Tank waste monitoring and closure

The most dangerous waste

Hanford's underground storage tanks hold the most dangerous waste created over four decades of plutonium production in Washington. All of these tanks are well past their design life of about 25 years. At least 67 tanks are assumed to have leaked in the past, though none are leaking at this time. An estimated 53 million gallons of mixed hazardous and radioactive waste remain.

If waste were to remain in the tanks, untreated, it would eventually enter the ground, groundwater, and Columbia River. The U.S. Dept. of Energy's Environmental Impact Statement projected that the river could be severely affected if that waste were to reach the river without any further action.

Handling millions of gallons of dangerous waste

Hanford's massive underground tanks range in capacity from 55,000 gallons to more than a million gallons. To build them, workers cleared out large flat depressions, then erected the tanks in groups called "tank farms." The tanks were then surrounded with soil, leaving the tops of the tanks about 7-10 feet below ground to provide shielding from radiation.

Pipes, called risers, provide access into the tanks. While some risers are larger, some are only a foot in diameter, and none were designed to make it easy to empty the tanks.

Although much of the liquid has been removed, it's nearly impossible to get all of the liquid out without emptying the tank. Think of it as trying to remove the water from a hole at the beach — you can scoop the water out but it seeps back through the sand.

Why is waste so hard to remove from the tanks?

Tank waste retrieval is extremely difficult, both technically and physically. Because of the limited access — not to mention the radioactive and toxic environment — retrieval equipment inside the tank must be operated using video monitors and remote equipment. The hostile conditions damage and wear out electronics and other equipment. As equipment is removed and replaced, workers must use extreme care to avoid exposure to chemical and radioactive waste. In addition, multiple pipes and rods obstruct access within the tank, creating physical barriers to waste removal equipment. Tanks are considered clean when no more than 360 cubic feet of waste remain — or less, depending on tank size.

As waste retrieval progresses, the waste from single-shell tanks is sent to double-shell tanks through a system of hose-in-hose transfer lines. As the waste is moved, it's run through an evaporator to remove excess water.

Eventually, waste will be transferred from the double-shell tanks to the Waste Treatment Plant to be encapsulated in glass through a process known as vitrification.

Meanwhile, tanks are continuously monitored to ensure that none are currently leaking. Monitoring occurs both in-tank, by measuring volume, and in the surrounding soil using moisture and radiation detectors.