Lasers Tackle Radioactive Concrete
ARGONNE, Ill. -- What do you do when you have terminated nuclear power, research and weapons development but still have radioactive buildings hanging around? That's the problem facing the US Department of Energy (DoE) as it decommissions its former nuclear installations. Researchers at Argonne National Laboratory are investigating a possible solution -- using pulsed lasers to ablate contaminated concrete.
The department's installations include concrete structures about a foot thick. Only a 1/8- to 1/7-inch-thick layer on the surface of the walls and floors is actually radioactive, however. Rather than demolition, which would produce tons of radioactive waste, the preferred approach is to separate the contaminated material.
Researchers at Argonne National Laboratory are investigating ablation of radioactive concrete with pulsed Nd:YAG lasers. Called scabbling, the process removes only the contaminated surface layer of the concrete for proper disposal.
This is done mechanically, explained Michael Savina, the lead researcher in the effort, which is funded by the DoE's environmental management science program and the division of materials science in its Office of Basic Energy Science. Workers employ scabblers, arrays of pneumatically or hydraulically driven pins that act like tiny jackhammers, to break up the concrete surface. The radioactive debris is then vacuumed up for proper disposal.
Mechanical scabbling has several shortcomings, however. The machines are heavy and vibrate a lot, which is hard on the operators. Moreover, they don't work well on cracked concrete or in tight spots.
Although the researchers have not worked with contaminated concrete, their initial findings, reported in the October 2000 issue of the Journal of Laser Applications, indicate that pulsed lasers are efficient at ablating concrete. They employed a 1.6-kW Nd:YAG operating at the 1064-nm fundamental wavelength for the tests. It produced 0.5- to 1.0-ms pulses at a repetition rate of up to 800 Hz, and a 10-m-long optical fiber delivered the output to the concrete samples.
Savina said the method could find a role in scabbling problem areas, such as cracked and irregular surfaces. "Right now, the laser isn't competitive, but that's primarily because the worst decontamination problems have yet to be addressed, because the technology isn't available to handle them."
The group would like to investigate the use of high-power diode lasers and to test a laser ablation system for civilian applications. "The environmental management science program would like to see a commercial company team up with us to develop a prototype," Savina said.
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