Bechtel Hanford has finished cocooning F Reactor almost 10 months ahead of schedule, with only some final paperwork to be completed this month.

That means three of Hanford's Cold War reactors have been sealed up in their main chambers, with five more left to go.

The Tri-Party Agreement, the legal pact governing Hanford's cleanup, called for F Reactor to be cocooned by Sept. 30, 2004.

Cocooning is a Hanford term for cleaning out and demolishing all the outlying buildings to a defunct Cold War plutonium-production reactor and sealing the actual 12,000- to 16,000-ton reactor inside the main chamber.

Consequently, an overall reactor complex is drastically shrunk. And a single 90- to 100-foot-tall concrete box remains with a new slanted roof to keep rainwater out. The sealed reactor chamber is then entered every five years to check for problems.

Hanford has nine defunct Cold War reactors, with eight to be cocooned. B Reactor is tentatively earmarked as a museum to mark its role in creating the plutonium for the world's first atomic bomb and for the bomb that destroyed Nagasaki.

Bechtel finished cocooning C Reactor in 1998 and DR Reactor in 2002.

F Reactor was the third Hanford reactor to produce plutonium, starting up in February 1945 and shutting down in June 1965. The initial engineering work on cocooning F Reactor began in 1997.

Bechtel has been cocooning two to three reactors simultaneously, shifting its 80 employees from one site to the next to keep overall momentum going when work slows down at a specific location.

The price tag for cocooning F Reactor is about $21 million, slightly higher than the other reactors. That's because Bechtel had to deal with a fuel storage basin with 17 buried pieces of spent nuclear fuel found in it, said Mike Mihalic, the company's cocooning project leader. The fuel was sent to the K Basins.

The F Reactor work had a couple of wrinkles. The complex was originally home to numerous bats. A one-way door had to be built so the bats could leave but not return to the facility. Bechtel also had to work around the nest of a great horned owl until the baby birds left.

The next reactor to be cocooned is D Reactor, which is scheduled to be done in September 2004. Most of the work is already completed, Mihalic said.

Slightly more than half of the work on H Reactor is done, with that project scheduled to finish in September 2005.

In either 2004 or 2005, Bechtel plans to study how it should cocoon N Reactor, the most modern of the nine reactors and which includes a steam-producing facility.

That facility sent steam to a neighboring now-defunct Washington Public Power Supply System power generation plant.

The Tri-Party Agreement calls for N Reactor to be cocooned by 2012. Mihalic said no schedules have been mapped out on when to tackle the K East and K West reactors because Fluor Hanford is still removing spent nuclear fuel and radioactive sludge from their fuel basins. The Tri-Party Agreement sets a deadline of 2011 to cocoon those two reactors.