The Department of Energy said it has made significant progress in resolving technical issues that have slowed progress on construction of the Hanford Site’s Waste Treatment Plant since 2012.
DOE’s Office of River Protection has sent letters describing resolution of three of the eight technical issues to the agency headquarters, where they are being finalized before submittal to the Defense Nuclear Facilities Safety Board. In addition, in late December DOE and plant contractor Bechtel National announced that full-scale vessel testing had started to resolve the fourth technical issue.
DOE in 2012 halted construction on the plant’s Pretreatment Facility and part of its High-Level Waste Facility due to technical concerns concerning high-level radioactive waste. Construction continues on parts of the plant, such as the Low-Activity Waste Facility, that will not treat high-level radioactive waste for final disposal.
Fifty-six gallons of radioactive and chemical waste is stored in tanks at Hanford, a byproduct of plutonium production at the DOE facility. Treatment of low-activity radioactive waste is expected to begin by 2022, and the full Waste Treatment Plant is required under a federal judicial order to be operational by 2036.
The three issues that appear to be resolved are the risk of combustion in waste-processing vessel headspace due to hydrogen accumulation; the risk of a criticality in vessels with pulse jet mixers when waste contains plutonium particles of a size and density prone to settling out of the material; and the risk of a deflagration event in piping and ancillary vessels.
The fourth technical issue involved maintaining sufficient mixing of high-level radioactive waste in vessels that will store and process liquid waste in the Pretreatment Facility. Former Energy Secretary Steven Chu ordered full-scale testing of certain vessels after he spent several days at Hanford with a team of experts in 2012. Rather than test vessels with multiple different designs, as had been originally planned for the Pretreatment Facility, Bechtel has moved to a standard vessel design.
Full-scale testing is the third phase of testing on the project and is being done at a laboratory built for that purpose by an EnergySolutions division that has since been acquired by Atkins. The lab has been donated to Washington State University Tri-Cities, but leased back until testing is completed. Testing now is focused on the control equipment and systems for pulse jet mixers in the vessel. “This represents substantial progress and will lead to restarting engineering, procurement and construction on the Pretreatment Facility,” said Bill Hamel, DOE assistant manager for the vitrification plant project, said in a press release.
The standard vessel is outfitted with an array of six pulse jet mixers designed to keep the contents of the 22,000-gallon tank safely mixed by keeping solid particles in the waste from settling at the bottom of the vessel. Because the mixers will be contaminated as soon as waste treatment begins, they are designed to have no moving parts that could require repairs. They work like a turkey baster, sucking up mostly liquid waste and then expelling it, mixing waste in the process and preventing solid particles from dropping to the bottom of the vessel.
Previous tests used smaller tanks to confirm that control equipment can reliably operate mixers before a full-size, 65-ton prototype vessel was fabricated and barged up the Columbia River to Hanford in July. The test vessel is 16 feet in diameter and 36 feet high.
“Proper mixing of waste in the vessels is critical to safely processing and testing the waste stored in Hanford’s underground tanks,” said Peggy McCullough, Bechtel’s project director for the vit plant, said in the release. Full-scale testing has started on a schedule of 24 hours a day for four weeks a day, and is due to move to around the clock testing seven days a week to complete testing in late 2017.
The Department of Energy has not released a timeline for resolving the last four technical issues. They include concerns over erosion and corrosion in piping and vessels that could prevent them from lasting for 40 years of waste treatment. Some additional work is needed related to criticality analysis and additional structural analysis of vessels in the Pretreatment Facility. Issues also have been raised regarding the ventilation system and process off-gas treatment.
