It looks like an upside-down lawn sprinkler.

But it's Hanford's first real-life experiment with removing solid radioactive gunk from inside one of its huge underground waste tanks.

Two weeks ago, CH2M Hill Hanford Group turned on the sprinkler hanging inside Tank U-107, allowing it to spray and gradually turn radioactive salt cake in the tank into waste-laced water to be pumped out.

By February, CH2M Hill and the Department of Energy's Office of River Protection hope to dissolve and pump out 100,000 gallons of the 320,000 gallons of solids inside Tank U-107.

Then they'll spend a couple of months analyzing whether the technique works effectively, said Jim Thompson, the Office of River Protection's single-shell tanks project manager, and Terry Sams, CH2M Hill's retrieval and closure projects strategic planner.

If the technique appears successful, CH2M Hill and DOE will discuss the study results with Washington's Department of Ecology to see if the state approves of the technique.

This sprinkler system is one of three techniques Hanford is considering to remove solid wastes from its 177 underground tanks -- which include 149 older, leak-prone single-shell tanks.

The tanks hold 53 million gallons of wastes. More than 22 millions are liquid, with most in 28 newer double-shell tanks awaiting eventual glassification. But 31 million gallons of solid wastes are in all 177 tanks.

DOE recently set a goal to remove all liquid and solid wastes from 26 to 40 tanks by the end of 2006, then close those tanks. First, however, officials need to decide the best way to do that.

The first technique to be tested is the sprinkler system in Tank U-107.

The second technique will be to insert hoses and pumps into tanks S-102 and S-112 to more forcefully break up and dissolve solid wastes so they can be pumped out. This will be attempted in late 2003.

The third technique will use a tank crawler -- a miniature bulldozer teamed up with a huge vacuum cleanerlike device -- that is expected to be tested in Tank C-104, possibly in 2004.

CH2M Hill and DOE will study the capabilities and limitations of each technique. The idea is to match the proper techniques with the types of wastes inside each tank, Sams and Thompson said.

Sams and Thompson believe the pace of cleaning out the 26 to 40 tanks will speed up after the tests because the equipment can be duplicated so several tanks can be pumped out simultaneously.