Decontamination of select infrastructure materials after a radiological incident using a water-based formulation

Penetration of fission product ions into complex solids and the effect of ionic wash methods

During washing of radiologically impacted building surfaces, penetration of radionuclide ions into complex solids associated with these surfaces may occur. This study investigates the penetration of 137Cs, 85Sr, and 152Eu solutions into numerous common building materials and radionuclide behavior when these materials were exposed to a static bath or low-pressure flow of tap water, 0.1 M potassium chloride (KCl), and 0.5 M KCl. The decontamination efficacy and the depth profile for residual contamination were measured to determine the conditions under which applying a wash solution has benefit compared to physically removing the surface material. On asphalt, 70-80% of the radionuclides were found to be within 0.02 mm of the surface. Concrete is more porous than asphalt, and 80% of the radionuclides were within 0.2 mm of the surface for 137Cs and 152Eu and 50-80% for 85Sr. Water effectively removed all contaminants from hard nonporous surfaces. Finally, this paper illustrates that a wash penalty factor concept-defined as ratio of the depth at which 50% of the radioactivity is found in the washed sample divided by the depth at which 50% of radioactivity is found in the control-can serve as a way to quantify whether the wash method increases the depth at which contamination penetrates into the material and thus the material becomes more difficult to decontaminate.

Large area decontamination after a radiological incident

Effective decontamination of large-scale areas such as roads and parking lots after an accidental or intentional radiological incident is important in order to contain the spread of contamination and avoid the need for long-term evacuation of urban areas. As a simulation, large coupons (surface area 3600 cm²) made of concrete patio stone and aged asphalt (from a parking lot) were contaminated with either ⁶⁰Co or ¹³⁷Cs solutions and then decontaminated. The decontamination process consisted of a six-component water-based chemical formulation applied using a common house-hold carpet cleaner. Tests were carried out to compare the effectiveness of decontamination using deionized water (simulating rain fall) and chemical formulation. Test results showed that rain fall prior to decontamination lowered the effectiveness of a subsequent decontamination regardless of the surface type or radionuclide. Tests were also carried out to determine if the decontamination effectiveness increased with multiple applications. Using multiple applications of the chemical formulation, the removal of ⁶⁰Co from concrete patio stone and aged asphalt were 65 ± 2% and 70 ± 3%, respectively, while the removal of ¹³⁷Cs was 53 ± 3% from asphalt surfaces and 21 ± 8% from concrete patio stone. This paper summarizes the work carried out to prepare for the tests, presents the test results and compares the process to several other processes in terms of effectiveness and suitability for application on a large scale.