Feasibility of WAND Sensors for Nuclear Power Plant Inspection
Hitachi in partnership with Inductosense and the University of Bristol, conducted lab-based testing to establish the suitability of the WAND sensors for monitoring pipe wall thickness on nuclear power plants.
Piping systems on a nuclear power plant are subject to corrosion or erosion which cause thinning of the pipe wall. It is necessary to take thousands of thickness measurement from specific locations on pipes manually during the outage of the plant. Much of the pipework is covered in a layer of insulation which needs to first be removed (and then replaced afterwards) which increases the time, cost and exposure of the inspector to radiation.
THE INDUCTOSENSE SOLUTION
The Inductosense ultrasonic WAND sensorsprovide accurate monitoring of wall-thickness and enable trending of corrosion or erosion rates. The sensors are permanently installed, battery-free and wireless. The sensors are activated when the WAND Data Collector is brought close to the sensor. In this application the WAND sensors can be permanently installed to pipework under insulation material saving costs, time, reducing exposure of inspectors.
A number of tests were undertaken, which are described in detail in the publication by Tamura A et al*:
- Comparison to conventional ultrasonic testing:Thickness measurements were performed on sample carbon steel plates representative of pipe sample thicknesses used in nuclear power plants (3.6, 7.7, 9.5, 19.7 and 49.5mm) using the sensors. Good agreement was found with conventional ultrasonic measurements
- Under insulation performance:Silicate calcium (commonly used as insulation in nuclear power plants) was placed between the probe and the sensor and it was shown that there was no change in the thickness measurements from the sensors with or without the insulation in place.
- Radiation tolerance:The sensors were exposed to radiation (gamma rays from Co-60 – 18kGy) corresponding to the total exposure for 10 years in a primary containment vessel. There was no deterioration in the signal from the sensors following exposure.
- Liquid droplet impingement (LDI) defect detection: LDI wastage defects are narrow and deep (compared to flow assisted corrosion). The sensors were tested on a range of machined defects (0.3, 0.6, 0.9, 1.2 and 1.5mm deep) and showed good agreement with simulation.
The testing confirmed that the WAND sensors have potential for monitoring different thickness of pipe walls under insulation used in nuclear power plants and can be exposed to radiation levels found in a plant.
* Tamura, A., Zhong, C., Croxford, A.J., Wilcox, P.D., A Feasibilty Study of Noncontact Ultrasonic Sensor for Nuclear Power Plant Inspection, Journal of Nuclear Engineering and Radiation Science, Vol3, 021012, 2017 [LINK]