Using the Disposal Systems Evaluation Framework to Evaluate Design Tradeoffs (original) (raw)
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Nuclear Engineering and Design, 1982
An approximate, semi-analytical heat conduction model for predicting the time-dependent temperature distribution in the region of a high-level waste repository has been developed. The model provides the basis for a systematic, inexpensive examination of the impact of several independent thermal design constraints on key repository design parameters and for determining the optimal set of design parameters which satisfy these constraints. Illustrative calculations have been carried out for conceptual repository designs for spent pressurized water reactor (PWR) fuel and reprocessed PWR high-level waste in salt and granite media. .ii.
Pre-Remedial Design Studies for Idaho National Laboratory Buried Waste
2005
(INL) is investigating potential treatment methods for the waste buried at the Subsurface Disposal Area, a radioactive landfill that is part of the Radioactive Waste Management Complex (RWMC). The wastes include a variety of sludges, debris, and nitrate salts, contaminated with hazardous chemicals and transuranic (TRU) and non-TRU radionuclides. Alternatives under consideration include in situ thermal desorption (ISTD), in situ grouting (ISG), and ex-situ grouting (ESG). The investigations involve literature searches and bench-and engineering-scale tests to determine the feasibility and applicability of the candidate treatment methods. Researchers have used both surrogate and retrieved waste in recent testing. The retrieved wastes were nitrate salts from Pad A and TRU sludge from composite samples collected during the Glovebox Extractor Method Project at Pit 9. Project personnel have collected information from previously performed ISV testing, but did not perform any additional ISV testing. Reactivity and thermal desorption tests have filled in gaps in support of in situ thermal desorption. At the same time, compressive strength, porosity, hydraulic conductivity, and leachability tests have generated data to assess the feasibility of grouting the SDA waste. Additional tests will be performed in fiscal year 2005. This paper summarizes the fiscal year 2004 testing and results.
A Demonstration of the Disposal Systems Evaluation Framework (DSEF)
The Disposal Systems Evaluation Framework (DSEF) is being developed at Lawrence Livermore National Laboratory (LLNL) to formalize and facilitate the development and documentation of repository conceptual design options for a range of waste forms, geologic environments, repository design concepts, and repository operating modes. It is a knowledge management system that allows the user to intelligently access and draw data from a case library of hundreds of completed thermal analyses (currently 300 cases in the library), and draw input from databases of material properties and repository development cost data (currently the data in these databases is drawn from more than 100 references). The core functionality of DSEF is provided by a Microsoft Office Excel 2010 workbook with macros and form controls that create a structured environment. The workbook walks the user through the steps of creating the input data required to perform disposal system evaluations by interfacing with external...
In Belgium, it is planned to dispose of long-lived and high-level waste in an underground facility. After disposal of the waste, the galleries will be back¬filled to provide stability to the galleries and to limit the amount of voids in the repository. To achieve those goals, the backfill material has to have a good flowability, a negligible bleeding, and a limited shrinkage. A limited grain size is also required to allow the injection of the backfill material. Despite the fact that the backfill supports the gallery lining, its strength must be low enough to enable the retrieval of the waste packages. The backfill material has to be chemically compatible with the Boom Clay and the waste packages. This means that it should not unduly perturb the clay or disposal packages. The thermal conductivity of the backfill material in the galleries containing high-level and thus heat-generating waste must be high enough to allow sufficient dissipation of the decay heat into the surrounding clay. Based on these objectives, material requirements were specified and the development of a backfill mixture was carried out. Initially, the mix composition was optimized in the laboratory. Thereafter, the backfill process of a gallery section was simulated. The investigations illustrate that this mixture can be transported via pipelines through the shaft and drifts and would fill completely the backfill sections in the galleries. Measurements of the porosity, the pore solution composition, the thermal material properties, and the strength illustrate the compliances with the requirements and the feasibility of backfilling the disposal galleries. ---- The Belgian National Agency for Radioactive Waste and enriched Fissile Material ONDRAF/NIRAS is studying the disposal of low and medium activity level, long-lived waste (category B) and high activity, heat-generating waste (category C) in an underground facility. The repository is built at a reference depth of approximately 230 m in the Boom Clay host rock. Two shafts are built for personnel and material transfer and to provide ventilation during the construction and operation of the repository. A third shaft will be constructed for the waste transport. The shafts are connected via horizontal access galleries. The disposal galleries are constructed perpendicular to the access galleries. They are blind or dead-end galleries with a diameter of approx. 3.0 m and a length of 1,000 m. Fig. 1 shows an overview of the repository layout. The galleries in the clay will be lined with concrete wedge blocks. In the order to transport and to support the waste packages after disposal, the galleries are outfitted with a concrete floor. It is planned to backfill the galleries section by section with a cement-based material, because grout injection is assumed to offer better opportunities for achieving the industrial performance that is required to backfill such volumes in a relatively short period of time. The current planning assumes a volume of the sections of approximately 85 m³, which will be backfilled in three and a half hours. Seals will be placed at the front-end of the disposal galleries. The main functions of the backfill mortar are (1) isolating the waste by forming an extra barrier to the waste, (2) providing the galleries with stability and thus avoiding a gallery collapse and (3) reducing the voids in the repository which is a regulatory requirement. As the backfill needs to realize a high filling degree, it has to show good flowability, negligible bleeding, and limited shrinkage. The grain size is limited to allow the injection of the backfill material. Another important requirement for the backfill follows from the potential requirement for waste retrievability. This means that the strength of the backfill has to be sufficient low so that the backfill can be removed at a later stage. In addition, a high porous backfill might be envisaged as it can provide a storage volume for gas generated in the repository and consequently limit the gas pressure build-up. This is in particular important for the category B waste for which the gas generation is expected to be more significant than for the category C waste. The backfill material has to be chemically compatible with the Boom Clay host formation and any other component of the disposal system like the gallery lining and the waste disposal packages. This means that it should not unduly perturb the clay or disposal packages. Finally, the thermal conductivity of the backfill material in the category C waste disposal galleries must be high enough to allow sufficient dissipation of the heat from the category C waste into the surrounding clay. Furthermore, it has to be thermally stable under the maximum temperature that will occur in the backfill material.
The Use of Clay as an Engineered Barrier in Radioactive-Waste Management – A Review
Clays and Clay Minerals, 2013
Geological disposal is the preferred option for the final storage of high-level nuclear waste and spent nuclear fuel in most countries. The selected host rock may be different in individual national programs for radioactive-waste management and the engineered barrier systems that protect and isolate the waste may also differ, but almost all programs are considering an engineered barrier. Clay is used as a buffer that surrounds and protects the individual waste packages and/or as tunnel seal that seals off the disposal galleries from the shafts leading to the surface. Bentonite and bentonite/sand mixtures are selected primarily because of their low hydraulic permeability in a saturated state. This ensures that diffusion will be the dominant transport mechanism in the barrier. Another key advantage is the swelling pressure, which ensures a self-sealing ability and closes gaps in the installed barrier and the excavation-damaged zone around the emplacement tunnels. Bentonite is a natural geological material that has been stable over timescales of millions of years and this is important as the barriers need to retain their properties for up to 10 6 y. In order to be able to license a final repository for high-level radioactive waste, a solid understanding of how the barriers evolve with time is needed. This understanding is based on scientific knowledge about the processes and boundary conditions acting on the barriers in the repository. These are often divided into thermal, hydraulic, mechanical, and (bio)chemical processes. Examples of areas that need to be evaluated are the evolution of temperature in the repository during the early stage due to the decay heat in the waste, re-saturation of the bentonite blocks installed, build-up of swelling pressure on the containers and the surrounding rock, and degradation of the montmorillonite component in the bentonite. Another important area of development is the engineering aspects: how can the barriers be manufactured, subjected to quality control, and installed? Geological disposal programs for radioactive waste have generated a large body of information on the safety-relevant properties of clays used as engineered barriers. The major relevant findings of the past 35 y are reviewed here.