Nuclear fuel cycle

Special rocks called uranium are dug from the ground.

First, workers grind the rocks into dust. They use liquids to pull the uranium out. This makes a powder called yellowcake.

Next, the powder is changed into a gas. This helps make the fuel stronger. The strong fuel is made into small, hard pellets. These pellets go into long metal tubes.

These tubes are used in power plants. The fuel makes heat to make power. When the fuel is used up, it is called spent fuel.

Some people recycle the old fuel. Others put it away safely. It is a big cycle that keeps working.

The nuclear fuel cycle is a set of steps. It shows how we make and use nuclear fuel.

First, workers find uranium in the ground. They mine it from rocks. Next, they use a way called milling. This pulls the uranium out of the rocks. It makes a powder called yellowcake.

Then, the yellowcake is changed into a gas. This helps with enrichment. Enrichment is a way to make the fuel stronger. Most reactors need more U-235 to work. U-235 is a special part of uranium.

After that, the gas is turned into hard pellets. These pellets go into metal tubes. We call these fuel rods. These rods make heat to create power.

When the fuel is used up, it is called spent fuel. This fuel is very hazardous. Some countries use an open fuel cycle. This means they store the spent fuel. Other places use a closed fuel cycle. They reprocess the fuel to use it again.

The nuclear fuel cycle is a long series of steps. It describes how we find, make, use, and store nuclear fuel.

This cycle is sometimes called the nuclear fuel chain. It has three main parts: the front end, the service period, and the back end. The front end is where we prepare the fuel. The service period is when the fuel works inside a reactor. Finally, the back end is for managing and storing the fuel once it is used.

Making fuel starts with finding uranium in the ground. Scientists use special tools to find deposits of uranium ore. Once found, the ore is taken out through mining. This can happen in big open pits or deep underground. In the United States, workers also use a method called in situ leach mining. This uses wells to pull uranium from the ground into a liquid.

After mining, the ore goes through milling. This turns the rock into a dry powder called yellowcake. This powder is mostly uranium oxide, known as U3O8.

Next, the yellowcake must be changed to work in a reactor. Most reactors need enriched fuel to keep a chain reaction going. This means the fuel must have more of a specific part called U-235. Natural uranium only has about 0.71% of this special part. For light water reactors, workers enrich it to about 3% to 5%.

To do this, the solid yellowcake is often turned into a gas called uranium hexafluoride. This gas is then processed using methods like gas centrifuges. This process creates a byproduct called depleted uranium. The United States alone has 470,000 tonnes of this material in storage.

After enrichment, the fuel is turned into something solid again. The gas is converted into a powder called uranium dioxide. This powder is pressed into small, hard ceramic pellets.

These pellets are very tough and can handle high heat. The pellets are stacked inside long metal tubes. These tubes are called fuel rods. Many fuel rods are grouped together to make a fuel assembly. These assemblies are then placed into the reactor to make power.

Eventually, the fuel is used up and becomes spent fuel. This fuel is very hazardous and must be handled with great care. There are two main ways to handle it. In an open fuel cycle, the spent fuel is simply stored away. In a closed fuel cycle, the fuel is reprocessed. This means the fuel is cleaned so it can be used again.

Reprocessing can recycle about 95% of the spent fuel. This helps make the most of the energy we have.

The nuclear fuel cycle describes the complete series of stages for nuclear fuel. This process includes the extraction, processing, use, and disposal of fuel. It is often called the nuclear fuel chain. The cycle is divided into three main parts: the front end, the service period, and the back end. The front end involves preparing the fuel for use. The service period is when the fuel operates inside a nuclear reactor. The back end is for the safe management, containment, and disposal of spent fuel.

Nuclear power relies on fissionable material to sustain a chain reaction with neutrons. Common examples include uranium and plutonium. In most reactors, a moderator is used to lower the kinetic energy of neutrons. This increases the chance that fission, or the splitting of atoms, will occur. Graphite and heavy water are very effective moderators. They slow neutrons through collisions without absorbing them. This allows some reactors to use natural uranium. Light water reactors (LWRs) use regular water as a moderator. These reactors require enriched fuel with higher concentrations of fissile isotopes.

The cycle begins with the exploration and mining of uranium. Geologists use geophysical techniques to find uranium deposits, such as uraninite. Once a deposit is found, scientists determine how much uranium can be extracted. Uranium is naturally found in two main isotopes: U-238 and U-235. About 99.28% of natural uranium is the fertile isotope U-238. Only 0.71% is the fissile isotope U-235. Fissile isotopes are special because their nuclei nearly always fission when struck by a neutron. U-238 is considered fertile because it can absorb a neutron to eventually become plutonium-239.

After mining, the ore undergoes milling to extract usable uranium. The ore is crushed or ground into a fine dust. It is then treated with chemicals, most commonly sulfuric acid. This process dissolves the uranium into a liquid solution. The solution is filtered to separate the uranium from undesirable solids called tailings. The uranium is then recovered using solvent exchange or ion exchange. Finally, the uranium is dried into a powder called "yellowcake," or U3O8. This material is then converted into uranium hexafluoride (UF6) for the next step.

Most commercial reactors require enriched uranium. This is because the natural 0.71% concentration of U-235 is too low for light water reactors. Enrichment increases this concentration to between 3% and 5%. This is often done using gas centrifuges or gaseous diffusion. This process produces a byproduct known as depleted uranium (DU). About 96% of the byproduct from enrichment is depleted uranium. As of 2008, the United States Department of Energy had 470,000 tonnes of DU in storage. This material can be used for radiation shielding or ballast.

Once enriched, the uranium hexafluoride is converted into uranium dioxide (UO2) powder. This powder is pressed into small, hard ceramic pellets. These pellets are fired in a high-temperature sintering furnace. The pellets are then ground to a uniform size and stacked into metal tubes. These tubes are called fuel rods and are made of corrosion-resistant alloys. Many fuel rods are grouped together into fuel assemblies. These assemblies form the fuel core of the power reactor.

During the service period, the fuel undergoes nuclear reactions. As fissile isotopes are consumed, fission products build up. These products are often radioactive waste. Eventually, the buildup of these products stops the reaction. The fuel is then considered "spent nuclear fuel." This spent fuel is extremely hazardous. However, nuclear fuel has a very high energy density. This means reactors produce much smaller volumes of waste than other power plants. If all the spent fuel from U.S. power stations were in one place, it would cover about one American football field.

There are two ways to manage the back end of the cycle. An open fuel cycle, or once-through cycle, means the spent fuel is not reprocessed. It is simply managed and disposed of. A closed fuel cycle involves reprocessing the spent fuel. In a closed cycle, about 95% of the spent fuel can be recycled for reuse. Reprocessing allows for the separation of plutonium and other materials from the waste. This can create new fuel types, such as mixed oxide (MOX) fuel. MOX fuel is made by blending plutonium with uranium.