Performance Considerations in Power Uprates of Nuclear Power Plants: A Case Study

Abstract

This paper examines the impact of power uprates on the performance of nuclear power plants. Since the 1970’s, power companies have been using power uprates to increase the output of their nuclear power plants. The plant systems and components should be capable of accommodating the accompanying increases in flow conditions. The affected components include the turbine-generator, pipes, valves, pumps, heat exchangers, electrical transformer, etc. The Nuclear Regulatory Commission has classified power uprates as falling into three categories: (1) measurement uncertainty recapture power uprates, (2) stretch power uprates and, (3) extended power uprates. Measurement uncertainty recapture power uprates are up to 2% and are achieved by using enhanced techniques for calculating reactor power. This involves the use of state-of-the-art feedwater flow measurement devices to reduce the degree of uncertainty associated with feedwater flow measurement which, in turn, provide for a more accurate calculation of reactor power. Stretch power uprates are typically up to 7% and within the design capacity of the plant. The actual percentage increase in power is plant-specific and depends on the operating margins included in the plant design. Stretch power uprates usually involve changes to instrumentation setpoints, but do not involve major plant modifications. This is especially true for boiling-water reactor plants. In some limited cases where plant equipment is operated at near capacity prior to the power uprate, more substantial changes may be required. Extended power uprates may be up to 20% and, usually require significant modifications to major pieces of plant equipment such as the high pressure turbines, condensate pumps and motors, main generators, and/or transformers. Using a case study, this paper examines the performance considerations involved in power uprates of nuclear power plants. Affected components such as the turbine-generator, moisture separators, reheaters, feedwater heaters and, condensers are discussed. The use of a performance modeling tool in evaluating the impact of power uprates on nuclear plant performance is discussed. The paper provides conclusions and recommendations for ensuring optimal performance in light of power uprates.