Lessons Learned from Existing Low-Level Radioactive Waste Disposal Facilities

RER-44

The United States has been disposing of low-level radioactive waste in shallow land burial facilities since the early 1960s. These facilities have been monitored, and lessons have been learned about how various siting, design, and operations choices affect a facility's ability to meet the objectives of low-level waste disposal. These lessons have provided valuable information for design, construction, and operation of future low-level radioactive waste disposal facilities. Many of them have been incorporated into the regulation that governs low-level waste disposal (Title 10, Part 61 of the Code of Federal Regulations). This fact sheet discusses some of the lessons learned.

Past and Present Disposal Facilities

Six commercial low-level radioactive waste disposal facilities have operated in the United States. These facilities are located in Beatty, Nevada; Maxey Flats, Kentucky; West Valley, New York; Richland, Washington; Sheffield, Illinois; and Barnwell, South Carolina. The site locations are shown in Figure 1. Only the sites in Richland, Washington, and Barnwell, South Carolina, are currently open. The Beatty site closed at the end of 1992, and the other three sites closed between 1975 and 1978. Shallow land burial in excavated trenches was used at all six sites.

Figure 1. Low-Level Radioactive Waste Disposal Facilities

Lessons learned from the first facilities built were used to improve the design and operation of Barnwell, the last facility to open. In the future, other kinds of disposal facilities such as above-grade vaults, below-grade vaults, and earth-mounded concrete bunkers are likely to be used, providing further improvement over current land burial techniques.

The primary objective of a low-level radioactive waste disposal facility is to isolate low-level radioactive waste from the public and the environment until the radionuclides (radioactive atoms) in the waste have decayed to levels at which the hazard is negligible. Two fundamental concerns must be addressed when attempting to isolate low-level waste in a disposal facility on land. The first concern is isolating the waste from water, or hydrologic isolation. The second is preventing movement of the radionuclides out of the disposal facility, or radionuclide migration.

Extensive monitoring of all of the commercial low-level waste disposal sites has provided valuable information on hydrologic isolation and radionuclide migration. Analyses of the data allow identification of the site characteristics, design features, and operating procedures that affect a facility's ability to maintain hydrologic isolation and prevent radionuclide migration.

Factors That Affect Hydrologic Isolation

The buildup of water in burial trenches at some closed sites (loss of hydrologic isolation) was caused by a greater rate of seepage into the trenches than out of them. This phenomenon is known as the bathtub effect (see Figure 2). It is of concern because water standing in a trench can corrode waste containers and carry away radioactive material. At both the Maxey Flats and West Valley sites, water buildup in the trenches led to site closure and corrective actions. The remaining four commercial sites did not exhibit the bathtub effect, possibly due to differences in their precipitation rates and/or differences in soil characteristics.

Figure 2. Bathtub Effect

One factor which led to increased seepage of water into trenches at some closed sites was subsidence or slumping of the cap. A cap is a layered barrier of packed clay and other materials covering a waste disposal trench to divert water away from the trench (see Figure 3). Very little water can pass through the cap. However, if the cap slumps and cracks, water can seep into the trench through the cracks (see Figure 4). Containers in some early facilities were not carefully stacked and settled over time, causing the cap above them to shift and crack. Lesson: Put waste in a structurally stable form, arrange waste carefully in the disposal facility, and fill spaces between containers to avoid settling.

Figure 3. Intended Cap Configuration

Figure 4. Slumping Cap

At Barnwell a layer of sand is placed on the bottom of each trench to provide an even foundation for waste containers and to ensure that water seeping into the trench will drain away from the waste. Naturally occurring layers of sand in the trench walls are replaced with compacted clay to reduce seepage of water into the trenches from the surrounding soil. Low-level radioactive waste is stacked in the trenches and spaces between containers are filled with sand to provide drainage paths away from the waste. Lesson: Design and operating procedures are important to facility performance.

Factors That Affect Radionuclide Migration

Migration of radionuclides may occur when water comes into contact with low-level radioactive waste and carries the radionuclides into the surrounding soil. The radionuclides are likely to migrate more rapidly when coarse-grained deposits, like sand and gravel, exist in the surrounding soil. Migration from disposal trenches has occurred at both the Maxey Flats and Sheffield sites. In both cases, follow-up investigations revealed the presence of coarse-grained deposits which were more extensive than discovered by the initial site investigation. Lesson: Do a complete geologic, soil, and water analysis to determine the site characteristics before constructing a facility.

At Barnwell some migration of radioactive hydrogen (tritium) from the buried waste in some trenches has occurred. Those trenches are being recapped. This has slowed the migration of tritium. Lesson: Keeping water out of trenches reduces radionuclide migration.

Disposing of low-level radioactive waste in a liquid form can increase migration of radionuclides away from the disposal facility. Liquid low-level waste has been found to be corrosive and can damage containers in which it is buried. If the liquid waste leaks from its container, it can migrate from the disposal facility. Lesson: Do not put liquid low-level waste into a disposal facility. (Regulations no longer permit disposal of low-level wastes in liquid form.)

Other Lessons About Operating Procedures

Other lessons have been learned about operating procedures that can improve worker safety. Questionable site management and disposal practices at the Maxey Flats site prior to its closure contributed to ground surface contamination from accidental spillage of waste, direct disposal of contaminated liquids on the slopes of the site, and spreading of liquid from the trenches by earth moving equipment. At Beatty employees removed a cement mixer and other tools which were brought to the site as radioactive waste, and used them in local construction projects. Lesson: A strong quality assurance program, employee training, and regulatory oversight are essential.

Operators of the Beatty site developed a third party inspection system which all generators shipping to Beatty were required to accept as a condition for receiving a permit to use the disposal site. Under the inspection system, which was conducted by a contractor to the state, permits were issued only after an initial onsite audit was performed. This audit was to verify the generator's compliance with federal and state regulations and with the disposal facility's license requirements. The inspection contractor also performed follow-up, unannounced audits of the generators. Fines of up to $20,000 per incident, suspension of permits, and criminal penalties could result from permit infractions. Lesson: Audits and regular inspections help to ensure that the waste reaching the disposal site has acceptable content and form.

For More Information

If you want to read more about the lessons that have been learned from existing low-level radioactive waste disposal facilities, some of the references listed below may be helpful.

Directions in Low-Level Radioactive Waste Management: A Brief History of Commercial Low-Level Radioactive Waste Disposal, The National Low-Level Waste Management Program, (DOE/LLW-103), October 1990.

Edward L. Gershey et. al., Low-Level Radioactive Waste From Cradle to Grave, Van Nostrand Reinhold, New York, 1990.

Robert E. Berlin and Catherine C. Stanton, Radioactive Waste Management, John Wiley & Sons, New York, 1989.

Author Notes:

Dr. Audeen W. Fentiman is an Assistant Professor in Nuclear Engineering at The Ohio State University. Jeffery A. Henkel is a Graduate Research Associate in Nuclear Engineering. Joyce E. Meredith is a Graduate Research Associate, Ohio State University Extension.