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Storing Spent Fuel
Nuclear power plants have traditionally stored spent fuel in secure water pools at the reactor site. In the early 1980s, as space in the pools at the reactor sites ran out, the nuclear power industry began to explore alternative storage methods. Today, plants can increase on-site storage capacity by "reracking," or placing fuel rod assemblies closer together in spent fuel pools, or by consolidating the fuel rods themselves. However, both these methods are also constrained by the size of the spent fuel storage pool at the plant.
Another option is to store the spent fuel in an independent spent fuel storage installation, which can be stored at the site or elsewhere. This option is referred to as dry cask storage. Dry cask storage has been in use at U.S. nuclear plants since 1986.
Dry cask storage is a remarkably simple, yet extremely safe and reliable system that seals used nuclear fuel in massive airtight steel and concrete canisters that provide both structural strength and radiation shielding. The system of concentric cylindrical containers provides above ground, long-term storage of spent nuclear fuel. Casks are placed upright on a concrete pad and are hardened structures capable of withstanding natural disasters and terrorist attacks. The vertical system is referred to as dry because the fuel is surrounded by helium gas rather than water. The canister/cask system is very robust, about 20 feet in height and 11 feet in diameter, with a cask wall that is over 2 feet thick and a total loaded weight of about 360,000 pounds. The inner canisters and outer casks have no operating equipment requiring regular maintenance. The fuel is cooled by passive means, with its heat dissipating via cooling channels in the outer cask that allow air to circulate naturally on the outside of the inner canister. This type of storage is also known as an Independent Spent Fuel Storage System ISFSI.
Entergy moved five casks of fuel to a highly protected dry cask storage pad on site in 2008.
Safety, Security & Environment
The NRC reviews and approves the designs for spent fuel dry storage systems as well as periodically inspects the design, fabrication and use of dry casks to ensure continued compliance with radiation safety and security requirements.
The NRC requires the spent fuel to be cooled in the spent fuel pool for several years before being transferred to dry fuel storage. Typically, the maximum heat generated from 24 fuel assemblies stored in a dry fuel container is less than that given off by a typical home heating system in an hour. The containers are cooled by the natural circulation of outside air. As the fuel cools further, the heat generated will decrease over time.
Dry Cask Storage is an efficient and safe way of adding fuel storage capacity. Dry Cask Storage DCS has been in use at various nuclear facilities in the United States, successfully, since the mid 1980s. It is a proven, safe technology. About half of the nuclear power plants in US are either using Dry Cask Storage now or have a project to implement the capability.
Dry Cask Storage is safe and environmentally sound, with four decades of exemplary safe performance worldwide. Since 1986, more than a dozen U.S. plants have successfully used dry storage facilities including Entergy. Strict federal regulations pertaining to environmental protection, radiation control, and occupational safety govern the process. The containers used in the dry storage systems are designed to resist floods, tornadoes, projectiles, temperature extremes, and other unusual scenarios. Over the last 20 years, there have been no radiation releases which have affected the public, no radioactive contamination, and no known or suspected attempts to sabotage spent fuel containers.
Dry Fuel Storage Locations in the United States
Spent fuel is currently kept in dry storage facilities located at 24 power plant sites, one decommissioned power plant site (Fort St. Vrain), two plants in the process of decommissioning (Rancho Seco and Trojan) and at an interim storage facility operated by the Department of Energy located at the Idaho National Engineering and Environmental Laboratory near Idaho Falls, Idaho.
The approximate twenty year operating history of dry fuel storage sites throughout the United States clearly demonstrates this storage method is safe and secure. Furthermore, once the federal government constructs the permanent facility these containers can then be shipped to the single national site.
For more information please go to http://www.nrc.gov/waste/spent-fuel-storage.html
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