Eli5: why isn’t radiation from under water/ ground nuclear tests a concern?

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Seems to me you’d still have radiation from the bomb regardless of where it was set off. Isn’t sea life endangered with underwater nuclear tests? How is the radiation kept from coming up into the atmosphere with either underground or underwater nuclear tests.

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Water is a great blocker of radiation. About 4 meters of water between the source and you decreases radiation by a billion-fold.

So yes, anything in the immediate vicinity gets boiled alive, but it’s a tiny tiny portion of the body of water you’re testing in, in the grand scale.

The number of undersea tests is quite low and the bomb have not been that large. Water can spread out the radioactive element produce just like if you do it in the air.

The number of underwater nuclear tests is a total of between 1946 and 1962 and the larges bomb was only 30kt

https://en.wikipedia.org/wiki/Underwater_explosion#List_of_underwater_nuclear_tests

Atmospheric tests result in the fallout spreading out over land and it can be a problem. It was recognized quite early on and as a result, the https://en.wikipedia.org/wiki/Partial_Nuclear_Test_Ban_Treaty was singe in 1963 that ban all these that is not underground tests. There was a total of 269 nuclear tests in the atmosphere before the ban. All of them were not large bombs, many of them are tested in the single-digit kilotons range for tecnical tests of different parts of nuclear weapons design.

Nuclear weapons produce a ton of radiation, yes, but it’s not like a single blast is going to poison the whole world.

So the shortest answer is, the radiation from underwater and underground tests is pretty nasty, but it was done in remote places that people shouldn’t go to. Those areas would still have radiation levels considered unhealthy to be exposed to, but it’s not they are so unimaginably radioactive that they can poison the whole world.

Yes, sea life in endangered, but the Venn Diagram of people who conduct nuclear testing and the people who are concerned about hurting Clown Fish are two distinct circles.

Yes, radiation is capable of escaping from the sites and into the atmosphere but in the grand scheme of things it’s just not potent enough to be worried about, just don’t travel to those sites.

Finally, environmental protection is on the list of reasons why nuclear weapons testing is banned by most counties. (the bigger reason being those of us that could already did and don’t need to anymore, and we don’t want anyone else getting them).

Good comments so far. What hasn’t been touched is that an efficient nuclear bomb produces littles radiation. It turns the most amount of material into fissile matter and splits damn near 100% of it. The more material turned into energy, the less radioactive material left around afterwards in the fall out. That’s the military ideal.

For less than moral applications, you could mix in other radioactive material that isn’t fissile material and contaminate a massive area and poison it for hundreds, thousands years, maybe even longer.

If you look at the 2 sites bombed in Japan less than 100 years ago, people are living there again. The destruction was massive, but the lingering radiation was low, they were efficient devices. On the other hand, you look at Chernobyl which only damaged a single building, but released all this radioactive material which blanketed a huge surrounding area making it still uninhabitable in some spots to this day. It is all the radioactive material not being consumed that poisons everything.

A lot of the radiation in a nuclear bomb blast is released immediately by the “flash” of the nuclear explosion. Running a test underground or underwater blocks direct exposure to the flash, which gets absorbed by the water or rock around the bomb.

Another radiation concern is the radioactive byproducts of the nuclear blast. For a properly conducted underground test, the blast is contained within a layer of rock, so all the radioactive stuff is locked below ground where it isn’t harming people. Assuming you don’t dig down to the blast, or ground water doesn’t seep through it, the radioactive material is trapped very well. For an underwater blast, the radioactive material isn’t nearly as well contained. For one thing, the material can contaminate the water and sea floor, and that radiation can be absorbed by sea life. Also, underwater tests tend to create a explosion on the surface of the water, blowing radioactive water and dust particles into the air. In one of the more infamous underwater tests, Ivy Mike, an underwater test of a hydrogen bomb vaporized a coral reef, and blew the radioactive calcium from the reef into the sky, where it rained down like snow over hundreds of square miles. An unlucky Japanese fishing boat was caught within the fallout zone, and the fishermen were coated in strange dust. This was highly radioactive and made the fishermen very sick after a few days.

To my knowledge, underwater tests were never performed to be “safer” than above ground tests. They were done to see how naval ships could stand up to nuclear blasts, and because it is a lot easier to find an unoccupied stretch of water than to find an unoccupied stretch of land. When the US switched to “safe” nuclear tests, they stopped doing underwater, above ground, or high altitude tests and just did underground tests. The US stopped testing nuclear bombs entirely in the early 1990s.