Does the vapor from the nuclear reactor cause radioactive rain?


My understanding is that vapor is continuously coming out of the nuclear reactor. Are there radioactive materials in there? Also, isn’t it dangerous if that vapor turns into clouds and causes rain, or if it rains with radioactive material in any way? (Male, 20s, Saitama)


It is understandable that people are worried about getting exposed to radiation from rain. There are vapors coming out of areas close to the nuclear reactors and water tanks containing used nuclear fuel. Even if the nuclear power plants are shut down, radioactivity from the fuel rods continues. The water remaining in the tank and the sea water that were discharged turns into vapor. Radioactive materials are released at the same time, so there is a possibility that the vapor is harmful.

First, the possibility of the vapor turning into clouds and causing rain is very small. However, what happens to the vapor afterwards remains a problem. Depending on the weather, the vapor containing radioactive materials may spread, but as it spreads the radioactive materials are diluted. For example, even if areas that are 10 kilometers away from the nuclear power plant have a high concentration, areas that are 100 kilometers away would have radioactive materials that have diluted to the point that it is impossible to detect.

Next we will talk about what happens when it rains. The radioactive material in the air falls down with the rain drops. The Ministry of Education, Culture, Sports, Science and Technology (MEXT) has made public the data that shows the amount of radioactive materials contained in precipitation (web site below). By looking at the website the amount of radioactive materials that have fallen due to precipitation in each prefecture can be monitored. For example, it rained in Ibaraki, Hitachinaka city on March 21, and there were more than 90 thousand mega-becquerel of Iodine contained in 1sq kilometer. The amount legally limited is 40 thousand mega-becquerel per 1sq kilometer, so it can be confirmed that a high amount of radiation was detected.

However, the radioactive materials that were emitted due to the hydrogen explosion have already descended, due to the rain. There has been no increase in the amount of radiation recently. It may be a good idea to wear raincoats just in case, but there is no need to be over concerned.

Science Communicator: Tomonori Hayakawa
Supervised by Japan Geoscience Union



MEXT: Reading of radioactivity level in drinking water by prefecture
MEXT: Reading of radioactivity level in fallout by prefecture