Well, it sure looked pretty, a field of sunflowers, but if the Ministry of Agriculture, Forestry and Fisheries is to be believed, it did not do much more than looking pretty, and creating radioactive sunflowers that'll have to be somehow safety disposed as nuclear waste.
Sunflower seeds were planted in many, many areas within the 20-kilometer radius exclusion zone. Who is going to dispose these nuclear waste, and how?
From Asahi Shinbun (9/14/2011):
The Ministry of Agriculture, Forestry and Fisheries announced the result of its study in Fukushima Prefecture on the effectiveness of various method of decontamination of the farmland that have been contaminated with radioactive materials. While it was confirmed that scraping off the surface soil was effective, planting sunflowers to absorb radioactive cesium proved to be hardly effective at all.
The Ministry has been experimenting on the decontamination methods since late May, using 6 locations in Iitate-mura and Kawamata-machi, which are close to Fukushima I Nuclear Power Plant.
Of different methods to scrape off the surface soil, the most effective was scraping about 3 centimeters with the shallow-rooted grass. This method decreased radioactive cesium by 97%. Scraping the soil alone about 4 centimeters achieved 75% reduction. If the surface soil was treated with solidifying agent before being scraped, the reduction was 82%.
Filling the rice paddies with water, then tilling and stirring the soil and draining the water reduced radioactive cesium by 36%. Digging the field 30 to 60 centimeter deep and burying the surface soil was also effective in reducing the radiation level in half.
On the other hand, the amount of cesium that sunflowers absorbed from the soil was only one-2000th of the density of radioactive cesium in the soil. The Ministry concluded that "there is no other candidate that has higher absorption ratio. Practically speaking, sunflowers are not effective in decontamination".
Based on the result, the Ministry disclosed its ideas of decontamination based on the density of radioactive materials in the soil.
The farmland whose radioactive materials in the soil would exceed 5,000 becquerels/kg (limit above which the planting of rice is prohibited) is estimated to be 8,300 hectares [about 20,500 acres]. From the result of the experiments, in case of the farmland whose radioactive material density exceeds 10,000 becquerels/kg, it may be difficult to reduce the level down below 5,000 becquerels/kg unless the surface soil is removed. Between 5,000 and 10,000 becquerels/kg, there may not be other choices but removing the surface soil.
If the surface soil is removed in 8,300 hectares, the amount of contaminated soil generated would exceed 3 million tonnes. The Ministry says it hopes to develop a technology to remove cesium from the soil so that the soil can be put back in the field. (reported by Keiichiro Inoue)
What about plutonium and strontium? Cobalt-60?
Isn't removing the surface soil what Russia/Ukraine/Beralus have done and to very little effect? The fresh supply of radioactive cesium and other nuclides come down from the mountains. What about decontaminating the mountains?
I wouldn't call Iitate-mura and Kawamata-machi "close to Fukushima I Nuclear Power Plant". They are more than 35 kilometers away. The reporter should have said "close enough for the government researchers to go anywhere near the plant".
By the way, as one refugee from Iitate-mura strongly hints in his tweets, Iitate-mura's political leaders seem in excellent terms with the national government and government-connected contractors keen on getting "decon" jobs. After all, 200 billion yen (US$2.6 billion) is to be spent on this village of 6,000 people alone so that the villagers can come home in 2 years.