[Madeleine Brand:] Britain, France and Germany warned Iran today not to resume its nuclear activities, saying such a move would bring negotiations on the issue to an end. Iran's government said yesterday that it plans to break the UN's seals on one of its nuclear plants and resume the production of uranium gas. In response, the International Atomic Energy Agency said it would inspect the seals once they're removed. So what exactly is a UN seal? Daniel Engber, who writes Slate's Explainer column, is here to tell us.
[Daniel Engber Reporting:] A UN seal is a tamper-proof tag placed on doors, containers, file cabinets and other sensitive parts of a nuclear facility. The IAEA, which monitors about 900 nuclear facilities worldwide, uses around 26,000 seals per year to ensure that equipment has not been used, moved or otherwise manipulated. There are several types of seals. To close a site for 24 hours, an inspector might wrap the door handles with an improved adhesive seal. This type of seal is the simplest and quickest to apply. It looks something like the sticky bracelet you'd get at a rock show. The most commonly used seal comprises a pair of metal disks, each about the size of a quarter, attacked to a thin piece of wire. The wire on a metallic seal might be run through a handle or latch, just as you might use a cable lock to secure a laptop. The ends are then pinched between the metal disks, one of which is embossed with IAEA and a special identification number. The wire isn't meant to prevent entry. It's just sturdy enough to withstand accidental bumps and tugs. But broken seals can't be reinstalled without a new pair of disks, and they're very difficult to counterfeit. Once the metal coins are removed at the Isfahan plant, IAEA officials will take them back to agency headquarters to verify their authenticity. For materials that need to be safeguarded and checked for extended periods, the agency uses more sophisticated contraptions. In a fiber-optic seal, strands of fiber-optic wire are pressed together in a clear plastic case when they're installed and cut in an irregular pattern. Unlike the metallic seal, the fiber-optic device doesn't need to be broken to be checked for tampering. Inspectors can simply take a digital photograph to examine the cut ends. The IAEA also uses an electronic seal that detects breaks using a beam of light that circulates every quarter of a second. Any interruption of that pattern gets stored online and inspectors can review evidence of tampering by downloading this information.
[Madeleine Brand:] That Explainer from Slate's Daniel Engber. Stay with us on DAY TO DAY from NPR News.