Figure 1. Vitrification Illustration ( simplified)
Audeen W. Fentiman
P. Andrew Karam
Ronald B. Meyers
Citizens, organizations, and industries are working to reduce the volumes of all waste streams, including low-level radioactive waste, to minimize the impact of human activities on the environment. In addition, increased disposal costs have created economic incentives to reduce low-level waste volumes.
The volume of low-level radioactive waste to be disposed of can be reduced either by minimizing the amount of waste generated or by treating existing waste before it is sent for disposal. Two previous fact sheet? RER-47 and RER-40, address low-level waste minimization and treatment, respectively. This fact sheet discusses the Ohio law dealing with low-level waste minimization, methods currently being used in Ohio and the Midwest Compact to reduce volumes of low-level waste sent for disposal, some new technologies being used to reduce the volume of low-level radioactive waste, and one volume reduction method still being studied.
Section 3747.17 of the Ohio Revised Code requires all low-level radioactive waste generators who will be sending waste to the Midwest Compact's disposal facility in Ohio to "have a program in place to limit and reduce the volume and activity of the low-level radioactive waste generated and submit an annual waste minimization report to the contractor [operator of the low-level radioactive waste disposal facility]..." The report must include descriptions of the practices the generator used to reduce the volume and activity of its low-level waste during the year for which the report was submitted.
The low-level waste disposal facility operator is authorized to verify that the waste minimization report is accurate. If it is not, and if it is not corrected within 60 days, the low-level waste generator will not be allowed to send its waste to the Midwest Compact facility until a corrected report is filed.
Since 1985 the number of national low-level radioactive waste disposal facilities accepting waste from the Midwest Compact has dropped from three to two. One currently operating facility is in Barnwell, South Carolina, and accepts all types of commercial low-level waste. The other, in Clive, Utah, is operated by EnviroCare and accepts only high-volume waste with relatively low concentrations of radioactive materials. The Barnwell facility was closed to states outside of the Southeast Compact for one year, from July 1994 through June 1995. This forced generators to store most of their waste temporarily at the sites where it was generated. In addition, since 1985, the cost of low-level waste disposal has risen from less than $50 per cubic foot to over $300 per cubic foot. As a consequence of shrinking and uncertain disposal facility capacity and increasing disposal costs, many generators in Ohio and the Midwest Compact seek to reduce waste volumes. They either treat their waste on site or send it to a specialized facility for treatment.
At their sites, generators seek to minimize the amount of low-level radioactive waste generated in several ways including: reducing the amount of packaging and other materials carried into areas where radioactive materials are used, washing and reusing protective clothing, and decontaminating equipment instead of throwing it away. They reduce the volume of dry low-level waste by compacting it and reduce the volume of liquid low-level waste by evaporating the water. These methods and others are described in fact sheet RER-47, "How Can Low-Level Radioactive Waste Be Minimized?"
Much of the low-level radioactive waste from generators in Ohio and the Midwest Compact is sent to a commercial low-level waste treatment facility near Oak Ridge, Tennessee, prior to disposal at the Barnwell, South Carolina, facility. This facility utilizes a number of methods to reduce waste volume. Some of the more traditional volume reduction methods are sorting waste and removing non-radioactive waste, super-compaction, and incineration. Some newer technologies for waste reduction are vitrification, plasma arc furnace treatment, and molten metal treatment.
Three relatively new technologies for treating low-level radioactive waste are described in this section: vitrification, plasma arc furnace treatment, and molten metal treatment. All of them use very high temperatures. At these temperatures, water is evaporated, and dry materials such as paper, wood, and plastic are vaporized. What is left is a small volume of residue containing radioactive materials and a much larger volume of gases. The gases are collected, sampled, treated if necessary, and then released. The filters and purifiers used to treat the gases capture radioactive materials and must eventually be disposed of as low-level radioactive waste.
In vitrification, the low-level radioactive waste is mixed with glass-making material and heated. The temperature is typically greater than 1200 degrees Celsius (2192 F). The mixture melts, and the melted material is used to make glass "beads" or disks about one inch in diameter and one quarter inch thick. One current research program related to low-level waste vitrification is called Minimal Additive Waste Stabilization (MAWS). Its goal is to minimize the amount of glass-making material that needs to be added to the low-level waste to produce glass of acceptable quality. This will minimize the volume of the vitrified low-level waste sent for disposal. One advantage of vitrified waste is that the radioactive material is bound up in the glass and is not easily released, even if water comes in contact with the waste after it is placed in a disposal facility.
Figure 1. Vitrification Illustration ( simplified)
Plasma is any high-temperature gas that has an electrical charge. While plasmas are often mentioned in science fiction, they have been used for decades in basic industrial applications such as metal processing, surface coating, and making new materials. Recently, high temperature plasmas have been used to cut and melt waste materials, thus reducing their volumes.
A plasma arc furnace is a chamber with a plasma torch, a port through which waste materials are fed, an exhaust port, and a tray to collect the melted waste. Waste material is fed into the plasma chamber, where it is melted by the torch at a temperature of 7,000 to 12,000 degrees Celsius (12,632 - 21,632 F). The melted waste, still radioactive, looks glassy when it cools. It takes up less space than the original waste and is in a more stable physical form.
Figure 2. Plasma Arc Illustration (simplified)
In molten metal treatment, low-level radioactive waste is passed through a bath of molten metal. The metals most often used are iron and nickel. They are heated to temperatures between 1500 and 1575 degrees Celsius (2732 -2867 F). Many of the radioactive materials are captured in a froth that rises to the top of the metal and is skimmed off. It hardens and becomes slag. Some radioactive materials remain in the molten metal. The slag is disposed of as low-level radioactive waste, and the metal may be disposed of or used as shielding inside containers for radioactive material.
Figure 3. Molten Metal Illustration (simplified)
One proposed waste treatment which has been studied recently is transmutation, the process of transmuting, or changing, the nucleus of an atom. It is possible to transform a long-lived radioactive nucleus into one that has a shorter half-life and will decay more quickly. In this process, radioactive nuclei of one kind are first separated from all other types of radioactive and non-radioactive nuclei. Then they are bombarded with high-speed subatomic particles from accelerators or nuclear reactors. When these subatomic particles are captured by radioactive nuclei, the nuclei change. The new nuclei have different characteristics, including a different half life.
As a method for reducing the volume of low-level radioactive waste, however, transmutation has several drawbacks. It requires the difficult and expensive separation of one type of radioactive atom from all other radioactive and non-radioactive atoms in the waste. It has only been done in specialized laboratories with small amounts of radioactive material. In addition, it requires the use of accelerators or nuclear reactors which are expensive to build and operate and which, themselves, generate radioactive waste.
If you would like to read more about reducing the volume of low-level radioactive waste, some of the other fact sheets listed below may be helpful.
RER-40, "How Is Low-Level Radioactive Waste Treated Prior to Disposal?"
RER-47, "How Can Low-Level Radioactive Waste Be Minimized?"
Dr. Audeen W. Fentiman is an Associate Professor in Nuclear Engineering at The Ohio State University. P. Andrew Karam is a Certified Health Physicist and a Graduate Research Associate in Geology. Ronald B. Meyers 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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