Skip to comments.Why I am not worried about Japanís nuclear reactors.
Posted on 03/13/2011 9:19:24 AM PDT by Errant
I am writing this text (Mar 12) to give you some peace of mind regarding some of the troubles in Japan, that is the safety of Japans nuclear reactors. Up front, the situation is serious, but under control. And this text is long! But you will know more about nuclear power plants after reading it than all journalists on this planet put together.
There was and will *not* be any significant release of radioactivity.
By significant I mean a level of radiation of more than what you would receive on say a long distance flight, or drinking a glass of beer that comes from certain areas with high levels of natural background radiation.
I have been reading every news release on the incident since the earthquake. There has not been one single (!) report that was accurate and free of errors (and part of that problem is also a weakness in the Japanese crisis communication). By not free of errors I do not refer to tendentious anti-nuclear journalism that is quite normal these days. By not free of errors I mean blatant errors regarding physics and natural law, as well as gross misinterpretation of facts, due to an obvious lack of fundamental and basic understanding of the way nuclear reactors are build and operated. I have read a 3 page report on CNN where every single paragraph contained an error.
We will have to cover some fundamentals, before we get into what is going on.
(Excerpt) Read more at morgsatlarge.wordpress.com ...
Obummer is a greater threat to the planet than the reactors, IMO.
Construction of the Fukushima nuclear power plants
The plants at Fukushima are so called Boiling Water Reactors, or BWR for short. Boiling Water Reactors are similar to a pressure cooker. The nuclear fuel heats water, the water boils and creates steam, the steam then drives turbines that create the electricity, and the steam is then cooled and condensed back to water, and the water send back to be heated by the nuclear fuel. The pressure cooker operates at about 250 °C.
The nuclear fuel is uranium oxide. Uranium oxide is a ceramic with a very high melting point of about 3000 °C. The fuel is manufactured in pellets (think little cylinders the size of Lego bricks). Those pieces are then put into a long tube made of Zircaloy with a melting point of 2200 °C, and sealed tight. The assembly is called a fuel rod. These fuel rods are then put together to form larger packages, and a number of these packages are then put into the reactor. All these packages together are referred to as the core.
The Zircaloy casing is the first containment. It separates the radioactive fuel from the rest of the world.
The core is then placed in the pressure vessels. That is the pressure cooker we talked about before. The pressure vessels is the second containment. This is one sturdy piece of a pot, designed to safely contain the core for temperatures several hundred °C. That covers the scenarios where cooling can be restored at some point.
The entire hardware of the nuclear reactor the pressure vessel and all pipes, pumps, coolant (water) reserves, are then encased in the third containment. The third containment is a hermetically (air tight) sealed, very thick bubble of the strongest steel. The third containment is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown. For that purpose, a large and thick concrete basin is cast under the pressure vessel (the second containment), which is filled with graphite, all inside the third containment. This is the so-called core catcher. If the core melts and the pressure vessel bursts (and eventually melts), it will catch the molten fuel and everything else. It is built in such a way that the nuclear fuel will be spread out, so it can cool down.
This third containment is then surrounded by the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. (this is the part that was damaged in the explosion, but more to that later).
Fundamentals of nuclear reactions
The uranium fuel generates heat by nuclear fission. Big uranium atoms are split into smaller atoms. That generates heat plus neutrons (one of the particles that forms an atom). When the neutron hits another uranium atom, that splits, generating more neutrons and so on. That is called the nuclear chain reaction.
Now, just packing a lot of fuel rods next to each other would quickly lead to overheating and after about 45 minutes to a melting of the fuel rods. It is worth mentioning at this point that the nuclear fuel in a reactor can *never* cause a nuclear explosion the type of a nuclear bomb. Building a nuclear bomb is actually quite difficult (ask Iran). In Chernobyl, the explosion was caused by excessive pressure buildup, hydrogen explosion and rupture of all containments, propelling molten core material into the environment (a dirty bomb). Why that did not and will not happen in Japan, further below.
In order to control the nuclear chain reaction, the reactor operators use so-called moderator rods. The moderator rods absorb the neutrons and kill the chain reaction instantaneously. A nuclear reactor is built in such a way, that when operating normally, you take out all the moderator rods. The coolant water then takes away the heat (and converts it into steam and electricity) at the same rate as the core produces it. And you have a lot of leeway around the standard operating point of 250°C.
The challenge is that after inserting the rods and stopping the chain reaction, the core still keeps producing heat. The uranium stopped the chain reaction. But a number of intermediate radioactive elements are created by the uranium during its fission process, most notably Cesium and Iodine isotopes, i.e. radioactive versions of these elements that will eventually split up into smaller atoms and not be radioactive anymore. Those elements keep decaying and producing heat. Because they are not regenerated any longer from the uranium (the uranium stopped decaying after the moderator rods were put in), they get less and less, and so the core cools down over a matter of days, until those intermediate radioactive elements are used up.
This residual heat is causing the headaches right now.
So the first type of radioactive material is the uranium in the fuel rods, plus the intermediate radioactive elements that the uranium splits into, also inside the fuel rod (Cesium and Iodine).
There is a second type of radioactive material created, outside the fuel rods. The big main difference up front: Those radioactive materials have a very short half-life, that means that they decay very fast and split into non-radioactive materials. By fast I mean seconds. So if these radioactive materials are released into the environment, yes, radioactivity was released, but no, it is not dangerous, at all. Why? By the time you spelled R-A-D-I-O-N-U-C-L-I-D-E, they will be harmless, because they will have split up into non radioactive elements. Those radioactive elements are N-16, the radioactive isotope (or version) of nitrogen (air). The others are noble gases such as Xenon. But where do they come from? When the uranium splits, it generates a neutron (see above). Most of these neutrons will hit other uranium atoms and keep the nuclear chain reaction going. But some will leave the fuel rod and hit the water molecules, or the air that is in the water. Then, a non-radioactive element can capture the neutron. It becomes radioactive. As described above, it will quickly (seconds) get rid again of the neutron to return to its former beautiful self.
This second type of radiation is very important when we talk about the radioactivity being released into the environment later on.
What happened at Fukushima
I will try to summarize the main facts. The earthquake that hit Japan was 7 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 7 times, not 0.7). So the first hooray for Japanese engineering, everything held up.
When the earthquake hit with 8.9, the nuclear reactors all went into automatic shutdown. Within seconds after the earthquake started, the moderator rods had been inserted into the core and nuclear chain reaction of the uranium stopped. Now, the cooling system has to carry away the residual heat. The residual heat load is about 3% of the heat load under normal operating conditions.
The earthquake destroyed the external power supply of the nuclear reactor. That is one of the most serious accidents for a nuclear power plant, and accordingly, a plant black out receives a lot of attention when designing backup systems. The power is needed to keep the coolant pumps working. Since the power plant had been shut down, it cannot produce any electricity by itself any more.
Things were going well for an hour. One set of multiple sets of emergency Diesel power generators kicked in and provided the electricity that was needed. Then the Tsunami came, much bigger than people had expected when building the power plant (see above, factor 7). The tsunami took out all multiple sets of backup Diesel generators.
When designing a nuclear power plant, engineers follow a philosophy called Defense of Depth. That means that you first build everything to withstand the worst catastrophe you can imagine, and then design the plant in such a way that it can still handle one system failure (that you thought could never happen) after the other. A tsunami taking out all backup power in one swift strike is such a scenario. The last line of defense is putting everything into the third containment (see above), that will keep everything, whatever the mess, moderator rods in our out, core molten or not, inside the reactor.
When the diesel generators were gone, the reactor operators switched to emergency battery power. The batteries were designed as one of the backups to the backups, to provide power for cooling the core for 8 hours. And they did.
Within the 8 hours, another power source had to be found and connected to the power plant. The power grid was down due to the earthquake. The diesel generators were destroyed by the tsunami. So mobile diesel generators were trucked in.
This is where things started to go seriously wrong. The external power generators could not be connected to the power plant (the plugs did not fit). So after the batteries ran out, the residual heat could not be carried away any more.
At this point the plant operators begin to follow emergency procedures that are in place for a loss of cooling event. It is again a step along the Depth of Defense lines. The power to the cooling systems should never have failed completely, but it did, so they retreat to the next line of defense. All of this, however shocking it seems to us, is part of the day-to-day training you go through as an operator, right through to managing a core meltdown.
It was at this stage that people started to talk about core meltdown. Because at the end of the day, if cooling cannot be restored, the core will eventually melt (after hours or days), and the last line of defense, the core catcher and third containment, would come into play.
But the goal at this stage was to manage the core while it was heating up, and ensure that the first containment (the Zircaloy tubes that contains the nuclear fuel), as well as the second containment (our pressure cooker) remain intact and operational for as long as possible, to give the engineers time to fix the cooling systems.
Because cooling the core is such a big deal, the reactor has a number of cooling systems, each in multiple versions (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and the emergency core cooling system). Which one failed when or did not fail is not clear at this point in time.
So imagine our pressure cooker on the stove, heat on low, but on. The operators use whatever cooling system capacity they have to get rid of as much heat as possible, but the pressure starts building up. The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200°C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time. Because the ability to do that in an emergency is so important, the reactor has 11 pressure release valves. The operators now started venting steam from time to time to control the pressure. The temperature at this stage was about 550°C.
This is when the reports about radiation leakage starting coming in. I believe I explained above why venting the steam is theoretically the same as releasing radiation into the environment, but why it was and is not dangerous. The radioactive nitrogen as well as the noble gases do not pose a threat to human health.
At some stage during this venting, the explosion occurred. The explosion took place outside of the third containment (our last line of defense), and the reactor building. Remember that the reactor building has no function in keeping the radioactivity contained. It is not entirely clear yet what has happened, but this is the likely scenario: The operators decided to vent the steam from the pressure vessel not directly into the environment, but into the space between the third containment and the reactor building (to give the radioactivity in the steam more time to subside). The problem is that at the high temperatures that the core had reached at this stage, water molecules can disassociate into oxygen and hydrogen an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel (because it was badly designed and not managed properly by the operators) that lead to the explosion of Chernobyl. This was never a risk at Fukushima. The problem of hydrogen-oxygen formation is one of the biggies when you design a power plant (if you are not Soviet, that is), so the reactor is build and operated in a way it cannot happen inside the containment. It happened outside, which was not intended but a possible scenario and OK, because it did not pose a risk for the containment.
So the pressure was under control, as steam was vented. Now, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed. Once the rods start to be exposed at the top, the exposed parts will reach the critical temperature of 2200 °C after about 45 minutes. This is when the first containment, the Zircaloy tube, would fail.
And this started to happen. The cooling could not be restored before there was some (very limited, but still) damage to the casing of some of the fuel. The nuclear material itself was still intact, but the surrounding Zircaloy shell had started melting. What happened now is that some of the byproducts of the uranium decay radioactive Cesium and Iodine started to mix with the steam. The big problem, uranium, was still under control, because the uranium oxide rods were good until 3000 °C. It is confirmed that a very small amount of Cesium and Iodine was measured in the steam that was released into the atmosphere.
It seems this was the go signal for a major plan B. The small amounts of Cesium that were measured told the operators that the first containment on one of the rods somewhere was about to give. The Plan A had been to restore one of the regular cooling systems to the core. Why that failed is unclear. One plausible explanation is that the tsunami also took away / polluted all the clean water needed for the regular cooling systems.
The water used in the cooling system is very clean, demineralized (like distilled) water. The reason to use pure water is the above mentioned activation by the neutrons from the Uranium: Pure water does not get activated much, so stays practically radioactive-free. Dirt or salt in the water will absorb the neutrons quicker, becoming more radioactive. This has no effect whatsoever on the core it does not care what it is cooled by. But it makes life more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water.
But Plan A had failed cooling systems down or additional clean water unavailable so Plan B came into effect. This is what it looks like happened:
In order to prevent a core meltdown, the operators started to use sea water to cool the core. I am not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us.
The point is that the nuclear fuel has now been cooled down. Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced now. The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure. Also, boric acid has been added to the seawater. Boric acid is liquid control rod. Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core.
The plant came close to a core meltdown. Here is the worst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the water steam to avoid pressure buildup. The third containment would then have been completely sealed to allow the core meltdown to happen without releasing radioactive material. After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor, and all radioactive particles to settle on a surface inside the containment. The cooling system would have been restored eventually, and the molten core cooled to a manageable temperature. The containment would have been cleaned up on the inside. Then a messy job of removing the molten core from the containment would have begun, packing the (now solid again) fuel bit by bit into transportation containers to be shipped to processing plants. Depending on the damage, the block of the plant would then either be repaired or dismantled.
Now, where does that leave us?
The plant is safe now and will stay safe.
Japan is looking at an INES Level 4 Accident: Nuclear accident with local consequences. That is bad for the company that owns the plant, but not for anyone else.
Some radiation was released when the pressure vessel was vented. All radioactive isotopes from the activated steam have gone (decayed). A very small amount of Cesium was released, as well as Iodine. If you were sitting on top of the plants chimney when they were venting, you should probably give up smoking to return to your former life expectancy. The Cesium and Iodine isotopes were carried out to the sea and will never be seen again.
There was some limited damage to the first containment. That means that some amounts of radioactive Cesium and Iodine will also be released into the cooling water, but no Uranium or other nasty stuff (the Uranium oxide does not dissolve in the water). There are facilities for treating the cooling water inside the third containment. The radioactive Cesium and Iodine will be removed there and eventually stored as radioactive waste in terminal storage.
The seawater used as cooling water will be activated to some degree. Because the control rods are fully inserted, the Uranium chain reaction is not happening. That means the main nuclear reaction is not happening, thus not contributing to the activation. The intermediate radioactive materials (Cesium and Iodine) are also almost gone at this stage, because the Uranium decay was stopped a long time ago. This further reduces the activation. The bottom line is that there will be some low level of activation of the seawater, which will also be removed by the treatment facilities.
The seawater will then be replaced over time with the normal cooling water
The reactor core will then be dismantled and transported to a processing facility, just like during a regular fuel change.
Fuel rods and the entire plant will be checked for potential damage. This will take about 4-5 years.
The safety systems on all Japanese plants will be upgraded to withstand a 9.0 earthquake and tsunami (or worse)
I believe the most significant problem will be a prolonged power shortage. About half of Japans nuclear reactors will probably have to be inspected, reducing the nations power generating capacity by 15%. This will probably be covered by running gas power plants that are usually only used for peak loads to cover some of the base load as well. That will increase your electricity bill, as well as lead to potential power shortages during peak demand, in Japan.
Because I live 12,000 miles away?
Why I am worried......Because it’s not suppose to happen!!!!
Can’t argue with that. :)
Can't argue with that either! :)
CNN should "snarf" him up ASAP!
Yeah, and it certainly wouldn’t be filled with graphite.
But he’s right about enough stuff to make this worth reading, and to calm down.
Having been a Radwaste Operator in the recent past, I know it’s gonna suck for them for a while. Processing all that sea water will be tedious and costly. But I guess it beats dealing with melted fuel.
This is what stopped me:
He is a PhD Scientist, whose father has extensive experience in Germanys nuclear industry.
My father was a mechanical engineer (Ga. Tech '39) with extensive experience in his field. I hold an MSEE and BSAE (also from the North Avenue Trade School '87), but that doesn't begin to make me an expert on mechanical engineering issues simply by virtue of being his offspring. The level to which this story is being hyped is unbelievable! Every ex-spurt and their brother is coming out of the woodwork. Some of what I've been reading is downright comical in it's sheer ignorance, not to mention what is making some of these self-appointed ex-spurts claim to be experts....
Excellent read! The situation is very serious, but it appears to be under control and likely has been all along.
I'd like to know your thoughts on a worst case and why not try to get at least one of the other plants online to provide power to the others, if you care to share them.
I don’t have fears.
I just think it’s a good idea to be prepared.
Hope for the best, but plan for the worst, that sort of thing.
That’s the grown up way of handling things, isn’t it?
There seemed to be alot of outright mocking of people who simply had legitimate questions, and I don’t think that is very much in the spirit of FReepers helping FReepers.
I agree. It may be that the wave of water contaminated the fuel, lubricating oils or damaged supporting systems like cooling, supply lines, controls and etc.
If the engines were running at the time, they may have been damaged beyond repair. Certainly they must be in pretty bad shape, since they've not gotten them back into service by now.
Maybe at this site, they're located outside the buildings?
There seemed to be alot of outright mocking of people who simply had legitimate questions, and I dont think that is very much in the spirit of FReepers helping FReepers.
Double Damn Right!!!
This points out the foolishness of having reactors that are inherently unstable when stable ones are available.
EXCELLENT article! Great work.
So you don't see a possibility of a molten core melting through the containment vessel?
Makes sense on using offsite power as you say, if available, instead of trying to get one of the other units online.
I'd be more worried if he were in control. But what difference does it make if he voices his opinion even if not entirely accurate.
There are big mouth pieces going around trying to stir up fear and panic. At least someone is trying to put some calm into the equation.
Sounds like they will have alot of work to do for all those fake stewardess robots they keep coming up with!
Run for your lives! It's the end of the world!!!
The interesting question at this point is What will be the legacy of the media-generated disaster hysteria? Will the public reject it? Or will the nuclear power industry be set back another 25 years.
I'm hoping that people don't buy the hype, but when it comes to nuclear power, emotion usually overides intellect.
He does sound like what he’s doing. And I’m not a physicist or a nuclear engineer, but when I see the ‘experts’ going on and on in the news sources, I have to take it with a grain of salt. To hyper-inflate and cast doom and gloom and advance the anti-nuclear agenda is to discredit your own credibility.
I hope we see actual people who can calmly explain like what this guy did instead of picking choice bits for a 1 minute interview.
I'm shocked by the lack of credible information available on outcome of a total reactor core meltdown.
I don't know if its because no one knows, if the information is just not getting out, or no one wants to believe the assurances of the engineers and scientists that built these things. One would think, after all these years, that the human race would build these power plants in such a way that massive contamination would be physically impossible. But perhaps economics outweighs safety of design.
The GE BWR-1 at Fukashima does not have a 3rd containment vessel like we had at TMI.
The reason is just as you said it. Irrational fear, phobia. No amount of reason can overcome it. Even if the worst happens, it isn't the end of the world. Atmospheric nuclear weapons testing didn't end the world. Besides, this is also a very very rare event.
It is physically impossible to make something 100% safe as everyone would like. There is always something else that could go wrong that isn't in the design. It's not so much economics as it is practicality that stops the design and begins the building.
Every now and then something entirely unprecedetented comes along, as this event has done, that will give us more information to put into the future designs and retrofit older designs where feasible. The future for nuclear power will be safer still.
Now is not the time to run away from nuclear power, there is too much energy available to ignore it. I'll take nuclear power over middle east thug oil any day.
In discussing additional possibilities, wouldn't the high heat of molten fuel rods vaporize any cooling water after some critical point.
Which brings to mind; why not build smaller reactor cores and containment vessels capable of handling complete meltdowns without the dependency on cooling?
I caught that from the diagrams shown.
Thank you for a very informative article. I’ve seen it referenced at two other sites and I’m sure it’s being read by a lot of people.
Unfortunately, it appears that we cannot automatically assume the author is right.
I’ve read the whole article at the source blog, including the comments.
There is apparently at least one significant error in the article. The reactors in question do NOT have a feature designed to catch and disperse the material from a core meltdown. That feature is apparently part of newer designs for reactors of this type, but this reactor is too old to have it.
If the comments at the source blog are correct, the author is NOT a specialist in nuclear reactors. He obviously knows more about them than the vast majority of us, but his expertise is limited.
All in all I’d say this an excellent article that adds to the discussion. But, if the comments on the source blog are correct, it cannot be considered authoritative.
All diagrams I see do not show one.
I think another part of it is because credible information is not readily available to the general public. I blame the MSM and the plant operators for not seeing that it is.
Also, I don't want to hear about all the fail safes that can't fail but do. I want to hear about what is or isn't physically possible. After that, I'll make up my own mind as to what is likely and I think that's what the average Joe/Jill wants to hear.
It only makes sense (forget economical sense) to build these things (and I know they can) so that massive contamination in event of total meltdown isn't physically possible.
That may mean building reactors that could never reach the temperatures required for meltdown, by simply making them smaller.
Let's give them a rating of say from 1 to 10 on possibility of catastrophe. Example: Reactors constructed near the ocean and along known tectonic plate lines get a 10. Any reactors with a rating greater than say 5, are to be converted to the pebble based system you mentioned. Over a period of time, all should be converted to a system whereby meltdowns are physically impossible.
Probably hugely expensive, but vastly superior to wasting billions on windmills and current solar PV installations (except of course in certain instances).
Making them safe would make more of them available and we really do need the power.
Thanks so much for posting.
I kinda had a feeling that once it was posted on FR, it would be dissected and the parts grouped into relevant and bogus piles. ;)
What is "massive contamination"?
Who says we will have "massive contamination"?
Depending on what your definition of "massive contamination" is, it may or may not be possible to build the perfect plant. There is always "something else" that could go wrong.
NP, thanks for the link.
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