In agreement with the US Department of Energy, the Department of Ecology of Washington State has responsibility for the clean-up process at Hanford, a nuclear site where plutonium production activities began in 1943. A key task is the safe storage, retrieval and treatment of waste in 177 underground tanks, which contain radioactive and chemical wastes from four decades of plutonium production activities at the site. The waste was generated when irradiated uranium fuel rods were reprocessed, during which the uranium fuel rods were dissolved and plutonium chemically retrieved. The resulting liquid chemical waste was put into the underground storage tanks in ‘tank farms’ in Hanford’s ‘200 Area’.
The tanks range from 55,000 gallons (208 m3) to more than a million gallons (3785 m3). To build them, workers cleared out large flat depressions, erected the tanks in situ and surrounded them with soil, leaving the tops of the tanks 3 m below ground to provide radiation shielding.
Of the tanks, 149 are single-walled. These tanks do not comply with Washington law, which requires that all underground storage tanks have a secondary container. In the late 1980s to mid-90s, much of the liquid was removed in hopes of making them more stable and reducing the risk of leaks. The remaining waste is similar to the consistency of sand.
The remaining 28 tanks are double-walled. Although they comply with state law in that regard, they, like the single-walled tanks, are well past their design life of about 25 years and at least 68 tanks are assumed to have leaked in the past. Two tanks are currently known to be leaking and are being managed under an agreed process (see box below). If waste were to remain in the tanks, untreated, it would eventually enter the ground, the groundwater and the Columbia River. Previous leaks have caused ground contamination.
Two leaking tanks
Tank T-111 was found to be actively leaking in 2013. Tank B-109 was found to be actively leaking in 2021 after a year-long leak assessment. As the toxic and radioactive waste is leaking into the soil over time it would reach groundwater and eventually the Columbia River. In addition, in 2014 the oldest double-shell tank (AY-102) developed a leak from its inner tank to the outer tank. Its contents have been moved to an intact tank.
The Ecology Department agreed a process with the US Department of Energy to address these active leaks and any future leaks from single-shell tanks. The site is now required to cover the T and B tank farms with surface barriers to prevent rain or snowmelt from seeping into the tanks, and to slow the migration of leaked waste toward the groundwater. It also agreed to:
- Evaluate the viability of installing a ventilation system to evaporate liquid waste in Tank B-109.
- Develop a response plan for future leaks from single-shell tanks.
- Evaluate conditions in and around tanks B-109 and T-111 to determine whether additional work is needed to prevent rain or snowmelt from getting in.
- Explore ways to accelerate the schedule to retrieve waste from tanks B-109 and T-111.
Tank waste retrieval is extremely difficult. Nevertheless, remaining waste from single-shell tanks is being sent to double-shell tanks through a system of hose-in-hose transfer lines. As the waste is moved excess water is evaporated.
Riser pipes provide access into the tanks, but many are only a foot in diameter and none were designed to make it easy to empty the tanks. Retrieval equipment inside the tank is operated remotely and the hostile conditions quickly wear out electronics and other equipment. Structures in the tanks also obstruct access.
Overall, an estimated 56 million gallons (212,000 m3) of mixed hazardous and radioactive waste remains in the tanks. As part of an agreement regulating Hanford clean-up, crews must remove at least 99% of the waste in every tank on the site, or at least as much waste as can be removed based on available technology. Tanks are considered clean when no more than 360 cubic feet (10 m3) of waste remains — or less, depending on tank size. The tank farm waste will be treated at a new Waste Treatment and Immobilisation Plant where the waste will be vitrified and stored in steel canisters for long-term disposal.
On 6 March representatives of the Hanford site gave an update to stakeholders.
Greg Jones is DoE assistant manager, business and finance and Hanford CFO. He said that the site’s use and clean up had been ongoing since 1943 but there was still 40-50 years of clean-up to go. The site was managed under a five-year rolling plan. The government-funded operation depends on funds being allocated so he said every year the site was working on three budgets. The current year is fixed – it was already executing FY24 budgets, although that budget would not be finally agreed until legislation was passed, which at the time appeared imminent. In the upcoming years the team had to make assumptions, and it was now formulating plans for FY26.
Discussing priorities looking towards 2026, he said in the last few years site management had focused on three types of risk reduction: the tank waste; the central plateau and river; and infrastructure to support work across the site.
The overall objectives were:
- Safe and secure operations
- Manage, treat and dispose of tank waste
- Stabilise ageing structures
- Demolish of retired facilities
- Remediate waste sites
- Treat contaminated groundwater
He said around 2.2 billion gallons (8.3 million m3) a year of groundwater was being treated each year.
In a major step for the site clean-up, the waste is about to begin the process of being transferred from the double-shell tanks to the Waste Treatment Plant for vitrification.
Vitrification campaign set to begin
Stabilising and immobilising waste using vitrification is the headline programme for the next few years, with work due to begin in 2025. As originally envisioned, the Hanford waste treatment plant (WTP) would have treated high-level and low-activity radioactive waste simultaneously. Instead, the DOE decided to begin treating low-activity waste as soon as practicable, and it expects to begin treating high-level waste about a decade later.
The programme is called direct-feed low-activity waste (DFLAW). It sends pre-treated low-activity waste from the Tank Farms, directly to the Low-Activity Waste (LAW) facility at the WTP. The distance between the tank farms and the waste treatment plant is approximately 22.5 miles (36 km).
At the LAW facility the waste will be vitrified – mixed with glass-forming materials and then fed into two 300 tonne melters and heated to 2,100 oF (1150 oC). The melters are approximately 20 feet by 30 feet and 16 feet high (7x10x5 m). The glass mixture will then be poured into stainless steel containers, each of which holds 6.6 tonnes of waste.
The Waste Treatment Plant has now been constructed and in 2023 it underwent cold commissioning. The melters were commissioned in December 2023, when the first clean (ie non-radioactive) molten glass was poured into the first container.
Jones explained that on any given day the programme will have 25 operations under way to address the 53 million gallons (200,000 m3) of waste in the double-walled tanks and bring it to the vitrification process. Waste is sent to underground tank AP107, where it is sampled for testing in the onsite laboratory. It undergoes caesium removal, by passing through an ion exchange column, which treats 5 gallons per minute or 7200 gallons per day (27 m3) . The first campaign using that process found that 99.9% of caesium was removed.
Following this process the waste is decanted to tank AP106 and sampled. From there it is transferred in batches to the low activity waste treatment plant. The WTP will accept up to 8,000 gallons (30 m3) per day when it is finally operable. The WTP has two melters which operate in parallel.
Several WTP infrastructure facilities have been modified to support the LAW Facility and Effluent Management Facility (EMF), which will process liquid secondary effluent.
The output from the vitrification process will be between 3.5 and 5 canisters per day (up to 2100 tonnes). These will be transported to a landfill site (the Integrated Disposal Facility) on the Hanford site.
During vitrification effluent will be generated, both from melters and when transfer pipes are flushed. The melters produce large amounts of heat, so the liquid waste processed in the facility results in a condensate. This goes into a liquid effluent treatment and liquid effluent retention facility (engineered settling ponds). A new pond has been added among other upgrades to support the needs of the waste treatment plant and the site. The remaining concentrate is sent back into the vitrification process. An on-site lab will ensure the glass product produced by the facility meets all regulatory requirements and standards, analysing approximately 3,000 waste samples each year.
During 2024 cold commissioning will continue at the vitrification facility. The target for a complete readiness review to authorise hot commissioning (ie with radioactive waste) is 2026, when hot commissioning of it and the Effluent Management Facility is due for completion.
Other processes
Completing the Hanford clean-up depends on the third pillar of work at the site, upgrading the site’s conventional infrastructure. The site’s daily needs are for 50 MW of power and 3.5 million gallons (13,000 m3) of water. To support the clean-up process those supplies have to be augmented and updated.
The site needs reliable water services for the next 40 years, but the water pumps in current use wereinstalled in 1943. So new water treatment works and water storage facilities will also be installed.
Similarly, the site’s aging power infrastructure must be made fit for its new purposes. The various utilities needed to support WTP operations include systems for electrical power distribution, backup power, compressed air, steam, chilled water, fire water and communication and control. Some systems can be scaled down, such as the steam plant.
But in some cases there are new requirements. Power supply to the melters in the WTP’s vitrification process, for example, cannot be interrupted or they become unusable and have to be replaced at a cost of million dollars. The electrical system has to be upgraded to get reliable power to working areas.
Looking ahead, 2026 will see the transfer of caesium and strontium waste from its current under water storage. In a process expected to take 27-36 months it will be transferred to interim dry storage.
The coming two years will also see ‘no regrets’ work on high level waste, specifically 324 hot cells. They are due to be demolished in 2026 and the area remediated. The first step in that process is construction and commissioning of a structure to weather-proof the area.
