TOKYO —
Japan raised the assessment of its nuclear crisis to the most severe rating Tuesday, on the same level as the Chernobyl disaster, the world’s worst to date. Some answers to questions about the assessment and health and safety concerns:
Has the situation at the Japanese nuclear power plant worsened?
No. The heaviest radiation leaks at the Fukushima Daiichi nuclear complex occurred in the first days after the March 11 earthquake-triggered tsunami crippled the plant’s cooling systems. Workers are trying to lower temperatures in the overheated nuclear reactors, but still don’t have full control. Problems persist, like the leak into the ocean plugged last week, but authorities say the radiation leaks are declining.
If the situation’s not getting worse, why did Japan raise its assessment of the crisis?
The decision was based on new assessments of radiation leaks since the crisis began, rather than on deteriorating conditions. The new data showed emissions exceeding the threshold for a “major accident,” level 7 on a 1-to-7 scale set by the International Atomic Energy Agency. Only one accident has previously rated 7, the 1986 meltdown at the Chernobyl nuclear power plant.
So is Japan’s crisis as bad as Chernobyl’s?
Not yet. Chernobyl was a fast-moving crisis. A routine shutdown went awry, causing a reactor to overheat, explode and burn. For 10 days, the reactor spewed high levels of radiation into the air and only cooled after helicopters dropped sand, clay, lead and other materials on it. By contrast, Fukushima crisis has been a slow cascade of problems over a month. Explosions occurred at three of Fukushima’s reactors and one may be leaking. But the two plants’ reactor designs are different. Unlike Chernobyl’s reactors, Fukushima’s have pressure vessels of steel 15 centimeters thick that may have helped contain the damage.
Then why the same severity level rating?
The IAEA defines a level-7 accident as one in which a large amount of radiation is released into the atmosphere, likely harming human health and damaging the environment over the long-term. That threshold is set at several tens of thousands of terabecquerels—a unit of radiation—of iodine-131, a radioactive element commonly released in nuclear accidents. Leaks at both plants have exceeded that limit, but the Japanese government says Fukushima’s are still one-tenth of those released by Chernobyl. The possibility Fukushima’s emissions could surpass Chernobyl’s is considered small, but still a risk until Fukushima’s cooling systems are restored.
What are the health risks?
Radiation normally occurs in the environment, and at low levels cause no health problems for people. In higher doses, radiation may cause types of cancer. Limiting exposure is key. Because radioactive elements are heavy, they tend to concentrate closest to the source, in this case the nuclear plant. The Japanese government has evacuated people living near the plant and advised people a bit farther out to stay indoors.
Are only people close to the plant at risk?
Winds have been blowing to the northwest of the plant, rather than out to sea, carrying radioactive elements farther inland. The government has banned the sale of vegetables and milk from certain areas after they showed contamination. The government on Monday also ordered people in five communities outside the evacuation zone to leave to avoid long-term radiation exposure.
What about people outside Japan?
Weather patterns are already carrying traces of radiation from Fukushima to South Korea and China. Airborne radioactive particles have also reached the United States. In all cases, the governments say the amounts detected aren’t dangerous.
Didn’t people die at Chernobyl?
Thirty-one men died mostly from being exposed to very high levels of radiation trying to contain the accident. About 5 million people were exposed to radiation. Higher rates of thyroid cancer have been found among people 18 or younger at the time of the accident. An IAEA study said about 4,000 people would ultimately die from cancer, though a U.N. study estimated cancer deaths at more than twice that number and other groups put the fatalities many times higher.
Is the same thing happening at Fukushima?
At Fukushima, 21 workers have been exposed to radiation doses the equivalent of 100 millisieverts. Two were treated for burns after walking in heavily contaminated water in a plant building. But no deaths from radiation exposure have occurred so far. Cancers often take years or decades to develop.
What radioactive elements have been found so far?
Most measurements have focused on two, iodine and cesium. Radiation from iodine-131 dissipates quickly, falling by half every eight days and nearly disappearing after 80 days. If inhaled or swallowed, it can concentrate in the thyroid and cause cancer. Cesium-137 lingers far longer, 30 years to decay by half and 300 to disappear. Cesium too can build up in the body and is linked to cancers, though studies after Chernobyl did not find an increase in cancers linked to cesium.
Radiation exposure before birth can increase a person's risk of getting cancer later in life. Unborn babies are especially sensitive to the cancer-causing effects of radiation. However, the increased risks depend on the amount of radiation to which the baby was exposed and the amount of time that it was exposed. For example, if the radiation dose to the fetus was roughly equivalent to 500 chest x-rays at one time, the increase in lifetime cancer risk would be less than 2% (above the normal lifetime cancer risk of 40 to 50%). Every day, Yokota Air Base publishes the radiation levels that are detected. For example, today's radiation level is 36.5, the same as it is in Bend, Oregon. We are nowhere near exposed to 500 times the amount of radiation at Yokota. Not even close. I can get more radiation from flying in an airplane or from watching t.v.
Health effects other than cancer from radiation exposure are not likely when the dose to the fetus is very low. Most researchers agree that babies who receive a small dose of radiation (equal to 500 chest x-rays or less) at any time during pregnancy do not have an increased risk for birth defects. The only increased risk to these babies is a slightly higher chance of having cancer later in life (less than 2% higher than the normal expected cancer risk of 40 to 50%).
During the first 2 weeks of pregnancy, the radiation-related health effect of greatest concern is the death of the baby. The fetus is made up of only a few cells during the first 2 weeks of pregnancy. Damage to one cell can cause the death of the embryo before the mother even knows that she is pregnant. Of the babies that survive, however, few will have birth defects related to the exposure, regardless of how much radiation they were exposed to.
Large radiation doses to the fetus during the more sensitive stages of development (between weeks 2 and 18 of pregnancy) can cause birth defects, especially to the brain. When a fetus is exposed to large doses of radiation (above the dose received from 500 chest x-rays) during the more sensitive stages of development (especially between weeks 8 and 18 of pregnancy), the health consequences can be severe, especially to the brain. Fetuses in the 8- to 18-week stage of pregnancy exposed to the atomic bombs dropped on Hiroshima and Nagasaki were found to have a high rate of brain damage that resulted in lower IQs and even severe mental retardation. They also suffered stunted growth (up to 4% shorter than average people) and an increased risk of other birth defects.
Between the 18th week of pregnancy and birth, radiation-induced health effects (besides cancer) are unlikely unless the fetus receives an extremely large dose of radiation. In the 18- to 25-week stage of pregnancy, health consequences similar to those seen in the 8- to 17-week stage could occur, but only when the doses are extremely large (more than about 5,000 chest x-rays received at one time). At this dose level, the mother could be showing signs of acute radiation syndrome, which is sometimes known as radiation sickness. I left Japan when I was 21 weeks pregnant. I am now 25 weeks.
After the 26th week of pregnancy, the radiation sensitivity of the fetus is similar to that of a newborn.
At the 26th week of pregnancy, the fetus is fully developed though not fully grown. Unborn babies exposed to radiation in the womb during this stage of pregnancy are no more sensitive to the effects of radiation than are newborns. This means that birth defects are not likely to occur, and only a slight increase in the risk of having cancer later in life is expected. By the time I return to Japan, I will be 28 weeks, well past the risk of fetal development or harm to my baby.
I borrowed this from a friends blog. She received an email from the US Embassy in Tokyo which clearly lays out why they've made this decision.

Oh Bridget....I am so happy to hear that you are going home. That is absolutely wonderful news. I told Amanda weeks ago that I felt so bad for you because this is the time that you want to be home nesting. You want to start on the baby's room and get your life in order before he/she arrives.
ReplyDeleteAlso, this is the time for you and Mike to enjoy your expanding belly and the chance for him to get to hear the heartbeat.
Really...I am so happy for you. You will be so happy at home and relaxed which is good for all of you.
I am doing the happy dance for you :)
Kathy
I'm so glad that you get to have Mike with you! I've birthed a baby with my husband--and it is DEFINITELY not ideal!! I'm so glad you can be together, whatever the circumstances are around you. I always feel safest with Phill nearby, no matter what's happening around me. So happy for you.
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