Nuclear-waste monitoring gets close to the source

From New Orleans, at a meeting of the American Chemical Society

Some forms of nuclear radiation–such as the beta-emission from radioactive technetium-99–are particularly difficult to detect underground, partly because the radiation doesn’t travel very far. A new prototype instrument may make this and other elements easier to trace in groundwater.

Technitium-99 is produced during nuclear-reactor operation and nuclear-weapons production. It has a half-life of 212,000 years, and once it finds its way into groundwater it moves quickly, says analytical chemist Oleg Egorov of the Pacific Northwest National Laboratory in Richland, Wash. For these reasons, this isotope needs to be carefully monitored in places such as the Hanford Site, near Richland, where nuclear weapon materials were produced from the 1940s to the 1980s.

Currently, researchers take groundwater samples from Hanford wells to a lab for a tedious analysis. If the water could be monitored by small detectors left inside the wells, analyses would be cheaper and quicker. Also, the containers now used to transport the well-water samples have to be treated as hazardous waste themselves, an issue that would disappear with in-well monitoring, says Egorov. “Our goal is something that you can take into the field and leave there,” he says.

Egorov and his coworkers have taken a step in that direction by building a prototype detector that monitors technitium-99 concentrations. The apparatus is roughly 1 meter long and contains a column packed with an absorbent material and so-called scintillation beads. When water tainted with technetium-99 passes through the column, the isotope gets trapped by the absorbent material. Then the emitted beta-particles–high-speed electrons–hit the scintillation beads, which respond by emitting light that’s picked up by sensors at either end of the column. The data can be transmitted to a computer as far as several miles away, says Egorov.

The researchers have proven the detector’s effectiveness in laboratory tests. They now plan to make their system more rugged so they can deploy it in a Hanford well by the end of next year.


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