Testing the AVEXIS in Fukushima

The AVEXIS^®is a small submersible tethered Remotely Operated Vehicle (ROV). It has been designed to fit through a 6 inch port, move through water, and characterise the space it is in. This essential information is difficult to assess within high risk environments such as nuclear storage facilities, or the hazardous environment at Fukushima Nuclear Power Plant.

The AVEXIS^®has a cylindrical body, housing all the electronics, camera and communications. The relatively large body allows the AVEXIS® to carry a sensor payload, such as gamma and neutron detectors, weighing up to approximately 1.5 kg. Movement forwards, backwards, left, right, up and down is possible through the positioning of 5 pumps on each end of the AVEXIS®. Excellent manoeuvrability, even within tight spaces, makes the characterisation of many diverse and unknown environments possible.

We recently collaborated with the Japan Atomic Energy Agency (JAEA), the National Maritime Research Institute (NMRI, Japan) and Nagaoka University to test the AVEXIS’s capabilities for characterising the physical dimensions and location of fuel debris inside a simulated nuclear pressure containment vessel (PCV) at Fukushima Daiichi. We used the Naraha test facility in the Fukushima prefecture for this exercise. Scans of the internal environment of the simulated PCV were acquired using sonar. The sonar was positioned on the bottom of the AVEXIS^®and integrated with the on-board electronics to scan the environment beneath. The AVEXIS^®was localised using a vision based system consisting of anchor points around the tank and LED markers on the ROV. Twinned with a depth senor, a real-world position could be returned. By stitching together the positional and sonar data we could create a 3D map of the simulated environment. Discussions and analysis conducted with our colleagues in Japan highlighted the success of the mapping of simulated debris. Accurate and representative 3D images were streamed to the surface and validated through visual inspection.

These same techniques could be applied to any underwater storage facility or complex environment. With the technical capabilities of the AVEXIS verified, interest turned to the radiation tolerance of the device. For practical applications, it will need to survive dose-rates of 10-100 Gy.h-1 for 8-10 hours. This was to be explored soon after with a trip to the Jozef Stefan Institute in Slovenia.