Radioactive contamination discovered Thursday night could be a sign that a second double-shell tank at the Department of Energy’s Hanford Site in Washington state is leaking waste into the space between its shells.
A robotic crawler had been inserted down a riser into the space between the shells, or the annulus, of Tank AZ-101 as part of ultrasonic tank integrity testing done every eight to 10 years. When the crawler was removed, the unit had contamination at three times the planned limit. One worker also had low levels of contamination on a leg of his protective clothing, according to tank farm contractor Washington River Protection Solutions.
Workers immediately exited the area and the contaminated section of clothing was cut off, per Hanford protocol. No other contamination was discovered in checks of the crew and all workers were cleared for normal duty. All were wearing supplied air respirators as protection against chemical vapors associated with tank waste produced by decades of plutonium production at Hanford.
The alarm for the tank’s continuous air monitor activated during the incident, according to DOE. However, leak detection instruments installed in the annulus did not detect any liquid on the floor. The contaminated crawler was expected to be analyzed at Hanford’s 222-S Laboratory over the weekend to help identify the potential source of contamination. Historic records also were being collected Friday to determine if Tank AZ-101 has a history of contamination in the annulus, including from spills or leaks during waste transfers or intrusion of precipitation that could carry contamination.
Washington state Gov. Jay Inslee called the incident “alarming.” “We are not aware of any nuclear waste leaking outside the AZ-101 double-shelled tank, but we expect the U.S. Department of Energy to immediately investigate and report on the source of contamination,” he said.
Hanford has just 27 double-shell tanks in service after the state required DOE to empty Tank AY-102 after a slow leak of waste into its annulus was discovered. Waste retrieval from the tank was completed this spring.
