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WARNING: Professor Ryugo Hayano is an expert in exotic atoms.  The answers to the questions below are not absolute as different researchers can easily have different opinions. 

The content on this page has been based on tweets gathered by Professor Ryugo Hayano (@hayano), School of Science, Tokyo University.  A number of questions have been answered by experts other than Prof Hayano.

 

The following is a collection of questions and answers regarding radiation and its health effects.
Please follow the link stated below to view the original posts (Japanese).

Responsibility for this published document lies with Science Media Centre of Japan (Corp.). The information below is based on information current at the time this document was written (2011/3/13 15:30-JST).

This document was translated with the support of the Australia-Japan Foundation

【To Physicists, Nuclear Engineers and other Researchers】
In regards to revisions based on the latest information, we would greatly appreciate it if you could provide any advice via the SMCJ inquiry form, or Twitter (@smcjapan).  Please include your name, post, and contact details (these details will not be made public).

【CONTENTS】
1. Radiation Exposure
2. Cooling with Fresh water and Seawater
3. Why use Boric Acid?
4. Regarding the Explosion
5. The Operational Status of the Nuclear Power Stations

1. Radiation exposure

Q 1-1: Are the amounts of radiation that are being released at the plant enough to cause radiation exposure? (Updated 14:00 March 14)

A: Geiger counters are sensitive enough to detect radiation if you have so many as fifty to several hundred radioactive atoms on your skin.  I do not know what the present level of exposure is, but I can say that even very low levels will be detected.

Q 1-2: Do we need to worry about secondary exposure to radiation?  For example, is seafood from this area safe to eat? (Updated 13:00 March 13)

A: If reports of how much radiation has been released are accurate, there should be no reason for concern. There is radioactive matter present in the natural environment as well.

Q 1-3: Is it a good idea to stay indoors? (Updated 15:00 March 13)

A. The most important thing is to stay away from the nuclear power stations. As the government has announced, an evacuation perimeter of 20 kilometers is a good estimate.  Also avoid exposure to the open air.

Q 1-4: You’ve said it’s safe as long as people stay 20km away, but should people living in Tokyo also stay indoors and avoid open air?  Should people living in Tokyo avoid going outside with their skin exposed? (Updated 14:27 March 14)

A: Tokyo is more than 200km away from Fukushima.  Radioactive matter carried by the wind can lead to people being exposed to radiation, but the further the distance the radioactive matter has to travel, the lower the radioactivity, so those living in Tokyo have nothing to worry about.

Q 1-5: Can you explain why the evacuation perimeter was extended to 20km within the plant? (Updated 15:00 March 13)

A: I’m not sure of what the Government's based their decision on, but during the US Three Mile Island nuclear power plant accident in 1979, no damage was recorded past 16km.  The Government may have adjusted the evacuation distance based on this observation.

Q 1-6: If radioactive matter leaks out of the power station, how far could it go? (Updated 15:00 March 13)

A: That’s extremely difficult to predict without knowing the amount of radioactive isotope being leaked and weather conditions (especially wind). This situation is similar to the Three-mile Island accident where the storage container remained intact and has been assumed to have not affected areas beyond a ten-mile (about 16km) radius.

Q 1-7:  At one point the radiation levels started fluctuating, why was that? (Updated 15:00 March 13)

A: It may have been caused by xenon and iodine that had leaked out when they released air from inside the container to lower the internal pressure.

Q 1-8. What is the worst-case scenario? (Updated 15:00 March 13)

A. That will all depend on how much radiation leaks and the weather conditions at that time.  Iodine 131 is heavier than air so if winds are mild, then it shouldn’t spread too far.  It also has a short half-life of eight days. (Last updated 13:00 March 13)

Q 1-9: I thought half-lives of radioactive substances was generally much longer. (Updated 15:00 March 13)

A: Xenon 137 has a 3.8-minute half-life but there's a risk it’ll change into cesium 137, which has a 30-year half-life.

Q 1-10: I don't understand how the radiation level could fall to 1/100th of what it was in just an hour. Does it have something to do with wind direction? (Updated 15:00 March 13)

A: Most of what gets released are rare gases such as Xenon and Krypton with short-lived radioactivity.  The fact that levels dropped so quickly suggests they were only released for a short period of time.

Q 1-11: It looks like patients and staff at Futaba Hospital, located close to the power station, have been exposed to radiation. (Updated 15:00 March 13)

A: The hospital is located about 4 kilometers north-northwest from the power plant. They were waiting outside in the grounds for Self-Defense Force helicopters to evacuate them.  The fact that they needed decontamination (first they needed to be washed) appears to indicate that they were exposed to radioisotopes carried by the wind. (Last updated 13:00 March 13)

Q 1-12: What's so dangerous about being exposed to Iodine-131 (radioiodine)? (Updated 15:00 March 13)

A: Of all the possible radioactive isotopes that may have been released this time, iodine-131 can be absorbed into the body because it vaporizes easily, which would cause internal exposure.  There's been a lot of talk about how to protect yourself, but iodine-131 is commonly used in treating thyroids, and there have been no reports about rising cases of thyroid cancer using the same amount used in treatments. (Last updated 13:00 March 13)

Q 1-13: Can commercial iodine products be a measure against exposure? (Updated 15:00 March 13)

A: With the exception of products labeled as, "stable iodine preparation", iodine products are not made to be consumed and doing so would be a health hazard so please don't drink any.  Please have a look at the following post about the dangers of consuming iodine that isn't stable (Japanese). (Last updated 13:00 March 13)

http://smc-japan.sakura.ne.jp/?p=750

2. Cooling with Fresh water and Seawater

Q 2-1: What does, "the reactor's cooling mechanism has failed," mean? (Updated 18:00 March 14)

A: It means that that the reactor, in particular the fuel part, has not been able to be cooled down enough.  In a nuclear power plant, the heat (energy) generated by the nuclear fuel is turned into power by the circulating water.  If the coolant (water) doesn't circulate properly, then the fuel can't be cooled down. 

Q 2-2: Is it safe to cool down the reactors with seawater instead of fresh water? (Updated 13:00 March 13)

A: Usually fresh water is used in this situation in order to extend maintenance periods and reduce costs. However, right now it’s far more important to cool down the reactor in any way possible. I doubt anyone would consider using this reactor again.

Q 2-3: What’s the problem with seawater?

A: Simply because the salt would rust the pipes and create holes for radiation to leak out from. That’s why fresh water is usually used as coolant. But now isn’t the time to be worrying over that so seawater’s being used as the coolant.

Q 2-4. Rusting and pipe holes seems like something that occurs over a longer period of time, so will we be okay as long as this reactor is no longer used? (Updated 13:00 March 13)

A. Yes, holes will start appearing after a longer time period.  Right now the priority is to cool the reactor down by any means possible.

Q 2-5: There’s a support ship heading this way from America. Would it be possible to get fresh water? (Updated 13:00 March 13)

A: We need to cool this down immediately. The reactor container will be filled with seawater containing boric acid to cool it down.  That's what's important.

Q 2-6: Why couldn’t the reactor be shutdown straight after an earthquake? (Updated 13:00 March 13)

A: It has been shutdown. Control rods have been inserted and the fission chain reaction has been stopped. However, the reactor needs to be cooled down to prevent the radioisotopes in the fuel rods and decay-heat from heating up the container.

Q 2-7: Was using seawater a last resort? What if there's a mistake? (Updated 13:00 March 13)

A: Since they made the decision, the container must be cooled down regardless of what method is used. I have confidence in the ground staff.

Q 2-8: Have we prevented a possible containment vessel rupture? (Updated 13:00 March 13)

A. Yes, it should be safe now, but it is imperative that they get the container cooled down.

Q 2-9: If they succeed in cooling the reactor, is it safe to say they’ve avoided a major disaster? (Updated 13:00 March 13)

A: Yes. I have faith in the ground staff.

Q 2-10: If the coolant has been leaking out from somewhere, doesn't that mean that it will all drain away from the hole?  Is that why they're going to fill the container itself with seawater? (Updated 13:00 March 13)

A. I don't have enough information to be able to answer that question.  It was assumed there was a leak because the water level kept going down. 

Q 2-11: Is there a possibility that the coolant simply boiled and evaporated away because it had stopped circulating properly? (Updated 13:00 March 13)

A. Even if water is compressed, the total volume doesn't decrease so the water level shouldn’t go down significantly even with a rise in water vapor pressure. It must be considered that water was being lost somewhere.

Q 2-12: What'll happen to the water that's being injected into the reactor when it's thrown out?  Will it pollute the environment?  (Updated 18:00 March 14)

A. Waste water with low levels of radiation will be passed through a filter before before disposed of.  Waste water with high levels of radiation will be boiled.   This will turn the radioactive material into solids which can be picked out before the water is disposed of.  But the amount of water being injected in this case is significantly large so right now I don't know what method they'll ultimately choose to treat the water.

3. Why use Boric Acid?

Boron isotopes, boron-10, effectively capture thermal neutrons. Boric acid is a water solution containing boron. This is being mixed with seawater and injected into the reactor as a coolant.

Q 3-1: What does boric acid do? (Updated 13:00 March 13)

A: It effectively absorbs neutrons in the reactor.  In case fuel ends up outside scope of the control rods inside, the boric acid will reduce the risk of a fission chain reaction starting up.

Q 3-2: By using the seawater and boric acid mixture now, does that mean the reactor will be unusable in the future when things have settled down? (Updated 13:00 March 13)

A: It’s clear that the fuel rods have been damaged so any immediate re-start would be out of the question.

4. Regarding the Explosion

Q 4-1. What was the explosion at the Fukushima 1 Nuclear Power Plant?  What did it do? 

A. It was a hydrogen explosion.  The containment vessel (fourth wall in the figure below) was not damaged, and there haven't been any reports of large amounts of radioactive material being detected in the area so far (as of 18:00 March 13). 

(Figure coming soon)

Q 4-2. How did hydrogen explode at the Fukushima 1 nuclear power plant? How did hydrogen get into the containing structure and vessel? (Updated 13:00 March 13) 

A. The material used in fuel rods, called zirconium, reacts with water at high temperatures and releases hydrogen gas. Hydrogen gas passed through the pipes, leaking out of the reactor vessel and built up in the housing around the reactor. It looks like the hydrogen gas reacted with oxygen and exploded.

Q 4-3. Despite the explosion, the reactor was not destroyed. Does this mean a hydrogen gas explosion isn’t enough to damage a reactor? (Updated 13:00 March 13)

A. Yes. The housing may break but the reactor containment is built on strength. This is a nuclear reactor’s last defense in order to prevent a serious accident.  It looks like the reactor wasn’t damaged so for the time being everything’s okay.  As long as the reactor is safe, disaster can be avoided.

Q 4-4. Assuming that hydrogen was leaking directly from the reactor, wouldn’t a hydrogen explosion lead to an explosion inside the reactor itself? (Updated 13:00 March 13)

A. The reactor is filled with nitrogen so it’s unlikely that an explosion would occur inside the reactor. 

Q 4-5. So the reactor hasn’t been damaged? (Updated 13:00 March 13)

A. As long as the radiation level reports released by the Fukushima 1 Nuclear Power Plant are true, I think you can be certain that the reactor is safe. 

Q 4-6. Is a hydrogen gas explosion the same as a hydrogen bomb explosion? (Updated 14:43 March 14)

A. A hydrogen explosion is not the same thing as a hydrogen bomb explosion.  It's just a chemical reaction where hydrogen and oxygen gas had mixed together, ignited, and exploded to make water.  A reaction like this wouldn't emit radiation.  It's only if the hydrogen was radioactive to begin with that such an explosion would create detectable radiation.

5. The Operational Status of the Nuclear Power Stations

Q 5-1: What is a "runaway nuclear explosion"? (Updated 13:00 March 13)

A: Like the Chernobyl disaster, it is when nuclear fission gets out of control and the reactor power output increases to 10 times more than its standard output.  However, this case is different because the nuclear reactor’s operations have been stopped.  Still, it’s important to ensure that water levels do not go down.

Q 5-2. Is it true that Tokyo Electric Power Company’s eight radiation-monitoring posts aren’t working right now? (Updated 13:00 March 13)

A. Plant 1’s (Daiichi) monitoring post isn’t working, but the posts at Plant 2 (Daini) are.

Q 5-3. Aren’t there any real-time monitors? (Updated 18:00 March 13)

A. While the monitors on Plant 2 (Daini) are working, the monitors on Plant 1 (Daiichi) haven’t been working since March 11. The Fukushima Prefecture radiation monitors also aren’t working.
(As of 13:00 JST March 13) the Tokyo Electric Power Company is using monitoring cars to continue measurements.

Q 5-4. I'm worried about Fukushima Plant 2 (Daini).  I’m guessing that it’s not getting enough coolant as it should, but would it be necessary to carry out the same measures as what’s being done at Plant 1 (Daiichi)? (Updated 13:00 March 13)

A. While the situation is worrying, as of 13:00 JST March 13, radiation levels in the area are normal. No radioactive material is coming out from exhaust vents at Fukushima Plant 2 (Daini).

This article is based on 'tweets' from the following sources and have been edited by Japanese Society for Science and Technology Studies, Science Philosophy, and Science Communication researchers and volunteers:

– Special thanks: @r_shineha @hal9000jp @Lezy_Flaxeu
– Special thanks to our volunteer translators: Masafumi Matsumoto, Bridget M. Beaver, Lindsey McDonald, Jarra McIntyre, Alex Ko Ransom, Alicia Tan, and Goh Hirose.

– Hayano Ryugo's tweets on nuclear power: http://togetter.com/li/110838
– Hayano Ryugo's series of tweets on nuclear power (17:38 – 20:20): http://togetter.com/li/110906
– The last 2 hours of Hayano Ryugo's informative tweets on nuclear power (Published 23:30 March 12th) : http://togetter.com/li/110898

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