Fallout Forensics: Fukushima’s radiation toll much higher than claimed

Far more radiation was released after the Fukushima Daiichi nuclear power plant accident than the Japanese government has claimed, new global data conclude.

This new study on the post-earthquake disaster in March combines radioactivity data from around the world to estimate the scale and fate of emissions from the plant. Nature News reports.

This is the most comprehensive effort yet to understand the amount of radiation released from the power plant (pictured), according to study researcher Andreas Stohl from the Norwegian Institute for Air Research.

Data from dozens of radiation monitoring stations in Japan and across the planet were used in this reconstruction. (Many are part of a network run by the Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna.) And some global meteorological data were added in.

Two things to know:

1. Xenon-133 doesn’t pose serious health risks because it isn’t absorbed by the body or the environment.
2. Cesium-137 fallout, however, is a long-lived contaminant that’ll linger in the environment for decades.

The latest report from the Japanese government, published in June, says that the plant released 1.5 × 10¹⁶ bequerels of cesium-137, and that a far larger amount of xenon-133, 1.1 × 10¹⁹ Bq, was released.

Challenging these numbers, the new study says the accident released:

• Around 3.5 × 10¹⁶ Bq cesium-137, roughly twice the official government figure, and half the release from Chernobyl.
• And 1.7 × 10¹⁹ Bq of xenon-133, greater than the estimated total radioactive release of from Chernobyl.

As it turns out, pools used to store spent nuclear fuel also played a big part in releasing cesium-137, which could’ve been prevented by prompt action.

Stohl believes the discrepancy can be partly explained by the larger dataset used: Japanese estimates rely primarily on in-house monitoring posts that never recorded the large quantities of radioactivity that blew out over the Pacific Ocean, and eventually reached North America and Europe.

Some caution about this new model: immediate aftermath measurements are scarce, and some stations were too contaminated by radioactivity to give reliable data. And we still don’t know exactly what happened inside the reactors.

However, the model does show that the accident could easily have been much, much worse. Higher levels of radioactivity were recorded in the soil where precipitation fell from cesium-137 clouds; and thankfully, densely populated areas had dry weather.

The analysis was posted online for open peer review by Atmospheric Chemistry and Physics.

From Nature News.

Image: after the earthquake and tsunami via Wikimedia