nuclear: Chernobyl vs Hiroshima and Nagasaki

ie7,

In the case of the uranium and plutonium bombs used for Hiroshima and Nagasaki, there were several factors at work. First of all, the total amount of radioactive material used was relatively small (64kg of uranium for Little Boy, estimated 6.2 kilograms of plutonium in Fat Man). Second, the bombs were both detonated in the air. In a bomb blast of either material, some portion of the material is consumed as a function of the explosion itself; the remaining material is widely distributed in the air, sucked up in the column of heat and smoke, and much of it is carried downwind and dispersed. Following the neutron bombardment of the target area that results from the exposion, some additional radioactive material is actually created, but it typically has a short half-life, and decays rapidly.

In the case of the Chernobyl incident, the total amount of radiation released is estimated at four hundred times more that that of the bombs dropped on Japan. The total amount of material present in the reactor was many orders of magnitude  higher than that used in the two bombs. The Chernobyl incident had several mechanisms of release, including the initial explosion, subsequent chemical explosions, ongoing fire, etc, which led to many different types of material with different half-lives and uptake (absorption) patterns in animals being released.

I hope that helps clarify things.

Cheers,
LHerrou

Hugely different circumstances between Hiroshima/Nagasaki and Chernobyl. A nuclear blast ends up converting significant amounts of the critical mass to other substances for one. And in the case of Chernobyl, the explosion liberated four hundred times as much radioactive material that the Hiroshima/Nagasaki weapons.

Additionally, the moderator in the Chernobyl reactor was 1700 tons of graphite, which what exposed to normal atmospheric oxygen and immediately burst into flames, fueling more of the critical mass that was no longer being cooled after the initial steam explosion. In other words, as the graphite moderator burned away, the runaway nuclear reaction from the core sped up as well. It took over four hours to extinguish the fires at the site.

The proximity of the reactor to the ground itself also played a role, as the reaction was more akin to a groundburst nuclear weapon for the purposes of creating fallout - both the  Hiroshima/Nagasaki weapons were airbursts and as a result had less fallout associated with them.

Hiroshima/Nagasaki weapons were done with their radiation production in thirty billionths of a second. The core of Chernobyl melted through the building and still produces fatal levels of radiation to this day.