Abstract: Material such as fissile material (2) requiring to be safeguarded is stored inside a container (1) which is subsequently sealed, for example by a closure comprising a cover (3) and sealing element (30). The whole structure of the container (1) is ultrasonically scanned initially using piezo electric transducers (T1, T2) to obtain an output from which is derived a distinctive identity for the container (1), determined by the particular characteristics of the internal structure of at least a portion of the container, and also a reference signal indicative of the whole container structure when its integrity is intact. Subsequent ultrasonic scanning of the whole container structure, for example intermittently, produces a monitor signal which if different to the reference signal indicates the occurrence of a breach in the container's integrity. The distinctive identity for the container (1) may be derived from a distinctive internal structure of the cover (3) which preferably contains a material matrix, e.g.

Abstract: To monitor a nuclear fuel element or fuel elements located in a store, e.g. a pond in a swimming pool reactor, the store is illuminated ultrasonically using one or more transducers transmitting ultrasonic signals in one or more predetermined directions to obtain an output which, because it depends on the number and relative location of the fuel elements in the store, and the structure of the store itself is distinctive to the fuel elements or elements stored therein. From this distinctive output is derived an identity unique to the stored fuel element or elements and a reference signal indicative of the whole structure when intact, the reference signal and identity being recorded. Subsequent ultrasonic testing of the store and its contents under identical operating conditions produces a signal which is compared to the recorded reference signal and if different therefrom reveals the occurrence of tampering with the store and/or the fuel element or elements.

Abstract: A system, suitable for use as an identity seal for an object, such as a container for fissile material, comprises a body including a cap for fitting over one end of the object, and a recess which contains a material such as "ARALDITE" or aluminium acting as a matrix for a plurality of inclusions of e.g. bronze embedded therein in a random configuration. The recess is closed by a cover which includes a central electrically conductive part. Also embedded in the matrix material and constituting further "inclusions" are two piezoelectric crystal transducers each electrically connected to the central cover part. In use, the transducers are electrically connected via the central cover part to external ultrasonic testing apparatus to provide a unique output indicative of the particular structure of the seal particularly the inclusion configuration and hence providing a unique "identity" and hence indication of integrity for the seal.