The science of nuclear energy
The science of nuclear energy

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The science of nuclear energy

3.2.5 Clean-up of Iitate

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I'm in Japan four months after the tsunami struck the plant. What remains of the radiation now, and does it justify the exclusion zone?
This is the village of Iitate, population usually 6,165. But it's been completely evacuated, even though it's outside the exclusion zone. That's because radioactive particles from the Fukushima reactor have been carried here by the weather. Now it's entirely abandoned-- every house, every street, even this school.
I've come here today to witness something I've never seen before. In fact, it's an event that's only happened a few times during my lifetime. And that's part of a radioactive cleanup operation. And so as a precautionary measure, I'm wearing these Wellington boots just to make sure that I don't get any contamination from any dust on the ground as I walk around.
Today, scientists from Fukushima University will take measurements of the soil, which is where most or all of the radioactive particles will be now, because they've fallen from the air to the ground. They're looking for two toxic elements which escaped from Fukushima - in particular, radioactive iodine and radioactive cesium.
But one of these elements - radioactive iodine - is only present for a short time.
Right now, because about four months has passed, I predict the iodine has disappeared.
And that's because radioactive elements decay over time, eventually changing into stable, non-radioactive forms. It's the half life of an element that's a good measure of how quickly this happens.
So only traces of caesium 137 and 134 are being detected.
So there will only be caesium in the soil. How dangerous is this? How long will it remain in the ground?
The half life of caesium is said to be close to 30 years. So for a long time, caesium will be the biggest problem.
Back in the lab, they found high levels of radiation in the top 2 and 1/2 centimetres of the soil. Other studies from nearby found levels more than 500 times higher than normal.
Removing this topsoil here will be an expensive option. And Iitate isn't even in the exclusion zone. Recently, the Japanese government has been monitoring the radiation level across 50 sites inside the zone. They've set their safety limit at 20 millisieverts per year, which is the same limit as for people working in the nuclear industry in the UK. And what they've found is that 35 of the sites exceeded this level, and the highest reading was 500 millisieverts.
The tests will help decide whether these people can go home. The government has decided to keep the exclusion zone in place. But that's a more complex decision than it looks.
For perspective, you'd get around that level - 20 millisieverts a year - from two CT scans per year. On one hand, setting such a limit protects people's health effectively. But on the other, that comes at a cost - the upheaval of 78,000 lives.
End transcript
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Iitate is a village outside the exclusion zone, 39km northwest of the Daiichi Nuclear plant. It is outside the exclusion zone but the prevailing winds were able to bring radioactive material with them and in April 2011 the village was evacuated.

The scientists are particularly interested in iodine-131 and caesium-137. The iodine is found to be decayed but the presence of caesium is still a worry. The top two and a half cm of soil are found to have high activity. This would need to be removed to make Iitate safe.

The evacuation order was listed on 1 April 2017. Residents were keen to go back to their homes and were proactive in measuring radiation levels themselves, so that they could make an informed decision about their return.

In the next section, you’ll find out how the accident was graded.


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