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Nuclear Waste Program

Tank AZ-101 incident

(Information on this site is considered to be accurate at the time of posting, but is subject to change as new information becomes available.)

Contamination raises concerns about double-shell tank


We received a report Friday, May 19, that Hanford work crews inspecting tank AZ-101 had discovered high contamination readings between the walls of the double-shell tank on the Hanford Nuclear Reservation. We immediately called for the Department of Energy to do an inspection to figure out the cause of the contamination. We’re concerned that it could have been a sign the tank is leaking. The tank is filled with 750,000 gallons of highly toxic, radioactive waste. We are actively engaged and closely monitoring this situation, including going on site for a first-hand perspective and information.

Double shell tank construction
Double-shell tanks under construction in the 1970s on Hanford. Once closed in, the tanks were buried in dirt, which protects people from tank radiation. It also means that the tanks can’t be visually inspected for leaks.



2017:  May 23 | May 24 |

May 24, 2017

Good news - AZ-101 primary tank isn't leaking

We’re relieved to report that AZ-101’s primary tank is not leaking. We have seen enough evidence from the Department of Energy to conclude that, while there are signs of some type of leakage in the tank, it does not appear to be coming from the main tank. Clear video pictures of the space between the tank’s inner and outer shells show some powder and other debris, but no liquid. Whatever may have leaked into the tank has evaporated.

Preliminary analysis of the contamination indicates that it is not from the main tank. It may have leaked in from a pipe that goes through the walls of the tank, but the specific source of the leak has not been identified. We will continue our investigation into the incident and oversight of the Department of Energy’s response.

How the contamination was discovered

The Department of Energy does routine inspections of its double-shell tanks. For this latest inspection, it was using a robotic crawler to go between the inner and outer tanks, using ultrasound to check whether the tank walls and floor are getting thinner. The crawler got stuck, apparently in debris on the floor. When the work crew lifted and shook the crawler in an attempt to dislodge the debris, an instrument that detects airborne radiation (continuous air monitor or CAM) sounded. Then, when the crawler was removed from the tank, it had radioactive debris on it. Some of that got onto one worker’s protective suit – the suit was cut off as part of standard practice, and no further contamination was found on him or the other workers.

Possible sources of contamination

Many of the double-shell tanks have existing contamination within their annulus. Some came from piping drips or small spills. Just knowing there is contamination does not confirm a tank leak. There are sensors designed to detect liquid on the bottom of the tank floor, and those have not shown the presence of liquid. The airborne radiation detector did sound an alert, but that was after they shook the crawler, so it’s possible that radioactivity came from the debris on the crawler. The tank has a ventilation pipe that connects the main tank with the space between the inner and outer shells. If everything is operating correctly, waste should not be able to travel out of the main tank. It’s possible that some sort of malfunction sent waste out that pipe.

  • In service in 1976
  • Capacity: 1 million gallons
  • Current contents: about 750,000 gallons
  • No waste added in the past three years
  • Radiation keeps waste in the tank at about 160 degrees
  • The Department of Energy last inspected in 2016 and noted that liquids evaporating quickly due to high heat
  • Holds waste from operations at the PUREX (Plutonium Uranium Extraction) plant
  • Tank is about the same age as AY-102, which was discovered to be leaking in 2012

May 23, 2017

Possible AZ-101 tank leak

We don’t know yet if tank AZ-101 is leaking. We are pressing the Department of Energy to move quickly on their inspections and tests to determine the source of the contamination.

Energy began inspecting the tank with a camera Monday, May 22. The first, low-resolution video images show a lot of debris but no liquid so far. It’s not possible to tell what the debris is – it could be dirt, flaking rust, solidified waste, or bits of concrete that have broken off. We expect to receive more video inspection results this week.

We’ve requested documents from the Department that will allow us to review the history of AZ-101 operations and inspections. Documents include:
  • Written operating record for the tank from May 17-23.
  • Daily surface levels for the tank from May 17-23.
  • Daily readings from sensors in the space between the inner and outer tanks.
  • Results from the May 17-19 robot crawler ultrasonic testing.
  • Results from the most recent annual inspection of the tank space.
  • Any videos taken inside the tank space in the past seven years.
  • Any videos or photos taken since May 17.
  • Documentation of any tank space radiation alarms in the year.
  • Readings from tank air monitor sensors since May 17.

We’re waiting for the test results to come back from the contamination that was found on the crawler. The results are not expected until the week of May 29. They’ll help give us a better idea of what caused the contamination, and whether or not the tank is leaking.


Date of Incident & Location:
May 19, 2017

At Hanford site in Richland, WA

Type of Incident:
Possible tank leak



Randy Bradbury