Reviews of Hanford double-shell tanks have raised new concerns about their ability to safely contain high-level radioactive waste.
The reviews, which use historical documents to reconstruct how the tanks were built, call for enhanced inspection of some of the 28 tanks.
The Department of Energy will be doing more frequent visual inspections of all 28 tanks in response to the findings of the construction reviews, said Tom Fletcher, DOE assistant manager of the Hanford tank farms.
The review of the newest tank farm, built in the 1980s, still is in progress.
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The reviews finished to date conclude that while there were continuing construction difficulties, none of the tanks had as troubled a construction history as the oldest double-shell tank, Tank AY-102, which is leaking radioactive waste from between its shells. No waste is believed to have leaked into the soil beneath AY-102, which is underground.
Sen. Ron Wyden, D-Ore., sent a letter Friday to Energy Secretary Ernest Moniz calling for DOE to provide a plan within 45 days to respond to what he believes are increased safety and operational risks associated with construction flaws.
Wyden wants the plan to include an assessment of long-term options, such as constructing more waste storage tanks.
However, Rep. Doc Hastings, R-Wash., released a statement saying there is no new threat to the environment and new storage tanks are not a panacea for Hanford waste issues.
It's important to keep Tank AY-102 in perspective with other Hanford projects, including building the vitrification plant to treat radioactive waste for disposal, emptying leak-prone single-shell tanks and cleaning up contaminated groundwater, Hastings said.
DOE earlier concluded that the interior leak in Tank AY-102 was the result of construction difficulties and the combination of waste stored in the tank. The waste is left from the past production of weapons plutonium for the nation's nuclear weapons program.
The waste at the bottom of Tank AY-102 did not have a corrosion-inhibiting chemical added to it. In addition, waste that generated high levels of heat was added to the tank, which made corrosion of the tank's metal more likely.
However, none of the other double-shell tanks has that same combination of high heat waste and waste without a corrosion inhibitor, Fletcher said.
DOE began video inspections of the six double-shell tanks it believed to be at the highest risk of a leak after it became clear in 2012 that Tank AY-102 had an interior leak. No leaks were found in those tanks and Hanford workers are continuing visual inspections of the remainder of the tanks.
Inspections had been done every five to seven years, but because of the construction review reports DOE will have the inspections increased to every three years, Fletcher said.
Tank AY-102, which was built in 1969, had 36 percent of its welds rejected after an inspection and some welds were redone as many as four times before they passed a radiography examination.
When the AN Tank Farm was built, the weld rejection rate decreased. However, a weld rejection rate of 9 percent to 20 percent leaves cause for concern, the construction review said.
Weld and other construction issues at the farm "leave room for uncertainty of long-term tank integrity," but the overall condition of the farm following construction was judged to be better than that of the earliest double-shell tank.
Other construction difficulties were outlined for different tank farms. For instance, some tanks in the SY Tank Farm had bulging in both of their shells, and that was addressed by adding grout underneath the bulges to support the inner shells.
However, construction practices improved with thicker steel used in tanks after the first one was built. At the SY Tank Farm, the thickness of the bottom of the inner shell was increased from three-eighths to one-half inch and the steel in the bottom of the outer shell was increased from one-fourth to three-eighths-inch thick.
"All tanks had some levels of construction challenges, but all were accepted or repaired and put into service," Fletcher said.
The number of rejected welds is an indicator of construction difficulties rather than the quality of the completed tank, since the problem welds were fixed, he said.
But Wyden's take on the reviews is that at least six other tanks holding 5 million gallons of waste have construction flaws similar to those at Tank AY-102, which has the interior leak. An additional 13 double-shell tanks, holding 12 million gallons of waste, also might be compromised, he said in his letter to Moniz.
DOE should have identified the tank vulnerabilities in a framework document released in September that discussed possible solutions to getting the waste treated for disposal, Wyden said. Not doing so was "indefensible," he said in the letter.
His worries are heightened by DOE's failure to release any firm schedule for starting or operating the vitrification plant to treat the waste and remove waste from Hanford tanks, he said.
"Given the information now available concerning the state of the Hanford tanks, it is essential that DOE quickly come forward and present the region with a genuine plan for dealing with these growing risks," his letter said. "It is time for the department to stop hiding the ball and pretending that the situation at Hanford is being effectively managed."
Hastings said it is no secret that Hanford tanks were never designed to last forever.
"It is also no secret that it is critical for the federal government to be aggressive when it comes to work at the (vitrification plant) and the tank farms," he said.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews