Strategy for identifying natural analogs of the long-term performance of low-level waste disposal sites (original) (raw)
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Journal of Hazardous Materials, 2007
In setting criteria for landfill classes in Annex II of the EU Landfill Directive, it proved to be impossible to derive criteria for stabilised monolithic waste due to the lack of information on release and release controlling factors in stabilised waste monofills. In this study, we present a scientific basis, which enables a realistic description of the environmental impact of stabilised waste landfills.The work in progress involves laboratory testing of different stabilisation recipes, pilot scale studies on site and evaluation of field leachate from a full-scale stabilisation landfill. We found that the pHs in run-off and in percolate water from the pilot experiment are both around neutral. The neutral pH in run-off is apparently caused by the rapid atmospheric carbonation of those alkaline constituents that are released. The soil, used as a liner protection layer, controls the release to the subsurface below the landfill. This soil layer buffers pH and binds metals. The modelling results show that the chemistry is understood rather well. Differences between predicted and actual leaching might then be attributed to discrepancies in the description of sorption processes, complexation to organic matter and/or kinetic effects in the leaching tests. We conclude that this approach resulted in a new scientific basis for environmental impact assessment of stabilised waste landfills. The integrated approach has already resulted in a number of very valuable observations, which can be used to develop a sustainable landfill for monolithic waste and to provide guidance for the management of waste to be stabilised (e.g. improved waste mix design).
2007
Argentina is faced with the challenging problem of developing technology for near-surface disposal and isolation of low-and intermediate-level radioactive waste (LILW). The preferred option for disposal of LILW (including both relatively short-lived and long-lived radionuclides) is to use disposal facilities that are near-surface-either above or below ground level [IAEA, 1985; 2001a; 2004]. How individual components of a waste disposal system perform (including waste forms, waste containers, engineered barriers and host environment) will determine system safety and the safety of the surrounding environment [IAEA, 1999]. The lack of appropriate engineering for the backfill, and for the selection of sealing and covering materials for trenches, vaults, and ditches, could result in the escape of radionuclides from the disposed wastes [IAEA, 1994a; 2001b]. Therefore, assessment and design of backfill, barriers, and cover materials are very important, both for preventing invasion of water into the disposal system, and for retarding radionuclides that could potentially migrate from the system into the atmosphere or groundwater [IAEA, 1982; 1994b; 2001a].
Performance Assessment Modeling and Sensitivity Analyses of Generic Disposal System Concepts
2014
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. DISCLAIMER This information was prepared as an account of work sponsored by an agency of the U.
Reliability Engineering & System Safety, 2014
This paper summarizes the evolution of consequence modeling for a repository for spent nuclear fuel and highlevel radioactive waste at Yucca Mountain in southern Nevada. The discussion includes four early performance assessments (PAs) conducted between 1982 and 1995 to support selection and to evaluate feasibility and three major PAs conducted between 1998 and 2008 to evaluate viability, recommend the site, and assess compliance. Modeling efforts in 1982 estimated dose to individuals 18 km from the site caused by volcanic eruption through the repository. Modeling in 1984 estimated releases via the groundwater pathway because of container corrosion. In combination, this early analysis supported the first environmental assessment. Analysts in 1991 evaluated cumulative release, as specified in the 1985 US radiation protection standards, via the groundwater pathway over 10 4 yr at a 5-km boundary by modeling waste degradation and flow/transport in the saturated and unsaturated zones. By 1992, however, the US Congress mandated a change to a dose measure. Thus, the 1993 and 1995 performance assessments improved modeling of waste container degradation to provide better estimates of radionuclide release rates out to 10 6 yr. The 1998 viability assessment was a major step in modeling complexity. Dose at a 20-km boundary from the repository was evaluated through 10 6 yr for undisturbed conditions using more elaborate modeling of flow and the addition of modules for modeling infiltration, drift seepage, the chemical environment, and biosphere transport. The 2000 assessment for the site recommendation refined the analysis. Seepage modeling was greatly improved and waste form degradation modeling included more chemical dependence. The 2008 compliance assessment for the license application incorporated the influence of the seismicity on waste package performance to evaluate dose at an~18-km boundary.
Swiss Journal of Geosciences, 2015
The geological disposal of radioactive wastes is generally accepted to be the most practicable approach to handling the waste inventory built up from over 70 years accumulation of power production, research-medical-industrial and military wastes. Here, a brief overview of the approach to geological disposal is presented along with some information on repository design and the assessment of repository postclosure safety. One of the significant challenges for repository safety assessment is how to extrapolate the likely long-term (i.e. ten thousand to a million years) behaviour of the repository from the necessarily short term data from analytical laboratories and underground rock laboratories currently available. One approach, common to all fields of the geosciences, but also in such diverse fields as philosophy, biology, linguistics, law etc., is to utilise the analogue argumentation methodology. For the specific case of radioactive waste management, the term 'natural analogue' has taken on a particular meaning associated with providing supporting arguments for a repository safety assessment. This approach is discussed here with a brief overview of how the study of natural (and, in particular, geological) systems can provide supporting information on the likely long-term evolution of a deep geological waste repository. The overall approach is discussed and some relevant examples are presented, including the use of uranium ore bodies to assess waste form stability, the investigation of native metals to define the longevity of waste containers and how natural clays can provide information on the stability of waste tunnel backfill material. Keywords Radioactive waste disposal Á Evaluation of long-term safety Á Repository design Á Natural systems Editorial handling: A. G. Milnes. This invited review article is published as the introductory paper to the special theme: Natural Analogue Research for Deep Disposal of Nuclear Waste.
Development of models for use in the assessment of waste repository performance
1989
Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract number W-740S-ENG-48. This document was prepared as au account of work sponsored by in agency of the United States Government. Neither the United States Government nor the University of California nor any of thei_ employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.
Sensitivity analysis and simulation uncertainties in predictive geochemical modelling
1999
Waste package model Repository model Ground water flow and radionuclide transport Radionuclide transport in biosphere Dose and health effects to man Waste package lifetime Engineered barrier lifetime Ground water travel time Containment requirement Ground water protection Individual protection requirements FOG is an electronic journal registered under ISSN
Performance Assessments of Nuclear Waste Repositories: A Dialogue on Their Value and Limitations
Risk Analysis, 1999
Performance Assessment (PA) is the use of mathematical models to simulate the long-term behavior of engineered and geologic barriers in a nuclear waste repository; methods of uncertainty analysis are used to assess effects of parametric and conceptual uncertainties associated with the model system upon the uncertainty in outcomes of the simulation. PA is required by the U.S. Environmental Protection Agency as part of its certification process for geologic repositories for nuclear waste. This paper is a dialogue to explore the value and limitations of PA. Two ''skeptics'' acknowledge the utility of PA in organizing the scientific investigations that are necessary for confident siting and licensing of a repository; however, they maintain that the PA process, at least as it is currently implemented, is an essentially unscientific process with shortcomings that may provide results of limited use in evaluating actual effects on public health and safety. Conceptual uncertainties in a PA analysis can be so great that results can be confidently applied only over short time ranges, the antithesis of the purpose behind long-term, geologic disposal. Two ''proponents'' of PA agree that performance assessment is unscientific, but only in the sense that PA is an engineering analysis that uses existing scientific knowledge to support public policy decisions, rather than an investigation intended to increase fundamental knowledge of nature; PA has different goals and constraints than a typical scientific study. The ''proponents'' describe an ideal, sixstep process for conducting generalized PA, here called probabilistic systems analysis (PSA); they note that virtually all scientific content of a PA is introduced during the model-building steps of a PSA; they contend that a PA based on simple but scientifically acceptable mathematical models can provide useful and objective input to regulatory decision makers. The value of the results of any PA must lie between these two views and will depend on the level of knowledge of the site, the degree to which models capture actual physical and chemical processes, the time over which extrapolations are made, and the proper evaluation of health risks attending implementation of the repository. The challenge is in evaluating whether the quality of the PA matches the needs of decision makers charged with protecting the health and safety of the public.
Composite analysis for low-level waste disposal in the 200 area plateau of the Hanford Site
1998
This report presents the f i r s t iteration of the Composite Analysis for Low-Level Wmte Disposal in the 200 Area Plateau of the Hmford Site (Composite Analysis) prepared in response to the U.S. Department of Energy Implementation Plan for the Defense Nuclear Facility Safety Board Recommendation 94-2. The Composite Analysis is a companion document to published analyses of four active or planned lowlevel waste disposal actions: the solid waste burial grounds in the 200 West Area, the solid waste burial grounds in the 200 East Area, the Environmental Restoration Disposal Facility, and the disposal facilities for immobilized lowractivity waste. A single Composite Analysis was prepared for the W o r d Site considering only sources on the 200 Area Plateau. The performance objectives prescribed in U.S. Department of Energy guidance for the Composite Analysis were 100 mrem in a year and examination of a lower dose (30 mrem in a year) to ensure the "as low as reasonably achievableyy concept is followed. The 100 mrem in a year limit was the maximum allowable all-pathways dose for 1000 years following Hanford Site closure, which is assumed to occur in 2050. These performance objectives apply to an accessible environment defined as the area between a buffer zone surrounding an exclusive waste management area on the 200 Area Plateau, and the Columbia River. Estimating doses to hypothetical future members of the public for the Composite Analysis was a multistep process involving the estimation or simulation of inventories; waste release to the environment; migration through the vadose zone, groundwater, and atmospheric pathways; and exposure and dose. Doses were estimated for scenarios based on agriculture, residential, industrial, and recreational land use. The radionuclides included in the vadose zone and groundwater pathway analyses of future releases were carbon-14, chlorine-36, selenium-79, technetium-99, iodine-129, and uranium isotopes. In addition, tritium and strontium-90 were included because they exist in groundwater plumes. Radionuclides considered in the atmospheric pathway included tritium and carbon-14. Most of the radionuclide inventory in past-practice liquid discharge and solid waste burial sites on the 200 Area Plateau was projected to be released in the f i r s t several hundred years following H d o r d Site closure and a significant fraction of the inventory was projected to be released prior to closure. The maximum predicted agricultural dose outside the buffer zone was less than 6 mrem in a year in 2050 and declined thereafter. The maximum doses estimated for the residential, industrial, and recreational scenarios, were 2.2,0.7, and 0.04 mrem in a year, respectively, and also declined after 2050. The radiological doses for all of the exposure scenarios outside the buffer zone were well below the performance. objectives.. Significant uncertainties exist in the f i r s t iteration Composite Analysis, with the largest uncertainty associated with the inventories of key mobile radionuclides. Other sources of uncertainty in the analysis arose fiom the conceptual and numerical models of contaminant migration and fate in the vadose zone, and assumptions regarding sourceterm release models and end states. These uncertainties reflect most on the performance of past releases of liquid wastes and past disposals of solid wastes. The review of existing plumes conducted as part of the first iteration Composite Analysis revealed that the exclusive waste management area and buffer zone should be expanded to include the retired Gable Mountain Pond. The Composite Analysis demonstrated a significant separation in time between past-practice discharges iii and disposals, and active and planned disposals of solid waste, environmental restoration waste, and immobilized low-activity waste. The higher integrity disposal facilities and surface covers of these active and planned disposals delay releases, and the delayed releases do not superimpose on the plumes fiom the near-term past-practice disposals.