Developing Surrogate Far-Field Nuclear Fallout and its Rapid Decontamination from Aircraft Surfaces
Naval aircraft and vehicles deployed in response to the tsunami of 2011 and subsequent nuclear meltdown at the Fukushima Daiichi nuclear power station were exposed to and contaminated with radioactive materials released to the atmosphere. In response, the Navy and Argonne National Laboratory are testing various decontamination methods to clean aircraft surfaces exposed to far-field nuclear fallout. Far-field fallout, which can travel hundreds of miles, includes dissolved radionuclides and fine particulate matter. To simulate contamination with such materials, dissolved cesium-137 ( 137 Cs) and radiolabeled particles were deposited on coupons (1 x 1 in. sections) of tire, acrylic, and painted metal surfaces. These coupons were subjected to six different decontamination methods, including ones involving four strippable products, a soap solution, and tap water. Removals of dissolved 137 Cs were generally high: over 90% of the deposited radionuclide was removed after three decontaminations. To simulate exposure to inert, radioactive fallout or other inert, airborne particulate, silica (SiO 2 ) particles were used as surrogate fine particulate matter. The silica particles were radio-labeled by first depositing europium-152 ( 152 Eu) or americium-241 ( 241 Am) on the particle surface as sesquioxides (Eu 2 O 3 or Am 2 O 3 ), then coating it with sodium silicate. Scanning electron microscopy confirmed that particle size was not altered by the treatment, while leaching studies into numerous solutions and decontamination agents confirmed that minimal amounts of the radiolabel dissolved into solution. Three different methods to apply the radioactive particles to the silica were evaluated. Pressing the coupons into a dish containing the particles resulted in particle clumping on the surface, while applying the particles within water also resulted in heterogeneous surface coverage. Suspending the particles in ethanol and then applying them to the surface supplied homogeneous surface coverage that provided acute and precise removal percentages. Finally, particle-surface interactions seemingly play an important role in radiological decontamination as the removal percentages were lower than those of soluble 137 Cs for aqueous decontamination methods. These decreased removal percentages indicate that more complex methods such as strippable decontamination agents are required to remove particulate far-field fallout from aircraft and similar vehicle surfaces.