Storage of nuclear materials by encapsulation in fullerenes

A method of encapsulating radioactive materials inside fullerenes for stable long-term storage. Fullerenes provide a safe and efficient means of disposing of nuclear waste which is extremely stable with respect to the environment. After encapsulation, a radioactive ion is essentially chemically isolated from its external environment.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the field of waste disposal, 
and, more specifically, to the encapsulation and isolation of nuclear 
materials, including waste products, inside fullerenes. The invention is a 
result of a contract with the Department of Energy (Contract No. 
W-7405-ENG-36). 
The disposal of nuclear materials, particularly nuclear waste materials 
created from sources such as nuclear power production, nuclear weapon 
programs, and medicine has plagued the nuclear power industry, as well as 
the scientific community, for decades. The facts that erected low level 
disposal sites have not opened, and that the current political climate 
does not favor the installation of new sites, indicate that the prospect 
for safe and adequate nuclear waste disposal in the near future is dim. 
This lack of disposal facilities will limit the future of nuclear power 
production at a time when a lowering of emissions from fossil fuel plants 
is needed. 
With some nuclear isotopes having half lives of thousands of years, the 
need to provide especially stable storage facilities is clearly shown. 
However, natural features, such as ground water levels, soil 
characteristics and earthquake potential, make finding a suitable site 
extremely difficult, even when disregarding the political problems. 
Examples of the problems involved with disposal is illustrated by the 
problems with the opening of the Waste Isolation Pilot Plant in New 
Mexico, and with the opposition mounted to development of the Yucca 
Mountain project in Nevada. With the increasing realization of the long 
term required for storage, and of the need to prevent escape of waste 
products into water supplies, renders the need for alternative safe 
disposal methods of paramount importance. 
Recently, researchers have discovered a new form of carbon molecules known 
as "fullerenes." This discovery has sparked the interest of a large 
segment of the scientific community, and has led to the conception of 
numerous practical applications for the molecules. Some of the better 
known fullerenes include C.sub.60 (buckminsterfullerene) which has 
icosohedral symmetry, consisting of 12 five-membered rings and 20 
six-membered rings, resembling the patchwork faces of a soccer ball; the 
ellipsoidally shaped C.sub.70, and C.sub.84 ; and the giant, spherically 
shaped C.sub.256. 
Studies of fullerenes have indicated that this material exhibits a 
remarkable range of physical and chemical properties. For example, various 
metal ions have been encapsulated within a fullerene cage. Also, 
fullerenes have been shown to have low density and unusually high thermal 
and mechanical stability, and have been generated with metals to form 
materials in which the metal ions are positioned inside the hollow 
fullerene cage. 
With the current state of concern over the proper storage of nuclear 
materials, it would be of immeasurable benefit to be able to encapsulate 
such waste inside a stable molecule. Previous attempts at such binding 
have involved encapsulation within glasses, ceramics, or cements. In this 
encapsulation technology, each metal ion or cluster of ions is surrounded 
by relatively few matrix atoms. Additionally, the stability of such 
glasses is affected by the encapsulated material. 
Because of radiation damage caused by the decay process, materials produced 
using the above methods suffer progressive degradation of the matrix 
molecular structure, allowing for the slow release of decay products, as 
well as the leaching of the parent isotope into the environment. This is 
not the case with fullerenes. 
The remarkable stability of the fullerene cages will allow them to 
withstand the nuclear decay processes without severe degradation, assuring 
that the nuclear products will remain immobilized. Additionally, the 
fullerene molecules exhibit self-healing properties, meaning that in the 
event of a rupture, the partially broken cage will reclose. It is also 
likely that the synthesis of fullerene encapsulated metals can be carried 
out efficiently on a large scale, making the process attractive for 
nuclear waste disposal and storage. These features have led to the present 
invention, in which radioactive wastes are encapsulated within the 
fullerene molecule. 
It is therefore an object of the present invention to provide a secure 
means for storage of radioactive materials. 
It is another object of the present invention to provide a method for 
storing radioactive waste materials. 
Additional objects, advantages and novel features of the invention will be 
set forth in part in the description which follows, and in part will 
become apparent to those skilled in the art upon examination of the 
following, or may be learned by practice of the invention. The objects and 
advantages of the present invention may be realized and attained by means 
of the instrumentalities and combinations particularly pointed out in the 
appended claims. 
SUMMARY OF THE INVENTION 
To achieve the foregoing and other objects, and in accordance with the 
purposes of the present invention, as embodied and broadly described 
herein, the present invention comprises a waste material encapsulated 
inside a fullerene molecule.

DETAILED DESCRIPTION 
The present invention provides for the safe storage of nuclear materials 
inside the molecular structure of fullerenes as waste form. In the 
invention, uranium, plutonium or another radioactive waste product, is 
encapsulated inside the fullerene structure. This arrangement provides for 
extremely stable storage of the radioactive waste. Upon such 
encapsulation, a radioactive ion is chemically isolated from the external 
environment. 
Additionally, because of the relatively low recoil energy of the 
radioactive decay fragments and the high number of modes in fullerene 
molecules available to dissipate that energy, the products from these 
nuclides will remain entrapped within the fullerene cage. The 
encapsulation of metal ions inside fullerenes has been previously 
demonstrated. However, the particular problem of fullerene encapsulation 
of plutonium or other radioactive material with high or low specific 
activity has not been addressed. 
With fullerenes, each metal ion is isolated both from other metal ions, and 
from the chemical environment. In the case of C.sub.60, each metal ion can 
be considered to be coordinated with 60 carbon atoms. 
To accomplish this encapsulation, fullerenes or fullerides are produced by 
conventional means, most likely through a three-step process. This process 
involves first generating a fullerene-containing soot. Next, the 
fullerenes are extracted from the soot. Finally, the different fullerenes 
are separated. For encapsulation, the metal ions are introduced into the 
reaction zone during the generation of soot. 
The step of soot generation and actinide encapsulation can be accomplished 
through various processes. One process is the consumption of composite 
graphite rods, which contain the actinide to be encapsulated, in an 
electrical arc in an inert atmosphere, such as helium or argon, and the 
simultaneous condensation if the resulting soot. Alternatively, fullerene 
encapsulated metals can be produced in sooting benzene flames, with the 
actinide vapor or halide vapor introduced into the flames, or by induction 
heating of composite rods with RF energy. An example of the benzene method 
is disclosed in "Combustion Synthesis of Fullerenes," J. T. McKinnon et 
al., Combustion and Flame, Vol. 88, pp. 102-112, 1992, which is included 
herein for all purposes. The RF energy method is disclosed in "A New 
Fullerene Synthesis," G. Peters et al., Agnew. Chem. Int. Ed. Engl., Vol. 
31, pp. 223-224, 1992, which is also included herein for all purposes. 
The fullerene and encapsulated actinide fullerene extracts are extracted 
using toluene or other appropriate solvents. They could also be separated 
by gaseous diffusion or fractional sublimation, which should yield the 
processing of much greater volumes without the use of any solvents. 
Perhaps the most important radioactive material to be encapsulated would be 
plutonium. However, other examples of radioactive materials are which 
could be encapsulated are all transuranic wastes, strontium, technetium, 
and thorium. 
The foregoing description of the preferred embodiments of the invention 
have been presented for purposes of illustration and description. It is 
not intended to be exhaustive or to limit the invention to the precise 
form disclosed, and obviously many modifications and variations are 
possible in light of the above teachings. The embodiments were chosen and 
described in order to best explain the principles of the invention and its 
practical application to thereby enable others skilled in the art to best 
utilize the invention in various embodiments and with various 
modifications as are suited to the particular use contemplated. It is 
intended that the scope of the invention be defined by the claims appended 
hereto.