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Hunkering Down with Radioactive Waste

New "gamma bunker" helps advance cleanup efforts at the Hanford Site

December 2015
Hunkering Down with Radioactive Waste
PNNL's "gamma bunker" (shown above without its radioactive source) is a unique capability at the Lab for producing very high-dose, long-term exposures for radiation studies.

A new tool for producing irradiated samples promises to tell researchers more about waste behavior during cleanup activities at the Hanford Site near Richland, Wash. The tool—known as an irradiator in the industry and dubbed the "gamma bunker" by the PNNL team that built it—consists of a lead-shielded cask with a radioactive source (1,760 curie cobalt-60) centered in the cavity. Researchers can arrange samples in different ways around the source depending on the desired exposure and dose and the shape of the test specimens.

A research team led by PNNL's Sam Bryan plans to use the bunker to study how radioactive waste from the Hanford Site tank farms will behave during cleanup operations at the Hanford Waste Treatment and Immobilization Plant (WTP). The study, for site contractor Washington River Protection Solutions (WRPS), will focus on hydrogen generation in the WTP ion exchange columns. Material in these columns separates the radioactive constituent cesium-137 from the waste stream for further treatment.

There is concern that, during WTP operations, exposure to radioactive constituents (cesium-137, in this case) could cause hydrogen to build up to a point where it becomes flammable. Using simulated waste samples—irradiated in the gamma bunker to the specific levels expected in the columns—the team will test the effects of exposure on hydrogen generation in the columns. Data from this testing could help to ensure safe design and operations at the WTP.

The gamma bunker is partially completed and should be commissioned in January in time to start the tests.

While PNNL has several different irradiators, PNNL's Jim Hilliard, project lead for the gamma bunker, is quick to point out that this unique capability at the Lab has broad usefulness far beyond this specific study. The gamma bunker specifically targets very high-dose, long-term radiation exposures, like those needed for the WRPS study, and it can be configured for many different types of samples and applications.

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