B.4.0 CAPSULES
The following sections describe each of the capsule alternatives. The capsules are currently defined as waste by-product, which means they are available for productive uses if uses can be found. If and when the capsules are determined to have no potential productive uses, it is assumed they would be subject to management and disposal as HLW under TWRS. The discussion includes a general description of the alternative followed by a description of the construction activities that would be included if the alternative were implemented. The discussion continues with a description of the process/operation and ends with a discussion of key issues associated with implementing the alternative. Engineering data for each alternative can be found in Section B.11.0.
B.4.1 NO ACTION ALTERNATIVE (CAPSULES)
B.4.1.1 General Description
The No Action alternative for the capsules would consist of continued safe management. Currently, the capsules are stored in water basins in WESF. Additional capsules are being returned to the Hanford Site and would be stored in the water basins. The capsules and basins would be maintained and administrative controls would prevent inadvertent human intrusion. WESF is scheduled to be decontaminated and decommissioned within the next 10 years, and administrative controls would be assumed to be effective until an alternative waste storage facility could be constructed. If this alternative is selected, within the next 10 years DOE and Ecology would need to decide on a strategy for continued storage elsewhere or select a disposal alternative for the capsule contents. This will be considered in the Cs and Sr capsule management plan.
Monitoring and maintenance activities for the capsules involve calculating the annual inventory, physically verifying that the inner capsule can still move independently of the outer capsule (Cs capsules only), and using online radiation monitors to detect pool cell water contamination. The annual inventory provides the exact storage location and accountability for all of the Cs and Sr capsules stored at WESF.
The Cs capsules are clunk tested on a quarterly basis. This involves physically grasping one end of a capsule with a pool tong and rapidly moving the capsule vertically approximately 15 cm (6 in.). This allows the inner capsule to slide within the outer capsule, making a clunk sound that is easily heard and felt by the operator performing the test. This test verifies that the capsule has not bulged. A capsule that failed the clunk test would be removed from the storage basins and placed into a hot cell for additional evaluation.
Leak detection in the storage basin would be performed by online beta monitors that would be set to alarm when the activity present in the pool water exceeded a set level.
Maintenance of the storage facility includes maintaining the electrical and mechanical systems required to safely operate the facility. This would include life extension or replacement for failed or aging equipment.
This alternative would meet all applicable regulations (Volume One, Section 6.2).
B.4.2 ONSITE DISPOSAL ALTERNATIVE
B.4.2.1 General Description
This alternative would consist of packaging the capsules into sealed canisters and placing them in a newly constructed subsurface disposal facility in the 200 Area. This alternative would be similar to the in-place stabilization and disposal alternative addressed in the Hanford Defense Waste EIS for Cs and Sr capsules (DOE 1987).
The Cs and Sr capsules would remain in storage in a series of water-filled storage pools at WESF until the modified capsule packaging facility was completed. They would be retrieved from the storage pools and inspected for surface contamination, corrosion, structural defects, and heat content before placing them in a capsule vault. The capsules would be stored in the vault until they would be transferred to the canister-packaging facility, also a part of WESF.
At the WESF canister-packaging facility, the capsules would be placed in a seal-welded canister, which would be placed in drywells for onsite disposal. Two to four capsules would be placed in a canister depending on heat load. The sealed canister package would be leak tested, ultrasonically scanned, checked for surface contamination, and decontaminated before being transported to the subsurface disposal facility. A shielded transporter would place the canister in the drywell.
For this alternative, it was assumed that the capsules would remain in dry-storage with administrative controls in effect (WHC 1995h). For the purpose of calculating the potential impacts, it is assumed that the controls would be terminated after 100 years.
B.4.2.2 Facilities to be Constructed
The capsule packaging operation would be performed in the existing WESF Building located in the 200 East Area, next to B Plant. Figure B.4.2.1 provides a plant layout diagram of WESF. The approximate dimension of the WESF Building is 90 by 120 m (300 by 400 ft).
Figure B.4.2.1 Waste Encapsulation and Storage Facility
Modifying existing hot cells and/or constructing new hot cells would provide the capabilities required for the capsule-packaging operation. There are currently eight hot cells: A, A Cell Hood, B, C, D, E, F, and G. Each cell has a viewing window and ports for two manipulators, except for G Cell, which has two viewing windows (each window has two ports for manipulators). Three additional hot cells would be constructed for the capsule-packaging facility for inspection, weld stations, weld integrity tests, contamination checking, and decontamination. In addition, facilities would be modified and/or constructed for capsule disposal vaults, canister storage and testing, and canister packaging operations.
A drywell disposal facility would also be constructed. The ground surface of the storage area would be graded flat and nearly level with only enough slope to provide for surface drainage. A total of 672 drywells (584 canisters plus 15 percent contingency) would be drilled to a depth of 4.6 m (15 ft). They would be arranged in a grid pattern (5 m [16.4 ft] center-to-center) occupying a surface area of 3.8E+04 m2 (195 by 195 m) (640 by 640 ft) with a 30-m (100-ft) buffer. The site selected for the drywell disposal facility is near the western boundary of the 200 East Area. Figure B.4.2.2 illustrates the drywell disposal facility casing assembly, and Figure B.4.2.3 is a representation of a drywell disposal array.
Figure B.4.2.2 Capsules Drywell Disposal Assembly
Figure B.4.2.3 Capsules Onsite Disposal Arrangement (Conceptual)
B.4.2.3 Process Description
The process activities for the Onsite Disposal alternative are divided into four major operations. A process flowsheet is provided in Figure B.4.2.4.
Figure B.4.2.4 Onsite Disposal Alternative - Process Flow Diagram
Waste Encapsulation and Storage Facility
The Cs and Sr capsules would be stored in the water-filled storage pools at WESF until a capsule-packaging facility is completed. When the capsule-packaging facility is completed, the capsules would be remotely removed from the pool and placed in an inspection cell where they would be checked for surface contamination, corrosion, structural defects, and heat content before being moved to the capsule-packaging facility. Capsules that fail inspection would undergo decontamination, rework, and testing until the capsules meet the requirements for the canister-packaging operation. After passing inspection they would be stored in the capsule vault until being transferred to the canister-packaging operation.
Capsule Packaging Facility
The capsules would be remotely removed from the vaults and then would be placed in racks and inserted into canisters. The loaded canister would then be remotely moved to a weld station where the lid would be welded in place. The canister would then undergo leak testing, ultrasonic scanning, and examination for surface contamination.
The canisters (3 m [10 ft] long) used for Onsite Disposal would be smaller than the canisters (4.5 m [15 ft] long) used for packaging and shipping to an offsite potential geologic repository. The canisters used for Onsite Disposal would be 0.3 m (1 ft) in diameter and 3 m (10 ft) long.
The allowable heat load for Onsite Disposal would be smaller than the allowable heat load for disposal at a potential geologic repository. The drywell heat load limit would be 0.55 kW per canister, which is estimated to be one to four capsules per canister (WHC 1995h). The canisters are expected to contain about three Sr capsules or four Cs capsules. Table B.4.2.1 summarizes the estimated capsules and canisters required for onsite disposal.
Table B.4.2.1 Estimated Capsules, Sealed Canisters, and Multi-Purpose Canisters
Disposal
After placing the capsules into canisters, the canisters would be transported by a shielded vehicle for placement in near-surface drywells to provide long-term, passively-cooled storage. There would be one canister per drywell. After placing the sealed canisters into the drywells an intrusion prevention barrier would be placed over each drywell.
Monitoring and Maintenance
All of the canisters in the drywell disposal facility would be closely monitored for radiological and nonradiological emissions. All associated equipment, instrumentation, and controls would be maintained. Continuous security and monitoring and maintenance operations would be performed for a period of 100 years, at which time institutional control would cease.
B.4.2.4 Implementability
Implementing the alternative would involve mechanical handling of the capsules and canisters and thus presents no new technology uncertainties that would require extensive research and development. One issue that would require evaluation would be the corrosion of the drywell casing and the performance of the disposal configuration.
This alternative would not meet the land disposal requirements of RCRA for hazardous waste. Near-surface disposal of HLW may not meet DOE Order 5820.2A requirements for disposal of readily retrievable HLW in a potential geologic repository (Volume One , Section 6.2).
B.4.3 OVERPACK AND SHIP ALTERNATIVE
B.4.3.1 General Description
For this alternative, the capsules would continue to be stored in a series of water-filled storage pools at WESF until a modified WESF capsule-packaging facility is completed. The capsules would be retrieved from the water-filled storage pools, inspected for surface contamination, corrosion, structural defects, and heat content, and temporarily placed in a capsule vault. The capsules would be stored in the capsule vault until they could be packaged into sealed canisters in the canister-packaging operations.
At the capsule-packaging facility, the sealed canisters would be packaged into HMPCs and placed in the onsite HLW interim storage facility. Monitoring and maintenance would be performed at the onsite interim storage facility while HMPCs are in temporary storage (WHC 1995h).
B.4.3.2 Facilities to be Constructed
The capsule-packaging operation would be performed in the existing WESF Building, whose location and size are described in the Onsite Disposal alternative (Section B.4.2.). While the building modifications would be almost identical, areas for overpacking the canisters into HMPCs would be constructed only for this alternative. Temporary storage for the HMPCs loaded with canisters would be on an engineered storage pad either in place of or near the interim storage of vitrified HLW with the approximate dimensions of 130 by 150 m (430 by 500 ft). The pad would have a stormwater collection and monitoring system, which would provide for collecting and decontaminating spills.
B.4.3.3 Process Description
The process activities for this are divided into five major operations. The process flowsheet for this alternative is provided in Figure B.4.3.1. Final design of the canister packaging would include design criteria for waste acceptance at the potential geologic repository.
Figure B.4.3.1 Overpack and Ship Alternative - Process Flow Diagram
Waste Encapsulation and Storage Facility
As in the Onsite Disposal alternative, the Cs and Sr capsules would be stored in the water-filled storage pools in WESF until a capsule-packaging facility is completed. When the facility is in operation, the capsules would be remotely removed from the pools and placed in an inspection cell where they would be checked for surface contamination, corrosion, structural defects, and heat content before transferring them to the capsule-packaging facility. Capsules that fail the inspection would undergo decontamination, rework, and testing until the capsules meet the requirements for the canister-packaging operation. After passing inspection they would be stored in the capsule vault until they could be transferred to the canister-packaging operation. The capsule vault is a shielded storage room that is used for storing the inspected capsules prior to loading into canisters, which are 4.57 m ( 15 ft) long.
Capsule Packaging Facility
In this operation, the capsules that were stored in the vaults would be transported to the capsule-packaging area, and placed in racks that would be loaded into canisters. Depending on the heat emitted by each canister, five to nine capsules would be loaded in one canister. After loading, the canisters would be moved to a weld station where the lid would be welded in place.
The seal-welded canisters would undergo leak testing, ultrasonic scanning, and checking for surface contamination. If the canister is found to be contaminated, it would go to electropolishing decontamination before overpacking in HMPCs. The HMPC can hold a maximum of four canisters.
The canisters used for packaging and shipping the capsules to an offsite potential geologic repository would be larger than the canisters used for drywell storage. The canisters used for packaging the capsules under this alternative would be 0.61 m (2 ft) in diameter and 4.57 m ( 15 ft) long. The allowable heat load for onsite disposal is 1.17 kW per canister for Cs and 0.80 kW per canister for Sr. Each canister would be expected to hold five to nine Cs or Sr capsules. Table B.4.2.1 summarizes the number of capsules, canisters, and HMPCs required to implement this alternative.
Onsite Interim Storage
The loaded HMPCs would be stored ready for transport on a separate engineered pad with dimensions of 130 by 150 m (430 by 500 ft) until the potential geologic repository is available. Loading of the capsules into the canisters and loading of the canisters into the HMPCs would be expected to be accomplished near the scheduled time for transport to the repository so that loaded HMPC interim storage would be minimized.
Monitoring and Maintenance
All the HMPCs would be closely monitored for radiological and nonradiological emissions. All associated equipment, instrumentation, and controls would also be maintained. Continuous monitoring and maintenance would be performed at the onsite interim storage facility until the HMPCs would be transported to the potential geologic repository.
Transport to the Potential Geologic Repository
When the potential geologic repository is ready to accept processed HLW the HMPCs would be removed from the onsite interim storage facility and transported by railcar to the repository.
B.4.3.4 Implementability
Implementability of this alternative could be affected by the acceptability of the packaged capsules at the potential geologic repository. The acceptability issue involves the waste form. The solubility of this waste may ultimately exceed the HLW acceptance criteria. The Cs and Sr salts would not be immobilized under this alternative but instead would be packaged to provide two additional barriers for containing the capsules. If it is determined that the salt form of these waste would not meet the Waste Acceptance Criteria, the capsule contents would have to be removed and processed appropriately to meet the Waste Acceptance Criteria. Further evaluation would be required to resolve technical and programmatic concerns associated with disposal of the Cs and Sr capsules in the potential geologic repository.
This alternative may not meet the land disposal restrictions of RCRA because of the characteristic corrosivity of the CsCl and SrF2. Assuming the waste is mixed waste, it would not meet the DOE restriction against disposal of mixed waste in the first potential geologic repository.
Also, the powder waste form of the SrF2 may not meet the waste acceptance requirement to immobilize particulate waste (Volume One, Section 6.2).
B.4.4 VITRIFY WITH TANK WASTE ALTERNATIVE
B.4.4.1 General Description
This alternative would consist of continued storage of capsules in water-filled storage pools inside WESF until the HLW vitrification facility is completed. Then the capsules would be retrieved from the storage pools and transferred to the HLW vitrification facility, which would include equipment to chemically process, if necessary, and blend the Cs and Sr with the tank waste feed to the HLW vitrification process. The remainder of the process would be similar to the process described for vitrifying HLW under the Ex Situ Intermediate Separations alternative (Section B.3.5).
As part of the HLW glass, the Cs and Sr would be monitored in temporary storage and transported by railcar to the potential geologic repository.
B.4.4.2 Facilities to be Constructed
The dismantling of Cs and Sr capsules and the processing of Cs and Sr salt would be integrated with the HLW vitrification facility. For this alternative, the Cs and Sr capsules dismantling facility would be built as part of the HLW vitrification facility.
The capsule processing facility would include hot cells to open the double-walled capsules, mixing and storage tanks for CsCl, a pulverizer and slurry tank for SrF2, chemical processing facilities if required, pumps for blending Cs or Sr compounds with HLW slurry prior to vitrification, and decontamination facilities for the empty capsules.
B.4.4.3 Process Description
The process activities for the extensive immobilization option are divided into four major operations, as shown on the flowsheet in Figure B.4.4.1.
Figure B.4.4.1 Vitrify with Tank Waste Alternative - Process Flow Diagram
Capsules Retrieval From Waste Encapsulation and Storage Facility Storage Pool
The Cs and Sr capsules would be stored in water-filled storage pools at WESF until the HLW vitrification facility is completed and ready for operation. The capsules would then be remotely retrieved, loaded in casks, and transported by truck to the capsule-dismantling hot cells that would be part of HLW vitrification facility.
Dismantling and Removal of Capsules Content
At the dismantling facility, the outer and inner walls of the capsules would be remotely cut open to remove the CsCl and SrF2 salts, and the empty Cs and Sr capsules would be decontaminated and disposed of with other low-level metallic waste.
Blending Cesium Chloride or Strontium Fluoride with HLW Slurry
The CsCl would be dissolved in water, blended with the HLW slurry from the tank farms, and used as feed to the vitrification facility. The SrF2 would be pulverized and then water would be added to make a slurry with a solids content of less then 4 volume percent. The SrF2 slurry would then be mixed with the HLW slurry and used as feed to the vitrification facility. An alternative treatment for the halides would be to convert them to nitrates prior to vitrification if the halide salts cannot be directly fed to vitrification.
Chemical Processing of Capsule Contents
This processing converts the halides to nitrates. The dissolved CsCl would be processed through ion exchange columns where the chloride ion would exchange for a nitrate ion, resulting in a cesium nitrate solution. Two ion exchange columns would be used to allow alternate processing and regeneration cycles. Regeneration would be with 1 molar nitric acid.
The pulverized SrF2 would be dissolved in sulfuric acid to produce a precipitated strontium sulfate and gaseous hydrofluoric acid that would be sent to the off-gas processing facility. The strontium sulfate would be reacted with sodium carbonate to form strontium carbonate. The last processing step would be to react the strontium carbonate with nitric acid to form a solution of strontium nitrate.
High-Level Waste Vitrification
The Cs and Sr salts would be blended with the tank waste and fed to the HLW melter feed section. The HLW would be stored onsite until the potential geologic repository is ready to accept HLW. When the potential geologic repository is ready to accept processed HLW, the Cs and Sr (as part of the HLW glass) would be transferred to the repository.
B.4.4.4 Implementability
This alternative could only be implemented if one of the tank waste ex situ alternatives or the Ex Situ/In Situ Combination alternative were selected. Chemical processing could be required to remove the chloride and fluoride from the Cs and Sr salts so that they meet the feed specifications that would be developed for the HLW vitrification feed stream. Further study would be required to determine if the capsule contents could be successfully treated as part of the calcination feed stream. Regenerating the Cs ion exchange media produces hydrochloric acid. Neutralizing the hydrochloric acid may produce a secondary waste product requiring further treatment and disposal. The production of hydrofluoric acid during strontium processing would require additional off-gas processing and would produce magnesium fluoride, which would require disposal as a secondary waste.
This alternative would meet all applicable regulations for disposal of hazardous, radioactive, or mixed waste assuming that the hazardous waste components are adequately treated during waste processing or vitrification.
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