Retrieval of waste from the Hanford Site’s oldest double-shell tank resumed Thursday after workers gained some control over the internal leak in the container. As waste was being retrieved from Tank AY-102 early Sunday morning an alarm sounded, indicating the rate of leakage within the tank had increased dramatically. The decades-old tank was being emptied after about 70 gallons of waste had leaked from the inner shell over several years and had dried in patches in three spots within the space between the shells, called the annulus. Work stopped Sunday as the annulus, which is 30 feet high and about 30 inches wide, filled to 2 inches deep. Throughout the day the level continued to rise, topping out at about 8.4 inches, or an estimated 3,000 to 3,500 gallons of waste. By Monday morning it had dropped by about three-quarters of an inch, and later in the week it dropped further to about 6.5 inches.
The Washington state Department of Ecology said in a statement early in the week that there was no indication the public is presently at risk or that waste has breached the outer shell of the tank. “Monitoring and inspections show no visual or chemical indications that waste from the tank has leaked into the environment,” the Department of Energy said in a statement Friday. Tank contractor Washington River Protection Solutions (WRPS) repeatedly checked the leak detection pit beneath the tank for any increase in its contents. The pit receives some precipitation intrusion. WRPS also checked the pH level of the contents of the pit without finding the high pH level indicative of tank waste.
Before work started March 3 to remove first the liquid waste from the tank and then start removing the sludge beneath it on March 31, a pump had been installed in the annulus as a contingency. “We were prepared for this event,” said Glyn Trenchard, DOE’s deputy assistant manager for the tank farms, in a statement. WRPS worked until Thursday to prepare to pump the annulus, including installing shielding on the hose that would transfer waste from the annulus back into the inner shell of the tank. Pumping of the annulus began late Thursday morning, but workers had to stop when the level had dropped to 4 inches, or about 1,500 gallons remaining, because they needed to replenish their supplied air. Self-contained breathing apparatus are used when there is a risk of exposure to chemical vapors.
Work also resumed Thursday to retrieve stored waste from the tank. “As we continue sludge retrieval, it’s predicted the waste level in the annulus will rise periodically to a pumpable level,” said Rob Gregory, WRPS chief operating officer, in a message to employees. Waste has to be at least 5 inches deep in the annulus to pump and the pump should be able to remove waste to as low as 2 inches. Already about 95 percent of the estimated 800,000 gallons of waste in the tank has been retrieved and sent to other double-shell tanks. The majority of the waste was liquid, which was removed in early March.
Beneath the liquid was about 151,000 gallons of sludge, which is more difficult to remove. Working mostly weekends in April when fewer workers were at Hanford, WRPS had removed all but 46,000 gallons of sludge before it had to stop retrieval Sunday. About 14 inches of sludge in the million-gallon-capacity tank remain. Under a settlement agreement with the state of Washington, DOE has until March 4, 2017, to remove the waste to allow an investigation of the original leak in the tank.
The federal agency had anticipated that the level of waste in the annulus could change during tank pumping as waste was removed or shifted, potentially opening up a less obstructed leak path into the annulus, DOE said. The department and WRPS had worked closely with the state Department of Ecology before pumping started to make a range of plans to address possible issues. The drop in the waste level in the annulus before pumping started there may be related to the refractory, the pad-like structure upon which the inner shell sits above the base of the outer shell, according to WRPS. The refractory has narrow air channels to help cool the waste and the leaked waste may have been flowing into the channels, Gregory said. Some of the waste might also have been absorbed into the somewhat porous refractory material.
Sen. Ron Wyden (D-Ore.) on Tuesday called for Energy Secretary Ernest Moniz to immediately convene an independent panel to monitor not only the condition of Tank AY-102 and the risks from retrieving its waste, but also to reassess the safety risks associated with Hanford’s other 27 double-shell tanks. “I do not believe that these determinations can be left to the Department and its site contractors,” he wrote in a letter to Moniz. Residents of the Northwest need assurance that there is no immediate danger from the conditions in Tank AY-102 and the continuation of retrieval operations, Wyden said. Hanford has had a panel of outside experts, the Tank Integrity Expert Panel, since 2004. The panel includes experts from industry, academia, and national laboratories. It evaluates data from ultrasonic testing looking for thinning of the primary walls of the double-shell tanks, from waste sampling and from videotaped inspections inside the tanks. A separate independent panel was named at Hanford to look at Tank AY-102 after its interior leak was discovered.
Wyden has previously criticized DOE’s management of its double-shell tanks. “It goes without saying that citizens in Oregon and I are concerned about this situation especially given the fact that previous analyses of this tank and other double-shell tanks, have raised numerous design and construction concerns and the exact cause of the original AY-102 leaks has never been determined,” Wyden said in a statement. DOE concluded after an earlier study that the leak within Tank AY-102 was the result of construction difficulties on the first double-shell tank to be built and the combination of waste stored in the tank, which generates high levels of heat that can contribute to corrosion of the tank.
DOE and its contractor also used historical documents to reconstruct how the other double-shell tanks were built. The evaluation found that subsequent tanks had fewer challenges in being built but that construction and weld issues “leave room for uncertainty of long-term tank integrity” for some of the tanks. Wyden said earlier that six tanks in addition to Tank AY-102 have construction flaws that could increase the risk of leaks and that 13 more tanks may have construction problems that will shorten their lifespan. The tanks were built from 1969 to 1986, with the earliest already surpassing their 40-year design life. The double-shell tanks, as Wyden noted in his letter, were the next generation of tank design at Hanford and were intended to provide a greater level of safety than the site’s 149 single-shell tanks.
