Why You Shouldn't Worry About Japan's Nuclear Reactor Problems

[rodsky]

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Very informative blog. Warning--nosebleed zone--very long reading, not for the impatient or stupid.

Why you shouldn't be worried about Japan's Nuclear Reactors:

This post is by Dr Josef Oehmen, a research scientist at MIT, in Boston.

He is a PhD Scientist, whose father has extensive experience in Germany’s nuclear industry. I asked him to write this information to my family in Australia, who were being made sick with worry by the media reports coming from Japan. I am republishing it with his permission.

It is a few hours old, so if any information is out of date, blame me for the delay in getting it published.

This is his text in full and unedited. It is very long, so get comfy.

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 Japan’s 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.

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 and concrete. 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), 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 typically 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 “control rods". The control 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 control 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 control 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 Argon. 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 5 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 5 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 control 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, control 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?

My assessment:

* 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)

* (Updated) I believe the most significant problem will be a prolonged power shortage. 11 of Japan’s 55 nuclear reactors in different plants were shut down and will have to be inspected, directly reducing the nation’s nuclear power generating capacity by 20%, with nuclear power accounting for about 30% of the national total power generation capacity. I have not looked into possible consequences for other nuclear plants not directly affected. 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. I am not familiar with Japan’s energy supply chain for oil, gas and coal, and what damage the harbors, refinery, storage and transportation networks have suffered, as well as damage to the national distribution grid. All of that will increase your electricity bill, as well as lead to power shortages during peak demand and reconstruction efforts, in Japan.

* This all is only part of a much bigger picture. Emergency response has to deal with shelter, drinking water, food and medical care, transportation and communication infrastructure, as well as electricity supply. In a world of lean supply chains, we are looking at some major challenges in all of these areas.

-RODION

[Visual C#]

I read this too, but sadly, people won't notice. Anytime they hear "nuclear", "blast", and "meltdown" in the same sentence, plus media hype and hyperbole, people wont' care about context anymore.

This will undoubtedly set back nuclear energy research for years. Tis sad, considering that nuclear power is a great alternative to coal, oil, and natural gas. Further research could have been done for safer nuclear reactor designs, but sadly, funding for them will have been dried up by the time this crisis is over.

[rodsky]

This will undoubtedly set back nuclear energy research for years. Tis sad, considering that nuclear power is a great alternative to coal, oil, and natural gas. Further research could have been done for safer nuclear reactor designs, but sadly, funding for them will have been dried up by the time this crisis is over.

I beg to differ. Quoting a portion of the text above...

"...The earthquake that hit Japan was 5 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 5 times, not 0.7). So the first hooray for Japanese engineering, everything held up.

I mean, there is absolutely no way to test the survivability of a nuclear plant other than a real incident, and in this case, the real incident was greater in magnitude than the predicted incident, and still, the plant *somewhat* survived the ordeal. An analogy would be like this:

I am building a bridge. In the course of the construction, say about 85% of the way before completion, I realize I made a mistake in the design that could prove to be harmful/disastrous (in fact, cracks have shown up here and there while the bridge was still being constructed). This doesn't mean I have to STOP building the bridge completely because of the faulty design--it simply means I have to destroy the existing one, and rebuild again from scratch, because I know that if I simply abandon the design, someone might end up doing exactly what I did and thus fall into the same pitfall, and thus by rebuilding the design to a more robust one, I am doing the rest of the bridgebuilders a favor in that I'm showing that a more rigorous design that could actually work, based on a mistake. This is why mistakes are important--because they eventually lead to better designs.

Now I am fully aware that, my analogy will work only in a sphere devoid of politics and economics...however, I still believe that, with the current world experiencing a myriad of energy problems associated with the dwindling fossil fuel resources, the (educated) world won't turn it's back on nuclear energy--another analogy is this: You don't give a child a box of matches because the child's curiosity can eventually lead to a house burning down...however, if you teach a child the proper way to deal with a box of matches, it won't do any harm, esp. if the child has grown to a more mature level. So I believe nuclear energy for humans is still possible with a lot of maturity and more excellent engineering.

-RODION

[stealthghost]

a very long read indeed but a very nice thread and information.. thanks..!

IMHO, all worst-scenario cases nga gi-huna2 daan sa mga engineers before they built the nuclear plant was not the worst when the earthquake + tsunami struck the plant recently..

good thing, the plant survived and kudos to those who made it happen!

[brandnewbien]

a very long read indeed but a very nice thread and information.. thanks..!

IMHO, all worst-scenario cases nga gi-huna2 daan sa mga engineers before they built the nuclear plant was not the worst when the earthquake + tsunami struck the plant recently..

good thing, the plant survived and kudos to those who made it happen!

kudos to those engineers.
and they have more work to do now.

[handsoff241]

That justified my "radioactive" temper when I received that chained text messages about radiation hitting the Philippines and that we should rub our necks with betadine because radiation will affect our necks (or something in our neck) first.

Very informative read, no need to be a physics genius to digest the whole idea that even Japan itself is safe. Keep it up!

So I was wondering if we can trace the people who started that chained text messages and throw them inside the nuclear-reactor's core.

[rodsky]

Additional information, this time from a friend who lives in Japan who received this circular:

The following information is from Dr. Alan Bolind, who took some time to post to his Facebook wall today. He has a PhD in Nuclear Engineering from the University of Illinois (2009). He has been living in Tokai-mura, Ibaraki, Japan, since December 2009, working for Ibaraki University. Alan would be the first to tell you that he’s not an expert on this topic, but he is knowledgeable, and he’s excited to share that knowledge to help everyone have a better understanding of the nuclear situation. Read on:

*****

Regarding the Fukushima nuclear power plant problems: Yes, there are problems. No, it is not at all dangerous for me or other people here in Ibaraki Prefecture. Tokai-mura is over 100 km (60 miles) away from the Fukushima II power plant. The evacuation zone is only 20 km around the power plant. The reason it is only 20 km is because people who live farther away than 20 km are not in danger.

Actually, 20 km is probably overkill, but the authorities want to be cautious and plan ahead for contingencies that may never happen. Yes, this morning, Prime Minister Naoto Kan said that the people between 20 and 30 km should stay indoors today, because of some increased emissions of radioactive particles from the reactors. OK, but even they don't need to evacuate. And I'm over 100 km away. So, no problem for me.

Now it's time for fun facts about nuclear reactors and radiological safety:

(1) The reactors are now shut down, and they have been since immediately after the earthquake. There is no nuclear chain reaction going on. What's happening now is the residual heat caused by the natural radioactive decay of the radioactive elements that have been produced inside the reactor while it was running.

This amount is about 7% of full power at the time of shutdown, and then it decreases quickly (like only about 1% of full power after about an hour). {These values are from "Introduction to Nuclear Engineering", 3rd ed., by John Lamarsh and Anthony Baratta.} But even though it is relatively small, you still have to get rid of this heat. If you let it build up, then the temperature inside the reactor slowly climbs up.

At the limit, the temperature will get so hot that it will cause some of the metal inside the reactor to melt. This is what is called a "melt down." But it doesn't necessarily mean a large release of radioactive particles. For example, at the Three Mile Island #2 reactor accident in Pennsylvania in 1979, part of the nuclear fuel did melt.

So, to this day, the utility company cannot run that nuclear reactor. But it still runs the #1 reactor next door.

(2) When a nuclear reactor shuts down, normally some diesel generators next to the plant turn on and provide electricity to run pumps to pump cooling water through the nuclear reactor to remove the heat from the radioactive decay. This can take place for awhile. I forget how long, and I can't find it quickly in my book, but I want to say it is about 2 or 3 days or so.

At Fukushima, the tsunami damaged these diesel generators, so that they couldn't pump in the water. That is what has caused the problems now.

So, they couldn't use the diesel generators to pump the water into the shut-down nuclear reactors. Eventually, though, they did figure out a way to get water into the reactors; I haven't yet heard how, but they did.

There are a couple of problems now (A) high pressure and (B) buildup of hydrogen gas.

(A) High pressure is easy to understand. The reactor is acting like a tea kettle. If you boil water in a tea kettle, it whistles, because the pressure inside has increased. The same thing is going on in the reactor, except that the utility company doesn't want it to whistle at all, because the steam is slightly radioactive.

It's not very radioactive; it's not enough to cause big problems for people. But they try to limit the amount of radiation to the public as much as possible. That's one of the reasons why they evacuated up to 20 km away. They eventually decided that the pressure was too high, and they'd rather let it "whistle" than blow up. But since nobody was around, it wasn't such a big deal.

(B) The hydrogen gas is a little more complicated. Basically, the problem is that the insides of the nuclear reactors were already really hot by the time that they got the water inside. When the water hit the hot metal inside the reactor, it not only made steam, but some of the water molecules actually split into hydrogen and oxygen. (Remember, the chemical formula for water is H2O?)

The radioactivity inside the nuclear reactor also facilitated this splitting of the water molecules. Then, the hydrogen gas--because it is a light gas--bubbled to the top of the nuclear reactor and then seeped out. (This is not so hard for hydrogen. The molecules of hydrogen are super small, so they can diffuse out through flanged pipe joints and stuff like that.)

Now, around the entire nuclear reactor is another thick, concrete shell. This concrete building is called the containment vessel. Its purpose is described by its name--it contains anything that might leak out of the nuclear reactor, such as in this case. So, the hydrogen that leaked out of the reactor built up in the top of the containment vessel.

Well, inside the containment vessel is air, of course. When enough hydrogen had built up, it ignited and exploded with the oxygen from that air. This is what has happened at two or three (I can't remember now) of the Fukushima reactors.

Back to the reactor: So, when you saw the video of a big puff of dust from the reactor, that was probably the lid of the containment vessel popping off. The dust was probably concrete.

So, that's not so good, because now the containment vessel has a hole in the top. On the plus side, now no more hydrogen can build up in it, right? Also, remember--the nuclear reactor itself (which is inside the containment vessel) is still intact. So, the guts are all still inside, holding together.

I heard this morning that there was another explosion at the Fukushima #2 reactor that damaged the suppression pool at the bottom of the reactor. I'm not sure what caused that (neither is anyone else), so we'll have to keep an eye on the news and see what's going on.

On the other hand, the utility company has been able to get cooling water into the nuclear reactors--sometimes more, sometimes less, but now always at least some cooling water. And, remember that the heat in the nuclear reactors now is just the heat from the radioactive decay.

So, the point is that this crisis is short-lived. There is only a limited amount of heat that needs to be cooled away, and it gets cooler and cooler with each passing hour. I would guess that yesterday or today was/is the worst of it, and probably everything will be fine by the end of the week. As long as they keep putting some cooling water in there, it's more a matter of how messed up the equipment is after this is all over than about any catastrophe.

In other words, does the insurance agency "total" this car, or can it go to the autobody shop?

The numbers that I heard this AM were 3 to 5 microsieverts (per hour) of radiation in the air around [Mito]. That's higher than normal, but it's not anything to get up in arms about. When you smoke, you get 80000 microsieverts per year. If you fly a lot (like airplane pilots and flight attendants), you get 1600 microsieverts per year.

So, if you decide to fly back to the US to wait this out and then fly again to return to Japan, you might get about the same amount of radiation as if you just sit cool here. And it's a lot less expensive to just chill here. (This radiation is from the cosmic radiation from outer space, which is more when you are up at 30000 feet than when you are safely at sea level here in Japan.)

Another unreasonable response: Staying inside and not going to the store to buy stuff for dinner tonight.A reasonable response: Postpone your soccer or golf game until Saturday. Play video games today. Besides, it's cloudy, windy, and cold today--not good soccer or golf weather.

Now... back to my numbered list of fun facts. Time for #3.

(3) The radiation levels in Ibaraki Prefecture (the next prefecture to the south of Fukushima) are very small and not worth getting all worked up about. I hinted at this in my most recent posts, but now let me explain it in a little more detail.

I mentioned smoking and airplane flying, but now let me list some other numbers for you to compare. Note that these numbers are averages and are per year, but it's the best I've got with the books I have with me.

**Remember, the numbers I heard this morning were 3 to 5 microsieverts per hour, outdoors. Indoors, it would be less.**

* Patients who get medical X-rays: 1000 microsieverts/year

* Medical personnel who give those X-rays: 3000 microsieverts/year

* Patients who get dental X-rays: 30 microsieverts/year

* Dentists who give those X-rays: 1000 microsieverts/year

* Patients who get chemotherapy and radiation treatments: 3000 microsieverts/year

* Medical personnel who give those treatements: 3000 microsieverts/year

* People who live near nuclear power plants that are operating normally: much less than 100 microsieverts per year

* Workers in nuclear power plants: 4000 microsieverts/year

* People who live in brick or masonry buildings: 70 microsieverts/year (from the natural radioactive elements in the building materials)

* Airplane passengers (average): 30 microsieverts/year, or 5 microsieverts/hour (the same as the radiation levels around here). So, a round-trip flight to the USA and back to Japan could give you as much as 120 microsieverts.

* Airplane crew (average): 1600 microsieverts/year

* Television: 10 microsieverts/year

* Smoking 1.5 packs of cigarettes per day: 80000 microsieverts/year (This is because there is natural radioactive dust that settles on the tobacco leaves while the plants are growing. Then, it gets rolled up into the cigarette, and when you smoke it, you breathe it into your lungs, which are one of the more radiation-sensitve organs in the body.)

* Living at sea level on the eastern or southern coasts of the USA: 500 microsieverts per year from radiation from outer space and from the rocks in the ground

* Living in Denver, where you are surrounded by radioactive rocks and are 1 mile closer to outer space: about 1500 microsieverts per year.

(4) This last point is why you can't really judge the situation by using the phrase, "The radiation levels are now XXX times the normal radiation levels." We happen to be living in a place with normally low levels of radiation, so multiplying a small number still gives you a small number.

Instead, you should judge by the absolute numbers: XXX microsieverts per hour. In my opinion, 3 to 5 microsieverts per hour is nothing to sweat about. When I would start to take action would be when the sustained radiation levels in Tokai are closer to 1000 microsieverts per hour. But this is the value near the nuclear power plant, which is why the authorities evacuated people within a 20 km radius of the plant.

I just read one of the more recent articles. It is saying that the radiation levels at the nuclear power plant have reached higher values. (But it doesn't say whether it is per hour or per year or what.) But again, this is why PM Kan has said the radiation levels are about where they can impact human health, and which is why the public and unnecessary personnel have been moved away from the reactor.

Based upon what I know and what I am hearing from the news, it seems like the Japanese authorities are taking reasonable actions and precautions. So, if they say to evacuate, then you should evacuate. And if they say that you don't need to evacuate, then you don't need to evacuate.

(5) Recently, I was asked about the rain that is supposed to fall near Mito tonight. Unfortunately, I don't know what kind of particles are in the air that are causing the 3 to 5 microsieverts/hour here, which determines the influence of the rain.

I am going to venture a guess that most of the radioactive particles are from radioactive hydrogen atom (called tritium) that are made from the water that is in the nuclear reactor (while it was running). In this case, it is the water vapor in the air that is slightly radioactive.

The other possibility is that the radioactive particles are dust particles, such as from the concrete dust that came from the breaking of the containment vessel, due to the hydrogen explosion.

In either case, actually, the rain would help. The water vapor would condense out of the air (into the rain drops), and the rain itself would tend to wash the air of the dust. So, the rain would cause the radiation levels in the air to decrease.

And the radiation dose is primarily from breathing the air into your lungs. Once it's on the ground in the rainwater, it doesn't hurt anything. (Your skin is an excellent radiation barrier for many radioactive particles.) So, my guess is that the rain will help, and you don't have to be worried about it. Besides, don't you normally stay indoors when it rains?

Again, here's my caveat: I don't actually know what kind of particles are in the air. When you find out, let me know, and I can revise my guesses.

Ok, so that's about it for now. I recommend the following link: ANS Nuclear Cafe | All Things Nuclear . This page is from the American Nuclear Society, of which I am a member; it is the professional organization for nuclear engineers and professionals in the United States. They are collecting links to news media reports about the Japanese reactors, so you can read stuff all at once.

FYI, the radiation numbers that I posted earlier (like from flying and smoking, etc.) are all from that same book I mentioned earlier, "Introduction to Nuclear Engineering," 3rd edition, by John R. Lamarsh and Anthony J. Baratta. Pretty much every nuclear engineering student has seen this book. (Hey, I'm an academic. I have to cite my sources.)

-RODION

[ethzneuron]

very informative.. now let me share this.

[Visual C#]

The only problem right now with this situation are the multiple conflicting reports from CNN, NHK, etc.. about the true extent of the disaster. I heard that one of the reactor cores (the "pressure cooker") has already exploded, spewing radiation all over. Then the government says "nothing to worry about".

Ah, media.. I can never trust you anymore, with all the hyperbole and sensationalism. I can't help but think that the Japanese government is being tight-lipped about the true extent of the disaster.

[treize]

That's a very long read... yet very informative... I'm amazed by it's defense mechanism was designed..