Fukushima radiation map: how was the risk in 2011?

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Series like The Days allow us to delve into the real-life situation experienced during an unprecedented disaster. The 2011 Fukushima nuclear disaster is still in the memory of everybody, but after the TV series arrived on Netflix, a genuine curiosity came up about the Fukushima Radiation Map back in those days: how intense was the radioactivity in the area after the reactor explosions, and how much was the risk living close to the power plant? This article will provide some data and information to help you understand.

You can watch the official trailer for Netflix’s The Days here on Youtube.

How much radiation is dangerous for our health?

First of all, it’s worth noticing that science has several units of measurement for radiation. One of the most common units of measurement is the sievert, which is often mentioned in Netflix’s The Days. The sievert measures the radioactivity-related health risks on the human body. Most of the times, the radiation maps shared after the Fukushima accident use the sievert or the mrem: mrem stands for millirem, the old notation. The relation is simple: 1 millisievert (mSv) = 100 millirems (mrem).

The sievert and the mrem are an intuitive way to measure how much radiation can become a risk to your health. The real risk also depends on how concentrated in time the radiation is absorbed: the same amount of radiation absorbed in a short time is much more dangerous than if it’s distributed over months.

So, how much radiation is dangerous for our health? Every country has different limits from this point of view. We can use the indications used in the United States, according to which, an adult should never exceed an exposure of 5000 mrem (50 mSv) per year. To have a reference closer to normal life: a single CT scan exposes you to 15 mSv (1500 mrem).

Speaking about more difficult situations: being exposed to 10.000 mrem (100 mSv) in a year drastically increases the probability of fatal cancer. 25.000 mrem (250 mSv) causes temporary sterility in adults. 100.000 mrem (1.000 mSv, 1 Sv) may cause a person to experience nausea or skin reddening. 500.000 mrem (5.000 mSv, 5 Sv) can cause a quick death if the individual doesn’t receive immediate medical treatment.

During the Chernobyl disaster, the threshold that triggered evacuation was an exposure of 350 mSv (35.000 mrem).

Coming back to Netflix’s The Days: the forecast produced at the beginning of Episode 4 said that if the venting wasn’t complete the day after the disaster, the reactor would rupture at 11pm, releasing more than 2 Sv (200.000 mrem) in the near area.

The Fukushima Radiation map after the accident

As we know, the venting procedure triggered the day after the Fukushima accident was successful, but that didn’t prevent the two hydrogen explosions on the reactors during those days. The radioactivity release out of those explosions was massive, and lasted for a very long time.

Below you can find one of the first accurate examples of a radiation map released four weeks after the Fukushima accident. You find it on the Wikipedia page dedicated to the Fukushima disaster, a combined result of aerial monitoring operations and ground measurements made by the Japanese government.

Keep in mind: 5.000 mrem is the standard limit of radiation a human should absorb in a year, 10.000 mrem increases the risk of fatal cancer. In the area close to Fukushima, one month after the accident, you were able to absorb more than 12 mrem in an hour, which is about 2.000 in a week, almost 9.000 in just one month. In other words: staying one month close to the Fukushima power plant after the accident would be enough to have a high chance of dying of cancer after a few years.

Taking into account the limit of 5.000 mrem in a year, that would mean around 0.57 mrem per hour. One month after the accident, there were places 70 km (45 miles) far from the power plant exposed to a similar radioactivity absorption.

You can find here the radiation map released by Japan government one year after the accident: as you can see, still one year later, there are areas 50 km (30 miles) far from Fukushima with an exposure of 0.4-0.8 mrem per hour (4-8 ÎĽSv), which is more than the annual limit considered safe.

Today, you can still monitor radioactivity around Fukushima from this Japanese website: the area around the old Fukushima power plant is still the most radioactive area in the country.

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