Here ya go...
During an investigation by the Department of Energy to determine how secure U.S. nuclear facilities were against terrorist attacks it was determined that there are more than 5,000 pounds (two and a half tons) of plutonium missing or unaccounted for, 2,400 pounds alone from its Rocky Flats weapons factory near Denver.
To demonstrate his point a DOE investigator, McCallum, had turned in 1996 to a sophisticated computer-modeling program designed to simulate terrorist attacks against each of the country's nuclear labs. NEWSWEEK has learned that in every one of the scenarios that the computer devised, the hypothetical terrorists succeeded in penetrating security at the Rocky Flats weapons factory near Denver and blowing up some of the highly radioactive plutonium used to make bombs. In 80 percent of the simulations, the attackers were able to get through the razor wire and security checks and walk out with enough plutonium to build a nuclear bomb—or poison millions of people with the radioactive dust.
Source: Newsweek Magazine
Date: May 3, 1999
Posted on this anti-nuke website FWIW.
Say you are working some Plutionium, you will start with X amount. After you're done you weigh your finished piece, you weigh your chips and you do not always come up even. The difference is usually in the milligram range, but after tens of thousands of parts and forty years of work it will add up to an impressive total.