Blast from the Past: Plutonium Contamination from Fukushima Daiichi Unit 3

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From Majia’s blog

I was reviewing my notes regarding plutonium found at Fukushima and I found this news story worth remembering:

Amina Khan (of the Los Angeles Times). (March 8, 2012). Plutonium near Fukushima plant poses little risk, study says Published: Thursday, March 8, 2012 http://www.heraldnet.com/article/20120308/NEWS02/703089849

The levels of radioactive plutonium around Japan’s Fukushima Daiichi nuclear power plant aren’t much higher than the amount of plutonium remaining in the environment from Cold War-era nuclear weapons tests, and it probably poses little threat to humans, a new study indicates.

The paper, published Thursday in the journal Scientific Reports, provides the first definitive evidence of plutonium from the accident entering the environment, the authors say. It examines the area within a roughly 20-mile radius of the plant and details the concentration of plutonium isotopes deposited there after explosions ripped open multiple reactors.

At the three sites examined, the levels for certain isotope ratios were about double those attributed to residual fallout from above-ground nuclear tests conducted by the U.S. and former Soviet Union at the dawn of the Cold War….

Robert Alvarez, who has served as a senior policy adviser in the U.S. Energy Department, said he would have been surprised if researchers had not found evidence of plutonium contamination near the plant. “They were irradiating plutonium in Unit 3, which experienced the biggest explosion,” he said. In fact, the explosion was so massive that investigators found fuel rod fragments a mile away, leading to speculation that a supercritical fission event may have also occurred, Alvarez said.

The article is referring to a study by Zheng et al. Here is my synopsis of the study’s findings:

A study released in Scientific Reports published by Nature titled ‘Isotopic evidence of plutonium release into the environment from the Fukushima DNPP accident’ by Zheng et al found that a wide array of highly volatile fission products were released, including 129mTe, 131I, 134Cs, 136Cs and 137Cs, which were all found to be ‘widely distributed in Fukushima and its adjacent prefectures in eastern Japan.’[i]

The study also found evidence of actinides, particularly Pu isotopes, on the ground northwest and south of the Fukushima DNPP in the 20–30 km zones. The study called for long-term investigation of Pu and 241Am dose estimates because of findings of ‘high activity ratio of 241Pu/239+240Pu (> 100) from the Fukushima DNPP accident.’

The study concluded that in comparison to Chernobyl, the Fukushima accident ‘had a slightly higher 241Pu/239Pu atom ratio, but lower ratio of 240Pu/239Pu.’ Unit 3 was seen as the likely source for the high Pu detections.

[i] J. Zheng, K. Tagami, Y. Watanabe, S. Uchida, T. Aono, N. Ishii, S. Yoshida, Y. Kubota, S. Fuma and S. Ihara (8 March 2012 ) ‘Isotopic Evidence of Plutonium Release into the Environment from the Fukushima DNPP Accident,’ Scientific Reports, 2, http://www.nature.com/srep/2012/120308/srep00304/full/srep00304.html.

http://majiasblog.blogspot.fr/2017/07/blast-from-past-plutonium-contamination.html