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Frequently Asked Questions
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There was severe ground contamination after the Chernobyl accident. Why wasn't it so serious after the Hiroshima and Nagasaki bombings?
Background
Release of radioactive materials after the Chernobyl reactor accident

Basic information
The Chernobyl reactor contained about 180 tons of nuclear fuel consisting of two percent, or 3,600 kg, total uranium. The amount of nuclear fuel released is estimated at seven tons (corresponding to 200 kg of uranium). Fission products increase the longer the fuel is used.

The Hiroshima bomb contained 25 kg of uranium, and about four percent (or 1 kg) underwent nuclear fission.

In a nuclear reactor, when the nuclear bed melts, volatile radioactive materials are released extensively. It is estimated that 100% of the rare gases, about 50-60% of the iodine, and about 20-40% of the cesium contained in the reactor are released.

  1. The total nuclear fuel in the Chernobyl reactor was 180 tons (corresponding to 3,600 kg of Uranium-235), more than 100 times greater than that of the Hiroshima bomb (total weight of the bomb was about four tons, but Uranium-235 is estimated at 25 kg).
  2. In the case of the Chernobyl accident, the nuclear fuel melted and volatile radioisotopes were released in large quantities. For example, as stated, 100% of the rare gases, 50-60% of iodine, and 20-40% of cesium were released. Thus, although the total nuclear fuel released is estimated at a few percent (7-10 tons), the release of other radioactive materials was quite extensive, in disproportion to the amount of nuclear fuel released.
  3. It is estimated that about four percent (or 1 kg) of the uranium of the Hiroshima bomb underwent nuclear fission. The bomb exploded in the air and formed a large fireball that subsequently ascended to reach the stratosphere. Part of it fell to the ground in black rain while the remainder was widely dispersed.