DNFSB Wants Info From DOE On Preventing Hydrogen Explosions at WTP
WC Monitor
1/30/2015
The Defense Nuclear Facilities Safety Board is questioning how the Department of Energy plans to prevent hydrogen explosions in some tanks holding high-level radioactive waste at the Hanford Waste Treatment Plant. The Board is asking for a written report in 90 days on DOE’s path forward on developing a safety control strategy for certain tanks at the vitrification plant’s High-Level Waste Facility. The Department of Energy says it had already identified the issue and begun work on plans to resolve it before the defense board made its request.
Pulse jet mixers are planned to be used to keep the waste mixed. They would work like an oversized turkey baster, sucking up waste and then shooting it back out to disperse the solids in the waste mixture as they start to settle in the tank. But if the pulse jet mixers lost air and stopped mixing, hydrogen could accumulate in the waste. DOE had a plan to use spargers to periodically agitate the waste by blowing air or other inert gases into the waste if the pulse jet mixers were not operating. However, Hanford officials determined that spargers could cause problems with meeting ventilation system requirements.
Now DOE is evaluating five different alternatives, which range from using ultrasound for mixing to a high-flow system to quickly clear hydrogen from the head space of tanks. It already is required to identify a solution as part of work to show it meets nuclear safety standards before it eventually begins operating the vitrification plant. Bechtel National plans to rely on evaluations for resolving similar hazards at the vitrification plant’s Pretreatment Facility, said Jessie Roberson, acting chair of the Defense Board, in a letter to Mark Whitney, the DOE acting assistant secretary for environmental management. However, there are significant differences in the design of the two facilities and evaluations for the Pretreatment Facility might not apply to the High Level Waste Facility, the letter said.
