All nuclear power reactors use uranium fuel to generate electricity. This fuel consists of small ceramic pellets stacked into metal fuel rods, which are bound together into fuel assemblies that are eight to 12 feet in length.
Once fuel has been used in a reactor, it needs to be stored. Currently, all used nuclear fuel is stored at the plant site in either used fuel pools or in dry storage. The Nuclear Energy Institute estimates that all the used nuclear fuel produced by the U.S. nuclear energy industry in nearly 50 years—if stacked end to end—would only cover an area the size of a football field to a depth of less than 10 yards.
Jason Smith, a lead engineer specializing in nuclear fuel management for Duke Energy, says that safe used fuel storage is a priority at all nuclear power plants. “Currently, every site is responsible for storing its used fuel. There’s a tremendous amount of work and planning that goes into managing used fuel. Whether it is stored in fuel pools or dry cask storage, it poses no risk to the public or our workers,” Smith said.
On average, nuclear fuel spends about four years in a reactor. Once removed from the reactor, the fuel is stored in the used fuel pool for a minimum of five years, which allows the fuel to cool and lowers radioactivity levels. The used fuel remains in the pool until it meets certain requirements necessary for it to be transferred to dry cask storage.
Dry cask canisters are concrete and stainless steel. To transfer fuel from the pool to dry storage, workers carefully place the canisters into the fuel pool and load the used fuel. Once the fuel is loaded into the canister, the water is removed and it is filled with helium and welded shut. At this point, the canister is transported into a storage module for long-term storage.
The fuel will continue to give off heat and radiation, but it is safely contained within the dry storage cask. “Once the fuel is placed in the concrete storage module, the exposure is very low and poses no threat,” Jason Smith said. “Of course, we continuously monitor it.” At the Robinson Nuclear Plant, the used fuel on site dates back to the beginning of operations in 1971.
Containers used to store and carry used fuel are extremely robust and provide additional layers of protection beyond that provided by the fuel rods themselves. The Nuclear Regulatory Commission requires thorough tests and analyses prior to certifying used fuel containers.
Facilities such as Sandia National Laboratories have tested containers under extreme circumstances to ensure they will protect the public in the unlikely event of an accident during transport. Tests have proven that containers can withstand high-speed crashes, extremely hot and long-lasting fires, puncture, and submersion in water.
The approved containers are massive, weighing 25 to 40 tons for truck shipments and 75 to 125 tons for rail shipments. Multiple layers of steel and other materials confine the radioactivity. Typically, for every ton of fuel, there is more than three tons of protective shielding.
There is still a need for a sustainable, long-term solution for storing used nuclear fuel. However, dry cask storage remains a viable, safe and security storage option for the foreseeable future.
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