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.

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 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.

The Strategy of the Belgian Nuclear Research Centre in the Area of High-Level Waste Form Compatibility Research

2007 ◽  
Author(s):  
Karel Lemmens ◽  
Christelle Cachoir ◽  
Elie Valcke ◽  
Karine Ferrand ◽  
Marc Aertsens ◽  
...  
Keyword(s):  
Nuclear Research ◽  
Waste Form ◽  
Research Centre ◽  
High Level Waste ◽  
Spent Fuel ◽  
National Agency ◽  
Waste Forms ◽  
In Situ Experiments ◽  
High Level

The Belgian Nuclear Research Centre (SCK•CEN) has a long-standing expertise in research concerning the compatibility of waste forms with the final disposal environment. For high level waste, most attention goes to two waste forms that are relevant for Belgium, namely (1) vitrified waste from the reprocessing of spent fuel, and (2) spent fuel as such, referring to the direct disposal scenario. The expertise lies especially in the study of the chemical interactions between the waste forms and the disposal environment. This is done by laboratory experiments, supported by modeling. The experiments vary from traditional leach tests, to more specific tests for the determination of particular parameters, and highly realistic experiments. This results in a description of the phenomena that are expected upon disposal of the waste forms, and in quantitative data that allow a conservative long-term prediction of the in situ life time of the waste form. The predictions are validated by in situ experiments in the underground research laboratory HADES. The final objective of these studies, is to estimate the contribution of the waste form to the overall safety of the disposal system, as part of the Safety and Feasibility Case, planned by the national agency ONDRAF/NIRAS. The recent change of the Belgian disposal concept from an engineered barrier system based on the use of bentonite clay to a system based on a concrete buffer has caused a reorientation of the research programme. The expertise in the area of clay-waste interaction will however be maintained, to develop experimental methodologies in collaboration with other countries, and as a potential support to the decision making in those countries where a clay based near field is still the reference. The paper explains the current R&D approach, and highlights some recent experimental set-ups available at SCK•CEN for this purpose, with some illustrating results.

scholarly journals Solubility Limits. on Radionuclide Dissolution

1984 ◽  
Vol 44 ◽  
Author(s):  
Jerry F. Kerrisk
Keyword(s):  
Yucca Mountain ◽  
Waste Form ◽  
High Level Waste ◽  
Spent Fuel ◽  
Dissolution Rates ◽  
Diffusion Limited ◽  
Dissolution Model ◽  
High Level

AbstractThis paper examines the effects of solubility in limiting dissolution rates of a number of important radionuclides from spent fuel and high-level waste. Two simple dissolution models were used for calculations that would be characteristic of a Yucca Mountain repository. A saturation-limited dissolution model, in which the water flowing through the repository is assumed to be saturated with each waste element, is very conservative in that it overestimates dissolution rates. A diffusion-limited dissolution model, in which element-dissolution rates are limited by diffusion of waste elements into water flowing past the waste, is more realistic, but it is subject to some uncertainty at this time. Dissolution rates of some elements (Pu, Am, Sn, Th, Zr, Sm) are always limited by solubility. Dissolution rates of other elements (Cs, Tc, Np, Sr, C, I) are never solubility limited; their release would be limited by dissolution of the bulk waste form. Still other elements (U, Cm, Ni, Ra) show solubility-limited dissolution under some conditions.

Repository Engineering and Demonstration: Special Challenges for TRU

2010 ◽  
Author(s):  
Ian G. McKinley ◽  
Hiroyasu Takase
Keyword(s):  
Rock Properties ◽  
High Level Waste ◽  
Heat Output ◽  
Spent Fuel ◽  
Diverse Range ◽  
Deep Geological Disposal ◽  
Safety Case ◽  
High Level ◽  
A Site ◽  
Term Performance

The diverse range of long-lived radioactive wastes without significant heat output specified for deep geological disposal (here termed TRU) pose challenges that are potentially more serious than those from vitrified high-level waste and spent fuel. Despite this, the latter tend to be the focus of R&D in national programmes. Such challenges are particularly severe for the case for countries that are not considering evaporite host rocks or have a volunteering approach to siting and for those with inventories of TRU resulting from reprocessing of spent fuel. While there is little doubt that safe disposal of TRU is feasible, it is tricky to develop a convincing safety case for a site during early stages of characterisation as, compared to HLW/SF, less credit can be taken for robust, long-term performance of current designs of the engineered barrier systems. In order to improve this situation and increase flexibility with respect to host rock properties, two different options are available — improving the conditioning of particular waste streams or improving the overall repository safety concept. Although the former has been a focus for work in some countries (particularly Japan), much less effort has been invested in the latter and hence this will be illustrated by some examples. These options are compared in terms of their pros and cons with respect to practicality of implementation, environmental impact and cost. Additionally, the ease with which the resulting safety case can be supported by demonstrations of key arguments will be discussed, which may indicate the likely degree of acceptance by stakeholders.

Performance Assessment of Geological Disposal of High-level Radioactive Waste in a Plastic Clay formation

2002 ◽  
Vol 713 ◽  
Author(s):  
Jan Marivoet ◽  
Xavier Sillen ◽  
Dirk Mallants ◽  
Peter De Preter
Keyword(s):  
Performance Assessment ◽  
Performance Assessments ◽  
High Level Waste ◽  
Spent Fuel ◽  
Scenario Development ◽  
Boom Clay ◽  
Site Characterisation ◽  
High Level ◽  
Clay Formation ◽  
The Impact

ABSTRACTIn Belgium the possibilities to dispose of high-level waste in the plastic Boom Clay formation has been studied since 1975. Consequently many results of the site characterisation programme are already available. Various performance assessments have been carried out dealing with the disposal of high-level waste arising from reprocessing and with direct disposal of spent fuel. The performance assessment consists of two main steps: scenario development and consequence analyses. The scenario analysis is based on a catalogue of features, events and processes (FEPs) having the potential to influence the behaviour of the repository system. Two main groups of scenarios are distinguished. The normal evolution scenario, including a number of variants, treats the FEPs that are fairly sure to take place. Altered evolution scenarios focus on FEPs having a probability of occurrence lower than one but that might influence the performance of the repository system. For the impact analyses, a robust concept approach was introduced, which focused the analyses on a limited number of well-characterised barriers and processes. The impact analyses are complemented with sensitivity and uncertainty analyses based on deterministic and probabilistic approaches.

Performance assessment of the disposal of vitrified high-level waste in a clay layer

2001 ◽  
Vol 298 (1-2) ◽  
pp. 125-135 ◽  
Author(s):  
Dirk Mallants ◽  
Jan Marivoet ◽  
Xavier Sillen
Keyword(s):  
Performance Assessment ◽  
High Level Waste ◽  
Clay Layer ◽  
High Level
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