As described in Section 14.3, a wide variety of radioactive waste is gener­ated during the operation and maintenance of a nuclear power plant and during the final decommissioning and dismantling of the reactor. They are generally distinguished as wet and solid waste. In addition also gaseous waste is generated. These wastes are released to the atmosphere after appropriate filtration and the filters containing the important radioactivity can be handled as solid waste.

The purpose of the treatment and conditioning is to produce a waste package that is suitable for the subsequent waste management steps, i. e. storage, transport and disposal (Fig.14.12). Another purpose is to reduce the volume as is much as is economically justified.

Liquid waste, i. e. contaminated water, is treated by chemical precipita­tion, ion exchange, mechanical filtering and/or evaporation depending on the concentration of radioactivity in the water and the cleanliness of the water, as well as the further use for the water. The products from these treatment processes are wet sludge (solid content <15%), spent ion exchange resins, and filter cartridges. The sludge and ion exchange resins are normally then conditioned to form a solid body (solidification) directly in a package suitable for handling and disposal, while the filter cartridges can be handled as solid waste.

The methods most commonly used for solidification of wet wastes are cementation, bitumination, polymerization and vitrification. In the cemen­tation process, which is the most widely used method, the waste is mixed with cement to form a concrete that is poured directly into the waste package. Care must be taken that the chemical composition of the waste is compatible with the cementation process. The process is fairly straightfor-

ward and is widely used in most nuclear power plants. A drawback is that it normally leads to a volume increase. In the bitumination process wet wastes are mixed with hot bitumen and the remaining water is driven off, thus providing a volume reduction. The bitumen/waste mixture is then filled in the final waste package, normally a 220-litre drum. Bitumination is used at some nuclear power plants and also some reprocessing facilities. More recently also polymerization and vitrification technologies have been devel­oped for wet LLW and ILW. In the polymerization process the waste is mixed with a polymer that uses the excess water for polymerization. In the vitrification process the waste is heated together with glass-forming com­ponents to create a radioactive glass. Vitrification normally requires that the wet wastes are pre-dried. The different processes considered for condi­tioning of wet wastes have different advantages and disadvantages. The choice of process will depend on many factors such as the volumes to be treated, the activity concentration, the chemical composition, the require­ments from the disposal facility and the end costs.

Solid waste has a wide variation in physical form and activity content and the chemical form of the activity. Metal waste is normally decontaminated with mild acids such that the material can be reused. When a material is finally declared as waste it is then separated into combustible, compactable or non-compactable waste. Combustible waste can be incinerated and the ashes taken care of as wet or solid waste and the filters as solid waste. An incineration facility for radioactive material is, however, an expensive instal­lation and will normally require a substantial volume of waste to be inciner­ated. Most of the incinerators installed are therefore central for a country, e. g. in France and Sweden. For compactable waste different types of com­pactors are used, ranging from simple drum compactors, where the waste is compacted directly in the waste package drum, to high pressure (>1000 Mg) supercompactors. In the supercompactors standard 220-litre drums with waste are compacted to form thin ‘slices’ that can then be pack­aged in a drum for subsequent handling. To stabilize the compacted waste or non-compactable waste in the final waste package, concrete is normally poured into the package to provide a solid monolith.

An important part of the waste treatment and conditioning processes is waste characterization. It has to be ensured that the waste form is suitable for the next step, e. g. has the suitable chemical form and/or activity concen­tration. It is particularly important that the conditioned waste package will fulfil the requirement, i. e. the waste acceptance criteria, for transport and disposal.

In most cases each nuclear power plant is equipped with the appropriate facilities for waste handling, treatment, conditioning and storage. In some countries centralized facilities, e. g. for incineration, have been built. In other countries mobile treatment and conditioning facilities have been intro­duced, that can serve several nuclear power plants.