The Fuel in the Reactor Core

In this the second-part of three-part series where we examine the phases of the nuclear fuel cycle. To read the first part of our series, click here.

Part 2

From Fabrication Facility to Reactor

After nuclear fuel assemblies are built at the fuel fabrication facility, they are transported to a nuclear power plant. Different types of nuclear reactors require different designs of fuel assemblies, so each shipment is tailored to the specific nuclear plant receiving the assemblies. 

Fuel assemblies arrive at Duke Energy's nuclear fleet by truck. During transport, the fuel assemblies are housed in robust containers. When the trucks arrive on site, the fuel shipping containers are inspected by Security and unloaded into the used fuel pool building.

Trained and experienced site personnel use remote-controlled cranes to lift each fuel assembly out of the container. They then meticulously inspect the assembly for any imperfections. Once the fuel assembly passes inspection, the fuel team inserts it into the used fuel pool or new fuel storage racks where it is stored until it is loaded into the reactor core. To load an assembly into the reactor core, it is laid-down horizontally and transferred underwater through a transfer tube to the containment building. The fuel assemblies are then up-ended and inserted into the reactor vessel by manipulator cranes, where they are used to generate heat (through fission) for 54 months until they are replaced with new fuel assemblies. 

Generating Heat through Fission 

Once the fuel is in the reactor, it undergoes the process of fission. Fission is a nuclear reaction and is the plant's source of energy. In the fission process, uranium in the fuel assemblies is bombarded with neutrons, which split the uranium atoms. Heat energy and neutrons are produced in the fission process. The energy heats the water in the reactor and the neutrons split other atoms, thus perpetuating the nuclear chain reaction.



One of the great advantages of producing energy at a nuclear plant is that refueling occurs only once every 18-24 months. As mentioned in a previous article, when a unit shuts down for refueling, the reactor cavity is flooded with water and about one-third of the fuel assemblies (the oldest assemblies in the reactor) are taken out of the core and placed in the used fuel pool. The remaining fuel is carefully relocated in the reactor to maximize the energy use from each fuel assembly, and the new fuel assemblies are loaded into the core.

During refueling, the top of the reactor, or head, is removed from the reactor vessel. The oldest fuel assemblies are removed from the reactor using manipulator cranes and transported through the transfer canal to the used fuel pool, where they are stored until they are cool enough for dry storage in large, robust concrete containers. After the fuel assemblies have been placed into the reactor to form the new reactor core, the reactor head is reinstalled. 

Be sure to stop by next week to read the third part of the nuclear fuel cycle series. In the last installment, we will examine the storage of used fuel.


Further Reading:

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