New Polymers Could Mop Up Radioactive Isotopes

Scientists from Germany and India say they have developed a new polymer that reduces the amount of radioactive waste produced during routine operation of nuclear reactors. The approach uses small beads of the material to "fish" out radioactivity from water pumped through the reactor’s core.

In pressurized-water reactors, the most common reactor, hot water circulates at high pressure through the steel pipes, dissolving metal ions from the walls of the pipes. When the water is pumped through the reactor’s core, these ions are bombarded by neutrons. Because the pipes are made of steel, most of the ions are common iron isotopes, which don’t become radioactive when bombarded by neutrons. But the steel in the pipes is usually alloyed with cobalt, and when this cobalt absorbs neutrons, an instable cobalt isotope emerges that is radioactive with a half-life of more than five years.

Usually the water is cleaned with ion exchangers. But this technique has a crucial disadvantage, because it doesn’t differentiate between nonradioactive iron ions and radioactive cobalt ions, say scientists Sevilimendu Narasimhan from the Bhabha Atomic Research Center in Kalpakkam, India, and Dr. Börje Sellergren from the German Institute of Environmental Research at Technische Universität Dortmund.

To overcome this problem, Sellergren and Narasimhan found a material that binds cobalt and not iron. They then developed a special polymer made in a cobalt-containing environment. The polymer undergoes a procedure called "molecular imprinting" — the cobalt-ions are extracted with hydrochloric acid, meaning that they are virtually washed out. The resulting cobalt-sized holes — the imprinting — are able to trap just the cobalt in other environments. The result, according to the scientists: A small amount of this polymer can mop up a large amount of radioactive isotopes.

The team is now forming the polymer into small beads that can pass through the cooling system of a nuclear-power station. They expect that it would be more economical and environment-friendly to concentrate radioactivity into such beads than to dispose of large amounts of low-level waste.

—Sonal Patel is POWER’s senior writer.