About the focus areas
The U.S. Department of Energy’s Office of Environmental Management has established an integrated approach for addressing waste issues based on focus, or problem, areas: deactivation and decommissioning; mixed waste characterization, treatment, and disposal; nuclear materials; radioactive tank waste remediation; spent nuclear fuel; and subsurface contaminants.

Mixed waste contains radioactive components, which are managed to requirements of the Atomic Energy Act, and hazardous chemicals, which are subject to requirements of the Resource Conservation and Recovery Act (RCRA). The Department of Energy has identified more than 2,300 mixed waste streams at its sites, including a stored inventory totaling hundreds of thousands of cubic meters and additional waste generated by ongoing processes and cleanup activities. About 60 percent of the total inventory is categorized as transuranic (TRU) and is packaged in containers ranging from 55-gallon drums to fairly large cargo containers. Most of the TRU waste is destined for disposal at the Waste Isolation Pilot Plant (WIPP).

The mission of the Mixed Waste Focus Area is to develop and implement technologies capable of treating DOE’s mixed waste. Managed by DOE’s Idaho Operations Office, MWFA operates in close partnership with end users to ensure that its efforts address and meet priority needs and with regulators to ensure that demonstrated solutions are accepted and approved for deployment. The focus area organizes its efforts into eight work packages devoted to solving DOE’s most important mixed waste problems.

Characterization
Regulatory drivers and management needs, as well as stringent WIPP waste acceptance criteria for the TRU waste portion, require detailed characterization of the mixed waste inventory’s radioactive and hazardous components. The characterization work package develops solutions for problems associated with detecting the concentrations of radionuclides and RCRA constituents. These techniques, particularly nondestructive waste assay (NDA), will enable waste containers to meet transport and disposal acceptance criteria. Current goals include improved NDA of highly radioactive packages and nondestructive characterization for RCRA constituents.

In fiscal year 1998, Gamma-Ray Active and Passive Computed Tomography was demonstrated and integrated into the Waste Inspection Tomography mobile laboratory trailer, and Combined Thermal/Epithermal Neutron Assay technology demonstrated the capability to accurately assay TRU wastes at low TRU mass loadings. An Expert System for NDA Data Validation developed and installed at Idaho National Engineering and Environmental Laboratory harnesses computer power to automate and increase the rate at which measurement data on containerized waste can be validated.

Mercury contamination
Because mercury is highly mobile and easily vaporized, its presence in many concentrations in several DOE mixed waste streams—including large volumes of soil and debris and several types of process residues—complicates the design of off-gas systems, the stabilization of treatment residues, and the monitoring of all effluents. Removing mercury before treatment would significantly simplify downstream treatment operations and reduce the cost of treatment facility design, construction, and operation, as well as the risk of operation. Recovered mercury must then be amalgamated or otherwise stabilized for disposal as a separate waste stream. The mercury work package develops solutions for the separation of mercury from both solids and liquids, the stabilization of mercury, and the amalgamation of free mercury.

Raduce, Inc. has developed a vacuum-assisted thermal desorption process called Sepradyne to separate volatile metals and organics from waste matrices. The system uses an impinger to extract contaminants volatilized from the waste matrix and then treats the off-gas with standard filters and ion-exchange resins. MWFA is working with Raduce to demonstrate Sepradyne on mercury-contaminated soils and other waste matrices. A bench-scale version of the Sepradyne process is scheduled to complete a treatability study at Brookhaven National Laboratory this summer. BNL has over 400 cubic meters of soil contaminated with mercury at levels above 260 ppm, which currently requires separation and amalgamation for RCRA compliance. Raduce hopes to demonstrate the technology’s ability to destroy dioxins in the ash to below the RCRA limit of 1 ppb.

MWFA is also combining efforts with the U.S. Environmental Protection Agency to investigate the feasibility of changing mercury treatment regulations to allow stabilization of mercury-contaminated mixed waste containing >260 ppm mercury. See the story entitled “Got mercury?” in this issue. For other information on mercury, see the section at the bottom of this page entitled “Mixed Waste National Technical Workgroup.”

Material handling
DOE has large volumes of waste, especially those designated as remote handled, that need improved handling techniques to allow for safe and efficient treatment and disposal. The material handling work package develops technologies for handling, sorting, and reducing the size of materials in connection with treatment systems, waste volume reduction, and repackaging of TRU waste. Commercially available equipment often requires modification and testing before use in radioactive environments.

In cooperation with the Robotics Crosscutting Program, MWFA is providing key solutions, such as the Handling and Segregating System for 55-Gallon Drums (HANDSS-55) of mixed waste. This system enables operators to remotely open drums, inspect the contents, remove noncompliant items, and repackage the waste for disposal, all in a safe and efficient manner. This development effort has strong end-user commitment by the Solid Waste Division at the Savannah River Site and is scheduled for deployment in two years. HANDSS-55 is being designed in a modular format, enabling the technology to be converted to a mobile format for use by sites with small amounts of high-activity waste.

Salt and ash stabilization
Portland cement is used to stabilize much of the sludge, soils, and homogeneous solids in DOE’s mixed low-level waste, but fly ash and scrubber blowdown residue from DOE incinerators present unique problems because they contain salts or heavy metals, which can prematurely degrade the waste form. This problem is currently resolved by mixing very low proportions of the waste material with the cement, but this approach significantly increases waste volume, multiplying waste handling and transportation costs and consuming scarce disposal capacity.

The salt and ash stabilization work package is improving product durability and waste loading. Three processes developed with MWFA support—polymer microencapsulation by extrusion (PME), polymer microencapsulation by kinetic mixing (PMK), and chemically bonded phosphate ceramics (CBPCs)—have been sufficiently demonstrated and tested to warrant full-scale implementation in a commercial facility. Brookhaven National Laboratory will support commercialization of the PME and PMK processes, which were developed and patented there, and Argonne National Laboratory–East will support commercialization of the CBPC process developed and patented there.

In the PME process, friction and some external heating generate the melting temperature of low-density polyethylene, and a turning extruder mixes it with waste. The process has been demonstrated on salts, dry ash, and soils. In the PMK technology, high-speed mixing quickly homogenizes a waste and polymer mixture in seconds, volatilizing water and other organic compounds, yielding a product ready for disposal. Generally, waste streams with greater than 2 weight percent water or organics must be dried before treatment. The PMK process dries and stabilizes the waste in one step and tolerates waste loading of 50 weight percent for most waste materials tested. Products of both technologies pass leach testing for RCRA-regulated hazardous metals. CBPCs also have high waste loading potential and can process very wet sludge.

TRU waste transportation
TRU wastes destined for storage in WIPP may be rejected for exceeding wattage limits. Wattage measurements are used to estimate the potential for hydrogen gas generation during the 60-day waste transport period. The TRU waste transportation work package develops solutions to increase the amount of waste that can be transported per container, while still meeting hydrogen gas limits in the waste container. One promising technology is “hydrogen gas getters,” solid materials that form irreversible chemical bonds with hydrogen. Successful development would mean that fewer drums of TRU waste will require treatment or repackaging into multiple containers, saving associated costs of characterization and additional transportation and storage.

Off-gas monitoring and control
In recent trial burns, three DOE incinerators failed to meet at least one emission or monitoring requirement in the EPA’s proposed rule for maximum achievable control technology (MACT) for hazardous waste combustors. Specific problem areas include dioxins and furans, multimetals, mercury, and other substances like chlorine. According to EPA’s current schedule, facilities not in compliance by January 1, 2002 will be shut down, threatening the ability of several sites to meet compliance agreements.

Mixed waste treatment and handling processes must be monitored to ensure that hazardous releases stay within regulatory limits, but current monitoring technologies are expensive and time-consuming. The off-gas monitoring and control work package is focused on measuring mercury and multiple metal emissions at the stack, removing mercury and particulate matter from off-gas streams, and preventing the formation of dioxan/furans during waste treatment. Continuous emission monitors (CEMs) like the MIT Microwave Plasma CEM, an R&D 100 Award winner, can save time and money by providing real-time data through automated monitoring. MWFA is teaming with EPA and the Department of Defense to develop improved off-gas filtration and facility operation procedures.

Alternatives to incineration
Incineration is the standard treatment for organically contaminated mixed waste, and previous issues of Initiatives have described several MWFA-funded thermal treatment technologies: Plasma Hearth Process (February 1996), Transportable Vitrification System (December 1996), and DC Arc Furnace (Spring 1999). But not all organically contaminated mixed waste can be incinerated, and potential release of process by-products is a concern. Indeed, incinerators are becoming more complex and more difficult and expensive to permit and operate. The alternatives to incineration work package develops alternatives to open-flame thermal treatment processes. Acid digestion uses a phosphoric acid/nitric acid solution to chemically oxidize organic mixed waste at moderate temperatures and less expensively than incineration. Direct chemical oxidation uses peroxydisulfate to achieve similar ends and may be commercially deployed this year.

Unique waste
Some 10–15 percent of DOE’s mixed waste inventory cannot be prepared for disposal using existing capabilities because of the nature of the hazardous contaminants, radioactive isotopes present and/or their concentrations, regulatory requirements, stakeholder concerns, or resource limitations. Though they represent a significant proportion of DOE’s mixed waste inventory, they are not typically included in privatized treatment contracts because their disposition requires highly specialized solutions, and their usually low volumes and special problems have kept them in relatively low priority for disposition at most sites. The newly established unique waste work package identifies and addresses issues associated with disposition of these problematic waste streams, which include organic wastes streams (e.g., tritiated and TRU PCBs), highly energetic waste streams (water reactives, pyrophorics, and high explosives), radioactive sources, and miscellaneous waste streams like batteries, activated lead, and gas cylinders.

End users are at stage center
The MWFA End User Steering Committee, established in FY98, includes federal employees representing the major sites with mixed TRU and low-level waste (LLW) needs. The committee is chaired by Helen Belencan, DOE Headquarters’ MLLW program manager. The vice chair is Greg Duggan, director of the LLW/MLLW Center of Excellence. Their involvement in complexwide waste management activities gives them unique insights for providing leadership to the steering committee.

Steering committee members chaired the panels in the February 1999 midyear independent review of the focus area’s technical work packages. End users from the sites helped plan sessions and participated in panels. Bill Owca, MWFA program director, calls this activity one of the most unique and effective examples of end user involvement in his experience: “The discussions regarding the usefulness of our solutions were frank and open. We heard both compliments and criticisms, but all the input we received was extremely valuable. Our fiscal year 2001 budget submittal reflects the input we received, and I believe this budget is the most consistent with end users’ needs and requirements we’ve ever submitted.”

The summary report of the review—Mixed Waste Focus Area, Fiscal Year 1999 Independent Review, Summary Report (DOE/ID-00483)—may already be available and will be published on the MWFA Web site at http://wastenot.inel.gov/mwfa.

Mixed Waste National Technical Workgroup
Streamlining the regulatory process and improving interagency and interstate communications

An interagency agreement between DOE and the U.S. Environmental Protection Agency created the National Technical Workgroup (NTW) for the Treatment of Mixed Waste to assist resolution of issues between regulatory agencies and mixed waste treatment facility operators. NTW enables regulatory personnel, including permit rule writers, to communicate with those who will be regulated in open and nonconfrontational forums in advance of issuing final regulations.

NTW sponsors workshops to support targeted technical areas. “Monitoring and Control of Mercury for Mixed Waste Thermal Treatment” was held in November 1998 to promote a common understanding of the maximum achievable control technology (MACT) rules for treatment of mixed waste containing mercury and DOE’s current capability to comply with them. More than 125 issues of concern were identified, many of which related specifically to technical challenges associated with implementing the new rules. Copies of presentations from the workshop, a summary of technical issues, and recommended approaches to resolve them can be found on the NTW Web site (see below).

In conjunction with the DOE Center for LLW/MLLW Excellence, the DOE Center for Risk Excellence, and MWFA, NTW cosponsored a June 1999 workshop on understanding and implementing EPA’s risk assessment protocols for combustion facilities. The workshop included sessions on EPA’s new human health risk assessment and ecological risk assessment protocols for hazardous waste combustion facilities, presented by primary authors of the protocols.

For additional information on the NTW and its activities, contact David Eaton, MWFA, (208) 526-7002, dle@inel.gov) or visit the NTW Web site at http://www.ntw-mixedwaste.org.