Dry Cask Storage
Dry cask storage
Dry cask storage is a method of storing the radioactive waste from nuclear reactors. Dry cask storage refers to the containers that hold the waste and the system of storing the waste above ground in containers.
After World War II, nuclear power plants began generating electricity. By the close of the twentieth century, reactors at nuclear power plants generated 20% of the electricity in the United States. To produce electricity, uranium is used as fuel. Each tiny uranium pellet produces almost as much energy as a ton of coal . The pellets are contained in long metal rods, and these rods are placed in a fuel assembly that hold from 50 to 300 rods.
The uranium undergoes fission, a process that heats water and converts it to steam. The steam propels the blades of a turbine. This in turn spins the shaft of a generator where electricity is produced.
A large reactor uses 60 assemblies annually, and assemblies must be replaced after several years. The waste called spent fuel is so radioactive that a person standing near an unshielded rod would die within a second. The spent fuel is also extremely hot. The used fuel rods are taken from the reactor core and stored in a concrete pool that is lined with steel. The rods are stored underneath at least 20 ft (6 m) of water. The spent pool set-up serves as a radiation shield while water cools the rods.
Spent fuel pools were regarded as temporary storage facilities. When operators built the first reactors, there were plans to extract and recycle unused uranium and plutonium from the fuel. However, the process would consolidate plutonium into a form that could be used in nuclear weapons . As a result of that consequence, the process was banned in 1977. By that time the United States had produced enough plutonium to satisfy its own needs for weapons production.
Five years later, Congress passed the Nuclear Waste Policy Act. Among the issues discussed was where to store spent fuel because power plants were starting reach to storage capacity. Congress amended the act in 1987 to designate a permanent waste disposal site in the Yucca Mountain area of Nevada.
Yucca Mountain had been proposed as a facility that would open in 1985. However, concerns about a nuclear explosion and other safety issues led to postponement of the opening. The opening was shifted to 1989, 1998, 2003, and 2010.
With no permanent site available, plant operators began to store spent fuel onsite in dry casks. In 1986, the United States Nuclear Regulatory Commission (NRC) licensed the first dry storage installation at the Virginia Electric & Power Company Surry Nuclear Plant in Jamestown, Virginia. The utility installed metal casks that were 16 ft (4.9 m) in height. Each dry cask held from 21 to 33 spent fuel assemblies. When filled, each cask weighed 120 tons. Casks were placed vertically on concrete pads that were 3-ft (1 m) thick. Each pad would hold 28 casks.
By 2001, the NRC had approved various dry casks designs. The container is usually steel. After it is filled, the container is either bolted or welded shut. The metal casks are then put inside larger concrete casks to ensure radiation shielding. Some systems involve placing the steel cask vertically in a concrete vault. In other systems, the container is placed horizontally in the concrete vault.
Discussions about dry cask safety in the twenty-first century have centered on the Yucca Mountain proposal. In May of 2002, the United States House of Representatives voted to approve the plan. That vote was an override of Nevada Governor Kenny Guinn's veto of the plan to send waste to Yucca. Opponents of the plan like the Nuclear Information and Resource Service maintained that casks of waste could not be transported safely by train or truck. In 2002, the facility was expected to cost $58 billion. It was scheduled to open in 2010 and hold a maximum of 77,000 tons of waste.
[Liz Swain ]
Murray, Raymond, and Judith Powell, ed. Understanding Radioactive Waste. Columbus, OH: Battelle Press, 1997.
Saling, James, and Audeen Fentiman. Radioactive Waste Management. Philadelphia, PA: Taylor & Francis, Inc., 2001.
United States Nuclear Regulatory Commission., One White Flint North, 11555 Rockville Pike , Rockville, MD USA 20852-2738 (301) 415-7000, Toll Free: (800) 368-5642, Email: [email protected], <http://www.nrc.gov>