Big changes at Hanford

Image: Grouting PUREX tunnel 1 (Credit: US DOE)

AT THE HANFORD SITE IN Washington state, USA, more than 20 million pieces of fuel were fabricated for nine nuclear reactors along the Columbia River. Five reprocessing plants in the centre of the site processed 110,000 tons of fuel from the reactors, discharging an estimated 450 billion gallons of liquids to soil disposal sites and 56 million gallons of radioactive waste to 177 large underground tanks.

Plutonium production ended in the late 1980s and cleanup began in 1989, when a landmark agreement was reached between DOE, EPA, and Washington State. The Tri-Party Agreement established 161 milestones for completing cleanup. The Comprehensive Environmental Response, Compensation, and Liability Act of 1980 set in place a regular 5-year review of remedial actions at the site. Each 5-year review evaluates a remedy’s implementation and performance to determine whether the remedy is or will be protective of human health and the environment.

Thirty cleanup projects, primarily focused on remediating contaminated soil and groundwater, are currently subject to these statutory reviews. More will be included as remedies are selected and documented in formal records of decision.

By the 2016 review the site had already made significant progress. Since 1989, when cleanup began, the active footprint had been reduced from 586 to 82 square miles. Spent nuclear fuel totalling 2300 tons had been moved to dry storage and 20 tons of plutonium removed from the Plutonium Finishing Plant and shipped offsite.

Of the nine production reactors, six had been ‘cocooned’ and one preserved.

The next Cercla review, covering the five years from 2016 to 2021, is due this year. Some major pieces of work have been under way in the period, latterly despite restrictions due to COVID-19.

Stabilising underground materials

In October and November 2018 crews worked mostly at night to place 4434 cubic yards of engineered grout into
a tunnel near the Plutonium Uranium Extraction (PUREX) facility. The tunnel had partially collapsed in May, requiring an emergency response and shutting down work at the site for two days.

The grout was flowed the length of the tunnel and around contaminated equipment inside. It was injected in several layers, and each was allowed to set before the next began. A foot of space was left between the topmost layer and the ceiling of the tunnel.

In April 2019 contractor CH2M HILL Plateau Remediation Company (CHPRC) completed grouting a second tunnel next to PUREX. Tunnel 2 contains 28 railcars with contaminated processing equipment and materials generated during Hanford’s weapons production era. Grouting was determined to be the best choice for stabilising the tunnel after an engineering evaluation of Tunnel 2 showed it was at high risk of collapse, as had happened at Tunnel 1.

Approximately 40,000 cubic yards of grout were placed in the tunnel. As with the first tunnel, the grout was injected in several layers, and each lift was allowed to set before the next began. This significantly reduced the risk of a collapse and possible release of radioactive materials.

“Even though the tunnel is full of grout, this does not preclude future remedial actions or limit final closure decisions,” said Joe Franco, DOE deputy manager for the Richland Operations Office. “It just means the risk to people and the environment is significantly reduced while those decisions are made.”

In April 2020 CHPRC awarded a $3.9 million subcontract to White Shield, of Pasco, Washington to design, engineer, and install a system to stabilise three underground structures at the Hanford Site’s Central Plateau by filling the structures with engineered grout.

The three underground structures are the 216-Z-2 Crib, 216-Z-9 Crib and 241-Z-361 Settling Tank, and are located near the former Plutonium Finishing Plant (PFP). The structures received liquid waste during Hanford’s plutonium production operations and contain residual radioactive and chemical contamination.

Initial work was conducted via email or conference call. After some post-demolition activities at the PFP, trucks will deliver engineered grout to be pumped into the structures using a conveyance system connected to pipes, called “risers” that stick out of the top of the structures.

Dealing with sludge

In 2018 CHPRC began removing highly radioactive sludge from temporary storage in containers located inside the 105-K West Basin near the Columbia River — a water filled pool.

The sludge is a mixture of tiny fuel corrosion particles, metal fragments, and accumulated dirt produced as irradiated fuel rods stored in the 105-K West Basin began to deteriorate. There was 35 cubic yards of sludge in the basin.

The sludge was transferred to a more secure long-term storage location near the centre of the site with secondary containment basins, leak detectors, and vents to keep the containers in a safe configuration. Workers spent years developing the sludge removal system.

“The sludge is some of the most hazardous material at Hanford, so moving it away from the river to safe storage in a robust engineered facility in the centre of the site significantly reduces risk,” said Doug Shoop, manager of DOE’s Richland Operations Office.

The sludge will remain at T Plant until final disposition decisions are made.

Changing the site skyline

In 2017 workers removed a landmark from the Hanford Site skyline, with the demolition of the ventilation stack at the PFP. The 200-foot-high exhaust stack serviced the PFP for 68 years. The subcontractor, Controlled Demolition, Inc, used a small amount of explosives to weaken the stack, allowing gravity to bring it to the ground. The same technique had been used to demolish similar structures at Hanford and was considered safer and more efficient than having workers, at elevated levels, use cranes and other equipment to demolish the tall structure.

Contaminated portions of the facility’s ventilation system had already been removed and crews spent six months planning for the demolition. With the ventilation building and stack removed, demolition was complete on two of the four main processing buildings that made up PFP. “The stack demolition is the result of years of preparation to clean out the contaminated facility to the point where the ventilation system isn’t needed and can be demolished,” said Tom Teynor, project director for PFP demolition at the Department of Energy (DOE) Richland Operations Office. “Removing the stack is not only historic, but it allows workers in heavy equipment to more easily access and demolish the remaining portions of the facility.”

The start of 2020 saw another change in the skyline when crews finished demolishing the PFP’s main processing facility. It had produced two-thirds of the nation’s Cold War plutonium and stood for 40 years of operations and 20 years of cleanout and demolition preparation.

The main processing facility was nicknamed “Z-Plant,” because it was the last stop of plutonium production at Hanford. It operated from 1949 to 1989 and contained two processing lines where workers working through gloveboxes would create hockey puck-sized plutonium “buttons” for shipment to weapons-manufacturing facilities. Plutonium production left gloveboxes and other pieces of plutonium processing equipment highly contaminated.

Decades of demolition preparations included decontaminating and removing about 200 pieces of plutonium processing equipment like glove boxes, 1.5 miles of ventilation piping, contaminated process lines, asbestos and other hazards. In some instances, such as cutting and removing two highly contaminated glove boxes, workers performed some of the most hazardous work anywhere across the DOE complex.

Demolition has been under way over the last five years, starting with connected buildings: an americium recovery facility (242-Z); fan house/ventilation stack (291-Z) and a plutonium reclamation facility (236-Z).

The final activities at PFP include packaging and safe disposal of rubble from the Plutonium Reclamation Facility (demolished in 2017), core sampling soil beneath the building pads and stabilization of the site with soil cover.

Regreening the site

In March 2019 contractor Mission Support Alliance (MSA) revisited 140 acres that had been revegetated but were found in 2017 not to be thriving.

Historically, if a location was found to be failing, it was cleared and planted again. Instead MSA used results from a Hanford Site pollinator study to create a specially formulated seed mix to encourage pollination and species diversity. It implemented supplemental planting (in lieu of full-scale revegetation) to save areas of successful growth. In some areas, it opted for plant flower plugs — small seedlings with a few inches of growth, soil and a root structure — which act as a seed source for the revegetation site.

Tank management

One of the site’s major activities was managing the waste in 177 underground tanks, more than a third of which were thought to be leaking. New technologies to manage these tanks have been developed during the cleanup process, and nine new retrieval technologies had been added to the original technology by 2016.

Site managers had begun to address the waste, with 2 million gallons of tank contents transferred to new double-walled tanks. That represents just 4% of the tanks’ total 56 million gallon contents, however, and the Hanford task remains a mammoth one.

The tanks had a design life of 40 years and now range in age from 40 to 70 years. The tanks contain the most complex heterogeneous radioactive waste at any US cleanup site. Waste is in the form of sludge, salts, and liquids. There are 1800 different chemicals in the tank waste and no two tanks have the same combination of waste.

Work on the tanks stepped up in 2020 to implement the Direct-Feed Low-Activity Waste (DFLAW) approach, which will send pretreated waste directly from the tank farms to the Low-Activity Waste Facility at the Waste Treatment and Immobilization Plant for vitrification.

DFLAW is a system of interdependent projects and infrastructure improvements, managed and highly integrated as a programme, that must operate together to vitrify, or immobilise within glass, Hanford tank waste.

“The waste in the tanks is very complex, and each batch of waste...must be sampled and analysed to ensure the vitrified end product meets regulatory standards,” said Mat Irwin, DOE Office of River Protection deputy assistant manager for the plant.

In December, contractor Bechtel completed construction of the last of 94 systems that comprise the Low-Activity Waste Facility. At the start of 2021 a third of them had been tested and handed over to plant management for commissioning. The DOE and Bechtel have begun startup testing in the Low-Activity Waste Facility itself.

The facility is over 2.5 acres in area and houses two large melters. The melters will vitrify low-activity tank waste after it is pretreated to remove caesium and solids at the tank farms and fed directly to the facility. The Tank-Side Caesium Removal system (TSCR) was delivered in October 2020. The pretreatment system will remove radioactive caesium and solids from tank waste and is critical to DFLAW.

In 2021 Bechtel began hiring and training laboratory and radiological technicians to prepare for cold commissioning of the Waste Treatment and Immobilization Plant. They join chemists hired last year and together will be responsible for analysing approximately 3000 samples of tank waste each year to support direct-feed low activity waste (DFLAW) operations.

Fourteen lab spaces will be used to conduct analyses of the elements within the waste, as well as determine the waste’s physical and chemical properties. The results will determine the type and amount of glass-forming materials that will be mixed with batches of tank waste during vitrification. Samples will also be taken throughout the process to confirm the plant is producing high-quality glass.

DOE Office of Environmental Management and BNI said the lab is ready for startup. “We expect to have 45 staff working 24/7 shifts in the Analytical Laboratory when DFLAW operations begin,” said Valerie McCain, Bechtel senior vice president and project director. “A second set of 12 lab technicians and 20 radiological technicians will be hired later this spring for commissioning and operations roles.”

In November 2020 a $13 million subcontract was awarded to Fowler General Construction to build a new Hanford Site water treatment facility that will automate water services, and support the tank waste vitrification programme and other risk-reduction cleanup projects across the site.

“When we get into 24/7 operations, having an uninterrupted supply of water and other infrastructure services will be critical, because once we turn the melters on, we won’t be able to turn them off until they are replaced periodically when they wear out,” said Mat Irwin, EM Office of River Protection deputy assistant manager for the Waste Treatment and Immobilization Plant.

The new water treatment facility will be able to produce 3.5-5 million gallons of clean water a day. Construction is expected to begin imminently.

As for DFLAW as a whole, it will be the most highly integrated operational programme at Hanford and the Office of Environmental Management says it will require significant upgrades to site infrastructure and coordination and integration among the site contractors. The plan is to begin DFLAW and start making glass in 2023.