Why can you live In Hiroshima but not Chernobyl?
In this article we’ll discuss Why can you live in Hiroshima but not in Chernobyl. Both cities suffered a major atomic disaster, where radioactive fallout was released. The uranium fissile atomic bomb, little boy, was detonated in Hiroshima with a yield of 15 kilotons of TNT. Chernobyl's uranium fissile reactors produced 3,200 MW (megawatts) of thermal power, — also using fissile uranium. As you know, the reactor blew up.
Hiroshima is now well and prospering but Chernobyl remains uninhabited. So what’s the difference between these disasters?
The short answer is the amount of radiation. DOH! obviously. But let’s look into a deeper answer.
The first reason is the type of detonation. The atomic bomb in Hiroshima was detonated hundreds of meters above ground to maximize its yield. Upon detonated the bomb is completely vaporized and therefore the radiation is distributed in a huge area by the blast.
That is why wind greatly affects the radioactive spread in an atomic bomb, as shown below;
Wind was not an important factor of the Chernobyl explosion , because it wasn’t nearly a powerful explosion as the little boy atomic bomb, furthermore the explosion occurred at ground level. While Chernobyl released plenty of radioactive fallout in the air, the pressure of the tank caused a ground level weak explosion. It left huge chunks of radioactive material in a smaller area.
Both the bomb and the reactor gets energies from fissioning uranium 235. I’ll briefly cover how it works, and then answer why it relates to our problem: “Why can you live in Hiroshima but not Chernobyl”.
In an atomic bomb, we want to release as much energy as fast as possible, this is done using a chain reaction where uranium 235 absorbs a neutron, undergoes fission, releases A Lot of energy and releases 3 new neutrons.
the 3 neutrons will then repeat this cycle. Such that the density of neutrons in the core is increasing and so we say criticality is obtained. This is what we want in an atomic bomb. You can see how quickly the chain reaction goes, 1 neutron duplicates itself to 81 in just two 4 cycles.
Just for scale, Complete fission of 1 kg of 235 U liberates energy equivalent to that of about 17 kt of TNT.
In an atomic reactor, we want to have stable constant power. We can use the same fission processes as mentioned above, but use control rods such that for each splitting only 1 new uranium 235 absorbs a neutron.
When a nuclear reactor’s neutron density remains steady from one generation to the next (creating as many new neutrons as are lost), the fission chain reaction is self-sustaining.
These reactions mechanisms are important because, in an atomic bomb, we burn through as much of enriched uranium as fast as possible and therefore we don’t need a lot of fissionable material. But in a reactor core, there needs to be plenty of material such that the reaction can be stable and self-sustaining. Therefore there will be much more enriched uranium present in a uranium power plant. Hiroshima had 46 kg of uranium while Chernobyl had 180 tons of reactor fuel.
A reactor also builds up a huge amount of nuclear waste, over the weeks it is running. There is a lot of different waste products, but the worst are cesium, iodine and irradiated graphite moderators. they all sit in the reactor until they are replaced with new fuel rods. Unlike the atomic bomb which only produces waste products from the fuel it is using in the explosion. The atomic bomb won’t contain waste products from the last few weeks.
While the dose of radiation from the atomic bomb would still give be lethal, all these reasons above combined are why the Chernobyl was much worse in terms of radiation.
Thanks for reading!