Assessment of Redox Conditions in the Near Field of Nuclear Waste Repositories: Application to the Swiss high-level and intermediate level waste disposal concept

2003 ◽  
Vol 807 ◽  
Author(s):  
Paul Wersin ◽  
Lawrence H. Johnson ◽  
Bernhard Schwyn
Keyword(s):  
Solid Phase ◽  
Near Field ◽  
Intermediate Level ◽  
Redox Conditions ◽  
High Level Waste ◽  
Redox Potentials ◽  
Spent Fuel ◽  
Reducing Conditions ◽  
High Level ◽  
Waste Repositories

ABSTRACTRedox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.

scholarly journals Spent Fuel as a Waste Form - Data Needs to Allow Long Term Performance Assessment Under Repository Disposal Conditions.

1986 ◽  
Vol 84 ◽  
Author(s):  
V. M. Oversby
Keyword(s):  
Performance Assessment ◽  
Waste Form ◽  
High Level Waste ◽  
Detailed Knowledge ◽  
Spent Fuel ◽  
Expected Performance ◽  
High Level ◽  
Term Performance ◽  
Physical And Chemical ◽  
Waste Repositories

AbstractPerformance assessment calculations are required for high level waste repositories for a period of 10,000 years under NRC and EPA regulations. In addition, the Siting Guidelines (IOCFR960) require a comparison of sites following site characterization and prior to final site selection to be made over a 100,000 year period. In order to perform the required calculations, a detailed knowledge of the physical and chemical processes that affect waste form performance will be needed for each site. While bounding calculations might be sufficient to show compliance with the requirements of IOCFR60 and 40CFRI91, the site comparison for 100,000 years will need to be based on expected performance under site specific conditions. The only case where detailed knowledge of waste form characteristics in the repository would not be needed would be where radionuclide travel times to the accessible environment can be shown to exceed 100,000 years. This paper will review the factors that affect the release of radionuclides from spemt fuel under repository conditions, summarize our present state of knowledge, and suggest areas where more work is needed in order to support the performance assessment calculations.

scholarly journals Is it Possible to Demonstrate Compliance with the Regulations for High-Level-Waste Repositories?

1992 ◽  
Vol 294 ◽  
Author(s):  
Felton W. Bingham
Keyword(s):  
Numerical Modeling ◽  
Data Collection ◽  
Performance Assessments ◽  
High Level Waste ◽  
Spent Fuel ◽  
Distant Future ◽  
Site Investigations ◽  
High Level ◽  
Waste Repositories ◽  
Shed Light

ABSTRACTThe regulations that currently govern repositories for spent fuel and high-level waste require demonstrations that are sometimes described as impossible to make. To make them will require an understanding of the current and the future phenomena at repository sites; it will also require credible estimates of the probabilities that the phenomena will occur in the distant future. Experts in many fields—earth sciences, statistics, numerical modeling, and the law—have questioned whether any amount of data collection can allow modelers to meet these requirements with enough confidence to satisfy the regulators. In recent years some performance assessments have begun to shed light on this question because they use results of actual site investigations. Although these studies do not settle the question definitively, a review of a recent totalsystem assessment suggests that compliance may be possible to demonstrate. The review also suggests, however, that the demonstration can be only at the “reasonable” levels of assurance mentioned, but not defined, in the regulations.

Packaging of High Burnup UO2 and MOX Spent Fuel Considering Temperature Restrictions in the Near Field of a Repository

1997 ◽  
Vol 506 ◽  
Author(s):  
D.F. McGinnes ◽  
J. W. Schneider
Keyword(s):  
Near Field ◽  
Management Program ◽  
High Level Waste ◽  
Heat Output ◽  
Spent Fuel ◽  
Ambient Temperatures ◽  
Heat Loading ◽  
High Burnup ◽  
Maximum Temperatures ◽  
High Level

ABSTRACTThe direct disposal of spent fuel is one of the options considered in the Swiss high level waste management program. One of the important questions, within this program, is the heat generation from high-burnup UO2and MOX spent fuels. Depending on the repository boundary conditions (e.g. ambient temperatures at depth, thermal properties of the host rock etc.), on the maximum temperatures allowed in the near field and on the heat output of the fuel, it may not always be possible to completely fill the conceptual waste canister. The aim of this paper is to address the potential loading of spent fuel into canisters for different possible repository heat loading restrictions

Integrated Model of Korean Spent Fuel and High Level Waste Disposal Options

2009 ◽  
Author(s):  
Yongsoo Hwang ◽  
Ian Miller
Keyword(s):  
Nuclear Fuel ◽  
Spent Nuclear Fuel ◽  
Fuel Cycle ◽  
Near Field ◽  
Integrated Model ◽  
High Level Waste ◽  
Spent Fuel ◽  
Parameter Uncertainties ◽  
Design Concepts ◽  
High Level

This paper describes an integrated model developed by the Korean Atomic Energy Research Institute (KAERI) to simulate options for disposal of spent nuclear fuel (SNF) and reprocessing products in South Korea. A companion paper (Hwang and Miller, 2009) describes a systems-level model of Korean options for spent nuclear fuel (SNF) management in the 21’st century. The model addresses alternative design concepts for disposal of SNF of different types (CANDU, PWR), high level waste, and fission products arising from a variety of alternative fuel cycle back ends. It uses the GoldSim software to simulate the engineered system, near-field and far-field geosphere, and biosphere, resulting in long-term dose predictions for a variety of receptor groups. The model’s results allow direct comparison of alternative repository design concepts, and identification of key parameter uncertainties and contributors to receptor doses.

Modelling sorption data for the actinides Am(III), Np(V) and Pa(V) on montmorillonite

2006 ◽  
Vol 94 (9-11) ◽  
Author(s):  
Michael H. Bradbury ◽  
B. Baeyens
Keyword(s):  
Near Field ◽  
High Level Waste ◽  
Spent Fuel ◽  
Data Set ◽  
Sorption Data ◽  
Deep Geological Disposal ◽  
Retention Characteristics ◽  
High Level ◽  
Trace Concentrations ◽  
First Time

The retention characteristics of the bentonite near-field engineered barrier proposed in most of the concepts for the deep geological disposal of high-level waste and spent fuel are an important component in repository performance assessment studies. Montmorillonite generally constitutes 65 to 90 wt.% of the bentonite. Sorption edge measurements have been performed at trace concentrations for the actinides Am(III), Np(V) and Pa(V) on purified and conditioned SWy-1 montmorillonite under anoxic, carbonate free conditions. To the best of the author´s knowledge, this is the first time a sorption data set has been measured for

Investigations of the Possible Separation Distance Between Spent Fuel/High-Level Waste and a Low/Intermediate-Level Waste Repositories due to Gas and Heat Generation

2011 ◽  
Author(s):  
R. Senger ◽  
J. Ewing
Keyword(s):  
Heat Generation ◽  
Thermal Effects ◽  
Intermediate Level ◽  
High Level Waste ◽  
Spent Fuel ◽  
Gas Generation ◽  
Pressure Buildup ◽  
Thermally Induced ◽  
High Level ◽  
Hlw Repository

This study is part of a generic investigation for the assessment of the required minimum distance between a Spent Fuel/High-Level Waste/ Intermediate-Level Waste (SF/HWL/ILW) repository and a Low/ Intermediate-Level Waste (L/ILW) repository. For this, a large-scale numerical model was constructed to investigate the two-phase flow behavior for such a repository configuration in a low-permeability claystone formation. The modeling focused on the pressurization mechanisms associated with (a) resaturation of backfilled underground facilities, (b) thermal effects caused by heat generation from the SF/HLW canisters, and (c) gas generation from corrosion and degradation of different wastes in the L/ILW and ILW caverns and in the SF/HLW emplacement tunnels. The model accounts for gas generation from corrosion and degradation of both L/ILW and ILW wastes indicating decreasing rates with time, and from corrosion of the SF/HLW canisters characterized by a constant rate. Heat generation from radioactive decay of radionuclides of MOX/UO2 wastes is described by an exponential decay with time. The preceding operational phases of the different repository components were simulated representing the transient initial conditions for the post-closure phase. The simulated pressure buildup in the L/ILW repository shows a near linear increase between 10 and 4,000 years when the peak pressure of 6.5 MPa is reached for a repository at about 370 m bg. This is followed by a similar decline, recovering to near hydrostatic pressures after 1 million years. The SF/HLW repository (repository level 600 m bg) indicates a pressure rise between 100 and 1,000 years affected by the early thermal effects, followed by a steep increase between 3,000 and 100,000 years when the pressures level off to a maximum of 6.5 MPa after 160,000 years (corresponding to a steel corrosion rate of 1 μm/year). This is the time when all the metal is corroded and the gas generation stops resulting in a sudden decline, and the pressures level off to about 4.5 MPa in the SF/HLW emplacement tunnel after 1 million years. The numerical modeling demonstrates that the main pressurization mechanism is from gas generation in the different repository components. The pressure histories show a distinct separation of the pressure peaks between the L/ILW repository and the SF/HLW/ILW repository. Moreover, the thermal phenomena affect the pressures in the SF/HLW repository at early time only (prior to about 2,000 years). The thermal expansion of the pore water in the nearfield around the SF/HLW tunnels does produce a relatively steep pressure buildup after 100 years, but it dissipates rapidly prior to the main pressure buildup caused by the gas generation and gas accumulation in the SF/HLW repository. The thermally induced pressure buildup is restricted to the vicinity of the SF/HLW emplacement tunnels (decameter range) and thus, significant interference of the thermally induced pressure perturbation around the SF/HLW/ILW repository with the early gas pressure buildup in the L/ILW repository can be excluded.

The IAEA Coordinated Research Programme on the Performance of High-Level Waste Forms and Packages Under Repository Conditions

1992 ◽  
Vol 294 ◽  
Author(s):  
Vladimir S. Tsyplenkov
Keyword(s):  
Near Field ◽  
Research Programme ◽  
High Level Waste ◽  
Future Research ◽  
Spent Fuel ◽  
Waste Forms ◽  
Safety Assessments ◽  
High Level ◽  
Coordination Meeting

ABSTRACTThe IAEA initiated, in 1991, a Coordinated Research Programme (CRP), with the aim of promoting the exchange of information on the results obtained by different countries in the performance of high-level waste forms and waste packages under conditions relevant to final repository. These studies are being undertaken to obtain reliable data as input to safety assessments and environmental impact analyses, for final disposal purposes. The CRP includes studies on waste forms that are presently of interest worldwide: borosilicate glass, Synroc and spent fuel.Ten laboratories leading in investigation of high-level waste form performance have already joined the programme. The results of their studies and plans for future research were presented at the first Research Coordination Meeting, held in Karlsruhe, Germany, in November 1991. The technical contributions concentrated on effecting an understanding of dissolution mechanisms of waste forms under simulated repository conditions. A quantitative interpretation of the chemical processes in the near field is considered a prerequisite for long-term predictions and for the formulation of a "source term" for performance assessment studies.

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