The level of radioactive waste in the space between the shells of Hanford Site double-shell Tank AY-102 remained stable Tuesday as Washington River Protection Solutions continued to prepare to pump the waste back into the tank. As waste was being retrieved from the tank Sunday the space between the shells, called the annulus, filled with waste about 8 inches deep. Early Monday morning the level dropped by about three-quarters of an inch. By 5 p.m. Tuesday the system to pump waste from the annulus was largely connected, but still undergoing checks. A pump had been installed in the annulus before retrieval of tank waste began in March in case disturbing the material caused more waste to leak into the annulus.
The Department of Energy is required under a settlement agreement with the state of Washington to have the tank emptied by March 4, 2017, after an estimated 70 gallons of waste leaked into the annulus over several years. On Sunday, an estimated 3,000 to 3,500 additional gallons leaked into the annulus. No evidence has been found that waste has escaped from the outer shell into the soil. The drop in waste may have been caused by waste escaping from the annulus into ventilation channels in the refractory at the bottom of the inner shell.
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,” Wyden wrote in a letter to Moniz. Residents of the Northwest need to be assured that there is no immediate danger from the conditions in Tank AY-102 and the continuation of retrieval operations, Wyden said. The Washington state Department of Ecology released a statement Monday saying there was no indication of a risk to the public at this time.
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 to look at Tank AY-102 after its interior leak was discovered in 2012.
Wyden has previously criticized DOE’s management of its decades-old double-shell waste 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.
The state is requiring Tank AY-102 to be emptied to determine why it is leaking. DOE concluded after an earlier study that the leak within Tank AY-102 resulted from construction difficulties and the combination of waste stored in the tank, which generates high levels of heat that can contribute to corrosion of the container. 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 construction issues but that construction and weld issues “leave room for uncertainty of long-term tank integrity.” 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. The tanks hold 56 million gallons of chemical and radioactive waste that were a byproduct of Hanford’s plutonium production operations during World War II and the Cold War.
