Clementine (nuclear reactor)
Encyclopedia
Clementine was the code name for the world's first fast neutron nuclear reactor
. It was an experimental scale reactor. The maximum output was 25 kW and was fueled by plutonium
and cooled by liquid mercury
. Clementine was located at Los Alamos National Laboratory
in Los Alamos, New Mexico
. Clementine was designed and built in 1945-46 and first achieved criticality in 1946 and full power in 1949. The reactor was named after the song "Oh My Darling, Clementine
." The similarities to the song include that the reactor location was a deep canyon and the reactor operators were themselves 49'ers as 49 (last digits of element 94, isotope 239) was one of the code names for plutonium at the time.
The primary goal of Clementine was to determine nuclear properties of materials for nuclear weapons research after the Manhattan project
. A number of other experiments were performed at the reactor, including investigation of the feasibility of civilian breeder reactors, and measuring neutron cross sections of various materials.
. They were each 1.64 cm (0.65 in.) diameter and 14 cm (5.5 in.) long. The fuel elements were clad in 0.5 mm (0.02 in.) thick plain carbon steel. The core was located at the bottom of the steel cylinder.
The core was cooled by liquid mercury
. The maximum output was 25 kW of thermal energy. The mercury was circulated through the core and out to a mercury-water heat exchanger at a maximum flow rate of 0.15 L/s by an induction type electromagnetic pump
which had no moving parts.
shell which provided additional shielding. A number of holes ran through the shielding to provide fast neutrons to the various physics
experiments.
so the position of the blanket controlled the number of neutrons available to the reaction. When the blanket was raised more neutrons were reflected back into the core causing a greater number of fissions and consequently greater power output.
Additionally there were 2 shutdown/control rods composed of natural uranium and boron which was enriched
in the boron-10 isotope. 10B is a very effective neutron poison that could be inserted to control and shut down the reaction.
Shutdown of the reactor involved simultaneously dropping the uranium blanket and inserting the two control rods into the center which absorbed neutrons and poisoned the reaction. Up to 20 other holes were available in the core for experimental configurations or additional control or fuel rods.
It was again operated successfully until 1952 when the cladding on one of the fuel rods ruptured. This caused contamination of the primary cooling loop with plutonium and other fission products. At this time it was decided that all the primary objectives of Clementine had been achieved and the reactor was permanently shut down and dismantled.
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...
. It was an experimental scale reactor. The maximum output was 25 kW and was fueled by plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
and cooled by liquid mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. Clementine was located at Los Alamos National Laboratory
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
in Los Alamos, New Mexico
Los Alamos, New Mexico
Los Alamos is a townsite and census-designated place in Los Alamos County, New Mexico, United States, built upon four mesas of the Pajarito Plateau and the adjoining White Rock Canyon. The population of the CDP was 12,019 at the 2010 Census. The townsite or "the hill" is one part of town while...
. Clementine was designed and built in 1945-46 and first achieved criticality in 1946 and full power in 1949. The reactor was named after the song "Oh My Darling, Clementine
Oh My Darling, Clementine
Oh My Darling, Clementine is an American western folk ballad usually credited to Percy Montrose , although it is sometimes credited to Barker Bradford. The song is believed to have been based on another song called Down by the River Liv'd a Maiden by H. S...
." The similarities to the song include that the reactor location was a deep canyon and the reactor operators were themselves 49'ers as 49 (last digits of element 94, isotope 239) was one of the code names for plutonium at the time.
The primary goal of Clementine was to determine nuclear properties of materials for nuclear weapons research after the Manhattan project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
. A number of other experiments were performed at the reactor, including investigation of the feasibility of civilian breeder reactors, and measuring neutron cross sections of various materials.
Core design
The core was contained in a 117 cm (46 in.) long mild steel cylinder which was 15.2 cm (6 in.) inside diameter and 0.6 cm (0.25 in.) thick. The fuel assembly was 15 cm (5.9 in.) in diameter 14 cm (5.5 in.) tall and contained 55 fuel elements. Each fuel element was composed of δ-phase plutonium-239Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
. They were each 1.64 cm (0.65 in.) diameter and 14 cm (5.5 in.) long. The fuel elements were clad in 0.5 mm (0.02 in.) thick plain carbon steel. The core was located at the bottom of the steel cylinder.
The core was cooled by liquid mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. The maximum output was 25 kW of thermal energy. The mercury was circulated through the core and out to a mercury-water heat exchanger at a maximum flow rate of 0.15 L/s by an induction type electromagnetic pump
Electromagnetic pump
An electromagnetic pump is a pump that moves liquid metal using electromagnetism. A magnetic field is set at right angles to the direction the liquid moves in, and a current is passed through it. This causes an electromagnetic force that moves the liquid.Applications include pumping liquid metal...
which had no moving parts.
Shielding and support structure
The reactor core was wrapped in a series of neutron reflectors and shielding structures starting with a 15 cm (6 in.) thick cylindrical blanket of natural uranium immediately surrounding the core. This blanket was open at the top and bottom and could be moved up and down. Next was a 15.2 cm (6 in.) thick steel reflector and 10 cm (4 in.) of lead. Finally most of the reactor was surrounded by multiple laminations of steel and boron plastic. This entire assembly was surrounded and supported by a thick concreteConcrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
shell which provided additional shielding. A number of holes ran through the shielding to provide fast neutrons to the various physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
experiments.
Reactor control
The reactor was the first reactor to demonstrate reaction control via control of delayed neutrons, this was more of a function of being one of the very early reactors rather than a special design feature. Control was accomplished by several means. The uranium blanket described above could be raised and lowered. 238U is a good neutron reflectorNeutron reflector
A neutron reflector is any material that reflects neutrons. This refers to elastic scattering rather than to a specular reflection. The material may be graphite, beryllium, steel, and tungsten carbide, or other materials...
so the position of the blanket controlled the number of neutrons available to the reaction. When the blanket was raised more neutrons were reflected back into the core causing a greater number of fissions and consequently greater power output.
Additionally there were 2 shutdown/control rods composed of natural uranium and boron which was enriched
Isotope separation
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes, for example separating natural uranium into enriched uranium and depleted uranium. This is a crucial process in the manufacture of uranium fuel for nuclear power stations, and is...
in the boron-10 isotope. 10B is a very effective neutron poison that could be inserted to control and shut down the reaction.
Shutdown of the reactor involved simultaneously dropping the uranium blanket and inserting the two control rods into the center which absorbed neutrons and poisoned the reaction. Up to 20 other holes were available in the core for experimental configurations or additional control or fuel rods.
Use and shutdown
Clementine operated successfully from 1946 until 1950 when the reactor was shut down to correct a problem with the control and shim rods. During this shut down it was noted that one of the natural uranium rods had ruptured. It was replaced and the reactor was restarted.It was again operated successfully until 1952 when the cladding on one of the fuel rods ruptured. This caused contamination of the primary cooling loop with plutonium and other fission products. At this time it was decided that all the primary objectives of Clementine had been achieved and the reactor was permanently shut down and dismantled.
Results of the Clementine experiment
The experience and data provided by operating the Clementine reactor was very useful for both military and civilian applications. One of the notable achievements of the Clementine project included measurements for the total neutron cross sections of 41 elements to a 10% accuracy. Additionally, Clementine provided invaluable experience in the control and design of fast neutron reactors. It was also determined that mercury was not an ideal cooling medium for this type of reactor due to its poor heat transfer characteristics.Specifications
- Type: fast neutron reactorFast neutron reactorA fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons...
- Fuel: plutonium-239Plutonium-239Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
- Coolant: mercury at 2 kg/s maximum.
- Moderator: none
- Shielding: multiple layers of uranium-238, steel, lead and boron-impregnated plastic.
- Power: 25 kW maximum.
- Core temperature: inlet 38°C, outlet 121°C, max core 135°C