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Nuclear Safeguards Education Portal

Ultrasonic sealing bolt (USSB)

The JRC CANDU sealing system (JCSS) and the ultrasonic sealing bolt (USSB) are systems for underwater sealing that use ultrasonically verifiable sealing bolts. The sealing bolt replaces one of the standard bolts of a container lid. It is constructed to contain a unique random pattern of metal discs and a frangible element (integrity feature) which breaks when an attempt is made to remove the seals. Verification is performed by transmitting ultrasonic pulses through the seal with a suitable transducer and observing the unique pattern of reflections, and is accomplished by comparing the pattern obtained upon installation with that obtained during subsequent in situ checks. Dedicated software guides an inspector through the installation and verification process and manages the seals database. When a broken seal is encountered, the reader detects the absence of the integrity feature and is still able to confirm the seal's identity.

These types of seal have proved particularly effective for underwater applications such as for stacks of CANDU fuel bundles (JCSS) or for bolts closing shipment and storage containers of LWR spent fuel assemblies (USSB). The main advantages of these seals are that they are insensitive to radiation, are particularly reliable even in very harsh environmental conditions and can last for decades.

(Source: IAEA Safeguards Techniques and Equipment)


USSB bolt + bolt head. (Source: IAEA)