Performance assessment of solute transport upscaling methods in the context of nuclear waste disposal
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Stochastic modelling
In the present work, a nonstationary stochastic model, which is suitable for the analysis and simulation of multivariate time series of wind and wave data, is being presented and validated. This model belongs to the class of periodically correlated stochastic processes with yearly periodic mean value and standard deviation (periodically correlated or cyclostationary stochastic process). First, the time series is appropriately transformed to become Gaussian using the Box-Cox transformation. Then, the series is decomposed, using an appropriate seasonal standardization procedure, to a periodic (deterministic) mean value and a (stochastic) residual time series multiplied by a periodic (deterministic) standard deviation. The periodic components are estimated using appropriate time series of monthly data. The residual stochastic part, which is proved to be stationary, is modelled as a VARMA process. This way the initial process can be given the structure of a multivariate periodically correlated process. The present methodology permits a reliable reproduction of available information about wind and wave conditions, which is required for a number of applications.
Stochastic modelling
Cyclostationary process
Stationary process
Discrete-time stochastic process
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The Japanese geological disposal programme has started researching disposal of spent nuclear fuel (SF) in deep geological strata (hereafter "direct disposal of SF") as an alternative management option other reprocessing followed by vitrification and geological disposal of high-level radioactive waste. In the case of direct disposal of SF, the radioactivity of the waste is higher and the potential effects of the radiation are greater. Specific examples of the possible effects of radiation include increased amounts of canister corrosion; generation of oxidizing chemical species in conjunction with decomposition of groundwater and accompanying oxidation of reducing groundwater; and increase in the dissolution rate of SF and the solubility of radionuclides. Focusing especially on the effects of α-radiation in safety assessment, this study has reviewed research into the effects of α-radiation on the SF, canisters and environment outside the canisters.
High-level waste
Vitrification
Nuclear Fuel
waste disposal
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High-level waste
Yucca
Underground storage
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The Yucca Mountain Draft Environmental Impact Statement (DEIS) analysis addressed the potential for transporting spent nuclear fuel and high-level radioactive waste from 77 origins for 34 types of spent fuel and high-level radioactive waste, 49,914 legal weight truck shipments, and 10,911 rail shipments. The analysis evaluated transportation over 59,250 unique shipment links for travel outside Nevada (shipment segments in urban, suburban or rural zones by state), and 22,611 links in Nevada. In addition, the analysis modeled the behavior of 41 isotopes, 1091 source terms, and used 8850 food transfer factors (distinct factors by isotope for each state). The analysis also used mode-specific accident rates for legal weight truck, rail, and heavy haul truck by state, and barge by waterway. This complex mix of data and information required an innovative approach to assess the transportation impacts. The approach employed a Microsoft{reg_sign} Access database tool that incorporated data from many sources, including unit risk factors calculated using the RADTRAN IV transportation risk assessment computer program. Using Microsoft{reg_sign} Access, the analysts organized data (such as state-specific accident and fatality rates) into tables and developed queries to obtain the overall transportation impacts. Queries are instructions to the database describing how to use data contained in the database tables. While a query might be applied to thousands of table entries, there is only one sequence of queries that is used to calculate a particular transportation impact. For example, the incident-free dose to off-link populations in a state is calculated by a query that uses route segment lengths for each route in a state that could be used by shipments, populations for each segment, number of shipments on each segment, and an incident-free unit risk factor calculated using RADTRAN IV. In addition to providing a method for using large volumes of data in the calculations, the queries provide a straight-forward means used to verify results. Another advantage of using the MS Access database was the ability to develop query hierarchies using nested queries. Calculations were broken into a series of steps, each step represented by a query. For example, the first query might calculate the number of shipment kilometers traveled through urban, rural and suburban zones for all states. Subsequent queries could join the shipment kilometers query results with another table containing unit risk factors calculated using RADTRAN IV to produce radiological impacts. Through the use of queries, impacts by origin, mode, fuel type or many other parameters can be obtained. The paper will show both the flexibility of the assessment tool and the ease it provides for verifying results.
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High-level waste
waste disposal
Containment (computer programming)
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Since 1983, under the Nuclear Waste Policy Act of 1982, as amended (42 U.S.C. 10101 et seq.), the U.S. Department of Energy (the Department) has been investigating a site at Yucca Mountain, Nevada, to determine whether it is suitable for development as the nation's first repository for permanent geologic disposal of spent nuclear fuel and high-level radioactive waste. By far, the largest quantity of waste destined for geologic disposal is spent nuclear fuel from 118 commercial nuclear power reactors at 72 power plant sites and 1 commercial storage site across the United States. Currently, 104 of these reactors are still in operation and generate about 20 percent of the country's electricity. Under standard contracts that DOE executed with the utilities, DOE is to accept spent nuclear fuel from the utilities for disposal. Until that happens, the utilities must safely store their spent nuclear fuel in compliance with Nuclear Regulatory Commission regulations. As of December 1998, commercial spent nuclear fuel containing approximately 38,500 metric tons of heavy metal (MTHM) was stored in 33 states. The balance of the waste destined for geologic disposal in a repository is Department-owned spent nuclear fuel and high-level radioactive waste. The Department's spent nuclear fuel includes naval spent nuclear fuel and irradiated fuel from weapons production, domestic research reactors, and foreign research reactors. For disposal in a geologic repository, high-level radioactive waste would be processed into a solid glass form and placed into approximately 20,000 canisters. No liquid or hazardous wastes regulated under the Resource Conservation and Recovery Act of 1976 would be disposed of in a geologic repository. The difficulty in siting new facilities, particularly those designed as nuclear or nuclear-related facilities, is well documented. In this context, national boundaries are not significant distinguishing barriers. As one publication observed, ''Environmental activists, local residents and governmental officials are protesting proposed waste facilities from Taiwan to Texas''. Here in Nevada, Yucca Mountain is no exception. The Department's study of the Yucca Mountain site for possible development as a permanent repository for spent nuclear fuel and high-level radioactive waste has been criticized by many, for many reasons. The Yucca Mountain Project is both controversial and complex--a fact that makes communication with the public a challenge.
High-level waste
Nuclear Fuel
Tonne
waste disposal
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A study was conducted to assess the feasibility of using multi-purpose canisters to handle spent nuclear fuel throughout the Civilian Radioactive Waste Management System. Multi-purpose canisters would be sealed, metallic containers maintaining multiple spent fuel assemblies in a dry, inert environment and overpacked separately and uniquely for the various system elements of storage, transportation, and disposal. Using five implementation scenarios, the multi-purpose canister was evaluated with regard to several measures of effectiveness, including number of handlings, radiation exposure, cost, schedule and licensing considerations, and public perception. Advantages and disadvantages of the multi-purpose canister were identified relative to the current reference system within each scenario, and the scenarios were compared to determine the most effective method of implementation.
High-level waste
waste disposal
Nuclear Fuel
Spent fuel pool
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Buffer (optical fiber)
Bentonite
High-level waste
Buffer zone
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Safe long-term storage of radioactive waste from nuclear power plants is one of the main concerns for the nuclear industry as well as for governments in countries relying on electricity produced by nuclear power. A repository for spent nuclear fuel must be safe for extremely long time periods (at least 100 000 years). In order to ascertain the long-term safety of a repository, extensive safety analysis must be performed. One of the critical issues in a safety analysis is the long-term integrity of the barrier materials used in the repository. Ionizing radiation from the spent nuclear constitutes one of the many parameters that need to be accounted for. In this paper, the effects of ionizing radiation on the integrity of different materials used in a granitic deep geological repository for spent nuclear fuel designed according to the Swedish KBS-3 model are discussed. The discussion is primarily focused on radiation-induced processes at the interface between groundwater and solid materials. The materials that are discussed are the spent nuclear fuel (based on UO 2 ), the copper-covered iron canister, and bentonite clay. The latter two constitute the engineered barriers of the repository.
Nuclear material
Nuclear Fuel
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The mission of the Office of Civilian Radioactive Waste Management (OCRWM) of the US Department of Energy (DOE) is to manage and dispose of spent nuclear fuel and high-level radioactive waste in a manner that protects health, safety and the environment, enhances national and energy security and merits public confidence. Consolidation of spent nuclear fuel and high-level radioactive waste from 126 sites in 39 states and safe disposal at Yucca Mountain are vital to the US national interests. The US geologic repository programme's key objective remains to begin receiving spent nuclear fuel and high-level radioactive waste at the US Nuclear Regulatory Commission (NRC) licensed Yucca Mountain repository in 2010. To achieve this objective, the DOE must, in less than 7 years, seek and secure authorization to construct the repository from the NRC, begin constructing the repository and receive a license amendment allowing receipt of radioactive materials and operation of the repository. DOE must also develop a transportation system to ship spent nuclear fuel and high-level radioactive waste from civilian and defence storage sites to the repository. This paper describes near-term efforts in developing the license application and transportation system. Successfully licensing, constructing and operating a repository will rely on information gained from more than two decades of scientific investigations at the Yucca Mountain site, all of which contribute to the technical basis for understanding the repository system. This paper also summarizes ongoing and completed in situ testing in the exploratory studies facility (ESF) and cross-drift. The ESF, a U-shaped tunnel approximately 7.9 km long and about 300 m below the crest of Yucca Mountain, has been used extensively to conduct tests in 13 alcoves and niches and to access a smaller cross-drift, 5 m in diameter and 2.7 km long.
Dispose pattern
High-level waste
waste disposal
Receipt
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