REPTIL: for keyhole inspection of steam generators18 February 2014
Automated remote tooling aiming to reduce dose in secondary-side inspections is moving from Europe to the USA. By Will Dalrymple
Rolls-Royce is finalizing US qualification of recently-developed remote tooling that performs automated in-bundle inspections of the secondary side of square- and triangular-pitch steam generators.
The system, called REPTIL, was developed in France in 2011 to reduce worker dose during steam generator inspections, saving nearly 80% total dose when compared to a manual inspection system. "It will not necessarily decrease inspection time, but inspections will be smoother, more informative and will cost a lot less dose," says Uriah Dean, REPTIL migration project manager.
The REPTIL system latches on to a steam generator handhole -- typically ranging from 50mm (2 in.) to 152mm (6 in.) wide -- and deploys a videoscope probe within a column of steam generator tubes.
Workers attach the device and can operate it from a remote control station in a low-dose area, occasionally returning to feed in or remove rigid guide tube sections.
A small drive motor pushes the probe through the no-tube lane and into the heart of the steam generator. The 2.4mm wide by 30mm tall ribbon-type flexible probe emerges from a 90° bend at the tip of the guide tube and traverses tube columns, recording video images (PAL or NTSC) of its journey and any scale or sludge deposits that it sees.
The camera, equipped with two variable-power LEDs on either side of the lens, has a 100° field of view and fixed-focus depth of field from 3mm-200mm. Motors and distance encoders enable the probe to move automatically down the column. It can complete inspection of four columns in an hour; there might be 120 such columns, each with anywhere from 15 to 100 tubes, in a standard steam generator.
Three potential uses
In France, REPTIL has typically been sent to investigate high-flow regions of the tubesheet, where any foreign materials and sludge deposits are likely to accumulate.
It has also been deployed at upper support plate levels to inspect clover-leaf shape holes called quatrefoils. These holes can become clogged by magnetite and sludge, reducing water flow and ultimately overall efficiency, according to Brian Webster, Rolls Royce project manager.
The probe may also be used after sludge lancing operations to verify their success. In the USA, Webster says that secondary-side steam generator inspections often follow up on eddy-current indications taken from the primary side of tubes (this probe is only intended for secondary-side inspections).
Qualified by Westinghouse
The REPTIL tool is currently designed for certain models of steam generators to go with Westinghouse-designed PWRs, including models 54F, F, and Delta 94.
The tool went through a qualification process through Westinghouse France. That process includes inserting the tool into small mock-up vessels to make sure it fits.
The current US qualification is less involved because US steam generator pitches are generally larger than French ones. For US qualification, REPTIL hardware has been manufactured in France and sent to the USA, where it is being integrated with existing operations software in the USA.
Deployment in France
The first REPTIL robot was developed in France in 2011 as a way to reduce dose when compared to the Manual In-bundle Guidetube System (MIGS). That first design had an 'open-loop' system without a lot of feedback; a second, fully-automatic 'closed loop' version was finished in 2012. The closed loop system now offers speed control, a safety interlock system (to ensure safe tool operation) and image metadata tracking which digitally tags each image taken with column, row and elevation data for easier sorting by utility customers.
There are now four systems in operation; they have been deployed into 24 different steam generators at multiple sites in France. The robots are manufactured by the Rolls-Royce Nuclear Services office in France for Westinghouse and are deployed on site by highly trained Rolls-Royce service personnel.
The REPTIL tooling system complements a range of other inspection tools for steam generators offered by Rolls-Royce. These tools include a remotely-deployed car that traverses the annulus region to inspect the inside surface of the steam generator shell known as SWATS (Shell, Wrapper Annulus Transport System), and the UBIB or Upper Bundle In-bundle Inspection System, a complex device that extends vertically from the tube sheet through the centre of the generator and then deploys a camera wand into the upper in-bundle region.
Will Dalrymple is editor of Nuclear Engineering International