Enough space to hold almost 2 million gallons of radioactive waste has been freed up in Hanford’s underground tanks through a series of successful runs of the nuclear reservation’s evaporation plant.
The 242-A Evaporator has completed four successful runs since returning to service a year ago after being shut down for four years for improvements.
The evaporator plant is central to DOE’s plans to meet its court-enforced consent decree obligations to empty 19 of Hanford’s leak-prone underground tanks. Waste is transferred into the 27 usable, newer double-shell tanks at the site until the waste can be treated for disposal at the yet-to-be-finished vitrification plant.
The Department of Energy has argued in federal court that the evaporator plant can provide enough space in the double-shell tanks that it will not need to build additional waste storage tanks.
But the state of Washington is not convinced the plant can be operated with the efficiency and frequency that would be required to continue emptying single-shell tanks. It has asked the court to order DOE to build four new million-gallon storage tanks by 2022 and possibly more by later deadlines.
The evaporator heats liquid tank waste under vacuum so it will boil at a temperature of about 125 degrees. Water vapor from the boiling waste is captured, condensed, filtered and sent to the Effluent Treatment Facility for treatment and disposal. The concentrated waste is then returned to the double-shell tanks.
70 million gallons of waste evaporated to date
Since starting operations in 1977, the evaporator plant has reduced the liquid in Hanford tank waste by more than 70 million gallons. Hanford has about 56 million gallons of radioactive waste stored in underground tanks from the past processing of irradiated fuel to produce plutonium for the nation’s nuclear weapons program.
In the first operating run since 2010, the 242-A Evaporator freed up space for almost 800,000 gallons of waste in the double-shell tanks in October 2014. That was followed by smaller runs in June and July that together removed about that much water.
The last in the series was this fall, with the plant operating nonstop for nine days to remove 375,000 gallons of excess water.
In total, the evaporation campaigns created almost as much storage space as two double-shell tanks.
DOE has said in court documents that it plans to conduct 23 more evaporator runs in the next seven years, including three to support emptying double-shell Tank AY-102. The tank has a leak between its shells and will be taken out of service.
“Although the 23 evaporator campaigns planned over the coming years represent an operational increase in terms of the number of campaigns per year, that increase is still within the facility’s capability,” said Tom Fletcher, DOE assistant manager for the Hanford tank farms, in a court document. “In addition, by increasing the number of campaigns, evaporator operations should become more routine.”
Operational delays caused by short-term startups and shutdowns should be minimized, he said.
“DOE anticipates that these more routine operations will allow for better maintenance of the facility, more efficient operations and improved planning of campaigns,” he said.
DOE has opposed building more tanks, saying the money would be better spent on work toward getting the waste treated. It has estimated that each new tank could cost $85 million to $150 million, which would include costs of permitting and design and acquiring nuclear-quality materials.
Over the four years the evaporator plant was shut down, DOE contractor Washington River Protection Solutions made improvements to it, including a control room revamp and changes to equipment and operating procedures. Equipment was replaced rather than waiting for it to fail, DOE told the court.
It acquired spare parts and made improvements recommended by the Defense Nuclear Facilities Safety Board to help it better withstand a severe earthquake. The contractor also conducted a complete review of how the facility meets safety requirements related to handling nuclear materials.
“The 242-A Evaporator facility is mechanically sound,” Fletcher said. “Continued integrity assessments and equipment upgrades, along with a proactive maintenance strategy, should keep the evaporator operating for another 30 years.”
The state told the court that DOE’s plans for operation of the evaporator plant may be overly optimistic. If DOE runs out of space in its double-shell tanks, it will have to stop work to empty its leak-prone single-shell tanks.
Given the history of evaporator performance, there can easily be delays ...
Jeff Lyon, Washington State Department of Ecology
“Given the history of evaporator performance, there can easily be delays” in planned evaporator campaigns, said Jeff Lyon, tank waste storage manager for the Washington State Department of Ecology, in a court document.
In 2004 an evaporator run was conducted using a transfer line with a tap improperly installed, causing waste to leak. Runs in 2007 were hampered by mechanical failures, Lyon said.
Other runs have started late and one run in the last five years had to be stopped early because sampling showed the the waste slurry being transferred to the plant contained excess solids, he said.
U.S. Judge Rosanna Malouf Petersen has said that DOE will be required to build new storage tanks if it does not meet certain deadlines yet to be determined. However, in that ruling in August, she stopped short of requiring DOE to build four more double-shell tanks by 2022 with up to eight more required after that, as proposed by the state.
The amount of tank space DOE must free up through evaporation campaigns and the schedule that will trigger the requirement for new tanks will be set after the state and federal government submit more information to the court.