A major leak of radioactive waste from the inner shell of Hanford Site double-shell Tank AY-102 into the space between the shells was detected this weekend as sludge was being retrieved from the tank. An alarm for a level detector in the space between the shells, called the annulus, sounded early Sunday morning. Retrieval work stopped as the level of waste within the annulus reached 2 inches. The level of waste continued to rise through the day to reach about 8 inches deep throughout the 18-inch-wide annulus of the 1-million-gallon capacity waste storage tank. The amount of waste in the annulus was estimated at 3,000 to 3,500 gallons. The material held in the tank was being emptied under a Department of Energy settlement agreement with the Washington state Department of Ecology after waste was earlier detected leaking into the annulus in three places in Hanford’s oldest of 28 double-shell tanks. About 70 gallons of waste had leaked and dried in three places in the Tank AY-102 annulus over at least a couple of years before the increased leakage was detected early Sunday.

Further concerns were raised early Monday morning when the waste level in the annulus dropped by about three-quarters of an inch, or an estimated 180 gallons, raising the possibility that the waste had breached the outer shell. The Department of Ecology, the regulator on the project, said Monday it did not appear any waste had leaked from the outer shell to reach the environment and that there was no risk to the public. Hanford tank farm contractor Washington River Protection Solutions (WRPS) checked the leak detection pit beneath the underground tank Sunday and again Monday, finding no increase in its contents, which includes precipitation that can infiltrate the pit. WRPS also conducted a pH test on a sample from the leak detection pit, determining that the pH of the pit’s contents did not have the high pH that would indicate waste from the tank had reached it. Hanford officials are considering the possibility that waste leaked from somewhere else in the outer shell, such as its sides. However, another possibility is that the waste level in the annulus dropped as waste from the annulus flowed into the ventilation channels in the refractory between the bottom of the inner shell and the bottom of the outer shell.

The Department of Ecology said the increased leaking into the annulus likely occurred because waste retrieval work dislodged material that was partially blocking leak sites. Hanford officials knew disturbing the waste in the tank during retrieval might increase leakage, and a pump had been installed in the annulus before work started in March to retrieve first liquid waste and then sludge from Tank AY-102. On Monday, WRPS hooked up a line from the pump into the inner shell of the tank and then worked to cover the line with radioactive shielding. DOE said in a statement Monday that it expected WRPS to begin pumping the waste from the annulus within the next two days. Retrieval of the sludge from the tank is expected to be restart at the same time. WRPS had been making quick work of retrieving sludge from the tank before retrieval was shut down Sunday. With work mostly done on weekends, about two-thirds of the sludge had been removed. Just 14 inches of waste remained on the bottom of the tank, or about 46,000 gallons by WRPS estimates, when pumping stopped Sunday.