Such checks typically have been carried out by taking bombs and warheads apart; scrutinizing them using chemistry, physics, mathematics, materials science and other disciplines; and examining data from earlier nuclear explosive tests. This time, however, the scientists and designers relied entirely on supercomputer modeling, running huge amounts of code.
Then came a surprise. The computer simulations showed that at a certain point from stockpile to target, the weapon would “fail catastrophically,” according to Bruce T. Goodwin, principal associate director at Livermore for weapons programs. Such a failure would mean that the weapon would not produce the explosive yield expected by the military — either none at all, or something quite different than required to properly hit the target.
“So we went in and thoroughly investigated that, and determined that the way the weapon is handled by the military had to be changed, or you would be susceptible to having the weapons fail catastrophically when, God forbid, they should ever be used,” Goodwin said. He added that the fault occurred in the “real dynamics of the vehicle” — a term describing the weapon’s trajectory and behavior — and could not have been revealed by underground explosive testing or by examining the components.
Following the discovery and a multi-year effort, the B-83 bombs and the military’s handling procedures for the weapons have been fixed, officials said.
The episode, details of which remain classified, offers a glimpse into a rarely seen but potentially significant shift in the nuclear weapons era. According to scientists and officials, the United States’ weapons laboratories, armed with some of the fastest computers on the planet, are peering ever deeper into the mystery of how thermonuclear explosions occur, gaining an understanding that in some ways goes beyond what was learned from explosive tests, which ended in 1992.
The Obama administration has said that with computing advances, the United States will never need to resume nuclear explosive testing. Undersecretary of State Ellen Tauscher said in May that “our current efforts go a step beyond explosive testing by enabling the labs to anticipate problems in advance and reduce their potential impact on our arsenal — something that nuclear testing could not do.”
The significant advance in computer modeling is at the center of a debate over the Comprehensive Test Ban Treaty, which was approved by the United Nations in 1996 but rejected by the U.S. Senate in 1999. Signed by 182 countries and ratified by 154, the treaty outlaws nuclear explosive testing and sets up a global monitoring system to detect any tests. The treaty needs several key countries, including the United States, to ratify it before it can enter into force. The Obama administration has urged the Senate to ratify the pact and continues to abide by the test ban.