BNS supplies fuelling ropes to Wylfa

Edited by the Engineeringtalk editorial team Oct 16, 2009

Fuelling ropes supplied by BNS Nuclear Services to Wylfa Power Station have proved so successful that Wylfa is looking to utilise the ropes elsewhere.

Phil Morgan, fuel and reactor systems section head at Wylfa, said: 'For various reasons, we began suffering technical problems with our ropes seven years ago.

'It has been a long journey, with my team working very closely with the BNS team, but now we are delighted that we have moved from ropes that previously lasted for 70 channels of refuelling on average, to ones that now last an average of 225 channels each.

'This is a significant improvement and we are investigating whether we can use the new design on both secondary and primary discharge routes at Wylfa as well.

'We are already implementing them on the transfer machine that moves the irradiated fuel from the primary cells to the secondary cells.' BNS was granted a five-year agreement to develop improved ropes and then supply them to Wylfa.

The team quickly identified that central to lowering the failure rate was determining the exact cause of failures.

The ropes had two parts that could fail, the rope and the solenoid.

With the existing integrated design, it was extremely difficult to obtain any meaningful results to identify which part of the assembly had failed.

A new rope and solenoid design was developed that incorporated a plug and socket arrangement between the two components.

This allowed the rope and solenoid assemblies to be tested and replaced individually.

As well as incorporating the socket assembly, the internal design of the socketed solenoid was significantly different, and in service use proved that solenoids manufactured to the new design lasted significantly longer.

Furthermore, if a failure occurred, and the solenoid was removed from the rope and found to be defective, a new one could be fitted without a re-rope of the hoist.

Andy Tranter, commercial engineer at BNS, said: 'Close liaison with the station, analysis of failure data, and development of the solenoid coil all resulted in further reductions in failure rates.

'However, the existing stock of anodised aluminium wire, which is used to wind the solenoid coil, was quickly becoming exhausted.

'The previous wire supplier was unable to produce further supplies.

'After extensive worldwide searches for suppliers who were both capable and prepared to supply the right quality, size and quantity of anodised aluminium wire, BNS realised there was no alternative but to build its own anodising plant.

'After successfully sourcing raw aluminium wire of the correct grade and hardness, we processed it through our own specially commissioned anodising plant.

'By developing a production process focused on quality, BNS has now stockpiled a quantity of wire to meet predicted requirements through the end of de-fuelling and has mothballed the anodising plant.' Although the solution to Wylfa's underperforming ropes was not as simple as the BNS team first hoped, the benefits are long lasting, both from a technical and from a business-partnership perspective.