Results 1 - 10 of 41
Results 1 - 10 of 41. Search took: 0.013 seconds
|Sort by: date | relevance|
[en] The results described in this report summarize the evaluations of potential benefits to a geologic repository for a variety of AFCI options that were studied during FY04. Many of the options were examined in response to a request by Burton Richter, chair of the Advanced Nuclear Transformation Technology (ANTT) Subcommittee of NERAC, to perform an initial evaluation of the potential benefit to a geologic repository from processing commercial spent nuclear fuel to separate certain chemical elements and to recycle some of these elements in thermal spectrum reactors such as light water reactors. The measure of repository benefit has been defined as the allowable increase in repository drift loading consistent with satisfying all repository thermal design limits, since loading of a geologic repository at Yucca Mountain is currently limited by temperature constraints. Such an increase in drift loading can be used to either reduce the size of a repository of given capacity, or to increase the capacity of a repository of a given size. Any changes in estimated peak dose caused by the resulting alteration in the radionuclide inventory of the repository have not been evaluated, but are the subject of a separate ongoing study
[en] Given the ability of fast reactors to effectively transmute the transuranic elements as are present in spent nuclear fuel, fast reactors are being considered as one element of future nuclear power systems to enable continued use and growth of nuclear power by limiting high-level waste generation. However, a key issue for fast reactors is higher electricity cost relative to other forms of nuclear energy generation. The economics of the fast reactor are affected by the amount of electric power that can be produced from a reactor, i.e., the thermal efficiency for electricity generation. The present study is examining the potential for fast reactor subassembly design changes to improve the thermal efficiency by increasing the average coolant outlet temperature without increasing peak temperatures within the subassembly, i.e., to make better use of current technology. Sodium-cooled fast reactors operate at temperatures far below the coolant boiling point, so that the maximum coolant outlet temperature is limited by the acceptable peak temperatures for the reactor fuel and cladding. Fast reactor fuel subassemblies have historically been constructed using a large number of small diameter fuel pins contained within a tube of hexagonal cross-section, or hexcan. Due to this design, there is a larger coolant flow area next to the hexcan wall as compared to flow area in the interior of the subassembly. This results in a higher flow rate near the hexcan wall, overcooling the fuel pins next to the wall, and a non-uniform coolant temperature distribution. It has been recognized for many years that this difference in sodium coolant temperature was detrimental to achieving greater thermal efficiency, since it causes the fuel pins in the center of the subassembly to operate at higher temperatures than those near the hexcan walls, and it is the temperature limit(s) for those fuel pins that limits the average coolant outlet temperature. Fuel subassembly design changes are being investigated using computational fluid dynamics (CFD) to quantify the effect that the design changes have on reducing the intra-subassembly coolant flow and temperature distribution. Simulations have been performed for a 19-pin test subassembly geometry using typical fuel pin diameters and wire wrap spacers. The results have shown that it may be possible to increase the average coolant outlet temperature by 20 C or more without changing the peak temperatures within the subassembly. These design changes should also be effective for reactor designs using subassemblies with larger numbers of fuel pins. R. Wigeland, Idaho National Laboratory, P.O. Box 1625, Mail Stop 3860, Idaho Falls, ID, U.S.A., 83415-3860 email 'roald.wigeland at inl.gov fax (U.S.)' 208-526-2930
[en] The sodium-cooled fast neutron reactor is currently being evaluated for the efficient transmutation of the highly-hazardous, long-lived, transuranic elements that are present in spent nuclear fuel. One of the fundamental choices that will be made is the selection of the fuel type for the fast reactor, whether oxide, metal, carbide, nitride, etc. It is likely that a decision on the fuel type will need to be made before many of the related technologies and facilities can be selected, from fuel fabrication to spent fuel reprocessing. A decision on fuel type should consider all impacts on the fast reactor system, including safety. Past work has demonstrated that the choice of fuel type may have a significant impact on the severity of consequences arising from accidents, especially for severe accidents of low probability. In this paper, the response of sodium-cooled fast reactors is discussed for both oxide and metal fuel types, highlighting the similarities and differences in reactor response and accident consequences. Any fast reactor facility must be designed to be able to successfully prevent, mitigate, or accommodate all consequences of potential events, including accidents. This is typically accomplished by using multiple barriers to the release of radiation, including the cladding on the fuel, the intact primary cooling system, and most visibly the reactor containment building. More recently, this has also included the use of 'inherent safety' concepts to reduce or eliminate the potential for serious damage in some cases. Past experience with oxide and metal fuel has demonstrated that both fuel types are suitable for use as fuel in a sodium-cooled fast reactor. However, safety analyses for these two fuel types have also shown that there can be substantial differences in accident consequences due to the neutronic and thermophysical properties of the fuel and their compatibility with the reactor coolant, with corresponding differences in the challenges presented to the reactor developers. Accident phenomena are discussed for the sodium-cooled fast reactor based on the mechanistic progression of conditions from accident initiation to accident termination, whether a benign state is achieved or more severe consequences are expected. General principles connecting accident phenomena and fuel properties are developed from the oxide and metal fuel safety analyses, providing guidelines that can be used as part of the evaluation for selection of fuel type for the sodium-cooled fast reactor.
[en] Reprocessing used nuclear fuel (UNF) is a multi-faceted problem involving chemistry, material properties, and engineering. Technology options are available to meet a variety of processing goals. A decision about which reprocessing method is best depends significantly on the process attributes considered to be a priority. New methods of reprocessing that could provide advantages over the aqueous Plutonium Uranium Reduction Extraction (PUREX) and Uranium Extraction + (UREX+) processes, electrochemical, and other approaches are under investigation in the Fuel Cycle Research and Development (FCR and D) Separations Campaign. In an attempt to develop a revolutionary approach to UNF recycle that may have more favorable characteristics than existing technologies, five innovative separations projects have been initiated. These include: (1) Nitrogen Trifluoride for UNF Processing; (2) Reactive Fluoride Gas (SF6) for UNF Processing; (3) Dry Head-end Nitration Processing; (4) Chlorination Processing of UNF; and (5) Enhanced Oxidation/Chlorination Processing of UNF. This report provides a description of the proposed processes, explores how they fit into the Modified Open Cycle (MOC) and Full Recycle (FR) fuel cycles, and identifies performance differences when compared to 'reference' advanced aqueous and fluoride volatility separations cases. To be able to highlight the key changes to the reference case, general background on advanced aqueous solvent extraction, advanced oxidative processes (e.g., volumetric oxidation, or 'voloxidation,' which is high temperature reaction of oxide UNF with oxygen, or modified using other oxidizing and reducing gases), and fluorination and chlorination processes is provided.
[en] Fundamental physics issues facing development of fusion power on a small-scale are assessed with emphasis on the idea of Inertial Electrostatic Confinement (IEC). The authors propose a new concept of accelerator-driven IEC fusion, termed Converging Beam Inertial Electrostatic Confinement (CB-IEC). CB-IEC offers a number of innovative features that make it an attractive pathway toward resolving fundamental physics issues and assessing the ultimate viability of the IEC concept for power generation
[en] The IAEA, NRC, and DOE regulations and requirements for safeguarding nuclear material and facilities have been reviewed and each organization's purpose, objectives, and scope are discussed in this report. Current safeguards approaches are re-examined considering technological advancements and how these developments are changing safeguards approaches used by these organizations. Additionally, the physical protection approaches required by the IAEA, NRC, and DOE were reviewed and the respective goals, objectives, and requirements are identified and summarized in this report. From these, a brief comparison is presented showing the high-level similarities among these regulatory organizations' approaches to physical protection. The regulatory documents used in this paper have been assembled into a convenient reference library called the Nuclear Safeguards and Security Reference Library. The index of that library is included in this report, and DVDs containing the full library are available.
[en] AFCI Storage and Disposal participants at LLNL, ANL and INL provide assessment of how AFCI technology can optimize the future evolution of the fuel cycle, including optimization of waste management. Evaluation of material storage and repository disposal technical issues provides feedback on criteria and metrics for AFCI, and evaluation of AFCI waste streams provides technical alternatives for future repository optimization. LLNL coordinates this effort that includes repository analysis at ANL and incorporation of repository impacts into AFCI criteria at INL. Cooperative evaluation with YMP staff is pursued to provide a mutually agreed technical base. Cooperation with select international programs is supported
[en] The Options Study has been conducted for the purpose of evaluating the potential of alternative integrated nuclear fuel cycle options to favorably address the issues associated with a continuing or expanding use of nuclear power in the United States. The study produced information that can be used to inform decisions identifying potential directions for research and development on such fuel cycle options. An integrated nuclear fuel cycle option is defined in this study as including all aspects of the entire nuclear fuel cycle, from obtaining natural resources for fuel to the ultimate disposal of used nuclear fuel (UNF) or radioactive wastes. Issues such as nuclear waste management, especially the increasing inventory of used nuclear fuel, the current uncertainty about used fuel disposal, and the risk of nuclear weapons proliferation have contributed to the reluctance to expand the use of nuclear power, even though it is recognized that nuclear power is a safe and reliable method of producing electricity. In this Options Study, current, evolutionary, and revolutionary nuclear energy options were all considered, including the use of uranium and thorium, and both once-through and recycle approaches. Available information has been collected and reviewed in order to evaluate the ability of an option to clearly address the challenges associated with the current implementation and potential expansion of commercial nuclear power in the United States. This Options Study is a comprehensive consideration and review of fuel cycle and technology options, including those for disposal, and is not constrained by any limitations that may be imposed by economics, technical maturity, past policy, or speculated future conditions. This Phase II report is intended to be used in conjunction with the Phase I report, and much information in that report is not repeated here, although some information has been updated to reflect recent developments. The focus in this Options Study was to identify any nuclear fuel cycle technology or option that may result in a significant beneficial impact to the issues as compared to the current U.S. approach of once-through use of nuclear fuel in LWRs or similar reactors followed by direct disposal of UNF. This approach was taken because incremental differences may be difficult to clearly identify and justify due to the large uncertainties that can be associated with the specific causes of the issues. Phase II of this Options Study continued the review of nuclear fuel cycle options that was initiated and documented during Phase I, concentrating on reviewing and summarizing the potential of integrated nuclear fuel cycles. However, based on the reviews of previous studies and available data, it was not always possible to clearly determine sufficiently large differences between the various fuel cycle and technology options for some of the issues or evaluation measures, for example, in cases where only incremental differences with respect to the issues might be achieved regardless of the fuel cycle option or technologies being considered, or where differences were insufficient to clearly rise above the uncertainties.
[en] This work demonstrates a technique for comparing the performance of waste forms in a repository environment when one or more of the waste forms constitute a small part of the total amount of waste planned for the repository. In applying the technique, it is important to identify radionuclides that are highly soluble in the transport fluid since it is only for these that the release is controlled by the dissolution rate of the waste form matrix. The techniques presented here have been applied to an evaluation of the performance of waste forms from the electrometallurgical treatment of spent fuel in the proposed Yucca Mountain Repository Engineered Barrier System (EBS)
[en] The sensitivity of the release of radionuclides from the engineered barrier system in the proposed Yucca Mountain Repository to the solubility of uranium is investigated. Factors ranging from 0.1 up to 100 were applied to the nominal uranium solubility assumed in one of the TSPA models used in support of the site recommendation for the repository. At times earlier than about 50,000 years, the release rate of uranium is proportional to the change in the solubility. By 100,000 years, the proportionality continues to hold when the solubility is reduced, but when the solubility is increased, the release rate changes by a factor less than the factor applied to the solubility. At times beyond about 300,000 years, when the solubility is varied from 0.1 to 100 times its nominal value, the release rate changes by less than a factor of 20. Over the same range of changes in the uranium solubility, changes in the release rates of uranium decay products are less than a factor of three. Because uranium and its decay products make relatively small contributions to the dose rate, the changes in the dose rate at a well located 20 km from the repository are estimated to be less than 20%