scholarly journals Waste Package Corrosion Studies Using Small Mockup Experiments

2008 ◽  
Vol 1107 ◽  
Author(s):  
B.E. Anderson ◽  
K.B. Helean ◽  
C.R. Bryan ◽  
P.V. Brady ◽  
R.C. Ewing
Keyword(s):  
Spent Nuclear Fuel ◽  
Sodium Metasilicate ◽  
Yucca Mountain ◽  
Corrosion Products ◽  
Nuclear Waste Repository ◽  
Low Oxygen ◽  
Waste Package ◽  
Reducing Conditions ◽  
Key Issues ◽  
Term Performance

AbstractUnderstanding the corrosion of spent nuclear fuel (SNF) and the subsequent mobilization of released radionuclides, particularly under oxidizing conditions, is one of the key issues in evaluating the long-term performance of a nuclear waste repository. However, the large amounts of iron in the metal waste package may create locally reducing conditions that would lower corrosion rates for the SNF, as well as reduce the solubility of some key radionuclides, e.g., Tc and Np. In order to investigate the interactions among SNF-waste package-fluids, four smallscale (∼1:40 by length) waste package mockups were constructed using metals similar to those proposed for use in waste packages at the proposed repository at Yucca Mountain. Each mockup experiment differed with respect to water input, exposure to the atmosphere, and temperature. Simulated Yucca Mountain process water (YMPW) was injected into three of the mockups at a rate of 200 μL per day for five days a week using a calibrated needle syringe. The YMPW was prepared by equilibrating 50 mg/L silica as sodium metasilicate with air, and adding enough HCl to lower the pH to 7.6 in contact with an excess of powdered calcite.X-ray powder diffraction and scanning electron microscopy confirm that, where corrosion occurred, the dominant corrosion product in all cases was magnetite. In the high temperature (60°C) experiment, hematite and a fibrous, Fe-O-Cl phase were also identified. The Fe(II)/Fe(III) ratios measured in the corrosion products using a wet chemistry technique indicate extremely low oxygen fugacities (10-36 bar). Experiments are in progress in which 0.1g powdered UO2 was included in the mock-up in order to investigate the relative kinetics of Fe and U oxidation and to identify the U corrosion products formed under these conditions.

scholarly journals Depleted Uranium Oxides and Silicates as Spent Nuclear Fuel Waste Package Fill Materials

1996 ◽  
Vol 465 ◽  
Author(s):  
C. W. Forsberg
Keyword(s):  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Chemical Species ◽  
Fission Products ◽  
Depleted Uranium ◽  
Improve Performance ◽  
Waste Package ◽  
Reducing Conditions ◽  
Nuclear Fuel Waste

ABSTRACTA new repository waste package (WP) concept for spent nuclear fuel (SNF) is being investigated. The WP uses depleted uranium (DU) to improve performance and reduce the uncertainties of geological disposal of SNF. The WP would be loaded with SNF. Void spaces would then be filled with DU (∼0.2 wt % 235U) dioxide (UO2) or DU silicate-glass beads.Fission products and actinides can not escape the SNF UO2 crystals until the UO2 dissolves or is transformed into other chemical species. After WP failure, the DU fill material slows dissolution by three mechanisms: (1) saturation of WP groundwater with DU and suppression of SNF dissolution, (2) maintenance of chemically reducing conditions in the WP that minimize SNF solubility by sacrificial oxidation of DU from the +4 valence state, and (3) evolution of DU to lower-density hydrated uranium silicates. The fill expansion minimizes water flow in the degraded WP. The DU also isotopically exchanges with SNF uranium as the SNF degrades to reduce long-term nuclear-criticality concerns.

Zircaloy Corrosion in a Repository Environment

1999 ◽  
Vol 556 ◽  
Author(s):  
Jerry D. Christian
Keyword(s):  
Spent Nuclear Fuel ◽  
Near Field ◽  
Yucca Mountain ◽  
Localized Corrosion ◽  
General Corrosion ◽  
Geochemical Environment ◽  
Waste Package ◽  
Saturated Water ◽  
Radionuclide Release ◽  
Corrosion Data

AbstractAssessments are made of the corrosion characteristics of spent nuclear fuel Zircaloy cladding in a Yucca mountain repository environment and the potential for the cladding to provide protection against radionuclide release following waste package failure. Considerations and assumptions includes a waste package life near 10,000 years and air-saturated water contacted with waste package corrosion product goethite, based on the near-field geochemical environment evaluated in the Yucca Mountain Viability Assessment [3]. Literature corrosion data (general, pitting, and localized crevice attack) are evaluated on the basis of these conditions and the expected chemical environments that can result on the surface of the fuel. General corrosion of Zircaloy is expected to be negligible and result in a lifetime of the SNF cladding of several hundred thousand years, approaching a million years. General surface pitting is not expected. Effects of crevice localized corrosion for periods beyond 10,000 years are uncertain and require modeling development and experimental characterization. Details of the evaluations that provide the basis for the conclusions are presented.

scholarly journals Localized Dryout: an Approach for Managing the Thermal-Hydrological Effects of Decay Heat at Yucca Mountain

1995 ◽  
Vol 412 ◽  
Author(s):  
Thomas A. Buscheck ◽  
John J. Nitao ◽  
Lawrence D. Ramspot
Keyword(s):  
Relative Humidity ◽  
Thermal Load ◽  
Large Scale ◽  
Thermal Loading ◽  
Yucca Mountain ◽  
Large Temperature ◽  
Nuclear Waste Repository ◽  
Waste Package ◽  
Decay Heat ◽  
Hydrological Effects

AbstractFor a nuclear waste repository in the unsaturated zone at Yucca Mountain, there are two thermal loading approaches to using decay heat constructively-that is, to substantially reduce relative humidity and liquid flow near waste packages for a considerable time, and thereby limit waste package degradation and radionuclide dissolution and release. “Extended dryout” achieves these effects with a thermal load high enough to generate large-scale (coalesced) rock dryout. “Localized dryout”(which uses wide drift spacing and a thermal load too low for coalesced dryout) achieves them by maintaining a large temperature difference between the waste package and drift wail; this is done with close waste package spacing (generating a high line-heat load) and/or low-thermal-conductivity backfill in the drift. Backfill can greatly reduce relative humidity on the waste package in both the localized and extended dryout approaches. Besides using decay heat constructively, localized dryout reduces the possibility that far-field temperature rise and condensate buildup above the drifts might adversely affect waste isolation.

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.

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