There's an "immense discrepancy in the accounts for how much plutonium" is being kept at Los Alamos, a team of watchdog groups is charging.

In a letter to lab director Pete Nanos, the groups note that, in 1996, top energy officials "prepared a memorandum detailing plutonium accounting discrepancies throughout the nuclear weapons complex."

"That] memorandum shows that the security-related nuclear materials accounts do not agree with the waste accounts. The Department of Energy reported a discharge to waste from [Los Alamos] of 610 kilograms of plutonium; Los Alamos indicates a figure of 1,375 kilograms... Evidently, there is a discrepancy of 765 kilograms, the equivalent of 150 nuclear weapons...

"To the best of our knowledge, LANL has yet to explain the large plutonium accounting discrepancy or address its security implications." (emphasis mine)