How Far from Fukushima Will Fallout Pose a Health Risk?
Amid conflicting evacuation recommendations, radiation experts say that exposures to date have been relatively low outside the power plant and that people in the U.S. will not face any danger
COUNTRY IN CRISIS: The March 11 earthquake and tsunami caused a nuclear crisis in Japan, but the effects are unlikely to spread to the U.S. Image: NASA/GSFC, MODIS Rapid Response
As the condition of the stricken Fukushima Daiichi nuclear power station in Japan continues to deteriorate, nuclear safety experts, government regulators and health physicists are keeping close watch on the situation to determine the danger—both real and hypothetical—that the incident poses to people near the plant.
Japanese authorities have carved the area around Fukushima Daiichi into two zones, recommending that individuals within 20 kilometers of the plant evacuate and that anyone living 20 to 30 kilometers from the plant take shelter and stay put. Nevertheless, after initially supporting that action, the U.S. Nuclear Regulatory Commission (NRC) took the dramatic step March 16 of recommending that Americans within 80 kilometers of Fukushima Daiichi evacuate the area.
U.S. federal guidelines set a much smaller standard boundary for radiation hazards, leaving some puzzled as to why American authorities would recommend such a large evacuation zone for Japan. (The 80-kilometer evacuation zone is larger than that implemented for the 1986 Chernobyl disaster in what is now Ukraine, after which 115,000 people were evacuated within roughly 30 kilometers of the nuclear plant.) And although radiation measurements in the vicinity of Fukushima Daiichi have varied greatly, it appears that exposures outside the 20-kilometer radius have not exceeded levels that would be cause for action in the U.S.
The differences in the responses of the U.S. and Japan to the crisis highlight the lack of detailed information on the rapidly shifting condition of the crippled nuclear plant, the inexact science of predicting what might happen next, and the difficulty of weighing the risks and benefits of taking protective action.
The NRC's recommendation for a widespread evacuation stems not from the present conditions but from projected radiation exposures in a worst-case scenario, according to agency spokesperson David McIntyre. "Basically it was projections by our protective measures team based on what information we had available, what was going on at the plant, weather conditions, and so on," McIntyre says. "They projected into the short-term future and reached the conclusion that in the near term people out to 50 miles [80 kilometers] would exceed the exposure levels at which we would recommend action."
U.S. guidelines recommend protective measures, usually evacuation, if individuals are expected to receive 10 to 50 millisieverts (mSv) of radiation. (The sievert is a measure of ionizing radiation equal to 100 rems; one millisievert is 0.1 rem.) The average American absorbs 6.2 mSv a year from natural and man-made sources of radiation.
In the U.S., each nuclear power plant is surrounded by an "emergency planning zone," extending 16 kilometers in each direction, which would bear the brunt of radioactive fallout from a nuclear accident. The U.S. regulations are predicated on the assumption that most partial meltdowns would not expose individuals beyond 16 kilometers to dangerous levels of radiation and that even in worst-case accidents "immediate life-threatening doses would generally not occur outside the zone."
Outside the immediate vicinity of the nuclear site, the primary danger is not radiation emitted directly from the plant as high-energy photons or subatomic particles but airborne radioactive material released from a damaged reactor into an atmospheric plume. The material in that plume, as it undergoes radioactive decay, gives off dangerous radiation in the form of gamma rays and can pose additional hazards if inhaled, swallowed or absorbed through the skin to emit radiation from inside the body.
"Internal exposure is very different than contamination you can walk away from," says Jerrold Bushberg, a health and medical physicist at the University of California, Davis. "If there's a plume that passes overhead and some of the material precipitates down, you may be externally contaminated, but it's nothing that a change of clothes and a shower can't take care of."
The "shelter in place" recommendation made by Japanese authorities for individuals between 20 and 30 kilometers from Fukushima Daiichi is intended to minimize ingestion of radioactive material and to prevent skin and clothing from becoming contaminated as the plume deposits radionuclides around the area.
Japanese authorities have carved the area around Fukushima Daiichi into two zones, recommending that individuals within 20 kilometers of the plant evacuate and that anyone living 20 to 30 kilometers from the plant take shelter and stay put. Nevertheless, after initially supporting that action, the U.S. Nuclear Regulatory Commission (NRC) took the dramatic step March 16 of recommending that Americans within 80 kilometers of Fukushima Daiichi evacuate the area.
U.S. federal guidelines set a much smaller standard boundary for radiation hazards, leaving some puzzled as to why American authorities would recommend such a large evacuation zone for Japan. (The 80-kilometer evacuation zone is larger than that implemented for the 1986 Chernobyl disaster in what is now Ukraine, after which 115,000 people were evacuated within roughly 30 kilometers of the nuclear plant.) And although radiation measurements in the vicinity of Fukushima Daiichi have varied greatly, it appears that exposures outside the 20-kilometer radius have not exceeded levels that would be cause for action in the U.S.
The differences in the responses of the U.S. and Japan to the crisis highlight the lack of detailed information on the rapidly shifting condition of the crippled nuclear plant, the inexact science of predicting what might happen next, and the difficulty of weighing the risks and benefits of taking protective action.
The NRC's recommendation for a widespread evacuation stems not from the present conditions but from projected radiation exposures in a worst-case scenario, according to agency spokesperson David McIntyre. "Basically it was projections by our protective measures team based on what information we had available, what was going on at the plant, weather conditions, and so on," McIntyre says. "They projected into the short-term future and reached the conclusion that in the near term people out to 50 miles [80 kilometers] would exceed the exposure levels at which we would recommend action."
U.S. guidelines recommend protective measures, usually evacuation, if individuals are expected to receive 10 to 50 millisieverts (mSv) of radiation. (The sievert is a measure of ionizing radiation equal to 100 rems; one millisievert is 0.1 rem.) The average American absorbs 6.2 mSv a year from natural and man-made sources of radiation.
In the U.S., each nuclear power plant is surrounded by an "emergency planning zone," extending 16 kilometers in each direction, which would bear the brunt of radioactive fallout from a nuclear accident. The U.S. regulations are predicated on the assumption that most partial meltdowns would not expose individuals beyond 16 kilometers to dangerous levels of radiation and that even in worst-case accidents "immediate life-threatening doses would generally not occur outside the zone."
Outside the immediate vicinity of the nuclear site, the primary danger is not radiation emitted directly from the plant as high-energy photons or subatomic particles but airborne radioactive material released from a damaged reactor into an atmospheric plume. The material in that plume, as it undergoes radioactive decay, gives off dangerous radiation in the form of gamma rays and can pose additional hazards if inhaled, swallowed or absorbed through the skin to emit radiation from inside the body.
"Internal exposure is very different than contamination you can walk away from," says Jerrold Bushberg, a health and medical physicist at the University of California, Davis. "If there's a plume that passes overhead and some of the material precipitates down, you may be externally contaminated, but it's nothing that a change of clothes and a shower can't take care of."
The "shelter in place" recommendation made by Japanese authorities for individuals between 20 and 30 kilometers from Fukushima Daiichi is intended to minimize ingestion of radioactive material and to prevent skin and clothing from becoming contaminated as the plume deposits radionuclides around the area.
10 Comments
- 1. Lance 03:59 PM 3/18/11
- Bushberg of U.C. Davis seems to have chosen his or her words very carefully. The fact is that significant radioactive plumes in Japan can easily get drawn up into high altitude jet streams which regularly cross high above North America and thence around the world. During their travels, material carried up to the jet streams will dissipate down from the jet streams. Regardless of how catastrophic the situation might become in Japan, it seems unlikely that any measurable health effects will be seen in North America any time soon. Whatever dissipates down will be seemingly small. Problem is that the dissipation will get absorbed into the North American food chain. It may take 20, 30 or more years before there is a measurable impact on health. Try explaining that to a person in 2040 who has an inexplicable cancer and is prematurely dying. I agree that runs on potassium iodide are a sad joke - unless you want to ingest potassium iodide for the next few decades and contribute to the bottom line of various pharmaceutical companies. To deflect some potential criticisms of what I have just said, please understand that I am an advocate of nuclear power. My problem is with nuclear agencies which do not take adequate measures to anticipate or deal with disaster scenarios which should be reasonably expected. The nuclear agency in Japan fits this model (hear no evil, see no evil, make money). Lance.
- 2. William McDavid 04:50 PM 3/18/11
- The horrible tragedies in Japan should be responded to by every nation on Earth which has the expertise and resources to do so. The fact is, no place on Earth is immune to natural disasters of that magnitude or greater. Americans must band together to make sure that greedy dirty energy companies can't keep us vulnerable to added threats to our lives and health in order to maximize their windfall profits. The nuclear emergencies and natural gas and oil fires in Japan should be an object lesson, and dire warning, to every nation. This is why it is of utmost urgency to convert the world's energy systems to TRULY clean, safe, abundant, inexhaustible and FREE energy sources, such as Wind, Sunshine, Geothermal Heat, Tidal/River Flows and Hydrogen/Oxygen extracted from Water using electricity from those sources. If you think massive conversion to clean energy would be "too expensive", I have 2 questions for you: 1) In your cost/benefit analysis, how do you value the lives of nuclear plant radiation victims, coal miners, drilling rig workers, billions of sea creatures and the millions of people who die from pollution-caused illnesses? 2) If we fail to restore and protect the ONLY known natural life-support system in the Universe, how will you justify that failure to your gasping, wheezing Great-Grandchildren, and what do you think the money saved will be worth to THEM? If Japan's energy came from self-renewing energy sources, there would be no oil and gas fires or nuclear emergencies adding to the other crises they are facing.
- 3. William McDavid 05:03 PM 3/18/11
- It is unbelievable that anyone, who has thought about it for more than a few seconds, could believe that energy sources that require exploration, drilling, mining, refining and transportation; and which create large environmental and health costs and risks could REALLY be less expensive than those that DO NOT. The reason that fossil fuels and nuclear APPEAR to be cheaper than Wind, Solar, Geothermal and Tidal/River Flows is that the environmental and health costs of dirty energy are hidden, and dirty energy companies are subsidized with our tax money.
- 4. Ronnie 05:47 PM 3/18/11
- The amount of radiation coming from the 4 damaged reactors has only increased over the past week everyday, Uranium, Plutonium and Spent Rods of Uranium and Plutonium released into the atmosphere. The first cloud that has arrived over California carries the lightest amounts of Radiation, this will build this week growing steadily in continuants? The radiation will stream on to the shore of Alaska, Washington, Oregon and California 24 hours a day, 7 days a week 365 days a year until the problem is resolved? I stated the first day of the disaster we should gather our top scientists to find a solutions but it was only yesterday that Obama said he would send 9 advisors to Japan, sad. The 64 million dollar question is, if Plutonium is airborne and it arrives in the U.S.next week and we inhale it and it gets into livestock, food storage and crops will we then say we should have taken stronger action now. Failure by the Obama administration is beyond comprehension, taking a trip to Rio is insane at this time and shows a complete disconnect. The entire world should have already been working to help the Japanese, the world can not wait for them to say, we have done everything we could and failed.
- 5. Lance 07:08 PM 3/18/11
- So far, I have seen a couple of comments from some seemingly brainwashed graduates of environmental science 101. Does anybody have anything useful to contribute to the discussion? Bear in mind that some may consider me to be an extreme cynic. McDavid makes a relatively good case, but with two attempts he is not very succinct with the real science. Ronnie harps about plutonium but does not even mention radioactive cesium fallout which is a real long term issue in North America. Politicians like Obama are quite irrelevant in the overall scheme of things. So, why even mention them? Obama and his ilk are a crop of lawyers. Few lawyers no anything about science, They will not plan against or care about scientific problems unless and until some chickens come home to roost and hit them squarely in the face. If and when a chicken comes home to roost, the politicians will probably dangle in the wind, speak eloquently with pretentious knowledge, and hope for the best in order to get re-elected.
- 6. Ronnie 07:28 PM 3/18/11
- The reason Plutonium is so important to the conversation is that all 4 Power Plants are releasing Plutonium into the atmosphere, with a half life of 270,000 years, once ingested fatality is increased 3000%? Cesium or Ceseium symbol Cs and atomic number 55 has physical properties of rubidium and potassium. The Human DNA latter is made of Potassium and the Human body will absorb Cesium just like Plants, Animals, Fish and vegetation, all Potassium base life forms. Cesium should be considered a serious threat to humanity attacking food sources and water. Scientist can calculate how much is being disbursed every hour from these 4 damaged reactors and on it's way to the U.s., failure to contain them is unimaginable.
- 7. Carlyle 08:02 PM 3/18/11
- No plutonium has been released. You people should get hold of a Geiger counter & check where you live. Radiation is everywhere. Do not eat bananas or any other food containing potassium, go any where near granite rock, have a smoke detector in your house, go anywhere near power lines, computers, TV, mobile phones, sunshine, beach sand. All give off radiation. Do not believe me? Try it for yourself. Your ignorance on the topic is remarkable. Small amounts of radiation hurt no body otherwise you would never have a CT scan. You would have to be standing near these reactors for over 100 hours to be subject to as much radiation as you would receive from one scan. Plutonium by the way could be carried in a paper bag in your pocket without doing you any harm. Only if it is inhaled is there an increased risk to health. You are millions of times more likely to die of even passive cigarette smoke induced cancer so what is your real agenda or is it truly just ignorance.
- 8. Daniel35 02:55 AM 3/19/11
- Let's all keep in mind that "radiation coming from the 4 damaged reactors" only has local effects. The escaping atoms of radioactive elements are what get into the air, cause radiation in our environment and bodies, and some of which stay in the environment almost till the end of time. Some from the WWII bombs and all the tests we've done since, plus Chernobyl and Three Mile Island and all the Carbon 14 created by cosmic rays are still around also. We all die eventually from something or other, but probably not today.
- 9. plenum 11:03 AM 3/19/11
- Did the U.S. advice to evacuate 80 kilometers reflect an anticipation that the situation would get much worse?
- 10. RNBlomquist 11:50 AM 3/19/11
- Plutonium is a very heavy element. Even at Chernobyl, all or nearly all of the plutonium ejected during the explosion landed within a very short distance of the reactor. There were no reactor explosions in Fukushima, only external ones not involving nuclear fuel, so there should not be any sort of plutonium contamination problem near the reactor, much less outside of Japan.
