Low- and intermediate-level waste

Bonotto, D. M. 1998. Generic performance assessment for a deep repository for low and intermediate level waste in the UK - a case study in assessing radiological impacts on the natural environment. Journal of Environmental Radioactivity, 66, 89-119. 

Low- and intermediate-level waste is currently converted to cement and bitumen waste forms, but the existing trend is toward an increase in the radiation safety levels and reliability of immobilization. From this point of view, LILW should also be incorporated in vitreous and crystalline matrices. Current Russian and US experience on vitrification of such waste demonstrates the potential of the melting/vitriflcation process. Major advantages of vitrification over bituminization and cementation are a greater waste volume reduction, higher productivity, and higher durability of the final product. 

As part of this study, proposed radioactive waste classification systems that differ from the existing classification system in the United States were reviewed and evaluated. Of particular interest is the classification system currently recommended by the International Atomic Energy Agency (IAEA). This classification system and the disposal options for each waste class are summarized in Table 1.2. The basic waste classification system consists of exempt waste, low-and intermediate-level waste, and high-level waste. 

Concentrations of shorter-lived radionuclides in low- and intermediate-level waste are limited by the criterion on thermal power density (decay heat). There is no such restriction on low-level waste as defined in the United States. 

To address the limitations of the waste classification system described above, new recommendations on waste classification were developed (IAEA, 1994). A particular aim of the new system was to associate waste classes with intended disposal technologies (options), at least to some degree. The recommended classification system includes the following three major classes of waste exempt waste, low- and intermediate-level waste, and high-level waste. These waste classes and the associated disposal options are summarized in Table 4.2 and described as follows. 

In IAEA s new recommendations, low- and intermediate-level waste thus contains concentrations of radionuclides above those for exempt waste but still sufficiently low that heat dissipation is not a concern in ensuring safe disposal. IAEA recommends that the thermal power density for this class of waste be restricted to about 2 kW m-3. This class would cover a wide range of radionuclide concentrations, and a variety of disposal methods may be appropriate depending on the radiological properties of the waste. 

Fourth, the definitions of waste classes in the United States are not related to requirements for disposal. In IAEA s waste classification system, there is some linkage between the definitions of waste classes and the types of disposal technologies that would be required, particularly for high-level waste. However, not all waste classes in IAEA s system are linked to required disposal technologies, because low-and intermediate-level waste could be acceptable for near-surface disposal or could require disposal in a geologic repository depending, for example, on the concentrations of long-lived radionuclides. 

Low- and intermediate-level short-lived waste. A common disposal site for all low- and intermediate-level waste should be established. It should be loeated underground, in the bedrock. 

For the treatment of low and intermediate level wastes, three processes are generally adopted, namely, chemical precipitation, ion exchange, and evaporation. The efficiency of the treatment scheme is judged by the values of decontamination factor (DF) and volume reduction factors (VRFs), which are defined as follows ... 

Andalaft, E., Vega, R., Correa, M., Araya, R. and Loyola, R 1997. Zeta potential control in decontamination with inorganic membranes and inorganic adsorbents. In Treatment Technologies for Low and Intermediate Level Waste from Nuclear Applications. Final Report of a Coordinated Research Programme 1991-1996. IAEA-TECDOC-929, pp. 15-32. IAEA Vienna. 

Solid-waste disposal and transport SoUd waste arises at various stages of the nuclear fuel cycle, and is classified as low- and intermediate-level waste (LLW) mainly from reactor operation, and high-level waste (HLW) from fuel reprocessing and from spent fuel meant for direct disposal. Low- and intermediate-level wastes are generally disposed of by shallow burial in trenches or concrete-fined structures. 

W. Pfingsten, Experimental and modeling indications for self-sealing of a cementitious low- and intermediate-level waste repository by calcite precipitation. Radioactive waste management and disposal, Nucl. Technol., 140 (2002) 63. 

The date is important for low- and intermediate-level waste so that decay corrections can be applied. The location allows a comparison of where the wastes were collected with the history of the accident. The type of packaging (dimension, shielding, etc.) and the type of waste (material, density) can be used, together with the exposure rates, to estimate the activity of the radioactive waste in the package. The surface and 1-m exposure rates are needed for labeling the package for transport (transport category). 

LILW (low and intermediate level waste.- Radioactive waste in which the concentration or quantity of radionuclides is above clearance levels established by the regulatory body, but with a radionuclide content and thermal power below those of high level waste. Low and intermediate level waste are often separated into short lived and long lived wastes. Short lived waste may be disposed of in near surface disposal facilities. Plans call for the disposal of long lived waste in geological repositories [3]. 

EXPERIENCE IN MANAGING SHORT LIVED LOW AND INTERMEDIATE LEVEL WASTE... 

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