The Department of Energy plans to close the Hanford Site’s waste storage Tank AY-102, which developed a slow leak from its inner shell into the space between its shells.

Tank AY-102 was the first of 28 double-shell tanks built at the Energy Department site in Washington state, leaving 27 in service to hold waste emptied from the site’s 177 leak-prone single-shell tanks until the material can be treated for disposal.

Under an agreement with the Washington state Department of Ecology, DOE pledged to empty most of the 744,000 gallons of radioactive and hazardous chemical waste in Tank AY-102 by March 4, 2017. Since meeting that deadline weeks early, Hanford tank farm contractor Washington River Protection Solutions (WRPS) has been inspecting AY-102 to learn more about the interior leak and evaluating the results. One of the goals of the evaluation was to consider whether the tank could be repaired, although officials conceded that was a long shot.

New high-definition video cameras were used to inspect one area of the bottom of the inner shell where tank farm workers suspected a leak might be found. After the bottom of the tank dried out, some liquid was added again. The video showed the liquid swirling down in seven places, all separate leaks. The Tank Integrity Expert Panel, an independent group of specialists that provides advice on Hanford tanks, attributed the leaks to pitting from corrosion and said similar pitting likely would be present in other areas of the bottom of the inner shell.

While weld problems in construction of the tank initially was suspected as the source of the leaks, the Tank Integrity Expert Panel concluded the pitting likely developed from inadequate management of the contents of the tank in its early years of use, said Doug Greenwell, WRPS manager of tank retrieval. The tank was put into service in 1971.

“We’re looking forward to moving into the next phase in the closure process, which will include setting measures in place to secure the AY-102 tank system in a manner that prevents threats to human health and the environment, until the final closure of the AY Tank Farm can take place,” said Alex Smith, manager of the Ecology Department Nuclear Waste Program.

DOE and Ecology are expected to discuss how to close the tank. Although no single or double shell tank at Hanford has yet been closed, the most likely method would be to fill tanks with grout and close them in place.