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Optical seals record nuclear tampering.

Optical seals record nuclear tampering

The International Atomic Energy Agency (IAEA) has begun field tests of a fiber-optic seal for use at nuclear facilities and on equipment the agency inspects. This seal permits on-the-spot identification of tampering--a capability not previously available to inspectors of the Vienna, Austria-based agency. One of IAEA's major responsibilities is detection of efforts to steal nuclear material for use in weapons.

The new seals, developed jointly by Sandia National Laboratories in Albuquerque, N.M., and the Alexandria, Va.-based Atlantic Research Corp., would replace the metal-and-wire seals IAEA now uses, which are removed for analysis of tampering, then discarded. Because the new seals can be analyzed in place, they should last indefinitely, says Dennis Mangan, Sandia's international safeguards supervisor.

To picture how the seals work, imagine the type of shackle lock used to secure a gym locker. The U-shaped arm that would be passed through the locker door is, in this device, a tiny cable containing 64 randomly twisted optical fibers. After being fed through openings on the device that will be secured, the cable's two free ends are threaded through holes in a plastic housing. Insertion of a serrated horseshoe-shaped blade through a slit in the housing's body manacles the cable ends in place.

In securing the cable, some of the blade's teeth will sever 40 to 60 percent of the optical fibers, making them unable to transmit light. Later, when light is shined into one cable end, a pattern of lighted dots will appear at the other end, identifying intact fibers. This pattern, the cable's signature, is unique to each secured seal.

The seal's sensitivity to tampering comes from the special blade used to secure the cable. Its teeth are angled in several directions. Upon entering the cable, only some cutting teeth are active. Others slide harmlessly through optical fibers in the downstroke, but actively cut additional fibers if an attempt is made to withdraw the blade.

IAEA inspectors would periodically query each seal with a device that shines light into one end of a seal's cable and takes a Polaroid snapshot of the signature emitted by the other end. It would be compared against the seal's initial signature.

Photo: Signature of a new seal (left) was altered (right) by tampering.
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Title Annotation:detection of efforts to steal nuclear materials
Author:Raloff, Janet
Publication:Science News
Date:Jan 18, 1986
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