Japan Detects Plutonium Outside Fukushima; Assessing the Risks

Kyodo news agency is reporting breaking news that plutonium was detected in soil samples outside Japan's Fukushima Daiichi plant. Tokyo Electric Power Company said March 28 that its own tests did not show plutonium in the soil but sent off samples for independent testing. It's that independent testing by Japan's Atomic Energy Agency and the Japan Chemical Analysis Center that now shows plutonium in soil samples collected from five different locations March 21 and 22.

Banners displaying breaking news updates on Kyodo's website indicate that officials don't know which reactor is the source of the radiation leak. The leaking of plutonium indicates presumptive fuel rod damage. Reactor 3 is the only reactor using a plutonium fuel mix called MOX; however, uranium fission creates plutonium as a byproduct, so the other reactors could also be the culprits.

What are the signs to look for in assessing the seriousness of Japan's plutonium contamination as this breaking news develops?

Information shared on University of California at Berkeley's Nuclear Engineering Department public forum included Russian guidelines for plutonium exposure. These guidelines set out health risks from different exposures.

Health Consequences of Plutonium Exposure

The Russians have published this information on the health consequences of varying levels of plutonium exposure:

* 370 kBq - fatalities during the first year after accident result from acute interstitial pneumonitis;

* 37 kBq...370 kBq - serious deterministic effects including disability caused by pneumosclerosis and high risk of lung cancer;

* 3.7 kBq....37 kBq - long-term lung pathologies;

* < 3.7 kBq - does not lead to reliable defined consequences.

Response to Plutonium Soil Contamination: Russia and USA

This is what the Russian decision-making criteria say about soil contamination with plutonium 239:

If soil contamination with plutonium reaches a density of .2 to .9 MBq m^-2, permanent or temporary relocation is required. The document says that comparable U.S. guidelines call for permanent or temporary relocation at .22 MBq m^-2.

Sheltering is called for if concentrations reach .008 to .09, whereas U.S. sheltering is triggered by a level of 2.2.

Russians take urgent protective actions when levels are between 10 and 70, whereas the United States mandates such actions when the concentration hits 22 MBq m^-2.

As the situation develops, Japan will need to decide whether precautions are necessary to protect residents from plutonium exposure.