Exploitable results
Thin layer activation (TLA) is a technique in which a small area of a component subject to erosion, wear or corrosion is made slightly radioactive using a nuclear accelerator. As wear of the activated area occurs the amount of radioactivity decreases proportionately. The chosen radioactive species (eg cobalt-56) should decay by emitting gamma rays, which can be detected online and remotely even through a wall, without any contact with the irradiated area. The detector can be up to 2 m away, and state of the art analysis equipment is used. The technique has been used in laboratories for many years, but this project has addressed the technical, licensing and human factors associated with using the technique in an industrial plant, in power plant boilers.
The thickness of oxide on the inside of ferritic boiler tubes can now be determined by ultrasonic measurements made from the outside of the tubes. The thickness can be used to estimate an average tube metal temperature if the time of exposure is known. The accuracy and sensitivity of the technique depends on the ultrasonic instrument and probe used, and a detailed knowledge of the properties of the oxide. Several commercial systems are now available with no public details of the basis of the results, but the system available from this project is based on a much more detailed understanding of the processes involved which is used openly to justify the results. It is considered that additional detailed long term data are needed to further substantiate the technique, and also to consider different methods of measuring the oxide thickness, which would further advance the value of the technique.
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