The Direct Feed Low-Activity Waste (DFLAW) facility will significantly reduce the time it will take to process low-level liquid waste. The goal is to start treating waste by 2022.
What is DFLAW:
To begin treating waste as soon as practicable, the Department of Energy developed a sequenced approach that would treat low-activity waste first, as soon as 2022. The sequenced approach is called Direct Feed Low-Activity Waste (DFLAW). This approach sends low-activity waste from the tank farms directly to the Waste Treatment and Immobilization Plant (WTP).
WRPS will feed treated waste to the WTP Low-Activity Vitrification facility where the waste is mixed with glass-forming materials and heated. The molten glass/waste mixture is poured into stainless steel containers, allowed to cool and then transported to the nearby Integrated Disposal Facility.
Hanford Tank Waste:
The waste in Hanford’s tanks is not a homogenous mixture. At the bottom of the tanks is sludge, varying from a fine silty clay to a gravel-like material. Liquid supernate, water with soluble radioactive isotopes, sits on top of the sludge. Saltcake, a rock-salt type of material, typically floats on top of the supernate. The high-level radioactivity is primarily in the solids in the tanks. The supernate consists of low-activity waste with cesium, a high-level waste, in solution. The cesium must be removed from the supernate before it can be processed as low-activity waste.
Tank Side Cesium removal (TSCR):
The Tank-Side Cesium Removal (TSCR) system will separate both cesium and undissolved solid materials from radioactive tank waste, providing a low-activity waste stream that can be sent to the Waste Treatment and Immobilization Plant’s Low-Activity Waste (LAW) facility for vitrification. Located just outside Hanford’s AP Tank Farm on a 3,000-square-foot site, TSCR is comprised of the main process enclosure, a control room and two other skids containing ancillary support and ventilation systems. Two backwashable filters and two ion exchange columns will operate during an initial demonstration phase to process approximately 170,000 gallons of waste. A third ion exchange column will be run during full operations. The control room will house work stations for remote monitoring and control for system operations and maintenance.
As part of DOE’s comprehensive DFLAW approach, TSCR provides several benefits:
- Places approximately 75 percent of WTP in operation.
- Addresses liquids, the most mobile form of tank waste.
- Creates double-shell tank space.
- Supports phased mission progression and a scale-up of treatment capabilities
- Supports the development of skills and experience in transitioning from design/ construction to startup, commissioning and operations
Radioactive cesium is soluble in water and cannot be filtered out. Ion exchange is used to remove the cesium molecules from the liquid supernate in Hanford’s waste tanks. Ion exchange resins are very small plastic beads placed in a column. Supernate pumped into the column comes in contact with the resin beads, which chemically remove the cesium from solution. The cesium is rinsed from the beads and returned to the underground tanks as high-level waste. When the resin beads lose their effectiveness, the columns are taken out of service and replaced with new ones.
Benefits of DFLAW:
Long-term waste will be stored safely and the risk to the environment will be reduced. DFLAW will maximize near-term risk reduction, target mobile constituents and create double-shell tank space.