A Research Summary on Combined Peaking Load Strategies of Nuclear Power Plant Tao Zhang 1, Xiaodong Ma 2, Yu Zhu 1, Gang Wang 1, Peng Ye 3

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1 Advanced Materials Research Submitted: ISSN: , Vols , pp Accepted: doi: / Online: Trans Tech Publications, Switzerland A Research Summary on Combined Peaking Load Strategies of Nuclear Power Plant Tao Zhang 1, Xiaodong Ma 2, Yu Zhu 1, Gang Wang 1, Peng Ye 3 1 State Grid Liaoning electric power research institute, Shenyang, , China 2 Electrical Engineering Department Shenyang University of Technology, Shenyang, , China 3 Electrical Engineering Department Shenyang Institute of Engineering, Shenyang, , China Keywords: peak load regulation mode; nuclear power plant(npp); coordinated operation Abstract: Based on extensive research, introduced the peak load regulation characteristics and capacity of different nuclear power plant (NPP) in this paper. The running mode of NPP participating in peak load regulation of power system, combined operation tactics of NPP with other peaking power source and synergistic scheduling of an integrated power generation system with wind, photovoltaic, energy storage unit and NPP were summarized, technology development trend of NPP participating in peak load regulation of power system was analyzed and forecasted. I. Introduction The power grid urgently needs a new economic and efficient energy to join. Because of wind power, solar power, tidal power and all kinds of new energy have the problem of large-scale power generation and economy, so accelerate the development of nuclear power has become an inevitable choice to solve the problem of China's power supply. According to the national "long-term nuclear power development plan", the new 30-million-kilowatt nuclear power plant, the total installed capacity of nuclear power reach 58 million kilowatts and 30 million kilowatts under construction in In the future, nuclear power will become a main power supply and will occupy more and more proportion. In recent years, the rapid growth of China's electric power load and the gradual wideness of peak -valley difference have brought greater pressure to the power network construction and operation. Due to the growth of the proportion of nuclear power in electric network, power system demands for nuclear power participate in power grid peak shaving is growing. Nuclear power can participate peaking operation, nuclear power peaking operation involved in what manner, the balance of power peaking will be what kind of impact has become a problem requires a high degree of concern. While the new energy in the grid and the rapid growth of network capacity, joint operations and coordination between the various power controls has become a key issue in modern grid operation. Nuclear power plants with other power peak load regulating operation for the joint in the system, the coordination of joint store nuclear power generation system scheduling and intelligent control is the future of NPP to participate in the operation of the technology development direction. Firstly, the various types of nuclear power load characteristics and load capacity of the unit were introduced in this paper. Secondly, the NPP s operation tactics combined with other peaking power source and synergistic scheduling of an integrated power generation system with wind, photovoltaic, energy storage unit and NPP were summarized. Finally, technology development trend of NPP participating in peak load regulation of power system was analyzed and forecasted. II. The Situation of NPP Peak Load Regulation Countries around the world especially focus on the peak load regulation of power grid, since the 1970s, the United States, Germany, France, Japan and other countries have implemented load tracking test and practical operation of pressurized water reactor (PWR), boiling water reactor and the improved thermal reactor nuclear power reactor type [1-5]. Pressurized water reactor more than 40 years of daily load tracking operation experience showed that daily or weekly load tracking has All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,21:04:35)

2 Advanced Materials Research Vols no adverse effect the performance of the fuel, the circuit of the coolant radioactive concentration not rise, verify the reliability and feasibility of daily load-following operation of PWR [6-9]. Foreign peaking running instance was shown in Tab.1. Tab.1 Foreign peaking running instance countries Type of reactor summary Output rate of change in a minute The US Pressurized water reactor Boiling water reactor often implement between 50% to 100% load operation of the output range every day Around 0.25%-1% French Pressurized water reactor often implement between 40% to 100% load operation of the output range every day Highest 5%, Usually 3% Germany Pressurized water reactor Boiling water reactor often implement between 50% to 100% load operation of the output range every day 5%-10% Our country existing nuclear power plants are built in the eastern or southern coastal developed areas, near the load center. Because of east and south China power grid capacity great, nuclear power installed capacity for a small proportion, local power shortage perennial, plan to maximize the power plant unit annual utilization hours, take maximum economic benefit of nuclear power construction, also based on the various consideration of nuclear power plant and power grid safe operation, at present, in addition to the first phase of Qinshan, Dayawan and the first phase of Lingao nuclear power plants in the past two years the Spring Festival, National Day and other special load days down load operation to peak load regulation, other nuclear power plants in any heap shape and size, are not to participate in power grid peak load regulation. However, as the growth of NPP and increase of peak-valley difference, wind, photovoltaic and other renewable energy, electric power system load situation more and more serious, the domestic many units have been conducted on the feasibility study of nuclear power to participate in power grid peak load regulation [10-12], growing demand for nuclear power plants in power grid peak load regulation. III. Peak Load Regulation Mode of NPP Once nuclear power are required to participate in peak shaving, Not only for the safe operation of NPP challenges, but also will have great influence on its economy [8], [13,14]. To alleviate the pressure of the system load, nuclear power plants are usually adopting the following three ways to participate in peak load regulation: (1) Reasonable arrange the refueling outage time After running a power generation cycle, nuclear power plants will be offline and the new fuel component replaced spent fuel components. During the refueling time, Nuclear power plants refuel overhaul of plant in order to maintain and improve equipment operating characteristics, to ensure the safety stability of the unit in the next cycle operation. Refueling overhaul of the plants in the winter can improve the operation rate of thermal power plants, the corresponding adjustable power ratio and the load capacity of the system. In this way, nuclear power participation in the system peaking makes its economy influence down to the minimum and easily to implement. It is a commonly used of current scheduling winter peak load regulation. (2) Load following peaking 1 Modern pressurized water reactor could be designed for a larger negative temperature coefficient. When the load increases, the core cools down will automatically increase the power, run and maintain the power levels, improve the ability of nuclear track to unit load, reducing the demand for reactor power regulating system, such as accuracy, etc.; 2 In response to the transient changes increase unit margin, on the design of unit, load linear change plus or minus 5% plus or minus 10% Pn/min or step change of Pn cases, one, two loop

3 198 Energy Research and Power Engineering 2014 safety protection device is not action, rely on the automatic adjustment to keep the unit stable operation; 3 The use of advanced control system and improve nuclear track load capacity. Using reactor and coordinated control of the steam turbine unit make a change, in the secondary circuit working condition, and large disturbance in cases such as the main process parameters of smaller, higher safety margin, fully digital instrument control system, which makes nuclear power units to load change of the parameters in the process of quality control is more ideal. (3) Compression load operation in special day In the case of system adjustable power supply dwindling, with power system peak-valley difference increasing, the load demand is more and more serious. If NPP can t peak load regulation, it needs to compression load operation to improve the boot capacity of hydropower and thermal power adjustable power supply in special load day, increase the peak load regulation capacity of the system. IV. Combined Operation Tactics of NPP and Other Power Source There are various modern power grid, and it is complementarily between the power on operating characteristics. Based on operating characteristics various power supply, considering the security constraints and system operating constraints of various power supply, order to safe and economic operation of the grid, we can combine to determine the power peaking mode of operation and coordinated control strategy through optimization methods. A. NPP Directly Involved in the Daily Load Peaking Regulation Modern Nuclear power plant have a excellent load following capability, but considering the safety of nuclear power itself and peaking speed and depth limit of NPP, the PWR nuclear power plant generally take " " mode of power regulation, as shown in fig β/% P/pu Curve fitting of power grid load rate Load factor reference curve of NPP peaking t/h Fig.1 Mode of NPP participating in peak load regulation of power grid The mode of power regulation of NPP in fig.1 can meet the requirements of peak load following, more in line with the trend of power grid load, the depth and speed of power regulation meet the constraints of NPP, actually it should order to the actual operation of NPP as a reference to determine the depth and speed of peak load regulation. B. Combined Operation of NPP, Hydropower and Thermal Power Hydropower, thermal power coordination and joint optimization of operation of nuclear power is a hot issue at home and abroad in recent years. The traditional short-term optimal operation of hydro-thermal model of the joint is usually simple to system operating costs a minimum of the objective function, to determine a certain period of time hydropower, thermal power joint power generation plan of the unit. However, a variety of joint supply planning to introduce nuclear energy structure after it is transformed into a high dimension, nonlinear, multi-constraint multi-objective optimization problem, it consider more factors, system load demand, spinning reserve, the unit output nonlinear characteristics, unit start-stop frequency and duration, flow, output and storage

4 Advanced Materials Research Vols constraints, the views of experts and decision-makers, and so generally include, It is a large-scale, mixed integer optimization problems. NPP, hydropower and thermal power combined operation reasonable load distribution shall be: First let's hydropower bring the peak load of the power system, NPP bring the base-load, thermal power balance the load-left, if thermal power does not meet the speed range of the motor group climbing, we will change the power regulation mode of NPP based on thermal power ramp rate and the remaining load characteristics, determine the depth and mode of nuclear power peak load regulation. This will not only avoid abandoned water peaking of hydropower, but also ensures that the thermal power run the optimal regulation. C. Combined Operation of NPP and New Energy Unit (1) Combined operation of NPP and Pumped storage power plant Pumped-storage plant has two major characteristics [15, 16]: Flexibility to switch between power generation and consumption for power system reduces the gap between peaks and troughs and double peaking capacity; the plant starts fast, flexible, reliable and able to respond quickly to changes in network load. It can assume the grid frequency, phase modulation, emergency reserve, black start and so on. The paper [17] has analyzed the issue of nuclear power and pumped storage plants participating in jointly power peaking. According to the operating characteristics of pumped storage plants, three models of nuclear power and pumped storage power joint peaking were presented: complete tracking mode, three sections of the system tracking mode and incomplete tracking mode. Through simulation analysis proved that nuclear power and pumped storage plants jointly run power peaking can satisfy the requirements, and ensured the safe operation of nuclear power plants with base-load, with high economy. (2) Combined operation of NPP, wind power, photovoltaic and energy storage unit Currently, there are many studies on wind power, photovoltaic power generation and energy storage technologies [18-20], unlike conventional power, wind power and photovoltaic power generation has random, volatility and intermittent characteristics. In addition, the technical bottleneck of forecasts, scheduling and control made it different from conventional power in independent source of power generation characteristics and network coordination compared with. When wind power, photovoltaic power generation and other large-scale renewable energy power system access to power system, the traditional plant s ramp rate often do not meet the requirements of dramatically and power fluctuations of short duration caused by renewable energy. Joint operation of wind, photovoltaic, energy storage plants and NPP can effectively weaken the fluctuations caused by wind power and photovoltaic power generation with alleviated stress of power peaking. For example, a region s power system contained nuclear power, wind power, photovoltaic power generation and energy storage power station. The four forms Combined to track grid load. During the day the wind power generating capacity is usually small, and the large amount of photovoltaic power generation. To ensure the operation of photovoltaic full generation power with base-load,the nuclear power should be adjusted according to changes of photovoltaic. When photovoltaic generation in large, the nuclear power will properly reduce operating. Energy storage units store energy in the load trough. Photovoltaic power plants do not generate electricity at night, but wind power is sufficient and volatile. The nuclear power should be adjusted according to changes of wind power. Storage or generation of energy storage power station needs to be based on load conditions. V. Conclusion Nuclear power load for optimizing the power structure, speed up the non-fossil energy alternatives to fossil energy has the effect that cannot replace. NPP has larger peak shaving depth and load capacity, can assist to complete the grid load demand. the peak shaving benefits include: (1) To improve the safety margin of the power system operation and scheduling flexibility, better adapt to all kinds of uncertainty factors;

5 200 Energy Research and Power Engineering 2014 (2) To reduce the thermal power load pressure; Drop the thermal power key; Bring down the high cost of fuel gas and fuel power generate operation cost; (3) To improve clean energy such as wind power and photovoltaic power generation access scale and efficiency. Based on the analyze of all kinds of nuclear power peaking capacity and regulating mode, the NPP s operation with other peaking power source and synergistic scheduling of an integrated power generation system with wind, photovoltaic, energy storage unit were summarized. Provides a reference for future nuclear power peaking. Joint operations and coordination between various power control is to ensure grid security, stability and economic operation. Acknowledgement The Science and Technology Program:Nuclear Power Plant Participate in Peak Load Regulation of Power System and Research of Combined Operation with Wind Light and Energy Storage,2014YF-22. References [1] Berkovich V M, Gorokhov V F, Tatarnikov V P. Possibility of regulating the capacity of a power system by means of nuclear power plants[j]. Teploenergetika,1974(6): [2] Grum A. Design of nuclear power plant with pressurized water reactor for optimum load follow capability[j]. Atomkernenergic Kerntechnik,1986,48(3): [3] Levent A H, Altin V. Rule-based fuzzy logic controller for a PWR-type nuclear power plant[j]. IEEE Transactions on Nuclear Science, 1991, 38(2): [4] Christenson J M. Application of optimal control theory to a load following pressurized water reactor[j]. Nuclear Technology,1992,100(3):361. [5] Wu Guo-wei, Tao Jin. Research of Load Follow for Nuclear Power Plant with Pressurized Water Reactors[J]. Nuclear Power Engineering, 1998, 19(5): [6] Ge Bin, Wu Yi[J]. A Study on a real-time simulation for the second loop of PWR nuclear power unit[j]. Proceedings of the CSEE, 2002, 22(6): [7] Wu Ping, Liu Di-chen, Zhao Jie, et al. Fuzzy adaptive PID control-based load following of pressurized water reactor[j]. Power System technology, 2011, 35(4): [8] Zhao Jie, Liu Di-chen, Wu Yao-wen. Modeling of pressurized water reactor nuclear power plant integrated into power system simulation[j]. Proceedings of the CSEE, 2007, 29(31):8-13. [9] Zhang Xue-cheng, Hu Xue-hao, Zhou Xiu-ming, et al. Development of MID term dynamic simulation program including nuclear power plant model and study of interaction between large nuclear power plant and power system[j]. Power System technology, 1995, 19(2):5-10. [10] Ma Xi-peng. Discussion on large-scale PWR power plants participating in sufficing peak- load of Grid[J]. Shandong DianLiJiShu, 2007(6): [11] Chen Han-xiong, Zheng Yong. Adaptability of large-capacity nuclear power plants accessing Sichuan and Chongqing grids and ability of participating in system peak-load regulation[j]. Electric Power, 2011, 44(3):1-5. [12] Zheng Xiu-bo, Liu Yun, Sun Jing-qiang. The peak load regulation of nuclear power plant in Guangdong power grid[j]. Electric Power Technology, 2010, 19(13-14): [13] Brendan K, John K, Harvey L, et al. Nuclear Generating Stations and Transmission Grid Reliability[C] // th North American Power Symposium. Las Cruces, USA:Power Engineering Society, 2007: [14] Maldonado G I. The performance of North American nuclear power plants during the electric power blackout of August 14, 2003[C]//Nuclear Science Symposium Conference. Rome, Italy:IEEE,2004: [15] He Yongxiu, Yang Weiwei, Lu Yu, et al. Peak-load regulation and emergency response function of weekly adjusted pumped storage station in Beijing-Tianjin-Tangshan Power Grid[J]. Power System Technology, 2006, 30(19):71-75.

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7 Energy Research and Power Engineering / A Research Summary on Combined Peaking Load Strategies of Nuclear Power Plant / DOI References [3] Levent A H, Altin V. Rule-based fuzzy logic controller for a PWR-type nuclear power plant[j]. IEEE Transactions on Nuclear Science, 1991, 38(2): /