What Disposal Methods Are Being Considered for Low-Level Radioactive Waste?

RER-42

Audeen W. Fentiman
Matthew E. Jorat
Ronald J. Veley

Nuclear power plants, industries, medical facilities, research institutions, and universities generate low-level radioactive waste. This waste must be shipped to a specially designed facility for permanent disposal. To ensure that disposal is performed properly, the federal government has established guidelines for disposing of low-level waste in the United States. Several types of disposal facilities have been proposed to meet these guidelines.

This fact sheet outlines the federal regulations governing low-level radioactive waste disposal and describes some types of disposal facilities.

Federal Regulations Governing Low-Level Radioactive Waste Disposal

Federal regulations restrict the concentration of radioactive material in wastes that may be placed in a low-level radioactive waste disposal facility. These regulations specify three different classes of waste that may be placed in such a facility. Packaging requirements are given for each of the three classes. Disposal facilities are designed to accommodate all three classes of low-level waste.

Title 10 of the Code of Federal Regulations ,Part 61, (10 CFR 61) defines the three classes of low-level radioactive waste (Class A, Class B, and Class C) that may be placed in a low-level waste disposal facility. The definitions of these classes are based on the specific radioactive isotopes present, their concentrations, and their half-lives. Any low-level waste with a concentration of radioactive material greater than that specified for these three classes is a federal responsibility and must be disposed of in a "deep geologic repository" like the one designed for high-level waste.

Class A, which has the lowest concentration of radioactive material and poses the least potential hazard, must meet minimum regulatory requirements specified in 10 CFR 61. Class B contains a higher concentration of radioactive material than Class A. It must meet additional standards and be packaged in a stable container. According to 10 CFR 61.7 , both Class A and Class B waste will decay in 100 years or less.

Class C has the highest concentration of radioactive material allowed in a low-level radioactive waste disposal facility. Class C waste must meet the same standards as Class B, and in addition, it must be packaged so that inadvertent intruders are protected from exposure to the waste both during the time the disposal facility is open and for 500 years after it has been permanently closed.

Methods of Disposal

The general approach to low-level radioactive waste disposal is to isolate the waste by minimizing its contact with water and reducing the release of radioactive atoms into the air. Multiple engineered barriers have been incorporated into disposal facility design to discourage inadvertent intrusion and to help isolate the waste.

Historically, two methods of low-level radioactive waste disposal have been used: (1) near surface land disposal and (2) ocean disposal. Near surface land disposal involves confining low-level waste either at or below the earth's surface. Ocean disposal, employed by the Atomic Energy Commission prior to 1970, involved depositing waste containers on the ocean floor. This method is no longer used. Other disposal options such as Mine Disposal, Deep Well Injection, and Beneath Seabed Disposal are used or being considered around the world but are not currently used or under consideration in the United States.

Near Surface Land Disposal Facilities

The Near Surface Land Disposal facility is the most commonly considered design in the United States for future low-level radioactive waste disposal. This includes both above grade and below grade facilities. Seven options are described here.

1. Improved Shallow Land Burial involves the placement of waste containers in trenches that are well above the water table (see Figure 1). Trenches are typically 20 - 30 feet deep and 100 feet wide. Sand, gravel, or crushed stone is spread on the bottom of the trench to promote free drainage of water and to provide a dry foundation for the waste containers. The trench has a drain system equipped with monitoring devices to detect water that has seeped into the trench and any radionuclides that may have escaped from their containers into the water. When the trenches are full, any spaces between containers are filled with sand, and the trenches are capped (covered) with compacted clay. Improved Shallow Land Burial is not an option currently being considered by the Midwest Compact.

   
   Figure 1. Improved Shallow Land Burial/Modular Concrete Canister Site (simplified)

2. Modular Concrete Canister Disposal is virtually identical to Shallow Land Burial except for the type of container used. In Shallow Land Burial, the waste is buried in the steel or wood containers in which it was shipped to the disposal site. In Modular Concrete Canister Disposal, the steel or wood containers are placed in large concrete canisters which are then stacked on top of each other in the trenches.

3. Above Grade Vaults are rectangular structures, similar in size to warehouses. They are built above grade using reinforced concrete, metal, or masonry blocks (see Figure 2). Each vault is graded for drainage and is equipped with monitoring systems and sump pumps.

   
   Figure 2. Above Grade Vault (simplified)

4. Below Grade Vaults (see Figure 3) are underground facilities similar in size to Above Grade Vaults. They are constructed of metal or reinforced concrete, and the floors are sloped for water drainage. Each vault has monitoring systems and sump pumps.

   
   Figure 3. Below Grade Vault (simplified)

5. Augured Holes are another disposal option. A hole about 10 feet in diameter and 120 feet deep is dug. The bottom of the hole must be well above the water table. The walls of the hole are lined with metal or concrete. Waste containers are stacked in the hole. Any spaces between containers are filled with sand or clay. A cap, usually made of concrete, plugs and seals the augured hole.

6. Earth Mounded Concrete Bunkers combine features of above and below grade disposal (see Figure 4). In this design, a trench is completely lined with concrete. Concrete wall panels are used to divide each trench into large compartments where containers of Class B and C waste are stacked. Spaces between containers are filled with concrete. Containers of Class A waste are stacked on top of the compartments. The Class A containers are situated above ground level and are covered with a cap of earth and clay. Grass may be planted on the cap to minimize wind damage and erosion.

   
   Figure 4. Earth Mounded Concrete Bunker (simplified)

7. A Combination Concrete Canister/Concrete Vault disposal facility is also possible. In this facility, concrete canisters containing the waste could be placed in an above grade or below grade vault.

For More Information

If you would like to read more about disposal of low-level radioactive waste, some of the references listed below may be helpful.

Code of Federal Regulations, Title 10, Part 61, "Licensing Requirements for Land Disposal of Radioactive Waste", 1992.

Conceptual Design Report: Alternative Concepts for Low-Level Radioactive Waste Disposal, National Low-Level Radioactive Waste Management Program, EG&G Idaho, Inc., Idaho Falls, 1987.

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. Matthew E. Jorat is a Graduate Research Associate in Nuclear Engineering. Ronald J. Veley is a Graduate Research Associate, Ohio State University Extension.