Browsing by Subject "Low-level radioactive waste"
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Item Modeling steel corrosion failure in reinforced concrete canisters (RMCCs) containing low-level radioactive waste (LLRW)(2016-05) Sablan, Gregory Anthony; Schneider, Erich A.; Landsberger, SheldonThe disposal of radioactive waste of all types and levels is of great concern today. Radioactive waste disposal itself is not new—procedures for its handling, safeguards, regulation, and implementation from the creation of waste to its final disposition continue to develop. Technologies spanning the last six decades enable the storage of hazardous materials over the long-term. Long-term disposal in the United States however, only applies to Low-Level Radioactive Waste (LLRW). Currently, legislation does not permit the final disposal of any other types of waste. Because LLRW is the only form of radioactive waste that is disposed of today, the precautions and conditions for setting it to its “final resting place” are important matters. At the Federal Waste Disposal Facility located in Andrews, Texas, LLRW is stored in what are called Reinforced Modular Concrete Containers (RMCCs) and are intended for final disposal deep underground. These RMCCs are initially checked for structural integrity to handle significant loading. While these RMCCs are designed to remain structurally sound under these loads, these concrete structures are susceptible to corrosion because of its steel reinforcement. When corrosion at the steel occurs, the RMCC will inevitably fail. The service life of the RMCC studied is calculated to be at least 300 years under ideal conditions. However, the design does not inherently consider the effects of corrosive elements that may be present in LLRW. This thesis provides a predictive model of the service life of the RMCC under the failure mechanism of steel corrosion by chlorides. Chloride concentrations in the LLRW will eventually make contact with the RMCC’s walls and will diffuse through concrete’s relatively porous network. Varying the mix designs between different cementitious materials, its water-to-cement (w/c) ratio, temperatures, and chloride exposure are critical to maintaining the RMCC’s service life. It shows that less supplementary cementitious materials, a higher w/c ratio, higher temperatures, and higher chloride concentrations lower the container’s time to failure. This information is critical to subcontractor construction of the RMCCs and confirms its suitability for long-term disposal of LLRW.Item Novel approaches in determining baseline information on annual disposal rates and trace element content of U.S. coal combustion residues : a response to EPA’s June 2010 proposed disposal rule(2010-12) Chwialkowski, Natalia Ewa; Groat, Charles G.; Grimshaw, Thomas W.; Kyle, RichardAlthough products of coal combustion (PCCs) such as coal ash are currently exempted from classification as a hazardous waste in the United States under the 1976 Resource Conservation and Recovery Act (RCRA), the U.S. Environmental Protection Agency (EPA) is now revising a proposed rule to modify disposal practices for these materials in order to prevent contamination of ground- and surface water sources by leached trace elements. This paper analyzes several aspects of EPA’s scientific reasoning for instating the rule, with the intent of answering the following questions: 1) Are EPA’s cited values for PCC production and disposal accurate estimates of annual totals?; 2) In what ways can EPA’s leaching risk modeling assessment be improved?; 3) What is the total quantity of trace elements contained within all PCCs disposed annually?; and 4) What would be the potential costs and feasibility of reclassifying PCCs not under RCRA, but under existing NRC regulations as low-level radioactive waste (LLRW)? Among the results of my calculations, I found that although EPA estimates for annual PCC disposal are 20% larger than industry statistics, these latter values appear to be closer to reality. Second, EPA appears to have significantly underestimated historical PCC disposal: my projections indicate that EPA’s maximum estimate for the quantity of fly ash landfilled within the past 90 years was likely met by production in the last 30 years alone, if not less. Finally, my analysis indicates that while PCCs may potentially meet the criteria for reclassification as low-level radioactive waste by NRC, the cost of such regulation would be many times that of the EPA June proposed disposal rule ($220-302 billion for PCCs disposed in 2008 alone, versus $1.47 billion per year for the Subtitle C option and $236-587 million for Subtitle D regulatory options).