Patent Number: 
Section: description

FIG. 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. FIG. 2 is a flow chart of a method 40 for expanding the operating domain of boiling water nuclear reactor 10. In one aspect, method 40 is applicable to boiling water nuclear reactor plants which can operate at higher than the original rated thermal power, where the fuel cycle performance at the higher load line is advantageous and plant performance at the higher power output is justified by appropriate safety analysis. In another aspect, method 40 provides the design concept and the analytical justification to operate boiling water nuclear reactor 10 in a significantly expanded region of the power/flow map. Method 40 includes the steps of determining an elevated load line characteristic that improves reactor performance 42, performing safety evaluations at the elevated load line to determine compliance with safety design parameters 44, and performing operational evaluations at the elevated load line 46. Method 40 also includes the step of defining a set of operating conditions for the reactor in an upper operating domain characterized by the elevated load line 48. Based on the results of the operational evaluations of step 46, constraints and requirements are established for plant equipment and procedures 50. The optimum applicable range of the expanded region of operation is established. Also, automatic adjustment of the control rod pattern, the flow controls, and the pressure controls based on the detection of a reactor transient 52 is provided. Additionally, method 40 includes modification of the reactor process controls and computers to permit reactor operation in the upper operating domain 54. To determine the desired elevated load line characteristic, evaluations at elevated core thermal power are performed. The desired load line increase is based on the thermal power increase and the fuel cycle performance improvement that is obtained at the elevated core thermal power. Calculations are performed to define the operating conditions of the reactor in the new operating region characterized by the elevated load line. Evaluations of the expected performance of the reactor throughout the new operating region are also performed. Operational evaluations performed at the elevated load line include, but are not limited to, evaluating plant maneuvers, frequent plant transients, plant fuel operating margins, operator training and plant equipment response and setpoints. Based on the results of the operational evaluations, constraints and requirements are established for plant equipment and procedures. Safety evaluations typically address the safety analysis Chapter 15 of the Final Safety Analysis Report (FSAR). Additionally, non-Chapter 15 safety issues such as containment integrity, stability and anticipated transient without scram (ATWS) are addressed. Safety analysis include demonstration of compatibility with the previous resolutions of reactor stability monitoring and mitigation of unplanned events. The safety evaluations are performed such that compliance to plant design criteria is demonstrated. Assurance of acceptable protection of the reactor and the public is performed and documented to satisfy regulatory authorities. A safety analysis report is generated to comply with regulatory requirements. To maximize the ability of the boiling water reactor unit to avoid trip during transients that may occur while operating in the extended region, automatic adjustment of some controls is provided. For example automatic adjustment of the control rod pattern, flow controls and pressure controls based on sensing the initiation of a transient, such as a pump trip, are provided. These automatic controls improve plant availability, even in the previous range of reactor operation. An operating domain 58 of reactor 10 is characterized by a map of the reactor thermal power and core flow as illustrated in FIG. 3. Typically, reactors are licensed to operate below a flow control/rod line 60 characterized by an operating point 62 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 below a flow control/rod line 64 characterized by an operating point 66 defined by 100 percent of the original rated thermal power and 75 percent of rated core flow. Some reactors have been licensed to operate at higher power as illustrated by lines 67 in FIG. 3. However, these reactors are constrained by flow control/rod boundary line 64. In an exemplary embodiment of the present invention, method 40 expands operating domain 58 of reactor 10 and permits operation of reactor 10 between about 120 percent of original rated thermal power and about 85 percent of rated core flow to about 100 percent of original rated thermal power and about 55 percent of rated core flow. Lines 68, 70 and 72 represents this new upper boundary of an upper operating region 74 of operating domain 58 of reactor 10. FIG. 4 shows another exemplary embodiment of the present invention where method 40 expands operating domain 58 of reactor 10 to an upper boundary represented by the operation of reactor 10 between about 120 percent of original rated thermal power and about 85 percent of rated core flow to about 60 percent of original rated thermal power and about 60 percent of rated core flow. Lines 70, 76 and 78 represents this new upper boundary of an expanded upper operating region 80 of operating domain 58 of reactor 10. Method 40 provides analyzed limits that permit licensed power operation of reactor 10 at a core flow lower than the constraint on core flow imposed by boundary 64. The increased boundary line 68 permits operation of reactor 10 over a larger core flow range and operating flexibility during startup and at full power. Method 40 further provides savings in fuel cycle costs and faster plant startups due to the increased ability to establish desired full power control rod pattern at partial power conditions. Also provided is reduced cycle average recirculation pumping power consumption resulting in an increase in net station output. Another embodiment of the invention includes providing analyses and evaluations to generate a safety analysis report as described above. Additionally, licensing support is provided to the owner, or managing entity, of the boiling water nuclear reactor, along with technical consultation during the implementation of reactor analyses and modifications described above. While the invention has been described and illustrated 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.