Management Of High-level Nuclear Wastes Research Articles

Structure of NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 glasses and glass-ceramics

AbstractThe crystallization of iron-containing sodium silicate phases holds particular importance, both in the management of high-level nuclear wastes and in geosciences. Here, we study three as-quenched glasses and their heat-treated chemical analogs, NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 (with nominal stoichiometries from feldspathoid, pyroxene, and feldspar mineral groups, i.e., Si/Fe = 1, 2, and 3, respectively) using various techniques. Phase analyses revealed that as-quenched NaFeSiO4 could not accommodate all Fe in the glass phase (some Fe crystallizes as Fe3O4), whereas as-quenched NaFeSi2O6 and NaFeSi3O8 form amorphous glasses. NaFeSi2O6 glass is the only composition that crystallizes into its respective isochemical crystalline polymorph, i.e., aegirine, upon isothermal heat-treatment. As revealed by Mössbauer spectroscopy, iron is predominantly present as fourfold-coordinated Fe3+ in all glasses, though it is present as sixfold-coordinated Fe3+ in the aegirine crystals (NaFeSi2O6), as expected from crystallography. Thus, Na-Fe silicate can form a crystalline phase in which it is octahedrally coordinated, even though it is mostly tetrahedrally coordinated in the parent glasses. Thermal behavior, magnetic properties, iron redox state (including Fe K-edge X-ray absorption), and vibrational properties (Raman spectra) of the above compositions are discussed.

Modelling the multiscale behaviour of claystone: deformation, rupture, and hydro-mechanical phenomena around underground galleries

In the context of underground exploitation, the behaviour of rocks near galleries and tunnels conditions their stability. Underground drilling generates deformations, damage, fracturing, and significant modification of flow characteristics in the surrounding rock. However, the influence of small-scale characteristics and behaviour on the rock deformations and damage at engineering scale remains a complex issue. Consequently, the multiscale behaviour of a clay rock is modelled starting from the large scale of the excavation damaged zone around galleries and then enriching the approach by considering microstructural characteristics from the scale of mineral inclusions. Lastly, a double-scale numerical framework is considered. It allows to relate small- to large-scale rock behaviour in terms of deformations and material rupture. In fact, the development of damage and cracking at microscale allows to predict large-scale fracturing. The developed method focuses on a claystone in the particular context of long-term management of high-level nuclear wastes by deep geological repository. The results highlight the possibilities of double-scale computing in the prediction of the behaviour of underground engineering structures.

Isotopic dilution model for36Cl in the French landscape

Chlorine-36 is one of the most critical radionuclides to consider in intermediate- and high-level nuclear waste management. Special attributes are long half-life, high mobility, biologically essential element, and massive isotopic dilution in the geosphere and biosphere. A model was developed to predict the radiological consequences of 36 Cl to human dose receptors. The approach had three parts, a literature and benchmarking review of other 36 Cl models and programs, the development of a 36 Cl model suitable for ANDRA applications within Aquabios, and the measurement of stable Cl concentrations and parameter values in the relevant landscape. A major issue was to resolve the degree to which specific activity relationships were useful. Soil-to-plant and aquatic food pathways were modeled using specific activity relationships. For subsequent transfers, the model used more traditional transfer factors. The use of the partial specific activity model simplified the problem and made the model and parameters more general. This is especially relevant for transfers of 36 Cl because the concentrations of stable Cl in the environment can vary substantially as a result of oceanic effects and local mineralizations. The preliminary field study confirmed some of the key parameters to add confidence to the chosen parameter values and their ranges.

High level nuclear waste management: how physics can help

The potential value of partitioning/transmutation (P/T) strategies for high level nuclear waste management has been investigated (one would be tempted to say 'periodically') since 1970. The basic physical phenomena are well understood, and scenarios for the fuel cycle can be envisaged. However, the criteria for judging the impact of P/T are still a matter for discussion (and controversy). Moreover the relation to disciplines other than reactor physics can be close (e.g. innovative fuels and actinoid chemistry). A number of key issues are revisited here and will be discussed in some detail.

High level nuclear waste management: how physics can help

High level nuclear waste management: how physics can help

High-Level Nuclear Waste Management: How Physics Can Help

ABSTRACTThe potential value of Partitioning/Transmutation (P/T) strategies for high-level nuclear waste management has been investigated (one would be tempted so say “periodically”) since 1970. The basic physics phenomena are well understood, and scenarios for the fuel cycle can be imagined. However, the criteria to judge the impact of P/T are matter for discussion (and controversy). Moreover the relation to disciplines other than reactor physics can be significant (e.g. innovative fuels and Actinide chemistry).A number of key issues are revisited here and will be discussed in some detail.

A Large Block Heater Test for High Level Nuclear Waste Management,

AbstractThe radioactive decay heat from nuclear waste packages may, depending on the thermal load, create coupled thermal-mechanical-hydrological-chemical (TMHC) processes in the near-field environment of a repository. A group of tests on a large block (LBT) are planned to provide a timely opportunity to test and calibrate some of the TMHC model concepts. The LBT is advantageous for testing and verifying model concepts because the boundary conditions are controlled, and the block can be characterized before and after the experiment. A block of Topopah Spring tuff of about 3 × 3 × 4.5 m was sawed and isolated at Fran Ridge, Nevada Test Site. Small blocks of the rock adjacent to the large block were collected for laboratory testing of some individual thermal-mechanical, hydrological, and chemical processes. A constant load of about 4 MPa will be applied to the top and sides of the large block. The sides will be sealed with moisture and thermal barriers. The large block will be heated by heaters within and guard heaters on the sides so that a dry-out zone and a condensate zone will exist simultaneously. Temperature, moisture content, pore pressure, chemical composition, stress, and displacement will be measured throughout the block during the heating and cool-down phases. The results from the experiments on small blocks and the tests on the large block will provide a better understanding of some concepts of the coupled TMHC processes. The progress of the project is presented in this paper.

High-level nuclear waste management: a geochemical perspective

Atomic Energy of Canada Limited is investigating the concept of the disposal of high-level radioactive waste in an underground vault in an intrusive crystalline rock formation. The environmental impact of such a disposal is, to a large extent, dictated by geochemical processes involving rock-forming minerals, groundwater, and fission products and actinides in the waste. These various geochemical processes impact on the transport of contaminants, including radionuclides and chemically toxic elements, from a used-fuel disposal vault towards the biosphere. The extent and importance of the geochemical processes on contaminant transport are discussed. The predominant processes controlling the velocity of contaminant transport are the various geochemical interactions of the dissolved contaminant species with the minerals lining the surfaces of conductive fractures and fracture systems. Key words: radionuclide, uranium, nuclear contaminant, transport, sorption, diffusion, geochemistry, fission products, granite.

On a Global Database Strategy for Public Engineering Decision Making

AbstractA historical review of how engineers contributed to the solution of societal (public) and individual (private) problems is presented, with emphasis on the last thirty years when computers began to alter drastically the practice of engineering.The concept of a 3-prong representation of the engineering decision making process, i.e., database, analysis, and judgment, is introduced. The importance of generating a suitable body of experimental and actual performance data and of coupling the database with a state-of-the-art analysis and extrapolation methodology for “public engineering” is illustrated in three case studies involving (a) the nuclear reactor safety study of 1975, (b) the Alaska pipeline weld defect assessment study of 1976, and (c) the Welding Research Council-Pressure Vessel Research Committee (PVRC) Round Robin Flaw Detection Program (1966-86) for thick-section steel welds.For most of the public engineering projects involving long-term prediction of performance from short-term test data, the time-honored approach of supplementing experimental or service data with engineering judgment is frequently open to a public challenge. To remedy the situation, a new approach of using both the personal computers (PC) and the mainframes to (a) accelerate the peer review of existing data, (b) design a strategy for acquiring new data, and (c) facilitate a regional or global exchange of field data with standardized format, is outlined.Application of the above approach to strengthen the judgment component of public engineering projects such as the management of high-level nuclear wastes is discussed through an example on the fatigue life prediction of stainless steel 304 piping and components.

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High-Level Nuclear Waste Management: Analysis of Options

A new approach is introduced for evaluating strategies for the safe disposal of high-level nuclear waste. Five strategies are considered, and by means of the effective method of ‘analytic hierarchy...