This weekend, the AP’s Katherine Shrader wrote a fine story about the “myth” of suitcase nuclear bombs.

“The suitcase nuke is an exciting topic that really lends itself to movies,” said Vahid Majidi, the assistant director of the FBI’s Weapons of Mass Destruction Directorate. “No one has been able to truly identify the existence of these devices.”

Many of the fears about suitcase bombs originated years ago in statements by a couple of Russians who may have had ulterior motives for inflating threats — including retired General Alexander Lebed who told “60 Minutes” about missing suitcase nukes back in 1997.

Shrader writes that “current and former government officials who have not spoken out publicly on the subject acknowledge that no U.S. officials have seen a Soviet-made suitcase nuke.” This might reflect successful Russian efforts to round up and destroy these weapons.

The U.S. developed backback-sized nuclear weapons during the cold war, but apparently got rid of all of them years ago. Even when they existed, it took two men to detonate those backback bombs.

Many scientists doubt that suitcase nukes are possible. The FBI’s Majidi, who formerly led the chemistry division of Los Alamos National Lab, is among the most skeptical:

Majidi says it would take about 22 pounds of plutonium or 130 pounds of uranium to create a nuclear detonation. Both would require explosives to set off the blast, but significantly more for the uranium.

Although uranium is considered easier for terrorists to obtain, it would be too heavy for one person to lug around in a suitcase.

Plutonium, he notes, would require the cooperation of a state with a plutonium reprocessing program. It seems highly unlikely that a country would knowingly cooperate with terrorists because the device would bear the chemical fingerprints of that government. “I don’t think any nation is willing to participate in this type of activity,” Majidi said.

That means the fissile material probably would have to be stolen. “It is very difficult for that much material to walk away,” he added.

There is one more wrinkle: Nuclear devices require a lot of maintenance because the material that makes them so deadly also can wreak havoc on their electrical systems.

“The more compact the devices are _ guess what? _ the more frequently they need to be maintained. Everything is compactly designed around that radiation source, which damages everything over a period of time,” Majidi said.

Representative Curt Weldon, a hawkish member of Congress known for inflating threats, also played a key role in the development of the suitcase nuke myth. In 1997, Weldon’s Research And Development Subcommittee (of the House National Security Committee) heard worrisome testimony from Dr. Alexie Yablokov, former Science Advisor to Boris Yeltsin.

Yablokov, I might note, expressed some important reservations in his testimony:

Any nuclear arms, any nuclear warhead, have to be replaced in several years. Fissile material have to be replaced, especially plutonium, after six or seven years … . It means that during this time, beginning from ’70s, this small-sized nuclear weapons have to twice … be replaced. I doubt that it have happened during — I don’t know — last ten years, at least.

Shrader’s story raises this same issue:

Colonel-General Viktor Yesin, former head of the Russian strategic rocket troops, said…that a true suitcase nuke would be too expensive for most countries to produce and would not last more than several months because the nuclear core would decompose so quickly. “Nobody at the present stage seeks to develop such devices,” he asserted.

Hat tip: Arms Control Wonk’s Jeffrey Lewis.