The Risks of Nuclear Radiation

How far do the risks of Japan's earthquake and nuclear emergency extend?

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Special Report: Fukushima and the Future of Nuclear Power

This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.

Steven Cherry: Hi, this is Steven Cherry for IEEE Spectrum’s “This Week in Technology.” On Monday, March 14, radiation levels at the Fukushima nuclear plants rose to 400 millisieverts but then quickly declined. In less than 24 hours, the levels were below 1 millisievert.

What exactly does that mean? How much is safe, and for how long? What levels should the residents of the town of Okuma and the rest of the Futaba District be worried about? What about the radiation risks to those downwind of the power plants—Pacific Island nations, and ultimately Hawaii and the North American west coast? By Tuesday afternoon, U.S. time, Bloomberg was reporting shortages of potassium iodide, for at least three companies approved to sell the substance in the U.S. Sensible precaution, or CNN-induced hysteria?

My guest today by phone from Milwaukee is John Moulder. He’s a professor of radiation oncology at the Medical College of Wisconsin and director of the Center for Medical Countermeasures Against Radiological Terrorism.

John, welcome to the podcast.

John Moulder: Welcome.

Steven Cherry: John, how about if we start at the plant itself, and, um, no pun intended, radiate out from there. The workers who were on site at the time—I realize we don’t know many of the details of these particular incidents yet, but generally speaking, when it comes to nonnuclear explosions and partial nuclear meltdowns, which we’ve apparently already seen in Japan, what is the health story for the workers who were there at the time when it comes to radiation?

John Moulder: Some of them may be at risk for some immediate injuries—it’s a little hard to tell. We are hearing doses, but we aren’t hearing doses for how long. So I believe you mentioned that at one point the doses were as high as 400 millisieverts. Now to try to put that in context, for that worker in the United States, their maximum permissible annual dose would be 50 millisieverts. In an emergency situation, that is, if a worker had to go in for literally for lifesaving purposes—saving somebody else’s life or keeping the thing from blowing up—the limit would be 250 millisieverts. So this is a high dose from the point of view of workers’ safety. If that’s the maximum dose anybody gets, they are probably not going to have any acute radiation injuries. That is, things that will happen, number of next days, weeks, and months. Doses that high, they are at risk for an elevated cancer rate in the future, but if you look at some of the things that are going on today, we know that they are rotating workers in and out. That would be the standard procedure in this country. Each worker probably almost certainly has an individual dosimeter, so you are going into the plant not for an hour or two hours or eight hours, but you are going into the plant till your individual dosimeter hits a certain number, and then you’re coming out.

Steven Cherry: Yeah, I wanted to ask you about that. So when we say, for example, 250 millisieverts, is that like per hour? Like getting that exposure for one hour and so if you were at 500 millisieverts for a half hour, that would be the same exposure?

John Moulder: Yes. Sievert is a measure of dose, not of dose rate.

Steven Cherry: Very good. Let’s move on to the nearby residents. What kind of risks are they facing, and what should they be doing about it?

John Moulder: Well, right now as I understand it there are no nearby residents, that there is now mandatory evacuation out to 20 kilometers. First it was voluntary at 10, then it was voluntary at 20; now my impression is—strong impression—is that it is a mandatory evacuation out to 20 kilometers, and a shelter in place, which means stay inside out to 30 kilometers. There is a group at risk in between, and that is, I’m pretty sure, there are still first responders looking for people, fighting fires, doing stuff in that 20-kilometer range. They are certainly at a potential risk, although my strong impression right now is that the doses in that area are more in the…oh, say, 10 millisievert range. They’re still quite low from the point of view of immediate health issues; it’s not a dose you want to live with indefinitely, but those people also will have protective gear and dosimeters. Now the next issue we have with how many millisieverts there are is it depends what this radiation is—I mean, some of this may be beta particles with a very short penetration range. In that case, people who are in good hazmat suits may not be getting much exposure from the betas that are on the suits, where if it’s a very hard radiation that can penetrate the suits, that’s a different issue. Some of the dose may be from iodine, probably iodine 131, and there, if they have the proper respirators—which I’m pretty sure they do—they’re not inhaling it. So you know, what dose people get in different places will also depend on what protective gear they have and how well they’re using it.

Steven Cherry: Now when it comes to residents, at a range of 20 or 30 kilometers we’re really talking about what? There’s the initial venting of steam, and then there was presumably some further release from the explosions. What stuff is in the air that these people need to worry about and how worrisome is it?

John Moulder: I certainly don’t know what is in the air. The fact that the U.S. military is giving some of its people potassium iodide indicates that they know that there is radioactive iodine in the air. That was one of the big isotopes we leased from the Chernobyl power plant disaster. But exactly what isotopes are up there other than that will very much depend on what exactly is going wrong at the power plants. One issue here is a lot of people are saying “a meltdown versus no meltdown.” Well, there are all sorts of things in between. Three Mile Island was not a total meltdown, but some fuel melted, so there are a variety of scenarios which could release different radio isotopes. The people there will have equipment to say not only how much radiation is there but also which isotopes, which would determine both how long it’s going to stay hot and what precautions you need to take.

Steven Cherry: Now when it comes to what’s in the air, as it drifts out it’s going to drift eastward and into the sea, and there’s really not that much directly east of Japan, fortunately.

John Moulder: That’s true right now, but I don’t—I simply don’t know enough about the meteorology to know whether that’s luck or whether that’s a consistent wind flow.

Steven Cherry: Very good. Well, generally speaking, I mean, I would imagine that whatever’s in the air will sort of dissipate the further away from the origin it gets. Do you have any general rules of thumb about at what point people shouldn’t stop—should people in Hawaii definitely not worry or definitely worry or what?

John Moulder: Well, right now as far as we know, as far as the radiological health people say in Hawaii, nothing has got there. I—very difficult for me to imagine the doses high enough to be a public health hazard will get to Hawaii. But it’s easy to imagine the detectable radiation isotopes would get there. And here’s one of the good or bad things about radiation: Good or bad, it’s extremely easy to detect. I mean, I have instruments that could detect a 20 percent increase in background, which would have no medical significance. My background radiation would go up that much if I moved from here, Milwaukee, to Denver. Physicists working for people like the NRC can probably detect less than a 1 percent increase in background, so I think they’ll probably be able to detect it, but they probably will not show it to be a medically significant dose. Remember, we used to be able to detect—or you may not know that. I’ll just tell you: We could detect here, in the state of Wisconsin, Chinese nuclear tests. But the level of concern was very, very low, but yet it was detectable.

Steven Cherry: Okay, so the idea of shortages of potassium iodide in the U.S.—is that unsurprising? Is that reasonable? Is it hysteria? What should we make of it?

John Moulder: It’s unsurprising and totally unreasonable. Okay, here’s the story: If you’re exposed to radioactive iodine, it can cause thyroid cancer because the thyroid picks up iodine. If someone’s going to get exposed to radioactive iodine, if they take large amounts of cold nonradioactive iodine in advance, it basically saturates the thyroid and the radioactive iodine is not picked up. So if you are in danger of exposure to high levels of radio iodine, taking cold potassium iodine—it’s usually potassium iodine—in advance will lower your risk of thyroid cancer. It will not decrease your risk of any other kind of cancer, and it will not detect your risk from any other radio isotope.

Steven Cherry: And I gather there are much more dangerous radioactive substances that we should worry about more.

John Moulder: Umm…there might be. Again, it depends exactly how the scenario goes. I mean, in certain kinds of scenarios you might get uranium, plutonium, cesium particles up in the air. Those would be considerably more dangerous, but I don’t know that that’s happened, and also those, being particles, may not travel as far. But yes, there may be considerably more dangerous particles out there. And also, even if you’re exposed to radioactive iodine, there are a lot of your tissues other than your thyroid that are going to get irradiated. So basically, it only protects you against one radio isotope, it only protects you from one kind of cancer—which is actually rather rare after irradiation—and in any case, you shouldn’t take it until you are about to be exposed to a high dose of radio iodine.

Steven Cherry: Well, that’s a good caution for our listeners. John, thanks for your time.

John Moulder: Yeah, it’s been an interesting last 36 hours or so.

Steven Cherry: We’ve been speaking with John Moulder, professor of radiation oncology at the Medical College of Wisconsin, about the radiation risks presented by Japan’s earthquake and nuclear emergency. For IEEE Spectru’s “This Week in Technology,” I’m Steven Cherry.

This interview was recorded 14 March 2011.
Segment producer: Ariel Bleicher; audio engineer: Francesco Ferorelli
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