DEVELOPMENT OF ADVANCED LIGHT WATER REACTORS

Transcription

1 DEVELOPMENT OF ADVANCED LIGHT WATER REACTORS Atambir. S. Rao General Electric, Nuclear Energy, USA Abstract New generation nuclear power plants have many economic challenges to meet before they become economically attractive to utilities. The economic challenges vary from country to country but have several common characteristics. First and foremost, a plant has to have the lowest construction costs to even be considered for design and construction. Additionally, the plant design has to have a reasonable chance of being licensed by the regulatory authorities in order to minimize the financial risk to the constructing utility. With the long lead times involved in the design and development of advanced plants nowadays, the overall development costs have also become a key factor in the evolution of advanced plants. This paper presents the approach to addressing the aforementioned economic challenges for Evolutionary and Passive plant designs using two advanced BWR designs as examples. The first plant is the ABWR and the second is the ESBWR. The ABWR relies on proven technology and components and an extensive infrastructure that has been built up over the last 20 years. Because it has proven and standard safety systems it has very limited uncertainty regarding licensing. Finally, it relies on the economies of scale and overall design flexibility to improve the overall economics of power generation. The ESBWR on the other hand has taken an innovative approach to reduce systems and components to simplify the overall plant to improve plant economics. The overall plant design is indeed simpler, but improved economics required reliance on some economies of scale also. This design embodied in the ESBWR, also has minimized the overall development cost by utilizing features and components from the ABWR and SBWR technology programs. Introduction The need for power is growing at a fast pace all over the world, especially in the fast developing economies of Asia. As the need for electricity increases, nuclear power will likely become the preferred source of electricity because of its benign environmental impact and because of its overall economic attractiveness [1]. However, since external factors such as public opinion and political considerations play an important part in decisions to build nuclear power plants, the overall economics has to be very attractive and the financial risk has to be minimal.

2 This paper presents two approaches - evolutionary and passive plant designs - to improving new nuclear plant economics and to containing the financial risk for utilities. The overall economic evaluations for new plant construction have the following minimum key factors to consider: a) Low capital cost and short construction schedule b) Low financial risk based on regulatory considerations c) Low plant design and development costs. Several companies in different countries are at different stages of developing reactors for construction. The plant designs generally fall into two categories - evolutionary and passive plant. The first category includes plants that involve evolutionary changes from existing plant designs - these generally include improvements in the overall safety systems and improvement of plant economics based on increasing power levels - in the range of 1300 to 1700 MW. The second category of plants tend to be at smaller power levels in the range of 1000 to 1200 MW and they rely on the use of simplified systems to improve the overall economy of the plant. Table I lists the various plant designs being developed in the two categories. Table I List of Advanced Plants Being Developed in Various Countries Company/country Plant Output, MWe Availability Reference date Evolutionary Plants ABB, US System now [2] KEPRI, Korea KNGR [3] NPI, EPR [4] France/Germany GE/H/T, US/Japan ABWR 1350 now [5] GE/H/T, US/Japan IER [6] ABB, Sweden BWR now [7] Mitsubishi, Japan APWR 1400 now [8] Westinghouse, US PWR 1350 now [9] Framatome, France N now [10] Russia VVER now [11] Passive Plants GE, US ESBWR [12] Westinghouse, US AP [13] Siemens, Germany SWR [14] Westinghouse, US EPP [15] 74

3 Table I clearly shows that most companies are focused on the development of the evolutionary concepts. These plant designs are clearly proven and have good safety records. There also is a lot of competition among the different companies in this area. However, in several markets there may need to be plants developed with a significant difference, for nuclear power to be politically acceptable. The passive plants offer the potential for both being more politically acceptable and simpler and possibly more economic. The rest of this paper will utilize two specific plant designs - ABWR and ESBWR - as examples to show how the economic challenges can be met. Similar approaches can be applied to any of the designs listed in Table I. A comparison of the key features of the two plants designs - ABWR and ESBWR - are given in Table II. Table II Comparison of Key Features of the ABWR and ESBWR Feature ABWR ESBWR Utility Requirements US/Japan EUR Power, MWth Power, MWe Vessel, diameter, m Vessel height, m Control rod drives, number Power density, kw/l Fuel height, m Turbine configuration 6 Flow 4 Flow Feedwater strings 3 2 Bypass capacity, % Accident prevention active passive Accident mitigation passive passive Seismic design, g Some of the key features that contribute to both plant economics are given in Table III. ABWR Approach to Improved Economics An overview description of the ABWR is given in Ref. [5]. The ABWR is the only Advanced LWR that is both being constructed and operated commercially - in Japan at the Kashiwazaki-Kariwa site of the Tokyo Electric Power Company (TEPCO). The recent selection of the ABWR design by Taiwan Power Company also indicates that it is most likely the lowest cost plant design available today. This selection was made in an international competition involving all light water reactor plant designs. 75

4 The following sections provide a discussion of the approach to maintain the economic competitiveness of the ABWR in the future as it becomes the lead LWR in the world. Table III Key ABWR and ESBWR Features Contributing to Improved Economics Economic Advantage Feature Reduced Capital Cost Reduced number/size of systems Reduced building volumes Modular, prefabricated construction Shorter Construction Schedules Improved Availability Predictable O&M Costs Low Fuel Costs Keeping the Capital Costs Low Multiplexed and reduced buildings/systems Cylindrical reinforced concrete containment Improved construction planning Improved plant materials and water chemistry Longer operating cycles Scram reduction Design features for outage reduction Design standardization Simplified nuclear island and turbine island Advanced control and instrumentation High burnup fuel Axial enrichment and gadolinia Use of latest fuel designs A multipronged approach is being followed to keep the ABWR capital costs competitive. a) Further improvements to the plant design Reference [6] provides an overview of the over 20 design features being considered to further improve the economics of the ABWR. The major changes include reduction of number of control rod drives (CRD) by use of larger bundles and an increase in the power level to 1500 MWe. These changes are expected to reduce the overall capital cost by at least 15% over the 1350 MWe ABWR design. b) Reduction in equipment/component costs One of the key approaches to keeping capital costs competitive is to have a multiplicity of international component suppliers. The resulting competition allows the utility to benefit from the increasing globalization of the world economy. c) Enhanced information management system 76

5 The inherent complexity of a nuclear power plant makes the use of the most technologically advanced information management system, extremely beneficial. This allows reduction in construction costs and overall schedule. Minimizing Risk and Uncertainty In the past, in several countries, the cost of nuclear power plants increased considerably as a result of regulatory delays and uncertainty. The ABWR design and development approach has addressed this uncertainty as follows: a) Improvement of safety features/performance The ABWR plant was designed using PSA results and the lessons learned over 20 years of operating nuclear power plants. This resulted in a significant improvement in the design of the safety and non-safety systems. b) Incorporation of severe accident features The ABWR specifically incorporated design features to minimize and mitigate severe accidents. c) Licensing approval in two countries The ABWR design has undergone extensive review by regulatory authorities in two countries. The reviews give confidence to any utility that the design does not have any significant uncertainty or a potential for significant construction delay. Low Design and Development Costs Even though the ABWR was initially developed for conditions in Japan and then adopted for application in the US, the plant design is versatile enough that it can be applied in any country. Any modifications are likely to be minor to meet site specific requirements. The versatile design, combined with the extensive detailed plant design make any additional design costs very minimal ESBWR Approach to Improved Economics Passive BWRs and PWRs have been developed by international teams over the last five to ten years with the objectives of improving the overall simplicity of nuclear plant designs and consequently improving the safety and economics of the designs. The simplicity objective was achieved in part by developing simpler passive safety systems. The promise of simplicity was achieved but radically improved economics had not been achieved. Nuclear power plants with power in the range of 1300 to 1500 MWe, like the EPR or the ABWR, have held an economic advantage resulting from economics of scale. Additionally these plants have an existing infrastructure, detailed design and hence a small uncertainty in design and licensing. To overcome these advantages, any new designs probably must be in the range of 10-15% less expensive in overall genera- 77

6 tion cost to be acceptable as a commercially viable alternative. Hence this was the goal established for the ESBWR when the program was undertaken four years ago. The next sections show how this goal can be achieved. Capital Cost and Construction Schedule The overall approach to improving the capital cost of the ESBWR compared to SBWR [16, 17] was to follow a two-pronged approach: 1. Take advantage of the modular design of the passive safety systems and economics of scale. 2. Take advantage of the simpler systems of the passive plant to reduce overall material quantities. The ESBWR takes advantage of the modular design approach of the SBWR safety systems to extend the design to a higher power level. The primary safety-grade inventory control system the isolation condenser _ is a simple heat exchanger. Consequently any increase in power level only requires the addition of additional heat exchangers. The backup low pressure inventory control system - the gravity driven cooling system (GDCS) - is not sensitive to power level and its capacity is primarily determined by geometrical considerations. The passive containment decay heat removal system also consists of modular heat exchangers, which can easily be increased for plants with higher power levels. As one increases the power level the reactor vessel size and number of control rod drives are increased to handle the larger number of fuel bundles. However, the containment dimensions are not increased significantly, as they are more controlled by the geometric relationships between the passive safety systems instead of the vessel dimensions. This small effect of vessel dimension on building size has a major implication to the overall economics. As the power is increased from the 600 MWe range of the SBWR, there is a very significant improvement in generation cost, since the material quantities do not increase significantly. The generation cost per megawatt is thus driven downward. The second means to improve the overall economics of the ESBWR has been to take advantage of the fewer number of systems in the design. Most of the safety systems are now either in the containment or directly above it. Any other systems in the plant are either non-safety grade or fairly small. This allows a significant reduction of the overall building volumes, especially for the expensive safety category buildings. A major effort has been completed to optimize the reactor building to achieve this cost improvement. Plant designs [18] show that a 40% reduction of building volume is possible compared to a scaled up SBWR. A reduction of the reactor building volume and footprint, Figure 1, has the added benefit of reducing the size of the building which is on the critical path for construction. This potential improvement time will also result in a significant cost reduction for the plant. 78

7 A Simplified 1190MWe BWR 1. Containment 2. CRD HCU s 3. Depressurization Valve 4. Drywell Head (storage) 5. External Equipment Removal Hatch 6. Feedwater Lines 7. Fine-Motion Control Rod Drives (FMCRD) 8. Grade Level (variable elevation) 9. Gravity Driven Cooling System (GDCS) Pool 10. Isolation & Passive Cooling (IC/PCC) Pools 11. IC/PCC Pool Cover 12. Isolation Condenser 13. LOCA Vents 14. Lower Drywell 15. Main Steam Lines 16. Reactor Building 17. Reactor Pressure Vessel (RPV) 18. RPV Head (storage) 19. RPV Pedestal 20. Reactor Water & Shutdown Cooling System 21. Refueling Machine 22. Safety Relief Valves (SRV) 23. Shield Wall 24. Spent Fuel Cask Pit 25. Spent Fuel Storage Pool 26. SRV Quenchers 27. Steam Dryer/Separator Storage Pool 28. Steam Tunnel 29. Suppression Pool 30. Under vessel Servicing Platform 31. Upper Drywell 32. Vent Wall Figure 1 Cutaway Section of the ESBWR - A Passive Plant Design Table IV: Features and Technology Common to ABWR and ESBWR Materials and water chemistry Fine motion control rod drives Miltiplexing and fiber optic data transmission Control room design Plant layout for ease of maintenance Reinforced concrete containment technology Pressure suppression horizontal vents Passive severe accident mitigation features Radwaste technologies Computer codes and analytical methods Information management technology Minimizing Financial and Regulatory Risk The ESBWR approach to minimizing financial uncertainty for the utility is twofold. 79

8 a) Adoption of several features from previously licensed plants like Dodewaard and ABWR [5]. Features and technologies common to the ABWR and ESBWR are listed in Table IV. b) Extensive technology and development activities for any new features. References [12] and [16] provide more information on the extensive technology development that has been completed for the ESBWR. Since the development activities have been international in nature, the new plant features are likely to be accepted by regulators all over the world. Keeping Design and Development Costs Reasonable One of the key challenges for a new plant design is to keep the development costs low. This is because these are on large number of designs competing for a limited amount of development resources. The ESBWR is adopting the following approach to develop the plant design. a) Utilize 10 years of SBWR design/technology Maximum use is being made of the design and technology from the over $250 million 670 MWe SBWR program. b) Minimize changes from the 670 MWe SBWR design Changes in the ESBWR design relative to the 670 MWe SBWR are only being made to either significantly improve economics or to meet specific European Utility Requirements (EUR). c) Utilize international cooperation International cooperation allows the gathering together of the limited resources from several countries. However, this cooperation has to be tempered with the thought that the design developed to meet every country s requirements may be uneconomical for all countries. Hence, a balanced approach has to be followed in this area. Summary and Conclusions This paper provides an overview of two approaches to low cost plant design and construction. The first approach - using the evolutionary ABWR plant design - has the advantage of having an established basis and a low uncertainty. The second approach - using the passive plant ESBWR plant design - has the potential for significant plant simplification and public acceptance, while building on an extensive technology program to minimize uncertainty. Each one of the two approaches has its advantages and challenges - giving utilities two viable options for the future. Moreover, each option will continue to complement and adopt beneficial approaches from the other. Similar approaches are being adopted by designers all over the world. Some of these approaches are discussed in References listed in Table 1 for each design. 80

9 References 1. J. R. Redding and C. Veitch, Nuclear Energy, - The Least-Cost Option, ANS Winter Meeting, Washington, D.C., November B. Ivung and R.A. Matzie, Economic Factors for the Next Generation NPPs, TOPNUX 96, Paris, France, Sept K. Y. Yoo and G. Ha, Economic Assessment of KNGR s Conceptual Design, TOPNUX 96, Paris, France, Sept U. Fischer, EPR: Advanced Technology but Competitive The French Answer for Future Nuclear Power Plants, TOPNUX 96, Paris, France, Sept W. A. Williams and P. S. Lee, Advanced LWR Technology for Commercial Application, International Conference on Nuclear Power Industry Development and Cooperation, Beijing, China, March 16-17, C. D. Sawyer, W. Mizumachi, K. Moriya, and A. Omoto A, Current Status of Improved Evolutionary Reactor Concept, ICONE 4, New Orleans, USA, March 10-14, B. Ivung and I. Tiren, BWR 90: The Next Generation Nuclear Power Plant, International Seminar - New Generation Nuclear Power Plants, Warsaw, Poland, September 25-27, T. Matsuoka, T. Naito, M. Nishimoto, T. Ueno, and K. Tabuchi, Development of Next Generation PWR Adopting Passive Safety System, TOPNUX 96, Paris, France, Sept H. J. Bruschi, Westinghouse Pressurized Water Reactor Designs for the 21st Century, International Seminar - New Generation Nuclear Power Plants, Warsaw, Poland, September 25-27, P. Cornon and P. Durey, The N4 CAD Chain: Another Breakthrough of Electricite de France in Nuclear Engineering, TOPNUX 96, Paris, France, Sept A. Afanasiev, L. Bolchov, and A. Karkhov, Economic Competitiveness of New Generation of NPP s with NP-500 Units in Russia, TOPNUX 96, Paris, France, Sept P. Stoop, H. Arnold, G. Yadigaroglu, A. Gonzales, A. Rao, From Dodewaard to a Modern Economic Passive Plant - ESBWR, TOPNUX 96, Paris, France, Sept H. J. Bruschi, Advanced Light Water Reactors: an Economically Viable Part of the World s Future Energy Mix, TOPNUX 96, Paris, France, Sept J. Mattern, W. Brettschuh, and E. von Staden, How Can the SWR 1000 Meet the Economic Objective?, TOPNUX 96, Paris, France, Sept M. Oyarzabal, and L. Noviello, The European Passive Plant (EPP): A Competitive Design for the 90 s and Beyond, TOPNUX 96, Paris, France, Sept A. S. Rao, Simplifying the BWR, ATOM, AEA Technology No. 430, September/October

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