No matter where you get your electricity, there is a fuel source involved. With solar, the light is collected with photovoltaic technologies to create energy. Fossil-fuel plants burn gas. Nuclear is a bit different, however. Nuclear plants don’t burn anything to generate electricity; instead nuclear energy is created through the natural process of fission.
Although fission has always been part of our world, nuclear fission is the newest technology for generating baseload electricity. Humans learned to create and control a self-sustaining fission chain reaction in 1954, and the first full-scale fission-based power plant started making electricity in 1957. Uranium is the ideal fuel for fission because it splits apart easily, and each time is splits, a small amount of heat is generated. That heat is used to turn water to steam to make electricity in a turbine generator.
Today, our nuclear reactors operate using fuel bundles, or assemblies, which are cycled through the reactor on a regular basis. These bundles are made up of a collection of rods which contain and protect the fuel pellets. Every 18-24 months, a reactor must be shutdown to replace about one-third of the fuel, this is known as a refueling outage.
Before new fuel is introduced into a reactor and the fission process starts, the bundles are benign. Think of it like bread yeast – initially bread yeast is just dry powder, but when introduced to warm liquid, the yeast is activated, it starts bubbling and expanding, then it can be used to make bread. Likewise, new fuel has little to no radioactivity until it is placed in the reactor.
Earlier in the year, we completed a refueling outage at Duke Energy’s Brunswick Nuclear Plant. The entire process started when new fuel bundles arrived at Brunswick from Framatome’s Richland, Washington, plant, where the bundles are manufactured. Next, our teammates went to work unloading and moving 228 new fuel bundles and channels to the top floor of the reactor building so inspectors could ensure they were free of defects. Like everything we do, getting fuel ready for the reactor is a team activity. Cranes are used to move the fuel bundles out of the shipping crates into inspection stands. Each box of fuel weighs about 2,200 pounds and each bundle weighs around 750 pounds.
Radiation Protection technicians survey each box, inner box and fuel bundle. Fuel inspectors perform a white glove examination of every inch of every bundle and every channel looking for any defects and debris that could interfere with the performance of the fuel or operation of the reactor. The inspectors are the last people to ever touch the fuel before it is placed in the fuel pool in preparation for opening the reactor.
Refueling outages are carefully planned and coordinated. Engineers pre-plan the outage (years in advance) and know exactly where each new bundle will be placed – so this is an assigned-seats event! The reactor core – or the seating chart for the fuel bundles – is carefully designed by the nuclear fuels engineering team and maintained by our reactor engineering team. New bundles are interspersed with two-year old bundles and four-year old bundles so there is an even distribution of heat. The new bundles will be a bit cool at the first, so they can be placed near a warmer bundle. This careful design process helps the reactor run reliably and ensures each fuel bundle will last up to six years.