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Nuclear Reactors: Materials Used
Nuclear reactors are devices used to initiate and control a sustained nuclear chain reaction. They are used for power generation, research and development, and other applications. radioactive materials, the use of nuclear reactor materials is of great importance to ensure the safe and reliable operation of the plant.
There are a number of different materials used in the construction and operation of nuclear reactors. These materials, generally referred to as “reactor core” materials, include fuels, moderators, coolants and primary and secondary containment structures. Fuel typically consists of uranium or plutonium, typically enriched, encased in pellets and sealed in tubes of zirconium alloys. Moderators are substances, usually liquids such as water or graphite, that slow neutrons down to levels necessary to sustain a chain reaction. Coolants are substances that are used to remove heat from the reactor core; they can vary in composition. Primary and secondary containment structures, usually of steel, provide barriers to radioactivity leakage.
Uranium is the fuel of choice for most commercial nuclear power plants since it can easily be enriched and produces more energy per unit mass than other fuels like plutonium. Most uranium fuel is composed of uranium-235 and plutonium-239 mixed with small amounts of other isotopes. The fuel is then formed into pellets roughly the size of a grain of rice and arranged in long tubes and sealed with end caps. The tubes are then grouped together to form a fuel element.
The moderator is used to slow down the neutrons created by the fission reactions in order to sustain the chain reaction. In most commercial nuclear power plants, the moderator is either water or graphite. In a pressurized water reactor (PWR), the water is kept under pressure to help prevent it from boiling. In a boiling water reactor (BWR), the water is allowed to boil in order to transfer heat to a steam generator. Graphite, an array of interlocking structures of carbon atoms, is used primarily in gas-cooled reactors since it has high neutron moderation efficiency.
Given the complexity of the reactor system and the specialized nature of nuclear reactor materials, the selection and design of these materials is a highly specialized process. Materials must be carefully chosen, designed and tested to ensure the safe and reliable operation of the plant. Extensive testing of materials, both in-house and through third party testing, is undertaken to ensure the materials meet all safety and performance requirements.
In addition to the materials used in the reactor core, other materials are used extensively throughout the remainder of the reactor system. These materials range from stainless steel for pumps and piping, to copper alloys for electrical cables and transformers, to graphite for nuclear disposal systems. Even materials such as cement, epoxy resin and lead are used in specific areas.
Nuclear reactors must be designed, constructed and operated with the utmost care. The use of nuclear reactor materials is of great importance to ensure the safe and reliable operation of the plant. Careful selection, design, and testing of the materials used in reactors is essential to ensure their proper performance and the safety of reactor personnel and the public.
