The Department of Energy expects to cut years from the time it takes to resolve technical issues at the Hanford vitrification plant under a new plan to simplify the design for key tanks.
Eight tanks with five different designs in the vitrification plant's Pretreatment Facility would be replaced with as many as 16 smaller and uniform tanks.
"DOE determined the costs of testing these five large vessel designs would be very large, and the testing schedule would span six to eight years," according to a DOE report on the new strategy released Thursday.
The tanks are designed to keep waste in the plant well-mixed.
The plan to use smaller tanks in the Pretreatment Facility would cut testing to three years and allow a high probability of success, said Langdon Holton, DOE senior technical authority for the vitrification plant. Testing could begin in July.
The estimated cost of the testing under the new approach is $147 million to $180 million, which the report said would be a savings of several hundred million dollars.
The new plan also would help address other technical issues.
Among issues that have to be resolved are preventing a buildup of waste that could lead to an unplanned nuclear reaction or a buildup of flammable hydrogen that could combust. They are unlikely events. There also are issues with the structural design of the mixing tanks and concerns that metal could erode during the 40 years the plant is expected to operate.
The Pretreatment Facility is supposed to separate up to 56 million gallons of radioactive waste held in Hanford's underground tanks into two waste streams -- low-activity radioactive waste and high-level radioactive waste -- for separate treatment and then disposal.
However, construction halted on the building, the largest on the vitrification plant campus, in 2012 until technical issues are resolved. Shortly after that former Energy Secretary Steven Chu said the testing program needed to be expanded to include full-scale tests on keeping liquid waste with high concentrations of solids well-mixed.
The Pretreatment Facility had been planned to house 34 tanks, including 26 that would have waste with no solids or low concentrations of solids. Those tanks have been installed.
Of concern are the final eight planned tanks that would hold waste with large concentrations of solids. They would vary in size, but the largest could hold 160,000 gallons of waste and measure 38 feet in diameter. It would require 18 pulse jet mixers, which would work like turkey basters to suck up waste through nozzles and shoot it back into the tank to keep particles suspended.
The mixing system would be so large and powerful -- mixers would stand 20 feet tall -- that it would need many supports to keep the tank from essentially rattling apart, Holton said. The supports would interfere with mixing and provide spaces for solids to collect.
Complete specifications of the smaller tanks under the new plan are being developed, but they are proposed to be 14 to 16 feet in diameter and hold 20,000 to 25,000 gallons of waste.
Because more of them would fit in the same space, tanks could be available for backup if a problem developed over the life of the plant, Holton said.
The smaller tanks would allow a simpler design, with fewer places for solids to collect. To help prevent solids from building up at the bottom of the tanks, they would be raised three to four feet off the floor and the discharge pipe would be redesigned. That would provide better access to fully remove solids, Holton said.
The tanks also would be constructed with thicker bottoms to reduce issues with erosion caused by the pulse jet mixers. Thicker piping would be sturdy enough to withstand the unlikely event of the hydrogen catching fire, he said.
Full-scale testing of the tanks in the new design would still be needed. But because tanks would be smaller there is no need to proceed with earlier plans to add a large tank outside a new laboratory built at Washington State University Tri-Cities in Richland to test vitrification plant mixing.
In the first phase, pulse jet mixing controls would be tested in a tank inside the new laboratory, with tests progressing from using water to using fluids with high concentrations of solids.
Next a prototype design of the new tanks would be tested at a small scale at Mid-Columbia Engineering in Richland, where clear acrylic tanks are used to observe mixing capabilities.
The final step would be full-scale mixing inside the WSU Tri-Cities laboratory to confirm the design with a range of fluids, Holton said.
Progress also is being made to resolve technical issues at the High Level Waste Facility at the vitrification plant. Some construction remains stopped there while technical issues are resolved. However, limited production engineering has resumed, which is a step toward returning to full construction.
-- Annette Cary: 582-1533; firstname.lastname@example.org; Twitter: @HanfordNews