Ukraine

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Chernobyl Exclusion Zone, Ukraine

51° 18′ 0″ N, 30° 0′ 18″ E

Aftermath of the Chernobyl Disaster

On April 26, 1986, in the middle of the night, a steam explosion tore the roof off reactor number 4 at the Chernobyl nuclear power plant in Ukraine. The reactor did not have a containment building, so the explosion exposed the reactor core directly to the atmosphere.

The reactor was operating at the time of the explosion, and the graphite blocks that surrounded the reactor fuel were red-hot. With the addition of oxygen from the atmosphere, the graphite began to burn fiercely. To make matters worse, the fuel in the reactor was close to the end of its useful life and was filled with a wide variety of different radioisotopes.

Between the explosion and the fire, the Chernobyl disaster was the worst radiation accident in history. It led to the evacuation of the nearby town of Pripyat, 56 deaths, and a large increase in cancer deaths among the most highly exposed people. Ultimately, a 30-kilometer exclusion zone was created around the reactor and the population within the zone was ordered to leave. More than 350,000 people had to be relocated.

Radioactive fallout from the reactor fire contaminated a wide area. Close to the reactor itself, a large forest of pine trees was killed by fallout and became known as the “Red Forest” because of the color of the dead trees. The forest was bulldozed a year after the disaster and buried.

The radioactive plume spread across Belarus and on to Finland and Sweden, across Northern Europe and into North America. Today, around 5 million people live in parts of Ukraine, Belarus, and Russia affected by radioactive fallout.

The exclusion zone is still in place today and is almost totally uninhabited, except for some elderly people who refused to leave the area or who returned to their homes shortly after the disaster. Still, it is possible to visit the Chernobyl Exclusion Zone on specially organized tours.

Tours start from the Ukrainian capital, Kiev, about 70 kilometers south of Chernobyl, and typically last an entire day. Visits usually take in the town of Chernobyl (which is about 12 kilometers from the reactor itself), where a few people still live and where you’ll find a poignant memorial to the firefighters who attempted to extinguish the burning graphite core.

Tours take visitors close to the power plant itself to see the massive sarcophagus built around the exploded reactor, and the partially constructed reactors 5 and 6 (reactors 1, 2, and 3 were kept operating until 2000). The tour also stops in the town of Pripyat, where time stopped in 1986. A ferris wheel sits abandoned and motionless in a disused amusement park. The blocks of flats, the cultural center, and the school sit with their furniture still in place, waiting for people to return. Books rot slowly in the library.

Above all, Pripyat is heartbreaking. A town of almost 50,000 people evacuated suddenly and with no warning, a testament to the long since passed Soviet Union, and by far the most striking reminder of the destruction a nuclear accident can create.

While you’re in Kiev, take the time to visit the National Museum of Kiev. The museum helps explain the disaster and has more than 7,000 objects on display, including original photographs, secret documents from the Soviet era, and items from the abandoned homes. A video presentation describes the disaster and its aftermath.

Practical Information

See http://www.ukraine.com/museums/chernobyl/ for information on the National Museum of Chernobyl.

Potassium Iodide and the Thyroid

One of the immediate dangers after the explosion was the presence of radioactive iodine in the food system. Radioactive iodine (iodine-131) is produced in nuclear reactors in normal operation as a product of the fission of uranium-235. The uranium-235 breaks apart when its nucleus is hit by a neutron, releasing energy and creating new elements from the split-apart atom. The elements typically created when uranium-235 breaks apart in a nuclear reactor are caesium, iodine, zirconium, technetium, strontium, promethium, and samarium. Typically, about 2.8% of these fission products are iodine-131.

Because the fuel in the Chernobyl reactor was nearing the end of its life at the time of the explosion, its uranium-235 had already been turned into fission products, which led to a large release of iodine-131. When nuclear fuel is extracted from a reactor and cooled for reprocessing or storage, the iodine-131 has enough time to decay, removing any danger of exposure.

Iodine-131 is particularly hazardous to humans because it concentrates in the thyroid gland and is easily passed into human foods. For example, cows that eat grass contaminated with iodine-131 will pass it into their milk, and when the milk is consumed by humans, iodine-131 will pass into the thyroid gland.

The iodine-131 concentrates in the thyroid because the thyroid uses iodine to create two hormones—thyroxine (C15H11I4NO4) and triiodothyronine (C15H12I3NO4). These two hormones—typically called T4 and T3, respectively—are involved in regulating the body’s metabolism.

If radioactive iodine is present, the thyroid will use it to create T4 and T3, and the concentration of iodine-131 in the thyroid will likely cause thyroid cancer. The cancer is created because radioactive iodine undergoes rapid decay (its half-life is eight days) and releases beta-radiation (high-energy electrons) inside the thyroid.

To prevent this from happening, workers at Chernobyl were immediately given potassium iodide (KI) tablets. Soon afterward, almost 17 million people in the path of the fallout in Poland were also given potassium iodide as a preventive measure. This was the largest ever “experiment” in the use of potassium iodide to prevent thyroid cancer caused by radioactive fallout, and it was shown to be effective.

If taken before radioactive iodine enters the body, potassium iodide works as a prophylactic, overwhelming the thyroid with a source of iodine so that it will not attempt to use iodine-131 if it is later ingested.

Conversely, radioactive iodine-131 can be used to treat thyroid cancer once it has begun. Low doses of iodine-131 are also used to test thyroid function; high doses are used to destroy the thyroid completely.