Cambridge Ultrasonics

Nuclear Application

Transducer quality testing

A major business in the nuclear industry wanted to investigate problems with ultrasonic transducers used in a reactor. Ultrasonic inspection was being used to locate the position of fuel rods, using the cooling fluid as the material through which ultrasonic waves would propagate. The high operating temperature of about 250^o C and radiation were causing damage to the transducers. Piezoelectric materials (polarized ferroelectric) were used in the transducers and the operating temperature was close to the Curie temperature, at which the ferroelectric materials spontaneously depolarize, so one possible problem was accelerated aging of the piezoelectric properties. It was also suspected that the adhesive between the piezoelectric material and the transducer housing was degrading. What was the mechanism of degradation?

Cambridge Ultrasonics' visualization system was used to look at the ultrasonic waves emerging from the transducers in water. Several transducers were tested, some were found to work well, others showed wave-fronts emerging from only part of the aperture (believed to be caused by adhesive failure), others showed reduced intensity of ultrasound (accelerated aging). Visualization proved to be a quick and easy way to check the operation of individual transducers and give valuable insight into the mechanisms of deterioration. Both failure mechanisms were active.

New transducer design

More recently Cambridge Ultrasonics has been involved in the design and validation of new transducers for a similar application - inspection of fuels rods in a new generation of sub-critical nuclear reactors. These reactors are intended to be intrinsically safe because they do not have sufficient density of fissile material for the core to become thermally unstable. The novel approach is that a linear accelerator is used to pump neutrons or protons into the core to stimulate fission. When the linear accelarator is switched off then fission quickly dies away because the fissile material is sub-critical. Hopefully, this new kind of reactor will be safer than the reactors in Chernobyl, Five Mile Island and Fukushima.

Cambridge Ultrasonics has devised a novel approach to the problem of the Curie temperature of the ferroelectric ceramic materials used in transducers that eliminates ferroelectric aging.

Monitoring power stations

Cambridge Ultrasonics has worked for many years on developing new methods for inspecting and monitoring of concrete structures. Nuclear power stations rely heavily on concrete as one of the main structural components and we believe our methods could be very useful for monitoring the concrete components. Two examples of major components in nuclear power stations that require monitoring are the confinement vessel for the reactor and the main support platform for the reactor vessel.

We have developed an ultrasonic monitoring system called CMS that employs a distributed array of ultrasonic transducers that are permanently attached to many points all over a concrete structure to monitor its structural integrity. Results of the CMS array are presented in two ways: (i) a CAD image of the structure being monitored has coloured icons positioned on it at the real locations on the structure - the colour of the icon changes to red if structural deterioration is detected; (ii) the probabilities of structural failure of the entire structure and its components are calculated and presented. The benefits of CMS are that the repair budget can be directed at locations where deterioration is happening most quickly and an early warning of structural failure is provided.

We have been working with a major international provider of components in nuclear power stations to find ways to introduce CMS structural monitoring to the industry.