I had a PM today that prompted me to create this thread. I was a bit uncertain about where to post it, travel inside information, general discussion or travel news. I settle in travel news because there is a bit in the news about this topic. I'll also provide some links. I should also say that I'll just be making general comments, I'm not a nuclear engineer or anything like that, that will share my thoughts as a radiation safety person. I'll try to decipher what is being reported as best I can based on my experience in this field. The other caveat is that this is a developing situation, things can change which would change my thoughts. This means that I'm going to use a lot of words like should, could, might and maybe. Actually one final caveat, please look at the official Australian Government Advice that can be found here: ARPANSA - Media Release March 2011 In terms of sources of information I have been following World Nuclear News, which seems to stick to facts and also have some numbers. These guys are also on Facebook. Also useful/interesting: The Nuclear and Industrial Safety Agency of Japan The International Atomic Energy Agency (having a bit of trouble with them at the moment. TEPCO who own the reactors A finally website that has some pretty good background explanation is here: BraveNewClimate The full stuff on the nuclear reactors in Japan is here: Nuclear « BraveNewClimate Along with some thoughts on how the explosions happened: Further technical information on Fukushima reactors « BraveNewClimate Which gets into my ramblings. Read it or ignore as you wish. The basic question that everyone seems to want to know, is it safe? Or to quote from the PM: This is a really hard question to answer many because there is a fairly limited amount of information. I've seen mention of 3 "types" of radiation and radiation monitoring. The first is that we keep seeing number like 3.1 mSv per hour, 800 mSv per hour, and the radiation levels around the reactor are going up or they are going down. This seem to be spot external radiation measurements. They tell you how much radiation (gamma/neutron radiation) is being emitted, basically the strength of the radiation field at that point, per hour. This radiation is directly linked to the source (I assume the reactor), walk away and that radiation exposure decreases, get far enough away and it stops. This is also time related, you get a lot less dose from being there for 5 minutes versus 1 hour. It is this radiation that has resulted in all except 50 workers being evacuated from the reactor site. I wouldn't expect anyone to be touristing it around the reactor and if you are travelling to Tokyo those types of numbers mean nothing. The next type of radiation that I've seen on the TV is the contamination checks, as they increase the evacuation zone for the public. People lined up and dudes waving monitors over them. They are looking for radioactive particles that have landed on people. This is related to the third type of radiation mentioned and that is the emitted radioactive particles like iodine and caesium. These have been emitted with the steam releases. Once the steam condenses or it rains these particles drop out of the air onto the land, houses and people. The spread of these particles is going to be limited around the reactors site. Note the evacuation zone is 30 km. So there would only have been limited distribution of this stuff at this stage. The monitoring numbers reported have been in counts per minute or even counts per second. What they are trying to measure is the total amount of radioactivity in a given area on a person as there are cut offs based on counts per minute per square cm. General these will be big numbers, for example 40,000 counts per minute. Sounds big, but with some assumptions that can be boiled down to an activity number and it turns out to be pretty low - maybe the same as the total radioactivity in a banana or brazil nut in that case. This type of monitoring can be complicated to get from an esoteric counts per minute to a real activity number and then a health effect. I won't bore you with details. The thing is that these monitoring numbers are still (only) relevant for the immediate area around the reactor. That sort of gets me back to particles being emitted. There are reports that radiation is being detected in tokyo. These are going to be those emitted particles. At this stage the airborne concentrations should be pretty low. The effect is going to be dependant on the radioisotope involved. One is iodine and an effective protection against this is to take in non-radioactive iodine, potassium iodide tablets. Iodine is absorbed by the thyroid, if it is radioactive then you risk getting thyroid cancer (not nice but a very treatable cancer). Non radioactive iodine will block all the receptor sites in the thyroid and then the radioactive iodine just passes through the body with limited effect. There are also other radioactive particles in the air, caesium has been mentioned. The problem with these is inhalation, that is why the news talks about staying inside. This is to limit inhalation of the particles. The only real way to combat this is to follow government instructions. I assume that this is why they have said that the radiation is dangerous in the exclusion zone. In tokyo I can't imagine there would be very much of this stuff in the area. Because there is no massive big burning black could of smoke from the reactor sending crap high into the atmosphere, it mainly seems to be localised around the reactor. It is possible to convert an airborne concentration of a radioactive material to an effective dose, which tells us about the risk to people. I would guess that the dose in Tokyo from these particles would be very much less that the public dose limit at this stage. This is the dose (risk) below which there is no controls required on the radiation dose to the general public. don't need to control it? then it's very low risk. So what does that mean in effect. Well first I'll bring in some numbers; (sorry) In Australia, the average annual background radiation dose is 2.5 mSv per year. The public dose limit here and in Japan is 1 mSv. So IF one inhaled 1 mSv of these particles you would get no more that an extra 50% of what you get every year of your life. In theory the risk of 1 mSv is that 1 in 20,000 people will get a fatal cancer sometime in their life, due to that radiation. So to answer the PM in more detail, yes there is a risk of getting cancer from being exposed to radiation from the reactor, in theory. I say in theory because the major problem is that no one can prove this risk. It would require something like 12 million people in a study to prove that risk. (Note anti-nukes will happily use this theory to say 100,000s of people are going to die from very small radiation dose) To answer the second question from the PM, there is no way that you can ever prove that the cancer was from that particular bit of radiation at such low dose levels (if it is greater than about 100 to 500 mSv the link is more certain). You also need to remember that 1 in 3 people get cancer in their life. Of those 20,000 people getting 1 mSv, 6,665 will have cancer from other reasons and 1 from the 1 mSv of radiation More generally on radiation risk. There is a lot of evidence that says a dose less than 100 mSv at a slow dose rate has no risk of cancer. There are also places in the world that have much higher background radiation. Denver has 10 mSv per year and the cancer incidence rates are the same as elsewhere in the world. Other places have upto 100 mSv and no greater rate of cancer. Finally, I'll just say that if I was going to Tokyo I would be highly concerned about the effects of that burning oil refinery.