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Radiation reassessed

POSTED 11 AUGUST 2005
Chernobyl -- ultimate open-air radiation experiment
On April 26, 1986, one of four reactors at the Chernobyl generating station in the Soviet Union melted down when operator error was compounded by unsafe design. Among other problems, the old reactor lacked a containment vessel to contain radioactive isotopes in an accident. Such vessels are standard in modern reactors.

map shows europe (in black  with Chernobyl location indicatedChernobyl, in the former Soviet Union, is now in Ukraine. Nearby Belarus was also heavily contaminated.

The heat ignited a vast pile of the carbon that was used to slow neutrons in the reactor, and a 20-day fire spread a fearful plume of radioactive isotopes across much of Europe, including heavy elements that were not expected to be released in a meltdown.

In other words, the disaster was exactly what the world has (sadly enough) long needed -- a vast test of the effects of the human health effects of low-level radiation.

In contrast to the nearly instantaneous Japanese exposure, Chernobyl exposures were mainly low-level and long-term. But the human tragedy was not exploited as it should have been, according to some scientists who tried to learn from it. In 1996, Armin Weinberg, a cancer prevention specialist at Baylor College of Medicine who helped set up a registry of Chernobyl survivors, told us, "There's been a lack of resources that should have been available to look at cancer and non-cancer cases in the population. There's been a disappointing ability for Western scientists to obtain funding and capitalize on this opportunity to study low-level effects."

Large building stripped and melted after fireThe meltdown at Chernobyl was contained by thousands of tons of sand and neutron-absorbing chemicals. A concrete "sarcophagus" was built around the reactor by the 600,000 "liquidators" who tried to clean up this mess. Photo: FAA

Nevertheless, a 2002 report on Chernobyl by the Nuclear Energy Agency of the Organization for Economic Co-operation and Development does pinpoint some of the effects.

The accident released 1.1 x 10 19 Becquerels of radioactive material (one Becquerel is one molecule undergoing radioactive decay per second).

About 116,000 people were evacuated from the area around the plant, and 134 were hospitalized for acute radiation sickness. The 31 deaths were mainly among fire fighters who fought the first fire without radiation protection.

The major health hazards came from iodine 131 (I-131) , which accumulates in the thyroid gland, and cesium 137 (Cs-137), which gathers in bone. The accident released 1,760 * 10 15 Becquerels of I-131 and 85 * 10 15 Becquerels of Cs-137.

This beautious graph shows increasing levels of radioactive substances
Original graph from Nuclear Energy Agency

I-131 was the most important source of internal radiation exposure in the short term, but over the longer term, Cs-137 will play a larger role.

5 million people lived in an area contaminated by Cs-137. Their individual exposures depended on location, wind, length of exposure, eating habits, and work.

Long-term studies have shown an increase in the rate and aggressiveness of thyroid cancer, especially in children who were younger than five during the meltdown. (Sadly, these cancers might have been prevented by immediately taking potassium iodide supplements, which slow the uptake of radioactive iodine in the thyroid.)

About 600,000 "liquidators" were pressed into service to clean up after the accident. Although they got an average dose of 170 millisieverts in 1986, studies have found they didn't have excess cancers.

Long-term studies found no increase in other cancers, birth defects, or injury to pregnant women or their children.

Survivors did show apathy and stress-related symptoms caused by fear, evacuation and the 1991 breakup of the Soviet Union.

One simple question: How much radiation is too much radiation?

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