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Staff Accomplishments

Hanford's younger tanks get a physical as new activities considered

July 2006
Sophisticated simulations and analyses show how nuclear waste tanks handle earthquakes and other stresses Engineers at Pacific Northwest National Laboratory completed a state-of-the-art study of the fitness of the underground double-shell tanks on the Hanford Site. The radioactive waste in these tanks will be removed and converted to a solid form that can be safely stored for thousands of years. To treat the waste, these tanks need to remain operational. Using computer modeling and extensive knowledge of the tanks, PNNL and M&D Professional Services Inc. conducted a three-year comprehensive analysis showing how the tanks would react to different situations, from earthquakes shaking the tanks to heat changes degrading the concrete. Taking a history of the tanks To conduct a complete evaluation of the tanks, the team gathered data on the double-shell tank designs. Located in southeastern Washington State, the double-shell tanks were built in the late 1960s through the mid-1980s and have a primary tank and a second steel wall, enveloped in concrete. The second wall gives them an extra level of containment, in case something happens to the primary tank. In addition, to evaluate how the tanks would perform compared to today's standards, the team gathered information on current engineering design codes and standards, including information from the International Building Code, American Society of Mechanical Engineers and the American Concrete Institute. Shaking up the tanks The engineers, computer modelers, and other researchers analyzed how the double-shell tanks would respond to an earthquake. Using the commercial modeling and simulation software ANSYSTM, the team used detailed models for the simulations. Some of the more complex simulations required weeks to complete. The team analyzed what would happen to the concrete and steel tank during and after an earthquake. The team analyzed key structural locations, such as where the tank steel wall meets the tank floor, and considered the behavior of the surrounding soil. In addition, the team looked at the response of the waste inside the tank. What would happen to the tank when nearly a million gallons of waste moved around inside? Tanks can take the heat PNNL also studied how the steel and concrete handled changes in temperature. "The waste in many of the tanks has generally been the temperature of warm bath water. A few of the tanks see higher temperatures, perhaps 250 degrees Fahrenheit," said project manager Mike Rinker from PNNL. The temperature of the surrounding soil varies, depending on the weather. Of special interest were the seams, where steel plates were welded together and then heat treated during construction. The concrete was also evaluated, as temperature swings can degrade concrete. The seismic and thermal studies show that the tanks will still be intact for the next 20-plus years. The structural integrity of the tank will be maintained during an earthquake. This work was prepared under the direction of CH2M HILL Hanford Group Inc. and was reviewed by nationally recognized experts in buried concrete and steel containment structures as well as seismic experts. These analyses were part of the required documentation sent to the Washington State Department of Ecology to demonstrate that the tanks are qualified for continued use. Contact: Terry Walton, Environmental Solutions Lead

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