Nineteen years after work began to empty the thick, radioactive sludge in Hanford’s C Farm tanks, the end may be in sight.
Work was expected to resume Thursday night for a final campaign to remove the remaining sludge in the last of the 16 tanks in the group called C Farm.
If work goes as planned, Tank C-105 could be emptied by the end of the year.
“This has been a very challenging one,” said Doug Greenwell, manager of single-shell tank retrieval for Department of Energy contractor Washington River Protection Solutions.
C Farm was the first group of leak-prone tanks tackled, with a goal of declaring all 16 emptied to regulatory standards by 2006.
That did not happen.
As the first tank farm where Hanford workers attempted to empty all tanks, C Farm is considered a demonstration project.
Lessons learned are to be used to retrieve waste from the remaining 132 single-shell waste storage tanks at Hanford, and there have been plenty of lessons.
But in the past 19 years, progress has been made to develop better equipment for moving the waste out of the enclosed underground tanks and to do the work more efficiently.
Tank C-105 was the first to use a new technology, a robust robotic arm called MARS, for Mobile Arm Retrieval System, equipped with a vacuum system.
Because the tank may have leaked before pumpable liquids were removed more than a decade ago, Hanford officials have wanted to avoid technologies that would use significant amounts of water or other liquid to break up the waste and move it toward a central pump.
In 2014 and 2015 MARS sucked up 92,000 gallons of the waste from the tank, which has a capacity of 530,000 gallons.
“At the end of the day it broke of old age,” Greenwell said. The hose on its vacuum end gave out after operating in the highly radioactive environment for 16,000 hours.
With an estimated 30,375 gallons of waste left in the tank, a decision was made to pull out the major components of the MARS vacuum system and try technology that has worked well at some other tanks.
Two extended reach sluicers have been installed in the tank. They are more compact that the MARS system, which required a hole to be cut in the top of the tank to insert it.
The sluicers spray liquid waste on sludge to break it up and move it toward a pump for removal from the tank. Unlike the sluicers first used in C Farm tanks, they are more flexible and can reach more areas within a tank.
We are trying to complete this before winter.
Doug Greenwell, Washington River Protection Solutions manager of single shell tank retrieval
Much of what is left in the tank is a hardened waste with complex aluminum components.
The waste is left from chemically processing irradiated uranium fuel from Hanford reactors to produce plutonium for the nation’s nuclear weapons program from World War II through the Cold War.
Washington River Protection Solutions plans a nine-step process, alternating sluicing with soaks of either hot water or a caustic solution to help dissolve aluminum compounds. Both types of soaks will be needed, since neither works well for all types of aluminum in the tank.
“We’re well-prepared to get the waste out,” Greenwell said.
Adding liquid to the tank, including with sluicers, is not ideal because of its history.
However, Hanford officials do not know for sure that it has leaked in the past.
A couple of times in the 1950s the tank was overfilled and waste spilled and contaminated the soil at the tank, Greenwell said. The tank may or may not also have leaked.
If it does spring a leak during retrieval, the leak will most likely be at the bottom of the tank and by then most of the waste should be removed, Greenwell said.
Washington River Protection Solutions would stop work to investigate any indication the tank might be leaking, and Hanford officials would decide whether waste retrieval could safely resume.
The goal is have no more than 2,700 gallons of waste left in the tank, which is about 1 inch of waste if it is spread evenly across the bottom of the tank.
Work is planned to start on weekends when fewer workers are at Hanford. Most workers work four 10-hour shifts, leaving a limited number of workers on the site from Thursday night through Sunday night.
When operations are stable and industrial hygiene data is available on chemical vapors, work could move to seven days a week around the clock.
Disturbing the waste and moving it to a sturdier double-shell tank to await treatment for disposal will increase the chance of chemical vapors being released. Most work in Hanford tank farms now is done with workers using supplied air respirators to protect against the vapors.
“We are trying to complete this before winter,” Greenwell said, after last year’s snow slowed work at the tank farms.
Completion would be well ahead of the most recent deadline set. A court-enforced consent decree requires all 16 of the C Farm Tanks to be emptied to regulatory standards by 2020.
In addition to the C Farm tanks, one of the tanks in the S Tank Farm also has been emptied, which would bring the total to 17.
Although the MARS vacuum did not finish emptying the tank, it still has promise, Greenwell said. Improvements could be made in the design of its suction head to make it work more effectively.
As work progresses to tanks that Greenwell calls “no-kidding leakers,” the MARS vacuum might be used again. Hanford officials also continue to look at new options offered by industry for retrieving waste.
While C Farm waste retrieval work is wrapping up, DOE and Washington River Protection Solutions have been preparing to start emptying waste from single-shell tanks in the A and AX Farms next.
In response to one of the lessons learned at the C Tank Farm, infrastructure will be installed across the tank farms before retrieval of waste in any tank begins. It should make emptying the tanks faster and more efficient, Greenwell said.