Nuclear shielding materials are used to protect people, equipment and components of nuclear reactors from radiation generated during the nuclear power process. Critical components of a nuclear power plant, such as the control rod drive mechanisms and other systems, are located behind layers of shielding material to prevent exposure of personnel to lethal levels of radiation. The primary purpose of shielding is to buffer people from unsafe levels of radiation released from nuclear materials and to limit the possible affects of radiation exposure to acceptable limits.
Nuclear shielding materials must be highly efficient at absorbing radiation, such as neutrons, gamma rays, and x-rays, to provide effective radiation protection. The most common shielding materials for nuclear reactors are made from lead, borated polyethylene, concrete, steel, and water. Materials used to produce shielding also include cadmium, cobalt, nickel, and aluminum metal alloys, as well as elemental boron.
Lead is the oldest and most widely-used shielding material. It is dense, can be molded easily and is a good heat conductor. Furthermore, it is effective at absorbing gamma radiation and charged particles when in deed form. Most nuclear shielding applications require one to two feet of lead to provide adequate protection.
Borated polyethylene is the most widely used shielding material for reactors and is often used to line the containment structure of a reactor. Borated polyethylene is an organic, low density plastic material containing small amounts of boron, which is an efficient neutron absorbent. Borated polyethylene, which resists neutron radiation, is more economically and efficiently produced and installed than other materials, such as granite or concrete.
Concrete and steel, two of the most commonly used shielding materials, are not as efficient at absorbing radiation as lead, but are better than many of the other materials used. Steel has a high density and toughness, making it suitable for use in parts of the container walls, pressure vessels, and other components of a nuclear reactor. Concrete is often used to construct the building or container that houses the core of a nuclear reactor, protecting personnel and other objects from radiation.
Water is also used as a nuclear shielding material, as it is heavy, benign, inexpensive and readily available. Water also removes heat generated by radioactive elements and acts as a moderator, slowing down the particles released from nuclear reactions.
In addition to these materials, scientists experiment with advanced shielding materials, such as depleted uranium and diamond, to improve the safety of nuclear power plants. Depleted uranium is a lightweight and malleable metallic material with a high melting point, and can absorb neutrons more efficiently than lead and concrete. Diamond is used to coat the inside of nuclear reactors and other nuclear facilities, helping to prevent exposure of employees to radiation.
Ultimately, all of these materials serve the same purpose: to protect people, equipment and components of a nuclear reactor from radiation. Necessary aspects, such as cost, weight and ease of use, influence the choice of nuclear shielding materials used. While a variety of shielding materials are suitable for use, some materials may be more effective and suitable than others, depending on the individual application.
