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Babcock has been contracted by British Energy to develop a hybrid trepanning tool for sampling the graphite of nuclear reactors.

Eventually, there will be four hybrid trepanning tools.

The new tool is intended to offer greater refinement and operational flexibility than its predecessors.

Alan Greenaway, British Energy team leader, said: ‘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,’ he added.

The hybrid trepanning tool must be able to cut 40-75mm samples and rotate within the reactor to sample at any selected angle.

It must also be able to jack tightly up to the face of the sample area.

The tool needs a highly engineered precision mechanism for cutting and should have the ability to view the trepanning area via an integral camera.

It also requires a dust extraction system and should work with the existing contained hoist.

Finally, the hybrid trepanning tool requires a control console to control all operations remotely.

John Holt, graphite inspection project manager at Babcock, said: ‘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 that the prototype cut prior to contract award,’ he added.

Since Babcock won the contract, further refinements have been made, such as making the hybrid trepanning tool 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 tool and to 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.

In addition, an inflatable seal closes off the channel bore to prevent any flow past the tool.

Babcock Nuclear Division

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