Ducrete
Encyclopedia
DUCRETE is a high density concrete
alternative investigated for use in construction of casks for storage of radioactive waste
. It is a composite material
containing depleted
uranium dioxide aggregate
instead of conventional gravel and a Portland cement binder.
Office of Environmental Managment initiated investigation into the potential use of Depleted Uranium in heavy concretes. The aim of this investigation was to simultaneously find an application for depleted Uranium and to create a new and more efficient method for the storage and transportation of spent nuclear fuels. The material was first conceived at the Idaho National Engineering and Environmental Laboratory (INEEL) by W. Quapp and P. Lessing, who jointly developed the processes behind the material and were awarded both U.S. and foreign patents in 1998 and 2000, respectively.
The key to effective shielding with depleted uranium ceramic concrete is maximun uranium oxide density. Unfortunately, the densest depleted uranium oxide is also the most chemically unstable. Depleted uranium dioxide, or DUO2, has a maximum theoretical density of 10.5 gm/cm3 at 95% purity. However, under oxidation conditions, this material readily transforms into the more stable depleted uranium trioxide (DUO3) or depleted triuranium octaoxide (DU3O8). Thus, if naked UO2 aggregates is used, this transitions can result in an expansion that could generate stresses that could crack the material, lowering its compressive strength. ).. Another limitation for the direct use of depleted uranium dioxide fine power is that concretes depend on their coarse aggregates to carry compressive stresses. In order to overcome these issues, DUAGG was developed.
DUAGG (depleted uranium aggregate) is the term applied to the stabilized DUO2 ceramic. This consists of sintered DUO2 particles with a silicate-based coating that covers the surfaces and fills the spaces between the grains, acting as an oxygen barrier, as well as corrosion and leach resistance. DUAGG has a density up to 8.8 g/cm3 and replaces the conventional aggregate in concrete, producing concrete with a density of 5.6 to 6.4 g/cm3, compared to 2.3 g/cm3 for conventional concrete..
Also, DUCRETE presents environmentally friendly properties. The table below shows the effectiveness of converting depleted uranium into concrete, since potential leaching is decreased in a high order. The leach test used was the EPA Toxicity characteristic leaching procedure (TCLP), which is used to assess heavy metal risks to the environment.
with Portland cement
. DU is a result of the enrichment of Uranium for use in nuclear power generation and other fields. DU usually comes bonded with Fluorine in Uranium hexafluoride
. This compound is highly reactive and cannot be used in the DUCRETE. Uranium hexafluoride
must therefore be oxidized into U3O8 and UO3. These compounds are then converted to UO2 Uranium oxide
through the addition of H gas. The UO2 is then dried, crushed, and milled into a uniform sediment. This then converted into small inch long briquettes through the use of high pressure(6000psi). The low atomic number binder is then added and undergoes pyrolysis
. The compound then undergoes liquid phase sintering at 1300 Celsius until the desired density is achieved, usually around 8.9g/cm3. The briquettes are then crushed and gap sorted and are now ready to be mixed into DUCRETE.
and UO2 after it is crushed.
system for high level waste
(HLW) and spent nuclear fuel
(SNF). In such a system, the composite would be the primary component used to shield radiation from workers and the public. Cask systems made from DUCRETE are smaller and lighter in weight than casks made from conventional materials, such as traditional concrete. DUCRETE containers need only be about 1/3 as thick to provide the same degree of radiation shielding as concrete systems.
Analysis has shown that DUCRETE is more cost effective than conventional materials. The cost for the production of casks made with DUCRETE is low when compared with other shielding materials such as steel
, lead
and DU metal, since less material is required as a consequence of a higher density. In a study by Duke Engineering at a nuclear waste facility at Savannah River, the DUCRETE cask system was evaluated at a lower cost than an alternative Glass Waste storage building. However, disposal of the DUCRETE was not considered. Since DUCRETE is a low level radioactive composite, its relatively expensive disposal could decrease the cost effectiveness of such systems. An alternative to such disposal is the use of empty DUCRETE casks as a container for high activity low-level waste.
While DUCRETE shows potential for future nuclear waste programs, such concepts are far from utilization. So far, no DUCRETE cask systems have been licensed in the U.S.
Concrete
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...
alternative investigated for use in construction of casks for storage of radioactive waste
Radioactive waste
Radioactive 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...
. It is a composite material
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
containing depleted
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...
uranium dioxide aggregate
Aggregate (composite)
Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. For efficient filling, aggregate should be much smaller than the finished item, but have a wide variety of sizes...
instead of conventional gravel and a Portland cement binder.
Background and Development
In 1993, the United States Department of EnergyUnited States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
Office of Environmental Managment initiated investigation into the potential use of Depleted Uranium in heavy concretes. The aim of this investigation was to simultaneously find an application for depleted Uranium and to create a new and more efficient method for the storage and transportation of spent nuclear fuels. The material was first conceived at the Idaho National Engineering and Environmental Laboratory (INEEL) by W. Quapp and P. Lessing, who jointly developed the processes behind the material and were awarded both U.S. and foreign patents in 1998 and 2000, respectively.
Description
DUCRETE is a kind of concrete that replaces the standard coarse aggregate with a depleted uranium ceramic material. All of the other materials present in DUCRETE (portland cement, sand and water) are used in the same volumetric ratio used for ordinary concrete. This ceramic material is a very efficient shielding material since it presents both high atomic number (uranium) for gamma shielding, and low atomic number (water bonded in the concrete) for neutron shielding. It exists an optimun uranium-to-binder ratio for a combined attenuation of gamma and neutron radiation at a given wall thickness. A balance needs to be established between the attenuation of the gamma flux in the DUO2 and the cement phase with water to attenuate the neutron flux.The key to effective shielding with depleted uranium ceramic concrete is maximun uranium oxide density. Unfortunately, the densest depleted uranium oxide is also the most chemically unstable. Depleted uranium dioxide, or DUO2, has a maximum theoretical density of 10.5 gm/cm3 at 95% purity. However, under oxidation conditions, this material readily transforms into the more stable depleted uranium trioxide (DUO3) or depleted triuranium octaoxide (DU3O8). Thus, if naked UO2 aggregates is used, this transitions can result in an expansion that could generate stresses that could crack the material, lowering its compressive strength. ).. Another limitation for the direct use of depleted uranium dioxide fine power is that concretes depend on their coarse aggregates to carry compressive stresses. In order to overcome these issues, DUAGG was developed.
DUAGG (depleted uranium aggregate) is the term applied to the stabilized DUO2 ceramic. This consists of sintered DUO2 particles with a silicate-based coating that covers the surfaces and fills the spaces between the grains, acting as an oxygen barrier, as well as corrosion and leach resistance. DUAGG has a density up to 8.8 g/cm3 and replaces the conventional aggregate in concrete, producing concrete with a density of 5.6 to 6.4 g/cm3, compared to 2.3 g/cm3 for conventional concrete..
Also, DUCRETE presents environmentally friendly properties. The table below shows the effectiveness of converting depleted uranium into concrete, since potential leaching is decreased in a high order. The leach test used was the EPA Toxicity characteristic leaching procedure (TCLP), which is used to assess heavy metal risks to the environment.
| Uranium form | U concentration in leachate (mg U/L) |
|---|---|
| DUCRETE | 0.42 |
| DUAGG | 4 |
| UO2 | 172 |
| U3O8 | 420 |
| UF4 | 7367 |
| UO3 | 6900 |
U.S. Method
DUCRETE is produced by mixing a DUO2 aggregateAggregate
An aggregate is a collection of items that are gathered together to form a total quantity.* Aggregate , in materials science, a component of a composite material used to resist compressive stress...
with Portland cement
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
. DU is a result of the enrichment of Uranium for use in nuclear power generation and other fields. DU usually comes bonded with Fluorine in Uranium hexafluoride
Uranium hexafluoride
Uranium hexafluoride , referred to as "hex" in the nuclear industry, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure , is highly toxic, reacts violently with water...
. This compound is highly reactive and cannot be used in the DUCRETE. Uranium hexafluoride
Uranium hexafluoride
Uranium hexafluoride , referred to as "hex" in the nuclear industry, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure , is highly toxic, reacts violently with water...
must therefore be oxidized into U3O8 and UO3. These compounds are then converted to UO2 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...
through the addition of H gas. The UO2 is then dried, crushed, and milled into a uniform sediment. This then converted into small inch long briquettes through the use of high pressure(6000psi). The low atomic number binder is then added and undergoes pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
. The compound then undergoes liquid phase sintering at 1300 Celsius until the desired density is achieved, usually around 8.9g/cm3. The briquettes are then crushed and gap sorted and are now ready to be mixed into DUCRETE.
VNIINM (Russian) Method
The VNIINM method is very similar to the U.S. method except it does not gap sort the binderBinder
The reaper-binder, or binder, was a farm implement that improved upon the reaper. The binder was invented in 1872 by Charles Withington. In addition to cutting the small-grain crop, it would also tie the stems into small bundles, or sheaves...
and UO2 after it is crushed.
Applications
After processing, DUCRETE composite may be used in container vessels, shielding structures, and containment storage areas, all of which can be used to store radioactive waste. The primary implementation of this material is within a dry cask storageDry 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...
system for high level waste
High level waste
High level waste is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:* First and second cycle raffinate and other waste streams created by nuclear reprocessing....
(HLW) and spent nuclear fuel
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...
(SNF). In such a system, the composite would be the primary component used to shield radiation from workers and the public. Cask systems made from DUCRETE are smaller and lighter in weight than casks made from conventional materials, such as traditional concrete. DUCRETE containers need only be about 1/3 as thick to provide the same degree of radiation shielding as concrete systems.
Analysis has shown that DUCRETE is more cost effective than conventional materials. The cost for the production of casks made with DUCRETE is low when compared with other shielding materials such as steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and DU metal, since less material is required as a consequence of a higher density. In a study by Duke Engineering at a nuclear waste facility at Savannah River, the DUCRETE cask system was evaluated at a lower cost than an alternative Glass Waste storage building. However, disposal of the DUCRETE was not considered. Since DUCRETE is a low level radioactive composite, its relatively expensive disposal could decrease the cost effectiveness of such systems. An alternative to such disposal is the use of empty DUCRETE casks as a container for high activity low-level waste.
While DUCRETE shows potential for future nuclear waste programs, such concepts are far from utilization. So far, no DUCRETE cask systems have been licensed in the U.S.