Why Can People Live in Hiroshima and Nagasaki Now, But Not Chernobyl?

Melissa 25
Olivia asks: Why is it that Chernobyl is still toxic, but there are millions of people living in Hiroshima and Nagasaki without dying?

nuclearOn August 6 and 9, 1945, U.S. airmen dropped the nuclear bombs Little Boy and Fat Man on the Japanese cities of Hiroshima and Nagasaki. On April 26, 1986, the number four reactor at the Chernobyl Nuclear Power Plant in the Ukraine exploded.

Today, over 1.6 million people live and seem to be thriving in Hiroshima and Nagasaki, yet the Chernobyl exclusion zone, a 30 square kilometer area surrounding the plant, remains relatively uninhabited. Here’s why.

Fat Man and Little Boy

Dropped by the Enola Gay on Hiroshima on August 6, 1945, Little Boy was a uranium- fueled bomb about 10 feet long and just over two feet across, that held 140 pounds of uranium and weighed nearly 10,000 pounds.

When he exploded as planned nearly 2000 feet above Hiroshima, about two pounds of uranium underwent nuclear fission as it released nearly 16 kilotons of explosive force. Since Hiroshima was on a plain, Little Boy caused immense damage. Estimates vary but it is believed that approximately 70,000 people were killed and an equal number were injured on that day, and nearly 70% of the city’s buildings were destroyed. Since then, approximately 1,900 people, or about 0.5% of the post-bombing population, are believed to have died from cancers attributable to Little Boy’s radiation release.

Squat and round, Fat Man, so named for its resemblance to Kasper Gutman from The Maltese Falcon, was dropped three days later on the city of Nagasaki on August 9, 1945. About two pounds of Fat Man’s 14 pounds of plutonium fissioned when it detonated about 1,650 feet above Nagasaki, releasing 21 kilotons of explosive force. Because the bomb exploded in a valley, much of the city was protected from the blast. Nonetheless, it is estimated that between 45,000 and 70,000 died immediately, and another 75,000 were injured. No data on subsequent cancer deaths attributable to radiation exposure from the bomb is readily available.

Chernobyl

Sadly, Chernobyl was likely preventable and, like other nuclear plant accidents, the result of decision-makers’ hubris and bad policy that encouraged shoddy practice.

The design of the reactors at Chernobyl was significantly flawed. First, it had a “built-in instability.” When it came, this instability created a vicious cycle, where the coolant would decrease while the reactions (and heat) increased; with less and less coolant, it became increasingly difficult to control the reactions. Second, rather than having a top-notch containment structure consisting of a steel liner plate and post-tensioning and conventional steel reinforced concrete, at Chernobyl they only used heavy concrete.

On April 26, 1986, engineers wanted to run a test of how long electrical turbines powered by the reactor would continue operating when the reactor was no longer producing power. To get the experiment to work, they had to disable many of the reactor’s safety systems. This included turning off most automatic safety controls and removing ever more control rods (which absorb neutrons and limit the reaction). In fact by the end of the test, only 6 of the reactor’s 205 control rods remained in the fuel.

As they ran the experiment, less cooling water entered the reactor, and what was there began to turn to steam. As less coolant was available, the reaction increased to dangerous levels. To counteract this, the operators tried to reinsert the remaining control rods. Sadly, the rods also had a design flaw in the graphite tips. This resulted in the displacement of the coolant before the reaction could be brought under control.  In a nutshell, as these tips displaced the coolant, within seconds the reaction actually increased drastically due to the heat, creating even more steam, and thus getting rid of more coolant.

This might have not been so bad had the control rods been able to be inserted fully to perform their function of absorbing neutrons and thus slowing the reaction, except the heat became so intense, that some of the graphite rods fractured, jamming the rods at about one third of the way in.

So, in the end, when the nearly 200 graphite tips were inserted into the fuel, reactivity increased rapidly, rather than slowed as was supposed to happen, and the whole thing blew up. It is estimated that about seven to ten tons of nuclear fuel were released and at least 28 people died directly as a result of the explosion.

It is further estimated that over 90,000 square miles of land was seriously contaminated with the worst effects being felt in Ukraine, Belarus and Russia. However, radiation quickly spread in the wind and affected wide swaths of the northern hemisphere and Europe, including England, Scotland and Wales.

Hard data on the number of people who died as a result of the radioactive release are difficult to find. It is known that of the 100 people exposed to super high radiation levels immediately after the accident, 47 are now deceased. Additionally, it has been reported that thyroid disease skyrocketed in those countries closest to Chernobyl; by 2005, 7,000 cases of thyroid cancer were recorded in Ukraine, Belarus and Russia.

Radiation Contamination

Most experts agree that the areas in the 30 kilometer Chernobyl exclusion zone are terribly contaminated with radioactive isotopes like caesium-137, strontium-90 and iodine-131, and, therefore, are unsafe for human habitation. Yet neither Nagasaki nor Hiroshima suffer these conditions. This difference is attributable to three factors: (1) the Chernobyl reactor had a lot more nuclear fuel; (2) that was much more efficiently used in reactions; and (3) the whole mess exploded at ground level. Consider:

Amount

Little Boy had around 140 pounds of uranium, Fat Man contained about 14 pounds of plutonium and reactor number four had about 180 tons of nuclear fuel.

Reaction Efficiency

Only about two pounds of Little Boy’s uranium actually reacted. Likewise only about two pounds Fat Man’s plutonium underwent nuclear fission. However, at Chernobyl, at least seven tons of nuclear fuel escaped into the atmosphere; in addition, because the nuclear fuel melted, volatile radioisotopes were released including 100% of its xenon and krypton, 50% of its radioactive iodine and between 20-40% of its cesium.

Location

Both Fat Man and Little Boy were detonated in mid-air, hundreds of feet above the Earth’s surface. As a result, the radioactive debris was taken aloft and dispersed by the mushroom cloud rather than being drilled into the earth. On the other hand, when reactor number four melted down at ground level, the soil underwent neutron activation, where the already active neutrons in the burning fuel reacted with the soil causing it to become radioactive.

Uncertain Future

Lately, some weird reports have been coming from the Chernobyl Exclusion Zone – wild animals have returned, and, for the most part, they seem fine. Moose, deer, beaver, wild boar, otter, badger, horses, elk, ducks, swans, storks and more are now being hunted by bears, lynx and packs of wolves, all of which look physically normal (but test high for radioactive contamination). In fact, even early effects of mutations in plants, including malformations and even glowing are now mostly limited to the five most-contaminated places.

Although not everyone is ready to agree that Chernobyl is proof that nature can heal herself, scientists agree that studying the unique ecosystem, and how certain species appear to be thriving, has produced data that will ultimately help our understanding of long term radiation effects. For example, wheat seeds taken from the site shortly after the accident produced mutations that continue to this day, yet soybeans grown near the reactor in 2009 seem to have adapted to the higher radiation. Similarly, migrant birds, like barn swallows, seem to struggle more with the radiation in the zone than resident species. As one expert explained, they’re studying the zone’s flora and fauna to learn the answer to a simple question: “Are we more like barn swallows or soybeans?

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25 Comments »

  1. none October 24, 2013 at 7:18 am - Reply

    graphite rods reduce reaction not encourage it

    • Daven Hiskey
      Daven Hiskey October 24, 2013 at 1:21 pm - Reply

      @none: Normally yes. But due to design flaws in the Soviet RBMK-1000 nuclear reactor, in the right circumstances, such as happened here, the opposite occurs. When the overheated controlling rods are lowered into water to cool, the resulting steam actually increases the reaction as the coolant is displaced, rather than reduces it, which creates a positive void coefficient, essentially, an ever increasing feedback loop. I’ll change the wording to make that more clear. Thanks for pointing out the ambiguity. :-)

  2. EditorAtLarge October 24, 2013 at 7:24 am - Reply

    “On August 26, 1986, engineers wanted to run a test” – Wrong date.

    • Daven Hiskey
      Daven Hiskey October 24, 2013 at 1:03 pm - Reply

      @EditorAtLarge: Thanks for catching that. Fixed!

  3. Jose Augusto October 24, 2013 at 2:30 pm - Reply

    Did you just enfer that Hiroshima and Nagasaki weren’t preventable?

    • KingGoogleyEye October 24, 2013 at 11:08 pm - Reply

      The way I read the article, the author pointed out that “Chernobyl was likely preventable” as a contrast to how people readers might think of the accident: a sudden, uncontrollable event—like a plane crash—not as a contrast to the bombing of Japan.

    • Doug May 8, 2014 at 6:31 pm - Reply

      Yes, both Hiroshima and Nagasaki were preventable; however, the Japanese chose NOT to prevent them. After the first bombing, the Japanese again refused to surrender and end the war, thus, it was necessary to send the second bomb. Thankfully, after Nagasaki, the Japanese surrendered. because of the two atomic bombs, untold thousands of lives, American AND Japanese were saved because an invasion and ground war was avoided.

  4. Dufty October 26, 2013 at 8:14 pm - Reply

    Saltwater wells in my eyes.

  5. Paul November 29, 2013 at 9:21 pm - Reply

    And what about Fukishima?

    • Dave December 1, 2013 at 11:22 am - Reply

      Fukushima is many times worse than Chernobyl

      • orwell December 18, 2013 at 2:37 pm - Reply

        Fukushima was no where close to as bad as Chernobyl

  6. Scott January 9, 2014 at 5:23 pm - Reply

    Can you provide the amount of uranium, plutonium, etc involved at Fukushima for comparison? I guess there is no way to know how much of these radioactive isotopes are going into the ocean.

  7. Dude April 22, 2014 at 11:49 pm - Reply

    Come on! Get it right. The graphite tips are moderators in this design. That means that the graghite slows the neutrons down so that they will have a higher probability of hitting a uranium atom and causing fission. If not moderated by graphite the neutrons travel too fast and will miss the uranium target. So the graphite tips were inserted and displaced both water and steam voids, causing the fission reaction to increase.

    • DudeIsCorrect May 23, 2014 at 7:08 pm - Reply

      Dude is correct. However the control rods did not have a graphite tip. The control rods are made of a neutron absorbing substance that slows the reaction. The graphite was used to slow neutrons in order increase the chance of a uranium atom splitting. It wouldn’t make sense to have a control rod that both increases and decreases reactivity. And yes there were design flaws but the engineers who built it were not retarded. the biggest design flaw was using the graphite as a moderator because as graphite gets hotter it better slows the neutrons hence the more uranium split and the more heat released. Creating a positive feedback loop in the reactor.

  8. CJ Morgan August 18, 2014 at 5:54 am - Reply

    Note within article:
    ” Most experts agree that the areas in the 30 kilometer Chernobyl exclusion zone are terribly contaminated with radioactive isotopes like caesium-137, strontium-90 and iodine-131….”

    The first two of these have a half life of approx. 30 years & 28 years respectively. However, the half-life of iodine-131 is about 8 days (and pretty much fully decayed after 80 days).

  9. nick turner August 20, 2014 at 7:40 pm - Reply

    This does not answer the basic question of how people can be living in Nagasaki and Hiroshima, Bikini Island, Australian outback etc when scientists say that nuclear bombs kill everything and make the place uninhabitable for thousands of years. This is clearly a false assumption.

  10. Erd August 22, 2014 at 4:23 am - Reply

    FYI

    you start your post with facts about Hiroshima and then move to Chernobyl and say it was sadly preventable.

    I’m sure that Fat man and litle boy where preventable as well.

  11. Michelle September 8, 2014 at 9:03 am - Reply

    Sad to see all the attacks on this well-written article. Check the facts, yes and get it right. But it’s as if focusing in on the minute details and picking apart this message somehow negates the reality that over 100,000 people died, 75,000 injured, and 7,000 cases of thyroid cancer were ALL AVOIDABLE. Humans created this damage. You should be angry! But your attacks are misplaced. You choose to shoot the messenger instead of remember who the real enemy is. Are you really part of the solution with these kinds of comments?

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