Polymer beads mean greener nuclear power

With 40 nuclear-power stations being built and 70 more predicted in the next 15 years, nuclear power is fast becoming the fuel of choice prompting scientists to find ways of reducing radioactive waste – one team’s answer – a ‘fishing’ polymer bead.

Börje Sellergren from the Institute of Environmental Research at Techniche Universität Dortmund – working with Sevilemendu Narasimhan from Bhabha Atomic Research Centre in Kalpakkan India - has created a small bead consisting of a special polymer which fishes radioactivity from contaminated waste water.

The waste water contains a radioactive isotope of cobalt – cobalt-60. In pressurised-water reactors – the most common type of reactor – hot water circulates at high pressure through steel pipes and dissolves iron and cobalt metal ions from the pipe walls. In the reactor core, these are bombarded with neutrons to become non-radioactive iron-56 and cobalt-60, which has a half life of more than five years.  The water is usually cleaned with ion exchangers, but this fails to differentiate between the iron and cobalt ions.

“The idea of imprinting metal ions is not new but rather the application to use an ion-selective polymer for concentrating radioactive isotopes,” Sellergren said, “The polymer was synthesised using a polymerisable iminodiacetic acid monomer as a ligand capable of complexing Co(II) in the form of a 1:2 metal-ligand complex. In principle the ligand is half of an EDTA molecule where the imprinting step essentially leads to recreation of the EDTA chelator but with an optimised geometry.”

Sellergren’s polymer is made through a procedure called molecular imprinting in an environment containing cobalt. This cobalt can be extracted using hydrochloric acid, and the resulting holes mean that cobalt from other environments, like the cooling water, can be trapped.  A small amount of this new polymer will be able to mop up large amount of radioactive isotopes.

The team are now working on forming the polymer into small beads that can pass through the cooling system of nuclear-power stations. They expect it to be more economical and environmentally friendly to concentrate the radioactivity into small beads rather than dispose of large amounts of low level waste.

Cobalt-60 can be dangerous to humans and other mammals – although most ingested cobalt is excreted in the faeces, a small amount can be absorbed by the liver, kidney and bones where prolonged exposure to its gamma radiation can cause cancer.