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Separation technologies are of crucial importance to the goal of significantly reducing the volume of high-level nuclear waste, thereby reducing the long-term health risks to mankind. International co-operation, including the sharing of concepts and methods, as well as technology transfer, is essential in accelerating research and development in the field. The writers of this book are all internationally recognised experts in the field of separation technology, well qualified to assess and criticize the current state of separation research as well as to identify future opportunities for the application of separation technologies to the solution of nuclear waste management problems. The major emphases in the book are research opportunities in the utilization of innovative and potentially more efficient and cost effective processes for waste processing/treatment, actinide speciation/separation methods, technological processing, and environmental restoration.
Disposal of radioactive waste from nuclear weapons production and power generation has caused public outcry and political consternation. Nuclear Wastes presents a critical review of some waste management and disposal alternatives to the current national policy of direct disposal of light water reactor spent fuel. The book offers clearcut conclusions for what the nation should do today and what solutions should be explored for tomorrow. The committee examines the currently used "once-through" fuel cycle versus different alternatives of separations and transmutation technology systems, by which hazardous radionuclides are converted to nuclides that are either stable or radioactive with short half-lives. The volume provides detailed findings and conclusions about the status and feasibility of plutonium extraction and more advanced separations technologies, as well as three principal transmutation concepts for commercial reactor spent fuel. The book discusses nuclear proliferation; the U.S. nuclear regulatory structure; issues of health, safety and transportation; the proposed sale of electrical energy as a means of paying for the transmutation system; and other key issues.

Nuclear Wastes

National Research Council (U.S.). Committee on Separations Technology and Transmutation Systems

Published: 1996

Total Pages: 600


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Presents a critical review of some waste management and disposal alternatives to the current national policy of direct disposal of light water reactor spent fuel. The committee explores the currently-used once through fuel cycle versus different alternatives of separations and transmutation techno
The production of electricity by nuclear fission is, at present, nearly 366- gigawatt electric (GWe), generated from 438 operating nuclear reactors. Unlike fossil fuel ash, with limited residual available energy content and negligible heat content, the spent nuclear fuel from power production reactors contains moderate amounts of transuranium (TRU) actinides and fission products in addition to the still slightly enriched uranium. Originally nuclear technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel for military purposes. Military plutonium separations had essentially ceased by the mid-1990s. Reprocessing, however, can serve multiple purposes and the relative importance has changed over time. In the 1960's the vision of the introduction of plutonium-fueled fast-neutron breeder reactors drove the civilian separation of plutonium. More recently, reprocessing has been regarded as a means to facilitate the disposal of high-level nuclear waste and thus requires development of radically different technical approaches. In the last decade or so, principal reason for reprocessing has shifted to spent power reactor fuel being reprocessed 1) so that unused uranium and plutonium being recycled reduce the volume, gaining some 25% to 30% more energy from the original uranium in the process and thus contributing to energy security and 2) reduce the volume and radioactivity of the waste by recovering all long-lived actinides and fission products followed by recycling them in fast reactors where they are transmuted to short-lived fission products; this reduces the volume to about 20%, reduces the long term radioactivity level in the high-level waste, and complicates the possibility of the plutonium being diverted from civil use - thereby increasing the proliferation resistance of the fuel cycle.
An accelerator-driven subcritical nuclear system is briefly described that transmutes actinides and selected long-lived fission products. An application of this accelerator transmutation of nuclear waste (ATW) concept to spent fuel from a commercial nuclear power plant is presented as an example. The emphasis here is on a possible aqueous processing flowsheet to separate the actinides and selected long-lived fission products from the remaining fission products within the transmutation system. In the proposed system the actinides circulate through the thermal neutron flux as a slurry of oxide particles in heavy water in two loops with different average residence times: one loop for neptunium and plutonium and one for americium and curium. Material from the Np/Pu loop is processed with a short cooling time (5-10 days) because of the need to keep the total actinide inventory, low for this particular ATW application. The high radiation and thermal load from the irradiated material places severe constraints on the separation processes that can be used. The oxide particles are dissolved in nitric acid and a quarternary, ammonium anion exchanger is used to extract neptunium, plutonium, technetium, and palladium. After further cooling (about 90 days), the Am, Cm and higher actinides are extracted using a TALSPEAK-type process. The proposed operations were chosen because they have been successfully tested for processing high-level radioactive fuels or wastes in gram to kilogram quantities.
Accurate knowledge of actinide fission yields is a prerequisite for numerous applications, such as nuclear forensics, nuclear safeguards, nuclear waste management, and sub-critical fission/fusion reactor kinetics. The experimental measurement of long-lived fission fragments of various actinides has been an active area of interest in the nuclear community over several decades. However, fission yields of the shorter-lived (half-life 3 days) radionuclides were typically obtained through modelling and extrapolation of the available data, causing relatively high uncertainties (up to 64%). The lack of experimental measurements for short-lived fission products is associated with a combination of challenges related to the complexity of the sample (a mixture of hundreds of radionuclides), controllability of the experiment (knowledge of neutron source), time management (pace of radioactive decay), and counting statistics (significant gamma-ray interferences). The experimental fission yield data limitations are particularly pronounced for the fast neutron (0.1 MeV) energy spectrum because of the limited availability of research nuclear reactors with hard neutron spectra. This research aims to fill this gap in nuclear data by measuring and characterizing short-lived (half-lives from 10 minutes to 3 days) fission fragments of Th-232, using rapid radiochemical separation techniques to remove interfering neutron activation products and using the Penn State Breazeale Reactor's (PSBR Fast Neutron Irradiator (FNI) fixture as a source of fast neutrons. As a part of this work, the neutron spectrum in the FNI was fully characterized using the multi-foil activation technique, Monte Carlo software predictions, and the Pacific Northwest National Laboratory's STAYSL neutron flux adjustment software. A high purity germanium (HPGe) gamma-ray spectrometer was fully characterized by using the GEANT4 Cascade Summing Correction (G4CSC) code, and the simulation results were validated by comparing them with experimental measurements of known standard sources. In addition, the HPGe detector was fully calibrated using a customized multi-nuclide multi gamma-ray emitting calibration source. The results of the FNI fixture characterization were used to determine the optimal experimental parameters for achieving approximately 108 fissions in the sample, and the expected gamma-ray spectra were simulated using the GEANT4 model of the HPGe detector. A 27.18 mg thorium sample was irradiated at the FNI fixture with the reactor power at 200 kW for 15 minutes. Then, the mix of fission products and Th-233 (an activation product) was measured using the HPGe (Blue) detector for 15 minutes, after 22.3 minutes from the end of irradiation. Next, the bulk of the fission products were isolated from the Th-233 using ion-exchange chromatography. The sample containing thorium fission products was repetitively counted sixteen times, ranging in durations from five minutes to 12 hours. The first 5-minute measurement was conducted 85.3 minutes after the completion of the irradiation. Finally, the experimentally determined fission yields were compared to the reported values in the Evaluated Nuclear Data Files (ENDF) and the Joint Evaluated Fission/Fusion Files (JEFF) libraries. The evaluation revealed that in this study, the cumulative fission yields of nine thorium fission products were determined with improved uncertainties compared to those reported in JEFF 3.3. The measurement uncertainties of ten fission products were also found to be lower than the uncertainties presented in ENDF/B-VIII.0. Furthermore, the scope of this research includes performing the necessary calculations and simulations for subsequent measurements of short-lived fission fragments of U-233, U-235, and U-238. Consequently, this work provides all the experimental parameters required for studying the uranium isotopes, as well as the estimated gamma-ray spectra at various decay times.