基于多层流模型的核电站警报分析系统的开发

开发了基于多层流模型(MFM)的核电站警报分析系统。系统通过在复杂的故障状态下自动识别主要根本原因,能够减轻运行人员的工作负荷。另外,由于多层流模型提供了一组蕴涵因果关系的图形符号,操作维护人员可以通过符号分析来验证诊断结果,从而可以提高警报分析过程的可理解性以及维护工作的可靠性。取自RELAP5/MOD2的19组数据用于评价系统性能。仿真实验结果显示了该系统在停堆前具有较好的及时检测和诊断故障的能力。     

基于MFM和SDG的二回路系统报警分析研究

将多层流模型（MFM）和符号有向图(SDG)相结合,对核动力装置二回路系统的报警信号进行分析。利用MFM对核动力装置进行抽象、分层,运用SDG的理论对MFM中的设备符号进行逻辑分析。对二回路系统的两种故障状态进行报警仿真分析,结果表明：两种方法的结合能准确地判断源故障,清晰显示报警信号传递路径,有助于操纵员进行判断。     

加速器驱动先进核能系统的乏燃料循环再生研究北大核心CSCD

乏燃料后处理是核燃料循环的关键环节,制约核电的可持续发展。借助于加速器驱动先进核能系统(ADANES)提供的高通量、硬能谱的外源中子,其乏燃料后处理只需除去乏燃料中的挥发性裂变产物和影响次锕系元素嬗变的中子毒物,长寿命的次锕系元素Np、Am、Cm可与二氧化铀一起转化为新的燃料元件在加速器驱动燃烧器中燃烧、嬗变、增殖和产能。基于此,本课题组提出了加速器驱动的乏燃料后处理及再生制备的技术路线,包括高温氧化粉化与挥发、选择性溶解分离和燃料再生制备。本文主要介绍了近几年本课题组在这三方面所取得的一些成就,希望能为加速器驱动先进核能系统的乏燃料后处理提供基础数据。     

Hydrogen and its relationship with nuclear energy

In broad terms it is estimated that the world will need 17 TW of additional primary energy to meet its needs by 2050. Much of this growth in energy demand will take place in developing countries. Wind, biomass, solar, nuclear and coal will all compete to fill this gap as oil market share declines. Economics, environmental issues, and public acceptance elements of sustainable development goals will be as important as the engineering issues of efficiency and reliability in this competition.

Nuclear power is increasingly recognized as a principal contender to provide economic, “carbon free” electricity for the grid, but it does not directly provide a transportation fuel as flexible as is gasoline. Nuclear-produced hydrogen might help to fill this transportation fuel gap. This presentation will discuss the processes for manufacture of hydrogen from nuclear heat, and the integration of nuclear-produced hydrogen into the transportation fuel system – in part via synergies with traditional oil, natural gas and coal, and/or synergies with nontraditional shale and tar sands. We will discuss the nuclear hydrogen system as we expect it to appear in 2050 and will discuss some of processes that will provide a pathway to creating that system.     

A new paradigm for core design aimed at the sustainability of nuclear energy: The solution of the extended equilibrium state

The future expansion of nuclear energy, a technology identified as one of the main candidates for reducing the world’s dependence on fossil fuels, requires a thorough analysis of the sustainability of this energy source for long-term supply. Generation-IV nuclear systems could represent a turning point for energy production by minimizing the environmental footprint of the fuel cycle. A new paradigm is thus required for reactor design, focusing, at the core design level, on both the closure of the fuel cycle and the effective utilization of natural resources.     

Comparative population dose risks from nuclear fuel cycle closure and renewal of the commercial nuclear energy alternative in the U.S.

The debate over a large expansion of commercial nuclear energy for electricity production in the U.S., termed a “nuclear renaissance,” has most recently focused on the issues of spent nuclear fuel transportation and the closing of the once-through nuclear fuel cycle through the licensing, construction, and operation of the national spent nuclear fuel repository at Yucca Mountain, Nevada. While such a commercial nuclear energy expansion is postulated to have environmental, climate, resource utilization, and economic benefits, the fundamental issue for typical U.S. citizens about nuclear energy concerns the potential for exposure to ionizing radiation. Two generations of U.S. citizens have experienced public and media “education” that has heightened their primal fears of ionizing radiation from commercial nuclear energy. In such an environment, comparing the risks of radiation doses from commercial nuclear energy fuel cycle closure and further nuclear energy expansion with ionizing radiation population doses experienced year after year, decade after decade from non-nuclear (conventional) industries seems worthwhile for use in achieving stakeholder education and concurrence. The U.S. National Academy of Sciences (NAS) has recently performed its own landmark risk assessment of spent fuel transport in the U.S., demonstrating the guiding principles and methods for use in comparative risk assessments involving radiation dose considerations. Using the NAS assessment approach, this paper broadens its application to the full consideration of the risk of nuclear fuel cycle closure and renewal of the commercial nuclear energy alternative in the U.S., to evaluate the ionizing radiation dose risks of such expansion compared to those routinely accepted for non-nuclear industries by policy makers and the public. The 50-year collective dose risk from the total commercial nuclear fuel cycle, even if the U.S. triples its installed nuclear capacity, transports spent fuel to Yucca Mountain, and operates the Yucca Mountain repository as planned, is shown to be in the range of 3.1-million person-cSv; for five selected non-nuclear industries, the corresponding 50-year collective dose risk exceeds 1 billion person-cSv, a more than 300 times greater risk. A key step towards renewing the commercial nuclear energy alternative, then, is to use this knowledge for education of various stakeholder parties.     

A comparison of Stefan and Phase Field modeling techniques for the simulation of melting nuclear fuel

Simulations of heat transfer in UO₂ at very high temperatures incorporating the effects of phase transitions are being conducted to help support the design and analysis of experimental work being conducted as part of nuclear safety research. This work includes the interpretation of the behaviour of nuclear fuel under conditions where centerline melting may occur. Models based on the Stefan formulation and Phase Field approach are derived from fundamental principles and implemented using recently published material properties. Both simulations compare well with laser flash experiments in recently published literature. The Phase Field model is recommended for further development due to its versatility in handling heat sources and robustness in simulating the evolution of the solid-liquid interface. These points are demonstrated with an example simulation of centerline melting resultant from fission heating for fuel performance analysis.     

中国工程试验堆堆芯入口流量分配特性实验研究

堆芯入口流量分配研究是新型反应堆设计过程中一项重要的工程验证实验,其结果能为反应堆的热工水力及安全分析提供数据支撑。本文针对中国工程试验堆（CENTER）,采用缩比模型开展了堆芯入口流量分配特性实验研究,在不同工况下获得了模拟燃料组件、铍/铝组件、钴靶组件及控制棒导向管内的流量分配因子。实验结果表明：在本文研究的工况范围中,堆芯中大部分冷却剂流过模拟燃料组件,同类型模拟组件间的流量分配较均匀,最大流量相对偏差在±4%以内。实验入口总流量对流量分配特性几乎没有影响。     

Techniques to derive additional information of operation actions for computer-based operating procedure

Most of the modern main control rooms of nuclear power plants are equipped with computer-based operating procedures (CBPs), which make it easier for operators to operate and control the reactor compared with paper-based operating procedure (PBP). However, most of the CBPs do not provide necessary information which is useful for operators, especially in an emergency situation. In addition, proper decisions and actions of the procedure steps are needed to prevent human errors in mitigating the accident. The additional information, which is the information of the impact of a counter action (by automatic system and human actions) such as the components influenced and future plant behavior will be very helpful for operators to understand the effects of the counter action. The aim of the study is to develop techniques to generate the additional information. Multilevel flow modeling (MFM) is applied to model a nuclear power plant and the counter actions described in CBPs. A simple emergency operating procedure of steam generator tube rupture accident of a pressurized water reactor (PWR) plant is used as a case study. The algorithm to generate the additional information is based on the influence propagation rules and cause–effect relations expressed in the MFM model of the PWR plant.     

The feasibility study on perfect burning reactor system

The system of 100% natural uranium burning with once-through fuel cycle is defined as the Perfect Burning Reactor System (PBRS). This kind of nuclear system can be expected to have some good characteristic such as resource efficiency, radiotoxicity reduction, proliferation and nuclear safety. Therefore, the feasibility of the concept is studied in this paper. The preliminary results show that the system of 100% natural uranium burning with once-through fuel cycle is physically possible with a plenty supply of external neutron, and that the system demands no activities concerning with fuel cycle such as uranium enrichment, fuel fabrication, spent fuel reprocessing and radioactive waste treatment. The study also quantitatively clarifies the external neutron source strength, the nuclear criticality safety, the demanded accelerator performance and the energy balance. In addition, the more precise analysis is requested for well understanding and improving the characteristic and economical rationality of the system.     

中国快堆及先进核燃料循环体系发展战略思考

中国是世界上最大的发展中国家,能源消耗位列世界第一。为实现社会、经济的可持续发展,确保能源供应安全和降低环境压力,大力发展包括核能在内的清洁能源是能源发展战略的必然选择。目前,中国的核能经过近30年的发展取得了长足进步,但在能源体系中依然占比很小。鉴于中国的铀资源总体储量有限,仅靠热中子反应堆支撑核能作为主力能源发展难以实现。快堆具有资源利用率高、固有安全性好等优点,配以先进核燃料循环系统,可实现核能的大规模、可持续、环境友好的发展。其中,快堆的发展应遵从先增殖、后嬗变的路线,燃料方面在经过氧化物陶瓷燃料后应尽快过渡到金属燃料;后处理方面初期主要通过水法处理压水堆乏燃料,为快堆提供初装料,后续要尽快实现干法后处理,以缩短增殖燃料的倍增时间和提高整个体系的经济性;同时,还需要同步发展高放废物的处理处置技术。在快堆和先进核燃料循环体系的支撑下,我国的核能能实现在千年量级上作为主力能源发展。     

Prospective scenarios of nuclear energy evolution on the XXIst century over the world scale

Different world scenarios of nuclear energy development over the XXIst century are analyzed in this paper, by means of the EDF fuel cycle simulation code for nuclear scenario studies, TIRELIRE - STRATEGIE.Two nuclear demand scenarios are considered, and the performance of different nuclear strategies in satisfying these scenarios is analyzed and discussed, focusing on the maximum deployable capacity and the natural uranium consumption. Both thermal-spectrum systems (Pressurized Water Reactor, PWR, and High Temperature Gas-cooled Reactor, HTGR) and different designs of Fast Breeder Reactor (FBR) are investigated. A sensitivity analysis on the FBR deployment date, Breeding Gain and fuel cycle options is also presented.     

A comparative study on recycling spent fuels in gas-cooled fast reactors

This study evaluates advanced Gas-cooled Fast Reactor (GFR) fuel cycle scenarios which are based on recycling spent nuclear fuel for the sustainability of nuclear energy. A 600 MWth GFR was used for the fuel cycle analysis, and the equilibrium core was searched with different fuel-to-matrix volume ratios such as 70/30 and 60/40. Two fuel cycle scenarios, i.e., a one-tier case combining a Light Water Reactor (LWR) and a GFR, and a two-tier case using an LWR, a Very High Temperature Reactor (VHTR), and a GFR, were evaluated for mass flow and fuel cycle cost, and the results were compared to those of LWR once-through fuel cycle. The mass flow calculations showed that the natural uranium consumption can be reduced by more than 57% and 27% for the one-tier and two-tier cycles, respectively, when compared to the once-through fuel cycle. The transuranics (TRU) which pose a long-term problem in a high-level waste repository, can be significantly reduced in the multiple recycle operation of these options, resulting in more than 110 and 220 times reduction of TRU inventory to be geologically disposed for the one-tier and two-tier fuel cycles, respectively. The fuel cycle costs were estimated to be 9.4 and 8.6 USD/MWh for the one-tier fuel cycle when the GFR fuel-to-matrix volume ratio was 70/30 and 60/40, respectively. However the fuel cycle cost is reduced to 7.3 and 7.1 USD/MWh for the two-tier fuel cycle, which is even smaller than that of the once-through fuel cycle. In conclusion the GFR can provide alternative fuel cycle options to the once-through and other fast reactor fuel cycle options, by increasing the natural uranium utilization and reducing the fuel cycle cost.     

我国乏燃料运输现状探讨

随着我国经济的持续发展,核能作为安全、清洁能源在我国能源战略中地位日益突出。在保证安全的前提下,我国核电机组按照国家规划合理增加,乏燃料的产量也将逐步增加。根据我国核电站乏燃料贮存及外运规则,以及我国核电站主要位于东部沿海,而乏燃料后处理厂处在西北腹地这一国情,必将面临乏燃料的大量、长距离及安全运输的问题。乏燃料运输作为联接核电站与后处理厂或最终处置场的纽带,在维持核燃料循环体系的正常运行上发挥至关重要的作用。对国内外乏燃料运输涉及的运输方式、运输容器、运输安全监管及事故应急体系等问题进行了分析和讨论,对我国乏燃料运输中存在问题的解决提出了建议。     

Improving the nuclear energy sustainability by decreasing its environmental footprint. Guidelines from life cycle assessment simulations

This paper describes the anticipated long-term evolutions of nuclear fuel cycles. The main driver for such an evolution is the need for improving the sustainability of global energy systems. Indeed, sustainability is becoming the international reference approach to reconciling the different fields of analysis, i.e. the technical performance, economic viability, environmental preservation and societal acceptance. While our societies have to face the issue of finding new energy models which help to mitigate climate change, global approaches are mandatory to select the relevant improvements for the different energy systems, including nuclear energy. In a first step, this paper focuses on the specific environmental footprint of nuclear energy and its position with regards the other energy sources. From this situation, this paper depicts the potential improvement to be studied in order to improve the overall environmental footprint.     

Thorium Molten-Salt Nuclear Energy Synergetics

In the next century, the “fission breeder” concept will not be practical to solve the global energy problems, including environmental and North-South problems. As a new measure, a simple rational Th molten salt breeding fuel cycle system, named “Thorium Molten-Salt Nuclear Energy Synergetics [THORIMS-NES]”, which composed of simple power stations and fissile producers, is proposed. This is effective to establish the essential improvement in issues of resources, safety, power-size flexibility, anti-nuclear proliferation and terrorism, radiowaste, economy, etc. securing the simple operation, maintenance, chemical processing, and rational breeding fuel cycle. As examples, 155 MWe fuel self-sustaining power station “FUJI-II”, 7 MWe pilot-plant “miniFUJI-II”, 1 GeV-300 mA proton Accelerator Molten-Salt Breeder “AMSB”, and their combined fuel cycle system are explained.     

Flow excursion time scales in the advanced neutron source reactor

Flow excursion transients give rise to a key thermal limit for the proposed advanced neutron source (ANS) reactor because its core involves many parallel flow channels with a common pressure drop. Since one can envision certain accident scenarios in which the thermal limits set by flow excursion correlations might be exceeded for brief intervals, a key objective is to determine how long a flow excursion would take to bring about a system failure that could lead to fuel damage. The anticipated time scale for flow excursions has been examined by subdividing the process into its component phenomena: bubble formation, flow deceleration, and fuel plate heat-up. Models were developed to estimate the time required for each individual stage. Accident scenarios involving sudden reduction in core flow or core exit pressure have been examined, and the models compared with RELAP5 output for the ANS geometry. For a high-performance reactor such as the ANS, flow excursion time scales were predicted to be in the millisecond range, so that even very brief transients might lead to fuel damage. These results have been useful for determining the significance of momentary flow excursion events calculated for accident situations in the ANS reactor. In addition, the methods presented are applicable for evaluating the timing of flow excursion transients in other facilities as well.     

Recycling as an option of used nuclear fuel management strategy

The paper presents recycling as an option of used nuclear fuel management strategy with specific focus on the Slovenia. GEN energija is an independent supplier of integral and competitive electricity for Slovenia. In response to growing energy needs, GEN has conducted several feasibility and installation studies of a new nuclear power plant in Slovenia. With sustainable development, the environment, and public acceptance in mind, GEN conducted a study with AREVA concerning the options for the management of its’ new plant's used nuclear fuel.After a brief reminder of global political and economic context, solutions for used nuclear fuel management using current technologies are presented in the study as well as an economic assessment of a closed nuclear fuel cycle. The paper evaluates and proposes practical solutions for mid-term issues on used nuclear fuel management strategies. Different scenarios for used nuclear fuel management are presented, where used nuclear fuel recycling (as MOX, for mixed oxide fuel, and ERU, for enriched reprocessed uranium) are considered. The study concludes that closing the nuclear fuel cycle will allow Slovenia to have a supplementary fuel supply for its new reactor via recycling, while reducing the radiotoxicity, thermal output, and volume of its wastes for final disposal, reducing uncertainties, gaining public acceptance, and allowing time for capitalization on investments for final disposal.     

Management of actinide waste inventories in nuclear phase-out scenarios

The improvement of the “radiological cleanliness” of nuclear energy is a primary goal in the development of advanced reactors and fuel cycles. The multiple recycling of actinides in advanced nuclear systems with fast neutron spectra represents a key option for reducing the potential hazard from high-level waste, especially when the fuel cycle is fully closed. Such strategies, however, involve large inventories of radiotoxic, transuranic (TRU) nuclides in the nuclear park, both in-pile and out-of-pile. The management of these inventories with the help of actinide burners is likely to become an important issue, if nuclear energy systems are eventually phased out, i.e. replaced by other types of energy systems.     

聚变裂变混合乏燃料焚烧堆FDS-SFB燃料循环方案设计与分析

针对聚变裂变混合乏燃料焚烧堆FDS-SFB(Spent Fuel Burner),基于湿法和干法两种后处理技术途径提出了不同的燃料循环方案。并分别对FDS-SFB燃料循环所需的初装资源量、燃料制备和乏燃料后处理能力进行初步质量流分析和可行性初步评估。基于较好嬗变和增殖性能的FDS-SFB典型中子学方案的质量流初步分析表明:两种方案燃料循环其所需的初装资源量、燃料制备、乏燃料后处理能力具有初步的可行性。