High level waste, or HLW, is the highly radioactive, chemical waste material left over when spent nuclear fuel is reprocessed. HLW can be a solid, a liquid, or a sludgy mixture of the two.

HLW is produced when spent nuclear fuel is reprocessed to recover uranium or plutonium. Although the United States no longer reprocesses spent nuclear fuel, some other countries still do.

liquids were typically high in sodium content and are thus referred to as sodium bearing waste. As the sodium bearing waste was inseparably mixed with the reprocessing waste, the entire volume is classified as high-level waste.

(Classification of the sodium bearing waste as either high level waste or mixed transuranic waste is an issue that will have a huge impact on the method selected for treatment and is currently being decided in the legal system.)

Because HLW contains components that are hazardous, as well as radioactive isotopes, it is a mixed waste. All of the regulations that apply to radioactive wastes and all of the regulations that apply to hazardous waste apply to mixed wastes.

When HLW is created, it is almost entirely liquid, although some undissolved particulate matter can be contained in the liquid. Making liquid HLW into a solid is a significant goal of the environmental management plan at INL, and a requirement of the Settlement Agreement.

Of the nine million gallons of HLW produced at the INL, most (eight million gallons) has already been treated to make it a solid and reduce its volume. The treatment was done between 1962 and 2002 in facilities called calciners, and the solid resulting from the treatment is called calcine.

For several years, the Idaho has participated in the processes DOE is using to select alternatives for the treatment, storage, and disposal of high level waste. DOE issued the final Idaho High-Level Waste (HLW) and Facilities Disposition Environmental Impact Statement in September, 2002.

Although DOE has not issued a Record of Decision for the alternatives presented in the document, it appears that a decision on some portion of the waste treatment will be forthcoming after the selection of a new primary site contractor early in 2005.

The options for closure and disposal of facilities used to store and treat high level waste are:

• Do nothing.
• Remove or treat all wastes and contaminated items so they pose no future risk to workers or the public. This option would result in radiation levels as if the facilities had never been in place.
• Close facilities in accordance with state and federal requirements for landfills.
• Close facilities on a case-by-case basis, removing structures, decontaminating facilities and monitoring to reduce risks as necessary to meet health-based levels set for workers and the public.

Ask people how to manage spent nuclear fuel and high level waste over the long term and you'll hear different answers. Some believe a permanent geologic repository should house this waste. Others think it should go to a central location where it can be monitored and retrieved if necessary. And others believe it should be stored near the reactors that create it.

Congress chose the repository approach in 1982. Following Congress' direction, DOE is working to license and permit the site—Yucca Mountain, Nevada—for a national geologic repository for high-level waste and spent nuclear fuel.

Aerial view of Yucca Mountain, proposed site of the HLW repository

Scientists have studied methods for permanent disposal of radioactive wastes for years, focusing on a geologic repository since 1957, when the National Academy of Sciences recommended a facility deep underground. In 1992 the Academy reaffirmed that decision. The question of whether to use a permanent disposal site or a site where waste could be retrieved is the subject of great debate.

There is currently spent nuclear fuel and high level waste stored in 34 states. Some of it is at commercial power plants. Other waste is at federal facilities like the INL. If a repository were to open, this waste would be sent there and be placed in tunnels within special disposal containers.

At Yucca Mountain, tunnels would allow waste to be placed about 1,000 feet below the surface and 1,000 feet above the water table. The repository concept relies on barriers to prevent radioactive material from posing health risks. Some of these barriers are natural, including the rock type, depth of disposal, and dry climate. Other barriers would be engineered, human-made ones. The State of Nevada and some other groups are opposed to the use of Yucca Mountain as the nation's spent fuel and high-level waste repository.

The state of Idaho is keenly watching the process of licensing and permitting for the Yucca Mountain disposal facility. As yet, Yucca Mountain remains the only possibility for a permanent disposal location for HLW. If there's no place to take high level waste or spent nuclear fuel, it will be difficult, if not impossible, to ship it out of Idaho.

If a permanent disposal site is not open, these wastes could be taken to an interim site. But opening an interim site may be as difficult as opening a permanent one. Risks and public concerns inherent in transporting the waste might compel DOE to transport the waste only once-to a permanent disposal site.

While the state of Idaho is anxiously waiting for DOE to select a treatment alternative for INL's HLW, activity is happening behind the scenes at INL that will help ensure success when the selection is made.

DOE has been consolidating the remaining liquid sodium bearing waste into a few tanks at the INTEC tank farm and has been cleaning out the rest of the tanks. The cleaning process includes pumping out as much of the waste as possible and then using a high pressure spray nozzle to spray off the interior of the tank, while sucking out the residual water and sludge that pools at the bottom.

After cleaning, samples are taken of whatever remains in the bottom of the tank, and these samples are analyzed for hazardous and radioactive chemicals to determine if the tank is clean enough. Once the tanks are verified to be clean, they are isolated to prevent admitting any additional waste.

The plan is to fill the tanks with grout after they are emptied and cleaned, but the actual grouting has been put on hold. Yet another lawsuit is in the courts related to whether DOE can grout the tanks or whether they have to excavate the tanks and treat them as high level waste. Some groups claim the tanks themselves are HLW, due to the small amount of residual waste that adheres to the inside of the tanks after cleaning.

Research is also underway related to treatment alternatives for the sodium bearing waste and for the calcine, as well as research on methods of getting the calcine out of the storage containers so that it can be treated. The next year or so should hold some interesting decisions related to treatment of HLW at the INL.