Development of passive safety systems for Next Generation PWR in Japan

Our country’s energy demand is expected to increase steadily into the future. When the situation of our country, which is not rich in energy resources, is taken into account, it seems that the importance of nuclear power generation will be heightened. Based on such a background, the basic policy for nuclear power generation is ‘from light water reactors to fast breeder reactors’. However, considering that light water reactors have become common, the recent outlook for the supply and demand for uranium resources, development trends of fast breeder reactor technology, etc., the light water reactor is expected to remain dominant in our country until at least the second half of the 21st century. Therefore, five PWR utilities in Japan (Hokkaido, Kansai, Shikoku, Kyushu, and Japan Atomic Power), Mitsubishi Heavy Industries Ltd and Westinghouse Electric Corporation have jointly started researching the Next Generation PWR (N.G.P) which is expected to be the leading nuclear power plant, taking place of APWR [T. Magari, Development of Next Generation PWR in Japan, Proceedings of the 10th Pacific Basin Nuclear Conference, 1996; K. Fujimura, et al., Proceedings of the Second International Symposium on Global Environment and Nuclear Energy Systems, 1996]. In this program, construction is targeted to start from 2010 based on expected future environmental conditions. Now, the capacity of more than 1500 MWe class PWR concept is investigated and a plant concept which has innovative features of a hybrid safety systems, i.e. an optimum combination of active and passive safety systems, and horizontal steam generators for core cooling at the accidents is developed as a promising candidate. The plant concept and the results of the investigation are presented in this paper.     

商用压水堆核燃料研发进展与应用展望

压水堆(PWR)是目前核电厂反应堆的主力堆型,而核燃料是反应堆的能量源泉和放射性裂变物质的主要来源,关乎核电厂的经济性和安全性。本文对当前国际上面向商用PWR应用研发的掺杂UO₂燃料、高铀密度燃料、微封装燃料和金属燃料的性能特点、技术状态及前景进行了归纳和评价。在掺杂UO₂燃料中,大晶粒燃料具有较高的技术成熟度,将在PWR实现大规模商用;高铀密度燃料和金属燃料在高温水腐蚀氧化问题以及事故下的行为仍待研究解决;具有极致安全的微封装燃料更适合特殊用途的小型反应堆。应协同开展先进燃料组件设计、建立设计准则以及研发高保真的性能分析技术等,以充分发挥新型燃料的可靠性及高燃耗优势。     

The history and the prospects of japanese nuclear power development program

FBRs are regarded as the most probable option among non-fossil energy resources which will underpin the future energy demand in Japan, considering the effective uranium utilization and the need to lower the burden on the natural environment. However, it will take a long time to utilize FBRs due to a number of pending technical issues and improvements of cost efficiency. For the time being, therefore, light water reactors will continue to play a dominant role in power generation: thus, it is urgently necessary to establish the quasi-domestic nuclear fuel cycle for them, especially in the field of enrichment and spent fuel reprocessing — a goal of the Japanese nuclear policy since the dawn. Furthermore, public acceptance is significant factor which must be considered. This can best be achieved by more safety performance of light water reactors and through publication of extensive information, including decisions by the industry and government.     

压水堆核电站含氚废水产生与排放

随着核能发展和环境保护的需要,核电站排氚的问题逐渐进入公众的视野。本文简要介绍了压水堆核电站氚的产生和释放机理,核电站运行时液态氚的排放情况,并对国内外法规标准进行了比较分析。通过上述分析,提出了对现有压水堆核电站含氚废液处理的需求。     

Boron transient effects on the behavior of IRIS reactor using dynamic modeling

Small Modular Reactors (SMR) are considered as having several advantages over typical nuclear reactors under various specific conditions. They are thought to be installed in countries with small or medium power grid, in which a large power plant is not necessary or in isolated communities far from distribution centers. A plenty of developing countries are in this situation, so that a significant demand on this type of reactor is expected in a near future. The IRIS reactor is the top-front of SMRs, making its complete development very attractive, since it can fulfill the essential requirements for a future nuclear power plant: better economics, safety-by-design, low proliferation risk and environmental sustainability. IRIS reactor is an integral type PWR in which all primary components are arranged inside the pressure vessel. This configuration involves important changes when compared with a conventional PWR. These changes require several studies to comply with the safe operational limits for the reactor. In light water reactors, a solution of boric acid is used in the coolant of the primary loop to absorb neutrons, aiming to adjust the reactivity of the reactor. A significant decrease in the boron concentration in the core might lead to a considerable power excursion. Several studies on PWR have established correlations between power excursions and deficiencies in homogenization of boric acid diluted in the coolant. The IRIS reactor, due to its integral configuration, does not possess a spray system for boron homogenization which may cause power transients. In this paper, a study has been conducted to develop a dynamic model (named MODIRIS) for transient analysis, implemented in the MATLAB'S software SIMULINK, allowing the analysis of IRIS behavior by considering the neutron point kinetics model for power generation. The methodology is based on generating a set of differential equations of neutronic and thermal-hydraulic balances which describes the dynamics of the primary circuit, as well as a set of differential equations describing the dynamics of secondary circuit. The equations and initialization parameters at full power were inserted into the SIMULINK and the code was validated by comparing with RELAP simulations for a transient of feedwater reduction in the steam generators. Furthermore, the current paper looks for studying and developing a dynamic model for calculating the variations in the boric acid concentration. Then, a simplified model for boron dispersion was implemented into the code MODIRIS to simulate power transients which occur due to variations in the boron concentration in the primary loop of the IRIS reactor. The results for boron concentration, inserted reactivity and steam production showed a good precision and represented the expected behavior very well in the range of operational transients.     

Nuclear power under the clean development mechanism

Not a few developing countries have been following a policy of positively introducing nuclear power to meet the predicted increase in energy demand in future, however, nuclear power development needs technically and financially advanced infrastructures. It is essential for the developing countries to receive technical and financial supports from a developed country or countries, in relation to procurement of funds, education/training of operation/maintenance personnel, assurance of safety, nuclear nonproliferation and safeguard etc., when they seek to introduce or develop nuclear power. It is expected that the developed countries would actively invest in the introduction or development of nuclear power plants in the developing countries, if the investing countries can get emission reduction credits through the Clean Development Mechanism (CDM) defined in the Article 12 of the Kyoto Protocol of the COP-3.

This paper examines effectiveness of the CDM, when it is used as an institutional means of funds raising and technical infrastructure development that are expected to be the greatest obstacles to introducing nuclear power in the developing countries, and proposes the guidelines which are specifically necessary to realize it. Funds that can be raised by Japan to a nuclear power project of developing country in return of the emission right of greenhouse gases were calculated, substituting coal-fired thermal power plants with nuclear power.     

Reducing future CO2 emissions — The role of nuclear energy

A study was made to analyze the potential of reducing CO₂ emissions and to identify important energy and technology options in future energy systems of Japan. The energy market optimum allocation model MARKAL was used for the analysis with a time horizon from 1990 to 2050.

The analytical procedures were as follows. First, a reference energy system was established by incorporating all important energy sources, energy carriers, and energy technologies that existed already or that might be introduced during the above time horizon. Second, future demand for energy services was estimated based on the two economic growth scenarios, high and low. Also, assumptions were made about the evolution of imported fuel prices, availability of energy resources, and so on. Third, under the above assumptions, the optimum energy and technology options were selected by minimizing a discounted system cost under different carbon tax schemes, and thereby the potential of reducing CO₂ emissions was analyzed.

The following results were obtained by the analysis. Without utilization of nuclear energy, the CO₂ emissions can be hardly stabilized at the 1990 emission level even in the case of the low economic growth and large scale deployment of CO₂ recovery and disposal assumed. A significant amount of fossil fuels will be used for power generation in order to meet the rapidly growing demand for electricity. Nuclear energy, by substituting fossil fuels for electric power generation, is expected to contribute to the reduction of CO₂ emissions. In addition, the average cost of reducing the emissions will be substantially lowered compared with a non nuclear scenario.     

Utilization of spent PWR fuel-advanced nuclear fuel cycle of PWR／CANDU synergism

High neutron economy, on line refueling and channel design result in the unsurpassed fuel cycle flexi-bility and variety for CANDU reactors. According to the Chinese national conditions that China has both PWR and CANDU reactors and the closed cycle policy of reprocessing the spent PWR fuel is adopted, one of the advanced nu-clear fuel cycles of PWR/CANDU synergism using the reprocessed uranium of spent PWR fuel in CANDU reactor is proposed, which will save the uranium resource (-22.5%), increase the energy output (-41%), decrease the quantity of spent fuels to be disposed (-2/3) and lower the cost of nuclear poower, Because of the inherent flexibility of nuclearfuel cycle in CANDU reactor, and the low radiation level of recycled uranium(RU), which is acceptable for CANDU reactor fuel fabrication, the transition from the natural uranium to the RU can be completed without major modifica-tion of the reactor core structure and operation mode.It can be implemented in Qinshan Phase Ⅲ CANDU reactors with little or no requirement of big investment in new design. It can be expected that the reuse of recycled uranium of spent PWR fuel in CANDU reactor is a feasible and desirable strategy in China.     

PWR/CANDU联合核燃料循环研究

根据我国已拥有PWR和CANDU核电站的具体情况 ,提出一种PWR/CANDU联合核燃料循环的策略 ,即把压水堆的乏燃料后处理后的回收铀 (RU)用作为CANDU堆的核燃料 ,既可节约铀资源 ,提高燃料的能量输出 ,又减少了废燃料的处置量 ,可大大降低核电成本。由于CANDU堆对核燃料循环的固有灵活性 ,堆芯结构及运行方式不需作重大改变 ,即可完成从天然铀到RU的过渡。又由于RU较低的放射性活度 ,这对CANDU堆的燃料制造是可以接受的 ,因而只需对现有燃料制造生产线稍加屏蔽措施 ,对运输和运行中燃料管理操作等都勿须改变。因而这一策略是具有重大经济效益和吸引力的     

Development of medium and small sized reactors: DMS

Nuclear power is expected to become the main source for electric power generation in Japan for the reasons of energy security and prevention of CO₂ emission. In addition, the slowdown of recent electric power demand and the liberalization of the electric power market are accelerating medium and small sized reactor development. (Hida and Ito, 2003) Furthermore, the needs of medium and small sized reactors have become greater in foreign countries where electric grid systems are weak. Under these circumstances, Hitachi has developed DMS's (Double MS: Modular Simplified & Medium Small Reactors) as 400 MWe class LWR's supported by The Japan Atomic Power Company. (Moriya et al., 2003) In addition, DMS's have been designed based on proven technology that requires no large-scale development, and can therefore be introduced in the market in near future.     

A very small LWR installed in the underground in the city

The effective of the nuclear reactor as the source of heat supply is more expected considering that the energy demand will increase and that the energy consumption structure will convert in Japan. The output scale of such reactors is to be less than 300MWt from the limit of supply area. We are studying two types of such reactors. One is the system for district heat supply with a nuclear reactor MR100 type and the other is for heat supply in buildings with a cassette type nuclear reactor MR1. The conception of these nuclear reactors is originated from the marine nuclear reactor technology. They are of highly safety with passively safe system and highly load following ability.     

核电厂流出物中14C的管理控制

介绍了国内外压水堆(PWR)和重水堆(HWR)核电厂流出物中14C的产生和释放管理现状、减少14C产生和释放的方法以及14C的提取、净化和分析方法,为我国核电厂气态和液态流出物中14C的监测和控制提供基础资料.此外,针对我国核电厂14C的排放和监测情况,提出了几点建议.     

Nuclear power development in China and uranium demand forecast: Based on analysis of global current situation

There are 438 units of operable nuclear reactors all over the world with a combined capacity of 374,127 MWe today, which generated a total of 2560 TWh in 2009, accounting for 14% of total electricity generation. By contrast, the corresponding indicators in China are merely 11 units, 8587 MWe, 65.7 TWh and 1.9% respectively. Nuclear energy has been regarded as an important component of China’s energy development strategy, and the development of nuclear power industry has been paid high attention by government. In order to speed up the development of nuclear power industry, government has increased the target of installed nuclear power capacity from original 40,000 MWe up to 70,000 MWe by 2020, as well as the under construction capfrom 18,000 MWe up to 30,000 MWe in the same stage. Based on the current development situation and the new national plan on nuclear power, prediction and analysis have been made for uranium supply and demand according to the future national nuclear power development, drawing the conclusion that China’s uranium resources could not satisfy with the demand of nuclear power, and the degree of external dependence would reach as high as 90% or more, indicating that in less than 10 years, nuclear energy, instead of oil, would become the energy with the highest dependence on foreign. In the end of this paper, some suggestion has been proposed for development of nuclear power in China.     

空间核反应堆电源用核燃料研制进展

核燃料是空间核反应堆电源的主要材料之一,由于空间核反应堆电源的运行条件明显有别于地面反应堆,空间核反应堆电源用核燃料的类型和技术要求也明显不同于地面反应堆。国际上空间核反应堆电源用核燃料研制取得了长足的进展,多种核燃料材料在工程应用中得到了检验,并在持续开发新型核燃料。我国在亚化学计量二氧化铀芯块、铀钼合金、铀氢锆合金、碳化铀芯块、氮化铀芯块等多种具备在空间堆中应用的燃料材料上开展了一定的研究,并掌握了部分材料性能数据。本文就上述内容展开论述,同时针对与国际相应领域明显落后的实际情况,提出了我国后续核燃料研究的初步设想。     

The design of the Prototype Fast Breeder Reactor

India has a moderate uranium reserve and a large thorium reserve. The primary energy resource for electricity generation in the country is coal. The potential of other resources like gas, oil, wind, solar and biomass is very limited. The only viable and sustainable resource is the nuclear energy. Presently, Pressurised Heavy Water Reactors utilizing natural uranium are in operation/under construction and the plutonium generated from these reactors will be multiplied through breeding in fast breeder reactors. The successful construction, commissioning and operation of Fast Breeder Test Reactor at Kalpakkam has given confidence to embark on the construction of the Prototype Fast Breeder Reactor (PFBR). This paper describes the salient design features of PFBR including the design of the reactor core, reactor assembly, main heat transport systems, component handling, steam water system, electrical power systems, instrumentation and control, plant layout, safety and research and development.     

Sustainable futures using nuclear energy

We present the role of nuclear energy in a sustainable future. This addresses the social, economic and environmental concerns of us all. Nuclear energy today avoids the emission of nearly two billion tonnes of greenhouse gases (GHGs) each year, thanks to over 400 reactors operating worldwide.

Nevertheless, there is no real recognition of real incentives for large-scale non-emitters like nuclear energy and for emissions avoidance in current Kyoto and other policies. These approaches rely heavily on conservation, renewables and efficiency. These measures alone also will not significantly reduce the atmospheric greenhouse burden, because the world is still growing. Also, our (the world's) future economic growth (in all countries) is tied to energy and electricity use. Our prosperity, the alleviation of poverty and the sustainability of the world depend on having a supply of emissions-free and safe energy.

Recent price hikes in fossil fuels and power blackouts also emphasize our need for reliable, safe and cheap power, as is offered by nuclear energy when coupled with effective and secure waste disposal.

A particularly important role for nuclear power in the future will be its links to the hydrogen economy. It is now recognised that the introduction of hydrogen into the transportation sector will benefit the environment only when low carbon sources, such as nuclear reactors, are the primary energy source for hydrogen production. The future could well be the Hydrogen Age. We show that a major reduction in GHGs worldwide can be obtained by nuclear-electric production of hydrogen, thus alleviating their potential effects on future generations. We also demonstrate a potential key synergism with renewable wind power in the hybrid production of distributed hydrogen. Thus, nuclear energy supports and enables the World in its journey to a sustainable, safe and secure energy future.     

Nuclear-Hydrogen Power

Methods for obtaining hydrogen and using hydrogen in power engineering, transportation, and industry, and methods for handling hydrogen (storage and safety) are examined.The concept of nuclear-hydrogen power – using the energy generated by nuclear reactors to produce hydrogen and using this hydrogen in power engineering and industry – is presented. The development of nuclear-hydrogen power will contribute to global energy security and decrease the demand for fuels which affect climate change on our planet.The technologies needed for nuclear-hydrogen power to become a reality – high-temperature nuclear reactors, apparatus for the efficient production of hydrogen from water, hydrogen fuel cells, chemothermal converters, and hydrogen storage and shipment technology – are analyzed.     

压水堆核燃料循环情景模式初步研究

根据我国核电发展现状和中长期发展规划及中长期（2030、2050）发展战略研究,假设2050年前我国压水堆核电发展规模,基于压水堆乏燃料后处理,回收的钚做成MOX燃料放入压水堆中使用,MOX燃料只使用1次的循环模式,进行核能发展情景研究。基于压水堆可装载30%比例MOX燃料的已有研究结果,考虑我国主要的两种压水堆堆型M310和AP1000,进行压水堆核燃料循环分析。利用核能发展情景动态分析程序DESAE-2,给出了不同情景模式下天然铀需求量、乏燃料累计量等。结果表明：至2050年,B₁和B₂模式较A模式分别节省天然铀4.1万t和2.9万t。     

Small PWRs using coated particle fuel for district heating, PFPWR50

It has been said that nuclear energy is an important option for especially developing countries to satisfy their increasing energy demand. However, it will be difficult to deploy first of a kind nuclear power plant in developing countries because extensive safety demonstration has to be conducted in industrialized countries. On the other hand, it will be essential to present rigid proof of reliable operational experience to develop proper understanding of the safety features of new reactor systems among the people around the demonstration plant sites. One of the ways to solve the issue is to integrate existing technologies supported by a great deal of data and experience into a new reactor design. Based on the consideration, a small-sized district heating reactor system based on the pressurized water reactor (PWR) technologies combined with the fuel concept of high temperature gas cooled reactors (HTGRs) has been studied. The purpose of the combination of these two existing concepts is to take the best advantages of both excellent operational experience of PWRs and the integrity of HTGR fuel, coated particle fuel, against fission products release even at high temperature. We expect that this approach will help create a breakthrough to the current stagnation of nuclear power deployment.