Basic categories of radioactive waste (RAW)

Radioactive waste (RAW) is generated in various activities and in a number of different facilities. The most significant source of RAW is nuclear energy generation; in particular, operation of nuclear power plants (NPP) and the disposition of the spent nuclear reactor fuel, i. e. whether the fuel is recycled or considered as waste. Other sources are so-called institutional applica­tions of radioisotopes: medical, research, educational, industrial and other facilities. The origin of the RAW usually also determines its basic characteristics and represents the principal information necessary for its categorization and classification as well as the information necessary for consideration and decision making on how the RAW is processed and the potential disposal routes.

There are several ways to characterize and categorize RAW. Besides chemical composition, aggregate state, mechanical properties, etc., the main characteristics are radiological properties, namely the activity concentration and the type and physical parameters of the radionuclides in the waste.

This book is aimed mainly at NPP operational and decommissioning radioactive wastes and spent fuel (if considered as a waste) management, with emphasis on technological aspects of RAW management. The aim of this chapter is to describe the categorization of these wastes.

2.1.1 Spent nuclear fuel (SNF)

Spent nuclear fuel (SNF) contains the major portion of the radioactive material generated in NPP. The SNF contains most of the highly radioactive fission products generated in a reactor as well as significant amounts of transuranium elements (TRU), generated in neutron activation of non­fissionable bulk fuel material and low activity bulk fuel material (e. g., uranium oxide). Under normal conditions fuel element cladding material should provide a tight barrier, providing for sufficient separation of the radioactive material from the environment during the entire fuel post­irradiation lifetime.

The SNF is the only nuclear fuel cycle material that can be considered either as radioactive waste or as a valuable source of fissile material. The decision between these options is usually not sharp and is based on various countries specific technical, technological, political, strategic and other con­siderations. It is common that the same type of SNF in one country may be slated for reprocessing and in another country it may be slated for final disposal. The following two options of SNF categorization also can influ­ence which management approach is applied:

• SNF is a valuable source of secondary fissile material (if a closed nuclear fuel cycle is applied). Secondary fissile material (in particular, Pu-239) together with non-used fissionable U-235 is separated from SNF in reprocessing facilities and used in the manufacturing of fuel for particu­lar types of nuclear reactors.

• SNF is considered and managed as RAW (if an open nuclear fuel cycle is applied). After proper cooling and packaging, SNF should be disposed of in deep geological repositories. If a deferred decision on disposal is considered or if a disposal facility is not yet available, then long-term storage under strictly controlled conditions must be applied.

SNF, as a potential source of nuclear weapon material, is fully covered by the IAEA safeguard rules and guarantees, which have to be obeyed and respected in each SNF handling and management step.

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