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タイトル: A Systems Analysis of Spent Nuclear Fuel Management and Storage
その他のタイトル: 使用済核燃料管理・貯蔵のシステム分析
著者: Nagano, Koji
著者(別言語): 長野, 浩司
発行日: 2003年3月12日
抄録: Spent nuclear fuel discharged from nuclear power reactors has accumulated to a considerable amount in Japan and the other countries with nuclear power generation stocks, which will lead to risks of their overflow beyond the existing management capacities at those nuclear power plants. If such overflow happens, the power plant has to be shut down until appropriate measures have been taken. Meanwhile, uncertainties have accumulated surrounding final treatment facilities, either reprocessing or geological disposal, reflecting difficulties to find appropriate sites caused by oppositions of local and/or general public and other factors. As a result, spent nuclear fuel has to be stored for the time being in interim devices for a certain time period, e.g. 20 years to 40-50 years, until such time that they can be moved to their final destination. The objective of this dissertation is to review theoretical background and thoughts relevant to policy considerations on spent nuclear fuel management and storage ranging from their discharge to final treatment, to obtain quantitative images, and ultimately to present desirable policies and their implications in medium and long range in Japan. Essential key questions to be addressed here include the following, to which the dissertation presents first the theoretical framework to obtain answers and then answers at the moment while encompassing underlying uncertainties://・When and to what extent spent nuclear fuel storage will be required, and which type of technology options should be applied?//・How long should it be the appropriate storage duration? How does it connect to the overall nuclear fuel cycle program?//・Which should be chosen, AR (At Reactor) storage, AFR (Away From Reactor) storage or a combination of both?//・How will it cost?//・How will the price for storage services be determined?//After presenting these objectives and key questions in Chapter 1, the dissertation first discusses in Chapter 2 the present status of spent nuclear fuel management in Japan, which clarifies where the dissertation stands at this moment. As spent nuclear fuel accumulates at all the nuclear power plants in Japan, enhancement measures of the management capacity, such as re-racking, have already been implemented by now where available. Since opportunities for further enhancement are narrow and scarce, implementation of AFR storage is justifiably needed in an appropriate time range. In fact, relevant institutional developments, namely policy formulation, such as statements in the Long-term Program of Research, Development and Utilization of Nuclear Energy, as well as legislation, especially the amendment of the Law for Regulation of Nuclear Reactors, Nuclear Facilities and Nuclear Materials, have already been completed and implemented. This clearly justifies the needs for the policy analyses in this dissertation, such as strategic planning of storage projects and their economic assessments. Chapter 2 also deals with the historical evolutionary patterns of spent nuclear fuel storage technologies. Various types of storage technique have been developed and are now available. Recently, new dry storage techniques, which are characterized as a combination of metal canisters and concrete blocks including concrete cask storage and horizontal silo storage, are receiving higher shares in the market. The analysis of the historical patterns of worldwide market penetration of various techniques, however, has found no clear sign of retirement of any technology from the global market, while each technique has comfortably found its own "niche" with its own strength and special features to form cohabitation of all. This may reflects the very characteristics of spent nuclear fuel storage market with limited number of projects for long lifetimes. This observation at this moment, meanwhile, does not rule out possibilities of different patterns of market evolution to take place in the future, since the world market will expand whilst choices of techniques will be put more on invisible hands of market economy. Chapter 3 presents the energy and nuclear fuel cycle modeling frameworks, with which the author attempts to describe optimal patterns of nuclear fuel cycle management in harmony with nuclear energy utilization pathways. Chapter 3 starts with the development of Fuel Cycle Optimization Model (FCOM) and extends to its integration with the LDNE21 global energy model, in order to analyze spent nuclear fuel management in an overall framework of nuclear fuel cycle and the global energy system. FCOM solves a long range (90 years) cost minimization problem of the LWR (light water reactor)- FBR (fast breeder reactor) symbiotic system based on linear programming. The optimal solution provides a desirable evolutionary pattern of plutonium (Pu) economy with Pu supply from reprocessing of spent LWR fuel as its key parameter. FCOM's superb feature is, despite a compact model, to obtain an optimal solution of management of spent LWR fuel integrated with reactor mix patterns. Through numerical experiments, it is concluded that spent LWR fuel storage is chosen to adjust future uncertainty as it gives flexibility to the whole nuclear fuel cycle to allow spent LWR fuel reprocessing according to Pu demand. The illustrative simulation runs showed that, while reprocessing of spent LWR fuel is undertaken in accordance with Pu demands, storage of spent LWR fuel provides the adjustment function between Pu supply and demand. This means that storage of spent nuclear fuel should be chosen actively as a measure to cope with uncertainty towards future as it gives flexibility to the management and operation of the whole nuclear fuel cycle. Chapter 3 further extends to the integration of FCOM with the long-range global energy model LDNE21 (Linearlized Dynamic New Earth 21). In this application, FCOM serves as a nuclear energy sub-model within the LDNE21 framework, which analyzes optimal global energy pathways in terms of minimum discounted total system costs up to the year 2100 under a certain set of global environmental and other constraints. The illustrative simulation runs showed that, under a constraint of atmospheric concentration of carbon dioxide (CO2) to be kept below 550ppm in the year 2100, the optimal global energy strategy will be chosen under competition between nuclear power generation and combined cycle generation by coal. This underscores the importance of nuclear fuel cycle and spent nuclear fuel management modeled in FCOM against global energy pictures. Meanwhile, necessity of global shift towards Pu economy does not necessarily maintain. Chaster 4 presents a theoretical analysis of optimal choice of storage duration. In this analysis, the fundamental roles and benefits of storage are understood as twofold; 1) postponement of subsequent processes, which leads to a decrease of present value of those costs, and 2) gains through R&D by earning time with storage. As the result, there could appear an optimal storage duration, which equalizes the following two indices; a) the incremental storage cost for 1 more year, in other words the marginal cost, and b) the increase of the sum of above mentioned benefits, or the marginal utility, through 1 year extension of storage. In the case of uncertainty, this optimal storage duration is prolonged accordingly through a risk-averse attitude. These findings stand also in the case of direct disposal of spent nuclear fuel. This analysis, however, omits certain factors such as specific lifetimes of storage containers and/or facilities, or societal anxieties, which may lead to additional costs when storage duration is prolonged. Chapter 5 deals with the methodologies of material balance calculation ranging discharge, storage, transportation and final processing of spent nuclear fuel. They are categorized into the following two kinds; 1) a microscopic accounting for each power station site or each power utility company, and 2) a macroscopic analysis, either simulation or optimization, in a region-wide or nationwide scale. In Chapter 5, development of a Japan-wide simulation tool SFTRACE (Spent Fuel Storage, TRAnsportation and Cost Evaluation System) is discussed. SFTRACE is mainly based on the 2nd methodology while taking the 1st microscopic accounting aspect fully into account. The illustrative simulation runs revealed various trade-off relations, such as the one between storage capacity to be installed and transportation requirements, the other among geographic coverage of AFR storage facilities as to whether to construct one to serve all over Japan or several to serve segmented regions. These trade-offs clearly demonstrate the necessity and usefulness of integrated analytic tools such as SFTRACE. Chapter 6 discusses the framework of economic analyses of spent nuclear fuel storage. Based on the methodological review of the following three categories, numerical applications are presented for each of them; 1) an engineering-economic cost calculation to assess levelized unit costs, 2) a total cost assessment with strategic planning, and 3) a project financing appraisal and storage price induction. Based on latest sets of data and information, the levelized unit storage costs lay in a reasonable range of 30-70 kJPY/kgU, which corresponds to 0.07-0.17 JPY/kWh at burnup of 49,000MWd/tU with no discounting applied between power generation and storage. With the strategic planning application, several key parameters are identified such as the geographic coverage of AFR centralized storage devices, economy of scale and others. Finally, the project financing appraisal method is applied to explore viable storage pricing schemes which maintain the project of 5,000MTU metal cask storage facility as healthy enough against financial criteria. Because of the highly investment intensive nature of the project, a combinatory pricing scheme of storage service is highly recommended with an initial payment upon receipt of spent nuclear fuel at the storage facility and annual fee payments per unit of spent nuclear fuel stored for each year of storage duration. As the conclusion of the analyses described in these Chapters, policy recommendations are presented in Chapter 7 for planning and implementation of spent nuclear fuel management in Japan. The demand of spent nuclear fuel storage will increase steadily and rapidly, to reach 7,000-10,000MTU by the year 2020 to 2030. In 2050, uncertainties surrounding spent nuclear fuel management will also accumulate. In a most likely scenario, the storage demand will level off at around 10,000MTU after 2020-30 to 2050, which suggests storage capacity of 10,000MTU must be installed by the year 2020. As concerns to the storage duration as well as the long-term planning of spent nuclear fuel management, unless utility values of Pu uses will improve significantly, processes after storage should be planned with reference of lifetime expiration of the storage facility.
内容記述: 報告番号: 乙15624 ; 学位授与年月日: 2003-03-12 ; 学位の種別: 論文博士 ; 学位の種類: 博士(工学) ; 学位記番号: 第15624号 ; 研究科・専攻: 工学系研究科システム量子工学専攻
URI: http://hdl.handle.net/2261/51172
出現カテゴリ:021 博士論文
工学

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