5/9/2011 | Chain Reactions Reignited At Fukushima After Tsunami, Says New Study

Source: The Physics arXiv Blog
Date: 5/9/2011

Chain Reactions Reignited At Fukushima After Tsunami, Says New Study 

Radioactive byproducts indicate that nuclear chain reactions must have been burning at the damaged nuclear reactors long after the disaster unfolded

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Nuclear reactors produce radioactive by-products that decay at different rates. One common by-product is iodine-131 which has a half life of about 8 days while another is cesium-137 with a half life of about 30 years.
When a reactor switches off, the iodine decays more quickly so the ratio between these two isotopes changes rapidly over a period of days. That's why measuring this ratio is a good way to work out when the nuclear reactions terminated.
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