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. 

High-level waste (HLW), intermediate-level waste (ILW), and low-level waste (LLW) are produced at all stages of the nuclear fuel cycle as well as in the non-nuclear industry, research institutions, and hospitals. The nuclear fuel cycle produces liquid, solid, and gaseous wastes. Moreover, spent nuclear fuel (SNF) is considered either as a source of U and Pu for re-use or as radioactive waste (Johnson Shoesmith 1988), depending on whether the closed ( reprocessing ) or the open ( once-through ) nuclear fuel cycle is realized, respectively (Ewing, 2004). 

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. 

Tolstova, O. V., Lashtchenova, T. N. Stefanovsky, S. V. 2002. Glassy materials from basalt for intermediate-level wastes immobilization. Glass and Ceramic, 6, 28-31 (in Russian). 

Fig. 6. The Nagra/PSI TDB 01/01 was used in this modelling chain for the performance assessment of a proposed Swiss repository for spent fuel, vitrified high-level waste, and long-lived intermediate-level waste.

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. 

Intermediate-level waste is waste with concentrations of radionuclides greater than NRC s Class-C limits but which does not pose a sufficient long-term hazard to justify disposal in a geologic repository. 

Intermediate-level waste is waste with high concentrations of intermediate-level, short-lived waste or intermediate-level, long-lived waste (IAEA, 1981). Such waste would be suitable for disposal in a near-surface facility incorporating engineered barriers and would include higher-activity Class-B and Class-C waste, as defined in NRC s 10 CFR Part 61 (NRC, 1982a). 

Intermediate-level waste is waste which, because of its radionuclide content, requires shielding but needs little provision for heat dissipation during handling and transport. 

Within the low-level and intermediate-level waste classes, a further distinction was made between short- and long-lived waste, as well as alpha-bearing waste (IAEA, 1981). Short-lived waste referred to waste that would decay to low activity levels during the time period of perhaps a few centuries when administrative control over the waste can be expected to last, and long-lived waste referred to waste that would not decay to low levels during an administrative control period. Alpha-bearing waste referred to waste that contains one or more alpha-emitting radionuclides in amounts above acceptable limits established by national authorities. 

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. 

The fuel pins are transferred into slotted cans and the redundant graphite sleeves and additional stainless steel components are stored in drums as Intermediate Level Waste (ILW). This not only converts the fuel into a form suitable for reprocessing but also results in a 3 or 4 fold increase in storage density. 

From the 86 streams selected as representative of Magnox reactor operational solid and mobile intermediate level wastes, 49 radionuclides were identified which are subject to detailed determination under UK Nirex requirements for radioactive ILW packages. 

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