Measurement of Gas Bubbles Encased in Bitumen Nuclear Waste Drums with Muon Scattering Tomography - 18237

In some countries low and intermediate level nuclear waste is stored in steel containers with either pure bitumen added to fill the free volume, or after mixing of the waste with bitumen. Oxidation of the bitumen by interacting with the nuclear waste results in the production of hydrogen. Since pure bitumen is impermeable to water and gases, this hydrogen can assemble in bubbles, possibly resulting in bitumen overflowing out of the waste containers. It is necessary to develop ways of measuring the gas bubbles present in nuclear waste without intervening and compromising the container. We show that this can be done using muon scattering tomography, by applying an analysis method, first developed to find high-Z materials in a lower Z background of concrete, to data from a low-Z material in a higher Z background. The performance of this method is shown, by implementing it on Monte Carlo simulation data. A resolution on the total gas volume of 1.6±0.8% has been achieved for bubbles of 2 liters or more. It is also shown that the method can determine if the gas is located in separate bubbles or concentrated in a bigger one. (authors)