Geosphere transport

GEOSPHERE TRANSPORT (HAZARDOUS SUBSTANCE TRANSPORT THROUGH THE GEOSPHERE)... 

Prediction of the consequences of degradation release conventionally involves data and models for three steps of analysis geosphere transport, biosphere transport, and biosphere consequences. I will discuss these and add two others analysis, rather than assumption, of repository degradation, and consideration of the geosphere/biosphere interface and its effect on biosphere consequences. These refinements to safety assessment procedures, when developed and implemented, can be expected to aid validation of results. 

Application of the geosphere transport models is highly site-specific i.e., data for the proposed repository site should be used. This requirement imposes a need to assess the viability of, and methods for obtaining, laboratory and field data. Capability to produce representative information is needed. Data used to date can best be characterized as generic for many nuclides, numerical values used to represent holdup phenomena are extrapolations of limited data for similar nuclides. The validity of such extrapolations should be evaluated. 

Radioactivity that enters the biosphere is subject to transport by a variety of pathways and mechanisms that need to be reflected in migration models for this regime. Factors to consider in biosphere transport models are similar in type to those considered for geosphere transport, but details will differ substantially. Pathways are more numerous in the biosphere, and phenomena such as weathering may change the physical and chemical properties of the nuclides. Such changes may alter the environmental behavior and biological consequences of the radioactivity. 

Models of biosphere transport have been developed. 5,6) As is the case for geosphere transport models, the data base for parameters in the biosphere models is limited. The scope of available data is being expanded, (7-9) but careful assessment is needed of the validity of the data, the validity of the models, and the need for the data and models to be site-specific. One site-specific factor to consider is the possibility that geosphere migration could extend for considerable distances from the repository radioactivity might therefore enter the biosphere in an environment different from that of the repository site. 

An example gathering some of the problems encountered in the analytical benchmarks is the PSACOIN Tevel E model. Nuclear Energy Agency (1989). As an optional element for the participants, a sensitivity study of the Level-E geosphere transport model was requested. Here Faciha and TUC provided results. 

Moreover, a time-dependent model which has some of these properties is the PSACOIN Level-E geosphere transport model. Some results on the SA of this complex model are also reported. 

Elemental solubility limits are a very important constraint on the releases of many radionuclides and selecting a set of more conservative values of this parameter significantly alters the profile of calculated doses as a function of time. Decay during near-field and geosphere transport minimizes the consequences of such changes for some nuclides as does the fact that, as solubilities increase, the glass corrosion rate takes over as a constraint on releases. 

The constant transport of material within and through the geospheres is powered by the sun and by the heat of the Earth s interior. A simple diagram of these geospheric concepts and the energy that moves material within them is presented in Fig. 1-1. The result of the interactions shown in Plate 1 and Fig. 1-1 is an Earth system that is complex, coupled, and evolving. 

Moulin V, Ouzounian G (1992) Role of colloids and humic substances in the transport of radio-elements through the geosphere. Appl Geochem (Suppl. Issue 1 179-186 Murakami T, Ohnuki T, Isobe H, Sato T (1997) Mobility of uranium during weathering. Am Mineral 82 888-899... 

Terrestrial plants function as conduits for the transport of elemental mercury from the geosphere to the atmosphere (Leonard et al. 1998a). Estimated mercury emissions from plants in the Carson River Drainage Basin of Nevada over the growing season (0.5 mg Hg/m2) add to the soil mercury... 

Radioactive waste management is a quite mature field of application of basic geoscientific disciplines. As we will discuss in forthcoming sections, the long-term performance and henceforth the safety of radioactive waste disposal systems, deeply relies on the basic principles that control the release, mobility, and transport of the chemical elements in the geosphere. In the context of radioactive waste disposal, the waste matrix constitutes the innermost of the barriers that may control the release and ulterior transport of radionuclides through the ground-water systems. 

The definition of environmental chemistry given above is illustrated for a typical environmental pollutant in Figure 2.3. Pollutant sulfur dioxide is generated in the anthrosphere by combustion of sulfur in coal, which has been extracted from the geosphere. The S02 is transported to the atmosphere with flue gas and oxidized by chemical and photochemical processes in the atmosphere to sulfuric acid. The sulfuric acid, in turn, falls as acidic precipitation, where it may have detrimental effects, such as toxic effects, on trees and other plants in the biosphere. Eventually the sulfuric acid is carried by stream runoff in the hydrosphere to a lake or ocean, where its ultimate fate is to be stored in solution in the water or precipitated as solid sulfates and returned to the geosphere. 

In chemistry, labelled compounds are used to elucidate reaction mechanisms and to investigate diffusion and transport processes. Other applications are the study of transport processes in the geosphere, the biosphere and in special ecological systems, and the investigation of corrosion processes and of transport processes in industrial plants, in pipes or in motors. 

A main concern of geochemistiy is the investigation of the abundance and the distribution of the elements on the surface and in deeper layers of the earth, and of transport processes. The components of the geosphere are the lithosphere, the hydrosphere and the atmosphere. The relative abundance of the elements on the surface of the earth is plotted in Fig. 15.1 as a function of the atomic number. This relative abundance is similar within the solar system. The elements H, O, Si, Ca and Fe exhibit the highest abundances and maxima are observed at the magic numbers Z = 8, 20, 50 and 82. The abundances of the elements and their isotopes are determined by the nuclear reactions by which they have been produced and by their nuclear properties, whereas the chemical properties of the elements are only responsible for distribution and fractionation processes. 

The abundances of the isotopes of the elements in the geosphere show some variations caused by their formation, by isotope effects or by transport processes. A certain isotope ratio IR is taken as standard and the relative deviation from this standard is expressed as the (5-value ... 

Mobility and transport of radionuclides in the geosphere are influenced markedly by their interaction with solids. Migration is retarded, or even stopped, if the interaction is strong, in particular if the radionuclides are incorporated into the solids. Sorption of radionuclides on solids has been investigated extensively for materials in the neighbourhood of planned high-level waste repositories. 

Petroleum products are released into the environment inadvertently and intentionally at all stages of petroleum use, from exploration, production, transportation, storage, use and disposal (Figure 3). The more volatile components of oil partition preferentially into the atmosphere and hydrosphere, and to a lesser extent, the geosphere (e.g., sorption onto sediments), and biosphere (i.e., bioaccumulation), whereas the higher molecular... 

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