Figure 1. Compacting Low-Level Radioactive Waste
Audeen W. Fentiman
Matthew E. Jorat
Joyce E. Meredith
Before low-level radioactive waste can be transported or placed in a disposal facility, it must be in an acceptable form. Regulations require that the waste be solid and structurally stable so that it can be transported more safely and does not settle after being placed in a disposal facility. When the waste meets these requirements, the risk of human exposure to radiation is reduced.
Low-level radioactive waste is generated in many forms. Some of it is solid, and some is liquid. Very little of it is structurally stable. Therefore, the waste must be treated to convert it to an acceptable form for disposal.
In addition, low-level radioactive waste is treated to reduce its volume as much as possible before disposal. Minimizing the volume reduces both the size of the disposal facility required and the cost of waste disposal. It should be noted that while treatments can reduce the volume of low-level waste, the amount of radioactive material present remains essentially unchanged.
This fact sheet describes the treatment methods used for the various forms of low-level radioactive waste.
Most of the low-level radioactive waste generated by nuclear power plants, industry, hospitals, and research institutions is in dry, solid form such as cardboard, paper, plastic, cloth, and glass. To reduce the amount of space required to store the low-level waste, three processes are used to reduce its volume: compaction, incineration, and shredding.
Compaction involves compressing the waste to reduce its volume, much like a kitchen trash compactor (see Figure 1). Compaction is a relatively inexpensive and widely available option which is used by many low-level radioactive waste generators.
Figure 1. Compacting Low-Level Radioactive Waste
Originally used to treat municipal solid waste, incineration can be used to reduce the volume of solid low-level radioactive waste. When any material is incinerated, the products are gases and ash. When radioactive material is incinerated, the gas and ash contain radioactive particles and must be treated. The gas is filtered to remove radioactive particles. The filters become contaminated and must be treated as radioactive waste. The ash is mixed with concrete or other material to prevent radioactive particles from blowing away.
Usually both compaction and incineration are performed in conjunction with shredding. Shredding involves cutting solid low-level radioactive waste into smaller pieces. This allows for more efficient compaction and a more uniform burn for incineration.
It should be noted that nuclear power plants, industry, hospitals, and research institutions also generate non-radioactive solid waste. Any non-radioactive trash that is put in a container with radioactive waste must be treated as radioactive waste because it might have become contaminated. One way to reduce the volume of low-level radioactive waste to be treated is to keep non-radioactive trash segregated from radioactive waste. While segregation is not a "treatment" of low-level waste, it is a way to reduce the volume.
Another source of low-level radioactive waste is contaminated equipment. If a piece of equipment used in a contaminated area is no longer needed there, it can either be disposed of as low-level waste or decontaminated and used in other, uncontaminated areas. Decontamination is the process of removing radioactive material from all interior and exterior surfaces of the equipment. While decontamination often requires a significant amount of time and can cause some exposure to workers, it can reduce the volume of low-level waste that must be disposed of.
Liquid low-level radioactive waste is generated primarily by nuclear power plants during purification of cooling water. Lubrication oil and sludges from filters are other examples of liquid low-level waste.
Liquid low-level radioactive waste must be solidified for transportation and disposal. Usually, as much water as possible is removed from the liquid waste, and the remaining material is immobilized. Methods for removing water include evaporation and filtration. The remaining material is immobilized with solidifying agents such as cement or asphalt. The cement or asphalt is in a structurally stable form which can then be sent to a disposal facility.
Medical facilities produce both solid and liquid low-level radioactive waste, but some of their wastes have short half-lives. That is, they decay quite quickly. These wastes are stored in a container at the hospital until they decay. (The actual storage time depends on the half-life of the radioactive materials present.) After the wastes are analyzed for radioactivity to confirm that they have decayed, they can be disposed of as ordinary trash. This method of handling low-level waste is called storage for decay. It reduces the volume of waste to be sent to a low-level waste disposal facility.
Low-level radioactive waste stability requirements and the rapidly rising cost of disposal have encouraged widespread treatment of waste and substantial reductions in volume. In 1981, 2,960,000 cubic feet of commercial low-level radioactive waste were accepted for disposal in the United States. Ten years later, in 1991, the amount of waste accepted for disposal had declined 54% to 1,369,303 cubic feet.
If you would like to read more about treatment of low-level radioactive waste, some of the references listed below may be helpful.
Edward L. Gershey, et.al., Low-Level Radioactive Waste: From Cradle to Grave, Van Nostrand Reinhold, NY, 1990.
Office of Technology Assessment, Partnerships Under Pressure - Managing Commercial Low-Level Radioactive Waste, 1989.
Raymond L. Murray, Understanding Radioactive Waste, Battelle Press, Columbus, Ohio, 1989.
Dr. Audeen W. Fentiman is an Assistant Professor in Nuclear Engineering at The Ohio State University. Matthew E. Jorat is a Graduate Research Associate in Nuclear Engineering. Joyce E. Meredith is a Graduate Research Associate, Ohio State University Extension.
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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
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