French soil decontamination tested in Fukushima

A demonstration test of a process to decontaminate radioactive soil was successfully carried out last November in Japan's Fukushima Prefecture, France's Alternative Energies and Atomic Energy Commission announced on 11 April. The technology was developed by CEA, Orano and Veolia.

A demonstration test of a process to decontaminate radioactive soil was successfully carried out last November in Japan's Fukushima Prefecture, France's Alternative Energies and Atomic Energy Commission (CEA) announced on 11 April. The technology was developed by CEA, Orano and Veolia.

Collection of the froth containing the caesium attached to the clay particles during testing in Fukushima (Image: J-L Sida/CEA)

France launched the Demeterres project in 2013 to develop bio- and eco-technological methods for the decontamination of soil and effluents in support of a strategy for post-accident rehabilitation. The EUR19 million (USD23 million), five-year project involves CEA, Orano, Veolia, the Institute for Radiological Protection and Nuclear Safety (IRSN), the National Institute for Agricultural Research (INRA), and the French Agricultural Research Centre for International Development (CIRAD) as partners.

One of the physiochemical processes developed within the framework of the Demeterres project by CEA, Orano and Veolia uses particulate flotation foams. The process involves mixing contaminated soil with water to form a suspension. This mixture is then introduced into the middle of a flotation column, with air injected into the bottom of the column to produce bubbles. The caesium-contaminated soil particles attach to the surface of the air bubbles, which float to the surface, while the non-contaminated particles sink to the bottom of the column.

The process was first tested in 2016 in a pilot column at CEA's Marcoule site using various non-contaminated soils. These tests served to collect date relating to the functioning of the process.

Some 22 million cubic meters of radioactive soil was removed from the surface of the ground in Fukushima Prefecture, Japan, following the March 2011 accident at the Fukushima Daiichi nuclear power plant. This was to make areas accessible to residents as soon as possible. The contaminated soil has been stored in giant bags at a number of dedicated storage sites. The Japanese authorities are seeking the best technology to reduce or remove the radioactivity from the soil.

In April 2017, the froth flotation technology was proposed within the framework of a call for projects for the demonstration of decontamination techniques launched by Japan's Ministry of the Environment. Last July, the process was one of ten technologies selected for on-site demonstration out of a total 19 put forward.

The technology was tested on several hundred kilograms of contaminated soil between 13-17 November at the municipality of Okuma in Fukushima Prefecture, which houses a storage facility for contaminated soil. On most of the soil tested, 70-80% of the fine particles previously released through agitation in water were separated by flotation. The radioactivity of this soil was reduced to 33-50% of the initial amount. In order to increase the amount of caesium extracted, changes in the way the soil is prepared - such as drying, crumbling, pre-sifting and dispersion in water - have been proposed.

"If the technology presented is selected by the Japanese authorities, the next stage will be to develop the process on a larger scale so that it can be used in the Japanese municipalities that house storage centres," CEA said.

Researched and written
by World Nuclear News