Today the IAEA has finally confirmed what some analysts have suspected for days: that the concentration per area of long-lived cesium-137 (Cs-137) is extremely high as far as tens of kilometers from the release site at Fukushima Dai-Ichi, and in fact would trigger compulsory evacuation under IAEA guidelines.
The IAEA is reporting that measured soil concentrations of Cs-137 as far away as Iitate Village, 40 kilometers northwest of Fukushima-Dai-Ichi, correspond to deposition levels of up to 3.7 megabecquerels per square meter (MBq/sq. m). This is far higher than previous IAEA reports of values of Cs-137 deposition, and comparable to the total beta-gamma measurements reported previously by IAEA and mentioned on this blog.
This should be compared with the deposition level that triggered compulsory relocation in the aftermath of the Chernobyl accident: the level set in 1990 by the Soviet Union was 1.48 MBq/sq. m.
Thus, it is now abundantly clear that Japanese authorities were negligent in restricting the emergency evacuation zone to only 20 kilometers from the release site.
Edwin Lyman is a senior staff scientist in the Global Security program at the Union of Concerned Scientists (UCS) in Washington, DC. This article was first published in the All Things Nuclear blog of the Union of Concerned Scientists on 30 March 2011; it is reproduced here for non-profit educational purposes.
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