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.