Patent Number: 051606968
Section: summary

Present nuclear waste strategies, centered about geologic repository storage, require geologic stability and separation of wastes from human contact for tens of thousands of years. Transmutation offers the potential for transforming the time scales associated with such storage to hundreds of years or less. Transmutation of long-lived nuclear wastes to short-lived or stable isotopes has been studied for many years. A sampling of illustrative techniques was presented in a recent symposium in a presentation entitled "A Conceptual Study Of Actinide Transmutation System With Proton Accelerator(1) Target Neutronics Calculation," by H. Takada, I. Kanno, T. Takizuka, T. Ogawa, T. Nishida, and Y. Kaneko, Proceedings Of The 2nd International Symposium On Advanced Nuclear Energy Research-Evolution By Accelerators, January 24-26, 1990, Mito, Ibaraki, Japan. The authors describe a transmutation apparatus using keV neutrons which requires large material inventories to achieve significant transmutation rates since cross sections for neutron capture are small at these neutron energies. Moreover, the proton beam is admitted to the subcritical reactor target using a window, which limits the neutron flux available for the process. The direct interaction between the proton beam and the sodium coolant will produce substantial quantities of oxygen, carbon, nitrogen, and hydrogen spallation products, which may combine to generate tar. Finally, degradation of the cladding material for the nuclear waste as a result of proton bombardment may present a lifetime problem. In "Accelerator Molten-Salt Breeding And Thorium Fuel Cycle," by Kazuo Furukawa, Yasuaki Nakahara, Yoshio Kato, Hideo Ohno, and Kohshi Mitachi, Proceedings Of The 2nd International Symposium On Advanced Nuclear Energy Research-Evolution By Accelerators, January 24-26, 1990, Mito, Ibaraki, Japan, the authors describe a windowless apparatus accepting high proton beam currents having GeV energies which are caused to impinge directly on the target materials as in the Takada et al. reference except cooled by molten salt. Transmutation is achieved using keV neutrons where the low cross sections of the neutrons require large inventories to achieve useful transmutation throughput. Additionally, since the thorium is mixed with lithium fluoride, proton spallation will again produce bothersome tars. In "Status Report Of The SIN Neutron Source," by F. Atchison and W. E. Fischer, Proceedings Of International Collaboration On Advanced Neutron Sources (ICANS-VII), Sep. 13-16, 1983, Atomic Energy Of Canada, Limited, Report AECL-8488, the authors disclose a low-power target for low flux neutron production in Pb-Bi from neutron bombardment with subsequent neutron thermalization using heavy water. Heat is removed from the target by thermal convection, and the low power levels also permit the use of a window between the accelerator vacuum and the target. The proton beam strikes the target from below which has advantages for the thermal convection cooling. Accordingly, it is an object of the present invention to efficiently transmute higher actinides and other nuclear wastes. Another object of my invention is to generate power from fertile materials while transmuting the fission and other waste in order to avoid long-term storage. Yet another object of the present invention is to generate tritium drawing on an external electric power source, and without generation of waste requiring long-term storage. SUMMARY OF THE INVENTION To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the apparatus for generating power from fertile nuclear materials and transmuting wastes therefrom to less radioactive species may include a source of high intensity, high-energy beam of protons, a liquid-metal spallation target having an upwardly facing open surface for producing a high neutron flux upon being impacted by high-energy protons, a substantially gas-tight enclosure surrounding the spallation target, windowless apparatus for directing the beam of protons onto the open surface of the spallation target, a neutron moderator for thermalizing neutrons generated from the spallation target, a container for holding fertile nuclear material located within the neutron moderator and spaced apart from and outside of the spallation target, and a container for holding materials to be transmuted located within the neutron moderator and spaced apart and outside of the spallation target, yet closer thereto than the fertile nuclear material container. In another aspect of the present invention, in accordance with its objects and purposes, the apparatus for transmuting higher actinide waste along with .sup.99 Tc, .sup.129 I, and other fission product waste may include a source of high intensity, high-energy of protons, a liquid-metal spallation target having an upwardly facing open surface for producing a high neutron flux upon being impacted by high-energy protons, a substantially gas-tight enclosure surrounding the spallation target, windowless apparatus for directing the beam of protons onto the open surface of the spallation target, a neutron moderator for thermalizing neutrons generated from the spallation target, and a container for holding the material to be transmuted located within the neutron moderator and spaced apart from and outside of the spallation target. In yet another aspect of the present invention, in accordance with its objects and purposes, the apparatus for simultaneously transmuting higher actinide materials and producing tritium may include: a source of high intensity, high-energy protons, a liquid-metal spallation target having an upwardly facing open surface for producing a high neutron flux upon being impacted by high-energy protons, a substantially gas-tight enclosure surrounding the spallation target, windowless apparatus for directing the beam of protons onto the open surface of the spallation target, a neutron moderator for thermalizing neutrons generated from the spallation target, a container for holding the higher actinide materials located within the neutron moderator and spaced apart from and outside of the spallation target, and a container located within the neutron moderator and spaced apart from the spallation target for holding materials which generate tritium upon interaction with neutrons. Benefits and advantages of the present invention include power production from .sup.238 U, .sup.232 Th, and from burning defense and commercial higher actinide waste without long-term waste management, avoiding long term management of commercial spent fuel by fission product transmutation using .sup.239 Pu from reprocessing tritium production while burning higher actinide waste, .sup.238 U and .sup.232 Th. Another benefit of the present invention includes the avoidance of the major problem of current nuclear reactors which is catastrophic runaway. Since the fission products can be continually removed from the molten salt stream and the inventory of fissile material is small, the probability and consequences of a loss-of-coolant accident also are significantly reduced. The probability of such an accident is greatly reduced since this system operates well below nuclear criticality and requires no control rods. 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 invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.