Hanford officials believe the chance of any other canisters leaking is minimal. The number of containers officials think could crack is classified. Weight gains in some PFP cans have pushed the issue higher on the defense board's priorities, and the board's staff plans to continue studying the situation. The roots of the problem go back to the 1960s, when the PFP was the final step in Hanford manufacturing plutonium for the nation's nuclear weapons. Air ended up trapped in each can as it was sealed and placed inside a slightly bigger supposedly airtight container.
Problems are all but guaranteed, experts say.
If a sealed container actually is airtight, that means the plutonium uses up all the trapped air to make plutonium oxide rust. That creates a vacuum that sucks in the sides of the can, increasing the risk of the top popping open. If the canister isn't airtight and outside air finds its way into the innermost container, that feeds the plutonium oxide layer around the metal, expanding it to push out the container's walls to cause a crack. This is where the defense board's and Hanford's experts see the danger differently. Hanford experts believe there is sufficient room between the plutonium oxide and the can's sides in most cases to last until the plutonium is neutralized by 2004.