BE orders trepanning tool

20 September 2010

BABCOCK has won a competitively tendered £1.3 million contract from British Energy to develop a new hybrid trepanning tool for sampling the graphite of nuclear reactors. Eventually, there will be four Hybrid Trepanning Tools. The new tool offers significantly greater refinement and operational flexibility than any predecessor.

Alan Greenaway, British Energy team leader, explained: “This tool is called a “hybrid”, because it brings together elements from existing tools. We recognised that it was important for us to have a tool that reliably breaks the sample or our data would cease to be as reliable. Graphite friability changes over time and it is important we are able to measure this process accurately as it occurs. However, the cutting mechanism is just part of the story. Our six strong graphite core inspection equipment team developed a list of scored criteria for the optioneering process.”

Important elements of the Hybrid Trepanning Tool design include:

• Able to cut 40 to 75 mm samples

• Will be able to rotate within the reactor to sample at any selected angle

• Will be able to jack tightly up to the face of the sample area

• Highly engineered precision mechanism for cutting

• Ability to view the trepanning area via integral camera

• Dust extraction system

• Works with existing contained hoist

• Control console to control all operations remotely

John Holt graphite inspection project manager at Babcock, explained: “Prior to tendering, Babcock built a prototype Hybrid Tool Cutter and with our knowledge of graphite densities, we were able to experiment on bonded samples to simulate irradiated graphite and prove our design. Our prototype got close to the final design very quickly and we were able to deliver for inspection all 50 samples the prototype cut prior to contract award. With delivery scheduled for May 2011, the programme is tight. However with an 18 strong, experienced team working on the project, both sides are confident that this ambitious deadline will be met.”

Since Babcock won this contract, further refinements have been made, such as making the Hybrid Trepanning Tool both lighter and narrower. These improvements mean that even if the graphite channels were to bow slightly or the graphite was to expand, narrowing the channels, the Tool would always be removable.

Babcock has also designed a control console to drive the Hybrid Trepanning Tool and monitor the camera output. The control console works with British Energy’s existing contained hoist, thus negating the need for additional equipment to be commissioned. The Tool’s dust extract system draws on existing Babcock experience and features an air mover that sucks graphite dust through the cutter and blows it out of the bottom of the Tool. Additionally, an inflatable seal closes off the channel bore to prevent any flow past the tool.

“Not only will the Hybrid Trepanning Tool deliver longer samples”, commented Greenaway, “but we will also benefit from the on board camera, as well as a marginally quicker operation time.

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