An internal Department of Energy watchdog recently gave a generally positive appraisal of evolving plans to protect workers and the public from potential hazards at the main treatment plant for the Hanford Site’s most radioactive liquid waste.
It was part of the Office of Enterprise Assessments’ recent review of the Preliminary Documented Safety Analysis for the High-Level Waste (HLW) facility at Hanford’s Waste Treatment and Immobilization Plant (WTP), which Bechtel National is under contract to build and which is supposed to stabilize some 55 million gallons of liquid radioactive waste left over from Manhattan Project and Cold War plutonium production.
DOE paused HLW construction in 2012 amid safety concerns, including the possibility of potentially explosive hydrogen buildup in the facility. HLW remains about 40% complete. DOE plans to “[p]erform initial planning to restart construction” of HLW in the fiscal year that begins Oct. 1, according to the latest budget request from the agency’s Office of Environmental Management.
HLW’s Preliminary Documented Safety Analysis weighs major types of “beyond design-basis accidents” such as full facility fires, unexpectedly severe earthquakes “and post-seismic or ashfall hydrogen explosions involving multiple vessels” inside the plant, the Enterprise Assessments Office wrote in its June 2021 review of the analysis. “The accident analysis demonstrates that all accident events are adequately prevented or mitigated.”
A worst-case accident from the safety analysis, “a hydrogen explosion in a melter feed vessel,” would deliver an estimated dose of 3.4 Roentgen Equivalent Man (REM) to the public and 660 REM to a co-located worker with HLW, according to the Office of Enterprise Assessments.
Vitrification involves mixing tank waste glass-forming materials in melters heated to 2,100 degrees Fahrenheit, the waste is mixed into the molten glass. Still in a liquid form, the glass is poured into steel canisters for cooling.
The office conducted its review mostly over the five months ended in March. Enterprise Assessments’ oversight of WTP has been remote only since April 2020, about a month after the COVID-19 pandemic hit, the office said.
Meanwhile, WTP is scheduled to begin converting Hanford’s less radioactive low-activity waste into a stable, glasslike form by the end of 2023. The current deadline for WTP to start processing the tanks’ more radioactive high-level waste is 2036, although site management has said this date might be missed.
Since 2014, DOE has worked with Bechtel to prevent potential hydrogen buildup in the facilities’ piping and vessels, which could cause an explosion, according to a May 2020 GAO report.
While DOE’s current cost estimate for the Waste Treatment Plant is about $17 billion, a Government Accountability Office report from May 2020 said the ultimate cost could run anywhere from $30 billion to $41 billion.
“Although Ecology does not have direct regulatory responsibilities for worker safety, our focus is on the preservation of human health and the environment,” Randy Bradbury, a spokesman with the Washington Department of Ecology said in a Friday email. “The emphasis on safety in facilities does contribute to the health of humans and the environment,” he said, adding the state will continue to monitor the various DOE safety reviews.
A DOE spokesperson declined to comment for this story.
