How far do the radioctivity of failed nuclear power plant can travel?

Answer 1

There are two primary forms of radioactive hazard that are associated with nuclear bombs and nuclear reactors:

1. Direct nuclear radiation from a radiation producing source. Sources might include the exposed core of a nuclear reactor, or a nuclear bomb exploding close to you. The fission process releases direct radiation that travels through space and does not linger. If you're not there when it passes by, it won't affect you and the area is safe to return to.

2. Radioactive fallout. The problem with the above is that human beings seldom encounter fission radiation in empty space. That is, there is material around you like dirt, water vapor (steam, fog), liquid water, plants, etc. All of these physical materials may stop and trap radioactive atoms, making that material radioactive.

Fallout is mainly a hazard of bombs, which kick up a lot of dust and pulverized rock from the ground. Such dust is radioactive and winds may spread it for a long distance. The good news is that the radioactive decay dropoff for fallout is very quick. While very high in the first few hours after creation, the danger of fallout is almost none after 48 hours from the time of the fallout's creation. Anything in a sealed container will not be poisoned by fallout. Canned food and bottled water, for example, are perfectly safe. Exposed water such as in a river or lake, however, should not be used. Contaminated water, however, can be filtered by particular methods (one of which involves nothing more than clay soil and pebbles) and made safe.

If the explosion is sufficiently large, a cloud of fallout may travel thousands of miles away from where it was created. The Chernobyl incident in 1986 resulted in an enormous steam explosion that destroyed the reactor containment and created a huge cloud of radioactive material that traveled into many countries to the northwest. In fact, that was how the Western world found out something had happened -- other countries started detecting the radiation. The USSR did not announce or admit that anything had happened for quite some time.

Japan: Since the Fukushima nuclear plant has suffered explosions in at least 3 of its 6 reactors, it is likely that a cloud of radioactive material was created in each case. The extent of the radioactivity at the site is currently uncertain and may never be known, since the radiation detectors at the plant were damaged by the earthquake and are not operating. All we can measure is the levels farther away.

The distance that a fallout cloud can travel will, of course, vary with altitude and wind conditions. Even if the fallout travels a long distance, the threat it poses depends largely on how much radioactive contaminated material is present. In the case of the Fukushima reactor, current information suggests that only areas within a few hundred miles of the site are at any significant risk.