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In a letter to a senator likely to bring enhanced political scrutiny to the Department of Energy, a federal panel has reiterated several concerns it lodged with the DOE over its partially built vitrification plant and waste storage at the Hanford site.

The Defense Nuclear Facilities Safety Board outlined several concerns it has raised with DOE officials in recent years. Among them, a recommendation made to the energy secretary in September called for an enhanced safety focus on hydrogen gas buildup in Hanford waste tanks, given the potential for an explosion to spread radioactive material.

"This recommendation identified concerns with DOE's administrative controls for monitoring flammable gas conditions in its double-shell waste tanks and recommended that DOE restore the functional classification of the ventilation systems in these tanks from general service to safety-significant. DOE's safety analyses show many of the double-shell tanks currently have enough flammable gas retained in the waste that, if released in the tank headspace, could create a flammable atmosphere. Furthermore, all the double-shell tanks contain waste that continuously generates some flammable gas," the board wrote, noting that the DOE has begun acting on its recommendation.

Other concerns addressed the vitrification plant under construction by prime contractor Bechtel. DNFSB correspondence from 2010, 2011 and 2012 raised plant design questions related to equipment corrosion, the potential for plutonium criticality in inadequately processed waste, and hydrogen buildup.

"DOE has not resolved key technical issues with the WTP (waste treatment plant) design, many of which were identified several years ago," the board wrote. Among them, " Flammable gases, such as hydrogen, generated by the wastes treated in WTP will accumulate whenever flow is interrupted in process piping and in regions of the piping system that do not experience flow, such as piping dead legs.  DOE has approved a strategy that allows hydrogen explosions in piping under certain conditions, and relies on a quantitative risk analysis (QRA) and other complex models to predict the magnitude of the explosions and the response of the piping system. The board remains concerned that DOE has not yet developed a QRA that demonstrates that explosions would not lead to a breach of the primary confinement."

The board's letter was sent to Oregon Sen. Ron Wyden at his request. He's been critical of hydrogen controls in Hanford tanks in years past, and he told the New York Times that he plans to raise the issue during a confirmation hearing for President Barack Obama's new energy secretary nominee.