Wednesday, February 15, 2012

Verbatim: "Copious Quantities of Cesium-137"

The Fukushima reactor situation worsened again last weekend.  Japanese authorities haven't released accurate data in the past, according to Geoff Brumfiel, writing in Nature:  "The disaster at the Fukushima Daiichi nuclear plant in March 2011 released far more radiation than the Japanese government has claimed." So concludes a study that combines radioactivity data from across the globe. The study also suggests that, contrary to government claims, pools used to store spent nuclear fuel played a significant part in the release of the long-lived environmental contaminant cesium-137. The analysis has been posted online for open peer review by the journal Atmospheric Chemistry and Physics. Andreas Stohl, an atmospheric scientist with the Norwegian Institute for Air Research in Kjeller, believes that the analysis is the most comprehensive effort yet. The reconstruction relies on data from dozens of radiation monitoring stations in Japan and around the world. Stohl cautions that the resulting model isn't perfect. Measurements were scarce in the immediate aftermath of the Fukushima accident, and some monitoring posts were too contaminated by radioactivity to provide reliable data. More importantly, exactly what happened inside the reactors remains a mystery. Nevertheless, the study provides a sweeping view of the accident. The latest report from the Japanese government, says that the plant released 1.5 × 1016 bequerels of cesium-137, an isotope with a 30-year half-life that is responsible for most of the long-term contamination from the plant. Cesium-137 fallout is the great concern. The new model shows that Fukushima released 3.5 × 1016 Bq cesium-137, roughly twice the official government figure. Japanese estimates rely primarily on data from monitoring posts inside Japan, which never recorded the large quantities of radioactivity that blew out over the Pacific Ocean, and eventually reached North America and Europe. The new analysis also claims that the spent fuel being stored in the Unit 4 pool emitted copious quantities of cesium-137. Japanese officials have maintained that virtually no radioactivity leaked from the pool. The latest analysis also presents evidence that xenon-133 began to vent from Fukushima Daiichi immediately after the quake, and before the tsunami swamped the area. This implies that even without the devastating flood, the earthquake alone was sufficient to cause damage at the plant. The model also shows that the accident could easily have had a much more devastating impact on the people of Tokyo. "There was a period when quite a high concentration went over Tokyo, but it didn't rain," says Stohl. "It could have been much worse." (Additional reporting by David Cyranoski and Rina Nozawa.)