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Weapons of Mass Destruction (WMD)

B.9.0 TECHNOLOGIES

As discussed in Section B.2.0, there are numerous technologies that could be used for remediating tank waste. Technologies are specific processes that form the building blocks of the alternatives. Alternatives are then made up of a set of technologies that have been designed to function together.

Technologies that were not included in the alternatives that were developed for impact analysis, but are still viable as potential components of a remediation alternative are discussed in this section. For example, the technology selected for inclusion in the alternatives for immobilizing the LAW was vitrification. However, the ceramic waste form may also be viable and could be substituted as a LAW immobilization process.

B.9.1 IN SITU WASTE TREATMENT TECHNOLOGIES

In Situ Grout

Grout is a common solidification and stabilization technology used in managing hazardous waste. Stabilization is a process in which additives are mixed with the waste to minimize the rate of contaminant migrating from the waste form. Solidification is a process in which additives are mixed with the waste to yield a physical waste form, as measured by properties such as permeability and compressive strength, that is acceptable for waste storage or disposal. Performance measures used to evaluate solidification and stabilization technologies are obtained through leaching tests that provide data on the rate at which contaminants are released from the waste form under the action of water.

In situ grout is a technology that could be used to immobilize the waste and stabilize the tanks as an option to the waste drying and gravel filling operations described in the In Situ Fill and Cap alternative. Applying this technology would involve adding a grout mixture to each of the tanks, mechanically mixing the waste with the grout mixture, and stabilizing the tanks by filling the dome space with grout. Using this technology would leave the waste its current locations for disposal as in the In Situ Fill and Cap alternative, except that the waste would be solidified in a grout matrix instead of dried. After completing grouting operations, a Hanford Barrier would be installed over each of the tank farms.

A pozzolan-based grout formulation made up of sand, flyash, water, cement, and air entrainment additive could also be used (WHC 1995f). Pozzolanic materials can react with lime in the presence of water to produce a solid cement-like material. Flyash is the most commonly used pozzolanic material. Other types of grout formulations include cement-based thermoplastics and organic polymer-based grouts. Implementation of this technology would require the following actions:

  • Reduce the volume of liquid in the DSTs by evaporation;
  • Construct a TFCF over each tank farm;
  • Remove the soil covering the top of each tank;
  • Remove the top of each tank (dome) for access by the grout mixer; and
  • Mix the waste mechanically in each tank with the grout mixture.

Grouting the tank waste in situ would result in a waste form with lower contaminant leachability compared to drying the waste and filling the tanks with gravel. However, if the rate of water infiltration to the waste form is controlled by using an effective surface barrier, the infiltration rate becomes the controlling factor in contaminant flux. Thus, the difference in performance of the in situ grout waste form in the In Situ Fill and Cap alternative is expected to be minor when a Hanford Barrier is used.

The impacts associated with implementing the in situ grout technology would be bounded by the impacts associated with the In Situ Vitrification alternative and the In Situ Fill and Cap alternative. In situ grouting would require a TFCF during operations, which would greatly increase the capital cost requirements and construction personnel levels over levels estimated for the In Situ Fill and Cap alternative. The capital costs and construction staffing requirements would approach those estimated for the In Situ Vitrification alternative. In addition, there would be an increase in offsite transportation associated with in situ grouting to bring the grout forming materials onsite.

In Situ Vitrification of Individual Tanks

The In Situ Vitrification alternative is based on the assumption that during operations, because of overlapping melt regions, the entire tank farm would be vitrified. In situ vitrification is a technology that could be applied to vitrify individual tanks or selected areas within the tank farms. Because the molten region would expand during vitrification, some overlapping of vitrified areas between tanks would be expected.

Minimal impacts would be associated with vitrifying the individual tanks and minimizing the vitrified region between the tanks as opposed to vitrifying the entire tank farm area. Using alternative confinement concepts that provided confinement and off-gas collection for an individual tank may reduce the construction and resource impacts compared to those associated with building a TFCF over each tank farm. This technology is not mature enough to accurately define the limits of the vitrified zone.

Use of Previously Contaminated Materials

To assess impacts and estimating costs, this EIS has assumed that all fill and borrow material is uncontaminated. However, it may be possible to use slightly contaminated material for glass formers in the in situ vitrification process. This alternate material must be characterized so that it would be added in the correct proportions and potential exposures would be within Site and DOE limits. The impacts associated with using previously contaminated materials would include a slight increase in groundwater contamination and potentially higher costs associated with added characterization and personnel protection. The amount of LAW from other areas would be reduced.

B.9.2 WASTE RETRIEVAL AND TRANSFER TECHNOLOGIES

The function of waste retrieval and transfer technologies is to remove the waste from the tank and transfer the waste to a treatment facility. Waste retrieval and transfer technologies are applicable to all ex situ alternatives where waste treatment will occur outside of existing storage tanks.

Retrieval Criteria

The current waste retrieval criteria is assumed to be capable of removing 99 percent of the existing waste volume from each tank during retrieval operations. This assumption is based on judgement and waste retrieval operations performed at the Hanford Site in the past. The current physical form of the waste stored in some of the SSTs appears to have dried and aged to the point that waste retrieval assumptions based on past practices may not be valid, and the criteria of 99 percent waste retrieval from each tank may be impractical or impossible using current retrieval concepts.

Retrieving 99 percent of the tank waste would leave a residual waste inventory of 1 percent in each tank. This 1 percent residual would be treated as a source of contamination that would, after a long period of time, migrate out of the tanks and become available for transport through the vadose zone. The rate of migration and transport of the contaminants would be highly dependent on the rate at which water infiltrates the residual waste, which would be controlled by installing a Hanford Barrier over the tank farms following retrieval.

Retrieving less than 99 percent of the tank waste would result in a larger residual inventory being left in the tanks for disposal. In turn, this large tank waste residual inventory would result in increased levels of long-term risk associated with the release and migration of contaminants associated with the larger residual inventory.

Retrieval Using Alkali Solutions

Retrieving alkali soluble residuals is a technology that could be used during retrieval operations for any of the ex situ alternatives. Retrieving alkali soluble residuals would involve washing the tanks with an alkali (sodium hydroxide) solution to remove the alkali soluble portion of the remaining waste solids for additional processing. Retrieving alkali soluble waste could allow increased retrieval for certain types of tank waste. The impacts of using this technology would be increased chemical additions to the waste inventory and potentially lower residual waste inventory left in the tanks following retrieval.

Retrieval Using Acid Solutions

Dissolving tank residuals in acid is a technology that could be used during the retrieval operations for any of the ex situ alternatives. This technology could be used to dissolve hardened sludges and waste that could not otherwise be retrieved, which would help achieve a specific retrieval criteria. The dissolving action of the acid on the residual waste would also act on the interior of the tank and could open or enlarge an existing leak path. This technology would be most applicable to DSTs because the outer tank shell would contain any leakage developed by the inner shell. Implementing this technology would require controls to minimize the potential for increased tank leakage. The impacts of using this technology would be increased chemical additions to the waste inventory and potentially lower residual waste inventory left in the tanks following retrieval.

Tank Waste Retrieval Technologies

Many different technologies to retrieve the tank waste have been identified and evaluated (Boomer et al. 1993). The function of a retrieval technology is to remove the waste from the underground storage tanks in a safe, effective, and efficient manner that meets a defined retrieval criteria for the volume of waste retrieved. Retrieval technologies that have been identified and could be used to retrieve tank waste during any of the ex situ alternatives include.

  • Mechanical retrieval would use a mechanical device like a back-hoe bucket or skip hoist to mobilize the waste and remove it from the tank. Mechanical retrieval would require an arm-based maneuvering device that would permit remote operation of the retrieval system.
  • The Houdini waste retrieval system is a small, remotely-controlled robotic crawler type vehicle that is being evaluated at other DOE sites for waste retrieval operations. This type of technology could be selectively applied following other retrieval technologies to achieve retrieval criteria. The Houdini system being developed would collapse to fit through existing tank openings and would have mechanical attachments that would be used to break up and mobilize waste.
  • Pneumatic retrieval is similar to hydraulic retrieval methods except that air would be used to move the waste as opposed to liquid.

Subsurface Barriers

Subsurface barrier technology could be used during retrieval operations for any of the ex situ alternatives. Subsurface barriers are most suitable for use in conjunction with hydraulic retrieval technologies, which have a higher potential for SST leakage. Subsurface barriers would not stop a leak but would provide containment to control the migration of tank leakage. Subsurface barriers are impermeable layers that would be installed in the soil surrounding a tank to contain any leakage that might occur during waste retrieval operations. The possibility of using subsurface barriers derived from concerns about using hydraulic sluicing for retrieval, and because some of the SSTs are either confirmed or assumed leakers. The function of the subsurface barriers would be to prevent tank leakage from migrating beyond the barrier into the vadose zone. This would help leak cleanup by minimizing the volume of contaminated soil.

A study titled Feasibility Study of Tank Leakage Mitigation Using Subsurface Barriers (Treat et al. 1995) has been completed in support of Tri-Party Agreement Milestones M-45-07A (Ecology et al. 1994). This feasibility study assessed:

  • The potential environmental impacts of waste storage and retrieval activities without the application of subsurface barriers;
  • Functional requirements of subsurface barriers to minimize the impacts associated with waste storage and retrieval activities; and
  • The application of existing subsurface barrier technologies and the potential of existing technologies to meet functional requirements for SST waste storage and retrieval activities.

Fourteen different tank waste retrieval alternatives were analyzed in the feasibility study. The alternatives ranged from a No Action alternative, in which none of the waste was retrieved, to clean closure, where waste retrieval activities were assumed to remove 100 percent of the tank waste. The alternatives analyzed represented combinations of technologies for waste retrieval, subsurface barrier containment, tank stabilization, and surface barriers. The 14 alternatives analyzed included 8 alternatives with subsurface barriers and 6 alternatives without subsurface barriers.

The following subsurface barrier technologies were screened in the feasibility study as potential technologies that could be used for subsurface barriers:

  • Chemical jet grout encapsulation;
  • Freeze walls;
  • Jet grout curtains;
  • Permeation chemical grouting;
  • Wax emulsion permeation grouting;
  • Silica, silicate permeation grouting;
  • Polymer permeation grouting;
  • Formed-in-place horizontal grout barriers;
  • Circulating air barriers;
  • Radio-frequency desiccating subsurface barriers;
  • Sheet metal piling subsurface barriers;
  • Close-coupled injected chemical barriers;
  • Induced liquefaction barriers;
  • Slurry walls;
  • Deep soil mixing;
  • Soil fracturing longwall mining;
  • Modified sulfur cement;
  • Sequestering agents;
  • Reactive barriers;
  • Impermeable coatings;
  • Microtunneling;
  • In situ vitrification; and
  • Soil saw (uses reciprocating high-pressure jets of grit or bentonite to create a vertical barrier).

Screening of the potential technologies resulted in selecting the following five barrier technologies for detailed analysis:

  • Close-coupled injected chemical barrier. This would involve injecting chemicals (e.g., portland cement) directly adjacent to the tank sides and bottom. The term close coupled indicates that the barrier would be right next to the tank walls;
  • Box-shaped chemical wall. A low-permeability basin would be formed beneath the level of existing soil contamination. This is a stand off type of barrier in which the bottom of the barrier would be sloped to a low point to help collect tank leaks. The barrier would be constructed of a low-permeability material such as portland cement;
  • V-shaped chemical barrier. This stand off type of barrier would use angle drilling techniques to construct a V-shaped barrier that would start at the surface on each side of a tank farm and angle down to meet in the middle. The slope of the angled barrier walls would facilitate liquid collection and removal;
  • Freeze wall. The V-shaped freeze wall would be similar to the V-shaped chemical barrier except that ice would be used instead of chemicals to create the barrier; and
  • Circulating air barrier. The circulating air barrier would rely on water evaporating from the soil, limiting the ability of a leak to migrate through the vadose zone.

A comparative risk assessment and cost estimate was made for each of the alternatives evaluated in the feasibility study. This analysis provided an evaluation of the impacts of waste storage and retrieval with and without the use of subsurface barriers. The following conclusions were drawn from the subsurface barrier study.

  • All functional requirements can potentially be satisfied using any of the subsurface barrier options evaluated. This conclusion is clarified with the observations that 1) little data on the performance of subsurface barriers exist; and 2) the draft functional requirements are largely and appropriately qualitative at this early state of development.
  • Using any of the subsurface barrier concepts in general applications to tank farms would result in relatively small incremental reductions in the risk level achievable using baseline retrieval technologies (traditional sluicing, empty tank stabilization, and surface barriers).
  • The cost-effectiveness of the subsurface barriers, calculated by the method most favorable to subsurface barriers, is about 1E-04 times that of surface barriers, and 1E-02 times that of the set of baseline technologies. Uncertainty in the performance of subsurface barriers is high, but because the impact of subsurface barriers on risk and cost-effectiveness is low, even the best-case assumptions of subsurface barrier performance have a relatively small effect on overall risk and cost-effectiveness of SST disposal options.

Waste Transfer Technologies

The function of waste transfer technologies in each of the ex situ alternatives would transport the waste as it was retrieved from the tanks to a nearby processing facility. The method of waste transfer would be through a pipeline. An alternate transfer technology would be containerized waste transfer. Containerized transfer of the waste would involve placing the waste into a container as it came from the retrieval system and transporting the containers to the waste treatment facility. Containerized waste transfer is better suited to mechanical and pneumatic transfer methods than hydraulic retrieval methods. Containerized transfer would avoid the potential mixing of incompatible tank waste. The impact of containerized waste transfer between the tanks and the treatment facility would include:

  • Increased radiological exposure;
  • Increased onsite transportation; and
  • No construction of the waste retrieval annexes described in the ex situ alternatives.

Truck Transfer

Truck transfer of waste using a modified tanker trailer truck or an LR-56(H) truck (specially designed vehicle for onsite transfers) is a technology that could be used as an alternative to the transfer of waste through pipelines. It could also be used to support various characterization activities and pretreatment/treatment activities. This waste transfer technology would use trucks to transport liquid waste between permanent or portable loading facilities. Waste transfer using trucks is better suited to limited waste volumes and intermittent transfers.

Truck transfer of waste was evaluated in the SIS EIS (DOE 1995i) as an alternative to constructing a replacement cross-site transfer system to transfer waste from 200 West to 200 East Area. A modified tanker trailer with a capacity of 19,000 L (5,000 gal) and the LR-56(H) with a capacity of 3,800 L (1,000 gal) were evaluated as options to pipeline transfer for an estimated 2E+07 L (5E+06 gal) of waste from the 200 West Area to the 200 East Area.

The analysis performed for the SIS EIS concluded that the environmental impacts associated with truck transfer of waste were not appreciably different from those associated with pipeline transfer except in the area of worker exposure. Worker exposure would be higher due to increased exposure for the truck driver and the workers involved with load and unload facility operations.

Table B.9.2.1 summarizes the number of LR-56(H) truck trips estimated to transfer waste from T Plant and PFP. The number of trips associated with using the modified tanker trailer would be fewer because of the larger capacity. These estimates were developed using the T Plant and PFP waste volume projections.

Table B.9.2.1 Estimated Truck Trips Required for T Plant and PFP Waste Transfers

The impacts from the transfer of the projected PFP and T Plant waste were estimated to be similar to the impacts associated with implementing the replacement of transfer lines. Implementing truck transfer to transport waste from T Plant and PFP to the DSTs in the 200 East Area would require constructing or upgrading loading facilities and improving Site roads to accommodate the trucks. The worker exposure associated with truck transfer of the waste would be higher than the exposure associated with pipeline transfer of the same waste.

LR-56(H) Truck for Transporting Liquid Radioactive Waste

The LR-56(H) truck is a specifically designed vehicle for transporting liquid radioactive waste between areas on the Hanford Site. The vehicle is designed to U.S. Department of Transportation standards and regulatory standards specific to the Hanford Site. The design includes lead shielding around a tank (capacity approximately 3,800 L [1,000 gal]) with redundant level and temperature monitors, alarms, and pumps for waste transfer. The truck can use either portable or permanent waste loading facilities at the point of origin and at the destination point.

Liquid waste could be transferred from such locations as PFP, T Plant, the 300 Area facilities, 100 Area, and the 400 Area to waste processing facilities or to the DST system . Other uses of the truck to transfer liquid waste could include transferring the following waste into the TWRS management system:

  • 100 Area cleanout waste from the 100 Area facilities;
  • 300 Area fuel supply cleanout, waste from the 340 Building, and other 300 Area facilities;
  • Miscellaneous transfers within the 200 Areas where pipeline transfer would not be an option due to failure, nonexistence, or lack of compliance status of existing lines;
  • MUSTs cleanout across the Hanford Site; and
  • Accumulations of contaminated rainwater (not greater in activity than HLW contained in DSTs/SSTs) from areas such as diversion boxes or tank vaults as needed to prevent spillage or leakage to ground.

B.9.3 EX SITU WASTE TREATMENT TECHNOLOGIES

Ceramic Waste Forms

Ceramic materials encompass a broad group of nonmetallic, inorganic solids with a wide range of compositions and properties. Their structure may be either crystalline or glassy. The ceramic form is often achieved by high-temperature treatment (burning or firing). Ceramics are stable, durable, and considered very leach resistant. Ceramics could be used in place of vitrified glass as an immobilization treatment for either HLW or LAW in any of the ex situ alternatives.

Immobilizing the tank waste using ceramic technologies would involve 1) retrieving the waste from the tanks; 2) potentially separating the waste into HLW and LAW components; and 3) performing waste pretreatment, which could include calcining, adding ceramic formers, and thermally treating in the range of 1,200 C (2,200 F) to obtain the desired properties.

Tailored ceramics have been identified and evaluated for immobilization of tank waste. Tailored ceramics refer to a mixture of different types of ceramic formers developed to immobilize a waste stream. Each of the different types of formers used would have the ability to chemically bind a specific waste element. Additional strength and chemical durability can be designed into the waste form when adding an excess of the tailoring species.

The ceramic form evaluated for immobilizing HLW was an aluminosilicate compound, Synroc D, which consists of zirconolite, perovskite, spinel, and nepheline. Sodium would be immobilized in this compound as nepheline. The theoretical sodium oxide loading based on all formulation assumptions would be 22 weight percent. For application at the Hanford Site, the ceramic form assumed to be produced would consist of nepheline, monazite, and corundum.

Ceramics could be formed into different physical forms including monoliths or pellets. Pellets could be manufactured in a continuously vertical shaft kiln while the ceramic monoliths would require a hot isostatic pressing operation to form the ceramic. Hot isostatic pressing is a commercial process in which the canister containing the waste and ceramic formers is evacuated and placed in a vessel that is pressurized between 15 to 70 MPa (2,000 to 10,000 psi) at a temperature of approximately 1,200 C (2,200 F). With similar waste loadings, the hot isostatic pressed ceramic technology and the vitrification technology would yield similar volumes of waste for disposal.

The impacts of using ceramic-forming technologies to process the tank waste would be approximately the same as those impacts associated with vitrifying the tank waste. Both technologies are ex situ waste treatments used to immobilize the waste. Ceramic technologies would require the following facilities to process the waste:

  • Retrieval and transfer systems;
  • Separations facilities if required;
  • Waste processing facilities;
  • Interim storage facilities for HLW; and
  • Disposal facilities for LAW.

Vitrification Technologies

Vitrification is a molten glass process in which the waste would be combined with glass-formers and heated to glass-forming temperatures. The melter is the piece of equipment that would take the waste material and glass-formers, heat the feed material to a glass-forming temperature of approximately 1,200 C (2,200 F) where chemical and organic destruction occurs, and output a molten glass product containing the waste.

Vitrification melters vary by their methods of heating the waste, feeding the waste, and the glass product produced. In addition, glass melters can operate in a batch or continuous mode. Some of the melter types identified for potential application to waste vitrification include the following:

  • Joule-heated ceramic lined melters;
  • Induction melters;
  • Microwave melters;
  • Plasma-arc melters;
  • Transferred plasma melters;
  • Fuel-fired melters; and
  • Cold-crucible melters that use a cooled-glass skull on the melter walls to prolong melter operating life.

Melters that require a dry waste feed stream would require calcining before being fed. The calcining step would remove excess water, destroy some of the chemical compounds, and convert the major constituent in the feed (i.e., sodium nitrate) into an oxide or a carbonate.

The French have developed and operated vitrification processes using a rotary calcine and metal melter to vitrify waste that resulted from reprocessing spent nuclear fuel from light-water reactors. This process calcines the acidic waste and continuously feeds an induction-heated metal susceptor and crucible. The borosilicate glass product formed is then poured into canisters approximately 1.3 m (4.2 ft) high and 0.43 m (1.4 ft) in diameter (DOE 1990).

The process developed for waste vitrification at the West Valley Demonstration Project in New York State and at the DOE Savannah River Site in South Carolina is the liquid-fed ceramic-lined melter. The liquid-fed ceramic-lined melter is a joule-heated melter developed from commercial ceramic-lined melters for use in vitrifying defense waste (DOE 1990).

The impacts associated with selecting a different melter type for the ex situ vitrification alternatives would involve potential changes in volume, composition, and treatment for the melter off-gas, changes in the resources required to fire the melter, and possible facility impacts required to accommodate the space requirements for the melter and off-gas equipment. For example, fuel-fired melters would generate a larger volume of off-gas than other melter types. This larger off-gas volume would require larger treatment equipment in the off-gas train for emissions control. One potential benefit of using a fuel-fired melter would be the higher throughputs that could be achieved. Some melter types might not be suitable for scaling up to high capacity and would require multiple melters operating in parallel to achieve high capacity production rates, which may increase the size of the facility.

Calcination Technologies

Calcination is the process of removing water and heating the waste to a temperature sufficiently elevated to decompose some of the chemical compounds such as hydroxides or nitrates. Calcination differs from vitrification in that calcination temperatures would not necessarily cause the reacting materials to melt and form a glass. The calciner is the piece of equipment that would heat the feed material to a calcination temperature of approximately 700 C (1,300 F) where the chemical and organic destruction occurs and output a solid waste product.

Calciners can vary by their methods of heating and feeding the waste, and the solid characteristics of the waste produced. Some of the calciner types identified for potential application to waste calcination include the following:

  • Spray calciners;
  • Rotary calciners;
  • Fluid bed calciners;
  • Indirect fired calciners; and
  • Electrically heated calciners.

The impacts associated with selecting a different calciner type for the calcination alternative would involve potential changes in: volume, composition, and treatment for the calciner off-gas; changes to or elimination of the compaction step required for the solid produced; changes in the resources required to fire the calciner; and possible facility modifications required to accommodate the space requirements for the calciner, compactor, and off-gas equipment.

Alternate Glass Compositions

Borosilicate glass is based on a composition of silicon dioxide, boron trioxide, sodium oxide, and lithium oxide. Borosilicate glass has been chosen by most countries as the standard final waste form for either HLW or LAW disposal. For possible use at the Hanford Site, borosilicate glass was chosen over other waste forms for its durability, ability to accommodate a varied range of waste feeds, and its adaptability for radioactive waste processing at an industrial level (DOE 1990).

Other types of glass, including the soda lime glass that would be produced by the Ex Situ No Separations alternative, could be selected as glass types for the final waste form for vitrified tank waste. The type of glass selected for use in the vitrification process is controlled by the types and proportions of glass formers used. The driving factors for selecting a glass type include waste loading, leachability, processability, and waste acceptance criteria at the potential geologic repository.

The impacts associated with changing the composition of glass produced in the vitrification process would be minimal for any of the ex situ vitrification alternatives provided the waste loading remained approximately the same. The glass waste loading limitations control the volume of final waste product requiring disposal. This in turn could have substantial impacts associated with transportation of the glass and charges assessed by the repository.

Separations Technologies

Separations refers to a broad range of technologies for removing or separating selected chemical constituents from other constituents. Application of separations processes would typically be designed to remove specific constituents from material flow streams within a processing plant and could be carried out in either a continuous or batch process. These processes fall into the general categories of chemical, physical, or a combination of chemical and physical.

New separations processes that show potential benefits in the areas of improved separations efficiencies, economic benefits, reduced secondary waste generation, superior performance, or environmental impacts are continually being identified and developed for potential application. One example is the application of amorphous silica gels that can be tailored to sequester selected elements at a specific pH.

The process described for the Ex Situ Extensive Separations alternative contains many but not all of the concepts that potentially could be used to extract specific components from the waste. Other concepts have been proposed that would potentially enhance the separation of other HLW components. However, adding other processes to the flowsheet would have a negligible effect on the impacts of this alternative. The quantity of HLW sent to the repository would not be materially decreased.

Off-Gas Treatment Technologies for Radionuclides

The design of off-gas treatment systems for each alternative would ensure that emissions of radionuclides would be below regulatory limits. For the In Situ Vitrification alternative, the probability of a cancer fatality to the maximally-exposed individual in the general public from exposure to routine off-gas emissions would be 1.6E-11. For the Ex Situ Intermediate Separations alternative, the probability of a cancer fatality to the maximally-exposed individual in the general public from exposure to routine off-gas emissions would be 3.3E-06. Volume Three, Appendix D of the EIS provides further discussion of the risk associated with each alternative. Should it be determined that radionuclide emissions from the stack gases were to be reduced to levels more restrictive than current regulations, specific treatment technologies would be examined on a case-by-case basis.

The I-129 in the tank waste would be volatilized as I2 during thermal treatment processes. Gaseous iodine would not be captured using traditional HEPA filtration. Two technologies that could be used to capture gaseous iodine would be adsorption on activated carbon and reaction with silver to form silver iodide. Recovering iodine in minute amounts is expected to be inefficient.

The control of C-14 emissions from any of the thermal treatment processes would be difficult. During vitrification the C-14 would be oxidized to CO2 along with all other nonradioactive carbon in the waste stream. The CO2 containing the C-14 would make up a small percentage of the total CO2 in the off-gas stream. However, any treatment technology used to capture the C-14 would have to capture all of the CO2. This potentially could be done by passing the off-gas through a recovery system in which CO2 is precipitated as calcium carbonate via reaction with a lime scrubbing solution. This process would generate a substantial secondary waste stream that would require further processing and disposal.

For the Ex Situ No Separations (Calcination) alternative process, the majority of C-14 present would be incorporated into the waste product in the form of solid carbonate salts. Only a small percentage of C-14 would be released as CO2 gas.

Grouting of Retrieved Tank Waste

Grouting of the retrieved tank waste is a technology that could be applied to any of the ex situ alternatives. As previously described, grout is a common solidification and stabilization technology employed in the management of hazardous waste. Grout is a general term that refers to a waste form obtained by mixing waste with chemical additives to stabilize and immobilize the hazardous constituents. The grouting process applied to the ex situ treatment of the tank waste would involve waste retrieval and transfer to a grout facility where the waste would be mixed with appropriate mixtures of grout formers. After the grout was mixed, it would be placed into containers for solidification and disposal.

Grouting of tank waste has been extensively studied at the Hanford Site for use as a technology for LAW disposal. Grouting of the LAW was selected as the LAW treatment method in the Hanford Defense Waste EIS (DOE 1987). The LAW described in the Hanford Defense Waste EIS included liquid waste from the tanks (after separation of HLW components) and secondary waste from the HLW vitrification facility, which would consist of waste from canister decontamination, drying of feed material, and off-gas treatment. As a result of a revised technical strategy and stakeholder input, grouting of LAW was replaced by vitrification of LAW as the proposed waste treatment technology. Even with this strategy, there still will be a requirement to grout the LAW generated as secondary process waste from the HLW vitrification facility and the additional LAW vitrification facility. However, this grouting facility would be greatly reduced in size.

The impacts associated with grouting the tank LAW for onsite disposal instead of vitrifying the LAW would include the following:

  • Potentially increased volume of waste requiring disposal. The estimated volume of grouted LAW would be approximately three times the volume of vitrified LAW. This would increase the number of vaults and the permanent land use commitment for disposal vaults by 14 ha (35 ac);
  • Increased contaminant flux out of the waste form during groundwater leaching because of a higher leachability of grout compared to glass. This would result in some increase in the long-term risk. Leachability and long-term impacts could be reduced by additional treatment such as calcination before grouting. However, calcination of the LAW would be necessary, which would result in emissions and short-term risk approximately equal to vitrification; and
  • Reduced complexity of the processing facility resulting in potential reduced capital cost requirements and reduced resource requirements. A grout facility (transportable grout facility) was constructed and operated in the 200 East Area in the late 1980's. It is currently in standby and could be restarted, which would avoid some capital cost. Capacity of the plant is about 500 tons per day.

Low-Activity Waste Disposal Technologies

There are a number of disposal technologies being used or developed for LAW. These technologies use a multiple barrier system, which include the solidified LAW form itself as well as primary and secondary containment methods for the solidified LAW.

The primary containment for the solidified LAW form could be metal, concrete, or a hybrid fiber-reinforced concrete. These containers, which would be made in various shapes and sizes, are commonly referred to as drums, canisters, or containers. The primary container would be placed in a belowgrade or abovegrade secondary containment vault constructed of concrete and/or an engineered soil structure. Alternately, the vaults would be the primary and only containment for the solidified LAW.

The most important protection against releases of contaminants after disposal in a multiple barrier system is considered to be the solidified waste form itself. Because complete isolation by land disposal is difficult, the practicality of minimizing releases through improved waste forms is now recognized as both desirable and necessary. The primary function of a waste form is the retention of its hazardous and radioactive components. Also important is its structural stability for handling, transportation, storage, and disposal. Numerous materials are being used or developed for the solidification of LAW. A short description of the main categories of these materials is given as follows. Some of the following categories (e.g., a modified sulfur cement to bond a LAW glass cullet) can be combined.

  • Hydraulic cements are binders that harden by chemical reactions with water. The major types of cement of interest to waste immobilization are portland, blast furnace slag, pozzolanic, aluminous, and masonry.
  • Modified sulfur cement is a recently developed material that is commercially produced in the United States. The basic raw material is elemental sulfur reacted with a small percentage (5 percent) of polymer to improve physical properties. Sulfur cement is highly resistant to alkaline and acidic environments. Sulfur cement has been proposed as a waste form matrix for vitrified LAW cullet in previous engineering studies and in the engineering data packages developed for this EIS. The stability of sulfur as a matrix has not been demonstrated. The reaction of modifiers with sulfur to form a linear polymer is exothermic and requires 24 hours to complete (Boomer et al. 1993). Further investigation would be required during the design phase to determine the viability of the cullet in sulfur waste form.
  • Glasses are high-melting-point materials, generally inorganic oxides, which on cooling, form an amorphous structure. For solidification, waste solids are generally incorporated into the glass structure as oxides produced during the high-temperature (1,200 C [2,200 F]) processing conditions.
  • Organic polymers consist of large molecules built up by the repetition of small simple chemical units. Although there are a large number of polymeric materials suggested for the solidification of LAWs, the most prominent systems are epoxies, polyethylene, and unsaturated polyesters.
  • Asphalt (or bitumen) is a complex mixture of high-molecular-weight hydrocarbons containing both aliphatic and aromatic constituents. Waste solids are mixed in and coated with liquid asphalt and mechanically held in a solid asphalt matrix after cooling.
  • Ceramics encompass a broad group of nonmetallic, inorganic solids with a range of compositions and properties. Waste forms can be crystallized, glass, or chemically-bonded ceramics.

Future evaluations of LAW disposal technologies may result in the selection of other solidified LAW forms or primary/secondary containment methods.



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