Resources & Stats

September 2012

Key Facts

• The independent U.S. Nuclear Regulatory Commission has said “there is no pressing safety or security reason” for transferring used fuel from storage pools at nuclear energy facilities to steel and concrete containers.

• Fuel pools are robust concrete and steel structures that are designed—like the nuclear power plants they are part of—to withstand extreme events such as earthquakes, floods, hurricanes and tornadoes.

• Fuel storage pools are an effective means to cool the fuel over many years and provide shielding against radioactivity when used nuclear fuel is transferred out of the reactor.

• Typically, a fuel pool is 40 feet deep and the used fuel is 20 feet below the water’s surface. It is standard practice to store used fuel in a pool for at least five years, usually longer, after it has been removed from the reactor core. Once the radioactivity and heat have decreased sufficiently, the fuel may be removed from the pool and relocated to storage containers.

• Despite the strongest earthquake in modern history in Japan, a tsunami estimated at 45 feet in height, loss of all off-site electric power for weeks, and explosions resulting from hydrogen buildup, all seven fuel pools at the Fukushima Daiichi power plant remained intact and the used fuel in the pools remained covered with cooling water.

• If electrical power is lost at a nuclear power station during an extreme event, a series of systems and procedures are in place to assure backup power and water are supplied to vital safety functions, including maintaining water levels in the fuel storage pool. If the water could not be cooled, operators would have days or weeks to resolve the situation because the water would not evaporate rapidly to uncover the used fuel.

No Damage at Fukushima Fuel Pools
In the early days of the 2011 Fukushima accident, there was speculation that the used fuel storage pools at the site had been damaged or that the water had drained out of some of the pools. Later observations and data showed this to be incorrect. Still, the misperception led to discussion in Congress on accelerating the transfer of used fuel rods at U.S. nuclear energy facilities from pools to storage containers.

The independent NRC says that fuel pools and containers are equally safe methods for storing used fuel and that both protect public health and the environment. The agency adds that “there is no pressing safety or security reason to mandate earlier transfer of fuel from pool to [dry] cask.”

For more on container storage, see the NEI fact sheet “Safely Managing Used Nuclear Fuel.”

Fuel Storage Pools Are Robust Structures
Used fuel storage pools are robust concrete and steel structures that are designed to withstand extreme events such as earthquakes, floods, hurricanes and tornadoes. To prevent water from escaping as a result of damage to piping or cooling systems, the pools do not have drains in their floors.

The storage pools vary in size, with a small pool measuring approximately 20 feet wide by 30 feet long. Most pools are approximately 40 feet deep. A pool can hold hundreds of fuel assemblies. Depending on the facility, the storage pool can be inside the reactor containment building or in a separate structure.

Water is an effective natural shield that protects workers and the environment from the radioactivity and heat produced by used fuel. To maintain radiation levels above the pool well below the limits specified in stringent NRC regulations, the water level above the used fuel is typically 20 feet deep.
Water in the pools is filtered and purified. It circulates through a heat exchanger for cooling, and then is returned to the top of the pool. The operating temperature of the pools is maintained at about 70 to 100 degrees Fahrenheit, less than the typical temperature of bath water.

Safely Managing Used Nuclear Fuel
It is standard practice to store used fuel in a pool for at least five years—and usually longer—after it has been removed from the reactor. Once the pools reach capacity with used fuel after many years, and after the radioactivity and heat have decreased, operators move the fuel into specially designed containers made of steel or steel-reinforced concrete. Each container design used for this purpose must be approved by the NRC. The containers are located on site but apart from the main reactor buildings in a safe and secure monitored area.

If off-site electrical power is lost at a nuclear energy facility during an extreme event, a series of systems and procedures is in place to ensure backup power and water are supplied to vital safety functions, including maintaining cooling and water levels in the used fuel storage pool.

Nuclear energy facility operators have emergency procedures and equipment that could be used in an extreme situation (such as loss of all electrical power) to provide water to fuel pools. An example is using backup water supply systems or hoses to provide cooling water. Emergency response equipment that does not need off-site electricity was added at U.S. facilities after the terrorist attacks of Sept. 11, 2001. More portable safety equipment is being added in response to the nuclear accident at Fukushima.

Even if those systems failed and there were no cooling water available, the water in the pool would heat and evaporate slowly, giving operators days or weeks to restore cooling and keep the water at a safe level.