Statistical Model for Grain Boundary and Grain Volume Oxidation Kinetics in UO2 Spent Fuel

1989 ◽  
Vol 176 ◽  
Author(s):  
R. B. Stout ◽  
H. F. Shaw ◽  
R. E. Einziger
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Density Function ◽  
Oxidation Kinetics ◽  
Yucca Mountain ◽  
Department Of Energy ◽  
Nuclear Waste Repository ◽  
Dissolution Behavior ◽  
Spent Fuel ◽  
Integral Forms

ABSTRACTThe Yucca Mountain Project of the U.S. Department of Energy is investigating the suitability of a site in the unsaturated zone at Yucca Mountain, NV, for a high-level nuclear waste repository. Most of the waste will consist of UO2 spent fuel in Zircaloy-clad rods from nuclear reactors. If failure of both the waste containers and the cladding occurs within the lifetime of the repository, then the UO2 will be exposed to oxygen in the air and higher oxides of uranium may form. The oxidation state of the spent fuel may affect its dissolution behavior if later contacted by water. A model for the kinetics of spent fuel oxidation under repository-relevant conditions is thus necessary to predict the behavior of the waste form for assessing the performance of the repository with respect to the containment of radionuclides. In spent fuel experiments, the UO2 oxidation front initially propagates along grain boundaries followed by propagation into grain volumes. Thus, the oxidation kinetics is controlled by two processes and the oxidation of spent fuel fragments will depend on the density and physical attributes of grain boundaries. With this in mind, concepts from statistical mechanics are used to define a density function for grain boundaries perunit volume per unit species in a spent fuel fragment. Combining the integral forms of mass conservation and this grain boundary density function, a model for the global rate of oxidation for a spent fuel fragment is obtained. For rapid grain boundary oxidation compared to grain volume oxidation, equations of the model are solved and results compared to existing data.

Gap and Grain-Boundary Inventories of Cs, Tc, and Sr in Spent LWR Fuel

1991 ◽  
Vol 257 ◽  
Author(s):  
W. J. Gray ◽  
D. M. Strachan ◽  
C. N. Wilson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Surface Area ◽  
Dissolution Behavior ◽  
Strongly Correlated ◽  
Spent Fuel ◽  
Geologic Repository ◽  
Metallic Particles ◽  
Waste Container ◽  
Fission Gas Release

ABSTRACTSoluble radionuclides concentrated within the gap and grain-boundary regions of spent fuel could dissolve relatively rapidly were the waste container to fail and the fuel to be contacted by water in a geologic repository. To provide an estimate of the quantities of radionuclides that may be rapidly released, fractional inventories of Cs, Tc, and Sr concentrated within the fuel/cladding gap region have been measured for U.S. LWR spent fuels with fission gas release (FGR) values ranging from 0.25% to 18%. Separate measurements of the grain-boundary inventories of Cs, Tc, and Sr have been made for the same fuels. The Cs gap inventories were generally found to be about one fourth of the FGR values. The Cs grain-boundary inventories were generally less than 1% of the total Cs inventories and were not strongly correlated with FGR. Both the gap and grain-boundary inventories of Tc and Sr were near the detection limits of the methods used, less than 0.2% of the total inventories of these elements. However, some of the Tc may reside at the grain boundaries in the form of relatively insoluble metallic particles and not be detected by these experiments. Data obtained by comparing the dissolution behavior of fuel fragments with that of fuel grains were used to estimate the dissolution rate of Cs from the grain boundaries of one of the fuels. Surface-area normalized dissolution rates determined for fuel fragments in these same tests exceeded those determined for grains. A likely explanation is that the estimated fragment surface area did not take into account the “effective” grain-boundary surfaces.

NNWSI Performance Assessment Considerations

1983 ◽  
Vol 26 ◽  
Author(s):  
L. D. Tyler ◽  
R. R. Peters ◽  
N. K. Hayden ◽  
J. K. Johnstone ◽  
S. Sinnock
Keyword(s):  
Performance Assessment ◽  
Nuclear Waste ◽  
Yucca Mountain ◽  
Department Of Energy ◽  
Nuclear Waste Repository ◽  
Nuclear Waste Storage ◽  
Human Environment ◽  
Assessment Task ◽  
Waste Storage ◽  
A Site

ABSTRACTThe Nevada Nuclear Waste Storage Investigations (NNWSI) project includes a Performance Assessment task to evaluate the containment and isolation potential for a nuclear waste repository at Yucca Mountain in southern Nevada. This task includes calculations of the rates and concentrations at which radionuclides might be released and transported from the repository and will predict their consequences if they enter the human environment. Among the major tasks required for these calculations will be the development of models for water flow and nuclide transport under unsaturated conditions and in fractured hard rock. The program must also quantify the uncertainties associated with the results of the calculations. The performance assessment will provide evaluations needed for making major decisions as the U. S. Department of Energy seeks a site for a repository. An evaluation will be part of the environmental assessments prepared to accompany the potential nomination of the site. If the Yucca mountain site is selected for characterization and development as a repository, the assessments will be required for an environmental impact statement, a safety analysis report, and other documents.This program has been divided into five tasks. Collectively they will provide the performance assessments needed for the NNWSI Project.

Powder Leaching Study for Grain Boundary Inventory of Two High Burnup Fuels

MRS Advances ◽  
2019 ◽  
Vol 4 (17-18) ◽  
pp. 981-986
Author(s):  
Alexandre Barreiro Fidalgo ◽  
Olivia Roth ◽  
Anders Puranen ◽  
Lena Z. Evins ◽  
Kastriot Spahiu ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Spent Fuel ◽  
Short Period ◽  
Fission Gas ◽  
Leaching Solution ◽  
Significant Release ◽  
Leaching Experiments ◽  
High Burnup ◽  
Fission Gas Release

ABSTRACTIn the context of safety assessment, the fraction of inventory that is expected to rapidly dissolve when water contacts the spent fuel is called the Instant Release Fraction (IRF). Conceptually, this fraction consists of radionuclides outside of the uranium dioxide matrix and therefore the fraction can be further divided into the radionuclides in the fuel/cladding gap and radionuclides in the grain boundaries. The relative importance of these two fractions is investigated here for two Swedish high burnup fuels through simultaneous grinding and leaching fuel fragments in simplified groundwater for a short period of time. The hypothesis is that this will expose grain boundaries to leaching solution and provide an estimate of the release of the grain boundary inventory upon contact with water. The studied fragments were used in previous leaching experiments and thus pre-washed to remove any pre-oxidized phases. The results showed a significant release of iodine, cesium and rubidium and to a lower extent molybdenum and technetium. The fraction of inventory in the aqueous phase of actinides and lanthanides was 1-2 orders of magnitude lower than for the elements associated to the IRF. Both fuels displayed a very similar behavior and no correlation as a function of burnup or fission gas release was found.

scholarly journals A Quantitative Assessment of Microbiological Contributions to Corrosion of Candidate Nuclear Waste Package Materials

1999 ◽  
Vol 556 ◽  
Author(s):  
T. Lian ◽  
S. Martin ◽  
J. Horn ◽  
D. Jones
Keyword(s):  
Corrosion Rate ◽  
Nuclear Waste ◽  
Fold Increase ◽  
Yucca Mountain ◽  
Department Of Energy ◽  
Microbiologically Influenced Corrosion ◽  
304 Stainless Steel ◽  
Detection Methods ◽  
Nuclear Waste Repository ◽  
Waste Package

AbstractThe U.S. Department of Energy is contributing to the design of a potential nuclear waste repository at Yucca Mountain, Nevada. A system to predict the contribution of Yucca Mountain (YM) bacteria to overall corrosion rates of candidate waste package (WP) materials was designed and implemented. DC linear polarization resistance techniques were applied to candidate material coupons that had been inoculated with a mixture of YM-derived bacteria with potentially corrosive activities, or left sterile. Inoculated bacteria caused a 5- to 6-fold increase in corrosion rate of carbon steel C 1020 (to approximately 7-8μm/yr), and an almost 100-fold increase in corrosion rate of Alloy 400 (to approximately μm/yr) was observed due to microbiological activities. Microbiologically Influenced Corrosion (MIC) rates on more resistant materials (CRMs: Alloy 625, Type 304 Stainless Steel, and Alloy C22) were on the order of hundredths of micrometers per year (μm/yr). Bulk chemical and surfacial endpoint analyses of spent media and coupon surfaces showed preferential dissolution of nickel from Alloy 400 coupons and depletion of chromium from CRMs after incubation with YM bacteria. Scanning electron microscopy also showed greater damage to the Alloy 400 surface than that indicated by electrochemical detection methods.

Unsaturated Zone Waters From the Nopal I Natural Analog, Chihuahua, Mexico - Implications for Radionuclide Mobility at Yucca Mountain

1999 ◽  
Vol 556 ◽  
Author(s):  
David A. Pickett ◽  
William M. Murphy
Keyword(s):  
Unsaturated Zone ◽  
Yucca Mountain ◽  
Nuclear Waste Repository ◽  
Spent Fuel ◽  
Path Modeling ◽  
Rock Interaction ◽  
Colloidal Transport ◽  
Natural Analog ◽  
Initial Silica ◽  
Radionuclide Release

AbstractChemical and U-Th isotopic data on unsaturated zone waters from the Nopal I natural analog reveal effects of water-rock interaction and help constrain models of radionuclide release and transport at the site and, by analogy, at the proposed nuclear waste repository at Yucca Mountain. Geochemical reaction-path modeling indicates that, under oxidizing conditions, dissolution of uraninite (spent fuel analog) by these waters will lead to eventual schoepite precipitation regardless of initial silica concentration provided that groundwater is not continuously replenished. Thus, less soluble uranyl silicates may not dominate the initial alteration assemblage and keep dissolved U concentrations low. Uranium-series activity ratios are consistent with models of U transport at the site and display varying degrees of leaching versus recoil mobilization. Thorium concentrations may reflect the importance of colloidal transport of low-solubility radionuclides in the unsaturated zone.

scholarly journals No Hurry to Recycle

2006 ◽  
Vol 128 (05) ◽  
pp. 32-35
Author(s):  
Frank N. Von Hippel
Keyword(s):  
Nuclear Waste ◽  
Nuclear Power ◽  
Power Plants ◽  
The United States ◽  
Yucca Mountain ◽  
Department Of Energy ◽  
Spent Fuel ◽  
National Academy Of Sciences ◽  
Academy Of Sciences ◽  
Nuclear Waste Policy

This article discusses the promotion of Global Nuclear Energy Partnership (GNEP) by US Department of Energy. GNEP is a strategy for dealing with the accumulation of radioactive waste from power plants by reprocessing some of the spent fuel. The primary domestic benefit of this initiative would be to reduce the quantity of plutonium and other transuranic waste that would have to be buried in Yucca Mountain, the Nevada site identified as the national depository for nuclear waste. The objective of GNEP is to fission all of the transuranics, aside from process losses. The National Academy of Sciences (NAS) study scaled its cost estimate to 62,000 tons of spent fuel because that is approximately the amount of spent fuel that the Nuclear Waste Policy Act allows to be placed in Yucca Mountain before a second repository in another state is in operation. The huge cost of the GNEP would likely be more of a burden than a help to the future of nuclear power in the United States.

The Dissolution of Uranophane in CaCl2-SiO2(aq) Test Solutions

2004 ◽  
Vol 824 ◽  
Author(s):  
James D. Prikryl ◽  
William M. Murphy
Keyword(s):  
Yucca Mountain ◽  
Ore Deposits ◽  
Nuclear Waste Repository ◽  
Chemical Analyses ◽  
Spent Fuel ◽  
Dissolution Reaction ◽  
Batch Dissolution ◽  
Siliceous Rocks ◽  
Waste Repository

AbstractUranophane [Ca(UO2)2(SiO3OH)2 · 5H2O] is a corrosion product of long-term leaching of spent fuel under oxidizing conditions and is a weathering product of uraninite in uranium ore deposits hosted by siliceous rocks. Incorporation of radionuclides into uranophane by coprecipitation may occur as a result of spent fuel alteration. Dissolution of uranophane leading to release of these radionuclides may therefore influence the longterm dissolved concentration and mobility of radionuclides at the proposed nuclear waste repository at Yucca Mountain, Nevada. In this study, the dissolution of uranophane in Ca- and Si-rich test solutions was investigated. Batch dissolution experiments were designed to approach uranophane equilibrium from undersaturated solutions at nearneutral pH (~6.0). Test solutions had initial U concentrations of 0.0 and 10-7 mol/L in matrices of ~10-2 mol/L CaCl2 and ~10-3 mol/L SiO2(aq). The test solutions were reacted with synthetic uranophane (confirmed by XRD and chemical analyses) and analyzed periodically over 10 weeks. Reaction quotients (Log Qs) derived from aqueous speciations of experimental solutions considered to be near equilibrium with uranophane ranged from 10.54 to 11.06 for the dissolution reaction: Ca(UO2)2(SiO3OH)2 · 5H2O + 6H+ ⇔ Ca2+ + 2UO22+ + 2SiO2(aq) + 9H2O.

Building the Yucca Mountain Repository

2003 ◽  
Author(s):  
R. Glenn Vawter
Keyword(s):  
Yucca Mountain ◽  
Department Of Energy ◽  
Nuclear Waste Repository ◽  
Private Industry ◽  
The World ◽  
Pros And Cons ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Federal Administration ◽  
The U.S

The U.S. Congress recently approved the Yucca Mountain Project in Nevada as the site for the nation’s high level nuclear waste repository. The Project now moves into the licensing, construction and operating phases. The question posed by this paper is what organization approach is best suited to carry out those functions as well as the affiliated transportation and waste acceptance activities? Currently the U.S. Department of Energy and its contractors are responsible for the implementation of the Project. Other alternatives include a government corporation, private industry, a different U.S. government agency, or a combination of the above? There are pros and cons to each approach. This paper will present pros and cons and discuss the implications of each alternative. It will also discuss experience from other similar endeavors around the world. The U.S Federal Administration will need to consider this important question to assure the success of the program, because it is so important to the energy and national security of the nation. And its success or failure will set a precedent for repository programs around the world.

Design Considerations To Minimize The Impact Of A Repository On A Host Rock

1983 ◽  
Vol 26 ◽  
Author(s):  
Leo W. Scully
Keyword(s):  
Conceptual Design ◽  
Yucca Mountain ◽  
Department Of Energy ◽  
Nuclear Waste Repository ◽  
Short Term ◽  
Engineering Designs ◽  
Design Activities ◽  
Isolation Requirements ◽  
The Impact

ABSTRACTA conceptual design is being developed in support of the Department of Energy's study of a potential site for a nuclear waste repository at Yucca Mountain. This design can be used to support the recommendation of that site for characterization if so designated by the Department of Energy. In the event that the Yucca Mountain site is chosen for development as the first repository, the conceptual design and subsequent preliminary engineering designs could be used to develop design specifications for repository construction. The design addresses the unique surface and subsurface characteristics of the volcanic tuffs at Yucca Mountain. A candidate horizon has been identified approximately 300 meters below the surface and about 100 meters above the water table.The design activities are being conducted in a manner to attempt to control and reduce to the extent practicable the impact exerted by the repository on the containment and isolation capability of the site. This process consists of careful iteration of design, analysis and interpretation of results to ensure long-term containment and isolation requirements are met and that short-term operations and costs are acceptable.

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