April 16, 2012 | After an earthquake and tsunami damaged the Daiichi nuclear power plant in Fukushima, Japan, on March 11, 2011, an unknown quantity of radioactive material was released into the surrounding air and sea. NCAR scientists and their Japanese colleagues are working to get a better picture of radioactive fallout from the event.

Japanese towns in and around the Daiichi nuclear plant exclusion zone. Areas within 20 and 30 kilometers (12–19 miles) had evacuation and sheltering orders after the incident. (Image courtesy Wikimedia Commons.)

By assessing the fuel rods that melted during the event, scientists and engineers are approaching a consensus on the total amount of radioactive material released from Daiichi. What remains unclear, however, is how much ended up on land and how much in the sea. The complexity of the disaster—which included multiple explosions and continuous release, along with rainfall during the incident—complicates any estimates.

A workshop held at NCAR in February brought an international group of researchers from academia, government labs and agencies, and private industry together with Japanese experts on Fukushima to look at the incident within the context of source term estimation (STE). NCAR scientists have been developing an STE system for the U.S. Department of Defense that combines meteorological information and other observations with transport and dispersion models to determine the source of chemical, biological, or nuclear material in the atmosphere.  The purpose of the work is to improve the tools used to protect civilians and military personnel against terrorism and nation-state use of such weapons.

One of the main conclusions from the workshop is there is currently no operational system anywhere in the world that can assess the rate of release of the radioactive material should a similar incident occur again. A combination of STE approaches discussed at the workshop that leverages their respective strengths is likely the best path forward, according to NCAR scientist Paul Bieringer. A research team led by Bieringer plans to publish a workshop summary in the Bulletin of the American Meteorological Society along with a journal manuscript summarizing STE methods.

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