The replacement of reactor fuel in a nuclear power plant is a major task that often needs a temporary shutdown for its implementation. The shutdown offers an opportunity to conduct major maintenance and refurbishment for the plant, to keep it in line with the safety levels prevalent at other nuclear power plants in the world. This shutdown period is generally known as a “refuelling outage” in the nuclear industry.

In a pressurised water reactor, which is the main reactor type in the world, nuclear fuel is loaded in the form of clusters or assemblies of cylindrical tubes holding enriched uranium oxide inside a sealed pressure vessel. To change the nuclear fuel, the reactor is shut down and, with the pressure vessel opened, the fuel assemblies are lifted individually out of the pressure vessel, transferred by a trolley, and loaded into an adjacent storage pool. Refuelling is the reverse of fuel loading, but with the partial replacement of the fuel assemblies with a new batch of fuel to refresh the nuclear reactor.

Opportunities are taken to conduct maintenance and refurbishment of plant systems and equipment that can be accessed only after plant shutdown, either because their operations are needed for power generation or because they are in plant areas that can only be accessed during shutdown.

In view of the multiplicity of the tasks that need to be performed during the shutdown, elaborate planning is necessary to ensure timely preparation, efficient task execution and proper inspections, so that work is completed to meet the expected quality, time and cost, and the plant can return to reliable services after an outage of typically no more than a month, though the duration may be considerably extended by up to a few months if the refurbishment is extensive.

Attention is necessary for good housekeeping to prevent unwarranted incidents or delays during the outage, and particularly for effective work planning and personnel shielding to control the radiation dosage of staff working in radiation-controlled areas so as to keep their dosage well within regulatory limits. Regulatory inspections and approvals are also needed to clear key stages of the refuelling outage.

This article is contributed by Ir Richard Fung with the coordination of the Nuclear Division.