Fukushima v. Hiroshima

Why is it that the Fukushima disaster is likely to leave some areas uninhabitable for decades, while Hiroshima could be rebuilt relatively quickly? Or were there similar uninhabitable areas in Hiroshima as well?

Or Chernobyl for that matter.

**Cecil **answers.


So that’s why the A-bombs were clean. But why are Chernobyl and Fukushima dirty? That’s the second part of the question.

Cesium. More specifically, cesium-137.

It is a byproduct of nuclear fission, that is normally processed but in Chernobyl and Fukushima was violently released into the environment. Cesium isn’t the only fission byproduct that was released. Large quantities of Iodine-131 was also produced. However, I-131 has a half-life of 8 days, whereas Cs-137 has a half-life of 30 years. Strontium and plutonium was also released, but at least in the case of Fukushima, the quantities were much less significant than cesium.

Atomic bombs also produce radioactive cesium, but the Fukushima accident released over 168 times the amount that the Hiroshima bomb did.


In an atomic bomb explosion like Hiroshima, one large bomb - say a ton or so of material - was vaporized; and close enough to the explosion to be heavily irradiated. You may have some radioactive isotopes created on the ground, but that was a mile or more away from the explosion generally so less likely to create problem material.

In Chernobyl and Fukushima, you have a giant core, tons of uranium (yes, mostly the non-radioactive type) first melting down in a glow of fission chain reaction to create radioactive isotopes of a lot of the core, plus a lot of the surrounding material. Then that material evaporates, or burns, and rises into the atmosphere to be distributed around the landscape.

So, probably the short answer is tons more material distributed around at a lower atmospheric level.

there is non-radioactive uranium?

The radiation level on U-238 is low enough to be used as radiation shielding.


Well, some isotopes are more radioactive than others.

(Darn ninjas)

Depleted uranium is commonly used as a weapon, since a slug is so dense; momentum vs. cross-section was pretty good. It is basically non-radioactive uranium. IIRC some airbus model has a slug of depleted uranium in the tail to aid in balance.

There’s what, U235 as the most common isotope and radioactive U238 (plus other les stable variations) , the U238 is prime weapon material. The biggest effort in making an atomic weapon is to separate chemically identical isotopes; the most common method is the centrifuge technology in the news lately thanks to Iran. They differ in weight by about 1%, so it takes a lot of work to do the separation - as I understand it, just continuous processing of steadily more concentrated batches. Regular mined uranium is relatively low in U238, and the more concentrated it is then the smaller the explosive critical mass.

Since (a) the process is not perfect, and (b) uranium is pretty much at the edge of stable nucleii, there is always a bit of radioactive decay even when “depleted”; but the same can be said of almost anything.

Many of the questions about depleted uranium weapons also revolve around whether it is toxic. Since much experience has been with the regular or radioactive mix, simple metallic toxicity has generally been the least of the worries.

Ya got that backwards. U238 is common, U235 is what is primarily needed for nuclear weapons.

Doh!!! (Thanks)