Context and challenges

A fuel element is a graphite sleeve containing 36 fuel pins, which is nominally 1000mm long. Eight elements are axially held together with a 10mm diameter steel bar – the lower tie bar.

A fuel stringer is an assembly of eight elements, plus a plug unit sub-assembly above it. The entire assembly is 23m in length. Fuel stringer tie bars are known to be susceptible to wear as a result of rubbing against other components of the fuel elements. The size and extent of wear scars has been observed by this client over many years. Only a small percentage of tie bars could be examined as it is a labour intensive activity and extremely expensive.

This client wanted to be able to measure more tie bars and obtain reports that provide quantitative data.

Assystem was contracted to develop an inspection system for nuclear equipment capable of inspecting tie bars within the tie bar decommissioning facility, capable of automation of the report production and providing quantitative data.

Project scope

  • Demonstration of the 3D inspection capability to measure wear scars on a tie bar simulant
  • Development of a system to automatically measure and classify wear scars, generate reports on the results of the tie bar scanning campaign
  • Production of detailed designs to enable the manufacture of all bespoke items of mechanical equipment to grade 2 quality assurance standards, able to operate within an extreme radiological environment
  • Deployment of acceptance testing within the Assystem development facility
  • Installation and commissioning of the 3D scanning equipment within the tie bar decommissioning facility
  • Training of client operators in operation and maintenance of the 3D scanning equipment
  • Establishment of procedures including outline method statement and designers risk assessment


  • Increase in the number of tie bars measured, enabling to collect larger amounts of data with reports of quantitative data
  • Enhanced efficiency concerning the cost and effort required to identify trends in tie bar wear


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