The Iranian government announced Monday it will break the United Nations seals on a nuclear facility and resume production of uranium gas. What is a U.N. seal? Slate contributor Daniel Engber explains.
MADELEINE BRAND, host: 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.</s>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.</s>DANIEL ENGBER reporting: 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.</s>DANIEL ENGBER reporting: 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.</s>DANIEL ENGBER reporting: 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.</s>DANIEL ENGBER reporting: 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.</s>MADELEINE BRAND, host: That Explainer from Slate's Daniel Engber.</s>MADELEINE BRAND, host: Stay with us on DAY TO DAY from NPR News.