METHOD FOR INCREASING POWER OUTPUT OF BOILING WATER REACTORS

Abstract: A method (60) for increasing power output of boiling water nuclear reactor electric power plants (8) includes determining (62) an optimum uprate of thermal power output (96) of the boiling water nuclear reactor (10), generating (64) output to facilitate a user in obtaining a license amendment from a nuclear regulatory body for operation of the boiling water nuclear reactor at the identified optimum maximum thermal power output, and generating (66) output to facilitate a user in modifying the boiling water nuclear reactor to operate at a target thermal power output that is less than or equal to the licensed maximum thermal power output. Further, the method includes generating output to facilitate the user in operating the nuclear power plant at a constant electrical power output (98) by varying the thermal power output so that the thermal output of the boiling water nuclear reactor does not exceed the licensed maximum thermal output.

Description: METHOD FOR INCREASING POWER OUTPUT OF BOILING WATER REACTORS BACKGROUND OF THE INVENTION [0001] This invention relates generally to nuclear reactors and more particularly to methods for increasing thermal power output of boiling water reactors. [0002] A typical bojling water reactor (BWR) includes a pressure vessel containing a nuclear fuel core immersed in circulating coolant, i.e., water, which removes heat from the nuclear fuel. The water is boiled to generate steam for driving a steam turbine-generator for generating electric power. The steam is then condensed and the water is returned to the pressure vessel in a closed loop system. Piping circuits carry steam to the turbines and carry recirculated water or feed water back to the pressure vessel that contains the nuclear fuel. [0003] The BWR includes several conventional closed-loop control systems that control various individual operations of the BWR in response to demands. For example a control rod drive control system (CRDCS) controls the position of the control rods within the reactor core and thereby controls the rod density within the core which determines the reactivity therein, and which in turn determines the output power of the reactor core. A recirculation flow control system (RFCS) controls core flow rate, which changes the steam/water relationship in the core and can be used to change the output power of the reactor core. These two control systems work in conjunction with each other to control, at any given point in time, the output power of the reactor core. A turbine control system (TCS) controls steam flow from the BWR to the turbine based on pressure regulation or load demand. [0004] The operation of these systems, as well as other BWR control systems, is controlled utilizing various monitoring parameters of the BWR. Some monitoring parameters include core flow and flow rate affected by the RFCS, reactor system pressure, which is the pressure of the steam discharged from the pressure vessel to the turbine that can be measured at the reactor dome or at the inlet to the turbine, neutron flux or core power, feed water temperature and flow rate, steam flow rate provided to the turbine and various status indications of the BWR systems. Many monitoring parameters are measured directly, while others, such as core thermal power, are calculated using measured parameters. Outputs from the sensors and calculated parameters are input to an emergency protection system to assure safe shutdown of the plant, isolating the reactor from the outside environment if necessary, and preventing the reactor core from overheating during any emergency event. [0005] Historically, reactors were designed to operate at a thermal power output higher than the rated thermal power level licensed by the nuclear regulatory body. To meet regulatory licensing guide lines, reactors are operated at a maximum thermal power output less than the maximum thermal power output the reactor is capable of achieving. These original design bases include large conservative margins factored into the design. After years of operation it has been found that nuclear reactors can be safely operated at thermal power output levels higher than originally licensed. It has also been determined that changes to operating parameters and/or equipment modifications will permit safe operation of a reactor at significantly higher maximum thermal power output (up to and above 120% of original licensed power). [0006] It would be desirable to provide a method for safely increasing thermal power output of a boiling water reactor in a manner consistent with the plant physical configuration and financial criteria of the owning/operating utility. BRIEF SUMMARY OF THE INVENTION [0007] A computer controlled method for increasing power output of boiling water nuclear reactor electric power plants, in one embodiment, includes determining an optimal uprate of thermal power output of the boiling water nuclear reactor. The optimal uprate includes an optimum maximum thermal power output. The method also includes generating output in a predetermined format to facilitate a user to obtain a license amendment from a nuclear regulatory body for operation of the boiling water nuclear reactor at the identified optimum maximum thermal power output. [0008] The method further includes generating output data to facilitate the user modifying the boiling water nuclear reactor to operate at a target thermal power output that is less that or equal to the maximum thermal power output approved by the nuclear regulatory body. Increased thermal power output can be obtained by maintaining a constant reactor pressure, or in alternative embodiments by increasing reactor pressure. Still further, the method includes generating output to facilitate the user operating the nuclear power plant at a constant electrical power output by varying the thermal power output so that the thermal output of the boiling water nuclear reactor does not exceed the maximum thermal output approved by the nuclear regulatory body. [0009] The above described method permits an owner/operator of a nuclear power generating plant to develop a cost beneficial approach to uprate the output of the power plant. The method permits the owner/operator to consider the plant physical configuration and the plant financial criteria to determine an optimum uprate approach. Further the above described method permits the operation of the nuclear power generating plant to operate at the maximum electrical rating of the plant turbine generator to maintain a constant electric output year-round. BRIEF DESCRIPTION OF THE DRAWINGS [0010] Figure 1 is a schematic diagram of the basic components of a power generating system that contains a turbine-generator and a boiling water nuclear reactor. [0011] Figure 2 is a graph of the percent of rated thermal power versus core flow illustrating an expanded operating domain and power uprate of the boiling water reactor shown in Figure 1. [0012] Figure 3 is a flow chart of a computer controlled method for increasing the power output of the boiling water nuclear reactor shown in Figure 1, in accordance with an embodiment of the present invention. [0013] Figure 4 is a graphical representation of a computer generated cost benefit profile. [0014] Figure 5 is a graph showing the relationship of a licensed power uprate, and a target power uprate. [0015] Figure 6 is a graph showing the relationship between thermal power output and electrical power output over time when thermal power output is held constant. [0016] Figure 7 is a graph showing the relationship between thermal power output and electric power output over time when electric power output is held constant, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION [0017] Figure 1 is a schematic diagram of the basic components of a power generating system 8. The system includes a boiling water nuclear reactor 10 which contains a reactor core 12. Water 14 is boiled using the thermal power of reactor core 12, passing through a water-steam phase 16 to become steam 18. Steam 18 flows through piping in a steam flow path 20 to a turbine flow control valve 22 which controls the amount of steam 18 entering steam turbine 24. Steam 18 is used to drive turbine 24 which in turn drives electric generator 26 creating electric power. Steam 18 flows to a condenser 28 where it is converted back to water 14. Water 14 is pumped by feedwater pump 30 through piping in a feedwater path 32 back to reactor 10. [0018] An operating domain 40 of reactor 10 is characterized by a map of the reactor thermal power and core flow as illustrated in Figure 2. Typically, reactors are licensed to operate at or below a flow control/rod line 42 characterized by an operating point 44 defined by 100 percent of the original rated thermal power and 100 percent of rated core flow. In some circumstances, reactors are licensed to operate with a larger domain, but are restricted to operation at or below a flow control/rod line 46 characterized by an operating point 48 defined by 100 percent of the original rated thermal power and 75 percent of rated core flow. [0019] It is desirable to operate at a thermal power greater than 100 percent of the original rated licensed thermal power, sometimes referred to as a power uprate. Lines 50 represent the potential upper boundary of operating domain 40. To operate in the uprate region of operating domain 40, operating conditions and/or equipment modifications are needed. An optimum power uprate level is defined based on the plant physical capabilities and financial goals of the owner/operator of the power plant. [0020] Figure 3 is a flow chart of a computer controlled method 60 for increasing the power output of boiling water nuclear reactor 10, in accordance with an embodiment of the present invention. Method 60, in one embodiment, includes determining 62 an optimum uprate of thermal power output of boiling water nuclear reactor 10. The optimal uprate includes an optimum maximum thermal power output. Method 60 also includes generating 64 output in a predetermined format to facilitate a user to obtain a license amendment from a nuclear regulatory body for operation of boiling water nuclear reactor 10 at the identified optimum maximum thermal power output. Method 60 further includes generating 66 output data to facilitate the user modifying plant equipment and/or operating parameters of boiling water nuclear reactor 10, and generating 68 output data to facilitate the user in operating reactor 10 at a target thermal power output that is less than or equal to the new maximum thermal power output approved and licensed by the nuclear regulatory body. In an alternate embodiment, method 60 includes generating 70 output data to facilitate the user in operating power generating system 8 at a constant electrical power output by varying the thermal power output so that the thermal output of boiling water nuclear reactor 10 does not exceed the maximum thermal output approved by the nuclear regulatory body. [0021] Referring to Figure 4, determining 62 an optimum uprate of thermal power output involves performing a cost-benefit analysis to produce a computer generated cost-benefit profile 80. A determination is made of potential plant equipment modifications and/or operating parameter modifications that can produce varying levels of thermal power uprate. The costs taken into account include costs associated with modification of plant equipment and/or operating parameters. For example, changes can include modification and/or replacement of a high pressure turbine, a low pressure turbine, a generator, a transformer, a feed water turbine, isophase bus cooling, and the like. Cost-benefit profile 80 is used to determine the optimum thermal power uprate by a comparison of the costs associated with a particular percent uprate with the resulting cost of producing electrical output in $/KW. Pinch points are identified based on the physical plant modifications and their corresponding costs. For example pinch points 82, 84, 86, 88, and 90 define cost- benefit profile 80. [0022] Point 82 represents an uprate to X, percent of original licensed core power at a cost of $25 million. In this example, a X, percent power uprate produces an associated cost of electric output of $364/KW. Point 84 represents an uprate to X 2 percent of original licensed core power with an associated total cost, including costs for physical plant modifications, of about $27 million and a resulting cost of electric output of about $306/KW. Point 86 represents an uprate to X 3 percent of original licensed core power at a total cost, including costs for plant modifications, of about $37 million and a resulting cost of electric output of $271/KW. Point 88 represents an uprate to X 4 percent of original licensed core power at a total cost, including costs for plant modifications, of about $42 million and a resulting cost of electric output of $274/KW. Point 90 represents an uprate to X 5 percent of original licensed core power at a total cost, including costs for plant modifications, of about $55 million and a resulting cost of electric output of $312/KW. [0023] The cost-benefit profile shown in Figure 4 identifies an uprate to X 3 percent of original licensed core power as being the optimum power uprate, assuming that the $37 million total cost, including costs for plant modifications and upgrades, is consistent with the owner/operator financial parameters. The uprate to X 3 percent produces the lowest cost electricity. [0024] The power uprate can be achieved with or without an increase to the established plant operating pressure. The reactor pressure control is maintained via programmed computer instructions. With the constant pressure approach (no increase in normal operating reactor dome pressure), the power uprate will include a reduced scope of safety evaluations and can be implemented as soon as the approval of the amended license is obtained. » The constant pressure approach is useful for a power uprate equal to or less than 105 percent of original licensed core thermal power output because of the inherent margin between the design basis power and the original licensed power. As such, the power uprate maximizes the utilization of the existing power generating plant capabilities. Because the constant pressure approach for an uprate equal to or less than 105 percent does not include physical plant modifications, the power uprate can be implemented without the need to shut down the reactor. [0025] Sometimes, utilizing the inherent safety margins do not achieve a 105 percent power uprate, and plant modifications become necessary. The increased pressure approach will minimize the required plant modifications. When the power uprate is greater than 105 percent, plant modifications are almost always necessary and the operating pressure is chosen commensurate with the planned hardware modifications and/or replacements. [0026] Figure 5 is a graph showing the relationship of a licensed power uprate 92, and a target power uprate 94 which represents turbine generator 26 power level capability. To be in compliance with the operating license, target power uprate 94 must be less than or equal to licensed power uprate 92. A long-time phase approach to power uprate implementation includes choosing a target power uprate 94 that is less than licensed power uprate 92 which permits the owner/operator of power generating system 8 to implement the needed plant modifications in stages. [0027] Figure 6 is a graph showing the traditional relationship between thermal power output 96 and electric power output 98 of power generating system 8 over time where thermal power output 96 is held constant. Seasonal changes in ambient conditions effect the efficiency of turbine 24 (shown in Figure 1) which in turn causes a fluctuation in electric power output 98 of system 8. Usually turbine efficiency decreases in the hot humid conditions of summer causing a decrease in electric power output during the season of high electric demand because of the use of electric appliances, such as, air conditioners. [0028] This problem is overcome by operating power generating system 8 at a constant electric output 98 as shown in the graph in Figure 7. To operate at a constant electric output, thermal power output 96 increases during the time of decreased turbine efficiency to overcome the lower turbine efficiency. The optimum power uprate level computed in method 60, as explained above, bounds the expected maximum thermal power level swing during the times of decreased turbine efficiency. This approach permits the owner/operator of power generating plant 8 to operate plant 8 at its installed generator 26 maximum capacity condition year-round which maximizes electric generation and the revenue obtained through subsequent sales of electric power. [0029] Computer controlled method 60, described above, in an exemplary embodiment is web enabled and is run on a business entity's intranet. In a further exemplary embodiment, computer controlled method 60 is fully accessed by individuals having authorized access outside the firewall of the business entity through the Internet. In another exemplary embodiment, computer controlled method 60 is run in a Windows NT environment or simply on a stand alone computer system having a CPU, memory, and user interfaces. In yet another exemplary embodiment, computer controlled method 60 is practiced by simply utilizing spreadsheet software. [0030] While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

Claims: WHAT IS CLAIMED IS: 1. A computer controlled method (60) for increasing power output of boiling water nuclear reactor electric power plants (8) comprising the steps of: determining (62) an optimum uprate of thermal power output (96) of a boiling water nuclear reactor (10), the optimal uprate comprising an optimum maximum thermal power output; and generating output (64) in a predetermined format to facilitate a user to obtain a license amendment from a nuclear regulatory body for operation of the boiling water nuclear reactor at the identified optimum maximum thermal power output. 2. A method (60) in accordance with Claim 1 further comprising the step of generating output (66) to facilitate the user modifying the boiling water nuclear reactor to operate at a target thermal power output (96), the target thermal power output being less than or equal to the maximum thermal power output approved by the nuclear regulatory body. 3. A method (60) in accordance with Claim 2 further comprising the step of generating output (70) to facilitate the user operating the nuclear power plant (8) at a constant electrical power output (98) by varying the thermal power output (96) so that the thermal output of the boiling water nuclear reactor (10) does not exceed the maximum thermal output approved by the nuclear regulatory body. 4. A method (60) in accordance with Claim 3 wherein operating the nuclear power plant (8) at a constant electrical power output (98) comprises operating the nuclear power plant at a constant maximum electrical power output. 5. A method (60) in accordance with Claim 1 wherein determining (62) an optimum uprate of thermal power output of a boiling water nuclear reactor (10) comprises the step of performing a cost benefit analysis by computing costs of increasing core thermal power (96) at varying levels of increased output and comparing such costs to benefits associated with each level of increased thermal power output. 6. A method (60) in accordance with Claim 5 wherein performing a cost benefit analysis comprises the steps of: identifying plant modifications and/or operating modifications needed to achieve each level of increased thermal output (96); computing an estimated a total uprate cost for each level of increased thermal power output, the total uprate cost comprising costs associated with plant modification and/or operating modifications; computing a total cost per KW of electrical output at each level of increased thermal output; and comparing the estimated total uprate cost and associated cost per KW of electrical output (98) of each thermal output level. 7. A method (60) in accordance with Claim 6 wherein determining (62) an optimum uprate of thermal power output (96) of a boiling water nuclear reactor (10) further comprises the step of selecting an optimal maximum thermal output level based on the total uprate cost and the associated cost per KW of electrical output in conjunction with predetermined budget constraints. 8. A system for increasing power output of boiling water nuclear reactor electric power plants (8), said system comprising a computer configured to: determine an optimum maximum thermal power output (96) of a boiling water nuclear reactor (10) by performing a cost benefit analysis which compares costs of increasing core thermal power (96) at varying levels of thermal power output to benefits associated with each level of increased thermal power output; and generate output data to facilitate a user obtaining a license amendment from a nuclear regulatory body for operation of the boiling water nuclear reactor at the identified optimum maximum thermal power output. 9. A system in accordance with Claim 8 wherein said computer is further configured to generate output data to facilitate the user modifying the boiling water nuclear reactor (10) to operate at a target thermal power output (96), the target thermal power output being less than or equal to the maximum thermal power output approved by the nuclear regulatory hody. 10. A system in accordance with Claim 9 wherein said computer is further configured to generate output to facilitate the user operating (10) the nuclear power plant (8) at a constant electrical power output (98) by varying the thermal power output (96) so that the thermal output of the boiling water nuclear reactor does not exceed the maximum thermal output approved by the nuclear regulatory body. 11. A system in accordance with Claim 8 wherein said computer is further configured to: identify plant modifications and/or operating modifications needed to achieve each level of increased thermal power output (96); compute estimated total costs for each level of increased thermal power output, the total cost comprising costs associated with each plant modification and/or operating modifications; compute a cost per KW of electrical output (98) at each level of increased thermal output; and compare the estimated total cost and associated cost per KW of electrical output of each thermal output level. 12. A system in accordance with Claim 11 wherein said computer is further configured to select an optimal maximum thermal output level based on the total costs and the associated cost per KW of electrical output (98) in conjunction with predetermined budget constraints.

Inventors: HOANG HOA, NIR ISRAEL, POPPEL IRA, HOANG, HOA, NIR, ISRAEL, POPPEL, IRA
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 2001
Main classification: G21D3
IPC codes: G21D3