26 August 2005: Northern lights inspire Finnish nuclear waste disposal
Finnish researchers are using energy more typically found in lightening or the local Aurora Borealis to minimise the waste output from nuclear power stations.
Inventors at the Technical Research Centre of Finland (VTT) are piloting a new low-temperature plasma burning process to incinerate waste resin from nuclear power plant primary circuits. The new process could slash the volume of radioactive waste from nuclear power plants by over 90 per cent, they say.
Using a low-temperature plasma process is unusual compared with competing technologies, project leader Antero Tiitta told Chemistry World. 'Plasma is a state of matter where individual atoms are ionised,' said Tiitta. 'Lightning is an example of a phenomenon with plasma in nature.' Another example, he said, is aurora borealis, the northern lights, which results from plasma generated in the outer atmosphere, where it emits visible and ultraviolet light. Plasma contains neutral atoms and molecules in excited electronic states, which are chemically active. 'If plasma contains oxygen it can oxidise organic substances,' said Tiitta. 'Plasma burning generally means producing plasma in a confined space.'
Mixed ion exchange resin, which is used to purify power plant primary circuit water, is a chemically-active mixture of anionic and cationic resin. The resin collects dissolved, radioactive ions in the plant's water and replaces them with H+and OH-ions, which then recombine to give H2O.
'By catching dissolved ions from the water the resin becomes radioactive,' explained Tiitta. 'When the resin is saturated with the ions it has to be replaced and the spent resin becomes radioactive waste.'
Operators incinerate the resin waste using plasma in a low-pressure chamber, which keeps the process sufficiently cool. The new process could be commercially-available in five years.
The spent resin will not lose its radioactivity as a result of the new VTT process, but will be converted to ash. The ash is chemically more stable than resin and cannot generate gases -a potential problem in long-term resin storage. 'The annual production rate of spent radioactive resin depends on the reactor type and size, but may be 10-20 cubic metres,' Tiitta estimates. Since the cost of waste disposal is based on volume, the vastly smaller volume of ash resulting from the new process will offer economic benefits.
VTT and its partners resin manufacturer Finex Oy, and nuclear energy companies TVO and Fortum Generation will build a half-scale plasma burning process pilot plant at the VTT site in Espoo, Finland. The project aims to put a process plant inside a transport container to provide mobile incineration to a number of power plants. Similar units have been developed elsewhere to deal with radioactive caesium and cobalt.
The project has been funded by the National Technology Agency of Finland (Tekes) and is a spin off from the Finnish National Fusion Programme. Tiitta says there are also plans to collaborate with the Helsinki University of Technology. Helen Carmichael