Project report (M. Eng.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (80-81). Also available via the Internet.

This thesis examines the practical engineering problems associated with high-activity radioactive waste disposal. It includes a critical review of all the available disposal options, but focuses on concepts involving deep underground burial in purpose-built repositories. The construction and waste containment properties of crystalline, argillaceous and saliferous host rocks are examined and some inherent uncertainties in predicting their performance as natural barriers to radionuclide migration are described. It is shown that repository construction can introduce anomalous migration paths via peripheral zones of disturbance, rock/backfill separation planes and structural linings unless special preventative measures are taken. For jointed rock masses, it is shown that repository excavations may short-circuit natural flow paths. Repository design proposals from the major nuclear power-producing countries are reviewed, with particular emphasis on crystalline rock repository systems. It is shown that although the international proposals demonstrate the broad feasibility of repository construction, they generally fail to achieve optimum solutions in terms of waste containment. For jointed rocks, an optimisation study is described which demonstrates how adjustment of pre-disposal strategies for conditioning high-level wastes, altering the construction sequence, and manipulating the emplacement configuration can effect reductions in repository size to mitigate against the adverse effects of discontinuities. It is shown that applying the minimum repository size philosophy to other host rocks can also produce benefits in terms of waste containment and construction costs, and some radical design alternatives are proposed incorporating relevant principles. The role of engineered barriers, in the form of high-integrity backfills and waste unit claddings, is examined. Potentially suitable backfills are identified by reference to geochemical stability and radionuclide containment properties, and cost implications are evaluated. Parametric sensitivity studies are performed to demonstrate the influence of waste unit and backfill properties on radionuclide containment, and some new practical design concepts and emplacement techniques are suggested.

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The increased worldwide interest in nuclear power and the politically charged threat of nuclear weapons release has made understanding the components, as well as the waste, of nuclear energy an important area of research. More specifically, the identification and selective extraction of the dioxoactinide cations uranyl (UO₂²⁺) and plutonyl (PuO₂⁺), low valent actinides scuh as Am³⁺ or Cm³⁺ and various anions, such as pertechnetate (TcO₄⁻), is essential in the event of a weapons release or the spill of nuclear waste. It has been previously demonstrated that the expanded porphyrin [24]hexaphyrin(1.0.1.0.0.0), commonly referred to as isoamethyrin, displays a dramatic color change, from golden yellow to red, upon coordination of uranyl, neptunyl and plutonyl cations. Chapter 2 details quantitative investigations of isoamethyrin with the uranyl cation as well as the interactions of isoamethyrin with other, potentially competing, cations. This work was carried out in order to assess the ability of isoamethyrin to serve as a colorimetric sensor for the actinide cations. Chapter 3 describes the synthesis and properties of periphery-modified isoamethyrin analogues. The addition of functional groups to this expanded porphyrin allows for immobilization onto a solid support and may enhance its utility as a sensor. Chapter 4 presents the preliminary investigations into the metalation and anion binding properties of a new series of macrocycles, the cyclo[n]pyrroles. Chapter 5 provides experimental methods and characterization data. / text

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