The status of development of small and medium sized reactors

Several IAEA Member States have shown their interest in reactor designs, having a smaller power rating [100–500 MW(e) range] than those generally available on the international market. These small and medium sized power reactors are of interest either for domestic applications or for export into countries with less developed infrastructure. There are different developments undertaken for these power reactors to be ready for offering in the nineties and beyond.The paper gives an overview about the status and different trends in IAEA Member States in the development of small and medium sized reactors for the 90's and provides an outlook for very new reactor designs as a long term option for nuclear power.     

中国核电发展现状与展望

主要介绍了我国在建、在运核电机组的基本状况和最新进展,以及我国在提升核设施安全水平方面的相关措施。在国家能源局印发的《能源技术创新“十三五”规划》要求之下,我国推出一系列先进核能和小型堆的发展计划,开展了“海洋核动力平台示范工程建设”并建立相关标准。最后总结了中国核电目前面临的挑战和未来的展望。      

Prospects of small and medium sized power reactors in Pakistan

To alleviate power shortages already being experienced and the impending crisis in the coming years, Pakistan is making all out efforts to harness the conventional sources of power production. However, the anticipated increase in generating capacity by the turn of this century shall not be sufficient to meet the moderately rising demand of power. Under these circumstances the only option is to get more power from nuclear plants.In this paper the existing electric power situation in Pakistan as well as the future requirements are briefly described. Suggestions are made to cope with the situation and the prospects of nuclear power in general, and of small and medium sized power reactors in particular, are discussed.     

Small high temperature gas-cooled reactors with innovative nuclear burning

Since the innovative concept of CANDLE (Constant Axial shape of Neutron Flux, nuclide densities and power shape During Life of Energy producing reactor) burning strategy was proposed, intensive research works have been continuously conducted to evaluate the feasibility and the performance of the burning strategy on both fast and thermal reactors. We learned that one potential application of the burning strategy for thermal reactors is for the High Temperature Gas-Cooled Reactors (HTGR) with prismatic/block-type fuel elements. Several characteristics of CANDLE burning strategy such as constant reactor characteristics during burn-up, no need for burn-up reactivity control mechanism, proportionality of core height with core lifetime, sub-criticality of fresh fuel elements, etc. enable us to design small sized HTGR with a high degree of safety, easiness of operation and maintenance, and long core lifetime which are required for introducing the reactors into remote areas or developing countries with limited infrastructures and resources. In the present work, we report our evaluation results on small sized block-type HTGR designs with CANDLE burning strategy and compared with other existing small HTGR designs including the ones with pebble fuel elements, under both uranium and thorium fuel cycles.     

Channel reactors as an integral part of nuclear power in Russia

The place and role of channel reactors in nuclear power in our country and the main measures for upgrading and improving the power generating units of nuclear power plants with RBMK reactors are described. It is shown that the risk indicators for serious damage to the core of power generating units with RBMK reactors are lower after upgrading and the corresponding IAEA criterion established for operating nuclear power plants. Upgrading and implementation of a service life extension program has made it possible to obtain licenses for continuing operation of power generating units with first-generation RBMK reactors and predicting a service life increase to 45 years. The characteristics of nuclear power plants with channel reactors with more highly developed internal and natural safety properties are shown in evolutionary designs of the power generating units MKéR-860,-1000, and-1500, which have protective shells and which meet all requirements for power generating units built today. It is shown that innovative solutions for the channel reactor concept can be implemented on the basis of the designs of power generating units with nuclear superheating of steam or on the basis of designs for developing reactors with supercritical parameters. __________ Translated from Atomnaya énergiya,Vol. 103, No. 1, pp. 29–36, July, 2007.     

Current and Future Problems of the Fuel Supply for Nuclear Power

The structure of the nuclear fuel cycle, consisting of the technological stages of uranium production, refining, enrichment, fabrication of nuclear fuel, and reprocessing of the spent fuel for reuse of the fissioning materials, is examined. Supplying fuel includes supplying fuel for Russian nuclear power plants, propulsion and research reactors, export of fuel for nuclear power plants and research reactors constructed according to Russian designs, export of low-enriched uranium and fuel for nuclear power plants constructed according to foreign designs. The explored deposits of natural uranium, the estimated stores of uranium in reserve deposits, and warehoused stores will provide nuclear power with uranium up to 2030 and in more distant future with the planned rates of development. The transition of nuclear power plants to a new fuel run will save up to 20% of the natural uranium. The volume of reprocessing of spent fuel and reuse of ²³⁵U makes it possible to satisfy up to 30% of the demand for resources required for Russian nuclear power plants. The most efficient measure of the resource safety of Russian nuclear power is implementation of an interconnected strategy at each stage of the nuclear fuel cycle.     

Global warming and nuclear power

In view of the potential consequences of the greenhouse effect, it is important to restrain consumption of fossil fuels by exploiting conservation, solar power, and nuclear power. The pressure on developing countries for increased energy consumption makes reduction of fossil fuel use in the industrialized countries all the more important. Nuclear power already has had a significant impact. Primarily through its use. France reduced carbon dioxide emissions by 24% from 1973 to 1986. Given a vigorous program of nuclear power development, electrification, and conservation, one can envisage a U.S. energy economy in which CO₂ production is halved. Standardized reactors, of small or medium size, may enhance the prospects for a nuclear renaissance in industrialized countries, and may be well matched to the needs of developing countries.     

Innovative development of nuclear power in Russia

The basic principles for performing analysis and the systems requirements for large-scale nuclear power in our country are formulated. The problems of modern nuclear power are examined and ways for modern nuclear power to transition to innovative development while satisfying these systems requirements for fuel use, handling spent fuel and wastes, and nonproliferation are indicated. The basic scenario of innovative development in the near term (up to 2030) is based on using predominantly ²³⁵U as fuel and water-moderated water-cooled reactors, which have been well mastered, for increasing nuclear capacities with limited introduction of fast reactors for solving the problem of spent fuel from thermal reactors. In the long term (2030–2050), a transition to ²³⁸U as the primary raw material with fast reactors predominating and complete closure of the nuclear power fuel cycle will be made. The journal variant of a report “New-Generation Nuclear Energy Technologies” presented at a meeting of the Scientific and Technical Council of Rosatom, Moscow, September 27, 2006. __________ Translated from Atomnaya énergiya, Vol. 103, No. 3, pp. 147–155, September, 2007.     

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.     

Compact Stellarators

Stellarators offer advantages for reactors, namely the potential for steady state operation with low recirculating power (high engineering Q) and without disruptions. A substantial portion of the world fusion program is devoted to the development of stellarators as a magnetic confinement system. The world stellarator program, as it currently exists, is focused on high-aspect-ratio (R/a = 5 ? 11) designs that lead to very large reactors. For example the German advanced stellarator reactor design HSR has an aspect ratio of 12 and a major radius of 22 m. An important issue for stellarator research is whether more compact reactor designs are possible. Could the advantage of stellarators also be realized at dimensions and performance levels closer to those of the advanced tokamak reactor ARIES-RS (R = 5.5 m, neutron wall load of 4 MW/m2)? Theory has identified a class of “compact stellarator” plasma configurations that could be the basis for such a design. They are promising, but need to be studied experimentally in order to realistically assess their potential. The most cost-effective way to accomplish this is to carry out the compact stellarator proof-of-principle program that has been proposed by the U.S. stellarator community. This program would answer the basic physics questions for compact stellarators and make important contributions to the world stellarator knowledge base at a cost (about $30M/year) that is modest compared to expenditures for stellarator and tokamak research world-wide.     

Actinide evolution and equilibrium in fast thorium reactors

The development of accelerator-driven sub-critical reactors operating with pure and enriched thorium fuel mixtures has been heralded as delivering a new era in sustainable nuclear power production. Many benefits have been claimed for these systems, particularly with respect to their ability to consume existing plutonium stockpiles and their inability to breed additional plutonium. This paper examines the operation of fast thorium reactors using a lumped model that can demonstrate to first-order accuracy the principles of actinide evolution and equilibrium and allow the identification of trends within the nuclide transformations. The fundamental mechanisms that affect nuclide evolution are demonstrated and the freedoms and constraints bounding this process are shown. Fast reactors operating with a 100% thorium fuel source are shown to generate plutonium and to offer no advantage over enriched thorium fuel in terms of actinide generation in longer-term operation.     

Analysis of the cost-effectiveness of low-capacity nuclear power plants

Autonomous low-capacity nuclear power plants are best suited as reliable sources of power in remote regions which are difficult to reach. This article presents a complete study of the cost-effectiveness of low-capacity nuclear power plants and possible ways to increase it. The economic acceptability of an almost two-fold increase of the run time of KLT-40S and ABV-6 reactors by switching to UO₂ with a larger load is analyzed. The possible organizational and economic mechanisms for implementing low-capacity nuclear-power designs are determined. At the present time, the optimal organizational form for implementing low-capacity nuclear power projects is a public-private partnership. The financial and economic instruments which work effectively within the framework of state-private partnership and which take account of the specific nature of nuclear technology are licensing and the construction-transfer-operation arrangement. __________ Translated from Atomnaya énergiya, Vol. 102, No. 6, pp. 331–336, June, 2007.     

Wireless sensors for predictive maintenance of rotating equipment in research reactors

In 2008–2009, the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) tested the potential of predictive or condition-based maintenance techniques to reduce maintenance costs, minimize the risk of catastrophic failures, and maximize system availability by attaching wireless-based sensors to selected rotating equipment at HFIR. Rotating equipment is an ideal “test case” for the viability of integrated, online predictive maintenance strategies because motors, bearings, and shafts are ubiquitous in nuclear power plants and because the maintenance methods typically performed on rotating equipment today (such as portable or handheld vibration data collection equipment) are highly labor-intensive. The HFIR project achieved all five of its objectives: (1) to identify rotating machinery of the types used in research reactors and determine their operational characteristics, degradation mechanisms, and failure modes, (2) to establish a predictive maintenance program for rotating equipment in research reactors, (3) to identify wireless sensors that are suitable for predictive maintenance of rotating machinery and test them in a laboratory setting, (4) to establish the requirements and procedures to be followed when implementing wireless sensors for predictive maintenance in research reactors, and (5) to develop a conceptual design for a predictive maintenance system for research reactors based on wireless sensors. The project demonstrated that wireless sensors offer an effective method for monitoring key process conditions continuously and remotely, thereby enhancing the safety, reliability, and efficiency of the aging research reactor fleet.     

Options for small and medium sized reactors (SMRs) to overcome loss of economies of scale and incorporate increased proliferation resistance and energy security

The designers of innovative small and medium sized reactors pursue new design and deployment strategies making use of certain advantages provided by smaller reactor size and capacity to achieve reduced design complexity and simplified operation and maintenance requirements, and to provide for incremental capacity increase through multi-module plant clustering. Competitiveness of SMRs depends on the incorporated strategies to overcome loss of economies of scale but equally it depends on finding appropriate market niches for such reactors. For many less developed countries, these are the features of enhanced proliferation resistance and increased robustness of barriers for sabotage protection that may ensure the progress of nuclear power. For such countries, small reactors without on-site refuelling, designed for infrequent replacement of well-contained fuel cassette(s) in a manner that impedes clandestine diversion of nuclear fuel material, may provide a solution. Based on the outputs of recent IAEA activities for innovative SMRs, the paper provides a summary of the state-of-the-art in approaches to improve SMR competitiveness and incorporate enhanced proliferation resistance and energy security.     

Preliminary study of the tight lattice pressured heavy water reactor loaded with Pu／U and Th／U mixed fuels

To improve nuclear fuel utilization efficiency and prolong fuel cycle burn-up,a tight ptich lattice pressured heavy water reactor was investigated as an alternative of next generation of power reactors.It is shown that the high conversion ratio and negative coolant void reactivity coefficient are challenges in the reactor core physics designs.Various techniques were proposed to solve these problems.In this work.a tight pitch lattice and mixed fuel assemblies pressured heavy water reactor concept was investigated.BY utilizing numerical simulation technique,it is demonstrated that reactor core mixed with Pu/U and Th/U assemblies can achieve high conversion ratio(0.98) ,long burn-up(60GWD/t)and negative void reactivity coefficients.     

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe – Part II: Thorium fuel cycle

Full recycling of transuranic (TRU) isotopes can in theory lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In Part I of this paper, TRU recycle over up to 5 generations of light water reactors (LWRs) or sodium-cooled fast reactors (SFRs) is considered for uranium (U) fuel cycles. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. U-fuelled SFRs operating a break-even fuel cycle are not particularly effective at reducing repository radiotoxicity as the final core load dominates over a very long timeframe. In this paper, the analysis is extended to the thorium (Th) fuel cycle. Closed Th-based fuel cycles are well known to have lower equilibrium radiotoxicity than U-based fuel cycles but the time taken to reach equilibrium is generally very long. Th burner fuel cycles with SFRs are found to result in very similar radiotoxicity to U burner fuel cycles with SFRs for one less generation of reactors, provided that protactinium (Pa) is recycled. Th-fuelled reduced-moderation boiling water reactors (RBWRs) are also considered, but for burner fuel cycles their performance is substantially worse, with the waste taking ∼3–5 times longer to decay to the reference level than for Th-fuelled SFRs with the same number of generations. Th break-even fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years. While this is a very long timeframe, it is roughly half that required for waste from the Th or U burner fuel cycle to decay to the reference level, and less than a tenth that required for the U break-even fuel cycle. The improved performance over burner fuel cycles is due to a more substantial contribution of energy generated by ²³³U leading to lower radiotoxicity per unit energy generation. To some extent this an argument based on how the radiotoxicity is normalised: operating a break-even fuel cycle rather than phasing out nuclear power using a burner fuel cycle results in higher repository radiotoxicity in absolute terms. The advantage of Th break-even fuel cycles is also contingent on recycling Pa, and reprocessing losses are significant also for a small number of generations due to the need to effectively burn down the TRU. The integrated decay heat over the scenario timeframe is almost twice as high for a break-even Th fuel cycle than a break-even U fuel cycle when using SFRs, as a result of much higher ⁹⁰Sr production, which subsequently decays into ⁹⁰Y. The peak decay heat is comparable. As decay heat at vitrification and repository decay heat affect repository sizing, this may weaken the argument for the Th cycle.     

The evolution of the structure and application of U.S. NRC regulations and standards

NRC regulations and standards and their implementation have evolved from early adaptations of conventional engineering practices to a mature, cohesive set of regulations that govern NRC regulation of nuclear power plant safety in the United States.From a simple set of rules and design criteria and from the standards of the professional engineering societies, a hierarchy of practices, standards, guides, rules and goals has developed. Resting on a foundation of industrial practices, this hierarchy rises through levels of national standards, regulatory guides and standard review plans, policy statements and NRC regulations.The licensing process is evolving today toward one that permits both site approval and standard design certification before the plant is constructed. At the present time, NRC is reviewing five standard designs for certification for a period of 15 years. NRC focuses its regulation of operating nuclear plants on inspections conducted from five regional offices. Resident inspectors, specialist inspectors, and multi-disciplinary inspection teams examine specific plant situations. The results of all these inspections are used to develop a complete understanding of a plant's physical condition, its operation, maintenance and management.To improve safe operation of nuclear plants in the U.S., a most important program, the Systematic Assessment of Licensee Performance, measures operational performance, using a broad spectrum of functional areas.     

基于安全围壁的浮动堆旁路泄漏设计研究

基于陆上核电厂二次安全壳的概念,引入了浮动堆安全围壁的构想,提出了“安全壳+安全壳围壁+堆舱”的放射性包容模式。研究了评价安全围壁的旁路泄漏设计思路,提出识别旁路泄漏途径和确定旁路泄漏率的方法。给出了安全围壁负压的设计依据,为后期浮动堆通风系统的设计提供参考。      

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.