Citation:

Jolin, W., M. Magnuson, AND M. Kaminski. High Pressure Decontamination of Building Materials During Radiological Incident Recovery. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY. Elsevier Science Ltd, New York, NY, 208-209:105858, (2019). https://doi.org/10.1016/j.jenvrad.2018.12.001

Impact/Purpose:

High pressure decontamination of certain surface building materials is concluded to be a promising rapid, readily available response technique, with the data from this study informing its practical implementation. Removal efficacy of radionuclides from concrete are high when performed systematically and thoroughly at low rates of moving across the surface. Ablating the concrete surface was the dominant removal mechanism and care should be taken in such a process to balance two factors. First, performing the decontamination insufficiently by removing too little of the surface (as seen at higher rates through the spray path) decreased removals and may hinder final decontamination by forcing radionuclides into surface. However, excess exposure of the surface to high pressure spray may cause aesthetic or even structural damage. As such, an automated system could be developed to move the sprayer at the low speed where was removal most effective (5 mm/s or ~1 ft/min) and avoid damage to the surface. In contrast, removals from asphalt were the result of both chemical and physical mechanisms. These mechanisms, coupled with the low penetration of the radionuclides into asphalt and the small amount of material removed from the surface, indicate that a quicker, lower pressure, decontamination is feasible and either pressure washing or washing with tap water can be effective with minimal risk of driving the radionuclide deeper into the surface. Such a realization has important practical implications, as only a minor decrease in the decontamination results would be expected using lower pressure application approaches and tap water. One such approach is through fire hosing, which is a ubiquitous capability. Another approach is use of pressurized street sweepers. Further, the addition of chemical removal agents (salts and surfactants) would increase effectiveness, making low pressure systems more suitable and comparable to high pressure washing, as higher application rates would be possible with less aerosol production. Finally, the low removals from brick indicate that high pressure decontamination may be insufficient and further investigation is required to identify a proper decontamination technique. Also of practical importance is that we can also extend our results to other radionuclides of potential interest. For instance, Eu-152 was a surrogate for other lanthanides and Am-241[24], indicating that high pressure decontamination is a viable method to remove those radionuclides and others that deposit near the surface. Further, other radionuclides with high affinity for mineral phases, e.g., Cs-134 and Ru-86, may be also removed effectively (> 50% removal on the first pass on concrete and brick) from the surface by high pressure spray and are bound to particles in solution. In contrast, radionuclides with low affinity for the surface such as, Sr-90, Co-60, and Na-24 may penetrate deep into the surface and require other decontamination means such as scabbling or grinding. A third finding of practical importance concluded by this study is that treatment of wash water containing these radionuclides should focus on removal of particles for Eu-152 and Cs-137 as the radionuclides are bound to particulates in the wash water. By contrast, treatment of water containing Sr-85 (or similar ions) should focus on sequestering the dissolved species. As discussed elsewhere [23], the treatment of radiologically contaminated water resulting from decontamination is an important part of the overall process and benefits from being integrated with the choice of decontamination approaches, including any chemical additives for specific radionuclides.

Description:

High pressure decontamination of certain surface building materials is concluded to be a promising rapid, readily available response technique, with the data from this study informing its practical implementation. Removal efficacy of radionuclides from concrete are high when performed systematically and thoroughly at low rates of moving across the surface. Ablating the concrete surface was the dominant removal mechanism and care should be taken in such a process to balance two factors. First, performing the decontamination insufficiently by removing too little of the surface (as seen at higher rates through the spray path) decreased removals and may hinder final decontamination by forcing radionuclides into surface. However, excess exposure of the surface to high pressure spray may cause aesthetic or even structural damage. As such, an automated system could be developed to move the sprayer at the low speed where was removal most effective (5 mm/s or ~1 ft/min) and avoid damage to the surface. In contrast, removals from asphalt were the result of both chemical and physical mechanisms. These mechanisms, coupled with the low penetration of the radionuclides into asphalt and the small amount of material removed from the surface, indicate that a quicker, lower pressure, decontamination is feasible and either pressure washing or washing with tap water can be effective with minimal risk of driving the radionuclide deeper into the surface. Such a realization has important practical implications, as only a minor decrease in the decontamination results would be expected using lower pressure application approaches and tap water. One such approach is through fire hosing, which is a ubiquitous capability. Another approach is use of pressurized street sweepers. Further, the addition of chemical removal agents (salts and surfactants) would increase effectiveness, making low pressure systems more suitable and comparable to high pressure washing, as higher application rates would be possible with less aerosol production. Finally, the low removals from brick indicate that high pressure decontamination may be insufficient and further investigation is required to identify a proper decontamination technique. Also of practical importance is that we can also extend our results to other radionuclides of potential interest. For instance, Eu-152 was a surrogate for other lanthanides and Am-241[24], indicating that high pressure decontamination is a viable method to remove those radionuclides and others that deposit near the surface. Further, other radionuclides with high affinity for mineral phases, e.g., Cs-134 and Ru-86, may be also removed effectively (> 50% removal on the first pass on concrete and brick) from the surface by high pressure spray and are bound to particles in solution. In contrast, radionuclides with low affinity for the surface such as, Sr-90, Co-60, and Na-24 may penetrate deep into the surface and require other decontamination means such as scabbling or grinding. A third finding of practical importance concluded by this study is that treatment of wash water containing these radionuclides should focus on removal of particles for Eu-152 and Cs-137 as the radionuclides are bound to particulates in the wash water. By contrast, treatment of water containing Sr-85 (or similar ions) should focus on sequestering the dissolved species. As discussed elsewhere [23], the treatment of radiologically contaminated water resulting from decontamination is an important part of the overall process and benefits from being integrated with the choice of decontamination approaches, including any chemical additives for specific radionuclides.

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