Across the U.S. Department of Energy complex, 332 large underground storage tanks contain hundreds of thousands of cubic meters of high-level radioactive mixed waste. Seventy-nine of these tanks are leaking and others are potentially explosive, giving impetus to the tanks focus area to develop safe, reliable, and cost-effective methods for characterization, retrieval, treatment, and final disposal of the wastes. On October 27, Initiatives interviewed Rod Quinn, technical program manager of the TFA. Quinn is employed by Pacific Northwest Laboratory in Richland, Washington, the technical lead organization for the TFA. The technical team headed by Quinn includes representatives from DOE's four primary tank sites and their respective M&O (managing and operating) contractors, and representatives from six national laboratories.
According to Rod Quinn, "Tank waste is probably DOE's major environmental management problem. Over 40 years of radioactive weapons production has resulted in tank storage of radioactive and chemical mixed waste containing millions of curies of radioactivity, stirred into a physically and chemically heterogeneous mixture." Quinn also describes DOE's tank waste problem as unique. "A lot of industries have contaminant plumes, buildings that have to be decommissioned, or mixed waste. But only DOE has radioactive waste tanks."
DOE has stored this radioactive and chemical mixed waste in underground single-shell and double-shell tanks made of stainless steel, concrete, and concrete with carbon steel liners. Their capacities vary from 5,000 to one million gallons. Underground storage tanks, or USTs, are covered with a layer of soil ranging from a few feet to tens of feet thick.
The four primary DOE tank sites are the Idaho National Engineering Laboratory near Idaho Falls, Idaho; the Savannah River Site near Aiken, South Carolina; the Oak Ridge Reservation in Oak Ridge, Tennessee; and the Hanford Site in Richland, Washington.
Leaking tanks and characterization problems
DOE's USTs are showing their age. Quinn said, "Sixty-nine of the 149 single-shell tanks at Hanford are known leakers. When it was found Hanford had leakers, we pumped the liquid out of the single-shell tanks into double-shell tanks." However, this movement of material changes the chemistry of tank contents and makes a difficult characterization problem more complex. "These tanks are living, evolving chemical factories. The chemistry does not remain constant. When you have organics in the presence of active radionuclides, you have chemical reactions.
"Cesium and strontium are heat generators. Cesium, a gamma-emitter, generates heat directly. Strontium generates heat as it decays. Twenty to thirty years ago, these heat emitters were processed with organics, which separated these high-level wastes from other wastes. That seemed like a good idea at the time. The problem is that organics in the presence of heat and radioactivity generate other chemical species. We may understand elementally what we put in the tanks, but we don't understand molecularly what their products are over time."
Characterizing tank waste is also complicated by its physical heterogeneity. Its several physical forms include salt cake, sludge, and supernate. Quinn said waste characterized as salt cake ranges from "soft enough to be broken up with your fingers to as hard as concrete. Sludge can be very appropriately compared to peanut butter" in its consistency. Supernate is solution which floats above sediment.
Retrieval and remediation
When treating radioactive tank waste, human exposure must be minimized. According to Quinn, established radiation control procedures involving glove boxes and hot cells are "extremely expensive and very speicalized." TFA works with the robotics crosscutting program to develop telerobotic operations to protect workers from radioactive exposure.
TFA also works with the efficient separations processing crosscutting program to develop processes for separating the waste into low-level, transuranic, and high-level portions, thereby significantly reducing the volume of high-level waste requiring costly processing and disposal. Plans call for the vitrification of high-level waste into glass logs. Quinn said, "The big driver in cost is the number of glass logs required to stabilize high-level waste. There are all kinds of predictions in costs; but in some cases, estimated costs have ranged from $1,000 to $1 million a log. The waste at Hanford alone would create something in the vicinity of 40,000 logs, each log being two feet in diameter by ten feet long."
To drive down processing costs, the challenge is to efficiently separate high-level wastes from the rest of the waste stream. The tanks focus area is developing and demonstrating separation technologies that can segregate radioactive ions from non-radioactive ions. (See related article). This challenge can be applied to many Hanford tanks containing high-sodium (alkaline) solutions. Quinn observed, "Sodium is very similar to cesium in its chemical properties. But sodium can be processed as low-level waste, while cesium must be processed as a high-level waste."
Sensors are being developed that can be used inside tanks. In-situ characterization of tank waste can be more accurate than removing samples for analysis in hot cells, specially constructed units engineered for analysis of radioactive waste. In-situ characterization eliminates the time delay between sample removal and sample analysis. This technique also decreases the cost of waste analysis, currently performed manually in laboratories on tank core samples. Most important, remote analysis eliminates sample handling and worker exposure.
The Light Duty Utility Arm will be used at Hanford as a way to deliver sensors into tanks for in-situ analysis. Analytical sensors will be deployed through risers, or tank entry holes, ranging from four inches to 12 inches in diameter. Quinn talked about the use of the LDUA for in-situ characterization. "Historically, most of the characterization has been done by running some kind of retrieval tool down risers and pulling out samples." He said, "For a tank with one-half to one million gallons of heterogeneous waste, that sample is not going to be representative of what's in the tank. The LDUA provides a way to get analytical tools in the tank to do spectroscopy and analyze a sample from an out-of-the-way spot."
But hot cell analysis won't be abandoned in favor of exclusive use of in-situ analysis. "At Hanford, we will deploy Raman and laser-based spectroscopy in a hot cell to scan core tank samples. The aim will be to drive down costs and improve data quality. We have begun deployment of an advanced hot cell to improve characterization capabilities."
Other tanks technologies address identified retrieval, treatment, and disposal needs. "We have ongoing activities for improved mechanisms for getting inside the tanks, analyzing what's in there, and also for beginning the retrieval process. The LDUA will be demonstrated at three sites over the next year. we're working on an improved mixer/pump capability to stabilize tank waste as a first step toward retrieval. we're looking at improved ion exchange techniques for cesium removal with demonstrations planned at Oak Ridge using a variety of tank waste from the four sites. And we're working on a retrieval and tank closure demo at Savannah River, which should be well into its operational phase in 14 months."
Quinn is convinced of the value of assessing needs at the four DOE tank sites. "A needs assessment is absolutely essential to ensure buy-in from users and stakeholders. Without a needs assessment, how are you going to convince stakeholders, regulators, investors, and users that you are really attacking the right problems? The tanks focus area interacted repeatedly with the four sites to come up with a needs assessment document. We worked with them to prioritize the identified needs into high-, medium-, and low-impact needs. What we're aiming to do is invest our technology development dollars in places where we can really make an impact on cost reduction, schedule reduction, or programmatic risk reduction."
In talking about TFA's stakeholder interactions, Quinn first defined TFA's user/producer/developer team concept. "Users are the people who actually own the responsibility for maintenance and operation of tanks. At Hanford, that user is Westinghouse Hanford Company." The producer conceptualizes the technology and may bring it to an early stage of development. The producer may also obtain intellectual rights to the technology. "Developers work on the idea to apply it to a particular problem. For the Light Duty Utility Arm, the producer is SPAR Aerospace Company of Toronto, Canada. The developers are Pacific Northwest Laboratory, Westinghouse Hanford Company, and Sandia National Laboratories."." Westinghouse Hanford Company will use the Light Duty Utility Arm for characterization and retrieval of tank waste.
According to Quinn, "Stakeholder activity has to come through the user, who has maintenance, operation, and cleanup responsibilities. The tanks focus area will help Westinghouse Hanford in achieving stakeholder involvement, but we won't usurp the contractor's responsibility [in this regard]."
Stakeholders are also involved through each site's Site Technology Coordinating Group. "Hanford's STCG has representatives from the Washington Department of Ecology, Washington small businesses, local Indian nations that may ultimately reclaim some of the land, and Heart of America and other environmental interest groups. These stakeholders validate that we are addressing the right problems and needs. They have a voice in the system and can understand the value of better, faster, and cheaper technologies."
Like the other focus areas and crosscutting programs, TFA is interested in finding industrial partners who are developing innovative technologies capable of filling the unique needs of the focus area. Quinn said, "My advice for someone who would like to approach the TFA with a technology would be to get a copy of our Multiyear Program Plan, which is our strategy to meet identified needs. When we request proposals, we communicate through the Commerce Business Daily and other publications. To get a copy of any RFP we send out, [interested parties] can get on our mailing list."
To receive a copy of the tanks focus area's Multiyear Program Plan, call the National Technical Information Service at (703) 487-4650. After January 1, the document will be available for a charge from $2.00 to $8.00.