Hanford vitrification plant testing has not shown that components that will be difficult to replace can last the required 40 years the plant is designed to operate, according to the Defense Nuclear Facilities Safety Board.
Whether vessels and piping for high-level radioactive waste in the plant will corrode is an issue raised by DOE scientist Donald Alexander in an unresolved Differing Professional Opinion in May. The defense board also has been evaluating wear issues for the past nine months.
The defense board sent a letter to DOE on Friday asking for a briefing within 45 days to provide confidence that the vitrification plant will operate safely and reliably for 40 years.
It noted that DOE, with contractor Bechtel National, is developing a course of action to address wear design issues.
“However, the current pace of the contractor’s efforts to close the issues does not support timely resolution,” said a defense board staff report that accompanied the letter.
Some of the vessels in question are scheduled to be installed at the vitrification plant in August and modification will become progressively more difficult and costly after the vessels are closed and installed, the report said.
The $12.2 billion vitrification plant is being built to turn radioactive waste left from past weapons production of plutonium at Hanford into a stable glass form for disposal.
Much of the piping and many of the vessels in the plant will be in areas called black cells that will be too highly radioactive for workers to enter once waste processing begins. Consequently, their design is required to be maintenance-free for 40 years.
“Component failure due to wear … could stop waste processing for indefinite periods, resulting in significant extensions in the time required to accomplish the facility mission,” the defense board letter said. “The existing design margins offer little or no flexibility for future operations or the opportunity to extend the life of the plant, if required.”
Experimental testing to validate the wear model was limited and the results were flawed, said the defense board letter.
The design wear rates were derived mainly from information found in literature, including from experimental studies performed using slurries and conditions not representative of vitrification plant processes, the letter said. Assumptions to apply information to the vitrification plant were not adequately validated, the letter said.
Project officials have said that the wear models are conservative but have not substantiated that with an analysis, the letter said. The defense board said it found wear allowances provided in the design of some vessels and the pulse jet mixers are not conservative.
The pulse jet mixers are designed to operate like turkey basters, sucking up a slurry of waste and shooting it back out, to keep waste mixed in vessels without relying on moving parts that would require maintenance.
Experimental testing that was done on mixing vessel erosion collected data that lacked a discernible trend and displayed physically unrealistic results, the letter said.
“The Department of Energy remains fully committed to safety at this important facility, including the safety of our workers and the public,” said DOE spokeswoman Lindsey Geisler.
Information from the defense board will be used as DOE further develops and implements action to address erosion and corrosion of piping, vessels and pulse jet mixers, she said.