Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – By fixation in stable solid media
Reexamination Certificate
1999-06-22
2001-11-20
Jenkins, Daniel J. (Department: 1742)
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
By fixation in stable solid media
Reexamination Certificate
active
06320091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a process for making a ceramic composition suitable for immobilizing actinides, in particular plutonium, thorium and uranium. The ceramic composition comprises pyrochlore, brannerite and rutile. The ceramic composition is attractive for immobilization of excess plutonium because of its extremely low leachability, the existence of natural mineral analogues that have demonstrated actinide immobilization over hundreds of millions of years in wet geological environments, and the high solid solubility of actinides in the ceramic thus providing a relatively low overall waste volume. Incorporation of plutonium into ceramic provides a form that is relatively easy to store but renders retrieval of the plutonium to be more difficult than other immobilized forms. The process relates particularly to a cold pressing and sintering process for making said ceramic composition, which allows for impurities in the actinides feedstock.
2. Description of Related Art
Because of their extreme durability, ceramic forms have been studied extensively since the late 1970s for the immobilization of high level waste (HLW). The material called Synthetic Rock (SYNROC) is a titanate-based ceramic composed approximately of 30% zirconolite, 30% hollandite, 30% perovskite and 10% rutile. In the HLW application, actinides partition into the zirconolite and perovskite phases. U.S. Pat. Nos. 4,274,976 (Ringwood), 4,329,248 (Ringwood), 4,645,624 (Ramm, Ringwood) and 4,808,337 (Ramm et al) disclose the immobilization of HLW in synthetic rock.
A form of synthetic rock to immobilize spent fuel (SYNROC-F) was reported by S. E. Kesson and A. E. Ringwood, “Safe Disposal of Spent Nuclear Fuel”, Radioactive Waste Management and the Nuclear Fuel Cycle, Vol. 4(2), pp. 159-174, October 1983. This form of SYNROC consisted of 90 wt % uranium pyrochlore, 5 wt % hollandite and 5 wt % rutile.
A variant of SYNROC-F, namely SYNROC-FA was reported by A. G. Solomah, P. G. Richardson and A. K. Mcllwain, “Phase Identification, Microstructural Characterization, Phase Microanalyses and Leaching Performance Evaluation of SYNROC-FA Crystalline Ceramic Waste Form”, Journal of Nuclear Materials 148, pp. 157-165, 1987. This form of SYNROC consisted of uranium pyrochlore, perovskite, uraninite and hollandite.
A cold press and sinter process is used in the production of mixed oxide (MOX) fuel from uranium and plutonium. The MOX process uses pressing pressures in excess of 20,000 psi and sintering temperatures of 1,700 deg C. in a 4% H
2
atmosphere on a 24 hour cycle. Because the final product is to be used as fuel, impurities in the feedstock cannot be tolerated.
SUMMARY OF THE INVENTION
An object of this invention is to provide a process for making a ceramic material for immobilization of actinides, including plutonium, uranium, thorium, americium and neptunium, said immobilized actinides then being suitable for storage in an underground repository.
The desired characteristics of such a ceramic material include: a) low leachability, b) high solid solubility of actinides in the ceramic, c) ability to incorporate “high-fired” PuO
2
of nominal particle size of 20 microns and less than 50 microns, d) sufficient compositional flexibility to incorporate significant concentrations of Pu and neutron absorbers (such as gadolinium and hafnium) as well as varying impurities in the feed streams, e) thermal stability during high level waste glass pouring in can-in-canister configurations, f) high chemical durability in the geologic repository environments both before and after undergoing radiation damage from alpha decay, g) difficult recoverability of plutonium from the ceramic to impede proliferation.
The ceramic composition comprises pyrochlore, brannerite and rutile. A pyrochlore matrix provides the means to incorporate a higher concentration of plutonium than a zirconolite matrix. SYNROC compositions have contained hollandite, which the present composition does not. Other compositions have utilized reactive plutonium (such as dissolved plutonium) whereas the present composition starts with unreactive (“high fired”) plutonium. The present composition also tolerates greater than 50 wt % impurities in the actinide feedstocks. The present composition has been found to be stable when subjected to high level waste glass pouring in a storage canister. More specifically the mineralogical composition remains unchanged and the pellets retain their physical integrity.
The present invention also relates to a process for making said ceramic composition which involves milling the actinides to a fine powder, blending the actinide powder with ceramic precursors, granulating the blend to facilitate flow into the press and die set, cold pressing the blend, followed by sintering. This is in contrast to the SYNROC process, which involves hot uniaxial or isostatic pressing. In addition, processes producing SYNROC have formed hollandite, which the present process does not. The production of mixed oxide (MOX) fuel also uses a cold press and sinter process, however there are critical differences in process parameters, which lead to differences in the end products. In addition, the MOX process cannot tolerate impurities in the uranium and plutonium feedstocks, whereas the present process does (up to 55.7 wt % in the actinide feedstock).
REFERENCES:
patent: 4274976 (1981-06-01), Ringwood
patent: 4329248 (1982-05-01), Ringwood
patent: 4383855 (1983-05-01), Aaron et al.
patent: 4645624 (1987-02-01), Ramm et al.
patent: 4778626 (1988-10-01), Ramm et al.
patent: 5597516 (1997-01-01), Feng et al.
patent: 5613243 (1997-03-01), Hollit et al.
patent: 5656009 (1997-08-01), Feng et al.
A.G. Solomah, T.M. Hare, and H. Palmour III, “Demonstration of the Feasibility of Subsolidus Sintering of Radwaste-Containing SYNROC-B Composition,” Nucl. Technol. 49, 183-185 (1980).
F.W. Clinard, Jr., D.L. Rohr, and R.B. Roof, “Structural Damage in a Self-Irradiated Zirconolite-Based Ceramic,” Nucl. Inst. And Meth. in Phys. Res. B1, 581-586 (1984).
A.G. Solomah, P.G. Richardson, and A.K. McIllwain, “Phase Identification, Microstructural Characterization, Phase Microanalyses and Leaching Performance Evaluation of SYNROC-FA Crystalline Ceramic Waste Form,” J. Nucl. Mater. 148, 157-165 (1987).
V.M. Oversby, R.A. Van Konynenburg, W.E. Glassley, and P.G. Curtis, “Immobilization in Ceramic Waste Forms of the Residues from Treatment of Mixed Wastes,” Materials Research Society Symposium Proceedings, vol. 333, Scientific Basis for Nuclear Waste Management XVII, A. Barkatt and R.A. Van Konynenburg, eds., Materials Research Society, Pittsburgh, PA (1994), pp. 285-292.
R. Van Konynenburg, memorandum to Bill Halsey, “A Titanate Mineral Waste Form for Dismantled Weapons Plutonium,” Lawrence Livermore National Laboratory, Livermore, CA (Feb. 10, 1994).
B. Ebbinghaus, R. Van Konynenburg, E. Vance, A. Jostsons, R. Anthony, C. Philip, and D. Wronkiewicz, “Status of Plutonium Ceramic Immobilization Processes and Immobilization Forms,” pp. 253-261 in Final Proceedings, Plutonium Stabilization & Immobilization Workshop, CONF-951259, U.S. Department of Energy, Washington, D.C. (May 30, 1996).
B.B. Ebbinghaus, R.A. Van Konynenburg, J. M. Lawson, W. L. Close, P.G. Curtis, M.W.A. Stewart, E.R. Vance and M.L. Carter, “Progress on Ceramic Immobilized Forms for Pu Disposition”, Presented at 20th Actinide Separations Conference, Ithaca, IL, USA, Jun. 13, 1996, (copy not provided).
B.B. Ebbinghaus, R.A. Van Konynenburg, H. Shaw, R. Ryerson, P.G. Curtis, W.L. Close, R. Burns, J.M. Lawson, E.R. Vance, M.W.A. Stewart, R.A. Day, M.J. Hambley, A. Brownscombe, J. Allender, T. Rankin, J. Congdon, E. Buck, A. Bakel, R. Putnam and A. Navrotsky, “Ceramic Formulation for the Immobilization of Plutonium”, Presented at 21st Actinide Separations Conference, Charleston, SC, USA, Jun. 23-26, 1997.
Farmer, J.C., “U.S. Fissile Materials Disposition Program Form & Process Development Activities,” UCRL-MI-127979, Lawrence Livermore National Laboratory,
Armantrout Guy A.
Brummond William Allen
Curtis Paul G.
Ebbinghaus Bartley B.
Farmer Joseph
Caress Virginia B.
Chang Randall W.
Daubenspeck William C.
Jenkins Daniel J.
The United States of America as represented by the United States
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