John R. Cochran

A probabilistic model and software tool for evaluating the long-term performance of landfill covers

Abstract A probabilistic model and software tool has been developed to assist in the selection, design, and monitoring of long-term covers for contaminated subsurface sites. The software platform contains multiple modules that can be used to simulate relevant features, events, and processes that include water flux through the cover, source-term release, vadose-zone transport, saturated-zone transport, gas transport, and exposure pathways. The component models are integrated into a probabilistic total-system performance-assessment model within a drag-and-drop software platform. Uncertainty and sensitivity analyses can be conducted that yield the following primary benefits: (1) quantification of uncertainty in the simulated performance metrics; (2) identification of parameters most important to performance; and (3) comparison of alternative designs to optimize cost and performance. A case study has been performed using the Monticello Mill Tailings Site in Utah to illustrate the important features and benefits of the modeling approach and software.

Development of a Risk-Based Probabilistic Performance-Assessment Method for Long-Term Cover Systems - 2nd Edition

A probabilistic, risk-based performance-assessment methodology has been developed to assist designers, regulators, and stakeholders in the selection, design, and monitoring of long-term covers for contaminated subsurface sites. This report describes the method, the software tools that were developed, and an example that illustrates the probabilistic performance-assessment method using a repository site in Monticello, Utah. At the Monticello site, a long-term cover system is being used to isolate long-lived uranium mill tailings from the biosphere. Computer models were developed to simulate relevant features, events, and processes that include water flux through the cover, source-term release, vadose-zone transport, saturated-zone transport, gas transport, and exposure pathways. The component models were then integrated into a total-system performance-assessment model, and uncertainty distributions of important input parameters were constructed and sampled in a stochastic Monte Carlo analysis. Multiple realizations were simulated using the integrated model to produce cumulative distribution functions of the performance metrics, which were used to assess cover performance for both present- and long-term future conditions. Performance metrics for this study included the water percolation reaching the uranium mill tailings, radon gas flux at the surface, groundwater concentrations, and dose. Results from uncertainty analyses, sensitivity analyses, and alternative design comparisons are presented for each of the performance metrics. The benefits from this methodology include a quantification of uncertainty, the identification of parameters most important to performance (to prioritize site characterization and monitoring activities), and the ability to compare alternative designs using probabilistic evaluations of performance (for cost savings).

Radioactive Waste Management Challenges and Progress in Iraq

The government of Iraq, through the Ministry of Science and Technology (MoST) is decommissioning Iraq’s former nuclear facilities. The 18 former facilities at the Al-Tuwaitha Nuclear Research Center near Baghdad include partially destroyed research reactors, a fuel fabrication facility and radioisotope production facilities. These 18 former facilities contain large numbers of silos and drums of uncharacterized radioactive waste and approximately 30 tanks that contain or did contain uncharacterized liquid radioactive wastes. Other key sites outside of Al Tuwaitha include facilities at Jesira (uranium processing and waste storage facility), Rashdiya (centrifuge facility) and Tarmiya (enrichment plant). The newly created Radioactive Waste Treatment Management Directorate (RWTMD) within MoST is responsible for Iraq’s centralized management of radioactive waste, including safe and secure disposal. In addition to being responsible for the uncharacterized wastes at Al Tuwaitha, the RWTMD will be responsible for future decommissioning wastes, approximately 900 disused sealed radioactive sources, and unknown quantities of NORM wastes from oil production in Iraq. This paper presents the challenges and progress that the RWTMD has made in setting-up a radioactive waste management program. The progress includes the establishment of a staffing structure, staff, participation in international training, rehabilitation of portions of the former Radioactive Waste Treatment Station at Al-Tuwaitha and the acquisition of equipment.Copyright

Taiwan industrial cooperation program technology transfer for low-level radioactive waste final disposal - phase I.

Sandia National Laboratories and the Institute of Nuclear Energy Research, Taiwan have collaborated in a technology transfer program related to low-level radioactive waste (LLW) disposal in Taiwan. Phase I of this program included regulatory analysis of LLW final disposal, development of LLW disposal performance assessment capabilities, and preliminary performance assessments of two potential disposal sites. Performance objectives were based on regulations in Taiwan and comparisons to those in the United States. Probabilistic performance assessment models were constructed based on limited site data using software including GoldSim, BLT-MS, FEHM, and HELP. These software codes provided the probabilistic framework, container degradation, waste-form leaching, groundwater flow, radionuclide transport, and cover infiltration simulation capabilities in the performance assessment. Preliminary performance assessment analyses were conducted for a near-surface disposal system and a mined cavern disposal system at two representative sites in Taiwan. Results of example calculations indicate peak simulated concentrations to a receptor within a few hundred years of LLW disposal, primarily from highly soluble, non-sorbing radionuclides.