Technical Background:
Depleted uranium (DU) is a residual material that results from the enrichment of uranium ore in the making of nuclear fuel. The U.S. Department of Energy (DOE) maintains large inventories of
depleted uranium at several sites. Approximately 560,000 metric tons of DU in the form of UF6,
containing an equivalent mass of 379,000 metric tons of uranium are stored at the DOE Paducah,
Portsmouth and Oak Ridge Gaseous Diffusion plants in cylindrical steel canisters. Maintenance of
these canisters is costly and some have begun to leak, creating potential environmental, health, and
safety hazards. DOE recently issued an Expression of Interest to private industry for the conversion
of UF6 to more stable oxide forms. Several U.S. and international companies have already been marketing their conversion capability (e.g. Thermuhex Technologies Initiative, Cogema). Beneficial
end-use of stabilized depleted uranium oxide powder would reduce overall process costs, eliminate
disposal cost, and facilitate secondary applications for this valuable resource.
Technology Description:
Brookhaven National Laboratory (BNL) has completed preliminary work to investigate the feasibility of encapsulating DU in low density polyethylene to form a stable, dense product(U.S. Patent No. 6,303,549). DU loadings as high as 90 wt% were achieved. A maximum product density of 4.2
g/cm3 was achieved using UO3, but increased product density using UO2 is estimated at 6.1 g/cm3. Additional product density improvements up to about 7.2 g/cm3 were projected using DU aggregate
in a hybrid technique known as micro/macroencapsulation.
A recent DU market study by Kapline Enterprises, Inc. for DOE thoroughly identified and rated
potential applications and markets for DU metal and oxide materials.[(1)] polyethylene encapsulated DU, because of its
workability and high DU loading capability, could readily be fabricated as counterweights/ballast (for
use in airplanes, helicopters, ships and missiles), flywheels, armor, and projectiles. Also, polyethylene encapsulated DU is
an effective shielding material for both gamma and neutron radiation, with potential application for
shielding high activity waste (e.g., ion exchange resins, glass gems), spent fuel dry storage casks, and
high energy experimental facilities (e.g., accelerator targets) to reduce radiation exposures to workers
and the public.
Treatment of DU materials by polyethylene encapsulation is a desirable option because of the
immediate availability of the technology and proven record to effectively and efficiently process similar
powder and granular materials. In addition, the process is very flexible. Polyethylene products can
be heated and reworked if future needs change. DU can also be retrieved from the matrix by thermal
processing if needed as a resource in the future. Recycled plastics from industrial or post-consumer
sources can be used in place of virgin materials to reduce costs and produce valuable products entirely
from recycled materials. BNL has extensively developed, tested and demonstrated polyethylene
encapsulation processes for low-level radioactive, hazardous, and mixed wastes. During processing,
waste materials are mechanically mixed into the molten polyethylene binder, producing a workable
homogeneous product. The process is not susceptible to chemical interactions between the waste and
binder, enabling a wide range of acceptable waste types, high waste loadings, and technically simple
processing under heterogeneous waste conditions. The process has evolved from proof-of-principle,
through bench-scale development and testing, to full-scale technology demonstration and technology
transfer.
References:
1. Kaplan, S.A., "Depleted Uranium Market Study," Kapline Enterprises, Inc., Y/NA 1801,
August 1995.
