はてなキーワード: Plan Bとは
12 Dr. Hiroshi Nishiura is one of the few professionals of mathematical models of infectious diseases in Japan, and it is well known that his ability is outstanding. However, many people don't understand mathematical models themselves (I must confess that I can't say that I understand all of the findings because I'm not a professional of mathematical models either), so his findings and comments are easily deified. Because the contents of the mathematical model are a complete black box to many people, it makes it seem like the oracle is coming out like a shrine's oracle. Much of Japan's infection control policy relies on the Nishiura theory. So there is nothing wrong with that, but one of the problems in Japan is that there is no plan B in case plan A goes bust. Dr. Nishiura is an excellent scholar. It is not God. Hence the need to have that Plan B with the possibility of making a mistake. I am greatly concerned that bureaucrats and politicians who are prone to infallibilism will mistake science for an oracle. It is only when falsifiability is assured that science can continue to be scientific.
Mathematical models are the product of deductive methods. The deductive method is complemented by the inductive or abduction method, which is the basis of scholarship and the common sense of clinical medicine. It's a common occurrence in this industry that no matter how deducibly correct it may seem, it's actually not true. Even a huge intellect like Hegel or Marx can make a mistake by deduction alone.
I'm not saying don't use the model at all. I myself write a paper using a model. However, the model is not infallible, there are assumptions that are assumptions, and the assumptions are often wrong. Making use of Gram's stain means having full knowledge of what Gram's stain cannot do and does not understand, and Gram's stain cannot be used by Gram's stain universalists. It's the same thing. Mathematical models are also utilized in the UK, which is why Brits are very sceptical of their conclusions, and there are always counter-arguments and objections. It is a sound and scientific attitude.
15 Japan's "now" is a well-controlled state of infection, which is much better than Wuhan at its worst, or Italy, Spain, France, England, or New York at the present time. The problem is that it doesn't guarantee that it will "always work".
It is Tokyo that is of concern. The increase in reports of infection is not the only problem. The problem is that more and more infected people are unable to form clusters and cannot be traced. And the number of tests is much lower than that number of positive cases; it's too little that they only tested less than 100 people (the date of testing for the positives is unknown, but it's probably around here) to capture 47 infected people.
Again, it's not necessary to figure out all the infected people. However, it is troubling that the flow of infection, movement and clusters are out of sight. Therefore, the threshold for testing must be lowered in Tokyo. The threshold for testing varies with the circumstances. That's what I explained with the Korean example. Sticking to the Ministry of Health, Labour and Welfare's "standards" will lead to a misunderstanding of the phenomenon itself. Already in the Kansai region, infected people have been found with taste and smell abnormalities, and clusters have been detected from there. I would like to make more use of the athletic sensibilities of these clinicians. I'm not sure "where" in Tokyo is the barrier to lowering the number of inspections, but that barrier needs to be removed immediately.
17 This conceptual diagram that everyone is looking at - lowering the peak of the infection and shifting it to the side. This is all a product of deduction, and I don't know if it's really true. As mentioned above, the UK estimates already suggest that this is not enough. It is possible that the damage that was shifted to the side could simply be "extra-long damage".
And this is the key point: the idea of lowering the peak should not become the notion that the peak must be lowered, or the belief that the peak must be lowered, or the self-implication that the peak is not happening. In a pattern of Japanese failure to stick to Plan A, Diamond Princess allowed no-guard disembarkation by changing "secondary infection should not occur" to "it can't have happened". We need to keep our eyes on reality so that "peak shouldn't happen" doesn't become "I don't want to see a peak. Even if it is an inconvenient truth that we don't want to see.
19 Repeatedly. It's common knowledge in this industry that deductive methods are complemented by inductive methods. Nevertheless, PCR is often false-negative and has little power to determine the status of infection. That's why "testing everything" is so wrong. However, a serum test measuring immunoglobulin IgM and IgG would provide a more accurate picture of the "status of infection in the population. This, however, is not infallible. It is difficult to use for individual cases because it misses early infection, which is why it misses early HIV infection.Whether antibody testing is useful in individual cases remains to be tested, but it is well suited for epidemiological studies on a population basis. Roughly speaking, we can confirm whether the "infection is rampant" in Tokyo right now, or whether it's just an unfounded fear.
As a precedent, serology tests in London showed that the 2009 pandemic flu was 10 times more likely than previously predicted. Antibody testing is often performed after an outbreak, but now is a good time to examine COVID-19, which is becoming a chronic pandemic.
The UK is even more aggressive. The idea is to test for antibodies at home, and if they are found to be infected, they will use it as a basis for self-isolation at home. That strategy is flawed because with the lockdown in place, a negative test does not mean "no self-sequestration". However, the idea is that we want to control the infection as a whole, and I think it is worth considering.
Inductive legal confirmation of how many infections are occurring in Tokyo is necessary and useful. I'm not a prophet, so I don't know what the outcome will be.However, no matter what the outcome, scientists need to accept it and not hesitate to change their thesis and move on to Plan B in some cases. Scientists have to be coherent in their inconsistencies.They may not be coherent in form, but they must be coherent in principles and professionalism. Good faith in the facts.
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.
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.
・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.
・I believe the most significant problem will be a prolonged power shortage. About half of Japan’s nuclear reactors will probably have to be inspected, reducing the nation’s 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.