EDF Energy has awarded James Fisher Nuclear (JFN) a contract to supply inspection devices to more precisely monitor the condition of graphite within the cores of its fleet of operating Advanced Gas-cooled Reactors (AGRs) in the UK.
JFN - in collaboration with EDF Energy, Serco (now Amec), Bloodworth Consulting and the University of Manchester - developed eddy current inspection tools (ECIT) designed to assess the condition of graphite within vacated fuel channels in AGRs.
|The ECIT device for examining graphite in AGR units (Image: JFN)
The tools apply an electromagnetic field to the graphite which, being electrically conductive, induce eddy currents in the material. These eddy currents can be used to measure the electrical conductivity and the inferred graphite density.
JFN project leader Sarah Town said, "We originally developed a proof of principle eddy current tool with EDF Energy which led to the prototype eddy current inspection tool. The prototype was only intended for a limited number of deployments but has exceeded expectation and now, several years later, is still providing EDF with valuable inspection information from within the graphite channels of their reactors."
Since the prototype was produced, the ECIT devices have been further developed "to be robust and adaptable enough to provide reliable and accurate data" from the cores of EDF Energy's operating AGRs, JFN said. The latest devices will enable EDF Energy to examine the condition of the graphite "to a level that has not previously been possible", it added.
JFN will start production of the probes during the next few weeks, with the first full deployment scheduled to be completed during 2018.
The contract also includes control consoles, girders to support and transport the ECIT devices, as well as a calibration unit for each device. Two test rigs will also be built to conduct factory acceptance tests and temperature controlled calibration tests.
AGRs feature a graphite moderator and are cooled using carbon dioxide. The graphite blocks cannot be replaced or repaired during the operating period of the reactors. However, radiation damage changes the shape and size of the crystallites that comprise graphite, a process known as dimensional change, which in turn degrades the mechanical properties of the graphite.
Graphite ageing is one area used to determine the lifespan of an AGR nuclear power station. Greater understanding of the ageing process by sampling and modelling can lead to them operating safely for longer, giving the UK secure and reliable low-carbon electricity, EDF Energy has said.
Researched and written
by World Nuclear News