The Defense Nuclear Facilities Safety Board is calling for more rigor in safety plans to ensure that pipes that transfer radioactive waste at the Hanford tank farms do not leak.
It's particularly important that the tank farms operate safely given the increased tempo of work once the Hanford vitrification plant starts treating waste, said Peter Winokur, board chairman, in a letter to the Department of Energy.
The piping system is used to move radioactive waste within the Hanford nuclear reservation's underground tank farms, which hold 53 million gallons of radioactive waste until it can be treated. That system moves waste from older, leak-prone tanks to newer double-shell tanks and also transfers waste between double-shell tanks to optimize the limited space in the newer tanks.
Treatment could start at the vitrification plant for some waste as early as 2016 under a new proposal, with DOE legally required to start treating waste in 2019.
The piping safety system is required not only to prevent leaks, but also, in unlikely events, fires that could result if hydrogen gas builds up in piping, including above-ground transfer lines.
Although increased safety requirements were adopted for new piping in 2008, the safety of the majority of the piping system is ensured through periodic assessment by a registered professional engineer.
However, the assessment does not factor in items such as pipe integrity to prevent pressurized spray leaks, chemical exposures and flammable gas fires, according to a report by the defense board staff.
The most recent assessment highlighted past failures in the piping likely linked to corrosion, and it questioned corrosion rate projections used to forecast the remaining life of the piping system, the staff wrote.
Yet the assessment concluded that failures linked to corrosion were not expected in the time the piping would be needed at the tank farms. DOE now plans to use the double shell tank system longer -- not just until 2028 but until 2048, the report pointed out.
The report also looked at policies for drips from the piping system, as opposed to leaks that allow continuous flows or sprays.
There is no formal inspection to find drips that could persist unobserved for extended periods or degrade into a more significant hazard, the report said.
If a drip is discovered, waste transfers at the site of the drip should stop until repairs are made or actions taken to prevent or detect further degradation, the report said. At some points, such as valve stem seals, drips might not present a significant hazard if promptly detected and corrected, but at other places they could signify corrosion issues, the report said.
Those and other issues listed in the report "collectively reduce the safety margin for operations within the Hanford tank farms," said Winokur's letter.
The DOE Office of River Protection, which is responsible for the tank farms, remains focused on safe operation of the tank farms and will brief the defense board on planned safety efforts, the ORP said in a prepared statement.
The defense board has requested a report within 90 days.
-- Annette Cary: 582-1533; firstname.lastname@example.org