Publications

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The U.S. Department of Energy's (DOE) National Nuclear Security Administration (NNSA) established the Global Threat Reduction Initiative's (GTRI) mission to reduce and protect nuclear and radiological materials located at civilian sites worldwide. Internationally, over 80 countries are cooperating with GTRI to enhance security of facilities with these materials. In 2004, a GTRI delegation began working with the Tanzania Atomic Energy Commission, (TAEC). The team conducted site assessments for the physical protection of radiological materials in Tanzania. Today, GTRI and the Government of Tanzania continue cooperative efforts to enhance physical security at several radiological sites, including a central sealed-source storage facility, and sites in the cities of Arusha, Dar Es Salaam, and Tanga. This paper describes the scope of physical protection work, lessons learned, and plans for future cooperation between the GTRI program and the TAEC. Additionally the paper will review the cooperative efforts between TAEC and the International Atomic Energy Agency (IAEA) with regards to a remote monitoring system at a storage facility and to the repackaging of radioactive sources.

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Yucca Mountain has been designated as the nation's high-level radioactive waste repository, and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. The temperature and humidity inside the emplacement drift will affect the degradation rate of the waste packages and waste forms as well as the quantity of water available to transport dissolved radionuclides out of the waste canister. Thermal radiation and turbulent natural convection are the main modes of heat transfer inside the drift. This paper presents the result of three-dimensional computational fluid dynamics simulations of a segment of emplacement drift. The model contained the three main types of waste packages and was run at the time that the peak waste package temperatures are expected. Results show that thermal radiation is the dominant mode of heat transfer inside the drift. Natural convection affects the variation in surface temperature on the hot waste packages and can account for a large fraction of the heat transfer for the colder waste packages. The paper also presents the sensitivity of model results to uncertainties in several input parameters. The sensitivity study shows that the uncertainty in peak waste package temperatures due to in-drift parameters is <3 C.

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The objective of this heat transfer and fluid flow study is to assess the ability of a computational fluid dynamics (CFD) code to reproduce the experimental results, numerical simulation results, and heat transfer correlation equations developed in the literature for natural convection heat transfer within the annulus of horizontal concentric cylinders. In the literature, a variety of heat transfer expressions have been developed to compute average equivalent thermal conductivities. However, the expressions have been primarily developed for very small inner and outer cylinder radii and gap-widths. In this comparative study, interest is primarily focused on large gap widths (on the order of half meter or greater) and large radius ratios. From the steady-state CFD analysis it is found that the concentric cylinder models for the larger geometries compare favorably to the results of the Kuehn and Goldstein correlations in the Rayleigh number range of about 10{sup 5} to 10{sup 8} (a range that encompasses the laminar to turbulent transition). For Rayleigh numbers greater than 10{sup 8}, both numerical simulations and experimental data (from the literature) are consistent and result in slightly lower equivalent thermal conductivities than those obtained from the Kuehn and Goldstein correlations.

Sandia National Laboratories has sponsored an LDRD (Laboratory Directed Research and Development) project to investigate and develop micro-chemical sensors for in-situ monitoring of subsurface contaminants. As part of this project, a literature search has been conducted to survey available technologies and identify the most promising methods for sensing and monitoring subsurface contaminants of interest. Specific sensor technologies are categorized into several broad groups, and these groups are then evaluated for use in subsurface, long-term applications. This report introduces the background and specific scope of the problem being addressed by this LDRD project, and it provides a summary of the advantages and disadvantages of each sensor technology identified from the literature search.

The thermal-hydrologic (TH) and coupled process models describe the evolution of a potential geologic repository as heat is released from emplaced waste. The evolution (thermal, hydrologic, chemical, and mechanical) of the engineered barrier and geologic systems is heavily dependent on the heat released by the waste packages and how the heat is transferred from the emplaced wastes through the drifts and through the repository host rock. The essential elements of this process are extracted (or abstracted) from the process-level models that incorporate the basic energy and mass conservation principles and applied to the total system models used to describe the overall performance of the potential repository. The process of total system performance assessment (TSPA) abstraction is the following. First is a description of the parameter inputs used in the process-level models. A brief description is given hereof past inputs for the viability assessment (e.g., for TSPA-VA) and current inputs for the site recommendation (TSPA-SR). This is followed by a highlight of the process-level models from which the abstractions are made. These include descriptions of TH, thermal-hydrologic-chemical (THC), and thermal-mechanical (TM) processes used to describe the performance of individual waste packages and waste emplacement drifts as well as the repository as a whole. Next is a description of what (and how) information is abstracted from the process-level models. This also includes an accounting of the features, events, and processes (FEPs) that are important to both the regulators and the international repository community in general. Finally, an identification of the TSPA model components that utilize the abstracted information to characterize the overall performance of a potential geologic repository is given.