F Reactor was sealed up in 2003. It was inspected in 2008 and hadn’t been opened since. But as part of the ongoing work at the Dept. of Energy’s Hanford Nuclear Waste Site in southeast Washington, crews from Mission Support Alliance entered the reactor for a periodic inspection, the first time such entry has gone on under the long-term stewardship program.

The 105-F Reactor was the last of the three original plutonium production reactors constructed as part of the top-secret Manhattan Project during World War II, operating from 1945 to 1965.

The reactor was sealed up in a secure, cocooned state in 2003, a process—also dubbed interim safe storage—that allows time for radiation levels to decay.

Going in for inspections, though, gives officials an opportunity to conduct radiological surveys, make any repairs to the roof and remove any hazardous substances.

With environmental cleanup at Hanford ongoing since 1989, entering F Reactor was a bit of a milestone.

“This entry marks a transition of sorts because the Hanford Long-Term Stewardship Program, for the first time, was responsible for conducting the entry and surveillance and maintenance activities,” says Keith Grindstaff, Energy Department long-term stewardship program manager. “As the River Corridor cleanup work is completed and transitioned to long-term stewardship, our program will manage any ongoing requirements.”

Fortunately for all involved, the inspection found F Reactor in “good shape” and “almost identical to the last time it was inspected,” said Rick Moren, Mission Support Alliance’s director of long-term stewardship.

Now that F Reactor has been re-sealed until the next time workers need to inspect it, crews will inspect four other cocooned reactors — 105-C, 105-D, 105-H and 105-N — in spring 2015. 

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.