Iran studied nuclear yields, leaked document indicates

VIENNA – Iranian scientists have run computer simulations for a nuclear weapon that would produce more than triple the explosive force of the World War II bomb that destroyed Hiroshima, according to a diagram obtained by the Associated Press.

The diagram was leaked by officials from a country critical of Iran’s atomic program to bolster their arguments that Iran’s nuclear program must be halted before it produces a weapon.

The International Atomic Energy Agency – the Vienna-based U.N. nuclear watchdog – reported last year that it had obtained diagrams indicating that Iran was calculating the “nuclear explosive yield” of potential weapons. A senior diplomat who is considered neutral on the issue confirmed that the graph obtained by the AP was indeed one of those cited by the IAEA in that report.

The IAEA report mentioning the diagrams last year did not give details of what they showed. But the diagram seen by the AP shows a bell curve – with variables of time in micro-seconds, and power and energy both in kilotons – the traditional measurement of the energy output, and hence the destructive power of nuclear weapons. The curve peaks at just above 50 kilotons at around 2 microseconds, reflecting the full force of the weapon being modeled.

The bomb that the United States dropped on Hiroshima in Japan during World War II, in comparison, had a force of about 15 kilotons. Modern nuclear weapons have yields hundreds of times higher than that.

The diagram has a caption in Farsi: “Changes in output and in energy released as a function of time through power pulse.” The number “5” is part of the title, suggesting it is part of a series.

David Albright, whose Institute for Science and International Security is used by the U.S. government as a go-to source on Iran’s nuclear program, said the diagram looks genuine but seems to be designed more “to understand the process” than as part of a blueprint for an actual weapon in the making.

“The yield is too big,” Albright said, noting that North Korea’s first tests of a nuclear weapon were only a few kilotons. Because the graph appears to be only one in a series, others might show lower yields, closer to what a test explosion might produce, he said.

The senior diplomat said the diagram was part of a series of Iranian computer-generated models provided to the IAEA by the intelligences services of member nations for use in its investigations of suspicions that Iran is trying to produce a nuclear weapon. Iran denies any interest in such a weapon.