Robot inspects structural damage in nuclear reactors

Abington-based research group, The Welding Institute (TWI), has designed a prototype inspection robot to detect structural damage in ageing nuclear reactors.

The work is part of the £1.3m NozzleInspect project, partly funded by the European Seventh Framework Program (FP7).

Existing structural inspections of nuclear plant are done by ultrasonic probes. Due to the shape of the nozzle surface, the probes need to be recalibrated by an operator to allow full inspection of the area.

‘This means that operators are exposed to a certain amount of radiation during installation,’ said project leader Dimos Liaptsis. ‘What we wanted to do was simplify the design of the scanning system so that the operators can quickly attach the system to the area, leave the vicinity of the reactor and do the calibrations remotely.’

The prototype uses 128 piezoelectric elements placed in a circular formation. The elements generate ultrasonic waves into the surrounding material. Reflections that come back are picked up by the elements, converted into an electrical pulse and analysed by software.

Liaptsis said adjusting the probe’s movements to the curvature of the nozzle had been the most challenging part of the project. The team solved this by using a flexible membrane that would sit beneath the probe holder.

‘There will be two spray nozzles placed outside the membrane to constantly spray water on the surface of the nozzle so the membrane will slide better and minimise friction,’ added Liaptsis.

Combined with the 3D beam steering capability, it is hoped the prototype will be able to inspect the entire volume of the weld in a single operation.

The design is currently undergoing final testing and the first demonstration of the system will be made in September.