Hanford officials have seen encouraging results in half-scale tests of a system designed to keep high-level radioactive waste well-mixed within certain tanks in the vitrification plant, according to Bechtel National.
“We’ve had a few surprises when we’ve been doing this testing,” said Rick Brouns, pulse jet mixing project manager. “I’m pleased to report they’ve been positive surprises.”
Pulse jet mixers will be used in the vitrification plant to ensure waste in tanks remains well-mixed. There has been concern that in some tanks, enough plutonium could collect to create an unplanned nuclear reaction or that flammable hydrogen could build up, particularly if there is a loss of power.
Because of high radiation levels once processing begins at the vitrification plant, the mixing system is designed to work without moving parts that would require workers to perform maintenance.
The pulse jet mixers work the same way as a turkey baster, sucking it in and expelling it to keep the waste mixed.
“We’re finding that we are actually able to clear the bottom of the vessel of solids at lower jet velocities than we had projected from prior testing and from looking at the correlations from the past,” Brouns said.
The system performed better than expected, despite fears that mixing issues would be very difficult to solve, he said.
“It appears from the design that we’ve put forward that we have a pretty robust system,” he said.
Testing at half-scale size in an eight-foot diameter vessel was done at Mid-Columbia Engineering in Richland, where clear acrylic tanks allow mixing capabilities to be observed.
The vitrification plant is being built to convert up to 56 million gallons of Hanford waste left from past weapons plutonium production into a stable glass form for disposal.
Its Pretreatment Facility will be used to separate the waste into low-activity radioactive waste and high-level radioactive waste for separate treatment and disposal. However, construction halted on the building, the largest on the vitrification plant campus, in 2012 until technical issues are resolved.
Last year the Department of Energy determined that years could be cut from the time it takes to resolve technical issues by adopting a plan to simplify the design for key tanks at the Pretreatment Facility.
The initial plan to have eight tanks with five different designs in the Pretreatment Facility was replaced with a plan for as many as 16 smaller and uniform tanks. They will have a simpler design with fewer places for solids to collect because the smaller tanks will need fewer supports.
The waste in the tanks will have a large concentration of solids. Bechtel has described the waste’s consistency as ranging from that of water to that of a milkshake.
“The half-scale tests confirm we have the right design and the right configuration of the internal mixing components to proceed to full-scale testing of the new standard design vessel,” said Felice Presti, the Bechtel area project manager for the Pretreatment Facility. The testing in the half-scale tank began in December.
The next step will be to build a full-size tank, 16 feet in diameter, for testing at the EnergySolutions Engineering Laboratory with mock waste of different consistencies.
EnergySolutions, which has a Bechtel subcontract for the testing, built the lab in north Richland and donated it to Washington State University Tri-Cities in August 2012. It is leasing it back until testing is completed.
The full-scale testing program is expected to start in summer 2016 and be completed in 2017, according to Bechtel.
The Washington State Department of Ecology has been following the testing closely but has not seen test results yet, said state spokeswoman Heather John.