Nuclear safetyA New Way to Remove Contaminants from Nuclear Wastewater
Nuclear power continues to expand globally, propelled, in part, by the fact that it produces few greenhouse gas emissions while providing steady power output. But along with that expansion comes an increased need for dealing with the large volumes of water used for cooling these plants, which becomes contaminated with radioactive isotopes that require special long-term disposal. New method concentrates radionuclides in a small portion of a nuclear plant’s wastewater, allowing the rest to be recycled.
Nuclear power continues to expand globally, propelled, in part, by the fact that it produces few greenhouse gas emissions while providing steady power output. But along with that expansion comes an increased need for dealing with the large volumes of water used for cooling these plants, which becomes contaminated with radioactive isotopes that require special long-term disposal.
Now, a method developed at MIT provides a way of substantially reducing the volume of contaminated water that needs to be disposed of, instead concentrating the contaminants and allowing the rest of the water to be recycled through the plant’s cooling system. The proposed system is described in the journal Environmental Science and Technology, in a paper by graduate student Mohammad Alkhadra, professor of chemical engineering Martin Bazant, and three others.
The method makes use of a process called shock electrodialysis, which uses an electric field to generate a deionization shockwave in the water. The shockwave pushes the electrically charged particles, or ions, to one side of a tube filled with charged porous material, so that concentrated stream of contaminants can be separated out from the rest of the water. The group discovered that two radionuclide contaminants — isotopes of cobalt and cesium — can be selectively removed from water that also contains boric acid and lithium. After the water stream is cleansed of its cobalt and cesium contaminants, it can be reused in the reactor.
The shock electrodialysis process was initially developed by Bazant and his co-workers as a general method of removing salt from water, as demonstrated in their first scalable prototype four years ago. Now, the team has focused on this more specific application, which could help improve the economics and environmental impact of working nuclear power plants. In ongoing research, they are also continuing to develop a system for removing other contaminants, including lead, from drinking water.
Not only is the new system inexpensive and scalable to large sizes, but in principle it also can deal with a wide range of contaminants, Bazant says. “It’s a single device that can perform a whole range of separations for any specific application,” he says.
In their earlier desalination work, the researchers used measurements of the water’s electrical conductivity to determine how much salt was removed. In the years since then, the team has developed other methods for detecting and quantifying the details of what’s in the concentrated radioactive waste and the cleaned water.
