Unit operations used to treat process and/or waste streams at nuclear power plants

Abstract

An attempt is made to identify the main sources of low-level radioactive wastes (LLW) that are generated at light water reactor (LWR) nuclear power plants in the United States. To place the LWR waste problem in perspective, rough estimates are given of the annual amounts of each generic type of LLW [i.e., government and commercial (fuel cycle and nonfuel cycle)] that is generated. Most of the wet solid wastes arise from the cleanup of gaseous and liquid radioactive streams prior to discharge or recycle. Many different chemical engineering unit operations have been, are being, and likely will be used to treat process and/or waste streams at LWR plants. These include adsorption, evaporation, calcination, centrifugation, compaction, crystallization, drying, filtration, incineration, reverse osmosis, and solidification of waste residues. The treatment of these various streams and the secondary wet solid wastes thus generated (e.g., filter cartridges, filter sludges, and spent ion-exchange resins) is described. The dry wastes from all LWRs have similar physical and chemical characteristics in that they can be classified as compactible, noncompactible, combustible, noncombustible, or combinations thereof. The various treatment options for concentrates or solid wet wastes, and for dry wastes are discussed. Among the dry waste treatment methods are compaction, baling, and incineration, as well as chopping, cutting, and shredding. Organic materials [liquids (e.g., oils or solvents) and/ or solids] could be incinerated in most cases. The filter sludges, spent resins, and concentrated liquids (e.g., evaporator concentrates) are usually solidified in cement, or urea-formaldehyde or unsaturated polyester resins prior to burial. Incinerator ashes can also be incorporated in these binding agents. Asphalt has not yet been used as a solidification agent in the United States, but it probably will be used in the near future. This paper presents a brief survey of operational experience at LWRs with various unit operations, including a short discussion of problems and some observations on recent trends. Such information is a valuable aid in retrofitting old equipment and in selecting new equipment. Some areas appearing to need more research, development, and demonstration are specifically pointed out.