UHTREX
Encyclopedia
The Ultra High Temperature Reactor Experiment (UHTREX) was an experimental gas cooled
nuclear reactor experiment starting in 1959 and lasting about 12 years UHTREX was located at Los Alamos Scientific Laboratory
. The reactor first achieved full power in 1969. The purpose of the experiment was to test the advantages of using a simple fuel vs the disadvantages of a contaminated cooling loop with the over all goal of finding ways to reduce the cost of nuclear power. The UHTREX concept came as a direct spin off from technology developed by the earlier ROVER
project
. The cylinder
was 70 in. OD x 23 in. ID x 39 in. high. The core had 312 fuel channels. The channels were equally spaced radially around the core at 15 degree intervals arranged in 13 separate layers of 24 channels each. Each channel held up to 4 fuel elements and extended completely through to the inside of the cylinder. The core could be refueled remotely while at full power . Refueling involved rotating the core to the channel containing the element requiring replacement and pushing in a new element. The used element would be pushed out into the center and fall to the base of the reactor to be collected. At full power the reactor used up 1 to 6 fuel elements per day depending on enrichment and porosity of the fuel element. It produced 3MW of thermal energy.
prevents the coolant medium from directly contacting the fuel pellets either by cladding the fuel pellets, sealing the fuel pellets inside a fuel rod
or running the coolant through separate piping. This prevents contamination of the cooling medium. One of the disadvantages of a sealed fuel assembly includes buildup of fission products inside the fuel element. Some of these products poison
the reaction ultimately leading to poor efficiency well before a significant portion of the fuel is used up. At this time the reactor requires re-fueling. Keeping the fuel and coolant separate can present significant design challenges as well. For example the metal tubing required to do so cannot be operated at temperatures above its melting point which is generally significantly lower than the fuel pellet. This lowers the maximum theoretical thermal efficiency
of the reactor.
The UHTREX used un-clad porous carbon extruded fuel elements each shaped like a long hollow cylinder. The fuel elements were manufactured by vacuum impregnating the porous carbon cylinders with aqueous uranyl nitrate
solution then air drying and baking them in a furnace ultimately producing a uranium oxide
coating tightly held in a porous graphite matrix. This fuel was expected to be substantially less expensive to manufacture than other types of fuel at the time. The primary advantages of this type of fuel was that the porosity of the pellet in addition to the high temperatures achievable would allow most of the poisons created by the fission products to migrate out of the fuel. The poisons would then be carried away by the coolant stream for eventual filtering out and removal. This allows a higher percentage of fuel to be burned up before the pellet needed replacement (up to 50%).
s, compressor
s and heat exchanger
s would be become highly contaminated with fission product
s. Contamination caused by a potential contaminated coolant
leak would pose a significant danger to personnel and the environment. The high contamination level precludes being able to open the reactor vessel for the eventual refueling. Therefore the reactor was designed for remote online refuelling
where ID and OD are the inner and outer diameter, respectively.
Gas Cooled Reactor
A gas-cooled reactor is a nuclear reactor that uses graphite as a neutron moderator and carbon dioxide as coolant...
nuclear reactor experiment starting in 1959 and lasting about 12 years UHTREX was located at Los Alamos Scientific 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...
. The reactor first achieved full power in 1969. The purpose of the experiment was to test the advantages of using a simple fuel vs the disadvantages of a contaminated cooling loop with the over all goal of finding ways to reduce the cost of nuclear power. The UHTREX concept came as a direct spin off from technology developed by the earlier ROVER
Nuclear thermal rocket
In a nuclear thermal rocket a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle to create thrust. In this kind of thermal rocket, the nuclear reactor's energy replaces the chemical energy of the propellant's...
project
Reactor core design
The UHTREX core was composed of a vertical hollow rotating cylinder (turret) constructed of solid graphiteGraphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
. The cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
was 70 in. OD x 23 in. ID x 39 in. high. The core had 312 fuel channels. The channels were equally spaced radially around the core at 15 degree intervals arranged in 13 separate layers of 24 channels each. Each channel held up to 4 fuel elements and extended completely through to the inside of the cylinder. The core could be refueled remotely while at full power . Refueling involved rotating the core to the channel containing the element requiring replacement and pushing in a new element. The used element would be pushed out into the center and fall to the base of the reactor to be collected. At full power the reactor used up 1 to 6 fuel elements per day depending on enrichment and porosity of the fuel element. It produced 3MW of thermal energy.
Advantages
A typical nuclear reactorNuclear 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...
prevents the coolant medium from directly contacting the fuel pellets either by cladding the fuel pellets, sealing the fuel pellets inside a fuel rod
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...
or running the coolant through separate piping. This prevents contamination of the cooling medium. One of the disadvantages of a sealed fuel assembly includes buildup of fission products inside the fuel element. Some of these products poison
Nuclear poison
A neutron poison is a substance with a large neutron absorption cross-section in applications, such as nuclear reactors. In such applications, absorbing neutrons is normally an undesirable effect...
the reaction ultimately leading to poor efficiency well before a significant portion of the fuel is used up. At this time the reactor requires re-fueling. Keeping the fuel and coolant separate can present significant design challenges as well. For example the metal tubing required to do so cannot be operated at temperatures above its melting point which is generally significantly lower than the fuel pellet. This lowers the maximum theoretical thermal efficiency
Thermal efficiency
In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...
of the reactor.
The UHTREX used un-clad porous carbon extruded fuel elements each shaped like a long hollow cylinder. The fuel elements were manufactured by vacuum impregnating the porous carbon cylinders with aqueous uranyl nitrate
Uranyl nitrate
Uranyl nitrate is a water soluble yellow uranium salt. The yellow-green crystals of uranium nitrate hexahydrate are triboluminescent.Uranyl nitrate can be prepared by reaction of uranium salts with nitric acid...
solution then air drying and baking them in a furnace ultimately producing a uranium oxide
Uranium oxide
Uranium oxide is an oxide of the element uranium.The metal uranium forms several oxides:* Uranium dioxide or uranium oxide * Uranium trioxide or uranium oxide...
coating tightly held in a porous graphite matrix. This fuel was expected to be substantially less expensive to manufacture than other types of fuel at the time. The primary advantages of this type of fuel was that the porosity of the pellet in addition to the high temperatures achievable would allow most of the poisons created by the fission products to migrate out of the fuel. The poisons would then be carried away by the coolant stream for eventual filtering out and removal. This allows a higher percentage of fuel to be burned up before the pellet needed replacement (up to 50%).
Disadvantages
The major disadvantage to porous reactor fuel is that the entire primary cooling loop including all the pumpPump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s, compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
s and 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 would be become highly contaminated with fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
s. Contamination caused by a potential contaminated coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...
leak would pose a significant danger to personnel and the environment. The high contamination level precludes being able to open the reactor vessel for the eventual refueling. Therefore the reactor was designed for remote online refuelling
Online refuelling
In nuclear power technology, online refuelling is a technique for changing the fuel of a nuclear reactor while the pile is critical.Online refuelling has been provided for three main reasons:...
Specifications
UHTREX had following specifications:- Fuel - highly enriched uranium
- Rated power - 3 MW (thermal)
- Core construction material - graphite
- Moderator - graphite
- Reactor vessel - carbon steel sphere 13 ft. 2 in. diameter 1.75 inches thickness.
- Fuel channels - 312 channels. Each one is 1.1 in. ID, 23.5 in. long and holds up to 4 fuel elements.
- Fuel element - 1 in. OD, 0.5 in. ID and 5.5 in. long (25.4 mm x 12.7 mm x 139.7 mm).
- Core power density - 1.3 W/cc
- Fuel utilization - up to 50%.
- Coolant - heliumHeliumHelium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
at 500 psiPounds per square inchThe pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
(3.45 MPa) - Coolant temperature - inlet 1600 °F , Outlet 2400 °F (871 °C and 1316 °C).
- Coolant flow rate - 10,250 pounds per hour (1.294 kg/s)
where ID and OD are the inner and outer diameter, respectively.
See also
- Omega West ReactorOmega West Reactor (OWR)The Omega West Reactor was an experimental nuclear reactor located at Los Alamos National Laboratory in Los Alamos NM. OMR was completed in 1956 and primarily used for scientific scale nuclear research until it was fully decommissioned in 1994. It operated 24 hours a day, five days a week until...
- ClementineClementine (nuclear reactor)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...