As Japan continues to recover from last years triple tragedy in Tohoku, one question looms large for many people: “How safe are we from radiation in Japan?” US Navy Captain Reid Tanaka, the US Pacific Commander’s Special Assistant on nuclear matters during the nuclear crisis, addressed this and other questions at an ACCJ talk hosted by the HRM & Healthcare Committees and organized by Ginger Griggs. Over the past year, Captain Tanaka has been advising civilian and senior military leadership regarding the risk posed by the Fukushima nuclear reactors, the on-going battle for security and stability in Tohoku and the radiological impact for people living in Japan.
Inside the 30KM zone. An abandoned milk farm in Namie Town. (Photo by Jiré Gözen)
US-Japan Joint Assessment and Monitoring Led to Constructive Debate
Shortly after the March 11, 2011 disaster, the US dispatched hundreds of nuclear experts to Japan from the Nuclear Regulatory Commission (NRC), Department of Energy (DoE) and the US military, among other agencies. Throughout the crisis, these experts were linked with the experts from Japan. These critical links not only ensured a healthy debate regarding the best approach in battling the unprecedented casualty, but also demanded objectivity and openness by the Government of Japan (GOJ).
Radiation Maps
Following the disaster, the US and Japanese governments conducted joint aerial surveys which provided area-wide maps depicting the magnitude and scope of the contamination. A fairly clear picture of the spread of contamination was quickly developed. These maps show a heavy distribution of radioactive cesium where the evacuation zones are established and a light amount of cesium deposits in areas up to 400km away. These radiation maps tell a story of “two” Japans: 1) The evacuated areas of Fukushima Prefecture, where radiation levels exceed government standards for continuous human settlement; and 2) everywhere else. It will be years, perhaps even decades, before complete resettlement can occur in the first area. For everywhere else, it is back to business.
But isn’t there radiation in Tokyo? Yes, definitely — radiation is everywhere. And yes, there is additional radiation from the cesium in Tokyo, albeit at a harmless level. As the maps depict, some of the cesium captured by steam from the reactors was blown by the wind in the first days of the crisis and settled on the ground. Radiation readings in Tokyo are a bit higher now than before the accident but still sit well within the normal historical Tokyo limits and well within the normal levels seen throughout the world. These days, Tokyo’s radiation readings are about 0.055 microGray (μmG) per hour. This reading is slightly higher than the 0.040 μmG per hour in Paris or Seattle, but is well below the 0.095 μmG per hour in New York City or Hong Kong.
Radiation Is All Around Us
Radiation is all around us; it’s part of nature and our environment. Radiation comes from space (cosmic rays), from the ground (rocks and concrete), from the air we breathe (radon), and even from our own bodies. Most people do not even know they are “radioactive,” and that sleeping close to someone adds a little extra radiation to each other’s total exposure. Many elements such as carbon and potassium have a natural mix comprised of radioactive forms in a tiny fraction. Our bodies (and every form of life) are similarly mixed. In addition to the natural background radiation just discussed, “human-made” sources such as medical procedures (x-rays and CT scans) and air travel (cosmic rays) contribute to a person’s annual dose. This number varies widely depending upon health care, where typically an older population receives more radiology such as CT scans.
Police officers checking documents near Namie Town. (Photo by Jiré Gözen)
Numbers for Comparison
Although naturally occurring background radiation varies widely from place to place, primarily due to the local mix of earth materials such granite and radium, the receipt of medical procedures are widely in variance. The National Council of Radiation Protection (NCRP) estimates the average person in the United States – let’s call him “Average Joe” – receives about 3 millisieverts (mSv) annually from natural sources and another 3 mSv from human-made sources per year. Altogether, Average Joe receives about 6 mSv in radiation exposure each year, just from living in normal places.
If Average Joe smokes cigarettes, his exposure will increase an additional 2.5 mSv a year for a pack-a-day habit. Oddly, that little bit of radiation will not cause any harm. It will be the carcinogens in the tobacco smoke that can lead to health problems.
How does that compare to the radiation readings in Tokyo? In Tokyo, we measure about 0.055 μmG per hour, the same as an average city in the US. And this includes that little extra from cesium from the Tohoku disaster.
In Fukushima City, the daily reported measurements are 15 times higher than in Tokyo. This additional radiation works out to be about 7.5 mSv per year. Even though the radiation readings throughout Fukushima Prefecture vary widely depending on the concentration of cesium on the ground, this number is still well below the level of concern for humans.
Food:Conservative Control Levels and Wide-Scale Contamination Prevention Efforts
Normally, food has so little radiation and is so transitory (since it passes through the body), that it is insignificant to our annual radiation exposure. But in Japan, we do have knowledge and respect for the potential of eating food which has elevated levels of radioactivity, so there is a substantial amount of on-going effort to minimize radioactivity from food sources. For the first year of the crisis, the GoJ set food standards to limit a person who consistently consumed contaminated food and water to not more than an additional 5 mSv per year. On April 1, the GoJ came out with new standards, to limit that radiation to 1 mSv per year from food and water. In essence, if you consistently ate contaminated food at the levels established by the GoJ, you might receive an additional 1 mSv to your average background average of 6 mSv.
One way to think about radiation in food is consider it like fat. A doctor suggests that you limit yourself to 30 grams of fat per day to avoid having a heart attack. But you ate that blueberry muffin with 35g of fat in it. That cheeseburger and fries is another 25g. If you eat that once, it’s not a problem.
But consuming such a diet every day would cause trouble. Radiation standards are like fat levels. Eating radioactive food above the control levels will not suddenly imperil you. The radiation goes through your body and is processed out. If you keep eating food at the control levels, you will be in fine health.
To help prevent contaminated food from getting to the table, Japan is using good science, statistics and an excellent sampling regimen. Experts who have looked at the processes have said this is better than we can do in the US. While there are holes, there is a wide net out there, and if you get something that slips through in one place, it probably won’t slip through the next. Cesium distribution is understood, and uptake into various vegetation is being studied. Understanding this flow will help prevent the cesium from getting into the food supply.
So even if you wanted to make a lifestyle out of eating contaminated food, you could not: there are too many people trying to keep contaminated food off the market. As a US military food expert described it when contaminated beef was first discovered: “if you ate enough of the contaminated beef to have a radiological concern, you would have first experienced a heart attack from the cholesterol.”
Meter readings at an abandoned milk farm in Namie Town. (Photo by B. Reifschneider)
Fukushima Reactors – Cold Shutdown
The affected reactors are all in a state of “cold shutdown.” A tremendous effort has been made to strengthen back-up systems and to prevent any more spread of contamination. It will take decades to reach the final end-state of defueling and cleanup, but the plan is good and is equal to the best that the international nuclear community could likely conceive. Moreover, the Japanese (and US) nuclear industry has applied everything it learned from the accident to backup systems for all the reactors around Japan.
One of the highest priorities is to prevent any additional contamination and radioactivity from leaving the site, so site containment is a huge effort. Covers have been built to prevent leakage to the air, dams and walls have been built to prevent leakage from spilling to the sea, and underground water table management systems have been built to prevent contamination from migrating to the sea or groundwater.
Contaminated Debris
The biggest problem moving forward for Japan remains radioactive debris: where and how to store the massive amounts created by the disaster. Large piles of radioactive debris lay everywhere, particularly around Fukushima. Decontamination efforts such as topsoil removal and the cutting down of contaminated forests are also producing large amounts of waste, as are decontamination efforts around the plant site. And very low levels of waste become measurable as they are concentrated. Incinerators concentrate contamination, so contamination is sometimes measured in the ash. Sewage systems produce contaminated sludge. How to handle the concentrates is an additional burden which will require long term efforts.
Sleep Soundly
The spread of radioactive contamination is a tremendously unfortunate outcome of the nuclear crisis. While the radiation itself is manageable if simple human health is considered, the fact that radiation is a complex and psychologically scary subject magnifies the fear and substantially multiplies the costs of long term efforts in mitigation. Japan is doing all it can to minimize further radiation exposure to the population and the country is clearly on the road of massive spending and effort to minimize the public fear. We who live in Japan are armed with that knowledge and perspective and can sleep soundly.
Captain Reid Tanaka is the US Pacific Commander’s Special Assistant on Nuclear Matters. He was invited to address the ACC J by the HR M Committee – co-chaired by Ginger Griggs and Taka Miyawaki – and by the Healthcare Committee, chaired by Bill Bishop and Vice-chaired by Ira Wolf.
