How do you seal a nuclear plant?

Answers to your questions about the news.
Aug. 1 2005 7:42 PM

How Do You Seal a Nuclear Plant?

With stickers, metal disks, and fiber optics.

Iran is back in the nuke business. 
Click image to expand.
Iran is back in the nuke business

The Iranian government has promised to break the U.N. seals on its Isfahan nuclear plant today and resume the conversion of yellowcake into uranium gas. Members of the U.N.'s nuclear oversight group, the International Atomic Energy Agency, will be on hand to inspect the seals once they're removed. What's a U.N. seal?

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

A tamper-proof tag placed on doors, containers, file cabinets, and any other sensitive part 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. Both sections of a facility and entire installations can be sealed; the Isfahan complex got shuttered last November.


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 a sticky bracelet you'd get at a rock show. The most commonly used seal comprises a pair of metal discs each about the size of a quarter attached to a thin piece of wire. The IAEA installs and checks about 20,000 of these metallic seals every year.

The wire on a metallic seal might be run through a handle or latch in the manner you'd use a cable lock to secure a laptop. The ends are then pinched between the metal discs, 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 discs, 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. Each seal has a series of lines of varying orientations scratched into its inside surface. Inspectors can verify the seal's authenticity by comparing its unique scratches to photographs the agency keeps on file.

Metallic and adhesive seals are good for one use, and then discarded. In the case of materials that must 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 upon installation 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; inspectors can review evidence of tampering by downloading this information.

In North Korea, as in Iran, U.N. seals didn't seal the deal. In 2002, the North Korean government broke IAEA seals and destroyed surveillance equipment at a five-megawatt nuclear reactor north of Pyongyang.

Explainer thanks Corey Gay Hinderstein of the Institute for Science and International Security and Terence Taylor of the International Institute for Strategic Studies.



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