The AIRIS 21™ Inspection System

Because of its compact, thin construction, the AIRIS 21™ robot can maneuver in the tight space between the interior wall of the pressure vessel (shown in diagram at left and in simulation tests at right), and obstructions created by shields and jet pumps.

The AIRIS 21™ scanner is relatively compact: 550 mm (22 in.) wide, 600 mm (24 in.) tall, and 55 mm (2 in.) thick; and it weighs 13.6 kg (30 lb.). The small, thin design makes the device ideal for use in a tight, narrow environment such as the annulus between a BWR core shroud and vessel wall.

AIRIS 21™ uses two small thrust propellers to "swim" to a predetermined location on the vessel wall. Once at the location, a flexible skirt makes contact with the wall and the thrusters create a partial vacuum, allowing the drive wheels to make contact with the vessel surface.

Two independent drive wheels (for traveling motion) and one caster-wheel allow free maneuvering around the vessel surface. Independent encoder wheels provide coordinated tracking of position, regardless of motion direction. A linear drive (for scanner motion) provides transducer movement perpendicular to the traveling motion of the device. Both the traveling motion and the scanner motion can be used for UT scanning.

Positional location of the AIRIS 21™ is accomplished using a combination of measurements integrated and displayed by the control system. An origin reference point is established for each examination zone by locating a specific elevation and vessel azimuth. Elevation is determined using two high-accuracy water depth sensors; one on the device, and one located at a fixed known location such as the vessel flange.

Azimuth reference location above the shroud is accomplished by driving the device to a fixed vessel component whose azimuth can be accurately computed, such as vertical guide rods. Behind the shroud, an optical beam transmitter/receiver system is used to determine azimuth location based on the known location of vertical internal reactor components such as jet pump assemblies.

Once the device is in the origin position on the vessel wall, the encoded drive wheels provide travel distance and a gravity sensor keeps track of device orientation. The control unit integrates this data and provides constant positional information relative to the device location. A graphic display unit also shows the orientation of the device and direction of movement. After the examinations are completed for a specific zone, the device is returned to the origin point and the origin position is rechecked.

The device is controlled through a single umbilical cable bundle, which contains all inputs to the control system as well as the ultrasonic transducer cables. This control cable contains a braided steel cable that it is strong enough to function as a retrieval mechanism in the unlikely event of a power failure or thrust propeller failure. Foam sections attached to the bundle provide floatation to facilitate cable tending operations.

Shortly after receiving the AIRIS 21™ system in 1997, SwRI began preparing it for field use. IHI conducted operational training for SwRI personnel and made several control system modifications, such as conversion of display information from Japanese to English and allowing use of either metric or English units.

The scanner was originally designed for Japanese Code UT techniques that are similar to standard American Society of Mechanical Engineers (ASME) Code techniques. SwRI's goal was to integrate Performance Demonstration Initiative (PDI)-qualified UT detection and sizing techniques and to provide for two-directional scanning. This required a redesign of the UT module and cabling to incorporate the additional, PDI-qualified transducers.

Published in the Fall 1998 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

Getting Near the Core Technics Fall 1998 Technology Today
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