What is Happening at the Fukushima Nuclear Power
高松聡
さんの福島原発で起きていることを英訳してくれました。
http://ameblo.jp/satoshitaka/entry-10834940369.html
（The continuance from the first half）
What is Happening at the Fukushima Nuclear Power Plant (2/2)
6. The intensity of radiation is inversely
proportional to the distance squared. In other words, the intensity would drop to 1/4th, if you are
40 Km away from the plant, which would be twice the 20 Km evacuation
range. It drops down to 1/16th at
80 Km (4X the distance), 1/64th at 160 Km (8X the distance), and
1/256th at 320 Km (16X the distance). The distance between Fukushima and Tokyo is around 300 Km.
Let us say that the level of radiation increases to 200X of the normal limit at the edge of the evacuation zone, at 20 Km away from the plant. The level of radiation would be negligible, because it would be 1/256th of 200X, or 0.7X the normal limit. More on this later.
7. The most important piece of information about the nuclear crisis that is also the most misunderstood is the fact that the automatic shut down process, which took place immediately after the earthquake, worked, and the uranium fission chain reaction was stopped. The power plant has been shut down. If it was not, there would have been a reactor meltdown in around 45 hours, and it would have been unstoppable.
If there had been a meltdown immediately after the earthquake, we would have faced the worst case disaster as of Sunday. But that did not happen, which means that the power plant has been shut down. There is absolutely no scientific reason to doubt this point. People seem to believe that the uranium is continuing to burn, and that the nuclear fuel rods are melting and spreading radiation. That is not so. Let us make sure we all understand that the uranium fission chain reaction has been halted.
Nor are the hydrogen explosions we saw among the buildings a major problem. They were to be expected. (I want to clarify here that a hydrogen explosion has nothing to do with a hydrogen bomb-like explosion.) These buildings, that were blown up, would not have done anything anyway in preventing the spread of radiation. The “real walls” around the nuclear reactors (storage container) are inside the buildings in three layers. (And they are, of course, still there.)
8. So what is really happening and what are they doing?
Although the reactors have been shut down, and the uranium fission chain reaction has stopped, it is necessary to continue cooling off the residual heat with water even after the shut down. The fourth reactor had been shut down even before the earthquake, and spent fuel rods were being cooled in a pool of water there, because they would remain exothermic even after the chain reaction had halted. The rate of heat release would gradually go down, and it would eventually be safe enough to move and treat the fuel rods.
I am now going to get a little technical. A nuclear reactor generates radioactive cesium and iodine as the byproducts of uranium fission chain reaction. These elements have shorter half-lives and are much less radioactive compared with uranium. These byproducts, however, also continue to release heat after the reactor has been shut down, although the amount of heat is miniscule compared with those from the uranium fission chain reaction. The byproducts would break down naturally with time (a breakdown is a process by which these byproducts become non-radioactive) and generate heat. The amount of heat that they release decreases rapidly with time.
With effective cooling, there will be less and less water required each day for the cooling.
As long as the heat is cooled off with water, the reactors will not go through a meltdown. Should there be a partial meltdown, it is still possible to prevent a catastrophe by cooling before the triple layers of walls are destroyed. Even if cooling were to fail, catastrophic damages will still be avoided, as long as the melted fuel remains contained. There is a possibility, according to the latest information, that the reactors are going through partial meltdowns. But, again, as long as the fuel remains contained inside the third wall (storage container), there should be no major impact outside of the plant.
The
third wall (storage container) is the last line of defense against the
meltdown. It is designed to
contain the melted fuel and keep it from leaking outside. The reactor was designed up front for
containment. At this point in time,
there is absolutely no information indicating that these third walls are
getting breached.
9. Nevertheless, you need water, pumps for pumping the water, and electrical power to drive the pumps in order to cool the residual heat. Under normal circumstances, distilled water is used for cooling to prevent rusting and contamination in the reactors. The problem that TEPCO faces is that it lost access to an adequate amount of distilled water and electrical power after the earthquake (more precisely, after the tsunami).
They are, however, already using the seawater for cooling. It means that the reactors can never be used again. The government and TEPCO have chosen to give up any hopes of running the plant again and have chosen the seawater option. It means that the supply of water is now unlimited.
The issue remains, however, with the electrical power. They relied on an emergency diesel generator immediately after the shut down following the earthquake. Everything worked as it should. However, the power from the diesel generator stopped, when it was damaged by the tsunami.
I’m sure they next used the emergency battery for approximately eight hours. But the battery power eventually ran out, and that was it.
People on the ground are now focused on restoring the electricity to the plant and running the pumps and cooling the reactors with seawater. The alternatives are to dump water using helicopters or hose water using fire engines. There was too much radiation on March 16 for the helicopter option, but they have been able to use the helicopters starting on the 17th. They are also mobilizing the specialized fire engines starting on the 17th.
Things remain critical for all six reactors at the plant, but there is no imminent catastrophe, as of March 17th.
Cooling on the reactor 1 is going well, although I do not know the exact status or how the water is being injected to the reactor. What is important is that we know the temperature has stopped rising.
Reactor 3 requires additional measures for cooling. In fact, a large-scale water cooling is planned for the 18th. The situation, however, does not seem to be critical.
Although the building housing reactor 2 has not been blown away, the pressure control room has been damaged, and something needs to be done. Because the roof of the building is still intact, reactor 2 remains to be the hardest to cool. As soon as the power is restored, they will attempt to restart the pumps on this reactor.
Although reactor 4 was not running, and the spent fuel rods were left in a pool, a fire nevertheless started, caused by the heat generated by the byproducts after the reactor was shut down, as explained earlier. As soon as the supply of water resumes, reactor 4 will be in a better situation than the reactors 1 through 3. It should be noted that water cooling is difficult here, because the building is still intact. They may use a relatively large hole that resulted from a fire for injecting the water.
Reactors 5 and 6 are so far all right, but they may become problematic in the future.
The No. 1 priority here is to have the electricity restored and line up the fire engines. As far as the electricity goes, GE, which manufactured the first and second reactors, is shipping ten mobile gas turbine generators on air. Before they arrive and go online, however, TEPCO is expected to somehow get the electricity to Fukushima restored through the transmission lines. I am hoping that they will make a big step forward on the 19th. (Once the power is restored, the situation will improve dramatically – that is, as long as the pumps have not been destroyed.)
Furthermore, a team of specialized fire engines from the U.S. base in Yokota are heading to Fukushima and are expected to be in action soon. The Japanese self defense force is also sending its water supply trucks.
A fire engine can remain in action for a limited amount of time each time, however, because of a need to limit the workers’ exposure to radiation and the limited amount of water it can transport. However, they are making a difference. Once the electricity is restored and the pump and emergency cooling systems run again, a continuous cooling will be possible.
If these efforts get results in preventing the fuel rod meltdown, the catastrophe will be avoided. We should also remember that, even if the cooling were to be inadequate and the fuel meltdown were to occur, the catastrophe will again be avoided as long as the fuel is contained by the third storage container. I will get into this in more detail.
10. What kind of radiation is detected now? And will they impact Tokyo?
It is also important to understand why we are seeing a spread of radiation now and how serious it is (or not). As I mentioned earlier, the reactors have been shut down, and there is no more nuclear chain reaction. However, the byproducts continue to release heat. Water cooling results in water vapor which raises the pressure inside the containers. Without a means for relieving the pressure, the storage container (and not the buildings) would explode. This would be the absolute worst situation that we must avoid. The effort to release vapor is ongoing. (Think about a pressure cooker. Once the pressure inside rises above a certain level, the pressure valve would open and release vapor. You would hear a whistling sound.)
The majority of radioactive materials released along with this vapor is so-called noble gas, such as Xenon 137 (I know they sound weird, but they are not scary.) Xenon 137 has a half-life of only a few minutes, after which it is no longer radioactive. It is not dangerous, as long as you keep a distance. Even if it were to be blown toward Tokyo, it would take more than a few minutes to arrive.
Iodine 131, which I believe is being detected among those people who were exposed in the evacuation zone, has a half-life of approximately eight days. Even if people were to come into contact with iodine, it would remain radio active for only eight days. The truth is it would get washed away when people bathe.
Let us look at two examples of the worst kind of exposures seen so far in Fukushima.
The individual reported to have been exposed to the highest level of radioactivity so far (according to a level measured on a shoe at a shelter in Futaba) is said to be at 0.53 mGy/h in absorbed dose rate (I’m going to skip the complicated calculations and scientific rigmarole), according to NIRS. You start to see damages to the skin at 2-3 Gy or more. At 0.53 mGy/h, this person is not likely to face any problems. Even if he/she were to remain exposed for eight days, the total radiation dose would only be 0.1 Gy (0.53 X 24 hours X 8 days X 1/1000th = 0.102).
The radiation measured at the front gate of the Fukushima plant hit a maximum of 1015 microsievert on March 12th. Let us say a person were to stand at this spot for an hour, and the level of radiation exposure would be approximately 1 millisievert. People who live in Japan are normally exposed to 2.4 millisievert of radiation each year and up to 10 millisievert at a higher altitude. The level of radiation exposure resulting from each x-ray screening is 4 millisievert. Pilots and flight attendants are exposed to additional 2 to 3 millisieverts each year. You are exposed to radiation every day anyway. These levels that I mention demonstrate how non-threatening a 1 millisievert of exposure is, standing for an hour at the front gate, where the radiation is said to be the worst.
Let us also remember that the intensity of the radiation drops rapidly with the distance (inversely proportional to the distance squared). And the majority of radioactive materials being released have a half-life of a few minutes to up to eight days.
Some people in Tokyo were scared by a report that the level of radiation in Chiba rose to several times the normal (at some instantaneous moment). Let us say it had increased by five-fold, and the level of exposure would have been the same as someone living at a high altitude. And people up there are routinely exposed to five times the normal level throughout the year. A temporary increase by 5X for a few hours or a few days would not be an issue at all. If you had to worry about this, you would not be able to go through an x-ray screening or CT scan at all, for instance.
The rise in the level of radiation in Tokyo is also miniscule compared with the amount of exposure on an individual flying from Tokyo to New York, for example, or going through a CT scan.
No one needs to worry about the exposure to radiation in Tokyo. You do not need to be cooped up indoors, or wear a mask when leaving your home, or keep the windows closed, or not use the air conditioner. All of these measures are completely unnecessary. (If you want to stop using the air conditioner to help reduce load on the power plants, that will be great.)
Nor is there any need to worry about radioactive exposure from rain at this moment. (Stay dry, if you want to stay warm.)
Unlike a nuclear bomb, there will be no nuclear fallout here.
The reactors at Fukushima have a fundamentally different design from the reactor at Chernobyl. There will not be the same kind of catastrophe as Chernobyl, even in the worst possible scenario.
Please also remember that a nuclear reactor will never ever turn into a nuclear bomb. Some people are worried that this may turn into another Hiroshima, but that will never happen, no matter what. Hey, if it were that easy to turn a nuclear reactor into a nuclear bomb, what are the Iranians and North Koreans waiting for? These two things are completely different.
People are more scared than they need to be, because the word “meltdown” is used imprecisely. First of all, “meltdown” is not a scientific term. People seem to be using the word “meltdown” to refer to serious radiation damages caused by the nuclear fuel rod melting down, breaching through the storage containers, and getting outside. If this were a meltdown, then even the serious accident at the Three Mile Island in the U.S. would not qualify as a meltdown. At Three Mile Island, the fuel started to melt and became uncontrollable. It melted the first and second storage containers and finally was stopped at the bottom of the third container. Eventually it was stabilized. As serious as this accident was, there was no impact on the outside environment, even within the 10 mile evacuation zone. There was not a single death reported due to the radiation exposure.
The accident at Three Mile Island happened 12 days after a movie called “China Syndrome” opened in the U.S. In the movie, a nuclear plant meltdown in the U.S. caused the nuclear fuel to melt down the storage container and penetrate all the way through to the other side of the earth in China. People probably react to the word “meltdown” in extreme ways because of this movie.
The reactors used in the U.S. and Japan are designed with the bottom of the third storage container capable of stopping the fuel, should the fuel rods melt down, and should the cooling fail.
Finally, let me talk about the “worst case scenario,” although it is very, very unlikely to occur. The probability, however, is not non-existent. People get worried the most, when they do not know what is likely to happen. So that is why I am going to explain what the “worst case scenario” would be.
The Worst Case Scenario
If the cooling remains inadequate, in spite of all the efforts by TEPCO, the fire department, the police, Japanese self defense force, American military, generators being air transported from the U.S., and electricity from Tohoku Power, then the fuel rods will melt in one or several or all of the six reactors.
Once that happens, the first and second storage containers will melt down, and the melted nuclear fuel will drop to the bottom of the third storage container. The bottom of the third storage container has been designed for this situation and is capable of absorbing and fixing the melting fuel. The fuel spreading and getting fixed at the bottom of the third container would be similar to a situation at Three Mile Island. Once this happens, it would take an enormous amount of time and expense to get the plant treated.
But please remember that even in such a situation, the fuel remained contained in the third storage container at Three Mile Island, and the fuel did not leak outside. There were no serious radiation damages.
In other words, even in the worst case scenario, the radiation damages to the surrounding areas will be minimal. There is no possibility that the damages will spread to Tokyo.
So that is it. But I am now also going to mention the “absolute worst scenario,” although it will be even less likely.
Let us say that the melted nuclear fuel would not get stopped by the bottom of the third storage container. In other words, the third storage container may get damaged with, for example, cracks, and the melted fuel and radioactive materials would leak through the storage container. This would be the absolutely worst scenario with tremendous radiation damages. The impact on the surrounding areas will be serious, but how serious will depend on the amount of radiation that leaks.
Should this happen, there would be mid and long term impacts on the people, the agriculture in the surrounding areas, and even on the fishing industry. (It is important for everyone to understand that the agricultural products from the Fukushima area so far are not impacted to an extent that would cause health issues, unless you are eating 100 heads of cabbage all at once. Let us make sure that we not harm the agriculture and fishing industries in Fukushima with misinformation.)
Even with the absolute worst case scenario, the radiation will not immediately hit Tokyo (at a level that would be harmful). The radioactive materials may get carried by wind or rain. Should this happen, I’m sure everyone will hear about it. The governments around the world, the worldwide media, IAEA, and the American military are all keeping a close eye on the situation. Google is periodically updating the satellite images provided through Google Earth. There would be no need to worry about this, until it happens.
Even if it were to happen, there will be no need to evacuate from Tokyo. We will simply pay attention to the information provided by the government and the media. We should not need to do more than, say, avoiding going outdoor and avoiding the rain.
Now that you understand the “absolute worst case scenario”, I hope you understand how unnecessary it is for people in Tokyo to worry with the situation such as it is now. Unless the “worst case scenario” happens, there is no need to worry.
So here is the conclusion. Let us stop worrying, hording, and sending e-mails that create panics unnecessarily. Let us stay positive. Let us be thankful to the people who are risking their lives to cool the reactors in Fukushima and quietly keep an eye on the situation. That is all we can do for now.
I have faith that there will be no worst case scenario, because we have the world-class technology and people who are willing to risk their lives to save others.
Satoshi Takamatsu
March 17, 23:20
高松さん、ありがとうございます。
