There are five general categories of radioactive waste:

1. spent nuclear fuel from nuclear reactors and high-level waste from reprocessing spent nuclear fuel;
2. transuranic waste, resulting mainly as by-products from defense programs;
3. uranium mill tailings, from the mining and milling of uranium ore;
4. low-level waste, from contaminated industrial or research waste; and
5. naturally occurring radioactive materials. Mixed waste is waste that contains both radioactive components and other hazardous components.

Transuranic, or TRU, waste generally consists of protective clothing, tools, glassware, equipment, soils, and sludge contaminated with manmade radioisotopes heavier than uranium. (The term transuranic is derived from “trans,” meaning beyond, and “uranic,” which refers to uranium; thus, transuranic elements are beyond or “heavier” than uranium on the periodic table of the elements.) These elements include plutonium, neptunium, americium, curium, and californium. Transuranic waste is produced during nuclear fuel assembly; during nuclear weapons research, production, and cleanup; and as a result of reprocessing spent nuclear fuel.

The WIPP Land Withdrawal Act defines transuranic waste as “waste containing more than 100 nanocuries of alpha-emitting transuranic isotopes per gram of waste, with half-lives greater than 20 years.” The law specifically excludes high-level waste and spent nuclear fuel from the definition, as neither is allowed to be disposed of at the WIPP.

Types of Transuranic Waste

Transuranic waste is itself divided into two categories, based on its level of radioactivity.

Contact-handled transuranic waste (CH-TRU) accounts for about 97 percent of the volume of transuranic waste currently destined for the WIPP. It is packaged in 55-gallon metal drums or in metal boxes and can be handled under controlled conditions without any shielding beyond the container itself. The maximum radiation dose at the surface of a contact-handled transuranic waste container is 200 millirems per hour. Contact-handled waste primarily emits alpha particles that are easily shielded by a sheet of paper or the outer layer of a person’s skin.

Remote-handled transuranic waste (RH-TRU) emits more radiation than contact-handled transuranic waste and must therefore be both handled and transported in shielded casks. Surface radiation levels of unshielded containers of remote-handled transuranic waste exceed 200 millirems per hour. Remote-handled waste primarily emits gamma radiation, which is very penetrating and requires concrete, lead, or steel to block it.

Transuranic Wastes Allowed at the WIPP

In addition to withdrawing the WIPP site from public use and transferring the land to DOE control, the 1992 WIPP Land Withdrawal Act restricted the amount and types of transuranic wastes than can be disposed of at the facility.

• DOE can store a maximum of 6.2 million cubic feet of transuranic waste at the WIPP. The existing inventory of defense-generated waste totals about 2.32 million cubic feet. In addition, an estimated 3.7 million cubic feet of transuranic waste will be generated over the next 35 years as DOE defense sites are closed.
• The WIPP cannot accept remote-handled transuranic waste with a surface dose rate in excess of 1,000 rems per hour.
• The WIPP can accept no more than 5 percent by volume of remote-handled transuranic waste with a surface dose rate in excess of 100 rems per hour.
• The WIPP can accept no more than 5.1 million curies of remote-handled transuranic waste. The State of New Mexico and DOE have an agreement that no more than 7,079 cubic meters (250,000 cubic feet) of remote-handled transuranic waste can be emplaced in the WIPP.