutdown and for a cool-down period thereafter. Liquid fluoride salts can carry fuel in a chemically-stable form that can be passively cooled without the need for pumps driven by emergency power generation. There are safe nuclear solutions even in extreme situations like those encountered at Fukushima-Daiichi, and it may be in our best interest to pursue them.

42 thoughts on “Thoughts on Fukushima-Daiichi

  1. Kirk,

    Love your site and thanks for hanging it out there with the forward thinking. It is generating some good conversation.

    Regarding the Facebook links, I would /think/ the following link might be helpful. If not, google "how do I add facebook links to a website page?" and you'll probably find lots of content. It seems, at a glance, to be straightforward to insert although I haven't done it myself (yet).

    I hope this helps.

  2. @Phred: I also hope there won't be a mass reaction against nuclear, but, going by the reactions of my friends, I'm not optimistic. Intelligent, well-educated friends (though non-scientists) are repeating the hysterical stuff they see on TV and in the press, e.g. "Well, the reactors have melted down, haven't they?", and "Nuclear reactors have the potential to contaminate vast swathes of the planet". No amount of referring them to articles like this one seems able to change their minds. These are the sort of people who run the country.

    My worry is that the plant operators and/or the Japanese authorities haven't been telling the truth, because that would make liars out of everyone who has done analysis based on what they said. I guess only time will tell.

  3. I am a retired Metallurgical and Nuclear engineer. I am quite familiar with the two first reactors built at Fukushima.

    1)Most experts in fact have probably never been inside a nuclear plant, they are probably experts of nuclear reactions – not nuclear plants.

    2) The GE mark I and II design is: compact, cheap and NOT safe. A number of Atomic Energy Commission experts have criticized these units since 1972 – the year after the first Fukushima reactor was installed.

    3)The Fukushima units are BWR units, boiling water reactors, in which the reactor cooling water boils and leaves the reactor housing to a long loop to the turbines. The reactor concrete pad is reasonably thick and allows the reactor to "float" during a severe quake.

    4) But the turbine building is on a completely different concrete pad. During the quake the two pads can move with respect to one another. This apparently broke the big pipes of the cooling system, the same pipes that are used by the emergence pumps. (Nice cheap compact design)

    5) At this point all the redundant (bad design to save money) pumps count for nothing because the pipes are broken.

    6) In 1972 the company I worked for negotiated for almost a year to install a competitive, safer and more expensive design for the second reactor.

    7) The Japanese are technically competent, and quite rigorous regarding maintenance – but are even more hard headed than either Germans or Americans. At the time a young Japanese engineer told me that the Japanese had already decided on a design and to accept our design would mean that they would have to admit to a mistake on the first reactor.

    8) I was informed unofficially that the primary decision makers would die before admitting that our design was better, and unfortunately take several thousand people with them.

    9) A simple fact that no one seems to be sufficiently competent to understand: In a high risk environment of rupture of the cooling piping (as a sub or war ship or highly seismic area) a PWR Pressurized Water Reactor is indicated. For a situation with a VERY low risk of cooling pipe rupture, A BWR Boiling Water Reactor is ok, but in my opinion not the Mark I or Mark II designs.

    10) The Japanese are much worse than Americans in hiding the real facts and cover ups of every type to avoid being blamed for screwing up and "losing face".

    11) Real honest to goodness "drop dead" safe nuclear plants can be constructed – but they are not from the lowest bidder and are probably not consistent with high company profit and or back room politics.

    12) I am sorry for the Japanese people, but they paid for a half assed design and that is what they got.

    13)The top of the secondary containment building, contains the "spent fuel" pools (check out the diagram). Has any expert explained how the top of the building can blow off and the primary and secondary containment remain ok???

    14) Well, I'll tell you. The Mark I design is very compact, and the tanks on either side of the secondary containment building (near the top of the reactor)are the spent fuel pools. Pools, as in concrete tanks, but not as robust as the secondary containment. During the quake, the cooling pipes to the pool were also ruptured, maybe even the tanks cracked. The water level lowered either due to a leak and or boiling in the tanks. Boiling is not just bubbling, it is the separation of the hydrogen and oxygen atoms forming the water.

    15) So when the top of the building (simple metal construction)fills with hydrogen and the pressure increases, it explodes due to pressure. The flame you could see in the explosion is the hydrogen recombining with atmospheric oxygen and creating a fast flame front or a slow molecular explosion, having nothing to do with the reactor or it's contents.

    16)The reactors however can continue their progression toward a melt down, but while possible, less likely.

    17) I hope this at least partially explains how we got here and why even considering the seriousness, is not a reason to automatically be anti-nuke. Anti-political for a technical issue is good sense. Purchase cost and utilization cost are not the same thing – either in dollars or safety


  4. Can you please elaborate how "decay heat" is produced for hours thought the fission has stopped.

  5. @Joydeep Banerjee:

    This explanation of "decay heat" is not exactly correct, but sufficiently correct to help non experts.

    Everyone is probably aware that food cooked in a microwave oven should "rest" for about 1.5 minutes per inch of thickness – after the microwave cooking stops. Why??

    A microwave heats by virtue of the radio waves that are "micro" and are a multiple of the atomic bonds holding the hydrogen and oxygen together to form the water molecules. This micro-ness allow the microwaves to "excite" or cause the atomic bonds to vibrate. This vibration causes the water molecule to heat up. Perhaps you have heard small "pops" in the microwave during cooking, this is surface water molecules becoming too excited and the vibration exceeds the atomic bond strength holding the water molecule together. So it sort of explodes, creating a small steam bubble. Once these atomic bonds begin to vibrate, they do not stop immediately. So if you take a bite of food too soon after microwave cooking, the water molecule is still vibrating – AND sucking air or a small sip of water will not stop the vibration immediately.

    But this is just vibration energy and it stops after a couple of minutes.

    The next most powerful heating is when molecules, explode, disintegrate and the atoms recombine to form molecules of less energy – giving off the lost energy as heat. This can be a fire (a slow flame front) or an explosion (fast flame front) and can be as simple as a forest fire or house fire which is a little more difficult to stop. The reason is that the fuel needs to be cooled to the point where it no longer gives off combustible gas (typically hydro-carbons) that mixes with oxygen creating other lower energy molecules and giving off heat.

    Next is atomic or atom explosion in which electrons of an atom escape and create a different atom.

    Now to your question. A nuclear reaction is the explosion of atomic nuclei, hence nuclear.

    When radioactive fuel is placed close together the high energy sub-atomic particles that fly around (and kill people) strike the nuclei of nearby atoms. This high speed impact causes the nuclei to sort of explode, creating more high speed particles – that in turn bump into other nuclei and split them also. In a bomb this happens very quickly, in a nuclear plant it goes much slower, but not easy to stop.

    The normal method of stopping the reaction is to insert "control" rods or "moderator" rods made of some appropriate material like carbon. These rods are inserted between the fuel rods, slowing the high speed particles flying around. But even after "nuclear shutdown" when the reactor is putting out perhaps as little as 2% of it's normal power – 2% of a big number is still a lot. So the high speed particles are slowed, but the nuclei just split create very high speed particles that can still hit and split another nuclei. Statistically this is much reduced and begins to slow down, but depending on dozens of factors as design and fuel type the requirement for cooling can be a week or so before the reactor is "cold".

    During the film clip of the "reactor explosion" you can see an orange ball of flame – what the hell is this??

    In the particular GE design and Mitsubishi construction of these BWR boiling water reactors, The thick metal reactor core is in the center, surrounded by a sort upside down light bulb shaped containment building. This building is quite thick and safe and narrow at the top. So GE to save space decided to place the "spent fuel" rods in a pair of cement pools on either side of the top of the reactor containment building. Spent fuel is not dead, just not sufficiently active to be used efficiently as fuel. BUT quite dangerous if it heats up.

    From the diagram of the plant, you can see the tanks and some schematic spent fuel containers in the pool on the right. The top of the reactor building is really not the reactor building but just a heave sheet metal shed covering the cranes, spent fuel pools and some other equipment.

    In my opinion, when the quake ruptured the reactor cooling pipes, it also ruptured the pool cooling pipes, and maybe even cracking the pools. In any case the spent fuel rods heat up, boil the pool water and create hydrogen. After a while, the pressure gets high and the building walls bulge out, this allows the hydrogen to recombine with oxygen in the atmosphere and blows the shed to bits. Very impressive, nice big orange flame and some radioactive stuff blown out of the water pools.

    But this is not either the containment building (pretty tough about 3 feet thick reinforced concrete) or the reactor vessel ( also pretty tough, usually 6 to 10 inch thick steel with a 3/16 inch stainless steel liner.

    Of course things can go bad in a hurry, but I doubt if the reactors or the containment building will explode. However the other spent fuel pools could. The problem is probably that radiation from the pools is preventing close in work to cool the reactors.

    Sorry so long and perhaps boring.


  6. @ Riccio,
    Brilliant to see a measured response based on fact and knowledge. The news agencies are doing their best to contradict each other at the moment even within their own companies. The fact is that no one really knows what is going on but the conclusions you have drawn certainly are the best I have yet to hear.
    Please share any more insight you have into this situation that will satisfy the minds of people who need something in a bit more detail than the news agencies can provide!

  7. Back again with just a couple of thoughts regarding the Fukushima nuke plants, and the Japanese and US generated comments.

    Two "once in 500 years" disasters can can happen in successive years or the same month. Everything is perfect from 1511, then two disasters, then everything calm again until 2511. You see, a once in 500 years occurrence, bad timing on your part – everything was fine, only two incidents for 1000 years – except you got fried. So be careful about probability and "how infrequent" something can happen.

    The other issue is ENGINEERING. No matter what your profession is, you probably know how to do something or make something. It could be as simple as baking a cake. This sounds pretty simple. What does it have to do with nuclear plants???

    The cake usually turns out as desired, but generally only when you spend the proper amount of money. Making a cake, but without some ingredients or less of the important ingredients can give you a bad cake.

    Now if you build a nuke plant to a required kw cost, or to a required maximum "foot print" area or other political or financial restraint for a purely technical problem — I see no way to not end up with a bad cake.

    There are definitely people who have graduated from big name Engineering schools, who in reality are not Engineers. But there are much greater numbers of accountants (whose job is)to contain costs, limit testing etc. and who proudly say they are not interested in technical issues – that is an Engineering problem. This explains why I left the nuke industry in the early 1980's.

    I think this is also a partial explanation of most major technical disasters, dams, maybe the shuttle, soviet nuke plants and perhaps other things that we were made to swallow as "unknowable" and unpredictable. I think that many Japanese knew with 100% certainty that there would be a big quake — only the when was a bit fuzzy.

    While in the nuke industry, my real specialty was high strength nuts and bolts – for primarily my own mental health I was merciless on suppliers as well as users.

    Maybe some of you have heard of the more recent theories about the Titanic: to save money they used cheap rivets, oddly enough an unsinkable ship had some significant vertical movement during it's scheduled horizontal ocean voyage.

    Last tidbit, are you really sure that all official communication is intended to communicate?? They need to seem to communicate, which causes a lot of people to flap their gums. Real communication, first requires something to communicate – then often a translation from big complicated words to simple un-confusing words. Non communication (while seeming to)is full of weasel words, using the correct words in a confusing manner and sort of like a condom — making you feel safe while getting it in the rear.



  8. @Riccio
    Thank you very much for your detailed analysis and explanation of the GE BWR at Fukushima.
    I'd like to know if the problem can be contained once power is restored to the plant, and the cooling system can once again be operated. Would the cooling systems have sustained any damage as a result of the explosions? Will these cooling systems have any effect on the spent MOX fuel rods in reactor 3?
    Thank you.

  9. @Porcine Majesty:

    1) The most probable damage outside the reactor containment building is:
    A) the primary pipes to and from the turbines
    and perhaps tens of thousands of feet of
    interconnecting electrical cables.
    B) the emergency power diesels – we don't know their
    C) it seems and is my opinion that the spent fuel
    tanks have sustained either integrity damage
    or cooling system damage, AND radioactivity
    damage from the hot stored "spent fuel"
    D) the sheet metal shed on top of the reactor
    containment building has been blown to bits,
    probably ruining the jillion dollar crane,
    and maybe further damage to the fuel pools.
    E) everywhere in a big power plant of any kind
    there are cable trays carrying both power and
    control to all the primary and secondary
    systems – these probably have to be replaced.
    F) plus there is junk everywhere.
    ** all of these things can be replaced or repaired.
    it is just a matter of money and two or three
    2) At this point we do not know exactly what has been damaged inside the reactor building. Really difficult and expensive, but they would probably fix it.

    3) In my opinion, if there is moderate damage to the fuel core inside the reactor – they would also replace the core – difficult and expensive. If however, the reactor vessel has been seriously damaged, it probably would cost less to get it cooled down, close it up and forget it — possibly moving the turbines and outside equipment.

    4) Keep in mind that no. 1 reactor came on line in 1971, no. 2 in 1974, I no was longer involved but I think no. 3 was in 1977, etc. So if you replace the engine in your 1975 Honda, replace all the pipes and cables, fix the starter, replace the fuel tank and then paint it. You have a $10,000 1975 Honda – that the insurance company may or may not insure.

    5) I really don't know how much or how many of their 6 on site reactor complexes are damaged. It may be cheaper just to "walk away", enter a nice comment in the shareholders statement and forget Fukushima or at least the three seriously wounded?? Don't be surprised. On the other hand the Japanese are strange folks, perhaps they will take it as a mater of national pride to clean-up a two or three billion dollar junk yard.

    6) from an "engineering" point of view, a non radioactive reactor building can be replaced (probably about 6 years), using all the outside equipment (including the generators and turbines) and don't forget the real estate issue. This area was setup and probably still is to transport millions of kw to the nearby areas.

    7) the biggest issue for people who have never been inside any BIG industrial plant, is how big everything is. Valves as big as an old Lincoln, pipes from 10 inches in diameter to 5 feet in diameter, just replacing a big valve can take several weeks – when everything is ok.

    This is like a bad cold, it will probably get worse for another two weeks and then slowly get better. Keep in mind it is hard to fix the kitchen sink if the house is upside down – Fukushima is like a war zone.

  10. @Steve:

    "Excellent post. The hysteria that the media has injected into all of this is totally irresponsible and maddening. More broadly, the whole thing speaks to a sad lack of quality in education systems.

    Well done and keep the objective sense coming."

    You said it better than I ever could. After a couple of days of fretting and worrying, common sense kicked in and I stumbled onto blogs such as this (and Atomic Insights). What I've seen and read here and there makes me want to kick myself for getting caught up in the panic and misinformation that's being spread in the MSM.

    There are thousands of people in Japan who are facing cold, hunger, and homelessness caused by a major earthquake and the resultant tsunami. Thousands are dead. Not one of these deaths resulted from Fukushima.

    Keep up the good work…

  11. I'm a 86 year old coger honorably discharged from
    the USMC in 1945 after 4 years of service. I finally
    got a BS in Engineering Physics from The University of
    Tennessee in 1953 and finished a career as an Inertial Guidance Systems Engineer in 1989. In that life I became
    a professional non-believer not inclined to go along to get along. In my terminal condition I am a Diest looking forward to whatever comes next.
    My education did not include much on the subject of nuclear physics but I do have an opinion on the subject
    of Uranium fueled vs Thorium fueled reactors. My opinion
    is derived from reading much recently about LTBR's and
    from the media regarding Uranium Reactors at Chernoble, Three Mile Island, and Fukushima with it's surrounding 50 mile radius of trash, cold, powerless heaters and broken lives.
    Nature's Formula For Success is found in a natural law of behavior ID'd by the late Richard W. Wetherill in his book, "Tower of Babel". He called it nature's law of absolute right. It states: Right Action Gets Right Results; Wrong Action Gets Wrong Results.
    Since I am a Diest I must say nature's law is God's law and Fukushima is God's way of telling humanity to
    drop Uranium in favor of Thorium.
    We built B29's and Tanks by the thousands In WWll. I
    think we should and will build LFTR's by the million as soon as we can get assorted bureaucrats out of the way.
    Hoo-Rah for Kirk Sorensen!
    Semper Fi
    Bill Javert

  12. @MarkMcenzie
    Good post.

    Adding to the mass "non-hysteria", I have a nasty, sarcastic and heartless thought.

    I see quakes in the middle east, asia, china etc. the stone houses with no steel reinforcing always cave in and kill everyone, and it is a big deal. But they lived fine for years in homes they couldn't afford – the bill just finally came due.

    In Japan as well as the rest of the modern world, there are nuke plants. Probably not ideal designs, probably not perfect construction and probably not perfect operation. But we could afford it, because it was cheap (a horse power hour or manpower hour costs practically nothing) and we have enjoyed a great, high quality lifestyle.

    So really, if we have a little nuke disaster that kills 10,000 or 20,000 people every 10 years or so (because the bill came due) where is the tragedy?

    It would be an insignificant percentage of the car related deaths — sure don't see the Emperor, Bill Clinton, Barack Obama etc. clamoring for the death penalty for my Ford truck.

    So why all the fuss?

    Actually I am about 98 % serious, and not criticizing your post.

    But if we want electrical power at a price too low for the technology, sooner or later – the bill will come due.

    Being as we are dumb shits, apparently we can't afford the Concord, NASA, drop dead secure nuke plants, clean air, really safe cars – yet we want all this neat stuff. So I am thinking that most big technical disasters (including living below sea level or too close to non-dredged rivers) is just getting the other half of the bill.

    Once everyone really digests this, maybe it will be easier to justify higher up-front costs – to save the bacon later.

    You know, you put too many people in India on a ferry – maybe it gets top heavy and flips over – is this a surprise?

    Just a thought on hysteria, the boogie man, (lack of) education and delayed payment projects.


  13. Thorium sounds good, but in the meantime if you want safe nuclear reactors you have only to go to the U.S.Navy.

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