The Effects of Carbonate-Bicarbonate Concentration on Empirical Corrosion Diagram of Mild Steel as a Material of Geological Disposal Package for High Level Nuclear Wastes

1996 ◽  
Vol 451 ◽  
Author(s):  
Guen Nakayama ◽  
Yuichi Fukaya ◽  
Masatsune Akashi
Keyword(s):  
Mild Steel ◽  
Human Life ◽  
General Corrosion ◽  
Nuclear Wastes ◽  
Bicarbonate Concentration ◽  
Sulfate Ions ◽  
Geological Disposal ◽  
Groundwater Environment ◽  
High Level ◽  
Corrosion Diagram

ABSTRACTIn the scheme for geological disposal of high level radioactive nuclear wastes, the burial pit is to be isolated from the sphere of human life by a multiple-barrier system, which consists of an artificial barrier, composed of a canister, an overpack and a bentonite cushioning layer, and a natural barrier, which is essentially the bedrock. As the greatest as well as essentially the sole detriment to its integrity would be corrosion by groundwater. The groundwater comes to it seeping through the bentonite zone, thereby attaining conceivably the pH of transition from general corrosion to passivity, pHd, the behaviors of mild steel in such a groundwater environment have been examined. It has been shown that the pHd is lowered (enlargement of the passivity domain) with rising temperature and carbonate-bicarbonate concentration, while it is raised (enlargement of the general corrosion region) with increasing concentrations of chloride and sulfate ions.

The Critical Condition for the Initiation of Localized Corrosion of Mild Steel Used for Nuclear Waste Package

1990 ◽  
Vol 212 ◽  
Author(s):  
Gen Nakayama ◽  
Mastsuna Akashi
Keyword(s):  
Mild Steel ◽  
Crevice Corrosion ◽  
Localized Corrosion ◽  
General Corrosion ◽  
Alkaline Water ◽  
Propagation Behavior ◽  
Neutral Water ◽  
High Level ◽  
Term Performance ◽  
Critical Ph

ABSTRACTThe general corrosion rate of mild steel is so small in neutral water environments that adequately provided corrosion allowance can ensure the requirement of one thousand years’ integrity of geological disposal package of high-level nuclear wastes. In alkaline water environments, however, mild steels can passivate themselves and often undergo localized corrosion in much the same manner stainless steels do in neutral water environments. This paper describes a study of localized corrosion behavior of the mild steel conducted to assess the long-term performance of the disposal packages. The critical potentials for pitting and crevice corrosion and critical pH for general corrosion-to-passivity transition were determined for neutral and alkaline water environments. Effects of temperature, pH, and chloride and other anion concentrations on the critical potentials and the critical pH were discussed. The initiation and propagation behavior of crevice corrosion was also analyzed under potentiostatic conditions.

Critical Conditions for Initiation of Localized Corrosion of Mild Steels in Contact with Bentonite Used in Geological Disposal Packages of Nuclear Waste

1992 ◽  
Vol 294 ◽  
Author(s):  
Guen Nakayama ◽  
Masatsune Akashi
Keyword(s):  
Mild Steel ◽  
Nuclear Waste ◽  
Localized Corrosion ◽  
Critical Conditions ◽  
Geological Disposal ◽  
Alkaline Environments ◽  
Current Design ◽  
Long Time ◽  
High Level Nuclear Waste ◽  
High Level

ABSTRACTIn the current design of geological disposal of high-level nuclear waste, the use of bentonite to stand as an artificial barrier-cum-buffer between the host rock and the packages made of mild steel is being investigated. Although mild steels commomly have been considered to be passivity in alkaline environments, under certain circumstances, they become liable to localized corrosion, e.g., pitting corrosion and crevice corrosion. Since bentonite can turn the environment alkaline to a pH of approximately 10 when it is mixed with groundwater, critical conditions for the initiation of localized corrosion of mild steel must be known to evaluate the extremely long time integrity of disposal packages serving in such an environment. This paper presents and discusses the observations and results acquired in a series of critical conditions for the initiation of localized corrosion of mild steels in various groundwater-bentonite environments at 20C, with a deaerated aqueous solution of 1 mMol/L [HCO3−] +10 ppm [CI−], simulating the natural groundwater and varying the bentonite content.

Solubility constraints on uranium concentrations in groundwaters of the Tono uranium deposit, Japan

2004 ◽  
Vol 92 (9-11) ◽  
Author(s):  
T. Iwatsuki ◽  
R. Arthur ◽  
K. Ota ◽  
R. Metcalfe
Keyword(s):  
Uranium Deposit ◽  
Thermodynamic Evaluation ◽  
Nuclear Wastes ◽  
Hydrous Oxide ◽  
Geological Disposal ◽  
Long Term Stability ◽  
Safety Assessments ◽  
High Level ◽  
Gifu Prefecture

SummaryA key concept underpinning most safety assessments of geological disposal systems for high-level nuclear wastes is that the maximum aqueous concentrations of actinide elements released from the waste will be limited by the solubility of the corresponding tetravalent oxide or hydrous oxide. The validity of this concept for U is evaluated in the present study using hydrochemical and mineralogical data from the Tono uranium (U) deposit in Gifu Prefecture, Japan. In addition, the long-term stability of U mineralization in the Tono deposit is assessed in terms of plausible range of U solubilities in paleogroundwaters migrating through the deposit.A thermodynamic evaluation of the aqueous-speciation and solubility behaviour of U indicates that U concentrations in the coexisting groundwaters greatly exceed the solubility of both uraninite [UO

Performance Assessment of a High-Level-Waste Repository in Clay

1988 ◽  
Vol 127 ◽  
Author(s):  
Jan L. Marivoet ◽  
Geert Volckaert ◽  
Arnold A. Bonne
Keyword(s):  
Performance Assessment ◽  
Maximum Dose ◽  
High Level Waste ◽  
Clay Layer ◽  
Geological Disposal ◽  
Dose Rates ◽  
Consequence Analysis ◽  
Calculated Dose ◽  
Order Of Magnitude ◽  
High Level

ABSTRACTPerformance assessment studies have been undertaken on the geological disposal of high-level waste in a clay layer in the framework of the CEC project PAGIS. The methodology applied consists of two consecutive steps : a scenario and a consequence analysis. The scenario analysis has indicated that scenarios of normal evolution, of human intrusion, of climatic change, of secondary glaciation effects and of faulting should be evaluated. For the consequence analysis as well deterministic “best estimate” as stochastic calculations, including uncertainty, risk and sensitivity analyses, have been elaborated.The calculations performed show that most radionuclides decay to negligible levels within the first fewjneters of the clay barrier. Just a few radionuclides, 99Tc, 135Cs and 237Np with its daughter nuclides 233U and 229Th can eventually reach the biosphere. The maximum dose rates arising from the geological disposal of HLW, as evaluated by the “best-estimate” approach are about 10−11 Sv/y for river pathways. If the sinking of a water well into the 150 m deep aquifer layer in the vicinity of the repository is considered together with a climatic change, the maximum calculated dose rate rises to a value of 3×10−7 Sv/y. The maximum dose rates evaluated by stochastic calculations are about one order of magnitude higher due to the considerable uncertainties in the model parameters. In the case of the Boom clay the estimated consequences of a fault scenario are of the same order of magnitude as the results obtained for the normal evolution scenario. The maximum risk is estimated from the results obtained through stochastic calculations to be about 5×10−8 per year. The sensitivity analysis has shown that the effective thickness of the clay layer, the retention factors of Tc, Cs and Np, and the Darcy velocity in the aquifer are parameters which strongly influence the calculated dose rates.

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