Spent fuel pool
Encyclopedia
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s. They are typically 40 or more feet (12 m) deep, with the bottom 14 feet (4.3 m) equipped with storage racks designed to hold fuel assemblies removed from the reactor. A reactor's pool is specially designed for the reactor in which the fuel was used and situated at the reactor site. In many countries, the fuel assemblies, after being in the reactor for 3 to 6 years, are stored underwater for 10 to 20 years before being sent for reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
or dry cask storage
Dry cask storage
Dry cask storage is a method of storing high-level radioactive waste, such as spent nuclear fuel that has already been cooled in the spent fuel pool for at least one year.. These casks are typically steel cylinders that are either welded or bolted closed. When inside, the fuel rods are surrounded...
. The water cools the fuel and provides shielding from radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
.
While only about 8 feet (2.4 m) of water is needed to keep radiation levels below acceptable levels, the extra depth provides a safety margin and allows fuel assemblies to be manipulated without special shielding to protect the operators.
The Nuclear Regulatory Commission
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...
estimates that many of the nuclear power
Nuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
plants in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
will be out of room in their spent fuel pools by 2015, most likely requiring the use of temporary storage of some kind.
Operation
About a quarter to a third of the total fuel load of a reactor is removed from the core every 12 to 18 months and replaced with fresh fuel. Spent fuel rods generate intense heat and dangerous radiation that must be contained. Fuel is moved from the reactor and manipulated in the pool generally by automated handling systems, although some manual systems are still in use. The fuel bundles fresh from the core normally are segregated for several months for initial cooling before being sorted in to other parts of the pool to wait for final disposal. Metal racks keep the fuel in safe positions to avoid the possibility of a “criticality”— a nuclear chain reactionNuclear chain reaction
A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...
occurring. Water quality is tightly controlled to prevent the fuel or its cladding from degrading. Current regulations in the United States permit re-arranging of the spent rods so that maximum efficiency of storage can be achieved.
The maximum temperature of the spent fuel bundles decreases significantly between 2 and 4 years, and less from 4 to 6 years. The fuel pool water is continuously cooled to remove the heat produced by the spent fuel assemblies. Pumps circulate water from the spent fuel pool to heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
s, then back to the spent fuel pool. The water temperature in normal operating conditions is held below 50°C (120°F)http://www.usainc.org/members/index.html?organization_id=47198. Radiolysis
Radiolysis
Radiolysis is the dissociation of molecules by nuclear radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux...
, the dissociation
Dissociation (chemistry)
Dissociation in chemistry and biochemistry is a general process in which ionic compounds separate or split into smaller particles, ions, or radicals, usually in a reversible manner...
of molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s by radiation, is of particular concern in wet storage, as water may be split by residual radiation and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas may accumulate increasing the risk of explosions. For this reason the air in the room of the pools, as well as the water, must be continually monitored and treated.
Other possible configurations
Rather than manage the pool’s inventory to minimize the possibility of continued fissionNuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
activity, the Chinese
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
are building a 200 MWt nuclear reactor to run on used fuel from nuclear power stations to generate process heat for district heating
District heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...
and desalination
Desalination
Desalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
. Essentially an SFP operated as a deep pool-type reactor; it will operate at atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
, which will reduce the engineering requirements for safety.
Other research envisions a similar low-power reactor using spent fuel where instead of limiting the production of hydrogen by radiolysis, it is encouraged by the addition of catalysts and ion scavengers to the cooling water. This hydrogen would then be removed to use as fuel.
Risks
If there is a prolonged interruption of cooling, including natural disasters or terrorist attacks, the water in the spent fuel pools may boil off, resulting in large amounts of radioactive elements being released into the atmosphere.In the magnitude 9 earthquake which struck the Fukushima nuclear plants in March 2011, one of the spent fuel pools lost its roof and was reported to be emitting steam so was possibly boiling. According to The Nation, "Spent fuel pools at Fukushima are not equipped with backup water-circulation systems or backup generators for the water-circulation system they do have." Later, there was some disagreement among sources as to whether the pool had boiled dry.
TEPCO, the plant owner, announced that if the rods were exposed, there was a small chance they would reach criticality
Criticality accident
A criticality accident, sometimes referred to as an excursion or a power excursion, is an accidental increase of nuclear chain reactions in a fissile material, such as enriched uranium or plutonium...
, setting off a nuclear chain reaction (not an explosion). According to nuclear plant safety specialists, the chances of criticality in a spent fuel pool are very small, usually avoided by the disposal of the fuel assemblies, inclusion of a neutron absorber in the storage racks and overall by the fact that the spent fuel has a too low enrichment level to self-sustain a fission reaction. They also state that if the water covering the spent fuel evaporates, there is no element to moderate the chain reaction. On April 1, 2011, United States Energy Secretary Steven Chu
Steven Chu
Steven Chu is an American physicist and the 12th United States Secretary of Energy. Chu is known for his research at Bell Labs in cooling and trapping of atoms with laser light, which won him the Nobel Prize in Physics in 1997, along with his scientific colleagues Claude Cohen-Tannoudji and...
said that after efforts by workers to pour water on the Fukushima pools, these were “now under control.”
Spent fuel pools lack the "4-ft.-thick (1.2 m) concrete cocoons" of operating reactors but are "housed in more conventional buildings that are conceivably more susceptible to aircraft strikes or explosives".
According to Dr. Kevin Crowley of the Nuclear and Radiation Studies Board, "successful terrorist attacks on spent fuel pools, though difficult, are possible. If an attack leads to a propagating zirconium cladding fire, it could result in the release of large amounts of radioactive material." The Nuclear Regulatory Commission
Nuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...
after the September 11, 2001 attacks
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...
required American nuclear plants "to protect with high assurance" against specific threats involving certain numbers and capabilities of assailants. Plants were also required to "enhance the number of security officers" and to improve "access controls to the facilities".
In 1997, the Brookhaven National Laboratory
Brookhaven National Laboratory
Brookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...
estimated that a "massive calamity at one spent-fuel pool could ultimately lead to 138,000 deaths and contaminate 2,000 sq. mi. (5,200 sq km) of land".
See also
- Deep geological repositoryDeep geological repositoryA deep geological repository is a nuclear waste repository excavated deep within a stable geologic environment...
- Dry cask storageDry cask storageDry cask storage is a method of storing high-level radioactive waste, such as spent nuclear fuel that has already been cooled in the spent fuel pool for at least one year.. These casks are typically steel cylinders that are either welded or bolted closed. When inside, the fuel rods are surrounded...
- Lists of nuclear disasters and radioactive incidents
- Nuclear fuel cycleNuclear fuel cycleThe nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
- Radioactive wasteRadioactive wasteRadioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...
- Spent nuclear fuel shipping caskSpent nuclear fuel shipping caskSpent nuclear fuel shipping casks are used to transport spent nuclear fuel used in nuclear power plants and research reactors to disposal sites such as the nuclear reprocessing center at COGEMA La Hague site...
External links
- Radiological Terrorism: Sabotage of Spent Fuel Pool
- Storage of Spent Nuclear Fuel U.S. Nuclear Regulatory Commission (NRC)
- An example diagram of a Spent Fuel Pool Indian Point Energy Center