Several of Japan's nuclear power plants, especially the Fukushima Naiishi plant in northeastern Japan, are experiencing serious problems in the wake of Friday's earthquake and tsunami. If you've been following the news, you've seen some pretty alarming stuff going on at this plant--terms like "explosion," "partial meltdown," "evacuation," and "radiation exposure." With details sparse from the chaotic scene, here's what you need to know to understand and make sense of the news unfolding in Japan.
What Is a Nuclear Reaction?
A nuclear reaction is at its most basic nothing more than a reaction process that occurs in an atomic nucleus. They typically take place when a nucleus of an atom gets smacked by either a subatomic particle (usually a "free neutron," a short-lived neutron not bound to an existing nucleus) or another nucleus. That reaction produces atomic and subatomic products different from either of the original two particles. To make the kind of nuclear reaction we want, a fission reaction (in which the nucleus splits apart), those two original particles have to be of a certain type: One has to be a very heavy elemental isotope, typically some form of uranium or plutonium, and the other has to be a very light "free neutron." The uranium or plutonium isotopes are referred to as "fissile," which means we can use them to induce fission by bombarding them with free neutrons.
In a fission reaction, the light particle (the free neutron) collides with the heavy particle (the uranium or plutonium isotope) which splits into two or three pieces. That fission produces a ton of energy in the form of both kinetic energy and electromagnetic radiation. Those new pieces include two new nuclei (byproducts), some photons (gamma rays), but also some more free neutrons, which is the key that makes nuclear fission a good candidate to generate energy. Those newly produced free neutrons zoom around and smack into more uranium or plutonium isotopes, which in turn produces more energy and more free neutrons, and the whole thing keeps going that way--a nuclear fission chain reaction.
Nuclear fission produces insane amounts of energy, largely in the form of heat--we're talking several million times more energy than you'd get from a similar mass of a more everyday fuel like gasoline.
Getting Usable Energy From Fission
There are several types of nuclear fission reactors in Japan, but we're going to focus on the Fukushima Naiishi plant, the most hard-hit facility in the country. Fukushima, run by the Tokyo Electric Power Company (TEPCO), has six separate reactor units, although numbers 4, 5, and 6 were shut down for maintenance at the time of the earthquake (and more importantly, the subsequent tsunami). Numbers 1, 2, and 3 are all "boiling water reactors," made by General Electric in the early- to mid-1970s. A boiling water reactor, or BWR, is the second-most-common reactor type in the world.
A BWR contains thousands of thin, straw-like tubes 12 feet in length, known as fuel rods, that in the case of Fukushima are made of a zirconium alloy. Inside those fuel rods is sealed the actual fuel, little ceramic pellets of uranium oxide. The fuel rods are bundled together in the core of the reactor. During a nuclear fission chain reaction, the tubes heat up to extremely high temperatures, and the way to keep them safe turns out to also be the way to extract useful energy from them. The rods are kept submerged in demineralized water, which serves as a coolant. The water is kept in a pressurized containment vessel, so it has a boiling point of around 550 °F. Even at such a high boiling point, the burning hot fuel rods produce large amounts of steam, which is actually what we want from this whole complicated arrangement—the high-pressure steam is used to turn the turbines on dynamos, producing electricity.
Since lots of heat is being produced, as well as the production and use of lots of pretty nasty radioactive materials, nuclear plants employ a variety several safety efforts beyond simply the use of the cooling water (which itself is backed up by redundant diesel generators--more on that later). The plant's core, the fuel rods and the water, is encased in a steel reactor vessel. That reactor vessel is in turn encased in a giant reinforced concrete shell, which is designed to prevent any radioactive gases from escaping.
Isn't There an "Off" Switch?
Sure! But needless to say, safely shutting down and controlling a nuclear reactor is not at all as simple as unplugging a rogue kitchen appliance. This is due to the extreme heat still present well after fission has subsided--mostly due to chemical reactions inherent in the fission reaction.
A functioning fission plant employs a system of control rods, essentially structures that limit the rate of fission inside the fuel rods by absorbing roaming free neutrons. The rate of fission can be controlled--even stopped--by inserting and removing the control rods in the reactor. At the time of the quake, the Fukushima reactors' control rods functioned normally, shutting down the fission reaction. But even with the fission reaction stopped, the fuel rods remain at extremely high temperatures and require constant cooling.
Which isn't typically a problem, so long as the cooling system (and, failing that, its diesel-powered backup) is still intact. But after losing main power in the quake, the subsequent tsunami wave also destroyed Fukushima's diesel backup generators. Which is a serious problem; even though the fission had stopped, coolant is still very much required to keep the plant safe.
That's due to the heat that remains in the nuclear core, both from the recently-disabled but still-hot fuel rods and from the various byproducts of the fission process. Those byproducts include radioactive iodine and caesium, both of which produce what's called "decay heat"--residual heat that is very slow to dissipate. If the core isn't continuously cooled, there's still more than enough heat to cause a meltdown long after it's been "turned off."
In the case of the Fukushima plant, with both the main and backup coolant systems down for the count, TEPCO was forced to rig a method to flood the core with seawater laced with boric acid (the boric acid to stave off another fission reaction if one were to restart due to a meltdown--more on that below). That's a bad sign--it's a last-ditch effort to prevent catastrophe, as the salt in the seawater will corrode the machinery. It's also a temporary fix: TEPCO will need to pump thousands of gallons of seawater into the core every day, until they can get the coolant system back online. Without it, the seawater method might have to go on for weeks, even up to a year, as the decay heat slowly subsides.
The Dreaded Meltdown
First of all, a "meltdown" is not a precisely defined term, which makes it fairly useless as an indicator of what's going on. Even the terms "full meltdown" and "partial meltdown" are pretty unhelpful, which is partly why we've written this guide--you'll be able to understand what's actually happening without relying on spurious terms that the experts themselves are often loathe to use.
Anyway, let's start at some of the less severe (though still unsettling) things that can happen when the coolant liquid is no longer present in the core. When the fuel rods are left uncovered by water, they'll get far too hot--we're talking thousands of degrees Celsius here--and begin to oxidize, or rust. That oxidation will react with the water that's left, producing highly explosive hydrogen gas. This has already happened in reactor No. 1 at Fukushima (see the video below). The hydrogen gas can be vented in smallish doses into the containment building, but if they can't vent it fast enough, it'll explode, which is exactly what happened at reactor No. 1. Keep in mind, this is not a nuclear reaction, but a simple chemical explosion that often (as in this case) results in little or no radioactive material being leaked into the outside world.
TEPCO has announced that after the explosion, radiation levels in the area around the plant were still within "normal" parameters. This is an important distinction--not to say that a hydrogen explosion at a nuclear plant is particularly fun news, but it is not nearly as panic-inducing as a meltdown.
What people mean when they say "meltdown" can refer to several different things, all likely coming after a hydrogen explosion. A "full meltdown" has a more generally accepted definition than, say, a "partial meltdown." A full meltdown is a worst-case scenario: The zirconium alloy fuel rods and the fuel itself, along with whatever machinery is left in the nuclear core, will melt into a lava-like material known as corium. Corium is deeply nasty stuff, capable of burning right through the concrete containment vessel thanks to its prodigious heat and chemical force, and when all that supercharged nuclear matter gets together, it can actually restart the fission process, except at a totally uncontrollable rate. A breach of the containment vessel could lead to the release of all the awful radioactive junk the containment vessel was built to contain in the first place, which could lead to your basic Chernobyl-style destruction.
The problem with a full meltdown is that it's usually the end result of a whole boatload of other chaos--explosions, fires, general destruction. Even at Chernobyl, which (unbelievably, in retrospect) had no containment building at all, the damage was caused mostly by the destruction of the plant by explosion and a graphite fire which allowed the corium to escape to the outside world, not the physical melting of the nuclear core.
Over the weekend, Chief Cabinet Secretary Yukio Edano somewhat hesitatingly confirmed a "partial" meltdown. What does that mean? Nobody knows! The New York Times notes that a "partial" meltdown doesn't actually need to have any melting involved to qualify it as such--it could simply mean the fuel rods have been un-cooled long enough to corrode and crack, which given the hydrogen explosion, we know has already happened. But we'd advise against putting too much stock in any term relating to "meltdown"--it'll be much more informative to find out what's actually going on, rather than relying on a vague blanket term.
As TEPCO grapples with the damage the earthquake and tsunami did to the nuclear system, there's going to be lots of news--there could be more explosions, mass evacuations, and more "meltdowns" of one kind or another. All we can do is learn about what's going on, think calmly about the situation, and hope that TEPCO can eventually regain control of the plants.
"Sure! But it's not as effective as unplugging a rogue kitchen appliance, mostly due to some chemical reactions inherent in the fission reaction"
Um...yea NO. Chemical reactions? Listen popsci, I expect this from gizmodo, really I do, and I'm ok with that. But from you guys I do expect a bit more. It's a NUCLEAR reaction. One of the main differences between nuclear reaction and chemical reaction is related to how the reaction takes place in the atom. While nuclear reaction takes place in the atom’s nucleus, the electrons in the atom are responsible for Chemical reactions. Chemical reactions involve the transfer, loss, gain and sharing of electrons and nothing takes place in the nucleus. Nuclear reactions involve the decomposition of the nucleus and have nothing to do with the electrons.
So next time. Please do your research.
By chemical reactions, he means the the reactions such as the rust, zirconium, and hydrogen reaction. A nuclear reactor has plenty of components that can undergo chemical reactions under the extreme heat. The reactors themselves have been shut down.
Dude its just an informative guide on the trems meltdown and how reactors work, there is no need to rant about the electron and neclear reaction differences. I respect your knowledge and I actually learned something, but people make mistakes, okay
Very informative and easy to understand. Thank you, Dan Nosowitz and PopSci. Let's hope TEPCO can get their reactors under control.
I am a retired Metallurgical and Nuclear engineer and am familiar with the two oldest Fukushima reactors, as the company I worked for offered a different (more expensive) design for the 1974 and later installations.
The Fukushima reactors are BWR (boiling water reactors) of which the early Mark I and Mark II installations had and have basic design problems. These design problems have been known and have been written about since 1972 by AEC officials.
The surprising issue is why the power company was not forced to increase the reliability of the emergency cooling system, in a highly seismic operating environment.
Very similar problems exist in similar US installations and the gov. officials (like the financial meltdown guardians) do not seem to be stepping up to the issues.
The primary issue in Japan is not specifically that the reactors are BWR units, but that the emergency cooling systems and the reactor are mounted on separate concrete pads which in the case of a bad earthquake can move relative to each other and break the emergency cooling piping. At this point, it makes no difference if the pumps work or not.
Nuclear "accidents" are caused by relatively boring but very specific technical details, a "valve failed". Fine but exactly how? We are talking about big valves (some bigger than a limo) that are mechanical devices, motor or hydraulically operated, electrically actuated and electronically controlled. So when we speak of "X failed", exactly what happened? Mechanical problem? What kind of mechanical problem? and so on and so forth. When we finally get the answers -- we will see that something or a series of something really quite stupid happened.
With regard to future nuclear accidents, lets make a few things points: 1)a truly 100% failsafe installation is probably too expensive. 2)the thick concrete pad containing the reactor can sort of "float" during a bad earthquake. 3)the emergency cooling systems MUST work even after normal shutdown. 4)a bigger more expensive containment building is better. 5)the emergency pumps and as much cooling piping as possible must be on the same "floating" concrete pad as the reactor. 6) chose something other than just the cheapest design and give it better maintenance than the Davis-Besse installation.
Bad car accidents are always caused by at least 3 or 4 issues. Bad tires, bad brakes and rain do not cause an accident ----- until you need to stop.
Nuclear accidents are not necessarily ENGINEERING problems as often as they are accounting problems. How many nuclear ships have blown up? The stakes are a little higher than private company profit.
Until we know in great detail all of the boring technical elements of the cooling failure, we cannot properly criticize anyone. However design shortcomings have been known for almost 40 years and should be a wake-up call for the US.
I am playing arm chair quarter about what went wrong with the Japanese nuclear reactors like most people are doing right now but if I am right maybe it will help.
I'm not in the least bit surprised they having a meltdown problem. Throwing salt water on the reactor is like throwing gas onto a fire or trying to put out a magnesium fire with a fire extinguisher ingredients made out of CO2...
Salt water ions very easily splits water molecules, H2O, in a current at a lower temperature than pure H2O, into its elementary hydrogen and oxygen components. Salt water is a much better conductor of electricity than plain old water. Pure water is an electrical insulator not a electrical conductor, through some other ingredients in the water and it quickly changes into a electrical conductor, with salt it is a very good electrical conductor. Therefore the buildup of hydrogen in the containment building is mostly caused by them trying to cool the radiation down with salt water. The fuel rods would have to get over 2500 C to split pure water molecules into hydrogen and oxygen, with saltwater the temperature can be much lower...
Had to comment. That's a nice basic description of electrolysis, but has nothing to do with what’s going on here. The Article mentions how the Zirconium in the fuel cladding reacts with the minimal water/steam present to create Zirconium dioxide and hydrogen. That hydrogen out-gassing is what caused the explosions. There is no current(amperes) present in the core that would cause electrolysis, and the introduction of seawater is purely for heat transfer away from the core and to keep it covered with water (below the temps that cause the H2 gassing, and ‘further’ core damage) Steam voids in a core = bad. Seawater is used primarily because there is nearly an infinite supply. I won't even touch the inaccuracies of: "trying to cool the radiation down with salt water."
formerNuke - I'm just playing armchair nuclear quarter back here and trying to see if there was a link between the salt water they used to cool the nuclear reactor and the overabundance of hydrogen gas leak. I am not in any way a nuke engineer although I do have several other engineering degrees. My hunch is that it also may be a product of what John Kanzius discovered last year where radio waves were used on salt water that caused an intense flame, that reaction was not conventional electrolysis as we know it.
With nuclear fission classical decay you have alpha decay, beta decay, and gamma radiation those different types of radiation interacting with salt water may also produce hydrogen gas, we just haven't discovered it yet, at least that is with the limited knowledge I have about what type of coolants are used today. Do they use salt water in nuclear submarines to cool them down, from all I read they use liquid metals. If you know of some other time salt water was used to cool a nuclear reactor down please enlighten me?
The sub and other marine reactors are not BWR units but rather PWR units. Pressure Water Reactors as well as the Fukushima installations are "light water reactors" light water meaning regular distilled water. However the Fukushima 1 to 8 are all BWR units. Liquid metals are normally used in "breeder reactors", with several isolated cooling loops.
The BWR, Boiling Water Reactors use the water that cools the reactor (and turns to steam, hence "boiling") to power the turbines. The BWR units are ALL cheaper and from a design point of view less safe in a seismic area, because the reactor water goes into a long loop outside of the reactor building, to the turbine building. (please read above comment)
A sub nuke is a PWR (pressurized water reactor) in which the reactor cooling water goes into a steam generator (big heat exchanger) then the second loop goes to the turbine. After the steam leaves the turbine, it then passes into another heat exchanger which has sea water on one side and the turbine steam / water on the other side. So no nuke water goes either into the turbine or the ocean. In a BWR the turbine becomes contaminated and all pipes and turbines must be shrouded. In a PWR the reactor pressure is higher, but does not leave the reactor building.
Next is a general statement, which is my opinion. A PWR is a safer, higher cost and higher tech system as compared to a BWR. The pressure inside the reactor is about 75 bar in a BWR and about 160 bar in a PWR. Generally A PWR has higher installation cost and higher maint. cost than a BWR. And due to the high pressure, dead sure maint. must be done. My opinion is that low cooling pipe rupture probability indicates a BWR. A high piping rupture possibility (as a war ship or highly seismic area) indicates a PWR unit.
Aside from all the "experts" who have been on TV lately, real down to earth issues are the ones that count. A nuke PHD can explain ad nausium nuclear reactions, but most problems are based on other issues ----- which in many cases are REALLY difficult to know, but once you know them - seem pretty stupid not to have been known.
For example, neutrons will always perform as the experts describe. But in a system involving tens of thousands of welds and thousands of yards of electrical cable, exactly which weld was marginal and how do you find it? or exactly which of several million electrical connections was a bit loose??. Light water cooling sounds pretty safe, and it is up to the point that it can have a drop dead guarantee. It seems as though everyone knows that the nuke reactions get upset in the absence of cooling. But the cooling guarantee is not "drop dead", particularly so in a BWR. Nuke plant designers and builders are limited by accounting (read Money) issues to a "most likely" scenario, we are kidding ourselves if we think that anything (except maybe NASA and the US Navy)gets real "drop dead" engineering. So I am really sorry for Davis-Besse, Three Mile Island and Fukushima, but "drop dead" quality usually means eliminating the accountants.
This creates a bigger problem however, the human race has to fork over the money or put up with the occasional disaster, or live in the dark or live with fossil fuel pollution. Wind, sea wave, river and other renewable power is great but I do not think there will ever be enough.
There are about 450 nuclear installations world wide, this almost means we are still in the "prototype" or "preproduction" phase. The world wide nuke issue REQUIRES standardized modular plants and should not be proposed and sold as either cheap to build or cheap to run or cheap to dismantle --- I wished I could see an alternative.
i say that we should make the containment vessel out of tungsten carbide it has the highest melting point 3410 °C (6170 °F)this should in the case of a melt down keep the corium contained. if im wrong about that feel free to viciously critisize me as us pop sci people tend to do
here is a site that shows what element react with and below is the link to the page talking about tungsten. oh and i didnt mean tungsten carbide i ment just pure tungsten.
I'm not a very technical person who looks more onto the details of these things and has fights about technicalities of the matter but all I have to say about this is what if it DOES go into full meltdown? My friend and I had a conversation about how dangerous it could be if all those nice gases came flying out of the core. Let's just say it wasn't a very good outcome.
Please read my two posts.
Good basic idea, unfortunately that which makes Tungsten ideal for a lot of things --- makes it impossible to create the big forgings necessary for nuclear reaction chambers.
I am a both a Metallurgical and Nuclear engineer, but I have relatively little practical experience with pure Tungsten. Usually the inside of the reactor vessel is lined with 3/16 inch thick high chrome stainless steel. Even this thickness is due to economic / "most likely" considerations.
I honestly do not know, but have colleagues who claim it would not be possible to line the reactor with pure tungsten.
In the real world, accountants and financial issues often take precedence over real "drop dead" 100% or even 99% safe engineering solutions.
Perhaps a SS / Tungsten alloy (decidedly more expensive) could be used for the reactor lining. Based on my 35 years of experience, this solution is not in the "most likely" category of anticipated problems to protect against. So even if technically doable, probably not within the economic limits of a profitable power plant.
very true i would never have thought of that as i am a high school student and not an engineer but thanks for the review
Riccio or others,
One thing I don't understand is the long term need for cooling. Obviously, when the core/fuel rods are hot (just after shut down), cooling was needed so they wouldn't degrade or melt. And this cooling must be active, I think, in that the cool water must be injected and warm water removed in a circulating process. Since circulating, it must be driven by an electric or diesel pump.
How long does this cooling need to continue? Is there ever a point or temperature or state of radioactivity where the rods can be left alone with no water circulation cooling need? (Though maybe submerged under water.)
i belive at the moment they brought in another smaller pump/generator to cycle salt water through the reactor
circulation needs to continue until radio active decay is complete and until nuclear fission stops at that point the rods should be cool and should allow for removal and or repair of the reactor.
feel free to correct me if im wrong Riccio
couldnt you simply pump some liquid nitrogen into the cooling chamber or would that be to cold and crack somthing vital?
It is important to realize there are two different key objects within the reactor vessel: Fuel Cells, and Control Rods. The Control Rods were inserted in between Fuel Cells to stop the fission process (neutron flux)that is ongoing (this is call a SCRAM) That basically kills the reaction, but as the article states (and hackerslayer787 is correct) the decay heat and SELF fission of radioactive isotopes keeps generating heat within the vessel. If proper cooling is maintained and the fission process is kept shut down, after a good amount of time, you don't need to continue to supply cooling water...just maintain a water blanket over the core. Any residual decay heat will be lost to the ambient environment (i.e. to the vessel, piping, air in the Reactor compartment, etc.) It will reach an equilibrium. The time it takes to reach equilibrium depends on things like reactor size, operational temps/press, fuel loading, etc.
as for the nitrogen...yes too cold...at that point you'd be worried about brittle fracture of the reactor vessel due to temp stresses...and then you just cause a release from the primary protection closure
Thank-you for the replies!
What if you dumped Liquid Nitrogen in at he top of the pool, and it didnt freeze the water? Just super cool the top half?
Corium - more wackadoodle stuff. No moderation no nuclear reacton and temperatures well under the melting temperature of steel. This was what happened at TMI when the cooling system shut off.
Barely scraped the inside of the vessel.
The example I would like to use is not exactly correct, but simple and sort of correct. Technical experts, please bear with an oversimplified story.
Perhaps almost everyone knows that when you cook food in a microwave oven, you should let the food "rest" for about 1.5 minutes per inch of thickness. Why?
A microwave heats food by bombarding the water molecules with a "microwave" that due to being "micro" and a multiple of the atomic bond between the hydrogen and oxygen atoms --- "excites" or increases the vibration of the water molecule components (H and O2. this vibration heats up the food.
** so microwaves excite and heat the water in the food, which is why you can cook in paper or some plastic plates that do not contain atomic bonds similar to water**
But immediately after the microwave shuts off, the atoms are still vibrating and a bite of hot microwave food too soon out of the oven will burn you --- and sucking air or drinking a sip of water will not immediately stop the atomic vibration.
Now without getting into some messy and complicated descriptions - another short example. A flame is a slow explosion. And an explosion is a very rapid flame. But the atoms do not disintegrate - they just recombine to form other molecules with less energy, releasing molecular energy as heat.
Now to the nukes. Nuclear heat is not generated by recombining molecules --- which on it's own can be difficult to slowdown or stop. As in a forest or house fire, which is just hydro-carbon atoms recombining to create carbon dioxide, acid rain etc.
Nuclear heat is instead created by the "explosion of atoms", but not just the simple explosion of electrons jumping around. A nuclear explosion (however slow or fast, regulated or not) is serious business because it basically explodes the nucleus of the atom -- hence "Nuclear".
Now sometimes in your microwave, you hear little "pops", this is a small group of water molecules "exploding" or boiling, because the vibration is too great and the strength of the atomic bonds holding the molecule together can no longer retain it's structure as a liquid and becomes a gas (steam).
In a nuclear "reaction", the "re" part of the action is as a result or "reaction" to having too many radioactive particles close together. And the atomic nuclei are "exploding" because they are being "bombarded" by fast moving sub atomic particles in nearby Uranium or other "nuclear" material. Just as a big fire cannot be stopped immediately. A serious explosion cannot be halted immediately. And an explosion involving atomic nuclei is very serious.
The carbon rods (or whatever they are made of, for different types of nuclear fuel) are pushed in between the fuel rods, they slow the sub atomic particles that were flying around.
When there are sufficient of these "moderator" rods in place, the speed of the "acting" particles is slowed to the point where they do not have sufficient energy to "explode" any more nuclei. But this takes quite a while, because the nuclei that just previously exploded are VERY fast and the moderator rods do not slow them down immediately.
So depending on the density of the radioactive nuclear fuel and the exact reactor construction, it can take a couple of weeks of normal (substantial) cooling to actually stop (and cool)the reactor core. Different designs have different cooling temperature curves with respect to time --- but there are NO nuclear power plants that can be either stopped to "cold" or started from "cold" in less than a week or so.
This is why newer generation designs rely on so called "passive", "gravity" or some other theoretically "natural" force that does not require human intervention to stop.
Unfortunately the real "worst case" ability of these designs to actually stop by themselves is very discuss-able.
Meaning that I would have to see it to be convinced.
Three mile Island had a partial meltdown and it is still locked up, so there are still fast sub-atomic particles jumping around.
This is why storing "expended" fuel is such a HOT topic. Expended fuel is not dead, just not sufficiently active to be used as fuel. But is still really serious stuff that can't be swept under the rug, and must be treated almost as carefully as usable nuclear fuel.
Sorry, this is probably pretty boring, but "reasonably" safe or "once in 100 years" is not "drop dead" safe. Especially if the once in 100 or once in 500 years happens "on your watch" when you are 20 years old. When did the 500 years start?, and two "once in 500 year" incidents can happen in year 500 and 501. Bad timing on your part, from 1511 to 2511 everybody else got off Scott free, you just got fried.
I do believe that truly "drop dead" safe nuclear reactors can be built --- but they probably do not conform to a high corporate profit or to back room politics.
More boring technical comments, that I think are correct.
My understanding is that 3 reactors were "shutdown" for maintenance. This means that their fuel cores were perhaps in the spent fuel storage pools. Even spent or exhausted fuel is not dead, and for sure the stored fuel from the deactivated reactors is still active. The storage pools have to be cooled. If cooling is not possible, perhaps the explosion that blew off the top of the reactor building was due to excessive hydrogen buildup in the upper part of the reactor building where the spent fuel rods are stored.
Quite a bit of conjecture here, but I do not believe that we really know and I don't trust either the authorities or the operating company to explain that they made a series of mistakes.
I would like to go on record at this time by saying that in addition to the reactor problems, I think that there are spent fuel rod storage pool cooling problems.
Bottom line is that we could be in for something of which we have seen only the beginning. The old fuel rods can eventually cause hydrogen explosions if exposed due to low water level. So while a true "meltdown" may be avoided, repeated hydrogen explosions due to excess hydrogen accumulation in both the reactor building and the fuel storage pools are likely.
Don't be surprised if it gets a lot worse.
If this Corium can burn through pretty much everything, whats to stop it from going straight through the ground forever? I know it sounds silly but if this stuff is that hot it almost seems like it can really create something catastrophic. Can the Corium then set off another natural disaster?
Riccio, thank-you for the new explanation. The idea of active pumping needed essentially all the time is crazy--there are so many scenarios that could lead to loss of the pumps, electricity, diesel fuel, people to run the pumps. It's shocking to think we allow designs like this. Passive sounds better, but, even if it works there are 100's of multi-billion dollar facilities that we'll never shut down.
I see many articles and discussions of the probability of something happening at a nuke power plant, like 10000 to 1 or something like that. But one of the things that I think is little discussed is the potential risks from nuclear power from these supposedly unlikely plant problems.
If there is an 0.0001 chance for a problem to occur that kills no one and destroys $1 million in equipment and facilities, that is bad. However, if you have an 0.0001 chance for a problem to occur that kills dozens, causes cancer in 1000's, destroys $billions in equipment, costs 10's of billions in associated costs and requires decades of human exclusion from vast areas, that's REALLY bad. Some might say unacceptable, even at 10000 to 1.
But I guess 1 in 10,000 sounds good as a sound bite.
although corium is hot i do not think its gonna melt through the whole earth nor do i think it can cause much more than some mutated Japanese workers.
And this is why we have CANDU (heavy water) reactors... Fewer parts = lower risk, to a point.
On a more relevant note, what bothers me most is when the media says "...radioactive steam has been released...". The steam is not any more radioactive than the cup of tea I put in my microwave. Just because something has come into contact with radiation doesn't mean that it becomes radioactive too. If that were the case the Japanese would all be glowing!
I am no scientist so this may be very naive. I have two questions in regards to the reactor problems in Japan.
1. Could workers use a fire hose type system to spray water on the reactors from the air? I heard they tried to dump water from the air but could not get above the reactors because of the radioactive steam.
Years (30+) ago working in landscape construction on interstate highways we used tanker with a water / hydro-muclh mix to protect grass seed on hillsides. It seems a similar type of solution could be used to get water to the reactors.
2. Could some type of foam be used to contain the fuel rods and protect the Japanese from radiation?
Thanks for listening.
The nuclear power plant and reactor construct that make it safe also makes it hard to fix.
The GE designed and Mitsubishi constructed power plant reactor building has a very heavy "reactor vessel" at the center. This is pretty tough, from 6 to 10 inch thick steel with a 3/16 inch stainless steel liner. This sets on top of a big donut shaped expansion tank, and everything is supported be a thick concrete floor that allows the building to sort of "float" during a big quake. At a distance of a few yards all around, this is covered by the primary "reactor containment building", (with the general shape of an inverted light bulb) this is also a tough nut, made of 3 foot thick steel reinforced concrete (the reinforcement bars are not coat hangers, but heavy, big and not junk steel).
The water that cools the reactor, actually boils - creates steam and is piped out of the reactor vessel, past the open space around the reactor vessel and through the reactor containment building wall. Then these pipes (for some reactors as big as 30 inches in diameter) are supported by the big heavy floor of the turbine building, and into the turbines.
Thus the two primary equipment platforms are big and heavy (hundreds of tons) but during a quake as bad as the one experienced, these two pads can move with respect to one another. This ruptures the pipe going to the turbine and the pipe going back to the reactor.
The regular cooling is dead. The emergency cooling is inside the reactor building and needs power for the pump motors. Apparently another bad design placed the emergency generators where the tidal wave either swept them away or rendered them unusable.
The spent fuel storage pools are near the top of the reactor building, on either side of the narrow top. Spent fuel is not dead and must be kept cool. The rectangular top of the containment building is really not part of the containment building but is simply a heavy sheet metal shed to protect the spent fuel storage pools, the crane and other misc. equipment.
Now to your question, The reactor core is of course inside the reactor vessel, which is inside the reactor containment building. For some reason the emergency pumping and cooling system doesn't work and things are getting hot. Probably some radiation is escaping from the broken regular cooling pipes.
Now to complicate things, I think that the fuel pool cooling pipes were sheared along with the reactor pipes. Maybe even the pool walls cracked. In any case the water begins to boil, but boiling is not just bubbling - boiling separates the water into hydrogen and oxygen. After a while the stored fuel rods peek out of the water, now high velocity rusting of the rod protection tubes starts, and the water boils faster. Eventually the steel shed fills with hydrogen and starts to bulge at the seams. When this happens, the trapped hydrogen escapes and recombines with the oxygen in the atmosphere --- this creates a nice big orange fire ball (which maybe you saw in the first film clips). This fireball is a fast moving flame or a slow explosion, but it blows the shed on top of the containment building to bits and probably blows out a few ton of radioactive water and maybe even some fuel rod material.
This is why only the top of the building blew up. The bottom part is the heavy cement structure.
My opinion is that this secondary outside radiation is making it almost impossible to get close to or inside the reactor containment building to start correcting / cooling the reactor vessel.
Unfortunately the heat inside the reactor is very high and I do not think that small amounts of anything (foam or liquid salt is going to work - they just need lots and lots of water.
If you are not already bored to death, please read some of my earlier posts.
Keep in mind that, the spent fuel pools in other reactor buildings could go the same way, but even as serious as this is --- it has almost nothing to do with a melt down or radioactive stuff escaping from either the reactor vessel or the reactor containment building. But some brave soul has to get inside and at least cool down the outside of the reactor vessel if it is not possible to rig temporary cooling through the broken reactor / turbine pipes.