Nuclear and Chemical Waste Management最新文献

Enzymes offer inherent advantages and limitations as active components of formulations used to decontaminate soil and equipment contaminated with toxic materials such as pesticides. Because of the catalytic nature of enzymes, each molecule of enzyme has the potential to destroy countless molecules of a contaminating toxic compound. This degradation takes place under mild environmental conditions of pH, temperature, pressure, and solvent. The basic limitation of enzymes is their degree of stability during storage and application conditions. Stabilizing methods such as the use of additives, covalent crosslinking, covalent attachment, gel entrapment, and microencapsulation have been directed toward developing an enzyme preparation that is stable under extremes of pH, temperature, and exposure to organic solvents. Initial studies were conducted using the model enzymes subtilisin and horseradish peroxidase.

A coupled geochemical/geohydraulic model is used to discuss and interpret possible mechanisms for contaminant transport and accumulation in inorganic environments. The geochemical part of the code, the triple layer model for adsorption, allows one to estimate the variation of the contaminant distribution coefficient with solution composition. The hydraulic part of the model establishes a deterministic correlation of the spatial variation of the distribution coefficient. Scenarios are constructed incorporating computed system behavior. A comparison of potential contaminant concentrations with acceptable ones allows one to quantify the degree of geochemical isolation of the contaminant which a chosen environment provides. Long lived waste, activated in the thermal neutron flux of a light water reactor, is classified using the proposed methodology and a very conservative scenario: beryllium, lead, molybdenum, selenium, tin and zirconium activated in the bulk of the reactor decommissioning waste (the bioshield) might be sufficiently isolated by the chemistry in common soils. The concentration of nickel in oxidizing inorganic noncomplexing drinking water has an upper limit given by the precipitation of nickel minerals. Above pH = 7 is an effective geochemical barrier for nickel activated anywhere in the reactor, except the high neutron flux region.

Field chemical analyses were applied to an investigation of the Rockaway Borough well field, located in northwestern New Jersey, USA, and the designated sole-source glacial aquifer supplying the well field. The aquifer and the Borough water supply were found to be contaminated with up to 680 μg/L of tetrachlorethylene (PCE) and 172 μ/L of trichlorethylene (TCE) in 1980. The sources of the contaminants had not been identified in 1982 when the well field was placed on the United States Environmental Protection Agency National Priorities List of uncontrolled hazardous waste sites. A limited site investigation was conducted using on-site chemical analyses of groundwater samples and soil sample headspace gases. The investigation identified optimal monitoring well locations, provided cost-effective time series sampling data, and identified the locations of three potential contaminant sources.

Image analysis techniques were used to characterize the composition of waste-entrained concrete, and to provide quantitative data on the size, shape and location of each component in the samples. Multiple samples were analyzed to determine the degree of heterogeneity in the sample. Homogeneous samples were characterized by soils that occur in numerous, small isolated islands within the large, convoluted cement objects. Compressive strength is high because of the presence of hardened concrete framework. Porosity is restricted to nonsoil zones, lowering the probability of leaching by percolating fluids. The heterogeneous samples contain numerous cement islands within a soil matrix. Compressive strength is low because the load must be supported by the soil rather than the cement. Long fluid pathways, often in contact with the soil characterize these samples.