The US Department of Energy’s (DOE’s) Office of Environmental Management (EM) announced that tank operations contractor Washington River Protection Solutions (WRPS) had finished construction of the pipeline that will carry treated waste from a Hanford tank to the Waste Treatment and Immobilisation Plant (WTP) for vitrification, or immobilisation in glass.
The Hanford Nuclear Reservation, established during World War II is the subject of a decades-long, multibillion-dollar clean-up effort. |t is the most contaminated site of radioactive waste in the USA. While operational, it produced about 66% of the plutonium used for US nuclear weapons. A series of massive underground storage tanks ranging in capacity from 55,000 gallons to more than 1,000,000 gallons were constructed to hold the wastes from plutonium production. They are located in a 18 “tank farms”, each comprising from two to 16 tanks.
“This is a significant step forward in our Direct-Feed Low-Activity Waste Program to treat tank waste,” said Brian Vance, manager of the Office of River Protection and Richland Operations Office. “The connection represents another example of this year’s progress and also demonstrates the strong commitment by the Department of Energy and our contractors to safely move our important site mission forward.”
The new 3500-foot pipe-in-pipe transfer line connects the plant to a double-shell tank in AP Tank Farm that will serve as a holding tank for liquid waste that has been treated by the Tank-Side Caesium Removal System to remove radioactive caesium and solids. Workers installed the caesium removal system next to the AP Tank Farm earlier this year and are conducting readiness reviews prior to starting to treat tank waste early next year.
“For the first time, tank farms are connected to the Vit Plant, providing the avenue for transferring treated tank waste to the plant for vitrification,” said John Eschenberg, WRPS president and CEO. “It’s exciting to be a part of putting the infrastructure in place to facilitate this critical mission.”
During hot commissioning and operations at the plant, the treated waste will be pumped in batches from the double-shell tank directly to the plant’s Low-Activity Waste Facility for vitrification and disposal.
“It’s exciting to see the physical connection from the tank farms to the Vit Plant,” said Valerie McCain, WTP project director and senior vice president for Bechtel National Inc., the contractor designing, building, and commissioning the plant. “This final tie-in symbolises the collaborative spirit at Hanford and how we are all committed to treating waste.”
Bechtel expects to heat up the first of two vitrification melters in the Low-Activity Waste Facility by the end of 2021 as part of the plant commissioning process. Hanford is preparing to start vitrifying tank waste by the end of 2023.
Materials delivered for vitrification
Earlier, local contractor Two Rivers Terminal made its first delivery of materials that will be used to immobilise Hanford Site underground tank waste in glass. EM Office of River Protection (ORP) prime contractor Bechtel National awarded a contract to Two Rivers Terminal of Pasco, Washington to source, import, store, and deliver materials that will be used in the glass-forming, or vitrification, process as part of the Direct-Feed Low-Activity Waste (DFLAW) programme.
The DFLAW programme is a system of interdependent projects and infrastructure improvements, managed and highly integrated, that must operate together to vitrify the waste. During vitrification, the contaminated waste and glass-forming materials are mixed and heated to 2,100 degrees Fahrenheit inside one of two large melters in the Low-Activity Waste Facility, then poured into stainless steel containers for safe storage.
The first delivery of a glass-forming material was lithium carbonate, an industrial chemical used in processes such as manufacturing lithium ion batteries. Other materials used in vitrification are varied, consisting of multiple silicate compounds and other chemicals — and even sucrose, more commonly known as sugar. Silica will be the major compound used in the process. The initial material delivered will be used in the process of starting up and tuning the first melter later this year.
Two Rivers Terminal will source the glass-forming materials domestically and internationally, with about half of the materials coming from locations around the USA. The contractor will be required to keep a three-month supply available. Before delivering the materials to the WTP, Two Rivers Terminal will work with another local business, Mukang Labs in Pasco, to ensure the materials meet quality specifications for vitrification. Mukang Labs will sample and analyse the material and coordinate results with Bechtel. Two Rivers Terminal is a fertilizer and chemical formulator, distributor, and importer that serves agricultural and industrial businesses.
Waste retrieval from AX-103
EM said on 17 August that ORP tank operations contractor WRPS had recently began retrieving radioactive and chemical waste from another massive underground storage tank at the Hanford Site.
Over the next several months, workers will retrieve approximately 104,000 gallons of solid and sludge-like material from Tank AX-103 and transfer it to a double-shell tank for safe storage until it is fed to the WTP for vitrification, or immobilisation in glass.
“Moving waste from older single-shell tanks to newer double-shell tanks is an important step in progressing our risk-reduction mission,” said Ricky Bang, Hanford EM Tank Farms Programme division director. “It’s not easy to access the tanks or move this kind of waste, and it takes specialized tools and techniques that have been developed, tested, and proved successful to meet this challenge.”
During waste retrieval, workers operate retrieval equipment inserted through relatively small openings in the top of the tank from a nearby control trailer. They use pressurised water to dissolve the solid, or salt-cake, waste and flush it to the pump that transfers the waste to a double-shell tank.
“It takes a particular combination of water and pressure to create a slurry, which suspends the heavier solids in a liquid that can be pumped out and sent via transfer lines to another tank,” said Peggy Hamilton, retrievals manager for WRPS. “We use lessons we learned and technologies developed during the successful retrieval of waste from other tanks to help us complete this challenging work.”
Tank AX-103 is the third million-gallon tank to have its waste retrieved in a group of four called the AX Tank Farm. WRPS has already retrieved waste from tanks AX-102 and 104. Retrieval of the last tank, AX-101, is scheduled to begin next year.
Preparing a decades-old tank farm for safe waste retrieval takes years of retrofitting. Workers remove old, contaminated equipment from the tank to make space for the equipment needed for retrieval of the waste. Then they install modern retrieval equipment, ventilation safety and leak-detection systems, and transfer lines to move the waste to a double-shell tank. They also install utilities and cameras with lighting so operators can see inside the tanks while operating equipment remotely.
To date, workers have completed retrieving the waste from 17 of Hanford’s 149 older single-shell tanks. Those tanks include the 16 tanks in the C Farm and a tank in the S Farm. Once tanks AX-102 and 104 go through a standard technical review for completion that can take several months, the list will grow to 19. Hanford’s single-shell tanks were constructed of carbon steel and reinforced concrete between 1943 and 1964 to store radioactive and chemical waste created during plutonium production operations in World War II and the Cold War era.
Photo: With the final sections of double-walled pipe in place, a Hanford Site tank farm is now connected to the Waste Treatment and Immobilization Plant (Credit: US DOE EM)