WTP Pulse Jet Mixing Tests Going Well, Officials Say
WC Monitor
4/10/2015
Hanford officials have seen encouraging results in half-scale tests of a system to keep high-level radioactive waste well mixed within certain tanks in the Hanford Waste Treatment 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 some tanks remains well mixed and can be safely stored. 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 plant, pulse jet mixers have been designed to work without moving parts that would require workers to perform maintenance.
The mixers work the same way as a turkey baster, sucking liquid 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, where clear acrylic tanks allow mixing capabilities to be observed.
DOE Looking to Simplify Tanks for Pretreatment Facility
Construction has been halted since 2012 on the vitrification plant’s Pretreatment Facility, the largest building on the plant’s campus, until technical issues can be resolved. Last yea,r the Department of Energy determined that years could be cut from the schedule 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, and 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.
Next Step: Full-Scale Testing
The next step will be to have a full size tank, 16 feet in diameter, built for testing at the EnergySolutions Engineering Laboratory with mock waste of different consistencies. EnergySolutions, which has a Becthel subcontract for the testing, built the lab 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.
