Halting the Legacy
The Bush administration's interest in increasing our reliance on nuclear energy gives renewed impetus to the ongoing debate on how to safely dispose of nuclear wastes. Much attention has been focused on Nevada's Yucca Mountain as a repository for nuclear fuel, the most long-lasting radioactive waste, but such material comprises only a minor percentage of the total legacy nuclear waste volume in the United States. The large majority of the legacy waste is mixed (chemically hazardous low-level radioactive material), and the good news is that it is finally being safely treated for permanent disposal.
Most Legacy Waste is Mixed
The vast majority of legacy waste is mixed (both radioactive and chemically hazardous), which is regulated not only by the Atomic Energy Act but also by the Resource Conservation and Recovery Act (RCRA) and the Toxic Substance Control Act (TSCA). The material must go to a licensed radioactive landfill for final disposal, and it must first be treated to meet "land ban" standards under RCRA, which requires the pretreatment of hazardous waste before it can be land disposed. If the material contained is listed under RCRA, the disposal facility must also be permitted as a RCRA cell. The waste is then placed in engineered cells that protect it from the environment. The success of low-level disposal when compared to high-level is a result of the redundancy built into the approach and the lower risk associated with the lower radioactivity.
For the mixed waste market, barriers to entry for treatment facilities are immense. Other than the obvious need for both a radioactive license and a hazardous waste permit, additional barriers include: national security issues, a much greater need for safety, higher levels for quality assurance/quality control (QA/QC), the need for a variety of different technologies and a contracting mechanism with the U.S. Departments of Energy (DOE) and Defense.
Incineration of mixed waste has been very difficult. |
In December 2001, Perma-Fix Environmental Services Inc. began shipping treated mixed waste from its third and largest commercial mixed waste facility to a licensed radioactive landfill for final disposal. The plant occupies 150,000 sq. ft. of space at the DOE's K-25 weapons plant in Oak Ridge, Tenn. The K-25 facility was one of the original sites of the Manhattan Project and was where uranium was enriched for the first atom bomb. Perma-Fix owns its Oak Ridge facility, which is the largest new hazardous facility built in the last 10 years. The company spent almost $30 million on its construction and development.
A Decade-Long Learning Curve
Perma-Fix's technologies depend upon the destruction or removal of hazardous components or chemically changing their state to put them in a form that will immobilize them for geologic time. In fact, many of the processes used by the company result in end products that are similar to how elements are found in nature. The company has developed different technologies for each type of waste. Treatment of metals and characteristic waste is accomplished by the company's proprietary Perma-Fix process, which has been used both at customers' sites and at its own non-radioactive hazardous facilities for more than 10 years. More than 1.5 million drums of waste have been treated with the process prior to adapting it to mixed waste.
The process is actually a series of processes that are each designed for not only the type of waste but also the matrix. The process is a water-based process operated at room temperature, usually in the actual drum the waste is received in. The waste is initially slurried with water in its existing container, and then appropriate chemicals are added to destroy the waste's hazardous characteristics. After verification that the treatment is complete, the slurry is stabilized in its drum to produce a solid monolith.
For example, lead is a highly toxic element if it is present in a soluble state or form that can leach into the environment, as is found in leaded paint. On the other hand, leaded glass (up to 50 percent lead), which is lead silicate, is nontoxic and unavailable to the environment. The Perma-Fix process can stabilize lead.
High capital costs, technical issues and, most significantly, public distrust have made incineration of mixed waste a very high-risk option. |
Treatment of organics and listed materials (all those wastes defined as listed under RCRA) is a greater challenge. Historically, non-radioactive organic hazardous materials are incinerated or used as a fuel in a BIF (Boiler & Industrial Fuels Regulations) facility. Incineration of mixed waste has been very difficult. DOE operated three incinerators (Idaho, Savannah River and Oak Ridge). Two have been closed, and the last, at Oak Ridge, is scheduled to close shortly. A commercial mixed waste incinerator was under construction in Washington state, but was halted due to the bankruptcy of the company. High capital costs, technical issues and, most significantly, public distrust have made incineration of mixed waste a very high-risk option.
DOE has been very interested in using vitrification not only for high-level but also for low-level waste. Vitrification on paper looks like the ideal process, combining incineration, chemical fixation (using the high temperature to produce insoluble metal species) and the most ideal physical form (glass blocks) in one process. But as has been learned in the waste business, a single solution for highly complex and variable waste usually is not the preferred option. Vitrification has been plagued with a variety of technical and engineering problems resulting from waste variables, the corrosiveness of molten glass and equipment issues due to the extreme conditions. The commercial Washington state incinerator was also a vitrification unit.
Perma-Fix has developed a series of processes (the Perma-Fix II Process), using a combination of separation and chemical treatment, to treat organic and listed materials and produce a solid waste that meets treatment standards, so that the solid produce can be disposed in a radioactive or a RCRA-permitted radioactive landfill. Since with organic RCRA contaminants, most of the actual waste is listed, it will continue to carry the original code when it is treated to meet land ban standards; and consequently, it can only go to a radioactive landfill that is permitted for RCRA hazardous materials (there are several).
The Perma-Fix II Process
Separation
Separation includes physical separation, solvent washing for non-volatile, semi-volatile and high organic matrices and distillation and desorption for volatile and low organic matrices. The processes are used individually or in combination and are operated until the solids are below land ban disposal standards, as spelled out in 40 Code of Federal Regulations 268.
Vitrification has been plagued with a variety of technical and engineering problems resulting from waste variables, the corrosiveness of molten glass and equipment issues due to the extreme conditions. |
Destruction
With the removal of the organics from the solid matrix, treatment or destruction of the organic contaminants is greatly simplified. Most radioactive isotopes remain with the solid. The destruction of organics includes a BIF boiler for treatment of radioactive liquids, chemical oxidation for organics remaining in the solids and chemical reduction for chlorinated and PCBs. The Perma-Fix II process has now operated at the company's Florida facility for more than two years and at its Oak Ridge facility for eight months and is very successful.
With the company's three mixed waste facilities now accepting waste from more than 40 DOE sites, the U.S. Department of Defense, nuclear utilities, hospitals and research facilities, a 50-year problem is now being solved as mixed waste is being treated to meet land treatment standards and sent for final disposal.
This article originally appeared in the September 2002 issue of Environmental Protection, Vol. 13, No. 8, p. 30.
This article originally appeared in the 09/01/2002 issue of Environmental Protection.