Defense safety board warns of flammable gas in Hanford tanks

By Annette Cary, Tri-City HeraldOctober 3, 2012 

The Department of Energy is not doing enough to prevent a buildup of flammable gases in radioactive waste tanks at Hanford, according to the Defense Nuclear Facilities Safety Board.

"A significant flammable gas accident would have considerable radiological consequences, endanger personnel, contaminate portions of the tank farms and seriously disrupt the waste cleanup mission," the defense board said in a report dated Friday.

It sent a formal written recommendation to Energy Secretary Steven Chu on Friday and publicly released it Tuesday. A written recommendation is the most powerful mechanism available to the defense board for advising DOE on safety matters.

The recommendation calls on DOE to work faster to upgrade the ventilation for each of Hanford's 28 double-shell tanks to ensure removal of flammable gases from the tanks' headspace and to install real-time monitoring equipment to measure tank ventilation flow rates.

Many of Hanford's double-shell tanks contain enough gas trapped in the waste that safe conditions could be exceeded if the gas were spontaneously released either in normal operations or during an accident, according to the recommendation report from the safety board.

"The current control strategy does not include any measures to periodically release the trapped gases in a controlled manner to preclude the accumulation of flammable concentrations," the report said.

Reducing the flammable gases retained in the waste and keeping the amount small would reduce the future hazards possible for gas releases, it said.

Each underground tank has a capacity of 1 million to 1.16 million gallons for waste left from the past production of plutonium for the nation's nuclear weapons program. Hanford has 56 million gallons of radioactive waste in underground tanks and work is under way to transfer as much of the waste as possible from leak-prone single shell tanks into the newer double shell tanks until the waste can be treated for disposal.

DOE has committed to upgrading the double-shell tank ventilation systems and other installed instrumentation necessary to maintain safety at the tanks, the defense board said in its report.

But "the board has concluded that no progress has been made in these areas, and the schedule for upgrades continues to slip," the report said.

DOE sent a letter to the defense board in April 2012 committing to finish upgrading three of the five double shell ventilation systems by fiscal 2014. But during the defense board June 2012 review, DOE indicated that was no longer a realistic schedule, according to the report.

Now DOE's plan is to upgrade only one of the ventilation systems, the one serving the AY and AZ Tank Farms, which have four tanks combined, by fiscal 2015 to support mixer pump testing that is planned for a year later, the board said.

No near-term purchasing or installation plans are in place for improving the four ventilation systems serving the remaining 24 tanks, according to the report.

Now DOE has no means to provide alternate ventilation if an existing ventilation system becomes inoperable, the report said. It recommended that compensatory measures be identified.

DOE is reviewing the board's concerns, said DOE spokeswoman Lori Gamache.

"We value input from the board," she said. "We are committed to maintaining safe operations at the Hanford tank farms, including protecting our workers, the public and environment."

-- Annette Cary: 582-1533; acary@tricityherald.com

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