DUCRETE (Depleted Uranium Concrete) is a high density
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
alternative investigated for use in construction of casks for storage of
radioactive waste
Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...
. It is a
composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
containing
depleted uranium
Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium with a lower content of the fissile isotope than natural uranium.: "Depleted uranium possesses only 60% of the radioactivity of natural uranium, hav ...
dioxide
aggregate
Aggregate or aggregates may refer to:
Computing and mathematics
* collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...
instead of conventional gravel, with a
Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
binder.
Background and development
In 1993, the
United States Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...
Office of Environmental Management 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
Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...
) 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.
[M. J. Haire and S. Y. Lobach,]
2)-concrete material"">"Cask size and weight reduction through the use of depleted uranium dioxide (DUO2)-concrete material"
, Waste Management 2006 Conference, Tucson, Arizona, February 26-March 2, 2006.
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
Gamma (uppercase , lowercase ; ''gámma'') is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter re ...
shielding, and low atomic number (water bonded in the concrete) for
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
shielding.
[ There exists an optimum 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 Depleted Uranium Oxide (DUO2) and the cement phase with water to attenuate the neutron flux.
The key to effective shielding with depleted uranium ceramic concrete is maximum uranium oxide density. Unfortunately, the densest depleted uranium oxide is also the most chemically unstable. DUO2 has a maximum theoretical density of 10.5 g/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 aggregate is used, this transitions can result in an expansion that may generate stresses that could crack the material, lowering its compressive strength. ). Another limitation for the direct use of depleted uranium dioxide fine powder 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
Toxicity characteristic leaching procedure (TCLP) is a soil sample extraction method for chemical analysis employed as an analytical method to simulate leaching through a landfill. The testing methodology is used to determine if a waste is charac ...
(TCLP), which is used to assess heavy metal risks to the environment.
Production
U.S. method
DUCRETE is produced by mixing a DUO2 aggregate
Aggregate or aggregates may refer to:
Computing and mathematics
* collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...
with Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
. 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 (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
. This compound is highly reactive and cannot be used in the DUCRETE.[ Uranium hexafluoride must therefore be ]oxidized
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
into triuranium octoxide
Triuranium octoxide (U3O8) is a compound of uranium. It is present as an olive green to black, odorless solid. It is one of the more popular forms of yellowcake and is shipped between mills and refineries in this form.
U3O8 has potential long-ter ...
and uranium trioxide. These compounds are then converted to UO2 ( uranium oxide) through the addition of hydrogen 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 (). The low-atomic number binder is then added and undergoes pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
. The compound then undergoes liquid phase sintering Liquid phase sintering is a sintering technique that uses a liquid phase to accelerate the interparticle bonding of the solid phase. In addition to rapid initial particle rearrangement due to capillary forces, mass transport through liquid is genera ...
at 1300 °C until the desired density is achieved, usually around 8.9 g/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 binder 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 storage system for high level waste
High-level waste (HLW) 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.
* Waste formed by vitr ...
(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
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
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.][ May 3, 2020]
References
{{Reflist, 33em
External links
* http://web.ead.anl.gov/uranium/pdf/IHLWM_Dole_paper.pdf
* http://web.ead.anl.gov/uranium/pdf/DUCRETEIntroductionJune2003.pdf
* http://web.ead.anl.gov/uranium/pdf/ducretecosteffec.pdf
* http://web.ead.anl.gov/uranium/pdf/Global99Paper2.pdf
Concrete
Radioactive waste